The Universal Prosthesis -- Report 2005-11-18

The Universal Prosthesis - Report

Feasibility of the Universal Below-knee Prosthesis

a Hands-Off PTB/TCB-Hybrid Prosthesis



with a Low-Expertise Fitting Method.



February - November 2005

Written by:

Boudewijn Wisse

Mentors:

Johan Molenbroek



Marc Tassoul



Just Herder

Delft University of Technology Faculty of Industrial Design Engineering The Netherlands

Preface This report is about a quest to improve prosthesis for lower-limb amputees and is a result of my graduation project.

Although

estimations vary wildly, it is certain that there are millions of limbless people in the world. In 2002 I went to Sri Lanka to see if my expertise (product design) could help at least some of them. All my tries, trials and adventures led to my graduation, of which this first report is lying in front of you. I hope you will find the report informative and inspiring.

It

all started with a contest by Johan Molenbroek and Henk Kooistra, who asked several groups of industrial design engineers to think about the land mine-victims in Sri Lanka. I entered the “Design for All” competition and was able to continue with an internship in Sri Lanka. Now, two years and much thinking later, I started this graduation project.

II

In practice, this project is about the design

of a universal transtibial prosthesis. Imagine a comfortable, adaptable and adjustable leg prosthesis, suitable for people with different residual limb shapes and sizes! It could reach at least some of the millions limbless, who now cannot receive the health care and product they need. I hope my graduation project will prove the universal prosthesis is feasible, so production can be started and amputees can be reached and benefit from this work.

This

report came into being from February to May 2005, at the faculty of Industrial Design Engineering, at the Delft University of Technology in the Netherlands. I would like to thank Just Herder, Marc Tassoul and Johan Molenbroek for their kind assistance and Wouter van Dorsser for his never ending support. Every day I work on this project , I think about all the knowledge the people in Sri Lanka taught me. Thanks again.

The Universal Prosthesis

Summary The universal transtibial prosthesis is a below-

ant areas (in particular the patellar tendon) and the injector pressurizes the inner space of the socket during fabrication, the socket is a patellar-tendon-bearing / total-contactbearing hybrid. (PTB-TCS-hybrid). This way, maximal comfort is achieved. The precise,

The fitting procedure results in a prosthesis

that can be used daily, in the same way as currently available designs.

Apart from the injector, which is part of the

distribution kit containing all components, no tools are needed that can not be found in local hardware stores to fit the prosthesis (basically, a saw and a screwdriver). The Universal Prosthesis is independent of local infrastructure which enables a broad and easy distribution.

Price

of the Universal Prosthesis can vary widely and is dependent on the amount of pieces produced a year. Market exploitation in developed countries becomes commercially feasible at a price for the distribution kit that is lower than 700 USD. Worldwide market exploitation of the Universal Prosthesis becomes commercially feasible at prices of the 100-200 USD, dependent on the situation of the users and the support of NGOs and aid-funds. To reach these prices, development and organisation of the Universal Prosthesis from this report to European distribution and from that to worldwide distribution both have to stay under 1,000,000 USD.

Criteria

Because the frame loads the pressure toler-

is achieved by supracondylar brims. In cases where this suspension is insufficient, a suspension sleeve can be added.

Stragegy

the fitting procedure the frame transfers half the weight of the body of the amputee to the residual limb’s pressure-tolerant areas. Then, a total contact fit is achieved by filling the inner and outer layer of the socket with rigid Poly-Urethane foam. The injector, that provides the foam, is basically a high-pressure aerosol spray with a special nozzle.

Suspension

Usage

During

design, with good stiffness and strength. The pylon is connected to the foot by a connective component with a pivot point. In this way, dynamic alignment or alignment adjustments stay possible after the fabrication of the socket, though limited in respect to stateof-the-art modular endoskeletal designs.

temporal, spare prostheses, and definite prostheses, especially for elder and still growing children. When fully developed and optimized, the Universal Prosthesis can be used for amputees worldwide in all circumstances. Because of variations in residual limb shape, length and health, the Universal Prosthesis is suitable for about 70% of the transtibial amputees in the target groups.

Prostheses

of a socket-pylon frame, a connective component to the foot and a “liner” that will function as the inner and outer layer of the socket, and an injector.

The socket-pylon frame forms an exoskeletal

Markets for the Universal Prosthesis include

Users

The Universal Prosthesis primarily consists

volume-matching fit provides good control over the prosthesis to the user.

Approach

knee prosthesis that can be fitted to the amputees residual limb by an inexperienced person. Due to the lack of (time of) prosthetist in many countries, amputees world-wide can profit from better health care because of the Universal Prosthesis. Nowadays, still one million people are in need of an artificial limb.

Boudewijn Martin Wisse TU Delft, 2005

Page: III

Field studies have to prove the effectiveness

of the Universal Prosthesis and will provide feedback for further improvements. These field studies are the next big step towards implementation. However, literature shows that one prefabricated socket can already be successfully used for 50% of the transtibial amputees. Outcome is expected to indicate that the Universal Prosthesis is suitable for 70-80% of the transtibial amputees.

Concluding, the development and implementation of the Universal Prosthesis is feasible.

IV

The Universal Prosthesis

Table of Contents 1

1

2.3

Transtibial Prostheses________ 24 Types According to the Patients Rehabilitation Stage__________ 25

4.1.1 Removable Rigid Dressing - RRD__ 26 4.1.2 Immediate Post Operative Prosthesis - IPOP_ ______________ 27 4.1.3 Removable Protective Socket - RPS 28 4.1.4 Temporary Prosthesis_ __________ 29 4.1.5 Definite Prosthesis______________ 30

4.2 Structural Designs ___________

31 4.2.1 Exoskeletal Structure____________ 31 4.2.2 Endoskeletal Structure___________ 32

4.4 Biomechanics of Transtibial Prostheses________ 4.5 Financial Issues & Distribution_ _________________ 4.5.1 4.5.2 4.5.3 4.5.4 4.6

To the Patient___________________ To the Practitioner______________ To the Producer_________________ To Governmental Institutions_____ Repair and Life-time_____________

45 49 49 50 50 50 50

Criteria

3.1.5 3.1.6 3.1.7

7 Anatomy of the Lower Limb_______ 7 Transtibial Amputations_ _________ 8 Residual Limbs_ _________________ 9 Patients Posture and Principles for Alignment___________________ 13 Basic Biomechanics of Gait _______ 16 Gait Deviations_ ________________ 19 Special User Groups; children and patients with a reduced activity level 20

4 4.1

4.3.4 4.3.5 4.3.6

Stragegy

3.1.1 3.1.2 3.1.3 3.1.4

6

22 3.3.1 Dutch Industry_ ________________ 22 3.3.2 Worldwide Industry_____________ 22 3.3.3. Component and fitting prices_____ 23

Usage

Actors and Users______________ The Patient____________________

2.2

21

4.3.1 4.3.2 4.3.3

33 Basic Components: Socket________ 33 Basic Components: Pylon ________ 36 Basic Components: Foot/Ankle System ________________________ 37 Basic Components: Suspension ___ 40 Additional Components__________ 43 Materials & Tools_ ______________ 44

Prostheses

3 3.1

2.1

4.3 Components_ _________________

Users

2.4 2.5

Project Background and Approach_ _____________________ 2 Time Line of Project and Design Philosophy_ ___________________ 2 The Need for More Prosthetists___________________ 3 Recommendation: The Universal Prosthesis_____________________ 4 Design Objective_______________ 5 Project Approach______________ 5

3.2 The Prosthetist and other Team Members in a Prosthetic Clinic_____________ 3.3 Producer of Prostheses_______

Approach

2

Introduction___________________

Boudewijn Martin Wisse TU Delft, 2005

Page: 

5 5.1 5.2 5.3 5.4

Life with a prosthesis -

6

the

amputee’s perspective_______ 51

Preprosthetic care____________ Selecting the aid _____________ Alignment and rehabilitation Daily routine: donning,

52 53 54

doffing and gait_ _____________ 55

5.5 Statistics on functional outcome and use______________ 58

5.6 Aftercare and concerns_______

58

6.1

Ethics, Marketing and Design Vision_________________________ Ethics________________________

7 60

60 6.1.1 A World-wide Smart-tech product 60 6.1.2 Social-political consequences 60 6.1.3 A product for the world__________ 61 6.1.4 Production_____________________ 62

6.2 Conclusions from the Sri Lankan test designs___________ 6.3 Marketing ___________________ 6.4 Substitute products and

71

7.1 7.2

competitive fitting methods___ 65

6.4.1 Fabrication and fitting methods___ 65 6.4.2 Substitute products______________ 66

6.5 Vision of the fitting procedure

7.3

VI

71

Criteria for cycle 1: Market exploitation in developed countries___________ 73

7.4 7.5 8

and usage_____________________ 67

6.5.1 Cycle 1 – for developed countries 67 6.5.2 Cycle 2 – for developing countries 69

Ten Design Criteria __________ Requirements for cycle 0: The preparatory design

trajectory____________________ 72

62 63

Design criteria and requirements

9

Criteria for cycle 2: World market exploitation___ Additional goals______________ Discussion and conclusion of part 1_ ____________________

75 76

77

Synthesis - from idea to prosthesis_ ______ 79

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Ideas__________________________ 80 Idea generation_______________ 80 Idea discussion________________ 81 Idea selection and integration 89 Evaluation of the integrated

92 92

The connector_______________ 101 Resulting fitting procedure__ 104 Daily usage & Suspension_____ 105 Production and price_________ 106

11.6.1 11.6.2 11.6.3 11.6.4

Production costs per part_______ 106 Development costs_ ____________ 107 Marketing and Distribution costs 107 Conclusion____________________ 108

109

R

References___________________ 126

F

Figures & Tables List________ 127

Criteria

12.2 Evaluation the concept against the requirements.____________ 115 12.3 Model and Fit of the Frame__117 12.4 Project evaluation___________ 119 12.5 Conclusions

Conclusion___________________ 124 Strengths____________________ 124 Project progression__________ 125 Final word___________________ 125

Stragegy

12 Evaluation___________________ 109 12.1 Scoring criteria in comparison with other prosthetic systems.___

14 14.1 14.2 14.3

Usage

11.1.1 Selection of loadable and avoidable area’s based on anatomy_________ 92 11.1.2 Determining the rough frame shape._________________________ 93 11.1.3 Optimizing the frame shape in regards to the anatomy.__________ 94 11.1.4 Back to 3D_____________________ 95 11.1.5 Material choice_________________ 96 11.1.6 Mechanical properties___________ 97

11.3 11.4 11.5 11.6

Prostheses

11 Concept_______________________ 11.1 The hard socket_ _____________

11.2.1 Fitting liner_ ___________________ 98 11.2.2 The Filler Material_ _____________ 99 11.2.3 Adding pressure_______________ 101

13 Recommandation_____________ 120 13.1 Fundamental research in prosthetics.__________________ 120 13.2 Improving the Universal Prosthesis___________________ 121 13.3 Project continuation_ _______ 122

Users

design and conclusion_________ 90

11.2 The soft socket _ _____________ 98

Approach

10 10.1 10.2 10.3 10.4

Page: VII

The Universal Prosthesis

1 Introduction During previous projects [Wisse et al. 2002,

design such a prostheses. It exists of three parts:

In the first part of this report, the analysis

The design of the universal prosthesis will

It all starts with the right ideas. Altough a

be based on existing knowledge, especially from current designs. Chapter 4 discusses current prostheses, existing types and their fabrication.

strong vision and general idea about how the prosthesis should look like and function was generated in Part I, a new set of ideas is formulated to be sure that no good alternatives were overlooked (chapter 10).

The

This ideas need to be integrated into a new

prosthetist needs to fit and align the prosthesis, but the patient needs to wear it daily. Chapter 5 discusses the daily use of current designs.

These analysis, combined with the strategic

principles from chapter 6, result in chapter 7 in the requirements as will be used for the design of the universal transtibial prostheses. in chapter 8, the conclusion states what needs to be done in the next phases of the project.

III

Feasibility Study

The concept has to be evaluated (chapter 12).

Will an universal prosthetic system become reality in the future? Chapter 13 gives some recommendations and an overview about what still needs to be done. Chapter 14 concludes with the answer to this question and gives a notion about what the future might bring.

Criteria

Finally,

fitting method and the components of which the universal prosthesis is constructed. The parts are optimized to ensure one integral system in chapter 11.

Strategy

and preconditions for this project can be found. It concludes with the possibilities and the design requirements for a universal prosthesis. This part will provide the information needed for the next phases in this research project. Those with some background in prosthetics and who are primary interested in the design requirements of the universal prosthesis are referred to chapter 6 and 7.

principle concept of a universal socket is described. Chapter 9 describes the followed process to reach this result.

Usage

I Analysis

In this part the development of a proof-of-

Prostheses

I Analysis II Synthesis III Feasibility evaluation

to use and feel comfortable with the universal prosthesis and are therefore the focus of the design process. In chapter 3 you will find a description of the actors and their relationships.

II Synthesis

Users

This is the first report of a project aiming to

The patient as well as the practitioner have

Approach

2003] it became clear that making, fitting and aligning prostheses for patients can be a time consuming activity. A universal prosthetic design for daily use could improve prosthetic health care, but is not yet available. Chapter 2 explains the source of this problem.

Boudewijn Martin Wisse TU Delft, 2005



2 Project Background and Approach This

chapter will describe how the need for a universal prosthesis was recognised. It explains the underlying problem and the process that uncovered this problem.

Those who understand the need for a universal prosthesis and are merely interested in the design analysis can skip to section 2.4.

2.1 Time Line of Project and Design Philosophy While

the project now focuses on a technologically advanced product, it started out focusing on low cost, easy producible and repairable prosthesis for use in developing countries (see TABLE 2-1 and Appendix C for an overview).

In April 2002, Johan Molenbroek and Henk

Kooistra started a “Design-for-All” contest in which several groups designed a prosthesis for Sri Lanka. Of course, I was part of a team that participated in this contest and the result was the report: “Prostheses for Sri-Lanka, prostheses for tibial amputees focused on the 3rd world “[Wisse et al. 2002] (See appendix A for a summary of the design for all project).



Mainly because of our force analyses and

international approach, we won the contest and were able to continue our work in an internship in Sri Lanka. During the internship, we worked at the Colombo Friends in Need Society (CFINS), a non-governmental organization (NGO). The CFINS provides prosthetic services all over Sri Lanka and uses mainly the Jaipur Foot technology [Wisse et al. 2003, p13]. Here we were able to build and test some of our ideas from the contest. This resulted in a new design philosophy and new designs, which we were able to present at a World Congress of Alternative Medicine [Wisse et al. 2003]. Our results can be read in the report: “The Alternative Prosthesis, final report internship Sri Lanka 2002” [Wisse et al. 2003] (See appendix B for a summary of the internship).

(pre-) Sri Lanka

This project

Time span

Till December 2002

December 2004 till August 2005

Problem perceived

Number of produced prosthesis too low

Number of professionals too low

Goal

Prosthesis easy to manufacture from basic materials

Universal prosthesis from plastics

Target group

Third world amputees

Patients worldwide

Costs

Extremely low costs

Cost reducing through time

Table 2-1: Project targets before and after the Sri Lanka internship [Adjusted from Wisse et al. 2003, Chapter 5] (For a complete timeline see appendix C).

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

At

However,

“Design-for-All” contest’s goal was improving help for land-mine victims in Sri Lanka. However, because land mines are used in specific zones only, and Sri Lanka doesn’t suffer from sliding landmasses, civilian causalities are few. Still, the amount of amputees is Worldwide an problem.

Worldwide

there are about 15 million amputees (also see appendix F). With 39 percent of them living in the Asia’s, this area deserves special attention. In some countries land mines are a problem, though most common causes are accidents, diabetics, cancer, infections and congenital deformities.

Criteria

care for the amputees is in many cases insufficient. The production capacity is low and there is a lack of experts (prosthetist) to fit the prostheses. “It has been estimated that it would require training up to 100,000 new prosthetists if conventional production methods are to meet the worldwide need” [Michael 1994]. This results in a lack in health care and aftercare. Although different groups are thinking about (and working on) this problem and developing alternatives, no alternatives are available yet.

Stragegy

Health

Usage

see Appendix D.

The

Prostheses

For a flowchart of the socket designs till now,

2.2 The Need for More Prosthetists

Users

during the internship, we found out that instead of producing prosthesis from aluminium, the advantages of using plastics were needed. Plastics offer a lot of design freedom for a decent final product price (only at higher quantities, so the product needs to be distributed to al least several countries). This design freedom is not only needed to provide a comfortable and stiff prosthesis, but moreover to assist the user in fitting and alignment. With plastics, primary functions, alignment functions and an adjustable shape can be integrated in one product. Costs are less an issue, as we see that US-Aid and other foundations have a “magical” 100$ border, which they are ready to pay for in case of humanitarian distribution of a prosthesis [Wisse et al. 2003].

Approach

the start of the internship, the design ideas were based on three basic forms, namely our redesign of the prosthesis by Inne ten Have, the design by Michelle Kriesels and conventional prostheses. The prosthesis by Inne consists of a long strap of metal, which can be folded to form a patellar bearing prosthesis [Wisse et al. 2002 for more information]. We initially improved it by adding some parts. Michelle Kriesels also participated in the “Design-for-All” contest and her design was based on (re)using bicycle parts to manufacture the prosthesis [Kriesels et al. 2002]. Of modern conventional prosthesis, the modular build-up (See section 4.2) and the patellar tendon bearing principle (See section 4.3.1), were adopted to our designs.



In general a better use of the prosthetists‘

time will result in better overall care, more patients helped, better aftercare and more attention to difficult amputations and special patients (such as children).

There

is a worldwide need for the

prosthetist’s valuable time.

2.3 Recommendation: The Universal Prosthesis

For developing countries, the philosophy for

As concluded in section 2.2, there is a need

“A new concept for a everyday prostheses could improve the situation of amputees.

Given

Evidence shows possibilities for an adjustable, easy-to-fit but comfortable socket. The more the patient can do himself, the fewer prosthetists are needed, thus reducing the lack of prosthetists. The higher quantities needed for the newly reached amputees enable mass production. Costs are reduced. Distribution will speed up, because the need for the patient to travel to distribution points is cancelled. This prosthesis can be produced in developing countries, but has market potential all over the world. It is especially better suitable for children [Red: because it is adjustable and children and their residual limb keep growing].

for more prosthetists.

a certain amount of amputees and the amount of care they need, the lack of prosthetists can be solved in three ways: 1 Increasing the amount of prosthetists. 2 Lowering the level of experience (knowl-

edge) needed to be a prosthetist. 3 Reducing the time asked per patient of the prosthetists, which implies: - Reducing the need for replacement. - Reducing the time per adjustment

The design and manufacturing of the prosthesis is a time-consuming event for the prosthetist. Research trails and prototypes strongly suggest that the prosthetist’s work can be more time-efficient with an alternative design for transtibial prostheses, the universal prosthesis.

the universal prosthesis design could be as follows:

Ideally, the end users are capable of adjusting the prostheses themselves. The product’s use should be self-explaining (e.g. by clues integrated in the product on how to use it).” [Adapted from Wisse et al. 2003].

N

ot only transtibial amputees will benefit in such a way. The freed production capacity can then be used to produce above knee prostheses or orthoses. 

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

2.4 Design Objective

The first step is to evaluate if the universal

prosthesis is a feasible product at all. Such a feasibility study is most easily conducted at the hand of a “proof-of-principle” design. As suggested by the name, such a design proofs the concept of a universal prosthesis. Because

- Analysing the possible markets and target groups for a universal prosthesis. (this phase) - Formulating a set of requirements. (this phase) - Designing one or more concepts for (the socket of) a universal prosthesis. (second phase) - Testing the best concept, preferably by testing a physical model /mock-up of the socket. (third phase) - Assessing the feasibility of universal prostheses in general and the concept in particular. (third phase)

Criteria

beneficial to the project, this project starts with finding out what the possibilities are for a universal prosthesis (solution -> problem) instead of finding the universal prosthesis as the answer to a specific problem (problem -> solution).

In which the major tasks are:

Stragegy

To determine which stages or scenarios are

- Analysis - Concept design - Feasibility assessment

Usage

stages (each with increasing design criteria) is a solution. As becomes clear later in the report, one possible stage is the universal prosthesis for use as a temporal prosthesis. Another possibility is developingthe prosthesis to be an avanced tool for prosthetists in developed countries.

the aim of this project is to design a concept of a universal prosthesis. This concept will be used to assess if the production of universal prostheses is feasible.

project will consist of three phases, that are parallel with the three parts of this report:

Prostheses

Development of the universal prosthesis in

Concluding,

This

Users

is clear that an easy-to-use, comfortable, adjustable and durable prosthesis for daily use could result in better health care for amputees all over. However, the design requirements for a daily usable (definite) universal prosthesis are quite high. Much development is needed before the definite universal prosthesis is a reality.

2.5 Project Approach Approach

It

the comfort of the prosthesis’s fit is the most important functional outcome factor, this concept will focus on the development of the socket.



3 Actors and Users An

analysis of the properties and behaviour of the actors is necessary to determine the better part of the design requirements. The user is the most important actor. In the case of prosthetics, the amount of actors is huge (see figure 3-1). The focus on the project will be on those actors who deal with the prosthesis most intensively: the patient, the prosthetist and the producer.

Traditionally, prosthetic designs were mainly

based on medical properties of the patient, especially the anatomy (of the residual limb) and biomechanics. Only recently more attention has been given to the production (the modular design as discussed in section 4.2, is only developed in 1970 by the U.S. Veterans Administration). Now, high tech (such as microprocessor control of joints) solutions are sought. [Seymour 2002, p7]. However, till 2002, innovations for the patient or the prosthetist, were sparse.

The prosthesis is only part of the total care

after an amputation and therefore in literature a team approach in rehabilitation of the patient is often mentioned [Seymour 2002, Chapter 3]. The team approach will be shortly discussed in 3.2.

Amputee Family Support network Occupation



Physician

Nurse

Therapist

Dietician

Social Worker Designer

In

this chapter the three most important actors will be introduced: The patient (3.1), the prosthetist (3.2) and the producer of components (3.3). This chapter focusses on their properties. Their actions will be discussed later. Everyday use of the prosthesis by the patient will be discussed in chapter 5. Most use by the prosthetist will be discussed in chapter 4, together with the fabrication, alignment and fit of the prosthesis.

Revalidation TEAM

Prosthesis Public Governament Insurances

Figure 3-1: The prosthesis and its total context.

Prosthetist Suppliers

Counsellor

Eduction

Component Producer

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

3.1 The Patient

Femur

Knowledge

Muscles

of the anatomy of the lower limb is the basic: it provides insight in which functions are lost by the amputation and is a major inspiration in how to reintroduce them by means of a prosthesis. Figure 3-2 shows the most mentioned bones and tissues.

Illium

Ischium

Users

Patella Tendons (Patella T) Tibia Fibula Calf Muscle

Femur

Scar

thesis is to improve the performance of functional activities and mobility, including ambulation. Some basic biomechanics of gait and of posture should be known (3.1.4 to 3.1.6).

Patella Tubercle

Tarsal bones

Tibia Gatrocnemius Tibialis anterior

Peroneus tertius Soleus

Figure 3-2: Bones of the lower limb (most right), muscles (middle) and anatomy of the residual limb (below) [Adapted from IMT-Baghdad and Wisse et al. 2002].

Fibula

Criteria

user groups, children and patients with a reduced activity level, have their own design requirements. They are introduced in section 3.1.7

Stragegy

Special

Tibials posterior

Usage

Of course, the primary purpose of a pros-

Prostheses

design, selection and use starts with a person who needs an artificial leg. Some are born without limb (congenital deficiency), others are amputated by trauma or disease. In case of the latter, the choice of amputation-level (3.1.2) is the most important for the eventual type of prosthesis and the functional outcome of use. Transtibial amputations are in about 70 percent of the cases the best solution, resulting in a below-knee stump -or better – a transtibial residual limb (3.1.3).

Approach

Prosthetic

3.1.1 Anatomy of the Lower Limb

Metatarsal bones Phalanges



3.1.2 Transtibial Amputations

The term trans is used when an amputation

extends across the axis of a long bone. When two bones are involved, such as the tibia and fibula, the primary bone is identified. Transtibial is the proper term for a belowthe-knee amputation. Amputations between bones or through a joint are referred to as disarticulations.

Levels

There are different levels of transtibial ampu-

most proximal to the transtibial are the kneedisarticulation and the Syme amputation. The Syme amputation is an ankle disarticulation in which the heel pad is kept for good weight bearing. See figure 3-4. Transfemoral (above-the-knee or thigh) amputations will be mentioned as well, because biomechanics and solutions for transfemoral prostheses are often comparable to transtibial amputations. Requirements: The universal prosthesis should fit most transtibial amputations, which implies a residual tibia length of at least 80 mm to 50% of the original length.

tations (different types), namely short, standard and long (figure 3-4). During amputation in a standard procedure, bone is cut shorter than skin and muscle, so that the skin and muscles can be folded over and the wound can be closed well (figure 3-3).

S



tandard transtibial amputation occurs when between 20 and 50% of the total tibial length is preserved. An elective amputation in the middle third of the tibia, regardless of measured length provides a well-padded and biomechanical sufficient lever arm. An amputation shorter than 80 mm is not advised because of the resulting small-moment arm, ill-fitting of the prosthesis and the fact that it makes knee extensions difficult. Long transtibial amputations result in poor blood supply in the distal leg. The two amputations

Figure 3-3: Amputation procedure [Seymour 2002].

Figure 3-4: Different levels of transtibial amputation [Seymour 2002].

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Prevalence

However,

In all zones, transtibial amputees form about Yearly

Residual limbs differ from patient to patient,

not only in dimension, but also in skin condition, flexibility and strength. [Seymour 2002, p38]. All these properties can change over time.

Stragegy

figures from the UK show that the percentage of lower limb amputations stay constant in the next few years. Data from the National Health Service shows that transtibial amputations account for about 50% of all 6000 yearly amputations and congenital deficiencies [UK NHS, 2005]. More figures of prevalence can be found in Appendix F.

possible, the physicians will try to save the original limb of the patient. However, when tissue-saving techniques are no longer holding out, the practitioners will decide to amputate the patients leg. This results in a residual limb, also called residua or stump. During the operation, the fibula is cut 20 mm shorter than the tibia, so the calf muscle has enough space to form a good stump. Compare figures 3-2 and 3-4.

Usage

53% of the total amputees and about 65% of all leg amputees. Calculations with these figures result in table 3-1.

Project: The universal prosthesis can be used to provide European and US amputees with an addition to their healthcare program. However, to reach full potential, the project should aim to reach 1 million limbless worldwide.

Where

Prostheses

worldwide prevalence is much higher, about 2.44 permillage.

3.1.3 Residual Limbs

Users

all around the world. In most developed countries the amputee point prevalence (amount of amputees in one thousand residents) is about 1.55 permillage and leg amputees make up about 1.33 permillage of the population (see Appendix F for sources).

transtibial is the most common level of amputation, the worldwide amount of transtibial amputees is quite high. Unfortunately, reliable figures on the amount of limbless (without a prosthesis) patients aren’t available. However, our research in Sri Lanka shows that from the 40-160K amputees (assume 80k) there, only about 10k were provided a prosthesis. At least a million limbless worldwide is very realistic assumption.

Approach

Amputation is a common medical treatment

Because

Population

Transtibial Amputees

Europe

450 M

370 K

U.S.

250 M

210 K

Worldwide

6,1 G

9,7 M

Table 3-1: Amount of amputees worldwide.

Criteria

Zone



Development

During the first 4 weeks, the residual limb

will significantly change in shape and properties, mainly due to tissue-healing. Then, up to 6 months after the operation, the limb will shrink to its final size.

Other

changes in size may occur after first 6 months. Some patients experience changes during use (every day). Also, limbs will change due to training and body-weight increase or decrease.

Finally,

skin conditions such as tissue damage, scar-forming, onset of callous spots and oedema can change the shape of the skin.

Project: The universal properties of the prosthesis can be especially useful direct after the operation (during the first 6 months). If the prosthesis can (also) be fine-tuned by the patient, it can be used to adjust for small daily shape-changes during day-to-day use (after 6 months). These adjustments should be very easy to do (few user actions). Slow, long term changes (taking weeks/months) (e.g. patient increases in weight) may be adjusted for using a tool.

10

Measurement and Shape

Measurements

of the residual limb can be taken in many ways. In practice, only basic measurements are taken, because in most cases a plaster cast from the residual limb itself is used to shape interfaces of the limb with prosthetic devices (see chapter 4). Measurements are important to keep track of the changes in the stump over time, especially during the first 6 months.

Requirements: The universal prosthesis should fit all three basic residual limb shapes. Residual limb lengths of 80 to 250 mm should be fitted comfortably. Circumferences around the patellar tendon should be varied from 250 to 350 mm.

Common measurements are: -

-

-

Length from the tibial tubercle (or from the middle of the patellar tendon) to the end of the bone. Length from the tibial tubercle (or from the middle of the patellar tendon) to the end of the soft tissue. Circumferential measurements from 0 mm (at the tibial tubercle or at the middle of the patellar tendon) and than at every 40 mm (downwards).

These

circumferential measurements are also an indication for the shape of the residual limb (figure 3-5). In appendix G statistics are presented that show the measurements of residual limbs in Sri Lanka. These measurements give an indication of in which range the prosthesis should be adjustable. A range of 80-250 mm covers most of the amputations.

Figure 3-5: Residual limb shapes: conical (a), cylindrical (b) and bulbous (c). [Seymour 2002]

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Skin

patients are left with a scar. Also skin conditions may vary. Patient may have several area’s and combination of the conditions mentionel in table 3-2:

There are more factors that indicate possible

After the healing of the residual limb, most

t)

tenderness

over sensitivity, NL: overgevoeligheid

a)

adherence

NL: aankleving

i)

invagination

to fold in so that an outer becomes an inner surface, NL: kloofvorming

c)

callus

a thickening of or a hard thickened area on skin, NL: eelt

d)

discoloration

reduction of health skincolor, NL: verkleuring

(nh)

nonhealing

NL: niet helend

Table 3-2: Skin conditions.

If the physician suspects blood flow problems,

blood flow tests of the remaining extremity may indicate general health of blood flow. Patients with blood flow problems cannot be ignored, because most elderly amputations are the result of reduced blood flow in the extremities (often due to diabetics).

“By the year 2005, the five countries with the highest incedence of diabetes will be India, China, the United States, Pakistan and Indonesia.” [ACA 2001, p79]

Criteria

explanation

Preconditions: The patient has a reasonable amount of loadable areas. The patient has a reasonable healthy residual limb. T

Stragegy

condition

due to the lack of feedback to the patient. On the other hand, the patient may report phantom pain in stead of pain with a evident physical cause.

Usage

code

Impaired sensitivity can lead to skin damage

Prostheses

abrasions (areas of skin breakdown), blisters (mostly caused by friction), contact dermatitis (inflammation), distal oedema (swelling) and skin ulcerations.

problems. A low temperature may indicate arterial insufficiency, abnormal warmth may indicate infection.

Requirements: In situations were pressure or friction on certain areas will cause pain or further complications, the universal prosthesis must be able to avoid loading these areas. The universal prosthesis should allow or stimulate blood flow in the residual limb. The socket has to make total contact with the residual limb to avoid oedema and invagination.

Users

Other skin complications that can occur are:

areas where these complications or conditions occur, are often very sensitive to pressure or friction. These areas should not be loaded (to much) by the prosthesis.

Approach

Skin and Tissue Conditions

11

Areas of Weight Bearing and Areas of Relief

The tissue in the residual limb is more or less

suitable for transferring load in certain areas. The loadable areas can be seen in figure 3-6 .

Areas of weight bearing include: - - - - -

Requirements: The universal prosthesis should offer areas of pressure and areas of relief according to the anatomy of the residual limb. In any case, load should be transferred to the patellar tendon. Preconditions: The patellar tendon, tissue medial and lateral to the tibial crest, and tissue on the posterior is loadable.

Patellar tendon Flare of the medial tibial condyle and the anteriomedial aspect of the tibial shaft Anteriolateral aspect (pretibial group) of the residual limb Midshaft of the fibula Gentle end-bearing if tolerated

Areas of relief include: - - - -

Anterior and lateral edges of the lateral tibial condyle Head and distal end of the fibula Crest and tubercle of the tibia Anterior distal end of the tibia

In general, relief areas include bony prominences, areas of poor blood supply, or areas that are near prominent nerves such as the common peroneal nerve.

