Radiographics.11.5.1947319.pdf

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Orthopedic T’i

Fixation 1

#{149}

ievices

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Richard MarjM RobertA. Wllliamj

M. Slone, MD Heare, MD Vander Griend, Montgomery,

MD MD

Orthopedic fixation devices are used in the treatment of fractures, soft-tissue injuries, and reconstructive surgery. After fracture reduction, internal, external, or intramedullary fixation devices may be used to provide stability and maintain the alignment of bone fragments during

the

healing

to allow

early

patient.

Compression

tact

area

process.

They

mobilization

and

the

must

of the

is used stability

be

strong

injured

whenever

between

and

part,

as well

possible

enough

as the

entire

to increase and

fragments

secure

the

to decrease

con-

the

stress on the implant. Screws are used primarily to provide interfragmental compression or to attach plates, which can then provide compression, prevent displacement, and support the fragments during healing. Pins and wires can be used for fixation of small fragments or fractures in small bones and for attachment of external fixation devices and traction. A basic understanding of the devices and principles of use

is needed

to interpret

of musculoskeletal

radiographs

obtained

after

the

treatment

injuries.

INTRODUCTION

U

The

development

of fixation

devices

part of the history

is an integral

of fracture

treatment. Until the 1900s, fractures were often life-threatening injuries, and amputation was recommended for many open and some closed fractures. Even if the fractune healed, the incidence ofdeformity and loss offunction was high. Accurate diagnosis and operative treatment of fractures became possible in the early 1900s with the discovery ofx rays, the availability ofanesthetics, and an understanding of surgical asepsis. Gradually, the goals offracture treatment expanded to include not only restoration of the normal anatomy but also complete recovery of function. For many types of fractures, these goals could be accomplished only with operative treatment. As new techniques and hardware implants were developed, the indications for openative treatment increased and the limits ofwhat constituted an acceptable reduction narrowed.

Abbreviations: Index

AP

term:

I

From

1991;

the

for a scientific

0

RSNA,

therapy,

May

40.41,

of Radiology

BoxJ-374,J. exhibit

K

=

Kirschner

40.43

11:823-847

Departments

ofMedicine,

received

anteroposterior,

Fractures,

Ra&oGraphics

lege

=

at the

31; acceptedJune

Hills 1990

(R.M.S., Miller RSNA

M.M.H.,

Health

scientific

13. Address

reprint

WJ.M.)

Center, assembly. requests

and

Orthopaedics

Gainesville, Received

(RAV.G.),

FL 32610.0374. February

12,

UniversIty

RecipIent 1991;

revision

ofa

of Honda, Cum

requested

Laude April

Col. award 4 and

to R.M.S.

1991

823

The current to reduce and niques

and

complete injury

devices

that

recovery to the

movement limb are disuse

goals of fracture treatment stabilize the fracture with result

with

bone

and

the soft

in healing

least

of the

bone

Early

of the injured stiffness and and

soft

fracture

‘

treated

with

closed

reduction

and

intramedullary fixation, condylar elbow fracture reduction and percutaneous An open reduction is require a reduction that

on a pediatric supratreated with closed pin fixation. used for fractures that cannot be achieved

with

The

closed

techniques.

fracture

is cx-

posed or opened to restore the anatomy, and some type of internal fixation device is usually needed to maintain the reduction. Common examples include intra-articular fractures that require an exact, anatomic reduction and adult forearm fractures; in both, a reduction is difficult

to achieve

on maintain

with

closed

treatment, and open reduction with internal fixation is needed. Other indications for open reduction with internal fixation include pathologic fractures and fractures associated with multiple injuries or neurovascular damage (1,2). Confusion arises because open reduction with internal fixation is often used to describe any type of operative fracture treatment involving a fixation device (screw, plate, pin, intramedullary nail, external fixator, etc), regardless of the mechanism of reduction used. The indications for operative treatment are affected by the treatment goals and factors mentioned above.

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1.

Figure passing

tissues.

These methods decrease the recovery and hospitalization periods, as well as the risk of malunion, nonunion, and infection. To achieve these goals, several different techniques of reduction and fixation may be used, depending on the patient, type and 1cation of the fracture, associated injuries, and experience of the surgeon. With various fractunes (eg, those in the shaft ofthe femur), an excellent result can be obtained without an exact or ‘anatomic’ reduction of each fractune fragment as long as the overall alignment of the bone is restored. In general, a closed reduction is used when the functional alignment of the bone can be restored and fixation achieved without exposure of the fracture. The reduction is then maintained with an external support, such as a splint or cast on some type of surgical fixation device. Common examples include a transverse tibia! shaft fracture treated with closed reduction and a cast, a femoral shaft ‘

\

and

additional

tissues.

and rehabilitation necessary to prevent atrophy

are tech-

Diagram

shows

perpendicular

plane

to maximize

a screw

to the

fracture

compression.