Figure 3-6: Pressure tolerant and sensitive areas. Most left: A scematic of sensitive (light red) and tolerant (dark red) areas [Seymour 2002]. 4 Right: anterior, lateral, anterior and medial view of a positive (cast), with pressure sensitive (red) and tolerant areas (blue).

12

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

R ange of Motion

- - -

In the case of an amputee wearing a prosthesis that weighs less than the original limb, the centre of gravity will shift proximally and away from the prosthesis. The amputee may lean the trunk towards the uninvolved side to compensate. For the best stability the line of gravity should pass through the base of the support (see figure 3-7).

Usage

Preconditions: The range of motion of the patient allows walking with conventional prosthesis.

is the alignment of the body segments in space. To maintain upright posture (to stand), the body must counteract the effects of gravity or other forces acting on it. This involves muscles, ligaments, capsules and other soft tissue, bone and the nervous system.

Prosthetic

alignment is the position of a prosthetic socket in relation to foot and knee. Alignment is performed in two phases, a bench or static alignment based on established guidelines and a dynamic alignment based on the patient’s gait patterns to finetune the device to achieve an optimal gait pattern.

Criteria

Figure 3-7: Base of support. The size of the base of support varies with a change in foot position. [Seymour 2002]

Stragegy

Requirements: The prosthesis should not be too light (<0.5 kg). Distal weight has more inpact on the energy consumption and experienced comfort. center of gravity

Prostheses

-

Anterior and posterior drawer Medial and lateral (valgus and varus) stability Crepitus (a peculiar crackling, crinkly, or grating feeling or sound under the skin or in the joints) Recurvatum (hyper extension of the knee)

Posture

alignment is the alignment of the socket and foot. The physician uses a plumb line from the centre of the posterior wall of the socket to a location about 10 mm lateral to the centre of the heel. This alignment maintains a fairly normal base of support and loads the more-pressure-tolerant areas on the medial residual limb rather than the fibular head region. In the sagittal plane, a plumb line should fall from the centre of the lateral wall of the socket to just anterior to the front edge of the heel (figure 3-8).

Users

knee joint should allow enough movement to properly use the prosthesis (range of motion or ROM). Additionally, the patient needs at least the strength to move the prosthesis. Before fitting a prosthesis, the knee is normally tested for:

Static

Approach

The

3.1.4 Patients Posture and Principles for Alignment

Figure 3-8: Static alignment for a transtibial prosthesis. A) In the frontal plane, B) In the sagittal plane. [Seymour 2002]

13

Static

alignment of the transtibial socket usually includes 5 to 10 degrees of flexion of the socket. A residual limb in a socket with vertical walls would easily slide up and down. Also, flexion allows greater exposure of the patellar tendon for weight bearing (figure 3-9 and figure 3-10).

Subjects

seem to find a PTB socket omst comfortable with a PTB-bar at 4 mm depth [kim 2003]. Furhtermore, according to Besser [1992] 45% of the total body weight can be carried by the Patellar Tendon.

Gravitational Force of Body-Weight

Requirements: Alignment of the prosthesis should allow more load to the medial residual limb rather than the fibular head region. Alignment allows 5 to 10 degrees of flexion of the knee (and the socket).The patellar tendon should be loaded most.

A well dynamic aligned prosthesis will not

rotate while standing, due to the equilibrium between the ground forces and the forces from the residual limb on the prosthesis. However, during gait the forces are not along the same line and the fit of the socket becomes crucial to resist the rotation during gait.

14

Figure 3-9: Inclination of the bulge of the PTB (see section 4.2) socket. The bulge provides more surface for weight bearing than the wall of the socket. Note the relatively longer horizontal component of the vector. [Seymour 2002]

Figure 3-10: Forces on the patellar tendon increase because of the need to compensate moments due to distance a and b and because the inclination of the force factor on the patellar tendon [Wisse et al .2002]

14

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Also,

Approach

the line of gravity of the prosthetic limb should run near or through the (knee) joint, because otherwise the body must compensate the resulting moments with muscle activity. This is mostly achieved by linear alignment. Figures 3-11 to 3-14 show linear alignment (in contrast to angular alignment) problems and their resulting forces.

Users Prostheses

Requirements. Rotational alignment of the prosthesis should result in a minimum of rotational forces while standing, while providing enough rotational support during gait. The line of gravity of the prosthetic limb should run through the knee joint. This might imply the need for linear alignment.

Usage Figure 3-14: Alignment in the frontal plane. Left: normal. Right: Foot placed to far forward. If the force though the spocket fell posterior to the ground reaction force vector, the prosthesis would tend to rotate.

Criteria

Figure 3-12: Alignment in the sagittal plane placing the foot lateral to the socket, resulting in pressure on the fibular head and distal medial residual limb. [Seymour 2002]

Figure 3-13: Alignment in the frontal plane. Left: normal. Right: Foot placed to far backward, causing pressure on the distal anterior part and proximal posterior part of the limb.

Stragegy

Figure 3-11: Alignment of the transtibial prosthesis in the sagittal plane, placing the foot medial to the socket. This placement tends to cause a rotation of the socket that then places pressure on the proximal medial and distal lateral residual limb. [Seymour 2002]

15

3.1.5 Basic Biomechanics of Gait Terms

For

an explanation of the terms used to describe the type of motion, rotary motions (such as flexion/extension, abduction/adduction, etc), the planes in the body (frontal or coronal, horizontal or transverse and sagittal) and biomechanical concepts (such as axes of joint motion, instant axis of rotation, kinematic chain, degrees of freedom), etc, I refer to standard reference books and figure 3-15.

Gait

or ambulation can be defined as the translation of the body from one point to another by way of bipedal motion (NL: gang, pas, loop). In both walking and running there is a rhythmic displacement of body parts that maintains the person in constant forward progression.

Normal gait is not easily defined. Therefore,

literature sometimes speaks of acceptable gait. From a mechanical perspective, it would seem logical to take energy efficiency and force transmission as main criteria, but in practise a naturally looking gait is most important. Overall the amputee should exhibit even step length, step timing and arm swing. Walking speed is less important (also see section 5.5).

Figure 3-16: Distance variables of giat. a) left step length, b) left stride length, c) right stride length, d) right step length, e) width of base support f) Right toe-out, g) left toe-out [Seymour 2002]

Requirements: The prosthesis should allow acceptable gait. Period

Phase

Description

Stance

Initial contact

When the foot hits the ground

Loading

Until the opposite foot leaves the ground

Midstance

Until the body is over and just ahead of the support

Swing

16

Figure 3-15: Planes of the body. [Seymour 2002]

Terminal stance

To toe-off

Preswing

Just after heel-off to toe-off

Initial swing

Until maximum knee flexion occurs

Midswing

Until the tibia is vertical

Terminal swing

Until initial contact

Table 3-3. Phases in gait. [Seymour 2002]

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Gait can be described from both a kinematic and kinetic standpoint.

Approach

Kinematics

Kinematics is the classification and compari-

Users

son of motions. In gait, the feet are moved in different phases (table 3-3).

In

To

Preconditions: The joint excursions during normal gait are the minimum required range of motion that is also needed for proper gait with the prosthesis.

midstance

terminal stance

prewsing

initial swing

midswing

terminal swing

0-2

0-10

10-30

30-50

50-60

60-73

73-87

87-100

Heel rocker

Ankle rocker

Ankle rocker

Forefoot rocker

rocker phase knee moment

extension; valgus

flexion; valgus

flexion to extension

extension

extension to flexion

gravity extending; accelration

gravity linear distracting

gravity flexing; deceleration

knee angle

0

0-15 flexion

15-5 flexion

5-0 flexion

0-30 flexion

to 60 flexion

to 30 flexion

0

ankle moment

plantarflexion; valgus

plantarflexion; valgus

plantarflexion todiorsiflexion

dorsiflexion

dorsiflexion

gravity plantarflexing

gravity plantarflexing

gravity plantarflexing

ankle angle

neutral

0-15 plantarflexion

15 planterflexion to 10 dorsiflexion

0-5 dorsiflexion

0-20 planterflexion

10 plantarflexion

neutral

neutral

Table 3-4: Phases of the gait cycle of the right leg. [Adjusted from Seymour 2002]

Criteria

affect normal gait. Among these are age, strength, cardiovascular status, habit, clothing, psychological status (including fear of falling) and factors that affect the location of the centre of gravity (COG) of the total body.

loading response

Stragegy

Apart from joint mobility other factors can

% of gait cylce

initial contact

Usage

provide adequate weight acceptance, single-limb support and limb advancement, the hip, knee, ankle and subtalar joints need to flex and rotate. Their range of motion (excursions) accompanying the phases of gait can be found in table 3-4.

Prostheses

figure 3-16 the different distance variables, occurring during the gait phases, can be seen.

17

Kinetics

Kinetics

is the branch of mechanics that is concerned with the forces that cause motions. The primary external forces acting on the body in normal gait are gravity and the ground reaction force. Muscles function to counteract these forces and to accomplish the forward progression of the body.

During

gait the COG moves side-to-side. Placing the feet further apart, thus creating a wider base of support increases stability, but results in an increase in the side-to-side excursion of the COG and thus an increase in energy cost.

knee passively extends with relaxation of the knee flexors. Requirements: The prosthesis should allow enough stability with a lateral feet placement which resembles normal gait. Requirements: The energy-cost of use of the universal prosthesis should be comparable to current prostheses. The ankle-foot complex should decrease the vertical excursion of the centre of gravity. The prosthesis should be light. Requirements: During swing, the toes may not hit the ground.

The ankle/foot complex plays a very important role in limiting the vertical excursion of the COG. A greater excursion will increase the energy required for gait.

At initial contact (see table 3-3), the critical

18

event for normal gait is that the heel should contact the floor first. Once the foot hits the ground, loading response occurs. In this phase knee flexion and plantarflexion occur for shock absorption. Hereafter, stability is of utmost importance. Especially during terminal stance, the gastrocsoleus contracts to stabilize the advancing tibial and to raise the heel (heel-off phase). During swing the muscles of the anterior compartment prevent the toes to drag on the ground. In midswing, the

Figure 3-17: Gait deviations to accommodate a long limb. A) Hip hiking, B) Lateral trunk lean, C) Circumduction, D) Vaulting, E) Excessive hip and knee flexion. [Seymour 2002]

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

3.1.6 Gait Deviations

Weakness

A common deformity is a leg length differ-

and anxiety are particular pertinent contributors to gait deviations among those with amputations. Vaulting may occur if there is a fear of stubbing the toe of the prosthesis during swing. If there is a lack of confidence in the prosthesis, the individual may try to get off the limb quickly, resulting in an uneven step length.

Criteria

of the device on the tissues of the body and can cause major gait deviations. The natural response to pain is to try to move away from it, to take the weight or pressure off the painful area. For example, an individual with pain of the distal residual limb may bend the trunk laterally to get more weight of the area. [Seymour 2002, p109-13]

Stragegy

Pain can develop from the stress and strain

Usage

ence. Either the leg consisting of a residual limb and prosthesis or the other side is to long. This can be caused by the prosthesis itself (pylon to long), or by insufficient flexion in the knee (or in the hip). Whatever the cause, it is more difficult to clear the ground during swing. An individual has several options to accommodate the long limb (Figure 3-17). An additional option to accommodate is a wide walking base, but walking this way is very energy inefficient.

Fear

Prostheses

of the residual limb with poor muscle tone can result in rotation of the soft tissue and of the prosthesis itself over the underlying bone. It can also increase pressure.

Users

fitted or poorly aligned prosthesis. Other common and often related causes include: muscle weakness, deformity (of bone or soft tissue), impaired control including sensory loss, pain, fear or anxiety.

amputees, the ability to know when the feet are in contact with the floor and to know where the joints are in space is lost. A person with an amputation must rely on the sensory input from the residual limb, a factor that may affect the individual’s confidence in gait. As a result, the walking speed (cadence) of individuals with amputations is lower than normal.

Requirements: The length of the universal prosthesis should be adjustable. The prosthesis must provide enough and direct sensory information to the residual limb. The prosthesis should be easily trusted (win the patients confidence), especially during gait. Pain, especially from to much stress or strain in the tissues of the residual limb, should be avoided.

Approach

Gait deviations are often the result of a ill-

With impaired sensory control in transtibial

19

3.1.7 Special User Groups; children and patients with a reduced activity level

There are several special patient groups, that can benefit from a universal prosthesis.

Project: These special user groups are being reviewed to see later on if the specific requirements they have for the prosthesis can give the Universal Prosthesis an edge over current existing systems for these groups

Children

Children

need a new prosthesis every six months. The universal prosthesis could improve their comfort, because changes in stump size are more often adjusted for. While the load during stance is lower (lower body weight) their life-style if often very active (many loading cycles). Children are very demanding and impatient users, the prosthesis should be even more easy to use than in the case of adult patients. The standard range of sizes the universal prosthesis would be usable for might not be sufficient. A smaller version may be needed.

Patients Level

with

a

Reduced Activity

Inactive, often elder patients are sometimes

bound to their beds. If their prognosis is not bright, the practitioners might decide not to make a prosthesis (due to costs). These people could benefit from the universal prosthesis. The load during stance is standard, but the load cycles and total usage time are much less.

With these patients, the donning and doffing should be very easy. Also, extra attention to the blood flow in the residual limb should be given.

Requirements: Design requirements may vary for these special target groups.

20



20

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Team Approach

Knowledge

and Education: To select, fit or train an individual in the use of a prosthesis, a practitioner must posses a basic understanding of biomechanical principles, normal alignment, movement and forces acting on the body or body segment. In addition, an understanding of normal gait and common gait deviations is important. Prosthetics is a profession that combines specialized clinical and technical skills.

Professionals are educated in these subjects

Prosthetic Fabrication Initial Check-out / Examination

Prosthetic Training Final Check-out or Examination

and may be certified as either an orthotist, a prosthetist, or both.

Prosthetist may own their own business as

a sole proprietor or work as an employee in a hospital, rehabilitation centre, research facility, or private business.

Return to Existing Employment or Vocational Training or On the Job Training

Criteria

lined in figure 3-18. The better the prosthesis assists several of these procedures, the more successful it will be.

Pre-Fitting Intervention

Stragegy

The procedures of a prosthetic clinic are out-

Prescription

Usage

Procedures of a Prosthetic Clinic

cial attention, because he or she is the team member who is most in contact with prostheses. In general, the prosthetist’s function is to design, fabricate and fit prostheses.

Prostheses

the amputation as an accomplished fact, a whole team of experts is needed to provide optimal rehabilitation of a patient. The team should include the physician, prosthetist, orthotist, physical and occupational therapist, vocational rehabilitation counsellor, social worker, psychologist, recreation therapist, dietician, nurse, the patient and the patient’s family or support network. The key to any team is communication. The patient should be regarded as the team leader and have clear expectations of the rehabilitation process.

In this project, the prosthetist receives spe-

Pre-Prescription Examination

Users

Considering

The Prosthetist

Approach

3.2 The Prosthetist and other Team Members in a Prosthetic Clinic

Placement

Figure 3-18: Procedures of a prostetic clinic [Adapted from Seymour 2002]

21

3.3 Producer of Prostheses

import/export centre [IEEE 1998].

In

3.3.2 Worldwide Industry

contrast with e.g. shoe manufacturers, who sell a complete product direct to the end-user, the manufacturers of prostheses sell system components and materials to the prosthetist, who fabricates the final product for the patient.

Big

producers of prosthetic components include Össur, Otto-bock and Endolite. A (more) complete list of producers can be found in appendix I.

In

1996, the World market for medical devices was estimated at US$ 94340 Million, of which 15.5% is within the orthopedic and prosthetic product sector (= 14717 Million) [IEE 1998]

Over

90% of the world market for medical devices and supplies consists of the regions USA (42%), Europe (28%), Japan and Australia.

In the Western European market (1996), big

players are France (17%), Germany (32%), Italy (10%) and The UK (11%). The Netherlands only make up for 4,7% of the market. In the European market, the orthopedic and prosthetic product category is a bit bigger: 18.5% [IEE 1998]

Total import to Western European countries

of other artificial body parts than artificial teeth (dentistry) and orthopedic implants was worth about 600 million US$.

3.3.1 Dutch Industry

Industry figures show a healthy grow in the

Dutch medical equipment industry (Table 35). Also, specific figures about the revenues show a healthy industry (Table 3-5).

Industry

statistics about the production of medical equipment and instruments, orthopedic devices, prosthesis and precision instruments. Dutch product price industry index figures can be found in table 3-6 [CBS 2005].

The Dutch industry is a relatively big importer 22

of medical devices: 2015 million US$ in 1996. The Netherlands only imported 30% from the EU, but this is most likely due to the status of the Netherlands as a leading European

Sells of prosthetic devices in Netherlands

2001

2002

2003

(Million Euros)

57

85

80

Table 3-6: Market for prostheitc devices in the Netherlands [CBS 2005]. The sales of the industry

The use of resources and half-fabricates

2000

2002

2003

2004

National

100

106

110

112

Foreign

100

102

103

104

Total

100

103

105

106

From National

100

103

105

108

Foreign (import)

100

97

93

94

Total

100

99

97

99

Table 3-5: Grow indexes of the sales in the medical equipment industry in the Netherlands [CBS 2005].

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

3.3.3. Component and fitting prices

They

Euros):

can vary wide and is dependent of many factors such as:

PTB

Prosthesists salary

27

39

COSTS FACTOR

ICEX

PTB

Technicians salary

7

49

Prosthesists salary

125

175

Transportation of the patient

44

88

Technicians salary

42

300

44

88

Component costs

1100

300

Transportation of the patient

TOTAL

1180

476

Component costs

1100

300

TOTAL

1311

863

However, it has to be noted that they calculated with an hour price for the technicians and the prosthetists of 22 Euros. It is clear that this calculation is without machine costs, facilitation costs, etc etc.

The

utes):

needed times where as follows (min-

TIME NEEDED

ICEX

PTB

Prosthesists

75

105

Technicians

25

180

TOTAL

100

285

And the price-difference is much less.

Stragegy

the study by D. Datta et al [2004] are used. They compared the cost, tima and functional outcome implications for changing from PTB to ICEX sockets. These commonly used socket systems are described in chapter 4.

ICEX

Usage

To give some indication, the numbers from

COSTS FACTOR

Prostheses

currency rates, place / country, hour costs /salary machnines and tools needed facility needed etc, etc

pice of 100 Euros this would lead to the following costs:

Users

- - - - - -

With an more realistic man/machine hour

Approach

The costs for fitting a prosthesis to a user

calculated the following costs (in

Criteria 23

4 Transtibial Prostheses The prosthesis is a device with perhaps the

most important function in the total care after an amputation. It restores some of the lost functions of the amputated limb. To do so, it will (1) suspend the limb (weight bearing), (2) give the patient stability (balance), (3) allow an acceptable gait (ambulation), (4) prevent further deformations of the body and (5) provide some sociopsychological support (cosmetics) for the patient. The choice of prosthetic design is therefore very dependent on the patient’s rehabilitation stage and prognosis (section 4.1).

Components come into existence in the factory and are assembled into a prosthesis by the prosthetists. Because of wear and changes in the patients situation, the prosthesis sometimes need to be repaired (4.6).

Almost

all current prostheses are buildup from pre-fabricated components and a custom-made socket (4.2). The fabrication supplies, in orthopaedics often called materials, and the components are bought from prosthetic device manufacturers and assembled by the prosthetist. Generally, components (4.3) offered by different manufacturers don’t differ much, because their shape, function and properties are dictated by biomechanics(4.4) and the anatomy of their users. Components and professional care are not cheap, but social services enable most Western patients to acquire the right prosthesis (4.5).

24

24

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

There are three types of prostheses (interim,

- - -

Universal Prosthesis Prefabricated Prosthesis (PFP) Preparatory Prosthesis

The prosthesis that the patient will use finally

is called the definite or permanent prosthesis.

Used till (after surgery)

Prosthesis type / Compression

Direct

1 months (wounds heal)

Soft and semi-rigid dressings

0 to 1 weeks

1 months (incision heals)

Rigid dressing interim, partial load possible

5 to 21 days

3 months (incision and sutures healed)

Rigid dressing interim, complete loading possible

10 to 21 days

6 months (residual shape almost stable)

Removable Protective interim, compression needed during use

1 to 3 months

6 months (residual shape stabilizes)

Temporary, compression during night

3 to 6 months

Prosthesis wears out

Definitive

Table 4-1: An overview of clinical patient stage and applicable prosthesis type. In practise, the choice is less time dependent, but is determined by the healing rate and activity level of the amputee.

Criteria

Start use after sur-

Stragegy

Other terms used for Interim Prosthesis include (common abbreviations are added in brackets):

-

is in almost all literature referred to as the temporary prosthesis. Terms which also refer to temporary prostheses are:

Usage

this section descriptions of these prosthesic types are given. While many terms are employed, the designs that are used in the early stages following amputation (in this report referred to as interim prostheses) are very similar in function.

The prosthesis that is used for gait training

Prostheses

In

- - - - - - - - - -

Immediate Postoperative Prosthesis (IPOP) Early Postoperative Prosthesis (EPOP) Immediate postoperative prosthetic fittings (IPPF) Custom Removable IPOP Weight Bearing Rigid Dressing (WRD) Removable Rigid Dressing (RRD) Post Surgical Prosthesis (PSP) Removable Protective Socket (RPS) Protective Prosthesis Early Fitting Prosthetic Socket Early Ambulatory Prosthesis Early Rehabilitation Prosthesis Adjustable Postoperative Protective and Preparatory System (APOPPS) – FLO-Tech. Initial Prosthesis

Users

temporary and definite) each appropriate for different stages after amputation. These stages can be determined by the health of the wound and the dressing that the wound needs to heal. A clear definition is difficult. In practise, the period in which a certain prosthetic type can be used overlaps several rehabilitation stages. Table 4-1 gives an overview.

- - -

Approach

4.1 Types According to the Patients Rehabilitation Stage

25

4.1.1 Removable Rigid Dressing RRD

The removable rigid dressing is a form of a

dressing (also see section 5.1 for preprosthetic care), which can be used very soon after the operation. The problem with rigid dressings is that the wounds cannot be inspected and attended to. A removable setup solves this problem. The Removable Rigid Dressing with integrated components for amublation is called an custom removable IPOP. In contrast with a conventional IPOP, it can be applied before the patients’ incisions are closed (and the sutures healed). Full load on the risidual limb is not possible till the wound is closed fully. Removable rigid dressings are always made by the prosthetist. The procedure includes making a rigid dressing, cutting it open along specific lines and applying Velcro bands (See figure 4-1). The materials needed are standard and easily available.

26

Advantages: Very early load on the residual limb, while wound inspection is still possible. It offers protection and access. Pre-ambulatory training is possible (limited load), An early start with patient education can be made.

There are no commercial packages that offer a complete solution including a rigid dressing and ambulation components.

Disadvantage: Time consuming to make and fit and highly skilled personnel needed.

Figure 4-1: Fabrication of a RRD and Custom Removable IPOP. Left: 3 spandex socks, pads and an attachment plate, 3 velcro straps and attachment base plates. Middle: fiberglass cast with cut lines and base plate attachment points and the result. Inset: anterior and posterior sections of the cast with gel pads. Right: Ambulation is possible, with weightbearing limited to 10-20 kg. [Walsh 2003]

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Disadvantage: High skilled personnel needed. Wound inspection is difficult.

An IPOP (see figure 4-2) is a combination

Some companies sell universal IPOPs based

on air compression. These prostheses exist of a universal outer socket and insertable aircells. An example can be seen in figure 4-3.

inflatable IPOPs are far less time consuming to apply to the patient and are used in many Dutch revalidation hospitals. However, the residual limb must be healed fully, the inflatable IPOP cannot be used too long and the weight distribution cannot be controlled. Therefore the inflatable IPOP cannot be applied to all patients.

In the first place, an IPOP can provide the

Usage Stragegy Criteria

Advantages: Control and shaping of the residual limb, protection of the surgical site, improving healing time, maintenance of residual and sound limb and upper body strength, reduction of contracture development, maintenance of cardiovascular status, early return to balance and ambulation, social and emotional support, shorter hospital stay, shorter overall recovery time, quicker identifications of the patients functional levels [Seymour 2002, p128].

Prostheses

psychological and physiologic benefits attributed to walking soon after the amputation. The early use of an IPOP is attributed many other advantages to the patient (although not by all researchers), but (because fabrication is time consuming and not easy), the IPOP is little used. IPOPs are made by the prosthetists in the hospital. While the original design is based on a plaster cast (rigid dressing), a fibreglass cast can also be used to reduce weight.

Users

of a rigid dressing, a pylon and a foot. It was developed in the late 60s. An IPOP is used while the residual limb still changes shape fast, but the incision of the operation is healed and the sutures removed.

These

Approach

4.1.2 Immediate Post Operative Prosthesis - IPOP

Figure 4-2: A complete IPOP (without pylon). [Source: Seattle Rehab Research, US Veteran Affairs]

Figure 4-3: The universal IPOP (Aircast Air-limb) is inflatable to accomodate different stump sizes. [source: ACA 2001,

27

4.1.3 Removable Protective Socket - RPS

If a (rigid) dressing is no longer needed,

but the residual limb still needs to be formed through compression, a compression device (see section 5.1) can be used in conjuncture with a removable protective socket. This socket is used for patients with very easily damaged residual limbs. Weight bearing tolerance is gradually build, to enable the patient to wear a firm definite prosthesis later [Seymour 2002, p138]. Over this custom-fitted device a Universal Frame Outer Socket (UFOS) can be put to enable weight bearing (See figure 4-4).

Advantages: The residual limb is well protected to additional trauma. The pressure and weight bearing tolerance of the Figure 4-4: The Flow-tech Adjustable Postoperative Protective and Preparatory System (APPOPS) provides a residual limb is gradually improved. The prefabricated prosthetic system offering protection, con- socket and the Universal Frame Outer trolled shaping of the residuum and early rehabilitation. Socket can be easily adjusted to accomThe TOR (top left) is a prefabricated socket (available in modate each patient. Easy access for 22 sizes) that fits over elastic wrapping and bandages. hygiene. The socket prevents knee contraction and provides protection for the residual limb. When fitted with a UFOS Disadvantage: Sockets custom made, (universal frame outer socket, middle) it functions as an expensive. interim prosthesis (top right). Full load and knee flexion becomes possible with the VCSPS (bottom). Fitted with a UFOS the VCSPS (available in 34 sizes) can be used as a temporary prosthesis. [Source: Flow-tech Brochures] 28

Flo-tech also provides pre-fabricated protec-

tive sockets (APPOP-system). Their system exists of a flexible outer socket which allows gentle reduction of the socket’s overall circumference. The mid-thigh design prevents knee flexion contractures. The Velcro bands help to shape the residual limb (see figure 44).

The Flow-Tech UFOS (Universal Frame Outer

Socket ), also fits over the VCSPS (Variable Circumference Supra Patellar Preparatory Socket), together forming a complete preparatory system to fit 80% of the transtibial amputations. [Source: flow-tech brochures]

Disadvantage: Many sizes needed, expensive.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

4.1.4 Temporary Prosthesis

systems are said to be usable as interim and temporary prosthesis, such as the Maramed components (figure 4-5).

Prostheses

Most

Stragegy Figure 4-6: Components of Maramed orhopedic Systems. Left: X-tender system can be used as a temporary prosthesis(middle). At the right a retainer is shown, in which a custummade socket can be attached. [Source: Maramed website]

Criteria

Figure 4-5: Connective part between socket and pylon, which can be used in temporary and definite prostheses. [Source: Endolite brochure]

Usage

companies offer a wide range of temporary components, because after the dynamic gait training the temporary parts will be replaced by definite components (of the same company). Also, many definite components can be adjusted quick enough to be suitable for a temporary prosthesis, such as the connective devices from Endolite (see figure 4-4 and section 4.3.5).

Advantages: Better control over the alignment for the prosthetists, the socket needs to be fabricated several times. Disadvantage: The system might be heavier, not all components can be fitted, the prosthesis lacks cosmetics.

Some

Users

and foot system which is used when the patient wounds are fully healed, while the residual limb still changes its shape fast and the socket needs to be replaced several times as the volume of the residual limb stabilizes. The temporary prosthesis came into existence in the 1970s, together with the development of the endoskeletal design (See section 4.2), which made the use of adjustable alignment components possible. It provides the same functions as a definite prosthesis, but the alignment can be adjusted more easily by the prosthetist to improve the patient’s gait. The patient can use the temporary prosthesis at home. However, in most cases the temporary prosthesis is not yet fitted with an optimal foot and additions such as a rotator or shock-absorber (see section 4.3.5). Also, aesthetically the prosthesis is not finished yet (e.g. no cosmetic cover) and the temporary prosthesis could be heavier than a definite.

by using a plaster mould of the residual limb as a template ( just as with definite prostheses, compare figure 4-8). The other components, such as the pylon and the foot, are standard available. In most cases, a SACH foot is used (see section 4.3.3). The connective components, such as the interface between the socket and the pylon, can be easily rotated. The alignment of the prosthesis is determined by the angle between the socket, pylon and foot.

Approach

The temporary prosthesis is a socket, pylon

The preparatory socket is normally created

29

4.1.5 Definite Prosthesis

The definite prosthesis is the prosthesis that

the patient will use in daily life. In most cases, it highly resembles the temporary prosthesis, now finished with a cosmetic cover or prosthetic skin (see section 4.3.5). The definite socket is difficult to adjust. When the residual limb changes in shape or pressure sensitivity, a new socket is needed.

Normally,

a plaster cast is made from the residual limb, of which in turn a positive cast is formed. This cast is then adjusted (see section 4.3.1) and the final socket is then fabricated by either vacuum thermoforming or applying epoxy resins (plastic lamination). (See figure 4-8).

Advantages: Firm fit and therefore the best gait and control over the prosthesis. Cosmetics are pleasing. Disadvantage: Difficult to adjust.

The definite prosthesis is always fabricated

by the prosthetists. However, there is a wide range of available materials and production methods. The choice of these have a great impact on weight (composites are very light), adjustability (thermoforming plastics can still be somewhat adjusted after fabrication by applying local heat) and comfort. An interesting commercial material is ICEX from Össur which consists of carbon fibre enhanced sheets that harden when mixed with water (see figure 4-7). The ICEX is one of the few systems which can be fabricated directly onto the residual limb.

30

Figure 4-7: The ICEX toolbox and component box. [Source: Ossur website]

Figure 4-8: Standard fabrication starts with taking a negative mold. Then plaster is poured into the negative mold to create a positive mold. At last, the positive mold is shaped by the prosthetist to emphasis the shape. The final socket is made by laminating or thermoforming it around the positive. [Seymour 2002, p179]

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

4.2 Structural Designs

4.2.1 Exoskeletal Structure

There

An

exoskeletal structure has a hard outer cover made of plastic laminate (figure 4-9). Socket and pylon are integrated into one product. Sometimes, the foot is a standard component, such as in the case of the Jaipur prosthesis (see figure 4-10), but it can also be integrated (figure 4-9).

Approach Users

are two solutions for the structural build-up of a prosthesis: the exoskeletal design, which is around for a long time and the endoskeletal or modular design, invented in 1970 (compare Appendix E). Nowadays, the endoskeletal design is by far the most common.

The

Prostheses

structure consists of soft foam contoured to match the other limb with a hard laminated shell.

Usage

Advantages: High strength, better suited for occupations that require great durability, such as farming or construction work. Better resistant against dirt. Sometimes also better heat resistant.

Stragegy

Disadvantages: Alignment and replacement are difficult. Difficult to fabricate. Flexion, shock-absorption and rotation is absent in the rigid prosthesis.

Figure 4-10: The Jaipur prosthesis, here Figure 4-9: The exoskeletal prosthesis (depicting socket, plastic exterior and foot) is one, integrated product. [Seymour

2002]

Criteria

Vision: An integration of the socket and the pylon, while allowing for adjustability, could result in a highly durable and resistant prosthesis.

drying from paint finish, consists of a exoskeletal structure with a separate manufactured foot. [Source: FINS- Sri Lanka] 31

4.2.2 Endoskeletal Structure

In an endoskeletal design, a pylon is used to

transfer forces from the residual limb to the floor. The endoskeletal or modular prosthesis is build from components. The basic components of an endoskeletal prosthesis (figure 411) are the socket (4.3.1), the pylon (4.3.2) and the terminal device (4.3.3) (almost always referred to as the foot). Every prostetic design needs suspension (4.3.4) to stay put when the leg is lifted. Sometimes additional components (4.3.5) are included such as a rotator, shock-absorbers, a sock or (gel-) liner, a cover or a prosthetic skin.

32

Figure 4-11: The endoskeletal prosthesis always contains a pylon. Very seldom the other parts are integrated. Normally, the socket and foot are modular components. [Seymour 2002]

Advantages: Being adjustable, being lightweight, this setup is cost efficient when components need to be replaced, the (mass-produced) components are of relatively low costs. The total system is highly customizable to the patient’s needs. Disadvantages: Not so strong, components may be expensive, custom-made socket needed.

Vision: The universal prosthesis will be really successful when the socket and the pylon can be used together with a wide range of (already available) feet.

A

combination of socket and pylon, while maintaining the endoskeletal principles is called a monolithic socket and pylon combination and may be attached to commercially available prosthetic feet. One thermoplastic design is the Endoflex [Valenti, 1991]. See figure 4-12 for an example without cosmetic cover. It is suitable for a majority of amputees and its advantages include increased flexibility, absorption of stress and shear and reduced cost.

Vision: An integration of the socket and the pylon, while allowing for adjustability, could result in a highly durable and resistant prosthesis.

Figure 4-12: The 4C Air Lite Monolithic (above 2 pictures show manufacturing steps. A carbon-fibre sock is one of the important materials) and the Endoflex (lower pictures) are two of the few designs in which the pylon and socket are integrated. [4C Air-Lite Tech Manual, Valenti 1991]

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

4.3 Components are widely available. This section offers an overview.

The

Sockets

There are different types of hardness for the

socket. Again, there is a multitude of terms in use and definitions are unclear: liner soft socket or softsocket semi-rigid socket Flexible socket Hard outer, soft inner socket system Hard socket

There

Figure 4-13: ISNY Components [Source: Website Otto-Bock]

Project: Recent developments in softsockets for transfemoral amputees, seem to suggest that a flexible socket could be well adapted to transtibial prosthetics.

Criteria

are primarily two socket designs used for transtibial amputations, the patellar tendon bearing (PTB) and the total surface bearing (TSB). Since the late 50’s, the PTB socket has been the design of choice for most traumatic transtibial amputees [VHI 2002].

Stragegy

- - - - - -

Usage

are generally created by using a plaster mould of the residual limb as a template. Some prosthetic manufacturing facilities use computer-assisted technology to “map” the residual limb and then manufacture a socket directly from that data (CAD-CAM fabrication).

Rigidity

Prostheses

socket is the connection between the residual limb and the prosthesis. It must not only protect the residual limb but also transmit the forces associated with standing and ambulation.

Vision: The universal prosthesis will be really successful when the interface with the body is as comfortable as current sockets.

the socket is constructed as hard as possible, because this rigid type of sockets transfer the forces well to the pylon and gives control to the patient. However, since the invention of the liner, a new development is the hard outer, soft inner socket (semi-rigid sockets). These sockets consist of a shell and a liner that are both formed to the residual limb. The outer sockets function is protection of the residual limb and the transfer of forces. The outer socket surrounds the liner, made of a flexible material (in most cases Pelite, a poly-ethylene foam). This socket helps with the better distribution of forces. The difference between a soft socket and a conventional liner [see section 4.3.5] is that the liner is a hollow, stretchable, standard tube, while the soft socket is fabricated to the shape of the residual limb of the patient. Soft sockets are more often used for transfemoral amputees than for transtibial amputees. Also, for transfemoral amputees there is a system that integrates hard elements (ISNY concept, figure 4-13 and 4-14) with flexible (polyurethane) parts into one socket. However, this socket type is only recently developed at Össur [2002] and information about development of a transtibial type is limited [COTA 2002].

Users

4.3.1 Basic Components: Socket

Traditionally,

Approach

Components for the endoskeletal prosthesis

Project: The definite socket is in practically every case custom made and therefore the most challenging part for a complete universal prosthesis. Therefore this project must focus on the socket and its effects on the patient and the prosthetist.

33

Rectification

There

are two principles for force distributions between the residual limb and the prosthetic socket. The first, “Rectified” takes in account which areas and tissues are less sensitive to pressure and the socket puts more pressure there. The second, “Unrectified” does not take the difference in tissue in account and the socket is fabricated such that it distributes the forces of the residual limb best distributed as possible (in most cases except the distal end). Interesting, there is little literature that compares these two types of pressure distribution. However, recent studies do suggest that unrectified sockets perform just as well as rectified sockets. Rectified sockets tend to be evaluated better in less active situations, while unrectified sockets are more comfortable during heavy use. [Weeks 2003]

O

34

Figure 4-14: Flexible ischial-containment socket for transfemoral amputees (this one from Otto-Bock, inset from Hanger) consist of a flexible inside and a frame. Other names include Total Flexible Brim, the ISNY and SFS (Scandinavian Flexible Socket)[Seymour 2002].

n the other hand, prosthetists at LIVIT (Den Haag) suggested that unrectified sockets tend to rotate around the residual limb and thus offer problems when subjected to torsion. Also, they mentioned that rectification (while years ago being quite exaggerated) is practically not so strongly emphasized anymore in the socket fabrication.

Patellar Socket

Tendon

Bearing

(PTB)

The PTB socket is the best known rectified

socket design. The PTB socket offers areas of pressure and areas of relief in accordance with figure 3-6 from section 3.1.3. As can be seen, important pressure bearing areas are the patellar tendon, the medial tibial flare (next to the tibial crest) and the posterior of the residual limb. The socket makes contact with the residual limb even in areas where no pressure is transferred, including the distal end, to avoid pockets of oedema. Requirements: The universal socket should make contact with all areas of the residual limb, to avoid pockets of oedema.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Total Surface Bearing (TSB) Socket

The plug fit prosthesis, mostly used for trans-

Hydrostatic socket is a socket that is unrectified, but in stead of determining its shape from the shape of the unloaded residual limb, it is formed around the (hydrostatic) loaded limb. This socket type is very comfortable while standing, because pressure distribution is optimal [SOURCE]. However, when soft tissue is hydrostatically loaded, it becomes more round shap round shaped. This may cause friction and instability when the prosthesis is subject to rotation or torque.

Usage Stragegy

Requirements: The socket can either transfer pressure equally or rectified, as long as the total area over which the pressure is distributed is optimized.

The

Prostheses

femoral amputations, was very popular from WWI to mid 1950’s, but is seldom used today. The socket shape is a simple cone (figure 415). Transtibially, this socket design provided weight bearing at the patellar tendon and was used in conjunction with a thigh lacer for suspension (see section 4.3.4). Additionally by tightening the thigh lacer additional weight bearing was transferred to the thigh. The distal end of the prosthesis is usually left open with no distal wieght bearing. [VHI 2002]

Users

TSB socket design is an unrectified design, that was developed in the mid 1980’s. It provides complete contact of the prosthetic socket to the residual limb with no built-in pockets for relief of bones and other sensitive tissue. By allowing total surface contact, all tissue of the residual limb is in contact with the prosthetic socket, thus reducing the loading on the medial tibial flare and patellar tendon. When using this type of design it is usually necessary to use a roll-on type of liner made of silicone, mineral gel or similar material. The thickness of these liners is usually three, six or nine millimetres. This design is fast becoming the socket design of choice for traumatic amputees. [VHI 2002]

Hydrostatic Socket Approach

The

Plug Fit Socket

Criteria

Figure 4-15: Plug fit socket. The first prosthetic socket without weight-bearing at the distal end by Verduin 1696 [Wetz 2000]

35

The before mentioned ICEX socket (figure 4-7,

figure 4-16) is produced on the residual limb. It is cast under pressure with a pressure-casting device. Due to this production method, it is a hydrostatic socket design. All pressure is distributed equally, but areas still be relieved from pressure by applying pressure pads.

4.3.2 Basic Components: Pylon

The pylon is a tube or shell that attaches the

socket to the terminal device. The main function of the pylon, is to transfer force from the socket to the ground. Pylons have progressed from simple static shells to dynamic devices that allow axial rotation and absorb, store and release energy.

Because

of the high forces involved, most pylons are made from titanium. For geriatric purposes (less use and low weight) sometimes aluminium is needed. Plastic pylons are used in designs meant for the third world, such as the ICRC-limb (figure 4-17) (polypropylene) and monolithic prostheses (see figure 4-12). In these cases, an addition exoskeletal can be applied after alignment, to enhance the durability of the prosthesis.

Also, there are low cost systems with mul-

tiple pylons, however these seem to be only used in Argentina (about 2000 produced in 1989, see figure 4-18).

New types of pylons are slightly flexible

and take-over some of the functions of the ankle (figure 4-19).

Pylons

can be orderd in standard sizes or sawn into the needed length by the prosthetist.

Figure 4-18: (left) Trimodular Pylon as used in the sauer-bruck trimodular physiological prosthesis [Angarami 1989]

36

Figure 4-16: Icex finished socket (left). Pressure pads are added to compensate for weight intolerant areas (cutt-through right) [Source: Ossur Icex brochures.]

Figure 4-17: The ICRC-limb makes use of a polypropylene pylon.. Its cross-section is H-shaped.

Figure 4-19: (right) Springlite Advantage DP flexible pylon and dynamic response foot by Hanger Orthopedic Group. [Source: website]

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

4.3.3 Basic Components: Foot/Ankle System

Better defined the functions of the prosthetic

terminal device. It does not try to resemble a normal foot, but is a stump end, which allows a very nice ambulation. This terminal device is most useful in interim prostheses.

SACH

foot: Solid Ankle Cushion Heel – Developed in the 1950s, the SACH foot is the simplest foot. It mimics ankle plantar flexion, which allows for a smooth gait. There are no moving parts, which makes this design very durable and ideal for children and for individuals whose ambulation is limited to walking (sedentary patients).

– This in 1980s developed foot is more flexible than the SACH foot. This design had an elastic keel, which enabled a smoother and easier rollover, which is more preferable than the rigid keel of the SACH foot. Some disadvantages include limited push-off, increased cost and added weight. [VHI 2002].

Stragegy

ankle function usually is incorporated into the terminal device. Separate ankle joints can be beneficial in heavy-duty industrial work or in sports such as mountain climbing, swimming, and rowing. However, the additional weight requires more energy expenditure and more limb strength to control the additional motion.

Rocker “foot”: The rocker is the most simple

Usage

The

SAFE foot: Solid Ankle Flexible Endoskeleton

Prostheses

foot are (1) to provide a stable weight-bearing surface, (2) to absorb shock, (3) to replace lost muscle function, (4) to replicate the anatomic joint, and (5) to restore cosmetic appearance.

Non-Energy-Storing Feet

SACH foot designs allow compression of the foam heel at heel-strike to simulate planter-flexion. A wooden internal keel provides stability in mid-stance and allows for a relatively easy rollover in late stance. [VHI 2002]

Users

device, but it may take other forms for water or sports activities, or for use as an interimprosthesis. The main function of the foot is to aid in gait and provide aesthetics.

The

cal parallel, designers often speak of the foot-ankle system. Prosthetic feet are broadly classified as energy-storing feet and non– energy-storing feet.

Approach

The foot is the typical form of the terminal

Because of the biomechanical and anatomi-

Criteria

Figure 4-20: Left: Principle of Rocker foot or sole. [Adapted from: www.customfootware. com] Right: Low cost prosthesis with cane pylon and rocker foot

Figure 4-21: SACH foot (Adapted from Seymour 2002]

Figure 4-22: SAFE II foot. (Original manufacturer is Campbell Childs Inc, now bought by 4C (Foresee Orthopeadic Products)).

37

Single-Axis foot: Predating the 1860s, single

axis feet contain an ankle joint that adds passive plantar flexion and dorsiflexion, which increase stability during stance phase. SingleAxis feet pre-date the American Civil War and still are used today on a limited basis. The main advantage is that the foot will allow for a quick foot-flat, which increases knee stability in an above-knee prosthetic wearer or in a below-knee prosthetic wearer who uses a thigh corset with knee joints in early stance. This feature is important in the individual who has knee instability. Disadvantages include weight, maintenance, abrupt dorsiflexion stop, noise and cost. [VHI 2002]

38

Figure 4-23: Single-axis foot. [Seymour 2002]

Multiple-Axis foot: The multiaxial foot adds

inversion-eversion and transverse rotation capabilities to the function of the single-axis foot and is often recommended to accommodate uneven terrain. Its weight and maintenance requirements are similar to that of the single-axis foot and is a good choice for the individual with a minimal-to-moderate activity level. [VHI 2002]

Figure 4-24: Multiple axis foot. [Seymour 2002]

Simple Energy Storing

STEN

foot: The STored ENergy foot is a simple energy storing foot that has a keel that compresses in the loading response to midstance of gait, thereby storing energy. The energy is released in the terminal stance to the preswing phase of gait. [Seymour 2002]

Figure 4-25: STEN foot. [Source: Kinsley Manufacturing Co brochure]

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Dynamic Response:

Figure 4-26: (Above) Though from the outside not visible, energy storing feet differ from the inside [Impulse foot, OHIO Willow Wood] Various energy-storing feet. Earch foot is composed of a compressible heel and a flexible keel spring. A) Seattle foot, B) Dynamic foot, C) STEN foot, D) SAFE foot, E) Carbon Copy II foot. [Hafner et al. 2002]

Usage Stragegy

Design feet (figure 4-28) are available that combine multiaxial ankle mechanism with dynamic response, such as the College Park foot/ankle and the Phoenix foot. These designs can be used for recreational and competitive sports, as well as for uneven terrain. Disadvantages would include maintenance and cost. [VHI 2002]

Prostheses

Hybrid

Users

Response (formerly known as advanced Energy Storing) feet have a plastic spring keel that provide a dynamic responsiveness during stance. There are numerous dynamic response feet available, such as the Carbon Copy, Seattle, Flex-foot, Springlite,etc (figure 4-26, 4-27). The more aggressive ambulator can use these designs, including runners and those participating in recreational or competitive sports who can load the forefoot for these activities. Disadvantages include increased fabrication time and increased cost for some designs. [VHI 2002]

Approach

Dynamic

Criteria

Figure 4-27: Advanced energy-storing prostheses: A) Modular III, B) Reflex VSP, C) Advanced DP, D) Pathfinder. [Hafner et al. 2002]

Figure 4-28: Two hybrids: The Seattle Cadence HP [Source: Seattle website] and the MICA Genisis II+. [Source: MICA website]

39

4.3.4 Basic Components: Suspension

Prostheses can be attached to the residual

limb by a variety of belts, wedges, straps, suction, or a combination of the above. Designs include differential pressure suspension systems, anatomical suspension systems, strap suspension, thigh corset with mechanical hinges, Silesian Belt and pelvic joint with belt.

Most important transtibial suspension methods:

1)

Supracondylar Cuff – A supracondylar cuff, affixed to a socket, allows the prosthesis to hang from the top of the knee (Anatomical suspension). In Dutch often referred to as the KBM design.

2) Joint and thigh corset – This suspension

method bears much of the patient’s weight on the thigh. (corset suspension)

3)

Waist belt suspension – In this design, much of the weight of the prosthesis is distributed around the waist (corset suspension).

4)

Sleeve suspension – An elastic or neoprene sleeve is pulled over both the prosthesis and a large area of skin, thereby suspending the prosthesis by partial suction (suction suspension).

5) Gel liner with shuttle-lock – One of the

40

Figure 4-29: (right) Anatomical Suspension. The supracondylar suspension is in this case removable due to the brim. (right, middle) The supracondylar suprapattelar system is fixed. [Seymour 2002]

more advanced designs, this pin, incorporated at the end of the liner, fits into a shuttle-locking mechanism fabricated into the bottom of the socket. (suction suspension). The liner is equipted with a pin or plunger threaded into the distal end. This pin can lock into the socket. to remove the prostesis, a button on the locking mechanism is depressed.

Anatomical Suspension

Anatomical

suspension designs (figure 29) are the second most desirable option for suspension of the prosthesis. Suspension is achieved by careful contouring of the socket walls over and proximal to the femoral epicondyles to lock the condyles in place. This method of suspension is known as supracondylar (SC, In Dutch often referred to as the Kondyl Bettung Munster, KBM) and can be very effective in suspending the prosthesis and in providing enhanced mediolateral stability in individuals with a shorter residual limb.

A variant to this design allows for moulding

of the socket anteriorly above the patella for added suspension and to control hyperextension in the shorter residual limb. This design is known as supracondylar/suprapatellar (SC/SP), sometimes referred to as the Patellar Tendon Suspension (PTS). [VHI, 2002] Advantages: Are increased medial-lateral stability with the SC and increased anterior-posterior stability with the SP feature. Disadvantages: include localized pressure over condyles and restriction of full flexion.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Straps

Corsets

Nowadays, there are to much disadvantages

in comparison to the other suspension methods to use corsets for definite prostheses, but they are still used in conjuncture with a interim or temporary prosthesis.

Advantages: In using the thigh lacer with joints include the reduction of weight bearing on the residual limb and can greatly increase the medial-lateral stability.

suspension uses an atmospheric pressure (vacuum) or suction to maintain the prosthesis onto the residuum. Suction suspension is broken down into 2 categories: standard suction and silicon suspension suction. A standard suction is simply a form-fitting rigid or semi-rigid socket into which the residual limb is fitted. The silicon suction uses a silicon-based sock, liner or sleeve (also see section 4.3.5) that slips onto the residual limb, which is then inserted into the socket. The silicon helps to form an airtight seal that stabilizes the prosthesis. [VHI 2002] Advantages: These designs tend to provide the amputee with enhanced function, greatest range of motion, added sense of security, greater control of prosthesis and no piston action when fitted properly. Of all suspension modes, suction designs tend to be the most desirable because of the enhanced retention of the prosthesis to the residual limb created by the vacuum.

Stragegy

Disadvantages: Include pistoning, added weight and bulk, difficulties in donning and excessive wear and tear on clothing.

Suction

Usage

Disadvantages: Include slight pistoning and belt irritation.

cal hinges was the design of choice up until the early 1960’s. [VHI, 2002] Also, a corset can be worn around the waist.

Prostheses

Advantages: This design can accommodate changes in volume and is relatively simple to adjust.

The thigh corset (figure 4-31) with mechani-

Users

it is not feasible to use differential pressure or anatomical modes of suspension, a strap (figure 4-30) can be used to suspend the prosthesis. A popular strap, called a PTB or supracondylar cuff, is attached to the medial and lateral walls of the prosthesis at their posterior-proximal juncture and is then angled proximally over the patella. The lower border of the cuff touches the superior border of the patella to achieve suspension. In addition to the cuff, a waist belt with extension assist can be attached to the proximal border of the cuff to increase suspension and to assist the individual in extending the prosthesis. [VHI, 2002]

Approach

When

Suction Suspension

Criteria

Figure 4-30: The PTB cuff or supracondylar cuff. [Seymour 2002]

Figure 4-31: The thigh corset can be used in conjuncture with a waist belt and an elastic strap. [Seymour 2002]. The suspension sleeve has a similar working principle (left) [Otto Bock].

41

S

everal suction suspension designs are used [VHI, 2002]:

1) One design incorporates an overall snug fit

with a valve placed distally into the prosthetic socket. The skin is in direct contact with the socket interface. In order to use this type of suspension, the residual limb has to be stable with no fluctuations in volume and generally free of scars that could prevent vacuum from being achieved

2) Another system includes the use of elastomer sleeves made of silicone, urethane or mineral gel. (Figure 4-32) These sleeves are rolled onto the residual and have a distal pin attachment (plunger) that anchors distally into the socket locking the prosthesis. in place. These systems allow for moderate volume changes by placing socks of varying plies on the outside of the sleeve to achieve a snug fit. Also, application for residual limbs that may have some scarring or grafts is possible.

42

Figure 4-32: Pin/Shuttle suspension. [Seymour 2002]

3

) Variants to these methods include the “hypobaric” design, which has a valve distally in the socket to expel air and a silicone rubber band (gasket) moulded into standard textile stump liners at the proximal socket. This gasket is positioned slightly distal to the socket edge, which creates a seal and maintains vacuum or suction. This silicone band is moulded into prosthetic sheaths and stump socks of varying plies to accommodate volume changes. Sometimes, to enhance the seal, a skin lotion is used for a wet fit.

5)

The simplest design of achieving suction suspension could be to use a rubberized sleeve over the outer socket surface and onto the mid-thigh, thus preventing air from entering into the socket. This design allows for stump socks and/or soft insert to be used.

4) Another design allows a mineral gel sleeve

to be rolled onto the residual limb, with a fabric backing and no distal pin. (Figure 433) Once the sleeve has been placed onto the residua, the residua is placed into the socket, where a distal valve expels the air. With all the air expelled, a second sleeve is placed over the inner mineral gel sleeve and outer socket, sealing any air from entering the socket, thus creating a suction or vacuum. This design can accommodate some volume changes by use of a thicker sleeve.

Figure 4-33: Mineral gel sleeve suction suspension. [www.customprosthetics.com].

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

4.3.5 Additional Components

Liners

Grace

All basic components are connected by specific components. These connective componvents (figure 4-36) often exist of a “male”and a “female”part, that can be attached in a range of angles. These angles determine the alignment. The connective component that is integrated with the socket is called the grace plate.

In case of suction suspension, valves need to be added. Locks are needed for above-knee prostheses.

Shock absorbing pylons allow for telescoping of the pylon to absorb shock to the residual limb that occurs in jumping and running activities, as well as aggressive walking.

Stragegy Criteria

Figure 4-34: Double/Single Socket Gel Liner [Silipos].

Torque Absorber (figure 4-35) allows the leg to rotate with reference to the socket during stance phase, automatically returning the leg to the normal position during swing phase. The torque absorber is excellent in activities where rotation is important: golfing, dancing, bowling, base-ball, standing and working at a bench for considerable periods of time. Generally, the shorter the residual limb, the greater the loss of natural torsional capabilities. A torsion absorber would restore the loss of torsion.

and

Usage

- - - - - -

Stockinet (tubular open ended cotton of nylon material) Sleeves Compressors Shrinkers (Elastic Wraps or compression sock) Socks (not only for the feet!, wool of cotton) Liners Gel sheath

The

Couplers, Locks, Valves Plates

Prostheses

-

Shock-Absorbing

Users

(figure 4-34) fit inside prosthetic sockets and are used to cushion and protect fragile limbs and to accommodate volume changes. They can be used to suspend prostheses by rolling them onto a residual limb to provide suction suspension or they can have wedges built into them to provide supracondylar suspension. They can be made of silicone, urethane, and mineral gel, rubbers and expanded polyethylene foam. The thickness of liners is usually three, six or nine millimetres and this thickness is referred to as a ply. [VHI 2002]

and

Approach

Liners and Socks

Rotators Systems

Figure 4-35: Demountable Torque absorber and its effects. [adapted from endolite]

Figure 4-36: Some examples of connective components [adapted from www.atlasti.com]

43

Covers and Prosthetic Skins

Most endoskeletal setups are finished with

a cosmetic cover. This cover usually exists of a foam inner part and is finished with a very flexible “sock”. In very expensive prostheses, the outer sock can resemble the remaining limb, including hairs, veins, etc. then the cover is called a prosthetic skin. Some manufactures speak of skin coatings. (figure 4-37)

44

Figure 4-37: Prosthetic skins can have a high life-like appearance [left, dorset and orthopeadic]. Uflate sleeve skin covers shrinks to fit the prosthesis when treated with a heat-gun.

4.3.6 Materials & Tools

Plastics, supplies, tools, alignment systems,

they are the resource for the prosthetist (figure 4-38).

Figure 4-38: Examples of supplies (above): Rivits, Polyester Resin-Laminae, box of stockinettes, pneumatic cast cutter, carbon tape [Fillauer Supplies brochure]. Static alignment is done on an alignment table [otto bock[. Supplies enable prosthetists to make custom liners [otto bock].

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Now

Orientation of axes of motion: For the total

However,

because of the closed kinematic chain (the foot stands on the ground), adjacent joints are likely to be effected. For example, when a prosthetic foot is locked in plantarflexion it will result in an abnormal knee angle (FIG 4-40). [Seymour 2002, p79]. This is an important observation, because for example an abnormal knee angle could result from a problem in the foot/ankle system. Requirements: The universal prosthetic system should include hints when it is aligned well.

Usage

Requirements: The universal prosthesis should be normally aligned similar to the axis of motion of the knee. Enhanced flexibility and additional joints (such as a flexible pylon) could be applied, but stability is more important.

of motion: The prosthetic device should allow normal range of motion in any plane, which for a transtibial prosthesis involves primarily the rotation of the knee and ankle in the sagittal plane.

Prostheses

limb to move in its normal path of motion (figure 4-39), the axes of the human joint and the prosthetic orientation must be aligned similarly. The choice of the type and location of the axes will affect the movement and stability of the prosthetic limb. [Seymour 2002, p78]. For example, a dynamic ankle joint can improve ambulation on rough terrain, but reduces the stability of the prosthetic limb.

Range

Users

the structure of prostheses and the used components are discussed, a application of biomechanics on the residual-limbprosthesis system is useful. From this analyses important criteria and insight why the endoskeletal structure is so popular can be derived. Again kinematics and kinetics are considered (compare sections 3.1.5 and 3.1.6). Both have implications for the selection, fit, use and design of prosthetic devices. Generally, kinematic considerations provide insight into the alignment of the prosthesis, while kinetic considerations will provide insight in the design requirements.

Kinematics

Approach

4.4 Biomechanics of Transtibial Prostheses

Stragegy

Figure 4-40: Limited dorsiflexion at the ankle. If the ankle can not dorsiflex normally, either A) the individual will weight bear on the toe or B) the knee must hyperextend to get the foot flat on the ground. [Seymour 2002]

Criteria

Figure 4-39: Pathway of the instant axis of rotation for the knee joint. [Seymour 2002]

45

Degrees of freedom: If the prosthesis has

a different number of degrees of freedom as the normal joint, the function of the joint will be affected. For example, some prosthetic feet, such as SACH feet, allow plantar- and dorsiflexion, but do not allow pronation/supination. This will affect the interface of the foot with the ground. Adaptation to uneven terrain is diminished and forces may be transferred to the residual limb. [Seymour 2002, p79]

Kinetics

Stress:

Stress or pressure considerations lead to a preference of a large surface to bear forces. A typical application of this principle is the use of a total surface-bearing (TSB) socket [See section 4.3.1]. High pressure on the tissue of the residual limb could occlude the vessels, creating ischemia (oxygen shortage) and tissue damage. Also, nerves are pressure sensitive, resulting in pain or nerve damage. [Seymour 2002, p80]

Deformation:

46

Tissues of the residual limb as well as materials used in prosthetics, vary in their stiffness (their ability to resist deformation). In the residual limb, the stiffer bone bears the brunt of the load, but is also more pain-sensitive to pressure. These considerations lead to designs such as the patellar tendon bearing (PTB) socket [See section 4.3.1] as shown in figure 4-41. All considera-

tions for the size and location of suspensions should take in account the relationship of force area, stress toleration and deformation. [Seymour 2002, p80]. Deformation of the tissue also occurs while the residual stump is loaded. Therefore, the shape during load can be different from the unloaded shape. Especially in hydrostatic socket, semi-rigid and softsocket designs this can be a problem. Under evenly distributed pressure, the soft tissues tend form a cylinder or cone. If this happens, the system will find it difficult to transfer torque (cylinder in cylinder). A solution is using a somewhat triangular socket. Requirements: the socket design should consider rotational forces, while the residual limb is loaded. Equal stess (pressure) throughout

A

Increased stess

Relief

B Decreased stress

Stress (pressure) equilized throughout

Relief

C Build up

D Build up

Figure 4-41: Stress on the residual limb from the prosthesis. A) The hypothetical situation in which the residual limb is of uniform firmness and the socket matches the circular shape of the limb. B) A residual limb of nonuniform firmness and a socket that matches the circular shape of the limb. This would result in increased stress on the firm areas of the residual limb. C) The same residual limb with a socket designed to equalize the pressures over the firm and soft areas. D) The same socket design used to accommodate pressure-sensitive areas and pressure-tolerant areas. [Adapted from Seymour 2002]

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Elasticity:

too hard

- foot rotation - execssive knee flexion

too soft

- foot-slap - absent or insufficient knee flexion

heel cushion

Displacement of the keel

posterior

- early knee flexion (drop-off)

anterior

- delayed knee flexion

dorsiflexion Excessive flexion of the prosthetic foot

- excessive lateral thrust of prosthesis

anterior

- absent or insufficient knee flexion - delayed knee flexion

posterior

- excessive knee flexion - early knee flexion (drop-off)

posterior

- delayed knee flexion

anterior

- early knee flexion (drop-off) - excessive knee flexion

too loosely

- foot rotation - pistoning

too tightly

- reduced knee flexion/exention

Table 4-2: Gait deviations due to materials and the alignment [Seymour 2002]. Note that many alignment choices can have the same effect. If the effect is unwanted, all can be adjusted, but some will cause other problems (because one alignment choice will have multiple effects).

Criteria

Socket fits

medial

Stragegy

Excessive tilt of the socket

- absent or insufficient knee flexion - delayed knee flexion - circumduction

Usage

Excessive placement of the foot in relation to the socket

plantarflexion

- excessive knee flexion - early knee flexion (drop-off)

Prostheses

prosthesis may cause or solve gait deviations. They will affect deformation and the energy deformed of returned, wit a result impact on gait. In transtibial conventional prosthesis, this principle is mostly used in shock-absorbing feet (compare table 4-2, first row). The socket and pylon are generally designed as stiff as possible.

Effect

Users

The materials used in the components of the

Area and Problem

Approach

Tissue should not be loaded beyond the yield point, which would result in permanent deformity. The same principle applies to materials used in the prosthetic design. The material characteristics such as yield strength and ductility affect their usage in the fabrication of prosthetic devices. [Seymour 2002, p82]

47

Strain:

Some materials exhibit a different stress/strain curve for increasing and decreasing stress, called hysteresis. Materials which can dissipate a lot of energy, such as vulcanised rubber, can be used to absorb energy. These materials will be selected for either their return energy or absorption of energy. Important here is that one material would not work for all individuals, because the load or stress placed on the material would be different from, for example a light individual and a heavy individual. A case in point would be the firmer heel of a SACH (see section 4.3.3) prosthetic foot for a heavier individual. [Seymour 2002, p83]

Bending

forces: The patellar tendon bearing prosthesis is in principle a three-point system, resulting in bigger forces than one would expect purely from the patients weight (see figure 4-42).

Tension,

compression and torsion forces play an important part in the design of the pylon.

Shear forces: The application of a shear or

tangential force can cause shear stress and strain on weight-bearing surfaces, for example, in a poorly fitted prosthetic device. Soft tissue in general should not be loaded with shear force. [Seymour 2002, p84]

48

Figure 4-42: Bending forces on the residual limb while standing. [Wisse et al. 2002]

Viscoelasticity:

Viscoelastic materials, such as the connective tissues of the body, exhibit some of the characteristics of both elasticity and viscosity. Viscous substances have the ability to resist loads that produce shear. Viscoelastic materials may be used in prosthetics to reduce shear and pressure, as can be seen in liners (often containing urethane) (see section 4.3.5). Viscoelastic materials demonstrate the characteristic of creep, the increase in strain with time under a constant load. Constant loading, subjects joints, surrounding structures and the prosthesis itself to the effects of creep. Deformation of the residual limb or of the prosthesis will be the result. [Seymour 2002, p88]

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Of course, the prosthesis and its components

ances, but reimbursement rates may vary widely. Usually an insurance company will pay for a new prosthesis every 3-5 years or sooner in cases of ill-fitting caused, for example, by weight gain or loss.

All transtibial components are part of a com-

ing on the degree of disability, activity needs of the wearer, and the types of components and materials used. The cost of a transtibial prosthesis ranges from $4,000 to $16,000 [Seymour 2002, p49], including components, materials, labour, office visits and adjustments (in the first 90 days).

Project: The universal could cut back total cost, because of the reduced need of office visits and adjustments.

In

Western countries the assurances will reimburse the more cheaper prostheses ($4000). The fight for reimbursement of more expensive components can be difficult and the improvement in functionality for the patient should be very clear. Raw Resources

Materials producer

Components producer

Product example

Carbon, Oil

Sheets

Feet

Company example

Shell

GE Plastics

Otto-Bock

Criteria

Party

Stragegy

Project: In the value chain, the universal prosthetic system can be regarded as a specific component.

The cost of a prosthesis varies widely depend-

Usage

plex value chain (figure 4-43).

Most prostheses are reimbursed by in assur-

developing countries, the patient will have to pay for the prosthesis themselves, or their “social insurance” will be provided by humanitarian aid organisations, such as USAid. Normally, a transtibial prosthesis can be provided between $60 and $100. $100 seems to be the “magic border” for the amount most NGO’s are willing to pay for prosthetic help. These costs include components, materials, labour, office visits and adjustments in the first weeks. However, long-term aftercare is generally unavailable until the time a patient really needs a new prosthesis.

Prostheses

are not fabricated freely. For every prosthetic design that becomes a success, benefits to the patient (such as improved comfort), the practitioner (such as reduced fabrication time), the producer (higher revenues or bigger market share) and to governmental institutions such as assurances (a clear solution with a good prognosis for a fair price) should be outweighing the costs.

In

Users

4.5.1 To the Patient

Approach

4.5 Financial Issues & Distribution

Distributor System Otto-Bock

LIVIT

Jan Klaas

Figure 4-43: A Simple model of the value chain of prostheses. Value is increased from left to right. Note that some companies have multiple roles.

49

4.5.2 To the Practitioner

The most valuable resource to the prosthetist is time. He needs this time not only to fit and fabricate the prosthesis, but also for meetings with other members of the team and to adjust prosthesis for patients in their rehabilitation. Project: The universal prosthesis could allow the prosthetist to cut back costs (time) or to improve his service to the patients.

4.5.3 To the Producer

Because

of the high requirements to the components (light, durability, etc), they can be quite expensive. The customer (the prosthetist) will suggest them to the insurance company or the patient as long as the benefit to the end user is clear (and that depends highly on the patients level of activity).

Project: The producer could improve his market share, while maintaining his profitrevenue ratio, especially in the niche for products between temporary and definite prosthesis.

4.5.4 To Governmental Institutions

Insurances primarily look for solutions, not 50

for the final price of the product. That is , they assess what the functional needs are of

the patient and how they will develop in time. Then they select the most price efficient solution over a longer period. Project: Even a more expensive universal prosthesis could in many cases be selected by the social insurances, because it will still function when the residual limb changes shape. Costs of maintenance and adjustments are decreased, especially when the patient can adjust (some aspects of) the prosthesis himself.

4.6 Repair and Life-time

Just as shoes, a prosthesis has a limited lifetime. A study done in the United Kingdom found that on average, a new prosthesis was needed every two years.

In some cases, the prosthesis can be repaired. In the same UK study, one major repair was needed every 5 years and two minor repairs were needed per year.

Requirements. The Universal Prosthesis has a lifetime comparable with normal shoes, 1 a 2 years.

5 Life with a prosthesis - the amputee’s perspective For a succesful design, insight into the expe-

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Discription

The accident or the disease

In a case of trauma the patient has to deal with the accident. Treatment is acute. In case of disease, such as diabetics (vascular), the patient has time to prepare for the amputation. He consults a practisioner and makes the decision (or hearing the annoucement that he needs) to be amputed.

Hospitalization

During the period of surgery to provide the patient with a clean and useable residual limb.

Preprosthetic care and rehabilitation

section 5.1

patient will experience a sequence of happenings as mentioned in table 5.1.

Shrinking of the residual limb with compressive wrappings. Physiotherapy to prevent contractures. Fit of a temporal prosthesis as a training to use and life with a prosthesis. The residual limb reaches final shape.

Definite prosthesis

section 5.2

All

The choice and fit of the prosthesis is based on the assessed functionality and the amputees life-style.

Dynamic alignment

Further rehabilitation and adjusting the alignment of the prosthesis.

section 5.3

Learning (daily routine).

Learning to maintain, don, dof and use the prosthesis.

section 5.4

Rebuilding life

Rebuiling his or hers life after a long period of rehabilitation. Best results with the help of a rehabilitation and aftercare team .

section 5.5

The

Usage

Stragegy

these situations will require sociopsychological adjustment of the patient and a lot of effort to learn how to use the prosthesis. However, life is not care-free. Some major concerns of users of prostheses are summarized in section 5.6.

Prostheses

reading: For additional information, the First Step guide from the Amputee Coalition of America is very useful. [ACA 2001]

Users

Recommended

See Section Approach

Phase

riences of the recently amputated is needed. From a patient’s perspective, the news that a leg or arm needs to be amputated can be shocking and comes with a lot of emotions and questions. In this chapter an overview of actions that a (new) amputee has to take is given.

Criteria 51

5.1 Preprosthetic care After the surgery (the incision is healed and

the sutures removed), a patient will need a compression device to contain residual limb oedema and to accomodate the shaping of the residual limb. Learning the patient to apply the compression device themselves is an important part of early rehabilitation. Most patients will need to wear a compression device during the night indefinitely because of oedema fluctuations. In the preprosthetic phase, compression devices should be worn 24 hours a day and reapplied about every 4 hours. Several types of compression devices are possible such as:

-

52

Elastic wraps (Bandages): Elastic wraps are strips of elastic fabric, which are wrapped around the residual limb. 50% of the patients will be able to wrap the elastic bandages themselves, but this is a difficult practice. Wraps are readily available and inexpensive, they promote a tapered shape to the residual limb (see figure 5-1). - Shrinkers: Shrinkers are preformed elastic “socks”. Shrinkers are easier to use, but are also more expensive. Because of the difficulty of applying wraps around the hip, shrinkers are very often used for transfemoral amputations. Shrinkers can only be used after sutures are removed. - Removable protective socket: This socket is often used with elastic wraps or shrinkers. The socket is a custom-fitted device made of

thermoplastics. It protects the wound from traumatic impact, shapes the residual limb and adjusts to volume changes in the residual limb (see also chapter 4.1.2).

Figure 5-1: Figure-8 wrap for the transtibial amputation: [Seymour 2002] A. First wrap max extend from proximal medial to distal lateral. B. Second wrap may extend from proximal lateral to distal medial. C. Thrid wrap may overlie first wrap. D. Bandage is looslely wrapped approximately 60 milimeter to the knee. E. Completed wrap.

During the first weeks after an amputation,

the psychological effect is the most severe. The patient will become conscious of the consequences of his amputation and the changes that will become evident in his life. To emphasize the fact that the patient can stay highly independent with the use of a prosthesis, an interim prosthesis is very useful. Also rehabilitation will start very soon. Pysiotherapy will prefend contractures and muscles need to be used to stay in shape. The sooner a patient is out of hospitalization, the cheaper his treatment becomes.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

5.2 Selecting the aid

making

When

Once

these basic requirements are met, a prosthesis can be provided to the patient. Stability, ease of movement, energy efficiency, and the appearance of a natural gait are key elements to achieve with prosthetic use. Considerations that influence the choice of type of prosthesis are:

- - - - -

-

Usage

-

Stragegy

What is the amputation level? What is the expected function of the prosthesis? What is the cognitive function of the patient? What is the patient’s vocation (desk job vs. manual labour)? What are the patient’s avocational interests (e.g., hobbies)? What is the cosmetic importance of the prosthesis? What are the patient’s financial resources (e.g., medical insurance, worker’s compensation)?

Prostheses

the amputation is a fact, the first decision to make is to fit the patient with a prosthesis at all, or if his functioning will be better by providing other solutions (such as a wheelchair). This is an important decision made by the prosthetic team in close collaboration with the patient and has to take many factors on account, including available finances. Most important functional requirements of the patient to fit a prosthesis are sufficient trunk control, good upper body strength, static and dynamic balance and adequate posture. Once these basic requirements are met, then

Considerations for prosthetic type

Users

prostheses, it is clear that the choice of prosthesis is vital to the successrate of prosthetic use. However, the patient is not aquintanced with all the available brands and systems. He will partly have to trust the prosthetist with his selection of the type of prosthesis. But, because of differnt finances (the approval of reimbursement of more expensive prostheses by social insurances can take months) patients will have to make some decisions themselves. The first decision for the patient is to buy a temporal prosthesis or a definite. (Temporal can cost more, but can also save money, because adjustments are easier). The second most imporant choice is which type of socket and in the third place comes the components, most important being the foot. Most patients will start with a decent but relatively simple temporal prosthesis. Later, especially when the patient’s prosthesis is not performing to expectations, he will look for other solutions himself.

criteria in clinical decision

Approach

Having seen the huge amount of available

Success

Criteria 53

Factors in outcome of prosthetic use

If

the chosen prosthesis is provided, the patient has, from a functional perspective, a proper prosthesis. However, there are more criteria for a successful outcome of prosthetic use:

- - - - - - - -

motivation individual team approach comfortable to wear easy to don (put on) and doff (take off) lightweight and durable cosmetically pleasing low maintenance requirements function mechanically satisfactory

As

will become evident in section 5.4, in many cases, the factors don’t add up, and the prosthesis is not used properly or not used at all.

54

5.3 Alignment and rehabilitation

Now the type of prosthesis is chosen, a temporary prosthesis can be provided to begin gait training and to determine the right fit and alignment.

Static alignment (see 3.1.4) is done on forehand and is primary dependent on the patient’s atonomy and posture.

Dynamic alignment needs to be done in gait. However, the patient needs to learn how to walk properly with the prosthesis (e.g. with enough confidence). His muscles need to be trained to accommodate for the higher energy requirements of ambulation with a prosthesis.

Adjustment

of the dynamic alignment and the patient learning how to ambulate is a cyclic process and can take months. For the patient, who’s energy is already used to heal the wounds of the trauma and the amputation, the rehabilitation is very tiring. That constricts the available time per day the patient can practise. Also, the forming residual limb is still sensitive and needs to get used to the high pressures of prosthetic gait (again constricting practise time). And the shape of the residual limb is not optimal yet. For example, oedema could make the residual limb more round, therefore rotational resistance is reduced, while the alignment and fit are right in principle. It is the experience of the prosthetist to determine where the problem lies (in the prosthesis or in the patient) and what can be done about it.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

5.4 Daily routine: donning, After

The inside of the socket should be cleansed

weekly, washed with warm water and mild soap and dried thoroughly [Seymour 2002, p141]. It needs to be inspected daily for cracks or rough areas.

Amputees don’t need to shave their residual

Prosthetic

socks are often worn over the residual limb, because they add cushioning, reduce friction and replace lost volume in the socket due to shrinking of the residual limb. As the residual limb size changes socks can be added and removed. Prosthetic socks are available in various thicknesses often called ply.

Wearing

the fewest number of socks to achieve the desired ply will help reduce bunching and wrinkling of the socks.

Liners

in most cases are rolled onto the residual limb, just like a condom is. This method prevents pre-stretching of skin by donning and ensures a tight fit between the liner and the residual limb. Applying a liner can sometimes be difficult. The liner needs to have the right orientation and the application of the liner requires some force.

Criteria

limb. Shaving can cause ingrown hairs, and often leads to infected hair follicles.

interfaces are clean, before the prosthesis is donned, because hairs and other small particles can cause pressure concentration and become a source of skin problems.

Stragegy

- - -

wet environment in the sockets combined with socks, inserts, and shrinkers may cause fungi and bacteria. Proper, daily care is needed. If there are problems, it might be necessary to temporarily pause using the prosthesis. Daily healthcare, such as washing and drying of the residual limb, the socket and socks or liners, will prevent most troubles. Shrinkers and socks should be changed more frequently during the day in humid, hot weather. If needed, a 2-liter bottle may be inserted to restore the shape.

Usage

-

Daily care for the residual limb Daily care for the prosthesis Donning: inner sockets, liners and socks, then outer sockets (and components) Wearing the prosthesis during activities (ambulation, work, sitting, etc) Changing the prosthesis? Doffing: removing the prosthesis Applying a compression device (see section 5.1).

The

It is important that the residual limb and the

Prostheses

- - -

the prosthesis

Donning and doffing

Users

the hospitalization and rehabilitation period, the patient will go home. His level of functional ability, will determine the things he can do with his prosthesis and thus his “daily routine”. Most actions however, will be comparable for the majority of patients. In a way, it is very comparable with wearing shoes:

care for the residual limb and

Approach

doffing and gait

Daily

Requirements: The socket should be washable. 55

Sockets

are donned in different matters, often dependent on the suspension system (see section 4.3). In some cases, the amputee wears only the hard socket and the prosthesis can be shoved right on the residual limb. In most cases however, users use a donning sock. A donning sock is a stockinette, without a end (a long tube). It is protruded through a hole at the distal end of the prosthesis. By pulling that sock, the residual limb is pulled in the prosthesis. In case of an amputee using a liner with a pin/shuttle lock, or a liner with suction suspension, the donning sock often can not be used (of course, there are systems in which the patient can pull the end of the donning sock through the valve). Also, the donning of (hard) sockets can be a problem with patients with a very bulbous residual limb shape.

Changing

the prosthesis for special

activities

Some

special activities, such as showering and all kind of sportsactivities (biking, skiing, swimming), require specialized prostheses, specifically made for that purpose. An example is the shower-limb (figure 5-2). In these cases, the requirements for the prosthetic design differ.

And for some activities the prosthesis is not

needed at all. Many amputees, especially kids, like to move in-house without their prosthesis (instead using a wheelchair or nothing).

Shoes are often changeable. Of course, most

persons wearing a prosthesis, also wear shoes, so that the artificial and the unaffected limb are harmonically clad.

56

Figure 5-2: LEFT: The endolite Aqualimb with anto-slip tread patterm on the sole for extra grip on wet surfaces. [www. endolite.com]. RIGHT: The rampro activankle swimming prosthesis [www.rampro.net].

Exercise is the key

The

prosthesis is (has to become) part of everyday life. All successful use of prostheses starts with the amputee. As Jon Holmes states it [ACA 2001, p84]: “The most important part of the prosthesis is the motor’’. And the motor is the amputee. Good functionality and control over the prosthesis is obtained by daily exercise. Keeping the muscles and joints in shape and keeping confidence by practicing and using the prosthesis. Use it or lose it!

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Ambulation during everday life very important factor in functional outcome and use of the prosthesis is the amount of energy it takes to use it.

People with amputations tend to walk slower,

using a unilateral transtibial prosthesis takes about 50% more energy than normal. Especially for elderly, this can be very significant.

Another

difficulty can be a limited range of motion in the joints. This can prevent the amputee from climbing and descending stairs, sidewalks, etc. Also, it can slow down the amputee when turning.

Prostheses

Standing and sitting

Usage

Requirement: The prosthesis must enable the patient to stand up fully (else it takes a lot of energy to stand) and to sit (allow enough movement and avoid painful brims).

Users

Stragegy

to bring the power needed to walk to normal levels. Since the disabled person, like the normal subject, tends to choose his most efficient speed of ambulation, it seems appropriate to let the subject pick his own speed, instead of imposing an unnatural speed of walking for the researcher’s convenience. [Seymour 2002, p.166]. Some general properties of ambulation with a prosthesis can be drawn from the averaging of the results of studies in which the subjects did choose their own speed. However, the results given should be taken as approximations and generalizations: [Fisher 1978]

Many prosthetist use the thumb rule that

Approach

A

1. The normal person walks 83 m/min and expends 0.063 kcal/min/kg and 0.000764 kcal/m/kg. 2. The average transtibial amputee walks 43% slower, and expends five% less kcal/min and 89% more kcal/m than the normal person. 3. Normal and disabled persons naturally attempt to walk at a speed which is most efficient in terms of Ee /kcal/min. 4. Disabled persons decrease their speed of walking, so that their Ee /kcal/min decreases toward the normal range. 5. The more disabled a person, the more determinants of gait are lost; therefore, the more Ee /unit distance is used in ambulating and the less efficient is the gait.

Criteria 57

5.5 Statistics on functional outcome and use

Practically, how often and intensive the prosthesis is used, is dependent on a lot of factors, most important being age.

Elderly

Functional outcome of elderly is partly pre-

dictable by age at amputation, one-leg balance on the unaffected limb and cognitive impairment [Schoppen, 2001]. One study found that of 50+ US amputates only 44% wore their prostheses every day [Seymour 2002, p71]. A Canadian study [Bilodeau et al, 2000] shows different statistics: over 70% of amputees 60 years or older used their prosthesis every day. It concludes: “A multiple regression analysis showed that satisfaction, not possessing a wheelchair and cognitive integrity explained 46% of the variance in prosthesis use”. It is safe to conclude that the comfort level of the prosthesis and its easy of use is a major factor determining functional outcome.

58

Young

5.6 Aftercare and concerns

people are much more forgiving to the design. A study of 88 children of transtibial amputation in the Netherlands found high use rates. 90% of them attended a regular school. This increased use is a result of various factors. These include early fitting, decrease in pain and home and work modifications. [Seymour 2002]

Amputation

Younger

Project: Comfort of fit and use are the most important criteria of the prosthesis

results in social losses due to amputation involve loss of function, loss of sensation and loss of body image [Seymour 2002, p63]. Successful adaptation to the disability results in change of behaviour, such as:

- - - - - -

Increased confidence Taken charge of life rather than allowing external factors to control one’s life. Return to work or hobbies, Focus on new activities and skills Renewal of friendships Increased feelings of independence

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

The patient himself is responsible for finding

Usage

-

Prostheses

- - - -

Health-care access and expense Financial concerns Coordination of social services benefits Disability rights and advocacy Lack of knowledge of new prosthetic components Fit of the prosthetic socket Functioning of the prosthesis Adaptation to life with the prosthesis Lack of available information on new technologies Accessibility to Commercial Services

Users

- - - - -

Approach

the right support in his neighbourhood, but the rehabilitation team will help him on his way. However, life after an amputation is challenging. The amount of concerns of patients show this [Seymour 2002, p70]:

Stragegy Criteria 59

6 Ethics, Marketing and Design Vision 6.1 Ethics To determine the design target, apart from

function and practical requirements, a discussion of ethical implications is needed. It provides insight in the social requirements of the product.

The

Universal Prosthesis is a healthcare product. Its benefits for the user are clear. It is evident that there are also benefits for the society. How to optimize these benefits? By assessing the positive and negative impact of the product and building on the strengths. The following sections discuss these strengths, especially in the Universal Prosthesis’s final form, as a worldwide available product.

6.1.1 A World-wide Smart-tech product

The

60

Universal Prosthesis is a product that improves the live of the limbless that it is provided to. It is clear that a wide distribution of prostheses is wanted. In developed countries, the amputees are generally provided good healthcare. The wealth is available to improve these person’s welfare and Quality of Life. However, in developing countries, there is still a high unattended need for healthcare. A low-cost universal prosthesis can reach a

big group of customers.

However,

low-cost products generally are quite stigmatizing. Even people in need want the best. High-end “Western” products are better accepted. The universal prosthesis could acquire a good reputation by beginning as a high-end product for developed areas. Later, it can become cheaper and available everywhere. In the controlled environment of orthopaedic clinics, the design can be perfected and later translated to a design that is better suitable for the “stand alone” distribution in developing areas.

How

can this evolution from high to lowcost product already be incorporated into the design now? The key is the use of smarttech and developing a smart-product. A smart product is a product, which development is dependent on high input levels of knowledge. Often, also high-end production facilities and technologies are needed. However, the need for resources and parts in the final product is low. Smart products generally consist of highend materials. While being expensive at the start-up, the price of a smart product reduces when the investments are turned over, the product can be produced in higher volumes (mass-production) and the price of the used materials and technologies drop as well.

Future requirements: The Universal prosthesis should consist of few parts. The price of the product (in higher production volumes) should fall in time. The Universal prosthesis should have a high-tech or modern look.

6.1.2 Social-political consequences

An

important factor to predict the socialpolitical consequences of a product is to look to the influence of the production and use of the product to the distribution of wealth in the society. Will the product contribute to an egalitarian or an in-egalitarian society?

The

Universal Prosthesis is a product that helps the users to better fulfil their daily tasks, needs and functioning. This makes them more interdependent of their environment. There social integration is eased, improving their social, educational and vocational chances.

The

differences between the transtibial amputees and other people become smaller, also there economical differences. We can say that a prosthesis is a product that advocates an egalitatian society by its function.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Politically,

the long term, the Universal Prosthesis will become available to a wide public. It is favourable to integrate this development in the current design.

second limiting factor is economics. There must be enough interest to produce and distribute the Universal Prosthesis worldwide. Even while in this cases humanitarian NGO’s and funds, and social insurance play an enormous role, costs will always be an issue.

As seen in chapter two, the distribution and

Demand

In

use of the Universal Prosthesis is the limiting factor in the feasibility. Economics comes in the second place.

Important for its distribution is the easy of

use. The product must be understandable for a wide range of people, from different cultures and languages.

guage

Criteria

distribution factor is the (in)dependency of the product on the local infrastructure of resources. For example, it can be assumed that water and electricity are available everywhere but helium-gas is not. The same story goes for dependency on the local infrastructure of knowledge. For example, electrical-engineers are not available everywhere.

markets) and a high comfort level in one product, a lot of knowledge is needed. Again, the smart-tech approach seems to be appropriate.

Stragegy

Another

To combine price, adjustability (to reach new

Usage

Requirements: use-cues should be multi-lan-

for the Universal Prosthesis is highly dependent on its comfort level during use.

Prostheses

Universal Prosthesis will advocate an egalitarian society. General healthcare will improve. The effect of the product will be most noticeable in developing countries.

The

Users

We can conclude that on the long run, the

6.1.3 A product for the world

Approach

there is a need for high knowledge and production technologies to produce the prosthesis. High investments are needed at the start-up of the implementation process. The resources for these investments need to be collected by a small group of people, who gain power by their possibilities. To accommodate such power/money concentrations, an inegalitarian society is needed. The differences between the rich and the poor become bigger. However, the improvement in social functioning of the owners of a Universal Prosthesis has a more powerful egalitarian impact on society. Especially, when the investments are returned and the prosthesis becomes available to the masses for a low price.

61

6.1.4 Production

To

ensure better distribution the Universal Prosthesis is adjustable. But more is needed.

While

designed as a total concept, the Universal Prosthesis will still have a modular setup. Especially the foot, because of the need for different sizes, left-and-right models and varying requirements will have to be produced separately. It could be possible to use existing designs for the feet (produced by now operating companies), but the feet could also be locally produced, in accordance with the local culture and needs.

On the other hand, the socket needs high

It is well possible (and probably smart) too

include many locally made parts in the kit, such as manuals or components. That gives the local production facility the possibility to give the product a local character. People and the local society will feel more involved with the product.

In

the world of tomorrow, environmental considerations can’t be ignored. In the case of smart products, when the applied production methods are reasonable, the product can have a low impact on the environment. Smart products are produced in mass and often efficiency of resources is needed. Also, they exist of fewer parts.

6.2 Conclusions from the Sri Lankan test designs Apart

from identifying the lack of prosthetists as the mean problem in developing countries, additional lessons where learned from the design made there and the tests conducted.

Trials

of amputees walking in open-frame sockets (see appendix D for some designs) indicate that open-frame sockets can be used to stand in. During ambulation the testmodels in Sri Lanka buckled within a few steps.

input of skills and knowledge. It is better to produce it centrally.

A

good option to combine these different production places is to offer the product as an assembly kit. The socket is build centrally and imported. Locally, (in the country of distribution) feet and other component are added to complete the kit. Final assembly can be done by the user or the local specialist. This strategy is very similar to current distribution strategies, where components and assembly kits are sold to the prosthetists.

62

WATCH THE VIDEO ON THE CD

Figure 6-1: A movie, in which an amputee walks several steps in a frame socket. [Wisse et al. 2002]

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

These results indicate that open-frame sockThe open-frame design was never reported

-

higher pressures on the interface between the limb and the open-frame on pressure-tolerant area’s (see section 3.1.3) less tissue deformation during load (prosthesis will be formed to the situation when the highest pressures find place). This results in more comfort during stance and probably to a higher overall comfort.

These

intermediate finds strongly suggest that the universal prosthesis should exist of a hard open-frame part and an easily deformable soft part.

In

chapter four we have seen that current prosthetic design vary widely in quality (comfort level) and price. The market in developing countries is completely different than that in western markets. This results in different criteria, a different maximum price and a different value the users will give to the universal prosthesis.

Because the current state of prosthetics in

developing countries has to be improved (and the amputees won’t accept else!), compromising comfort is not an option.

Given

Stragegy

the high requirements on comfort level, it is challenging to offer the universal prosthesis for a low price (for a better fit, more or better adjustable parts are needed). This leads to a multi-step approach to the world market. Because each step requires a new design (optimization), the phases in this approach are referred to as cycles:

Usage

fort comparable to current sockets) as many areas as possible must assist in weight-bearing and control (up to their maximum pressure tolerance).

-

6.3 Marketing

Prostheses

To achieve a comfortable fit (a level of com-

socket can be used to stand in during the fitting procedure, the prosthesis can be fitted while the residual limb is under load. A total contact socket can than be formed in respect to the loaded limb. The resulting unique fitting procedure will result in:

Users

as being comfortable. One problem was the connection between the back and front part of the open-frame (usually a leather belt). The system had to be very precisely dimensioned and stiff connected; otherwise the amputee would slip downwards into the prosthesis (pistoning).

This is an important find. If an open-frame

Approach

ets can be used to stand in and might be developed further, so that even ambulation is possible.

Criteria 63

-

-

-

64

Each cycle will have a different target group.

Cycle 0 - The preparatory design trajectory: In this phase, the feasibility of the universal prosthesis is shown by developing a proof-ofprinciple design (this graduation project) and testing it with users (continuation).

-

Cycle 1- Market exploitation in developed countries: A high quality (medium-high costs) design is made. In this phase, the design is tested on a broader scale, while production quantities can stay low. It will be used by many experienced prosthetists, whose feedback is invaluable.

Cycle 0 – “Standard group”: Healthy man and women with a unilateral transtibial amputation. The age group for which the universal prosthesis is designed, will be around 20-60, because (anatomical and statistical) data is used from this agegroup (see appendix G).

-

Cycle 1 – “Inactive amputees”: such as bed-bound people, because the limited use of the prosthesis leads to low structural/mechanical demands. In this case, the universal prosthesis can be designed lighter (and more easily adjustable if deformation forces are needed). The quickly fitted prosthesis results in more elders that are fitted.

-

Cycle 1 – “Kids”: The lower body weights leads to low structural/mechanical demands. Also, because of the growth of the younger, more frequently new prostheses have to be fitted. The universal prosthesis can lead to a higher replacement rate. The design can be smaller, or issued in multiple sizes.

Most users of the universal prosthesis will be part of these groups:

Cycle 2 – World market exploitation: A high quality, low coast design is made. The product can be low in costs because the product is produced in large quantities (>10,000 a year). This high volume production is supported by a well organized distribution around the world (compare 6.1.4).

-

Cycles 2: - Standard group”, “Kids” and “Inactive”. The final design has to combine all the positive sides of the universal prosthesis. If feasible, multiple versions will improve the comfort for the target groups. The “UP Kids” can be smaller and the “UP Senior” can be lighter than the “UP Standard edition”.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

6.4 Substitute products methods

Most

A scan of the advantages of the systems can

be found in table 6-1. Concluding from it, if the universal prosthesis can keep its promise, it will be a good alternative (also see evaluation chapters).

Usage

the prosthesis has to be more wanted than two important substitute products, the wheelchair and the cane.

Standard: make a negative of the residual limb with plaster of Paris, make a positive with plaster of Paris, rectify for pressure distribution, laminate with fibre and resin. Sand-cast: put residual limb in plastic bag, Put the limb in a container, fill the container with sand, suck air out of container (negative shape forms), fill the negative with sand and evacuate air (positive sand form), rectify, vacuum form or laminate socket.

6.4.1 Fabrication and fitting methods

Rectification?

Expertise level needed?

Tools needed

Standard

Yes (PTB)

High

often vacuum forming

Sand-cast

Yes (PTB)

Medium-High

Pressure device + air-tight container

Water-cast

No

Low

Pressure device + water-tight fitting-tank

Icex

No (but pads)

Medium-High

Icecast compact component

Uni. Pros

Yes (PTB)

Low

None other than for do-it-yourself (saw, screwdriver, etc)

Table 6-1: Several fitting methods and their properties.

Criteria

Product

Stragegy

In

section 4.1.5 the standard fabrication method is shown (figure 4-9) and the ICEXsystem is introduced, which is an example of a pressure-cast method (see 4.3.1). Its fabrication manual can be found in appendix N. The sand-cast-method is developed for use in the third world as another pressure-cast method (fabrication details in appendix O). Finally, the water-cast-method, currently in development at orthopaedic centre “de Hoogstraat” in Utrecht and the University of Strathclyde, is developed with the same target group in mind. These last three, all pressure casts, aim

Prostheses

For the acceptance in developing countries,

Basic procedures:

Users

direct competitive products for the universal prosthesis are mentioned in chapter 4, during the discussion of the different prosthetic types. However, the most distinctive property, the fabrication method, is only discussed very briefly in section 4.1.5.

Water-cast: wrap residual limb in plaster of Paris, put limb in pressure-tank, add pressure while hardening, make a positive with plaster of Paris, laminate with fibre and resin. Icex: Fit liner with silicone pads to protect bones, prepare Icecast component, calibrate, wrap limb, shove on residual limb, harden (plaster of Paris or directly laminated), finish. Universal prosthesis: For an impression see section 6.5.

Approach

and competitive fitting

to alleviate the same problem as the universal prosthesis does, namely, the lack of experts and the difficulty of making new prosthetic (sockets). They compare as follows:

65

6.4.2 Substitute products

The

wheelchair and the cane are widely spread and used in developing countries. They compare as presented in table 6-2.

The

universal prosthesis can alleviate the problem with the quality of currently produced prosthetics in developing countries. It will stay more expensive than a cane, and 100 USD will stay a high amount for a large part of the world population. The wheelchair has to be available, especially for people with other amputations or disorders than a transtibial amputation.

66

Product

Comfort

Availability / support

Price

Prosthesis

The prosthesis can be very comfortable, but the user has to have a decent residual limb (health and length). Social acceptation is high.

A comfortable prosthesis is difficult to make. Because of this, properly functioning prostheses are not wide-spread. On the other hand, a robust prosthesis can be used in many situations (city, farmland, etc)

± 100

Wheelchair

The comfort level of the wheelchair is high, especially for people with difficult amputation levels.

Wheelchairs are easy to manufacture from blue-prints. Wheelchairs are wide-spread, but use is limited because the user needs flat roads and other adaptations of the environment. These adaptations are part of normal life in developed countries, but not so in developing countries.

± 100 USD

Cane

The comfort level is low during ambulation. The user needs an arm while walking. However, the cane can easily be put away. Social acceptance is low, but some make use of this (beggars).

With a cane most places are accessible. Also, canes are easily produced and distributed

± 10 USD

Universal Prosthesis

High-comfort fit made possible without expertise for a select group (of medium-active, healthy, transtibial amputees).

Better distribution

? USD

Table 6-2: Several walking and mobility aids and their properties

USD

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

6.5 Vision of the fitting

6.5.1 Cycle 1 – for developed countries

Distribution:

- -

-

-

Criteria

-

The kits are easy to lift, they don’t weigh more that 5 kilograms. The can be easily stored due to their form. The prosthetist opens the kit, when basic information on the residual limb is known, before the patient arrives, so he has time to prepare the parts he will need. The socket can be connected to a fitting pylon/foot if the prosthetist doesn’t know yet which type of foot he will use for his client. If he knows, he can immediately connect the selected foot.

Stragegy

Use – fit and alignment procedure:

-

Usage

The kits cost about 500 USD. The kits are being advertised as an (cost)effective, customizable, base from which a prosthetist can (time)efficiently fit a prosthesis. The kits are being sold via existing reselling companies, from two centralized points, one in the United States and one in Europe. The kit is bought in conjuncture with a service contract. This service contract will help the prosthetists with information and will sell additional parts when needed. The service contract will provide the producer of the universal prosthesis with addition feedback on usage and functioning.

Prostheses

After the feasibility of the concept is proven, the product has to be developed into a final design. This development can be conducted at universities or at one of the big companies, such as Otto-Bock or Ossur, that can finance it. A new team, combining industrial design engineers, technical engineers and prosthetists optimizes the design. The existing requirements list (chapter 7) defines the design target. - With a small number prostheses clinical tests are conducted to answer questions as: “can the universal prosthesis find its way in current (orthopaedic) practise?” and “what is long-term functional outcome?”. - Now, after evaluation and redesign, production can be started. The first batch will exist of 10,000 pieces. The assembly of the prosthetic parts is mostly left to the prosthetists. They buy assembly kits, so that they have greater influence on the final shape of the fitted prosthesis. The kits don’t contain feet, which are easily available through the common distribution channels. - The kit contains: a manual for the prosthetist, a manual for the user, the parts needed for the prosthesis, additional parts that can improve the fit for non-standard residual limbs (such as gel pads), a brochure that explains the long term project objective. The main part of the prosthesis, the socket, is

Users

bined with the market possibilities from section 6.3 and the project and vision remarks found all over chapter 3 and 4, lead to one vision about how the prosthesis and its fitting procedure should be. This vision is hereafter presented for both cycle 1 and 2 and follows the life-cycle of the product (design and production, distribution, fitting procedure, use by patient, disposition).

Design and production

-

Approach

procedure and usage

The results in Sri Lanka (section 6.2), com-

easily visible from the outside of the package. On the box is basic information about the range in stump shape, circumference and length for which the kit is suitable.

67

-

-

-

-

68

When the patient arrives, the basic setup is ready. The patient has to sit and to stand during the fitting procedure, so a frame or a walking aid and a chair are needed. The order of the parts in the box support the procedure the prosthetist has to follow. SITTING: To protect the residual limb of the client, a sock is donned. The still (de)formable socket is being donned over it. The prosthetist adjusts the total limb length by adjusting the length of the pylon. The socket is provided in its biggest shape, the prosthetist can by deforming it, globally adjust the form to the shape of the residual limb. If needed, gel pads or gel stickers are attached on the sock over wounds or extra-sensitive areas. STANDING: The patient can stand now. The hard part of the socket provides weight bearing. The pylon is aligned in such a way, that the line of gravity is normal on the axis of rotation of the knee. The feet of the patient have a natural distance and angle. STANDING: The soft part of the socket now exactly forms itself around the loaded residual limb. The prosthetist can aid this formation. When the soft part has the right shape, the prosthetist starts the hardening phase. The soft socket now quickly settles, the complete hardening doesn’t take longer than 10 minutes. Meanwhile, the patient is standing in the prosthesis (with about half its body weight supported by the prosthesis).

-

-

-

SITTING: The prosthesis now can be doffed. The fitting sock and gel stickers can be disposed of. A thin liner or sock (as thick as the fitting sock) can be worn during the use of the prosthesis. AMBULATION: The client walks. The prosthesis now behaves as a PTB-prosthesis. To improve pressure distribution (more TCB-behaviour), a thick, but viscous liner is donned. The user himself can choose the most comfortable combination. The fitting procedure is finished. The fitted pylon and foot are definitely attached to the socket. The client can take the result home, together with the manual. Not-used parts, which might be used later for repairs or when a new prosthesis is fitted, can be given to the client or send back to the factory.

Use- daily use by the client:

-

-

-

- -

PREPERATIONS: The socket has to be clean, especially on the inside. The user can, dependent on the type of foot that was provided with the prosthesis, don socks and shoes over the prosthesis. DONNING: The user dons a liner or sock. The prosthesis is donned over the liner or sock. If needed, a suspension belt or sleeve is attached. AMBULATION: The client now can do his normal, daily activities. In the beginning, the patient has to get used to the prosthesis. He has to gradually increase the daily period of use. DONNING: The prosthesis is donned. It can be stored everywhere. Socks need to be washed. MAINTENANCE: For reparations and maintenance, the client visits the prosthetist. The prosthesis is checked every half a year.

Disposition - - -

The prosthesis is returned to the prosthetist, who will provide a new one. The prosthetist detaches the foot. The prosthetist sends the prosthesis back to the factory. The factory will check the prosthesis on wear and will evaluate the way it was used.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

6.5.2 Cycle 2 – for developing countries

If the use of the prosthesis is successful in

the developed countries, the transition to the use for the developing countries can be made.

Distribution:

Design and production

-

Use – fit and alignment procedure:

-

-

-

-

Criteria

The kits are easy to lift; they don’t weigh more that 5 kilograms. The can be easily stored due to their form. The user is able to fit the prosthesis himself, but aid is useful. The helper and the user together open the kit. The order of the parts in the box supports the procedure the users have to follow. The socket, the pylon and the foot are connected by them. The user has to sit and to stand during the fitting procedure, so a frame or a table and a chair are needed. For the functioning of the prosthesis, a right alignment of the feet is required. The user can easily see this on the fit-sheet, which is placed on the ground and has an image of to feet printed on it.

Stragegy

-

-

Usage

-

-

Prostheses

-

After the success on the markets in the developed countries, the product has to be improved further. The producers of the prosthesis, in combination with subsidy and grants, finance the new development. The new team, again with multi-disciplinary now also combines members from all around the world. With a small amount of prototypes new clinical tests are conducted. Now, the ability of the prosthesis to function in area’s such as farmland and the ease of fitting need to be assessed. After redesign and optimization, mass production can be started. At least 10,000 prostheses a year are fabricated. The prosthesis will be as much as possible pre-assembled in the factory. The result will be distributed in assembly kits, which consist of the socket parts, pylon and a foot. The kit contains: the parts needed for fabrication, a manual for the one who will help during the fitting procedure (hereafter called helper), a manual for the user, a fit-sheet with feet positions printed on it and gel-stickers

The kits cost about 100 USD. The kits are being advertised as a good, complete and easily fitted prosthesis.. The kits are being sold in every country from centralized spots. Additional parts are easily available through the centralized selling points.

SITTING: To protect the residual limb of the client, a sock is donned. The still (de)formable socket is being donned over it. The helper adjusts the total limb length by adjusting the length of the pylon. The length can be easily determined by comparing the resulting knee heights. The socket is provided in its biggest shape, the helper can, by deforming it, globally adjust the form to the shape of the residual limb. If needed, gel pads or gel stickers are attached on the sock over wounds or extra-sensitive areas. STANDING: The patient can stand now. The hard part of the socket provides weight bearing. The pylon is aligned in such a way, that the line of gravity is normal on the axis of rotation of the knee. The feet of the patient have a natural distance and angle. STANDING: The soft part of the socket now exactly forms itself around the loaded residual limb. The helper can aid this formation. When the soft part has the right shape, the helper starts the hardening phase. The soft socket now quickly settles, the complete hardening doesn’t take longer than 10 minutes. Meanwhile, the user is standing in the prosthesis (with about half its body weight supported by the prosthesis).

Users

- -

-

-

Approach

and a liner. The final product (after fitting procedure) is shown on the outside of the box. On the box is shown for which residual limb sizes the prosthesis is suitable and the size and side of the foot that is in the box.

69

-

-

-

SITTING: The prosthesis now can be doffed. The fitting sock and gel stickers can be disposed of. A thin liner or sock (as thick as the fitting sock) can be worn during the use of the prosthesis. AMBULATION: The amputee walks. The prosthesis now behaves as a PTB-prosthesis. To improve pressure distribution (more TCB-behaviour), a thick, but viscous liner is donned. The user himself can choose the most comfortable combination. The fitting procedure is finished. The user take the result home, together with the manual and unused parts, which might be used later for small repairs.

Use - daily use by the client:

-

-

-

- -

70

PREPERATIONS: The socket has to be clean, especially on the inside. The user can, dependent on the type of foot that was provided with the prosthesis, don socks and shoes over the prosthesis. DONNING: The user dons a liner or sock. The prosthesis is donned over the liner or sock. If needed, a suspension belt or sleeve is attached. AMBULATION: The client now can do his normal, daily activities. In the beginning, the patient has to get used to the prosthesis. He has to gradually increase the daily period of use. DONNING: The prosthesis is donned. It can be stored everywhere. Socks need to be washed. MAINTENANCE: Small reparations and adjustments can be done by the user himself. For bigger defects, a new prosthesis has to be fitted. The manual will advice the user to replace the prosthesis every year.

Disposition

-

The prosthesis can be send or brought back to the factory, who will issue a new kit against a slightly reduced price.

7 Design criteria and requirements In chapter 3 it became clear that transtibial

needs to be successful. The design can comply with the criteria in a higher or lower level (score better or worse). In order of importance the 10 criteria are:



Stragegy Criteria

requirements for the design and doesn’t contain solution on how to meet these requirements. In the list of requirements hereafter, this principle is not used. This project is a continuation from the internship in Sri Lanka and the results of that work determine the global design and project form.

Design criteria follow from what the design

Usage

A good list of requirements only consists of

7.1 Ten Design Criteria

Prostheses

ent on the cycle (see section 6.3) in which the development of the prosthesis is. However, requirements for a later cycle, are always goals (Dutch: wensen) for the preceding cycle. That’s why the requirements can be found per cycle (section 7.2 to 7.4). Additional goals can be found in section 7.5.

1. Universal The prosthesis can be fitted to a big group of transtibial amputees. 2. Comfortable The prosthesis is comfortable during use by the amputee. 3. Easily fitted The prosthesis can be fitted easily to the amputee by low educated. 4. Controllable The prosthesis provides the control and feedback during use. 5. Usable The prosthesis can be easily used (especially donning, doffing and cleaning) by the amputee. 6. Safe The prosthesis is safe in respect to health of the user and of the planet. 7 Affordable The price of the prosthesis is low. 8 Cosmetics The cosmetics of the prosthesis are pleasing. The amputee blends easily into the society. 9 Quickly fitted The fitting procedure takes little time. 10 Distributable The distribution is easy and the prosthesis is complete or well compatible with other systems. The (fitting of the) prosthesis is independent on locale infrastructure.

Users

The requirements (Dutch: eisen) are depend-

The complete set of requirements relates to the complete service that de producer and the prosthetist offer to the client (of which the prosthesis is a part). That would be a long list. Here is chosen for a shorter, better usable list, that suits the purpose of this project, namely to conduct a feasibility study. Areas which won’t be the bottleneck for the feasibility of the project are not worked out.

Boudewijn Martin Wisse TU Delft, 2005

Approach

amputation is the most prevalent level of amputation. Therefore, the universal prostheses should be usable by this group. But what are other requirements? Ten criteria, which are constantly used while evaluating ideas, and the total concept can be found in section 7.1.

The list of requirements also isn’t complete.

The Universal Prosthesis

71

7.2 Requirements for cycle 0: The preparatory design trajectory

Corresponding brackets ().

sections are given between

Total distribution kit /prosthesis:

- - - - - -





72

The prosthesis can be donned seated. The prosthesis can be doffed seated. The prosthesis has roughly the same shape as the natural leg. The fitting procedure takes little time. The prosthesis is suitable for at least 70% of the transtibial amputees (2.3). The prosthesis improves the functional activities and mobility of the user in a similar way as existing prostheses. Inclusive ambulation and body posture. - The prosthesis provides an acceptable gait (3.1.5). - Ambulation is possible without the toes touching or skimming the ground. - The prosthesis provides enough stability (during ambulation that resembles normal gait). - The prosthesis provides enough perception and control.

The socket:

- -

-



-

The interface with the residual limb can not be poisonous or irritate the skin (for P99). The socket is suitable for more than 70% of the transtibial amputees (2.3). - The socket is suitable for residual limbs with lengths of 80 to 250 mm (3.1.2, 3.1.3). - The socket is suitable for residual limbs with circumferences of 250 to 350 mm (at patellar tendon height) (3.1.3). - The socket is suitable for residual limb shapes that are conical and cylindrical (3.1.3) During the fitting procedure: - The socket is formed while the residual limb is loaded (while the user stands in it): - The socket provides weight-bearing at beginning of the procedure. The unhardened socket is enough flexible and deformable, so that the prosthetist can shape it in the shape of the residual limb. - The socket loads the pressure-tolerant areas of the residual limb. - The socket has to harden so that the total area can add up to the transfer of loads between the socket and the residual limb. The prosthetist has to be able to decide the moment of the hardening. The hardening won’t take longer than ten minutes. During daily use: - The sensitive areas of the residual limb will not be overloaded. Most of the loading is on the load tolerant areas (3.1.3 – 3.1.5).





-



- The socket makes total contact with the residual limb. Every area of the residual limb, inclusive the distal end, has to make contact with the socket (so no “holes”) (4.3.1) - The pressure-distribution is optimized to the PTB or the TCB-model or a hybrid/combination of those. (4.3.1) The socket is not uncomfortable (2.3), the comfort level is comparable with existing prostheses. (4.3.1) - The socket does not hurt. - The socket does not obstruct normal movement. - The socket can not have obtruding or sharp parts as well on the inside as on the outside.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Pylon:

-

developed countries Corresponding sections are given between brackets ().

Total distribution kit /prosthesis:

- -

-

-

-

-

-

Criteria

-

The product is optimized for production quantities over 10,000 pieces. (4.1) The prosthesis complies with the current West-European and American industry standards. (3.3) The final price of the distribution kit is maximal 700 USD. Using the universal prosthesis will (in general) reduce the costs of the total rehabilitation trajectory. (4.5.1-4.5.5) The prosthetist assembles the socket, the pylon and the foot within 2 minutes, so that it is ready to be fitted. The final prosthesis will weight between 2.2 and 3.5 kilograms (3.1.4, 3.1.5) with the centre of gravity of the prostheses as proximal as possible. The prosthesis will stay functioning properly at normal use (average usage of the target group) al least one year. (4.6) The prosthesis doesn’t attract attention when worn under a pair of trousers, socks and shoes (4.1). The donning and doffing of the prosthesis does not take longer than one minute (5.4).

Stragegy



-

SUSPENSION: The comfort level has to be minimally equal to the comfort level of the currently used “knee-cuff” solution. CONNECTIVE COMPONENTS: The connection between the socket and the pylon can be rotated. The connection between the pylon and the socket can be rotated.

Usage



Additional parts:

-

7.3 Criteria for cycle 1: Market exploitation in

Prostheses



A “rocker foot” suffices.

Users

-

Foot:

-

Approach

-

The pylon can be adjusted in length. The total height of the prosthesis is the same as that of the opposing leg. The pylon can transfer the forces that act upon it during stance (maximal 700 N) to the ground without plastic deformation. The total elastic bending may not be more than 6 mm at a length of 240 mm and the total elastic rotation may not be more than 10 degrees, when the pylon is loaded with a torque of 60 Nm at a length of 240 mm. The pylon can be aligned: - The pylon can be aligned is such a way, that the medial side transfers more load than the fibular head region (3.1.4). - The alignment is done with 5 to 10 degrees flexed knees (3.1.4). - The complete prosthesis can be aligned in such a way, that the rotation-forces on the residual limb while standing are minimal (no more than current prostheses) (4.4). - The pylon can be aligned in such a way that the line of gravity of the body will be normal to the rotational axis of the knee during stance.

73

-

- -

The prosthesis aids the prosthetist in finding the right alignment (use-cues). The prosthetist has to experience the fitting and alignment procedure as more natural and intuitive than the procedures of current prostheses (2.3-4.4). The prosthesis is suitable for daily use (2.3). The energy expenditure of normal use of the prosthesis is comparable with that of current prostheses (maximal 30% more) (3.1.5).

The socket:

- -

The total production cost of the socket is maximal 500 USD. The socket must be easy to clean (5.4).

Additional parts:

-

-

-

-

Pylon:

- -

The total production cost of the pylon is maximal 100 USD. The pylon can be fitted with a shock-absorption component or rotator.

Foot:

-

74

REMARK: In this distribution kit, no foot is supplied. Standard feet designs can be connected to the universal prosthesis.

-

SUSPENSION: The included suspension will keep the prosthesis connected to the residual limb during swing-phase. CONNECTIVE COMPONENTS: The included connective components provide connection with popular feet designs. The connection to the feet stays adjustable (translation and rotation), even when the prosthesis is hardened. (4.2) FITTING SOCK: The supplied fitting sock can be donned sitting. The fitting sock protects (the skin of) the residual limb during the fitting procedure. PRESSURE-RELIEVING-PARTS (GEL PADS): These included parts will diminish the pressure on extra sensitive areas of maximal 600 mm2. FITTING PYLON – OPTIONAL FOR CYCLE 1: The fitting pylon is an extra pylon part that can be attached to make up for the lacking foot during the fitting procedure.

Packaging and manuals:

- -

- -

-

-

The manual for the prosthetist contains a (textual) description of the preferred procedures. The manual for the user contains information about donning and doffing, the maintenance and cleaning of the prosthesis, how the user can recognize problems and what actions to take. OPTIONAL FOR CYCLE 1: A brochure that explains the long term project objective. On the outside of the distribution box (packaging) is printed for what range of residual limb sizes and shapes the prostheses is suitable. The socket is visible from the outside of the packaging. The total package is easily displaceable by a single person. It is not bigger than 0,12 M3) and it has sides shorter than 800 mm. The package is not heavier than 5 kg. The order in which the parts come out of the package supports the fitting procedure.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Marketing:

-

7.4 Criteria for cycle 2: World market exploitation Corresponding sections are given between brackets ().

-

-

The total production cost of the socket is maximal 80 USD.

The total production cost of the pylon is maximal 30 USD.

- -

Criteria

Pylon:

-

-

Stragegy

The socket:

-

- -

CONNECTIVE COMPONENTS: The included connective components provide connection to the included foot. The connection to the foot stays adjustable (translation and rotation), even when the prosthesis is hardened. FITTING SOCK: Included. SOCKS FOR DAILY USE: Included in 2 thicknesses. The wearing of these socks increases the pressure in the socket. LINER FOR DAILY USE: Included. Wearing of the liner results in a more evenly distributed pressure in the socket. PRESSURE-RELIEVING-PARTS (GEL PADS): Included. FEET-SHEET AND OTHER ASSISTIVE DEVICES: Simple products that can improve the ease of aligning (the residual limb in) the prosthesis.

Usage

-

Additional parts:

-

Prostheses

-

The final selling price of the distribution kit is maximal 200 USD. The total prosthesis will keep functioning satisfactory for two years when normally used. The assembly has to be finished as far as possible in the factory. Pylon and socket are one part. The prosthesis can be worn without shoes (without attracting negative attention). The prosthesis can be fitted by non-experts.

- -

The total production cost of the foot is maximal 30 USD. The foot has a natural appearance. - The foot is available in left and right. - The foot is available in several sizes. The foot can be fitted with sandals.

Users

Total distribution kit /prosthesis:

-

Foot:

-

Approach

-

The distribution kit is being advertised as an (cost)efficient, customizable, base from which a prosthetist can (time)efficiently fit a prosthesis. The kit is bought in together with a service contract.

75

Packaging and manuals:

- -

The manuals are internationally interchangeable. It uses mainly figures / drawings. On the package (distribution kit) the final product and the included foot-size and footside are printed.

Marketing

-

The kits are being advertised as a good, complete and easily fitted prosthesis.

7.5 Additional goals If possible, the following goals can add value to the solution:

-

- -

-

-

-

The prosthesis is adjustable after the fitting procedure. The prosthesis is as light as possible. The prosthesis fits into the locale culture. (Part of the) production is conducted locally. Local, social involvement is stimulated The prosthesis exists of as few as possible parts (2.3). The prosthesis is accepted by the total rehabilitation team (3.2)

Socket:

-

- -

The socket is transparent (makes evaluation of the interface between the socket and the residual limb easier) The socket is adjustable during use (adjustments take place several times a year). The socket is adjustable during use (adjustments take place multiple times a day).

Pylon:

- -

The pylon is adjustable during use (adjustments take place several times a year) The pylon is an integral part of the socket and forms an exoskeletal design (4.2).

The included foot is suitable for multiple weights, multiple foot sizes and for left and right use (adjustable foot).

Additional parts:

Total prosthesis:

-

76

Foot:

-

SOCK: The sock is transparent. The sock is as thin as possible. The fitting sock and the sock for daily use are the same. SUSPENSION: The suspension is as easy and comfortable as current suction suspensions.

Marketing:

-

In an early stage, a big organization (producer), such as Otto-Bock or Ossur is involved.

The Universal Prosthesis

8 Discussion and conclusion of part 1 The

A broad range of market options.

The pylon has to stay adjustable. To allow for

dynamic alignment of the pylon/foot after socket production is an important factor to improve gait and will make the Universal Prosthesis easier accepted by current day prosthetists (see section 3.1.4).

high comfort level of the socket can be reached best if pressure tolerant areas are loaded more than pressure intolerant areas (PTB-principle, section 3.1.3). The bony prominences (figure 3-6) and the distal end are the areas of relief and the patellar tendon is very pressure tolerant. The limited variation in these areas (except in distal end height) indicated that a standard socket shape is possible (appendix F, elaborated on in chapter 11 and appendix R).

J.

Criteria

Foort (appendix X) even concludes that the use of prefabricated Below-knee sockets “taught us that five sizes for each side of the body were sufficient to fit all the new amputees managed in this way and that one size alone met 50% of the needs”. However, the use of prefabricated sockets in current prosthetic practise is not mainstream. The adjustability of the universal prosthesis could improve the trust prosthetists have in the fit of the prefabricated (universal) socket and increase it use.

Stragegy

unique selling point of the Universal Prosthesis is that it is quickly fitted by loweducated experts. For the amputee, this means better access to prosthetics and more often replaced prostheses. On the other hand, because the shape of the socket has to be formable, the strength and stiffness of the Universal Prosthesis could be limited. These facts combined indicate that the Universal Prosthesis is especially suitable for two specific target groups, namely children and elder (see section 3.1.7 & 6.3). It also is useful as a temporal prosthesis (3-6 months after amputation) or a spare one (see section 2.4, 4.1.4). When, by smart design, stiffness and strength become less a problem, the Universal Prosthesis can be used for daily activities.

A

Usage

The

tion 2.4) is if the adjustability of the design refers only to the fitting procedure or also to periodically or even daily adjustments. However, it became clear that comfort and control acre the main determines for functional outcome (see section 5.5) and these requirements are met by a socket with a stiff fit and an appropriate pressure distribution (see section 3.1). Current solutions for daily adjustable sockets are few and only improve comfort significantly for a very select group of users. Adjustability of the socket during use therefore is not a requirement for the Universal Prosthesis to be successful.

Prostheses

the world, amputees and prosthetists, becomes clear. The fact that designing a prosthesis takes time is recognised and the project is split into phases. These phases are design cycles and are “a preparatory design trajectory”, “market exploitation in developed countries” and “world market exploitation” (see section 6.3).

Still unclear in the design objective (see sec-

A high comfort level can be reached

Users

In chapter 2 the benefit for users all around

Focus on fitting procedure

Approach

analysis indicates that the design an implementation of the universal prosthesis is possible, although with some constraints.

Boudewijn Martin Wisse TU Delft, 2005

77

A vision of the socket design

User

tests in Sri Lanka show that weightbearing in a frame is possible, but total contact is necessary for comfort. This leads to a socket system that consists of a hard, weightbearing frame and a flexible total contact part. The form and properties of these are determined in part 2 of this report: “synthesis”.

78

The Universal Prosthesis

9 Synthesis - from idea to prosthesis Having

The base for the new design is the design

In

part 3 (chapter 12, 13 and 14) of this report, the universal prosthesis will be evaluated.

Concept

form of the rigid parts needs to be refined. A study of the anatomy of the residual limb and the (expected) biomechanical behaviour is the basis for their shapes (section 11.1). The (fabrication of the) flexible parts is another important design step (section 11.2). The connector, connects these parts with the foot (section 11.3). When the shape of the frame is determined, the prosthesis is ready to be optimized for daily use (11.4), the fitting procedure (11.5) and production (11.6).

Ideas

made in Sri Lanka. However, because of changes in the design philosophy (from cheap production to easy fitting procedure) and the preferred production method (from low-budget to mass-production) a review of the (sub)problems is needed (section 10.1) and solutions need to be re-evaluated (section 10.2). The real synthesis can now take place; the chosen ideas are integrated into a final concept (section 10.3).

The result exits of rigid and flexible parts. The

Synthesis

determined the project target and design requirements, the materialization of the design can begin.

Boudewijn Martin Wisse TU Delft, 2005

Evaluation Recomm. Conclusion

79

10 Ideas In

Sri Lanka it became clear that weight bearing can be achieved by making an openframe based socket (see section 6.2). However, made from aluminium and basic production methods, the open frame socket was not comfortable enough to be used for ambulation (for a prolonged period of time). Another problem was that the design was not stiff and strong enough, which resulted in buckling (during ambulation).

A

better fit and pressure distribution as well as higher stiffness and strength can be achieved by new form-giving and new material choice.

80

10.1 Idea generation From

the criteria and design requirements, sub-problems follow:

1 Universal (1) How can one socket vary in length, circumference or shape (the socket has to be hollow)? (2) How can one pylon/ total prosthesis vary in those properties (the pylon can be solid)? (5) How to align a loadable frame or pylon? 2 Comfortable (6) How can one prosthesis make total contact with different shaped residual limbs? (7) How to improve weight bearing properties and pressure distribution in the socket? 3 Easily fitted (8) How can the fitting procedure made easier? 4 Controllable (together with 6) How can a tight fit be assured by a wide range of residual limb shapes? 5 Usable (11) How can a prosthesis be donned and doffed? (12) Even when the patient has a bulbous residual limb shape? 6 Safe (13, 14, 15, 16) How can stiffness and strength be guarantied? 7 Affordable (Optimization) 8 Social (Optimization) 9 Quickly fitted (Optimization) 10 Distributed (17) How can integration with existing parts (connective components and the suspension system) be made easy?

Conflicts in the criteria

Two specific equilibriums need to be found in opposing criteria which are:

Variable vs. stiff Stiffness is an important aspect of safety and control, while variability or adjustability is an important aspect of the universality. How can the prosthesis be made stiff enough, while still being variable? We know that the prosthesis will incorporate an open-frame socket design. Therefore this question can be restated as: (3) “How to make a frame (that can transfer loads) deformable?” and (4) “How to attach a deformable part to a rigid skeletal frame?”. Comfort vs. control More control can be achieved by a tighter fit, which means higher pressures. However, control is more important during ambulation/stance than during sitting or swing, so the problem is: (9) “How can a tight fit be accented during load and a comfortable fit during rest?”.

Another way to improve comfort is to reduce

pressure-peaks by vertical dampening. The problem is: (10) “How to improve vertical dampening while keeping control (and direct sensory feedback) during use?

The

problems are explored in appendix Q. The presented solutions were obtained by looking at existing solutions, looking into other products with similar problems and by creative thinking.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

1

Subproblems and ideas (solutions) can than

The

Each

number correspondences with the number and the figures in the Appendix.

The “multi-link” option is also very interesting. Theoretically, the more parts an openframe socket consists of, the better the fit is that can be achieved. J. Foort formulated the potential usefulness of the multi-link option in 1977 and proposed that “Shapeable matrices can be used to construct biomechanical structures directly”.

Conclusion

matrices should consist of are not satisfactory developed until now. Cousins proposes that “hybrid modular-matrix systems may develop as stepping stones to either matrix or modular structures” [J Foort, 1986]. The Universal Prosthesis, with its hard openframe and connective soft-frame parts does in a way resemble a modular-matrix system. Belts as seen in the “ellipse with belts” option are suitable to transfer tensile forces between frame parts over a variable length. If adjust-

Recomm.

However, elements of which these shapeable

Evaluation

follows a short discussion and some considerations of the subproblems and the solutions that can be found in appendix Q.

Concept

Hereafter

“flower principle” is a very interesting to use for an adjustable socket. It promotes a pylon at the distal end of the socket and the “opening of the flower” is the normal response of shell parts when loaded from the inside (when you try to stand in it. The flower principle can be used, but the normal response should be counteracted, for example, by a belt all around the socket.

Ideas

be evaluated by rating them against the 10 criteria. However, selected solutions have to be integrated into one prosthesis. Also, we know that the socket will exist of hard and soft parts and that the hard parts will function as an open-frame socket (see 6.3). It is therefore important to select idea’s that integrate well into each other and that contribute to an integrated fitting procedure.

able belts are chosen as part of the final solution, the user has to be able to determine the length of the belt quite precise. (see 6.2). The “harmonica” option can also be used in a tapered socket shape, so it can accommodate for variable stump sizes and lengths.

Synthesis

10.2 Idea discussion

81

2

The “saw it” option for the pylon is basic and can be integrated well into designs that can only be fitted once (can only be made shorter after the fitting procedure). For additional adjustments during use, a combination with the “telescope” or “screw it” options can be chosen.

3

Building the prosthesis from parts that are deformable of displaceable when separated, but are that are rigid when connected, is a good option. It compares well to a modular “Lego” kind of build-up.

”One-way-deformation can be unsafe for the

patient and result in a locked-in residual limb. On the other hand, it might be a useful tool during the fitting procedure. In this case, the “one-way-deformation” has to be reversible or to be reset.

4

“Gluing parts together” is a good option in case it can be done during the production of the prosthetic components. Glue is difficult to use during the fitting procedure: it can get quite messy and results may vary. These difficulties can partly be removed by using a bag around the glue and the parts that need connecting. However, in this last case it is difficult to add a reaction agent or to start the reaction otherwise.

82

w

“ raps” can be used, especially in combination with Velcro (NL: klittenband). “Dip and coat” is another option that is only usable in the factory.

”plait/weave”

is an option that can lead to advanced designs with varying stiffness (or other properties” in direction and place. However, the production method for woven components is not easy, especially when the textile has to be integrated into hard frame parts. Another limit is that it is not easy to predetermine the shape of the end-product.

5

A “standard solution” (multi-axis) pivot at the distal end of the pylon seems a natural and satisfying solution, especially when multiple distal ends can be inserted (see subproblem 17). However, the proximal bending point will differ from location, according to the length of the residual limb of the amputee. For this “pivot” point the “angle by deformation” or “bend” solutions seem to be more appropriate. These deformations must hen be easy for the prosthetist to apply, while the pylon still has to provide weight bearing after the bending. This is a typical example of the variable-stiff conflict which makes the design of the universal prosthesis such a challenge.

6

Total contact is of utmost importance for the comfort and function of the socket.

”Following

the contour” of the (unloaded) residual limb, in literature sometimes referred to as surface matching, is currently the most used method for determining the stump shape. However, due to the compressive forces, deformation of the soft tissue is to be expected. Deformation of the soft tissue is used in the first (3 to 6) months after the amputation to promote a stiffer residual limb, with a taper shape (see section 5.1). Also, deformation of the residual limb will not stop blood flow up to a internal (skin) pressure of 35 kPA (Sangeorzan et al. 1989). For posterior soft tissues in the residual limb (the calf muscle) this implies that load pressures of up to 70 kPa are allowed (Sangeorzan et al. 1989). Deformation of the limb will then be up to 5.4 ± 1.1 mm, dependent on the amount of soft tissue, it stiffness and other factors (Sangeorzan et al. 1989).

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Also,

deformation is therefore not only a design option, but a tissue reaction to load that has to be taken into account. Also, tissue cannot be deformed to much, especially when the amputee has a bony residual limb.

Extra

Smart designs can further improve the weight-bearing and pressure-distributing properties of the socket.

dampening can reduce shocks and therefore decrease the amount of pressure peaks and promote comfort (also see section 4.3.5). On the other hand, the extra freedom of movement decreases the direct feedback and control over the prosthesis. In this light, vertical freedom of movement is less problematic than horizontal or rotational movements (see subproblem 10).

Most

Increasing

7

Evaluation Recomm. Conclusion

the pressure (perpendicular forces on the residual limb) increases the control and can improve weight bearing. On the other hand, during swing-phase and other cases in which there is no load on the prosthesis (e.g. sitting), constant elevated pressure on the residual limb should be avoided to avoid tissue damage. Several idea’s are shown in the appendix that increase the pressure during load, but keep pressures low without the load. All these solutions react on a displacement (that is caused by the loading of the prosthesis). The “four bar mechanism” is the most basic solution of which some other presented solutions are spin-offs. The “force redirected with pulleys”-option uses the vertical dampening displacement to increase the posterior(-anterior) pressure. This way, control is only limited decreased. However, these systems introduce moveable parts in the prosthesis thus decreasing life-time, easeof-use and increasing costs.

Concept

professional prosthetists agree that in general, the distal end of the residual limb should not be loaded. The distal end pad (an idea that came into existence in Sri Lanka) does exactly that, but in a very controllable manner. It contributes to the total weight bearing properties of the socket, if the amputee has some pressure tolerance in that area. Because there is always some pistoning of the residual limb in the socket (or the residual bones in the soft tissue), the distal end pad has to be designed in such a way that it will not exceed the tolerance level during stance and ambulation. In the appendix, a possible solution with springs, one with elastic band and the commonly used gel pad are shown. The distal end pads should be inserted at different distances from the Pattelar tendon, because of variations in the residual limb lengths.

Ideas

Figure 10-1: Otto-Bock Harmony system

Tissue

Synthesis

pressure cast methods deform the soft tissue, but the volume (is assumed to) stays constant. This is called volume matching. The “inflate/fill” option is therefore a deisgn option that promotes volume-matching (and a TSB socket fit). The big difference between this solution and current pressure cast solutions is that the currently pressure is applied by an apparatus that completely envelops the socket. In the presented solution, the pressure is added to the socket itself. The “suck/vacuum” solution is used in the otto bock Harmony system. In this system (figure 10-1) every step is used to decrease the pressure between the socket and a special liner, thus improving the connection between them. The fit is said to be comfortable and provides excellent control.

83

8

The success of the universal prosthesis is highly dependent on the east of the fitting procedure. Several strategies can be followed to keep the fitting method simple.

First of all, use-cues can be added where use

is ambivalent. Examples are the length of the total prosthesis and the socket-residual limb angle. Use-cues are tips that are part of the design. For example, by accenting the patellar tendon and the tibial crest on the outside of the socket, users immediately know what the front side of the socket is. The total height of the prosthesis can be shown by tagging the height which the prosthesis should have when the user stands in it (mid-patellartendon is easily comparable with the opposite leg). Another option is to attach a temporal part that needs to be level with the top-knee height of the opposite limb when the amputee sits (figure 10-2).

Another way to improve the easiness of the

fitting procedure is to standardize it. The universal prosthesis will standardize it, because it will incorporate a hands-off fitting procedure for the socket. Further standardization can be achieved throughout the procedure by copying the fitting techniques now commonly used. These are practical and using them will improve the acceptation rate of the universal prosthesis for the current prosthetists.

84

Simplifying

the fitting and production of the universal prosthesis can be achieved by combining them into one procedure. In this respect the “immediate production method” is similar of that of the ICEX (see section 4.3.1 – hydrostatic socket). If this can be achieved, the universal prosthesis not only reduces the need for skilled prosthetists, but also for technicians and machinery.

Quick feedback of the user will also reduce

the time the prosthetist needs per client. Especially when feedback can be incorporated and reacted on immediately. When the patient is loading the residual limb during the fitting procedure, it becomes directly clear when the fit is not optimal and the prosthetist and the amputee can take action by adding pressure pads, realigning the hard parts of the socket or realigning the residual limb. If this direct feedback will reduce the visits of the amputee to the prosthetist in practise, clinical tests have to determine.

9

The advantages of promoting a tight fit during use have been mentioned while discussing subproblems 6 and 7. Also rotation (displacement) can be used to achieve this. The “strangle-fit” will tighten when rotational forces are applied. Two springs, one winded clockwise and the other counter-clockwise, will make sure that rotation in both directions will result in this behaviour. An advantage of this system is that a relatively small rotation is needed to increase the pressure. A difficulty is that spring hat to be deformed to be used for amputees with variable stump circumferences.

Another way to increase the feedback is to

make as many parts as possible transparent. If this is the case, the prosthetist can check if sensitive area’s are avoided, if all the tissue makes contact with the socket and how the tissue reacts to the pressure. Figure 10-2: Possibilities for adding use-cues to ease the fitting procedure.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

A completely other solution is to change the

Conclusion



Discussed with 11

Recomm.

Donning and doffing the prosthesis is an important factor in how user friendly the prosthesis will be experienced. Also, because the socket will be formed directly on the residual limb, the doffing should get extra attention. In most cases the residual limb shape will be taper (see section 3.1.3) and the socket can just be slipped of the limb (“shove”-option). However, caution has to be taken when handling bulbous shaped residual limbs. In these cases the directly on the residual limb fabricated socket can get locked in.

the donning and doffing of the liner. If it is applied on the socket itself, this would result in a very flexible socket and force transfer would be a problem. However, the roll on principle can be very useful during the fitting procedure, because it results in a very precise total contact fit. Even while a liner can’t transfer loads, it will prevent oedema.

12

Evaluation

11

The “roll on” idea is now commonly used in

Concept

Vertical dampening can increase comfort, but also means less control (also see subproblem 7). Currently, most dampening systems are integrated into the foot. In general, the more distal the dampening system is placed, the better the experienced control will be.

is very suitable for the fitting procedure. With the wrapping method, a material can be applied around all sorts of residual limb shapes. The same principle is used in the ICEX-system see section 4.3.1 – hydrostatic sockets), in which carbon fibre reinforced wraps are used, that during the fitting procedure are impregnated and hardened.

Ideas

10

The wrapping solution is another idea that

Synthesis

(transversal) shape of the socket. The rounder the shape, the more volume it can contain with the same circumference, resulting in lower pressures. On the other hand, the round shape is not resistant to torque. The triangular shape results in higher pressures and is far better in transferring rotational forces from the socket to the residual limb.

One basic way to avoid this problem is to use a flexible socket, that when donned is fastened or tightened (“fix it with a rubber ring”, “tightening”, ”zip” and “belt” idea’s). In the “bend /deform” idea, the socket is elastic but the force needed for deformation is higher than the forces during ambulation. This can only be achieved when and additional device or tool is used for donning and doffing, which doesn’t fit the design philosophy.

85

13

The pylon has to deal with the same stiffness-deformable conflict. Does it have to change shape? Well, extra leverage acting on the residual limb should be avoided, because that implies extra pressure. Normally, that is solved by connecting the pylon to the socket at the intersection with the line of gravity (figure 10-3, compare section 3.1.4).

A

nother option is to use multiple pylons (see section 4.3.2). In function this last solution resembles an exoskeletal prosthesis (see section 4.2.1). The exoskeletal setup is in this regard very suitable for the universal prosthesis. It provides a very stiff and strong prosthesis, while it can easily adept to variable residual limb lengths.

The H-basic shape is also interesting. When

15

This increases the stiffness of the total struc-

The soft parts can add “tensile forces” to the

14

Problematic is the variance in residual limb

two vertical pylons are connected by an additional surface, a transversal H-shape will be formed (figure 10-4)

ture. In the same way, many connections with a stiff socket can also enhance the stiffness (“attach-surface-above” idea). This connective surface can be integrated into one part by adding surfaces that can be rotated from parallel (deformable status) to perpendicular (stiff status). Discussed with 13

Because

the universal prosthesis incorporates a hard open-frame, the pylon will have properties of both the multi-pylon and exoskeletal solution. The basic shape used for the pylon will than be the round or triangular shape.

86

Figure 10-3: Moments around the socket, as a result of diffrent pylon types.

Figure 10-4: H-profile.

To achieve a light but stiff total concept design, the flexible part of the design has to contribute to the total stiffness. The fitting procedure is an important factor in this. open socket frame. Imagine this principle as elastic bands or springs between the hard frame parts. The tensile forces increase the pressure on the residual limb. As long as this pressure doesn’t exceed the threshold of the residual limbs tissue tolerance, the total stiffness of the system will improve.

circumferences. If the connective bands are stretched to accommodate for bigger residual limbs, the elastic bands will exert higher forces, which can result in higher pressures. Ideally, the tensile force, or even better, the extra pressure resulting from the tensile forces, can be controlled. This implies that the elastic bands can at least be adjusted in length. One fundamental problem is that (elastic) bands will always try to find the lowest force route, which results in straight lines and can result in pressure peaks on the tissue between the hard parts (figure 10-5). Figure 10-5: Flexible bands that connect parts will result in pressure peaks.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

That last property of elastic bands is some-

Other options, that require the addition (or removal) of parts or the use of specific tools or machinery (“deform it”-option), are less useable for the Universal Prosthesis. The additional parts or tools have to be included into the distributed package or kit, thereby increasing its costs.

In cycle 1 of the marketing (see section 6.3),

multiple or easily interchangeable pylon ends, will make sure that the Universal Prosthesis can be used in conjuncture with existing feet. For cycle 2, a foot has to be part of the distribution kit.

The

suspension system (see section 4.3.4) is another integral part. Suction suspension is regarded as the most comfortable option nowadays. It does demand a highly accurate fit of the socket.

Knee straps or suspension sleeves are somewhat less comfortable during the donning and doffing of the prosthesis, but provide excellent suspension.

Recomm. Conclusion

circumstances and become deformable when altered. The most commonly used materials in which this principle is used, are plastics that can be heated, (de)formed and then cooled again (“freeze it” idea). A current application of these materials can be found in ski-shoes, violin supports. This are heated to approximately 60 degrees Celsius to fit the user’s body shape. This principle could be applied to the hard open socket parts, if more variance in these parts proves to increase the comfort level of the fit.

The completeness of the UP is in regard to its distribution options very important.

Evaluation

First of all, the parts can be hard in normal

17

Concept

There are a few options for hardening flexible parts. Two fundamental principles both can lead to a satisfying solution.

solution allows for a high freedom of shapes that can be given to the socket and is successfully used in the ICEX-system (compare subproblem 11 and 8). The big disadvantage of the ICEX system is that water has to be added as the reaction agent. This makes the fitting procedure a complicated and timecritical happening. Because the universal prosthesis eventually has to be fitted by inexperienced people, this solution is not optimal. Better are solutions that can use (UV)-light, heat or electricity as the reaction trigger or reaction agent. However, these agents bring along their own difficulties, sometimes in regard to the fitting procedure, sometimes in regard to the safety of the amputee.

Ideas

16

This

Synthesis

thing that “hardening” the connective flexible parts can prevent. Of course, the flexible part than no longer generates tensile forces, but the hardened part can transfer tensile (and compressive) forces. The pressure on the residual limb is now determined by the shape and circumference of the socket. For satisfactory results with the “harden”-option, the shape has to be determined very precisely.

Secondly,

for the flexible parts, “chemical reactions” can be used, that harden a mix of (carbon) fibres and resin, exactly in the same way currently PTB-sockets are produced.

Figure 10-6: Suspension sleeve

87

Problems

arise when the suspension is to loose and the residual limb starts pistoning in and out the prosthetic socket.

Supra-condylar

and supra-patellar sockets (section 4.3.4 – anatomical suspension) enclose the hard parts of the residual limb and the knee. This suspension “cups” are stiffly connected to the socket. In current condyle suspended sockets, such as the KMB, the suspension parts are integrated into the (high) socket.

88

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

10.3 Idea selection and Having

discussed all these possibilities, those who integrate well into a total design have to be selected.

To

achieve this pressure casting, the outer and inner layer of the socket with a material that will become hard after filling and apply pressure. The outer layer of the socket can also exist of a roll-on component. To avoid deformation on the outside, the outside layer needs to be either very stiff or restricted. For the Universal prosthesis, this restriction can be achieved by simply wrapping the outside with difficult to expand material or textile.

For the fitting procedure of the soft socket, this results in figure 10-8.

Evaluation

area of the residual limb should make contact with the socket, to prevent oedema (see section 3.1.3). This can most easily be achieved by rolling a highly flexible and stretchable textile or material on the residual limb, as is currently done with liners (subproblem 11). If we can harden this flexible material (subproblem 15,16) or fill the space behind it (subproblem 15), the total contact surface can become weight bearing and thereby increasing the comfort level of the socket. In this case, pressure has to be applied onto the material that will become rigid and the residual

Concept Recomm. Conclusion

has to exist of both hard and soft parts and that it will at least contain an open-frame socket that can provide weight bearing for the amputee. This open-frame socket can at least partly morph into a multi-pylon / exoskeletal pylon (as discussed in subproblem 13/14). The pylon can end in a multi-purpose connection component (subproblem 17). Alignment can be improved if this component can be rotated (subproblem 5). To attach the frame parts, (elastic) bands or belts can be used (subproblem 1, compare subproblem 15/16) but it has to be possible to adjust them precisely in length. More distal the length of these bands has to vary more, because of different residual limb shapes. Velcro can be used to attach these bands. Velcro is commonly used in orthopaedic appliances and a blood pressure meter (sphygmomanometer) illustrates that the connection can cope with medium-high pressures (200 mmHg = 26,6 kPa) of the connective area is big enough.

In contrast to the open-frame principle, every

Ideas

In section 6.2 it became clear that the socket

this results in figure 10-7.

limb, because else the socket becomes shape matched instead of the preferred volume matched (subproblem 6).

Synthesis

integration

For the fitting procedure of the hard frame,

Figure 10-7: Steps for fitting the hard frame

Figure 10-8: Steps for fitting the soft frame

89

The two fitting procedures have to be integrated into one, resulting in figure 10-9.

10.4 Evaluation of the integrated design and conclusion

If

we quickly evaluate the resulting procedure and design, we see that the total has high potential to achieve that:

-

-

-

The fitting procedure is a hands-off method which combines the best of the TCB and PTB principles. The fitting procedure is suitable for a wide range of residual limb shapes. The range is primarily dependent on the shape of the openframe parts. The resulting prosthesis is not too heavy, not bulky, comfortable and siff.

The distribution kit will contain at least 2 or

3 hard frame parts, several Velcro bands, a special fabrication liner, an connective component, a filler (material), a means to apply pressure to the inside of the socket while hardening, wraps. The only tool needed is a saw, which is widely distributed and accessible.

90

Figure 10-9: Steps for fitting the combined system

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Comparison

Discussion

If the currently presented fitting procedure

intermediate design can be scored against the commonly used PTB-procedure and the ICEX-system (table 10-1):

1 Universal

++

+

+

The UP combines the best of two worlds, because it’s a PTB-TCB-hybrid.

2 Comfortable

++

+

+

(needs clinical test)

3 Easily fitted

++

+

-

UP has many steps, but ICEX requires knowledge to apply pads, apply wrappings and steps are time-critical

4 Controllable

+

+

++

PTB can be adjusted better after the fitting procedure.

5 Usable

0

0

0

The PTB might not need a cosmethic cover, because it is an exoskeletal design.

6 Safe

+

+

++

There are no problems expected, but PTB is used for many years by now. PTB normally produced with toxic resins.

7 Affordable

0

0

0

Dependent on the costs of personel and the tools needed such as a compressor.

8 Cosmetic

0

+

+

(needs to be improved)

9 Quick fitted

+

+

-

PTB needs many steps.

10 Distribution

+

+

-

PTB needs specific tools

Table 10-1 Quick comparison between the Universal Prosthesis and two popular fitting systems.e

The

Universal prosthesis has some other advantages. It is fitted with the amputee standing and it uses the PTB-principle, thus using pressure tolerant area’s to a much better extend. These two features will very probably lead to a more comfortable fit (especially during stance). Clinical test will have to prove this in practise.

Conclusion

Main argument / comments

Recomm.

Standard PTB

Evaluation

ICEX

Concept

Universal Pros.

Ideas

Criterium

can be realised, the Universal Prosthesis is very comparable with the ICEX-system in performance. This is not so surprising because the ICEX-system is also a hands-off fitting method (and also needs a compressive device). However, the ICEX-system is not to suitable for inexperienced prosthetists, because pressure-pads have to be applied by the prosthetists on pressure sensitive area’s and the wrapping of the residual limb (and pads) is difficult.

Synthesis

This

91

11 Concept Having

determined the global design and fitting procedure, the final shape and the properties of each part have to be chosen. The final design evolves over multiple cycles, because each change in a part influences other parts. Hereafter the most important design considerations for each part are discussed, but not (necessarily) in chronological order..

The

hard open-frame socket parts (section 11.1) are the base of the design. They are the parts of which the most clear idea about how they should look exists, because they evolved out of the designs made in Sri Lanka and it became clear what improvements were needed in the analysis.

The

best argument against an open-frame socket design (that total contact is needed to prevent tissue damage and oedema), is solved by adding a soft socket (section 11.2).

The

pylon (section 11.3) is the connection between the socket and the foot (and indirectly to the ground). Especially the connective component at the distal end is important. It is needs to connect the hard socket to the foot while providing an air-tight seal for the soft socket.

92

Having redesigned the parts, the resulting

fitting procedure (section 11.4) needs to be optimized. Incorporating a low-expertise fitting procedure is the unique selling point of the universal prosthesis and therefore it has to be solid (no buyers means no product). The user-friendliness of the design is discussed in section 11.5 (no satisfied users means no buyers). The high-tech design that is the result has to be produced in such a way that, in time, the universal prosthesis becomes affordable for a broad group of users around the world (section 11.6).

11.1 The hard socket 11.1.1 Selection of loadable and avoidable area’s based on anatomy

The open-frame socket has to make contact

with the pressure-tolerant areas of a variation of residual limbs. The variance in circumferences and lengths of these residual limbs can be found in appendix G. As emphasized in section 3.1.3, these measurements where taken in Sri Lanka. Amputation procedures in developed countries are somewhat more standardized, resulting in a lower standard deviation. However, residual limb lengths in developed countries will vary from 100-180 mm, quite comparable with the data gathered in Sri Lanka. It is clear that the first 100 mm from (mid) patellar tendon are the most important for the open-frame socket. Luckily, the variance in circumference is also the smallest around that area. At 50 mm from mid patellar tendon the P5-95 spread is 230-340 mm). At 150 mm distance from mid patellar tendon, the circumference can vary from 170-320 mm. That apart from the fact that many amputees will have a shorter residual limb length (and no circumference at all).

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

In appendix R, this data is combined with the

On overlay 7, an estimation of the maximal

deformable to fit the varying residual limb shapes. More distally, the variance is bigger and therefore the parts have to be better deformable there. To maximize contact, multiple strips downwards are chosen where possible. Near the patellar tendon and on the opposite side (posterior), the variance in residual limb shapes can be compensated by translation of the frame.

This stiff frame can be translated because of

two vertical areas where no frame is present. This effectively splits the frame into two parts.

Conclusion

that the Free Body Diagram shown is not in equilibrium. The current forces will coerce the soft-tissue to deform and the residual limb to rotate and translate (if the socket is regarded as fixed in space). Also, resulting shear stresses are not taken in account. However, this behaviour cannot be predicted without more knowledge of the (properties and shape of the) frame parts. It is assumed that the user will compensate for pressure overload and that the maximum upwards force will not diminish significantly by the relocations.

The interface frame can be some what easier

Recomm.

Note

overlay 7, lead to the frame parts as shown in overlay 8, shown in blue. These parts will form the interface to the residual limb and still need to be connected by a stiff frame that is able to transfer the loads between the interface parts and to the ground (overlay 9, shown in red).

Evaluation

load that can be carried by the soft tissue is given. Every surface has a maximum pressure tolerance, an area (size) and an average angle in respect to the gravitation load line of the total body mass. From these, the maximal upward force is calculated.

The preferred area’s of load as presented in

Concept

lay 5, it becomes clear that there are quite some areas that overlap (mid patellar tendon taken as a fixed point). The pressure sensitive area’s are shown in red and don’t dominate. The big blue and green area is loadable. This results in overlay 6, where the loadable and avoidable areas are selected. The chosen areas are shown till approximately 130 mm from patellar tendon, after which they fade out, in conjuncture with the variable residual limb length.

selected the loadable areas, the interface frame that will transfer the load to the residual limb have to be materialized. The bigger these parts are, the better the pressure distribution will be. The smaller these parts are, the better they will be adaptable to accommodate for the wide range of stump sizes and shapes.

Ideas

Interpreting the data from appendix R, over-

Having

It is concluded that the interface surfaces of the frame will have to be maximized to ensure a comfortable fit during the fitting procedure.

Synthesis

anatomy of the residual limb (overlay 1 to 4). Overlay 5 shows the resulting spread in pressure sensitive and tolerant areas. The bony prominences are the most important factor in determining these areas. These were scaled in respect to the circumference variance (P5P50-P95). It has to be noted here that these areas are estimations, because in reality the anatomy of everybody differs. It would be far better if the data would be obtained from (scans of) a large amount of residual limb shapes and measured tissue properties. However, that information is not available in literature and time-consuming to generate. The estimation here is reasonable and makes use of the same assumptions as prosthetists do while fitting a prosthesis.

11.1.2 Determining the rough frame shape.

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Tensile

forces (that need to be transferred from the anterior from the anterior to the posterior to prevent the parts to part and the residual limb to slip downwards) are transferred by belts of connective textile, shown in green in layout 9.

Layout

10 summarizes the tough frame design. The belts can be fastened by a tightening mechanism or by Velcro. The space in between the frame parts is filled with carbon or glass fiber textile, which will help to strengthen the connection between the parts after hardening of the soft socket (see section 11.2). The stiff frame parts are lengthened so that they will function as a pylon. For small amputees, these frame parts can be shortened by sawing the distal end. A connective part (see section 11.3) is added to connect the foot.

11.1.3 Optimizing the frame shape in regards to the anatomy.

the border) will not result in tissue damage.

Having determined the rough shape of the

frame parts, these have to be (re)matched to the anatomy of the residual limb.

In overlay 11 this process is shown. In the

top row, slices from the “visible human project” are given at steps of 10mm, from the patellar tendon, to 130mm distal.

These slices give a good impression of the

bone structure of the residual limb. As a reminder:

- - -

Bony prominences (with only skin over them) cannot be loaded. Muscle with bone “behind” it can be loaded well, but perpendicular. Large areas of muscle can be loaded well, but deformation has to be restricted.

The general shape of the bones is shown in

black. Muscle that borders these lines can be loaded (perpendicular). The green lines indicate where the stiff frame can part. Variation in residual limb circumference can be compensated by moving the green lines together or away from each other.

94

Tensile parts (straight lines between them on In the second row, the cross-sections of the

rough frame design from layout 9 are shown. These are used as a guide to determine the optimised shape.

To

stabilize the forces resulting from pressure on the inside of the frame, the supportive areas and stiff frame parts need to be divided as good as possible over the circumference.

Having

tree strips downwards this means that midpoints of the strips have to be equal distance from each other (an isosceles triangle).

In

row 3 this has been pursued, without neglecting the tissue pressure tolerance. The V-shape of the anterior part is to protect the tibial crest. The patellar tendon indent can be easily recognised in blue (at PT-height).

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

To

They were connected and a little smoothened.

11.1.4 Back to 3D

The optimized cross-sections from Appendix

R, layout 11, were stacked together in 3D, resulting in figure 11-1.

This was necessary because the slices from the “visible human project (see layout 11) proved not to be well centred.

The

result is as seen in figure 11-2 and appendix R - layout 12,

Ideas

for aligning the cross-sections.

Concept

In row four, these strips are connected proxisupra condylar brims

In row five, the frame is optimised for the

Recomm.

some cross-section placements needed to be adjusted. The slices from the visible human project where not aligned before processing.

Conclusion

basic shape of the pylon.

Figure 11-1: 13 stacked layers that where derived from the anatomy of the residual limb. Top view and isometric view.

Evaluation

mally to bridge over and protect the pressure intolerant areas. Also, the stiffness of the stiff frame parts is added to maximise the contact area with the residual limb. Where necessary, direct contact with the hard borders of the stiff frame is countered by overlapping the soft frame with the interface frame.

variance in residual limb circumferences. The more flexible blue parts that are not supported or attached to the stiff frame are given a curvature that is equal to that of P5. These parts also bend in more distally, to extra support smaller residual limbs.

Synthesis

prevent the limb from slipping through the frame near the distal end, the anterior strip and the medial strip get closer together near the end. This is in line with the higher distal forces during gait in anterior-posterior direction to compensate the then acting moments and the higher force to compensate for the moment caused by the load on the patellar tendon (see section 11.1.5).

Figure 11-2: Together with the resulting frame parts. [Top] stiff frame, two views. [Below] interface frame.

95

Note that the tensile textile (see layout 10

and section 11.1.2) has been replaced by extensions of the frame parts. These extensions are thinner and more flexible as the rest of the stiff frame. They are connected to the opposing frame by Velcro. This improvement was made to ensure that:

- - -

the frame parts are on the proper height in respect to each other there will be some curvature of a straight line, improving comfort. assembly is quicker because there are less parts.

The most distal end of the stiff frame strips

has been punctured to enable the connection of the connective component on the desired height.

Several,

11.1.5 Material choice

To assess the mechanical properties of the frame, first the material has to be specified.

Material of the interface frame

For the interface frame (blue) a plastic will

be used. It should be possible to deform the interface frame to fit the varying residual limbs, but it should also be able to transfer some forces. Solution to this contradictory is found in deforming the plastic by heating it, and then fix it into the desired position while cooling down. This should be possible with normal heating equipment, so the softening temperature should not be higher than 150°C. But it also should not deform at a temperature lower than 50°C, as it might turn soft during use in the sun on a hot day.

commonly available plastics are suitable; PP, PVC, PS, ABS, PMMA, POM, PPO. PVC is toxic for the environment and will therefore not be used. POM and PPO have softening temperatures which are quite high, 155°C and 130°C respectively. It would be possible to use them, but there are other possibilities with lower softening temperatures (table 11-1).

ABS was chosen from those four, as it is said

to have good chemical and mechanical properties. Examples of applications are security helmets and profiles for skis and surfing boards.

Technical

drawings of the frames can be found in appendix Z.

PP

PS

ABS

PMMA

40-115

80

55-80

140

Modulus of elasticity (N/mm )

1250-2200

2600-3200

1800-2500

3250

Softening temperature (C)

90

100

90

115

Bending strength (Nmm ) 2

2

96

Table 11-1: Four material options for the interface frame.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Material of the stiff frame

Other options are:

ABS known and the frame design available as an 3D model, the behaviour of the parts under load can be simulated (finite elements methods).

Many

studies to socket fit and socket deformities were conducted in literature. These in-depth studies were demanding and the shear and stress forces in the total socket

Carbon fibre reinforced resins Aluminium Titanium Glare

Appendix S - FBD shows the main resultant

forces when standing with 50% of the body weight (100% of the load on the prosthesis) supported by the patellar tendon. It again illustrates (as in section 3.1.4) that the PTBbearing principle increases the loads on the anterior distal end and the posterior mid of the residual limb. For people with sensitive distal ends, this can be a problem. In that case, a TCB-approach is more suitable (see section 11.2).

The

3D-application of thise forces and the frame’s displacement behaviour can be found in appendix S - FEM.

Recomm.

- - - -

With the material properties of Hylite and

Evaluation

machined, hinges can be formed as is shown in figure 11-3. It can also be formed in the desired shape by deep drawing as shown in figure 11-4.

mechanical properties of the frame can be assessed in several ways. The best way is to build the frame and to experiment. However, production of several parts of the frame is expensive.

Concept

When the aluminium layers are grinded or

The

Ideas

material developed by Corus) will by used. This is a sandwich material, existing of two aluminium layers with a plastic layer (polypropylene) in between. It is a very lightweight and strong material. At a thickness of 1.2 mm it has the same flexural stiffness as steel at 0,74mm and aluminium at 1.06mm, while having a much lower mass.

or in the residual limb were assessed. In this stage of the development these specific FEMmodels are too time-consuming. Instead, a quick indication of the stresses during standing on the two force conducting frame parts (red frame) and on the connective components (strips & Velcro) between these frames is given. The applied loads were chosen as shown in appendix S - FBD.

Synthesis

For the stiff frame (red) Hylite, a composite

11.1.6 Mechanical properties

Conclusion

Figure 11-3: Applying hinges to Hylite (source: Corus)

Figure 11-4: Deep drawed car part from Hylite. (source: Corus)

97

What we can conclude is that with the current thickness (2 mm) and shape, (Hylite and) aluminium has such a stiffness, that major deformations can be expected. Solutions can be found in applying ribs, thickening the structure or increasing the area of the frame parts. Also, the residual limb will constrict the total amount of deformation. And, as can be seen in figure 11.2, the general shape that follows the anatomy of the user will not change much, thus staying comfortable while deforming.

The socket/pylon in this shape is not suitable

for prolonged ambulation. Because of its freedom to move, it will become subject to fatigue and break. However, the addition of the soft socket will improve this.

11.2 The soft socket

The soft socket exists of a flexible closed tube

or “fitting liner”, that will become the inner and outer layers of the prosthesis, and the filler that will harden in between these layers (also see 10.3).

11.2.1 Fitting liner

The fitting liner is rolled on to the residual

limb and, after placing the frame parts, rolled down over them again. It will function as the inner and outer layer of the prosthesis. These fitting liner will envelop empty space and the frame parts. The resulting inner space or chamber will be filled with a filler or foam.

The material choice of the fitting liner deter-

98

mines most of its properties. In its relaxed form it has the smallest circumference. Because it has to fit around the connector and the frame this minimal circumference is about 200 mm. While rolled on to the knee or even higher, it has to be stretched to at least the p95 maximal circumference (at 25 mm proximal from patellar tendon), which is about 370 mm (see appendix F) and, when taking a maximal thickness of 10 mm of the socket in account is about 430 mm.

Because the fitting liner will be the outside

of the prosthesis, it also makes contact with the skin and the environment. Resulting in the following requirements:

- - - -

The material has to be able to lengthen more than 215% in transverse direction. The material has to be non toxic / non-irritating. The material has to be smooth and repel dirt. The material has to resist impact.

One

possible material is a combination between PP and PU. PU (on the inside) will stretch easily (up to 500%) and will integrate with the PU-foam (see later this section). PP (on the outside) will be smooth and non-irritating. If necessary, for example when the amputee has work that is very demanding on the prosthesis, the outer layer can be coated (with for example epoxy resin) to increase impact resistance.

The fitting liner can be tube-shaped, but has

to have a padded distal end to overcome high distal-end pressures. This is common for most liners.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

11.2.2 The Filler Material

Filling

Foams have some special properties that are useful in prosthetics:

It has a very good mass-volume ratio It can take make shapes It is available with a great variation of properties, including mass, rigidity /stiffness, yield strength, etc.

is one material that is easy to foam and is available for a broad range of applications. Polyurethanes and derived plastics are used in PUR-foam, but also in dashboards of cars, for cushions in seats and chairs, for shoes (soles) and in other flexible, semi-rigid and rigid applications.

The

application examples, especially the use in shoes, show that PU can meet these requirements. Its use in aerosol sprays, such as PUR, makes it plausible that it also can be distributed in a spray. It can use water (a component of air) as the reagent (in a spray the reacting chemical components of polyurethane are prepared in a special way) and use the air in the chamber in the prosthesis as the filling gas. It is no problem when the reaction increases the inner pressure, because this is an effect that is wanted for weight-bearing anyways.

Conclusion

Polyurethane

- -

Recomm.

- - -

-

It connects to the frame parts and the outer layer of the prosthesis It does not grind to powder (wears) under dynamic load It divides itself well within the prosthesis. It reacts slow enough, so that the pressure can be homogenous increased. But within 10 minutes, so that the fitting procedure stays comfortable

Evaluation

prosthesis is that it will contribute in weight bearing. The prosthesis will effectively become a total contact bearing socket (TCB). Without pressurizing the foam (0-5 kPa), this would already prevent oedema. However, with higher pressures ranging from 30-40 kPa (50% TCB-behaviour) to 60-80 kPa (100% TCB-behaviour, comparable pressures as used in the hydro-cast and ICEX methods), the socket will contribute more and more to the weight-bearing properties of the total.

Polyurethane

-

Concept

A completely other advantage of filling the

prosthesis can also be filled with resins. When combined with fibres, the result can be very stiff and strong. In the case that resins are used, a suction method as is commonly used while fabricating prostheses (resins applied from above, air sucked out below, so that the resin will divide through the space) is preferred. In that case, the inner space of the prosthesis is minimized and the increase in weight will be minimal.

prosthesis if a mix can be found that meets the following requirements.

Ideas

the space inside the prosthesis will contribute to the stiffness of the whole. However, to contribute significantly, the foam has to have stiffness in the same order as that of the load bearing frame. Foam that will have this type of stiffness is often very brittle and in that case, the inside would deteriorate with use. Filling the inside with foam can best contribute to compressive forces (in between the frame parts). However, weight-bearing will result in the frames wanting to part and thus in tensile forces.

The space within between the layers of the

Polyurethane can be used in the universal Synthesis

Effects of filling

Resins

99

To optimize the properties of the universal

prosthesis, the choice of foam is very important. Because the application is very specific, it is probably a better option to develop a “new” foam in corporation with a producer of PU.

Fibre reinforcements

In this example, the (massive) PU layer can

be stretched up to 500% of its original length, where no fibres are integrated and can not be stretched where the fibres are integrated. The two layers can slide along each other. The foam will “glue” then together and a much stiffer connection is obtained than when the foam or PU directly connects the frames.

Even

when instead of resin PU (foam) is used, glass or carbon fibres can enhance the stiffness of the prosthesis. Note that the bottleneck is the connection between the fibres. However when the connective material (foam) would strain 25% when a certain force is applied, the distance between the two attachments of the material to the stiffer components becomes critical in the stiffness of the whole, as explained in figure 11-5.

This principle can be used by applying thin

extensions of carbon or glass fibres to the weight bearing frame parts as shown in figure 11-6.

100

Figure 11-5: Less space in between the frames is better; it results in a stiffer prosthesis.

Figure 11-6: A Polyurethane layer is partly reinforced with fibres. The Hylite is milled to better attach the reinforced PU. The two Polyurethane layers can slide along each other

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

11.2.3 Adding pressure sure has to be added before it has taken its final form. This can be achieved in several ways:

-

connector has several important functions in the design. It has to:

- - - - -

connect the weight-bearing frame parts. connect the frame to the foot. be adjustable in height. be airtight. be stiff.

Connection to the frame

Because the frame parts will be completely

The use of screws is chosen for safety rea-

Conclusion

Figure 11-8: Two ways to connect the frame parts. Because all mayor forces between the frame and the connector work in vertical direction, fitting of the frame on just shape is sufficient (left). However, to be sure the frame parts connect well, also during ambulation, and the connection is airtight, screws can be added (right). Both solutions are cheap, intuitive understandable and position the posterior and anterior frame parts on the right height from each other.

sons. A disadvantage of this system is that it results in that the prosthesis can only be lengthened or shortened in steps. This can be solved by adding an extra lengthening component between the foot and the frame.

Recomm.

surrounded by (foam) and the outer layers they can contain holes. There are two basic options to connect the frame parts to the connector. One is with screws and the other is without.

Evaluation

Figure 11-7: The airman Panter is an example of a hand-pump.

The

Concept

-

11.3 The connector

Ideas

- -

Using the pressure from the aerosol spray, at the same time injecting the foam. Current sprays have a nozzle that will vaporize the contained liquid. In this application, the nozzle is not necessary and the needed pressure can be directly added to the prosthesis. A mini hand pump or compressor A separate CO2, N or air spray or gas patron. The volume that needs to be filled when a residual limb of length 100 mm and a maximal socket height (430) is fitted is estimated to 1.5 litres. To apply a pressure of 0.8 bar (80 kPA) to such a volume, the following gas patrons can be used: 0.97 litres at 2 bar, 0.36 litres at 4 bar or 0.16 litres at 8 bar. A compressor.

situations where only a few prostheses are fitted. The spray is easily distributed and relatively cheap. In situations where more prostheses are fitted, such as an orthopaedic workshop, a compressor can be cheaper and more environment friendly.

Synthesis

When the chamber is filled with foam, pres-

Using the spray is the preferred solution in

101

Connection to the foot

The connection to the foot is a standard pyramid alignment core (see Appendix M) that is commonly used. When screwed in tight, it can be removed with a tool and replaced with another alignment core when necessary. To resist the torque that acts upon it as a result from turning (the foot), it is better when it is attached permanently (figure 11-10). In the latter case, transition extensions to other systems can be made available, possibly integrated with the extension as shown in figure 11-9.

Airtight

The connector has to seal the inner chamber of the prosthesis, while allowing the frame to protrude.

Figure 11-10: The connection to the foot is achieved by either screwing a standard pyramid alignment core into it (changeable) or by integrating the alignment core in the piece (improved strength). The dome increases the range in which the foot can be aligned.

102

Figure 11-9: An extra component that can finetune the length enhances the adjustability of the prosthesis.

Figure 11-11: (Up and Left) The airlock is achieved by an outer and an inner seal. NOTE: The dome on the connector is drawn on the wrong side!

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

The airlock can be made from two seals. The

Fill channel and valve

Recomm. Conclusion

Figure 11-12: The fill channel and the valve in the connector. To transfer the filler up to the proximal side of the prosthesis, flexible tubes (straws) and splitters can be used. The entrance of the channel has to be distally or on the bottom of the connector, because else the air seals would be in the way.

a distal alignment core, but also a proximal alignment core is added. The universal prosthesis only uses one alignment core (distally). One would expect that this results in reduced possibilities for alignment. However, traditional endoskeletal systems did not incorporate a proximal alignment core. The placement of the connection to the pylon was determined during the fitting procedure. In practise, this went wrong so often that an extra alignment core was added to the system. In the universal prosthesis, the socket and pylon are integrated and the alignment between them cannot go wrong! The distal alignment core provides sufficient adjustability.

Evaluation

In current endo-skeletal prostheses, not only

Concept

Note on alignment

Ideas

layer is interrupted, it is also the perfect spot from where to inject the foam and apply the pressure. To achieve this, a channel that connects the outside with the inside is drilled in the corner of the component (figure 11-12). For safety, a Minivalve is added. These valves are mass-produced and very cheap (figure 1113).

Synthesis

Because it is the only place where the outer

first seal is made from a compressible rubber or plastic, and will be placed on top of the connector and between the connector and the frame parts. The second seal is placed over on the outside of the connector and the frame parts. This part is made from an elastic and compressive material. Its elasticity is used to generate the force that is needed to keep the whole airtight, even when applying the maximum pressure (80 kPA) and the compressibility to fill height differences and filleted corners.

103

The

placement of the residual limb in the socket will determine the right alignment. This placement will only be problematic in (the few) cases where contractures are a problem. In those cases, the pylon can be shortened (at 260 mm from patellar tendon) and a normal pylon can be attached with standard screw connections as seen in appendix M).

11.4 Resulting fitting procedure

The fitting procedure doesn’t change fundamentally (see section 10.3). With optimized components it adds up to the figure in appendix U and the following steps:

SITTING

1) The foot is connected to the connector. 2) The user rolls the fitting liner that will become the outer layer of the prosthesis, onto his residual limb and up to his thigh or knee. 3) The needed length of the prosthesis is measured with the frame parts and the connector. The height of the total has to end on top knee height. 4) The frame parts are attached to the connector. The connector is already distributed with the inner air seal and straws attached (see section 11.3), so the connection is immediately airtight. The needed screws are included in the distribution kit (TOOLS NEEDED: SCREWDRIVER). 5) The frame parts are placed on the residual limb.

STANDING 104 Figure 11-13: An example of a Minivalve (source: www.minivalve.com)

6) The frame parts are connected to each other and the user can stand in the prosthesis. The Velcro can be detached and reattached until the user can stand in the prosthesis (50% of

his body-weight on each leg) without sliding down, while experiencing the most satisfactory fit. If the prosthesis seems too long or too short, the connector can be re-adjusted. If specific areas are painful, gel pads can be added or the interface frame parts can be adjusted by heating and deforming. 7) It is made sure that the supracondylar brims press against the knee (see section 11.5). 8) The prosthesis is taken off the residual limb (doffed) and the distally extending frame parts are sawn from the prosthesis. (TOOLS NEEDED: SAW) 9) The straws inside the prosthesis are cut on to the right length (10-20 mm from the upper border of the frame parts). 10) The prosthesis is donned again and the fitting liner is rolled down, over the frame parts. 11) The outer seal is pulled over the connector and the fitting liner. The extending liner parts are cut off (TOOLS NEEDED: KNIFE OR SCISSORS). 12) The prosthesis and the knee are wrapped (tight) with wrapping bandage. 13) The foam spray is attached to the connector. 14) The foam is injected. 15) The pressure is increased till a comfortable level is found or the maximal pressure of 6080 kPa is reached. 16) Waiting 10 minutes. 17) The wraps can now be taken away.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

18) The user can now walk around. The alignment of the foot can be adjusted when necessary.

3) Supracondylar cuff suspension or suspension sleeve. A cuff or belt is attached to the finished prosthesis. A suspension sleeve can also be attached.

11.5 Daily usage & Suspension

The

Suspension and donning/doffing

Suction

suspension might be integrated in the system in the future.

Cleaning & Cosmetics

Whether or not the prosthesis is cleanable

Figure 11-14: Height of supracondylar suspension.

Conclusion

is mostly dependent on the outer layer (see section 11.2). An extra outer layer could be applied that makes cleaning easier. This extra layer could also function as a cosmetic transition from the pylon to the foot (add an ankle shape) and make the pylon more oval shaped.

Recomm.

1) Standard supracondylar brim suspension. The integrated brims on the interface socket make contact with the knee at the broadest part of the fibular head (see figure 11-14). The variance in this distance from patellar tendon is expected to be small, so the brims can be fabricated on a predetermined length. 2) Shuttle lock suspension. In this suspension type, a shuttle lock is added to the standard fitting liner and an extra liner is rolled on before the fitting procedure with a pin or plunger threaded into the distal end of the liner (compare figure 4-32). The shuttle has to be unlocked before doffing, so a button needs to be brought to the outside of the socket. One possible solution is shown in figure 11-15 (next page).

Evaluation

Suspension can be achieved in three ways:

1) In the standard (supracondylar) solution, the residual limb slides, while pushing the brims slightly apart, into the prosthesis. When the user has to little force to do so (for example elder), or when the condyles are too sensitive, a hole can be made in the prosthetic socket after the fitting procedure. Through this hole, a sock can be pulled, which assists in the donning of the prosthesis. The hole has to be finished to protect the (rigid) foam that will otherwise wear too fast.

Concept

same way as currently available prostheses (see section 4.3.4). Most important aspects of use are donning/doffing, suspension and cleaning.

Ideas

The universal will basically be used in the

suspension types result in a different donning/doffing approach

2) The second, more expensive solution, provides an easier to use and in cases where pistoning is a problem, more comfortable suspension. This option can be used for people who are sensitive, have less force, have problems with pistoning or whose anatomy doesn’t allow for supracondylar suspension with the integrated brims. Before the donning of the prosthesis, the user has to roll on the liner with the pin threaded in. The pin has to be positioned well, because it has to lock in the shuttle. 3) If the integrated brim solution fails, and finances are limited, a very functional and quite comfortable (except in some case where knee flexion (sitting) results in high forces in the popliteal space [Seymour 2002]) solution is the knee cuff.

Synthesis

WALKING

105

11.6 Production and price

11.6.1 Production costs per part

Warning: Keep in mind that the estimations

Interface frame

in this section are quite rough.

The production price and production method

is dependent on the amount of produced parts (production volume). Estimations are made for 1000 and for 10.000 pieces. For this relatively low amount of pieces produced (per year) the production can be out-sourced. The estimated prices can be found in appendix V.

The interface frame exists of two parts, each

in a left and right version. The frame parts can be made by cutting and deep drawing. When higher quantities are produced, the frame parts can be injection moulded.

Weight-bearing frame

The

Hylite, used for both the higher and lower production volume, is relatively expensive, but easily processed.

Fabrication liner

The basic version of the production liner for

the universal prosthesis (without pin/shuttle suspension) uses a simple tube on which a distal end pad is welded together by sonar heating. The distal end pad is made of silicones.

Connector

For

the lower quantities, the connector is milled and drilled. For the higher quantities a redesign might lead to a decent solution that can be injection moulded (in high quality plastic, ceramic or aluminium). The inner air seal has to be produced, other parts are bought in.

Distribution Kit

In the kit, that protects the parts, extra components can be found, such as manuals, gel pads and a sock (also see section 10.4).

106

Figure 11-15: The shuttle for the pin/shuttle suspension can perforate the outer layer. The rings will restore the system to an airtight state. The shuttle can be attached on most heights (with varying circumference). During the fitting procedure the pin is locked in the shuttle.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

This results in a production cost price of 110 11.6.2 Development costs

-

-

- -

The R&D prices can be lowered significantly

by intensive collaboration with big orthopaedic producers (who have a lot of knowledge in-house and who can divide the R&D-costs over multiple products), and by attracting grants and subsidies.

Marketing

The marketing, especially for the first cycle,

has to be pro-active and direct. The buyers of the universal prosthesis are well known (prosthetists, orthopaedic workshops, hospitals, etc), so the campaign can be reasonably focussed. On the other hand, the endusers or amputees need to be informed as well, because they might opt for the universal prosthesis while choosing the prosthesis that will be fitted. Also, they have to know the universal prosthesis is available for them in the case they need a spare one.

Conclusion

- -

results in a R&D and production cost price of 370 and 70 Euros respectively.

will make the universal prosthesis a well known alternative for the prosthetist. Sales and services are needed to distribute the product.

Recomm.

-

This

Marketing

Evaluation

-

(1) researching the pressure tolerance of the residual limb. (2) collecting data about residual limb variances, including bone-shape and soft tissue properties. (2) development and selection of the right materials. (2) optimizing the design of the components and parts. (4) clinical trials. (2) re-evaluate and improve business-setup and distribution strategy. (1) project management. (3) project office support.

costs

Concept

universal prosthesis will be primarily made of developing costs. The way to a market-ready product is long. Among others, to make the prosthesis ready for the first market (cycle 1 section 6.3), time (FTE’s in brackets) should be invested in (also see chapter 13):

11.6.3 Marketing and Distribution

Ideas

It is clear that the costs of developing the

would imply that a team consisting of about 17 full-time workers could launch the universal prosthesis in one year. With a FTE price (including accommodation, etc) of 47,000 Euro a year, the first cycle costs would add up to 800,000 Euro. If 1000 universal prostheses are sold for a period of 5 years, this would be a 160 Euro increase of the cost price of the product. For the next cycle (world market), another development round of the same magnitude (800,000 Euro)is expected to be needed, resulting in an increase of 14.5 Euro a piece (over 11,000 sold prostheses a year).

Synthesis

(at 1000 pieces a year) to respectively 55 (at 10,000 pieces a year.

This

107

For the second cycle, the initial buyers are

even better known (local workshops and hospitals) and distribution or collaboration with expert NGO’s, such as the World Health Organization and the Cambodia Trust Foundation has to be sought. A budget for both marketing campaigns has to be reserved: Cycle 1: 100,000 Euro, resulting in an increase of 100 Euro and a total price of 470 Euro. Cycle 2: 100,000 Euro, resulting in an increase of 9 Euro and a total price of 79 Euro.

Sales and Service

The service has to be good, because this is an

important source for feedback. Feedback will reduce design cycles and R&D-costs. Also, it is the most important factor for a good customer base. Cycle 1: 4 FTE at 50,000 Euro a year, resulting in an increase of 50 Euro and a total price of 520 Euro. Cycle 2: 6x4 FTE at a mean of 25,000 Euro a year, resulting in an increase of 55 Euro and a total price of 134 Euro.

108

11.6.4 Conclusion

Keeping in mind that the estimations in this

section are quite rough, the expected costs stay well within the requirements. For both the prices (European/US and World market) the R&D-costs are significant, but there are possibilities to lower them by attracting grants and by choosing the right businesspartners. Delivering a quality product will result in lower costs on the long term, so cutting down on the input in research is not an option.

For

the world market product, collaboration with NGO’s such as the Red Cross, WHO, Cambodia Trust Foundation, etc can further lower the price. Costs of this product are made up from service and sales for 40% and from marketing costs for 7%. Collaboration with well organized NGO’s can reduce both costs significantly and the costs price of the Universal Prosthesis could fall under 100 USD.

The Universal Prosthesis

12 Evaluation The concept as presented in chapter 11 can be evaluated in several ways:

section 10.4, Table 10-1, a rough comparison between the Universal Prosthesis, the Ossur ICEX-system and a standard PTBsystem was given.

However, the ICEX-system can be used with

direct fabrication on the residual limb (the IDC-Icelandic Direct Casting system) and without direct fabrication (with plaster of Paris as shown in appendix N).

Both systems use the Ice-cast Compact pressurizing device as shown in figure 4-7 and appendix N.

Also, the PTB is produced in two ways. The

of which some are further specified:

1) Universal 2 ) Comfort A)Socket fit B) Prosthesis weight C) Materials used and their effects (such as perspiration). 3) Easy fit A) Easy fit Amount of steps needed to fit and produce a socket/prosthesis B) Specific knowledge needed 4) Control 5 Usable A) Donning/doffing and suspension B) Cleaning

Conclusion

first is the vacuum technique with fibre reinforced resins and the second is a polypropylene vacuum-forming technique. The latter fabrication method is used often in developing countries, as a part of the ICRC (red-cross) design, by the aluminium/wood hand produced Jaipur-system is very commonly used as well (see Wisse et al. 2002,2003 for more information about these production methods). Water-cast/sand-cast prostheses are an important development, not to be neglected. This adds up to the following production

This six can be weighted against the criteria,

Recomm.

section 12.3 a model is presented that was build. This model can be used for assessing the shape of the frame parts (evaluation method 5), but it is not able to provide weightbaring (evaluation method 6). In section 12.4, a conclusion is given in which remarks of experts are integrated (evaluation method 4).

In

Evaluation

In

prosthetic systems.

1) PTB-resins (standard PTB) 2) PTB-ICRC 3) PTB-Jaipur 4) The Universal Below-knee Prosthesis 5) ICEX-IDC 6) ICEX-resins 7) Hydro-cast/sand-cast

Concept

are taken together and a discussion with the requirements as a guide (method 2) is added in 12.2.

comparison with other

methods and designs to be compared:

Ideas

In section 12.1 evaluation method 1 and 3

12.1 Scoring criteria in

Synthesis

1) Review it against the criteria (section 7.1). 2) Review it against the requirements and the additional goals (section 7.2-7.5). 3) Review it in comparison with other prosthetic systems for transtibial amputees. 4) Have it reviewed by professionals (experienced prosthetists). 5) Build a model and evaluate the design by inspections 6) Build a working model (prototype) and try that out in practise.

Boudewijn Martin Wisse TU Delft, 2005

109

6 Safe A) Design toughness B) Toxicity of the fitting materials and the interface for user and environment 7 Affordable A) Material/component price B) Service 8) Cosmetics 9) Quick fit 10) Distribution

1)

The

Universal

Universal prosthesis offers a TCB-PTYhybrid for amputees with a healthy residual limb, within a specified range of residual limb lengths, sizes and shapes. From data (appendix G) this range is expected to be P10-P90. For most of the amputees in this range it will provide a comfortable fit, however problems can be expected with amputees that:

used PTB-resin system taken as a 100% reference-index. The resulting table can be found in appendix Y, and a discussion per criterion below.

- Have contractures (reduced knee movement) because of the reduced alignment possibilities of the prosthesis - Have a bulbous residual limb shape. - Have a deviating bone structure (for example as a result of bone fractures). - Have too little weight-bearing tolerance on the interface with the frame (but just enough to allow total contact weight bearing).

Note that the final verdict about for example

For

These are all compared with the commonly

affordability will be dependent on multiple points in the table (7,9 and 10) and the situation that is reviewed (the market cycles as mentioned in section 6.3).

the latter, a prosthesis could be fitted without the user initially standing (with half of his body weight supported) in it fully. All these exceptions don’t add up to a group of more than 10% of all transtibial amputees, resulting in that the Universal Prosthesis is expected to be suitable for about 70-80% of all transtibial amputees that will ever find a comfortable socket.

Of course, this needs to be validated in practise (see chapter 13).

110

The PTB-socket is, because all features are

hand made from direct measurements, suitable for all residual limb shapes, lengths and seizes, al long as they result in enough weightbearing area’s (residual limb length is more than 80 mm). In practise, not all amputees fint the PTB-socket comfortable (because of pressure concentrations and fabrication mistakes made by prosthetists). Probably around 90% of the fitted prosthesis will be experienced as comfortable.

The same reasoning goes for the TCB-socket,

only with less influence of prosthetist-mistakes and a suitability of around 95% can be assumed. The IDC-fabricated TCB-socket can not be fitted to bulbous residual limbs and will be confronted with roughly the same problematic residual limbs as the Universal Prosthesis.

The PTB-Jaipur system is made from drawing

and measurements and doesn’t have a distal end pad. This results in higher pressures and will the system is comfortable for a smaller group than standard (70-80%).

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

2 A) Socket fit

The mass of the Universal Prosthesis frame

is nearly nothing (<200 grams), but the socket will be filled with foam, increasing the weight. The foam itself is expected to weight up to 1 kg, but more heavy are the fibre-reinforcements as proposed in section 11.2. Still, the total prosthesis (without foot) is expected to stay under 2 kg.

In

optimized by either taking by either taking redundant material away or examining the possibility to use other materials, resulting in about the same weight for all connectors used in the compared prostheses.

Conclusion

The Universal Prosthesis’s connector can be

sockets envelop the complete residual limb. Also in all cases, the prosthesis will be worn with socks or liners. The Universal Prosthesis might feel more hot, because of the isolating property of foam, however, after a few days of wearing a prosthesis (even in tropical countries) problems with perspiration usually disappear. The Jaipur might feel more foreign, because of the cold metal feel of the aluminium used.

Recomm.

the endoskeletal prostheses, where the pylon is separate from the socket, the pylon can be either heavy or expensive. This is important because weight more distally is experienced more cumbersome (and will take more energy during ambulation) that weight more proximal. The Jaipur and the Universal Prosthesis are the only exoskeletal systems in this comparison.

All

Evaluation

nation of both, resulting in 85-90% comfort. However, because of less optimal use of pressure tolerant area’s and possibly a pressure differences during the TCB-fitting (pressurizing the inner chamber of the prosthesis) as a result of the frames being in the wat, this percentage will drop to about 75-80%. Other systems compare, except the Jaipur which performs a little worse due to the lack of the distal end pad and due to the fabrication method. Again, 100% is taken as all amputees that can find a comfortable design.

2 C) Materials used and perspiration

Concept

The Universal Prosthesis will have a combi-

weight of the socket is highly dependent on the material used. This results in the following order from light to heavy: carbonresins, glass-resins, either the Universal Prosthesis or the PP-ICRC-sockets and the most heavy being the Jaipur-socket.

The

the weight-scores (compensated for the distal-weight) will all be close together.

Ideas

rience and therefore can not really be predicted. Also, it has to be mentioned here that most literature (studies) in which prosthetics are functionally compared are with only a few subjects (n < 15) so significant data is limited. However, standard PTB-sockets are found to be satisfying in most cases (lets say 80%) and TCB-sockets even perform a bit better (85%).

Conclusively,

Synthesis

Socket comfort depends on the users expe-

2 B) Weight

111

3 A) Amounts

of steps needed to fit

and produce the prosthesis

The

Universal Prosthesis ant the ICEX-IDC are two systems in which the measurement/ fitting and the fabrication method are integrated. Comparing appendix N and other sources on www.ossur.com with section 11.4, they both need about the same amount of steps to fabricate the sockets.

PTB-sockets

have a separated fitting and fabrication method, which does increase the amount of steps needed. Because adjustments are might manually, the socket often has to be adjusted after fabrication. Even more so for the Jaipur socket, which is hand-made and adjusted many times, until a decent fit has been achieved.

112

3 B) Specific knowledge needed

4) Stiffness

tems to be fitted.

to be almost equally stiff, because the socket designs are optimized that way. The resins will be slightly stiffer that the ICRC and the Jaupir, but not very significantly. The stiffness of the Universal Prosthesis is for the biggest part dependent of the function of the foam. The foam has not been developed yet, so the stiffness cannot be assessed. However, with the suggestion from section 11.3, a sufficient stiffness seems to be feasible. The Universal Prosthesis can always be made stiffer, by coating it with fibre reinforced resins, but at the cost of weight and size. Also, more straps can be added. Note that the strap at 100 mm below patellar tendon as shown in appendix R-12, cannot be found in the final design. It is expected to be unnecessary, until proven otherwise.

Specific knowledge is needed for all the sys-

For

the Universal Prosthesis, this is basic knowledge, such as the preferred 5 degree flexion of the knee and the right foot positions, can be communicated easily with manuals with figures or with easy-to-use measurement tools, such as the proposed fitting-foot-board (see chapter 10). All other systems require advanced knowledge of biomechanics and the residual limb anatomy. Even the pressure-cast/TCB-systems are produced after the prosthetist has applied pressure pads on the specific area’s of the residual limb that need to be shielded from the pressure. Additionally, the Universal Prosthesis and the IDC prosthesis do not require knowledge about the fabrication technique used, in contrast with the other systems.

All current socket systems can be assumed

By

mechanical principle, the exoskeletal designs are more stiff than the endoskeletal designs. The Jaipur and the Universal Prosthesis score well here, but overall stiffness (control) is not expected to improve significantly by this.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

5 A) Donning, doffing and suspension

All

When the prostheses fail, their failure will

probably be tearing of the material (especially so with the exoskeletal systems), so that the user will have time to notice and does not fall.

the

fitting

materials and the interface for user and environment

Toxicity

of the materials used is an important factor during use and during the fitting method, both in respect to the user/ prosthetist as to the environment.

The used materials in all prosthetic components are generally non-toxic to humans.

However, glass-fibres, epoxy and especially polyester resins are difficult and dangerous to work with.

The

heating and forming of the PP is not dangerous, when performed well.

Most methods (PTB,ICEX-resin, ICRC, hydro-

non-toxic. In addition, the prosthetist and the user cannot come into contact with it.

Conclusion

The Universal Prosthesis uses foam which is

Recomm.

cast) use plaster of Paris to cast and fabricate positive and negative moulds of the residual limb to form the socket around. The impact of plaster of Paris on the environment is low.

Evaluation

modular/endoskeletar systems can be more difficult to clean, because of the attachment points. However, most systems are finished with a cosmetic cover, eliminating problems. The Universal Prosthesis does not really provide a good protection for the transition between the connector and the foot. Something that might prove easy to solve, either by adding a cosmetic cover for the complete prosthesis or the ankle piece only. The Jaipur-system consists of many material (finished with leather and paint) and is most difficult to clean.

can easily be bended in transverse directions. However, Appendix S shows that they will not buckle. Performance will improve after the fitting procedure, because of the filling of the soft socket. Long term outcome (more than 2 years under dynamic loading) has to be assessed experimentally. All prostheses can be assumed to be safe. Some problems with ICRC prostheses have been observed when they where produced with recycled PP.

of

Concept

5 B) Cleaning

The frame parts of the Universal Prosthesis

Toxicity

Ideas

donning/doffing-ease is dependent of the suspension type. In the comparison table, all possible suspension types of each system is shown. Except for the designs made for developing countries (ICRC, Jaipur), each can be fitted with all popular suspension systems. Beside this, no real differences for donning and doffing can be identified.

6 B)

Synthesis

The

6 A) Toughness

113

The

7B) Service

When discarded

the ICRC (from the International Committee of the Red Cross, factories in Switzerland and Ethiopia) the presented systems are widely available from a broad range of suppliers.

asically, all systems can be fitted with a (foam) aesthetic cover. Only the Jaipur system, though looks are acceptable because of the paint and because it is the only affordable system with a life-like foot under it, scores worst. It has a make-shift look.

This

The Universal Prosthesis is thicker than the

Universal Prosthesis doesn’t produce much residual material and powder, except for the aerosol spray with probably some spare foam left in it.

(end-of-life of the prosthesis), the Universal Prosthesis is difficult to recycle. After fitting, the socket has become a mix of glass fibre, foam PP, aluminium, ABS and PU. Also the resins-based prostheses cannot be recycled. The Jaipur, made of basic material can be recycled best. The PP used in the ICRC-design can be recycled as well.

7 A) Material costs

Material

prices are taken from 11.6, 3.3.1 and Wisse et al, 2004. They are summarized in the comparison table. For the comparison, the high (first-cycle) Universal Prosthesis price is taken, in which a budget for research is taken in account.

Except for the ICEX (system from Össur) and

implies that the prosthetist should deliver service and guarantees about the fit and comfort level. Knowledge about and experience with the fitting procedure is spread and varies in quality, but the amount of prosthetists that are known with the systems is huge.

The

Universal Prosthesis and the ICEX-systems both have a centralized selling strategy, better enabling feedback and future developments. Service in respect to material quality (for example wear resistance) can be considered equal for all components, except for the Jaipur system, which is 100% dependent on the local workshop.

8) Cosmetics

Cosmetics

is most important during daily use (how does the finished product look), but also before and during the fitting procedure (trust of the user and the prosthetist in the system might depend on it). 114

B

average prosthesis, which might show, even when the prosthesis is worn under a pair of trousers. The frame does show that it has been thought about, tough that won’t be visible anymore after fabrication.

9) Quick fit

The

time-consumption of the prosthetist and technicians is related to the amount of steps taken to produce the socket (see point 3). Times of standard PTB and ICEX-IDC are known from literature (see section 3.3). Estimations for other systems can be found in the comparison table. It has to be emphasized that all technicians and prosthetists have to be educated, except in case the Universal Prosthesis is used. This is also true for the Jaipur-socket. Its fit is highly dependent on the skill of the technician.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

10) Distribution dependent of:

the tools needed the compatibility with currently used systems services (see point 7B) life-time/visits needed per year and of course the dependency of the system on the infrastructure (such as water, electricity, etc) and on the availability of prosthetists.

specified in the table.

1 to 5 years (dependent on the activity of the user, with a mean of 2.5 years), which is comparable to the use of a pair of shoes.

All

systems are well compatible with commonly used connection systems (such as the pyramid connection core) except the ICEXIDC (standard distributed with Össur components) and the Jaipur (though the used woodblock can be adapted at will by the technician).

The

prosthesis can be donned seated, certainly when only reviewing the hard frame. It can be that the soft frame will be too long at the posterior side, because the fabrication liner can stay in between the brims (figure 121). In that case, some of the fitted and hardened prosthesis might need to be removed. Or an extra brim has to be developed that keeps the foam below while hardening and pressurizing.

Figure 12-1: A high posterior socket as a result of the fitting of the soft socket. The brims will keep the fitting liner high (dotted lines).

Conclusion

current design for the Universal Prosthesis might have a shorter life-time, but a decent optimization and the right choice of foam will result in a lifetime in the same order.

The Posterior side of the soft-socket:

Recomm.

The

Evaluation

The life-time of all systems can be taken as

requirements and design goals as presented in chapter 7, are divided per cycle. During this project a concept was developed (chapter 11) that should comply with cycle 0. All requirements for cycle 1 and 2 where design goals, but not required as such. Also the requirements where catagorized by prosthetic component or part. Hereafter follow remarks about the concept where necessary and which are not discussed in section 12.1 or where the Universal Prosthesis is expected to perform as well as a PTB-standard design.

frame parts can be adjusted by the prosthetist, either by plastic deformation of the hard frame parts) or by heating the interface frame parts. The small distal ends of the interface frame parts can easily be adjusted to provide extra weight-bearing, and no special knowledge is needed. However, changing the proximal end of the interface frame parts, needs experience and insight, and is not recommended (nor necessary) for the un-experienced. The flexibility is added to the design to facilitate the acceptance of the system by current prosthetists.

Concept

From the list, the tools and service types are

The

The

Ideas

- - - - -

against the requirements.

The Flexible socket: Synthesis

How well the system can be distributed is

12.2 Evaluation the concept

115

The Advanced fit sock:

Cycle 1 Prices:

The

fit sock can be further developed, so that it is thickened at places where the eventual pressure will have to be lower than the pressure used during the foaming of the soft socket, especially the distal end. This will result in a bit more distance between the residual limb and the fabricated socket. After fabrication and without wearing the special sock, the pressure in those area will be lower than that used during the filling of the soft socket. This sock is comparable with the gel pads used during the fabrication of the ICEXsocket.

The Mechanical pylon:

properties

of

the

It

has to be mentioned here, that analysis of the mechanical properties of the pylon is incomplete. A working model has to be build and tested, to see if the pylon/socket combination comes up to the requirements.

The whole design of the pylon might have to

be rotated (about 5 degrees) to take the optimal 5 degrees of knee flexion in account. This is not so in the concept, the frame shapes have been derived from a stretched leg.

116

Tough the maximal total price for the system

is correct and the concept does complies with it (see section 11.6), the maximal production costs of the parts is formulated completely wrong. For example, the socket mentions a total production cost price of maximal 500 USD. This has to be either the price inclusive R&D, or a percentage of the total production costs price. For example, the production cost price of the socket should not be higher than 80% of the production cost price of the total.

Market share:

For Cycle 1 a price was calculated with 1000

pieces sold a year for 5 year, resulting in an break-even price of 700 Euros. For Cycle 2 a break-even price of 200 was calculated with 10,000+1000 sold a year for 5 years.

These amounts of products sold are huge for the prosthetic market. For cycle 1 the market size

1.416.000 Amputees in Europe (see appendix F) X 54% which have a transtibial amputation (see appendix F) X 70% that can be fitted with the UPis (see 12.11) X 0.4 new prostheses needed a year for each amputee (see 12.1-10) = 215.000 prostheses a year (total market size).

This is a market share of 0.47%, which is a lot considering:

- - -

The current prosthetists have been using the current system for over 20 years. It will be difficult to reach all amputees in Europe. In Lower-income countries such as Rumania and Poland, the price of 700 Euro is high in comparison to the hour-price of technicians and prosthetists.

For

cycle 2 the total market size adds up 2,300,000 pieces needed worldwide a year, with the same calculation:

This is a market share of 0.48%, which is a lot considering:

- - - -

The current prosthetists have been using the current system for over 20 years. Worldwide a lot of initiatives exist to promote the education of prosthetists. It will be impossible to reach all amputees. The price of 200 Euro or even 100 Euros can be considered high. Development of cheap systems that work on known systems (PTB-PP for example), with cheap components is being conducted and prices of other systems are expected to drop.

These

market shares can only be reached within the 5 year periods when using existing distribution channels, such as that of wellknown companies or in this field operating NGO’s.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Synthesis

12.3 Model and Fit of the Frame Shape

If

Ideas

we evaluate the shape of the interface frame, two things can be noticed. One, the model is slightly to big. This is an effect of the slices used of the Visual Human project. These were bigger than P95, probably because of conversion mistakes (see appendix R-10).

Concept

Secondly, the interface frame performs well

Evaluation

in avoiding the pressure-sensitive areas and loading the pressure tolerant areas. The exception to this is the lateral place is the lateral edge of the lateral tibial condyle (figure 12-2). This load is the result of the need to connect the interface parts as defined in section 11.1.3. This place should be avoided better, possibly by increasing the distance between the interface frame and the residual limb.

Recomm. Conclusion

Figure 12-2: Assessing the fit of the interface frame parts.

117

Flexibility

of

the

weight-bearing

frame

The model that has been build demonstrates

that the first 200 mm from PT, the shape of the frame parts contributes to the strength and stiffness. Even when thermoformed, the frame parts do have enough flexibility to accommodate for a wide range of circumferences at patellar tendon height, while staying in shape, so that the pressure-tolerant areas are loaded, and the pressure-intolerant areas are avoided.

However,

the posterior weight-bearing frame is too flexible from 200 mm below PT and downwards. This can be solved, either by adjusting the material used, or by adding a rib. The anterior frame does perform well, as a result of the shape that it has to follow the tibial crest. Giving this shape to the two extensions of the posterior frame is another good option to improve weight-bearing performance. Additionally, a second connector can be added, that can be used for long amputees at PT-260 mm.

Figure model.

118

12.3 gives an impression of the

Figure 12-3: Impression of the model build.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

12.4 Project evaluation Looking back, it becomes clear that at the

aluminium frame sockets in Sri Lanka, with anvil and hammer, was necessary to learn the properties of the materials and of the human body.

the vision of the Universal Prosthesis clear and keeping trust in the intuitive notion that this vision is good, in spite of negative advices of some individuals, was needed to keep going on until the needed technological innovations were conceived. Listening to other people is essential but never without listening to your own intuition.

Conclusion

Keeping

the most innovative steps have been taken, and the system needs to be optimized, bringing a team together of prosthetists, engineers, market experts, etc is the only way to ensure a practical and high-quality product.

Recomm.

what the wants and musts are of both prosthetists and users worldwide. In this project, the target was not to develop a cheap but inferior product for developing countries. Instead, the aim was to develop an excellent performing product for a good price that an be used worldwide.

Now

Evaluation

Being in Sri Lanka was necessary to learn

1950 the quadrilateral AK-socket and the PTB-socket were developed (also see appendix E). These socket designs were two of the few fundamental innovations in prosthetics after WWII. It can be said that these and other important innovations are the work of a small group of people, one of them being J. Foort. In appendix X, the story of his experiences can be found. I found reading them really intriguing, because the development methods and processes he describes highly resemble the methods and processes of this graduation project. A few quotes to give an impression:

Around

Concept

Producing

back-to-base strategy was needed to come up with a completely new system. In current day scientific research (also see section 13.1) the focus is too much on FEM-analyses and modelling and functional outcome analyses between PTB and TCB-sockets. This also explains why this project was done by an industrial design engineer, and not by a team of prosthetists. Prosthetists know too much to even think about making a low-expert system.

This

Ideas

beginning of the whole trajectory toward the Universal Prosthesis (the design-for-all subject, the internship in Sri Lanka and the graduation project), all knowledge has been gathered from base.

The road to innovation Synthesis

Building from base

Independency

119

13 Recommandation In

the evaluation it has become clear, that the concept presented in this report needs to be further improved (better properties) and further developed (made market ready). In section 13.1 recommendations for fundamental research that needs to be conducted can be found. Section 13.2 offers specific suggestions for improvements of the universal prosthesis.

Section 13.3 discusses possibilities on how to continue the development of the universal prosthesis.

13.1 Fundamental research in prosthetics. All

interface design starts with knowledge about human behaviour and the human body and its properties. Prosthetists make products for people. The prosthesis replaces a (lost) body part and restores a function that is lost and is needed for the participation of the user in society. Logical, it seems.

120

The

lack of knowledge about pressure

The

lack of knowledge about shape

tolerances

and property variances

Now, the amazing part of the story is that

For

fundamental knowledge about the anatomy and properties of the human body (needed to design an interface) in literature is either extremely out-dated and lacking or not public available. Ming Zhang concludes in his overview of FEM-analyses [Zhang 1998], that mechanical properties of the soft tissues are little known. A bigger question is the tolerance to load of the tissue. Zheng in “state-of-the-art methods for geometric and biomechanical assessments of residual limbs: A review” states: “While FE analysis can estimate the stress distribution within the residual limb and the socket interface, it cannot tell us whether a stress distribution is good or not. A good interface stress distribution should facilitate effective load transfers during gait and should be well tolerated by the residuum soft tissues. Such tissue tolerance involves tissue damage criteria and tissue adaptation mechanism in response to external loading. How residuum tissues react and adapt to external loading deserve much further investigation.“ While FEM-analyses are numerous, nobody actually knows what pressure distribution they are looking for.

the development of the Universal Prosthesis, the data that was gathered in Sri Lanka (appendix G) was of utmost importance. It was assumed that the bone-structure for everybody is the same and only proportions (scale) differ. This assumption has to be validated.

This can be achieved by scanning the limbs

of a range of people (N>100). Scans can be made with CT or MRI. Other (less preferred) approaches are the study of corpses and the study of 2D-X-ray images. These people don’t have to be amputees, though this would improve the data.

Better

insight in the variance of the bony structure and the soft tissues of people leads to a better optimized interface frame fit, and a better overview of the group for who the Universal Prosthesis would provide a comfortable solution.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

The PTB-TCB battle

Worse,

-

A study determining the functional outcome differences between hands-off and hands-on systems. A study determining the functional outcome between rectified and unrectified systems (such as the PTB and the TCB sockets).

Before

the development of the Universal Prosthesis this could be achieved by:

- Comparing hands-on and hands-off produced TCB’s. - Comparing hands-on produced PTB’s with hands-on produced TCB’s.

more data about the variance in residual limb shapes and tissue structures and more data about the pressure tolerance of residual limb tissue is obtained, the frame shapes can be optimized in respect to anatomy.

FEM-analyses can be a valuable tool for the

optimization in mechanical properties. Ribs on the frame parts, especially the injection moulded interface frame parts, can improve their properties significantly. It might be necessary to add more connective belts between the weight-bearing frame parts.

Other materials might prove more suitable

Conclusion

for the frame. For example, Hylite could also be used for the interface frame, while glare or possibly normal aluminium could improve the performance of the weight-bearing frame parts.

Recomm.

hands-off produced PTB also it can also be compared with hands-off produced TCB’s. None of the mentioned comparisons have been made in literature.

When

Evaluation

Now, because the Universal Prosthesis is a

The frame

Concept

the studies that are conducted are functional outcome studies in which both sockets are fabricated for the same subject (in which a slight, but often insignificant preference for the TCB-sockets can be seen). However, the PTB-socket is a hands-on socket design, which means that the experience and the knowledge of the prosthetist are the determining factor. The prosthetist will make “mistakes” which results in a negative outcome bias for the PTB-socket . The TCB-socket on the other hand is a hands-off socket design. There is less chance that the fit will not be optimal after the fitting procedure.

-

13.2 Improving the Universal Prosthesis

Ideas

sure distribution is good or not results in a battle between promoters of the PTB and promoters of the TCB-system. Comparative studies are being conducted but with a small population in subject groups.

separately:

Synthesis

This lack of knowledge about whether a pres-

These two factors should be split and studied

121

Improvements would include: - - - -

a better, more comfortable fit a wider group that can be fitted with the Universal Prosthesis (bigger target group) a lighter prosthesis a stiffer prosthesis (more control)

The soft socket

Absolute

priority is the development and testing of the foam that will fill the prosthesis. Without a proper foam, the complete concept fails. The posterior side of the prosthesis might prove to be in the way for donning/ doffing and sitting as shown in figure 12-1.

Cosmetics

C

osmetics after fabrication of the Universal Prosthesis can and needs to be further improved. A prosthetic cover can be put over the outside, but it can also be put inside the prosthesis. In that case the fitting liner is pulled over the frame and the cosmetic socket. Another option is to integrate it in the frame (as was the intention). Now, the problematic shape difference between the Universal Prosthesis and a natural leg occurs near the connector, where the frame is too triangular. 122

Cost reduction

To make the Universal Prosthesis a real success in cycle 2, it have to overcome the high competition during cycle 1 (section 6.3). A lower price would give the system the edge over the ICEX-system it needs. Costs can be reduced by smart use of subsidies and grants. Also, this project might best be developed in universities. In that case, initial investments needed for R&D are lower, but the problem might be that no companies are willing to take the risks that come with production, because the design is not patented or protected otherwise, as discussed in the next section.

13.3 Project continuation There are basically three realistic options to continue this project:

1) Find an enthusiastic entrepreneur, that is willing to start a company, bring together several business-partners, such as a orthopaedic workshop, a hospital, a knowledge institute (university) and try to start independent production of the Universal Prosthesis. The success of this enterprise would be highly dependent on the amount of subsidies and grants that can be attracted. 2) Find a big player in the current market, such as Otto-Bock or Össur, and start in-house development of the Universal Prosthesis as a new addition to their assortment. 3) Try to encourage America/Canadian research institutes, such as the US National Rehabilitation Information Center, to take up the project and develop it further with help of the world-wide prosthetic scientific research community.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

O

It might well be that the time just is not ripe

Ideas Concept Evaluation

for the Universal Prosthesis to appear on the market. Tough the tendency (trend) of the branch towards standardized systems, with customized results has been identified, prosthetists still keep using their well known systems, such as the PTB-resin system. And why not, it does perform well, and the needed knowledge to fabricate them has been invested in (years of training by exactly those prosthetists). The negative attitude towards the new systems by some (and the naïve positive attitude to new technologies by others) can even be read between the lines in literature publications. It takes time for the prosthetists to realize that with the Universal Prosthesis (and other low-expertise systems) their knowledge doesn’t become obsolete, but that it can be used better and with more effect elsewhere.

Synthesis

ption two is preferred, because in this way quality and development speed of the Universal Prosthesis can be controlled. Also, when production is started, a company will benefit most by wide-spread use of the system and will actively promote it. Contact has been sought with Össur to discuss this possibility. However, to make commercial exploitation feasible on a broad scale, protection of the intellectual property is a must. A patent is a way to protect the knowledge. It has to be emphasized that the development of the Universal Prosthesis will cost considerately and that the investments for this R&D will have to return to the entrepreneur to ensure future developments and continues production.

Recomm. Conclusion

123

14 Conclusion “I urge you to do this – aim for universal solutions “ J. Foort, Appendix X.

14.1 Strengths The

Yes it is.

Universal Prosthesis has some unique features or Unique Selling Points (UPS). Its strongest point is that the Universal BelowKnee Prosthesis combines a customized, comfortable fit with a low-expertise fitting procedure. This strength fits in the market trend toward standardized systems that provide a customized fit.

But the road is long.

COMFORT:

Is the development, production and distribution of an Universal Below-Knee Prosthesis feasible?

The

Universal Prosthesis combines the Total Contact Bearing (TCB) and the Patellar Tendon Bearing (PTB) weight-bearing principles. During the fitting procedure, the amount of pressure added during the filling of the soft socket, will determine if the prosthesis will behave more like a TCB or more as a PTB socket. This flexible system ensures that a wide range of amputees can be fitted with a comfortable prosthesis.

124

QUICK:

The Universal Prosthesis can be fitted within

an hour. The efficient use of the prosthetist’s time, can lead to cost reduction and better overall healthcare in current orthopaedic workshops. Patients for which a prosthesis is now regarded as too expensive or time-consuming (for example bed-staying elder, with a bad prognosis), can be fitted more easily. Also, the amputee can be a prosthesis more often, for example during the post-operative period (1-6 months after amputation) or as a spare one when the custom-made prosthesis is being repaired or being replaced.

LOW-EXPERTISE:

The

Universal Prosthesis can be fitted by relatively un-educated people. This unique features addresses the lack of experienced prosthetists worldwide. The educated prosthetists can use their valuable time to solve orthopaedic problems for people with non-standard BK-amputations. In the long run, more people can benefit from proper prosthetic care.

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

14.2 Project progression

is clear that a huge amount of research and development work has to be done before the Universal Prosthesis can be a qualitative system, that has an edge over other current prosthetic systems. And R&D-work is an expensive investment that needs to be returned by the revenues of the product.

History learns us that innovation in socket

It

With 2 x 800.000 Euros R&D-investments,

Prosthesis is not finished. But I feel that the here presented concept is a good step towards the next generation of prostheses. Whether the concept is freely developed or commercialized, I believe that within 10 years, many people can benefit from the Universal Prosthesis or similar innovations. And I hope that some of the 1,000,000 people that currently are without proper prosthetic care, will be able to walk once more.

Conclusion

-

I know that the development of the Universal

Recomm.

-

Cutting down on R&D-costs by attracting grants and encouraging many parties to participate. Get support from existing distribution networks, including NGO’s, producers of prosthetic components and governments. Integrate the Universal Prosthesis into an assortment of prosthetic systems, components and methods, so that the R&D costs can be spread over a group of products.

uct that will only be economically feasible when produced in large quantities, for this new innovation commercial exploitation might be the best option.

Evaluation

-

Because the Universal Prosthesis is a prod-

Concept

the Universal Prosthesis can be developed. Return of investment is possible when selling 1000 Universal Prostheses for 5 years at a price of 700 Euros and then selling 11,000 pieces a year for 5 more years at a price of 100-200 Euros. These market share of 0.47% will be difficult to reach. Strategies to do so include:

designs doesn’t occur often. However, innovations that occurred, such as the PTB-socket and the quadrilateral socket, did become mainstream. These innovations were not patented, were not commercialized, but were developed by a relatively small group of enthusiastic scientists and practitioners.

Ideas

here-presented concept if far from finished. A lot of fundamental questions have to be researched to improve the base of knowledge on which this innovation is build. Apart from that, the frame parts have to be optimized and the formation of the soft-frame, by filling the prosthesis with foam, has to be developed from scratch. When the first series of prostheses become available clinical/field test have to make sure the procedure is indeed understandable and efficient when performed by non-experts. After that, bringing it to other markets, other cultures and other environments brings along a complete new set of challenges.

14.3 Final word Synthesis

The

Commercial feasibility

125

R References - - - -

- - - - -

-

- -

- -

126

-

Wisse BM, WD van Dorsser, F Soleymani, Prosthesis for Sri Lanka – Prosthesis for tibial amputees focused on the 3rd World, Delft, 2002 Wisse BM, WD van Dorsser, The Alternative Prosthesis – final report internship Sri Lanka 2002, Delft, 2003 Seymour R, Prosthetics and Orthotics: lower limb and spinal, USA: Lippincott Williams & Wilkins, 2002 IMT-Baghdad, Institute of medical technology department of rehabilitation, Baghdad, Iraq, Education for orthopedic technician, Part 1 – Symes and partial foot prostheses and below knee prostheses, year unknown CBS, Centraal Bureau voor de statistiek, Statistisch Bulletin, 60e jaargang no. 5 / 3 februari 2005 CBS, Centraal Bureau voor de statistiek, Statline online database (website): statline.cbs.nl, 2005 IEE, Medical Equipment Industry-potential for growth, edited by professor Alan Murray (Freeman Hospital), 1998 VHI, Veteran Health Institute, Traumatic Amputation And Prosthetics, Independent Study Course, May 2002 Weeks DL, Preliminary Investigation Comparing Rectified and Unrectified Sockets for Transtibial Amputees, Journal of Prosthetics and Orthotics 2003; Vol 15, Num 4, p119 Fisher SV, G Gullickson Jr., Energy cost of ambulation in health and disability: a literature review, Archives of Physical and Medical Rehabilitation. 1978 Mar; 59: 124-133. Angarami GR, An Efficient Low Cost Prosthetic Structural System, Journal of Prosthetics and Orthotics 1989; Vol 1, Num 2, p86. Valenti TJ, Experience with Endoflex: A Monolithic Thermoplastic Prosthesis for Below-Knee Amputees, Journal of Prosthetics and Orthotics 1991, Vol 3, Num 1, p43. Schoppen T, Physical, Mental and Social predictors of functional outcome, Rijks Universiteit Groningen 2001 ACA, Amputee Coalition of America, FirstStep 2001, www.amputee-coalition.org/aca_first_step.html. Kriesels M, Protheses voor Sri Lanka uit fietsonderdelen, 2002, please contact the writers for more information

- - - -

-

-

- -

-

-

-

-

UK NHS, 2005 (website): www.pasa.doh.gov.uk/prosthetics/ Walsh TL, Custom Removable Immediate Postoperative Prostheses, Journal of Prosthetics and Orthotics 2003; Vol 15, Num 4, p158-161. COTA, Centrum voor Orthopedie Techniek Amsterdam, De Softsocket, 2002 Hafner BJ, JE Sanders, JM Czerniecki, J Fergason, Transtibial energystorage-and-return prosthetic devices: A review of energy concepts and a proposed nomenclature, Journal of Rehabilitation Research and Development 2002; Vol 39, Num 1, p1-11. Michael JW, JH Bowker, Prosthetics/Orthetics Research for the Twenty-first Century: Summary 1992 Conference Proceedings, Journal of Prosthetics and Orthotics 1994; Vol 6, Num 4, p100. Sangeorzan BJ, Harrington RM, Wyss CR, Czerneicki JM, Matsen FA, Circulary and Mechanical Response of Skin to Laoding, Journal of Orthopaedic Research 1989, Vol 7, p425-431 Foort J, 1986, Innovation in prosthetics and orthotics, The Knud Jansen Lecture, Copenhagen 1986 Kim WD, Lim D, Hong KS, An evaluation of the effectiveness of the patellar tendon bar in the trans-tibial patellar-tendon-bearing prosthesis socket, Prosthetics and Orthotics International 2003, Vol 27, p23-35 Reswick JB, Rogers JE, Experience at Rancho Los Amigos hospital with devices and techniques to prevent pressure sores, Bedsore Biomechanics, 1975 Convery P, Buis AWP, Socket/stump interface dynamic pressure distributions recorded during the prosthetic stance phase of gait of a trans-tibial amputee wearing a hydrocast socket, Prosthetics and Orthotics International, 1999, Vol 23, p107-112 Zhang M, Mak AFT, Roberts VC, Finite element of a residual lowerlimb in a prosthetic socket: a survey of the development in the first decade, Medical Engineering & Physics 1998, Vol 20, p360-373 Datta D, Harris I, Heller B, Howitt J, Martin R, Gait, cost and time implications for changing from PTB to ICEX sockets, Prosthetics and Orthotics International 2004, Vol 28, p115-120.

The Universal Prosthesis

F Figures & Tables List Tables and figures Table 2-1:

Figure 3-9:

Table 3-4: Figure 3-17:

Figure 3-18: Table 3-5: Table 3-6:

Conclusion

Figure 3-10:

Figure 3-15: Table 3-3. Figure 3-16:

Recomm.

Figure 3-8:

Figure 3-14:

Evaluation

Figure 3-7:

Figure 3-13:

Concept

Table 3-2: Figure 3-6:

Figure 3-12:

Alignment of the transtibial prosthesis in the sagittal plane, placing the foot medial to the socket. This placement tends to cause a rotation of the socket that then places pressure on the proximal medial and distal lateral residual limb. 15 Alignment in the sagittal plane placing the foot lateral to the socket, resulting in pressure on the fibular head and distal medial residual limb. [Seymour 2002] 15 Alignment in the frontal plane. Left: normal. Right: Foot placed to far backward, causing pressure on the distal anterior part and proximal posterior part of the limb. 15 Alignment in the frontal plane. Left: normal. Right: Foot placed to far forward. If the force though the spocket fell posterior to the ground reaction force vector, the prosthesis would tend to rotate. 15 Planes of the body. [Seymour 2002] 16 Phases in gait. [Seymour 2002] 16 Distance variables of giat. a) left step length, b) left stride length, c) right stride length, d)right step length, e) width of base support f) Right toe-out, g) left toe-out [Seymour 2002] 16 Phases of the gait cycle of the right leg. [Adjusted from Seymour 2002] Gait deviations to accommodate a long limb. A) Hip hiking, B) Lateral trunk lean, C) Circumduction, D) Vaulting, E) Excessive hip and knee flexion. [Seymour 2002] 18 Procedures of a prostetic clinic [Adapted from Seymour 2002] 21 Grow indexes of the sales in the medical equipment industry in the Netherlands [CBS 2005]. 22 Market for prostheitc devices in the Netherlands [CBS 2005]. 22

Ideas

Figure 3-3: Figure 3-4: Table 3-1: Figure 3-5:

Figure 3-11:

Synthesis

Figure 3-1: Figure 3-2:

Project targets before and after the Sri Lanka internship [Adjusted from Wisse et al. 2003, Chapter 5] (For a complete timeline see appendix C). 2 The prosthesis and its total context. 6 Bones of the lower limb (most right), muscles (middle) and anatomy of the residual limb (below) [Adapted from IMTBaghdad and Wisse et al. 2002]. 7 Amputation procedure [Seymour 2002]. 8 Different levels of transtibial amputation [Seymour 2002]. 8 Amount of amputees worldwide. 9 Residual limb shapes: conical (a), cylindrical (b) and bulbous (c). [Seymour 2002] 10 Skin conditions. 11 Pressure tolerant and sensitive areas. Most left: A scematic of sensitive (light red) and tolerant (dark red) areas [Seymour 2002]. 4 Right: anterior, lateral, anterior and medial view of a positive (cast), with pressure sensitive (red) and to 12 Base of support. The size of the base of support varies with a change in foot position. [Seymour 2002] 13 Static alignment for a transtibial prosthesis. A) In the frontal plane, B) In the sagittal plane. [Seymour 2002] 13 Inclination of the bulge of the PTB (see section 4.2) socket. The bulge provides more surface for weight bearing than the wall of the socket. Note the relatively longer horizontal component of the vector. [Seymour 2002] 14 Forces on the patellar tendon increase because of the need to compensate moments due to distance a and b and because the inclination of the force factor on the patellar tendon [Wisse et al .2002] 14

Boudewijn Martin Wisse TU Delft, 2005

127

Table 4-1:

Figure 4-1:

Figure 4-2: Figure 4-3:

Figure 4-4:

Figure 4-5:

Figure 4-6:

Figure 4-7: Figure 4-8:

Figure 4-9:

128

An overview of clinical patient stage and applicable prosthesis type. In practise, the choice is less time dependent, but is determined by the healing rate and activity level of the amputee. 24 Fabrication of a RRD and Custom Removable IPOP. Left: 3 spandex socks, pads and an attachment plate, 3 velcro straps and attachment base plates. Middle: fiberglass cast with cut lines and base plate attachment points and the result. Inset: ant 25 A complete IPOP (without pylon). [Source: Seattle Rehab Research, US Veteran Affairs] 26 The universal IPOP (Aircast Air-limb) is inflatable to accomodate different stump sizes. [source: ACA 2001, Aircast brochures] 26 The Flow-tech Adjustable Postoperative Protective and Preparatory System (APPOPS) provides a prefabricated prosthetic system offering protection, controlled shaping of the residuum and early rehabilitation.... 27 Connective part between socket and pylon, which can be used in temporary and definite prostheses. [Source: Endolite brochure] 28 Components of Maramed orhopedic Systems. Left: X-tender system can be used as a temporary prosthesis(middle). At the right a retainer is shown, in which a custum-made socket can be attached. [Source: Maramed website] 28 The ICEX toolbox and component box. [Source: Ossur website] 29 Standard fabrication starts with taking a negative mold. Then plaster is poured into the negative mold to create a positive mold. At last, the positive mold is shaped by the prosthetist to emphasis the shape. The final socket is made by laminat 29 The exoskeletal prosthesis (depicting socket, plastic exterior and foot) is one, integrated product. [Seymour 2002] 30

Figure 4-10:

The Jaipur prosthesis, here drying from paint finish,

Figure 4-11:

The endoskeletal prosthesis always contains a pylon. Very seldom the other parts are integrated. Normally, the socket and foot are modular components. [Seymour 2002] 31 The 4C Air Lite Monolithic (above 2 pictures show manufacturing steps. A carbon-fibre sock is one of the important materials) and the Endoflex (lower pictures) are two of the few designs in which the pylon and socket are integrated. [4C Air-Li 31 ISNY Components [Source: Website Otto-Bock] 32 Flexible ischial-containment socket for transfemoral amputees (this one from Otto-Bock, inset from Hanger) consist of a flexible inside and a frame. Other names include Total Flexible Brim, the ISNY and SFS (Scandinavian Flexible Socket)[Seym 33 Plug fit socket. The first prosthetic socket without weightbearing at the distal end by Verduin 1696 [Wetz 2000] 34 Icex finished socket (left). Pressure pads are added to compensate for weight intolerant areas (cutt-through right) [Source: Ossur Icex brochures.] 35 The ICRC-limb makes use of a polypropylene pylon.. Its cross-section is H-shaped. 35 (left) Trimodular Pylon as used in the sauer-bruck trimodular physiological prosthesis [Angarami 1989] 35 (right) Springlite Advantage DP flexible pylon and dynamic response foot by Hanger Orthopedic Group. [Source: website] 35 Left: Principle of Rocker foot or sole. [Adapted from: www. customfootware.com] Right: Low cost prosthesis with cane pylon and rocker foot 36

Figure 4-12:

Figure 4-13: Figure 4-14:

Figure 4-15: Figure 4-16:

Figure 4-17: Figure 4-18: Figure 4-19:

Figure 4-20:

consists of a exoskeletal structure with a separate manufactured foot. [Source: FINS- Sri Lanka] 30

The Universal Prosthesis Boudewijn Martin Wisse TU Delft, 2005

Figure 4-21: Figure 4-22:

Figure 4-34: Figure 4-35: Figure 4-36:

Table 4-2:

Figure 4-42: Figure 4-43:

Conclusion

Figure 4-32: Figure 4-33:

Figure 4-41:

Recomm.

Figure 4-30: Figure 4-31:

Figure 4-40:

Evaluation

Figure 4-29:

Figure 4-39:

Concept

Figure 4-28:

Figure 4-38:

Prosthetic skins can have a high life-like appearance [left, dorset and orthopeadic]. Uflate sleeve skin covers shrinks to fit the prosthesis when treated with a heat-gun. 43 Examples of supplies (above): Rivits, Polyester ResinLaminae, box of stockinettes, pneumatic cast cutter, carbon tape [Fillauer Supplies brochure]. Static alignment is done on an alignment table [otto bock[. Supplies enable prosthetists to ma 43 Pathway of the instant axis of rotation for the knee joint. [Seymour 2002] 44 Limited dorsiflexion at the ankle. If the ankle can not dorsiflex normally, either A) the individual will weight bear on the toe or B) the knee must hyperextend to get the foot flat on the ground. [Seymour 2002] 44 Stress on the residual limb from the prosthesis. A) The hypothetical situation in which the residual limb is of uniform firmness and the socket matches the circular shape of the limb. B) A residual limb of nonuniform firmness and a socket that 45 Gait deviations due to materials and the alignment [Seymour 2002]. Note that many alignment choices can have the same effect. If the effect is unwanted, all can be adjusted, but some will cause other problems (because one alignment choice will h 46 Bending forces on the residual limb while standing. [Wisse et al. 2002] 47 A Simple model of the value chain of prostheses. Value is increased from left to right. Note that some companies have multiple roles. 48

Ideas

Figure 4-27:

Figure 4-37:

Synthesis

Figure 4-23: Figure 4-24: Figure 4-25: Figure 4-26:

SACH foot (Adapted from Seymour 2002] 36 SAFE II foot. (Original manufacturer is Campbell Childs Inc, now bought by 4C (Foresee Orthopeadic Products)). 36 Single-axis foot. [Seymour 2002] 37 Multiple axis foot. [Seymour 2002] 37 STEN foot. [Source: Kinsley Manufacturing Co brochure] 37 (Above) Though from the outside not visible, energy storing feet differ from the inside [Impulse foot, OHIO Willow Wood] Various energy-storing feet. Earch foot is composed of a compressible heel and a flexible keel spring. A) Seattle foot, B) Dynamic foot,C) STEN foot, D) SAFE foot,E) Carbon Copy II foot.[Hafner et al. 2002] 38 Advanced energy-storing prostheses: A) Modular III, B) Reflex VSP, C) Advanced DP, D) Pathfinder.[Hafner et al. 2002] 38 Two hybrids: The Seattle Cadence HP [Source: Seattle website] and the MICA Genisis II+. [Source: MICA website] 38 (right) Anatomical Suspension. The supracondylar suspension is in this case removable due to the brim.(right, middle) The supracondylar suprapattelar system is fixed. [Seymour 2002] 39 The PTB cuff or supracondylar cuff. [Seymour 2002] 40 The thigh corset can be used in conjuncture with a waist belt and an elastic strap. [Seymour 2002]. The suspension sleeve has a similar working principle (left) [Otto Bock]. 40 Pin/Shuttle suspension. [Seymour 2002] 41 Mineral gel sleeve suction suspension. [www.customprosthetics.com]. 41 Double/Single Socket Gel Liner [Silipos]. 42 Demountable Torque absorber and its effects. [adapted from endolite] 42 Some examples of connective components [adapted from www.atlas-ti.com] 42

129

Figure 5-1:

Figure-8 wrap for the transtibial amputation: [Seymour 2002] A. First wrap max extend from proximal medial to distal lateral. B. Second wrap may extend from proximal lateral to distal medial. C. Thrid wrap may overlie first wrap. D. Bandage is looslely wrapped approximately 60 milimeter to the knee. E. Completed wrap. 51 Figure 5-2: LEFT: The endolite Aqualimb with anto-slip tread patterm on the sole for extra grip on wet surfaces. [www.endolite.com]. RIGHT: The rampro activankle swimming prosthesis [www. rampro.net]. 55 Figure 6-1: Snapshots of a movie, in which an amputee walks several steps in a frame socket. [Wisse et al. 2002] 61 Table 6-1: Several fitting methods and their properties. 64 Table 6-2: Several walking and mobility aids and their properties 65 Figure 10-1: Otto-Bock Harmony system 82 Figure 10-2: Possibilities for adding use-cues to ease the fitting procedure. 83 Figure 10-3: Moments around the socket, as a result of diffrent pylon types. 85 Figure 10-4: H-profile. 85 Figure 10-5: Flexible bands that connect parts will result in pressure peaks. 85 Figure 10-6: Suspension sleeve 86 Figure 10-7: Steps for fitting the hard frame 88 Figure 10-8: Steps for fitting the soft frame 88 Figure 10-9: Steps for fitting the combined system 89 Table 10-1: Quick comparison between the Universal Prosthesis and two popular fitting systems.e 90 Figure 11-1: 13 stacked layers that where derived from the anatomy of the residual limb. Top view and isometric view. 94 Figure 11-2: Together with the resulting frame parts. [Top] stiff frame, two views. [Below] interface frame. 94

130

Table 11-1: Figure 11-3: Figure 11-4: Figure 11-5: Figure 11-6:

Figure 11-7: Figure 11-8: Figure 11-9: Figure 11-10: Figure 11-11: Figure 11-12:

Figure 11-13: Figure 11-14: Figure 11-15:

Figure 12-1: Figure 12-2: Figure 12-3:

Four material options for the interface frame. 95 Applying hinges to Hylite (source: Corus) 96 Deep drawed car part from Hylite. (source: Corus) 96 Less space in between the frames is better; it results in a stiffer prosthesis. 99 A Polyurethane layer is partly reinforced with fibres. The Hylite is milled to better attach the reinforced PU. The two Polyurethane layers can slide along each other 99 The airman Panter is an example of a hand-pump. 100 Two ways to connect the frame. 100 An extra component that can fine-tune the length enhances the adjustability of the prosthesis. 101 The connection to the foot is 101 (Up and Right)The airlock is achieved by an outer and an inner seal. 101 The fill channel and the valve in the connector. To transfer the filler up to the proximal side of the prosthesis, flexible tubes (straws) and splitters can be used. The entrance of the channel has to be distally or on the bottom of the ... 102 An example of a Minivalve (source: www.minivalve.com) 102 Height of supracondylar suspension. 104 The shuttle for the pin/shuttle suspension can perforate the outer layer. The rings will restore the system to an airtight state. The shuttle can be attached on most heights (with varying circumference). During the fitting .... 105 A high posterior socket as a result of the fitting of the soft socket. Assessing the fit of the interface frame parts. Impression of the model build.