Fracture healing generally requires apposition of the fracture surfaces and some degree of stability. Compression of these surfaces increases the contact area and stability, decreases the fracture gap, and places less stress on the implant, since bone surfaces in continuity bear some of the load. Whenever possible, fixation devices are applied to produce compression across the fracture. Ideally, the entire fracture interface should be uniformly compressed. With adequate compression, movement is eliminated and callus formation is small. Large callus formation may indicate movement at the fracture site. Compression produced by a fixation device alone is static compression. Dynamic compression occurs when fixation devices are applied in such a way as to allow the weight of the body or muscle forces to produce additional compression. Transverse or oblique fractures

are

best

suited

to fixation

in com-

pnession; however, compression cannot be applied to all fractures. Fractures caused by compression, comminuted fractures, and fractures with bone loss cause the bone to become shortened or unstable in compression; the fixation device must support or “buttress” the bone during the healing process. The art of internal fixation is complex, with each case placing unique constraints on the orthopedic surgeon. Ideal fixation is not a!ways possible, and modification of techniques, implants, or both may be needed to accomplish the treatment goals. The radiologist should interpret the radiographs with this in mind and should be slow to criticize the position of the components. In this article, the most common fixation devices (used mainly for open reduction) and the biomechanical principles for their use are reviewed to help the radiologist better identify these implants and interpret the radiographic consequences of their use. Three major categories of fixation devices-internal (screws, (pins

plates, and

rods, and plications

staples,

traction),

nails)-are associated

and and

wires),

intramedullary

described, with their

Volume

external (pins,

and the cornuse are briefly

11

Number

5

2a.

2b.

SHANK CORE DIAMETER

:::

-

THREAD DIAMETER

3-

2c.

Figures 2, 3. (2a) Diagram chase only in the distal (far) threads

crossing

the

shows

a cancellous

fragment.

(2b)

fracture

line,

screw

Diagram

resulting

shows

in inadequate

screw used as a lag screw, with the threads crossing been overdnilled so that the threads gain purchase achieved.

and

(3)

Diagram

a partially

shows

threaded

a fully

cancellous

threaded

screw

used

with

screw

compression.

(2c)

the

used Diagram

the fracture line. The proximal only in the distal (far) fragment

cortical

(right).

as a lag screw,

a cancellous

Deep

screw

(left),

threads

a fully

gaining

shows

pun-

with

the

a cancellous

fragment, however, has and compression is

threaded

are designed

threads

as a lag screw,

cancellous

to grip

screw

cancellous

(center),

bone.

compression across the fracture site and to attach plates to bone. Any screw that crosses a fracture line should be placed as a lag screw. The term lag screw refers to the use of a screw to achieve interfragmental compression rather than to a specific type of screw. To provide maximum intenfragmentary compression, lag screws are placed perpendicular to the

purchase on both sides of the fracture, each turn of the screw causes both fragments to move an equal distance and compression is not achieved (Fig 2b). This can be overcome, however, by overdnlling (enlarging) the near fragment, which allows free passage of the threads (Fig 2c). The length and orientation of the fracture line determine the number of lag screws used and how they are positioned. Although lag screws compress the fracture surfaces, they do not provide sufficient fixation to protect most fractures from the normal bending, rotation, and axial-loading forces encountered by the bone. These forces must be neutralized, usually by a plate, or the lag screw will fail. There are many types of screws available,

fracture

characterized

discussed.

Spinal

plasty tunes, tions U

instrumentation,

devices used and a detailed are

beyond

the

INTERNAL

are

site

tenfragmental passes

freely

torque used

(Fig

manner,

of this

into

compression

to provide

1). A lag

through

when

article.

DEVICES

screw

provides

when the

“near”

the cortex

line, with the threads in the “far” fragment. the

and

interfragmental

compression

across the fracture ing purchase only this

scope

FIXATION

#{149} Screws Screws convert primarily

arthro-

in the treatment of fracdiscussion of complica-

screw

is tightened,

in-

screw and

gainIn the

diameter threads), threaded head (1). ofscrews:

by

their

overall

length,

thread

and pitch (distance between shaft diameter and length (unsegment), and design ofthe tip and There are, however, two basic types cortical and cancellous (Fig 3).

head pulls against the near cortex and the threads against the far fragment, bringing the two together and compressing the fracture surfaces (Fig 2a). If the screw threads have

September

1991

Sloneeta!

U

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U

825

U 4.

Figures screw,

4, 5. with

(4) Diagram

the

proximal

shows or gliding

a cortical hole

screw

ovendnilled,

used

as a lag

allowing

static

interfragmental compression to be achieved. (5) Radiograph shows small cortical screws used as lag screws to fix an oblique fracture through the end of the proximal phalanx.

e_

WASHER

=

:w:

It

I

ii

COUNTERSUNK

6.

Figures 6, 7. (6) Diagram shows the use of a washer with a cortical screw to increase the area over which the force is distributed. Countersinking the screw achieves a similar effect. (7) Anteropostenor (AP) radiograph shows optimum purchase of cortical screws in the cortex.

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Cortical Screws.-Cortical screws are threaded over their entire length and usually have blunt ends (1,3). The threads are shallower and more closely spaced than on cancel!ous screws for better purchase in cortical bone. For most cortical screws, a hole is drilled and tapped before the screw is inserted. Tapping refers to the prethneading of a hole and is accomplished with a special cutting

device.

Cortical

screws

can

be

lag screw if the cortex adjacent to overdrilled to the diameter of the that the threads do not gain purchase 5). This is referred to as the gliding hole in the far cortex is tapped and the thread hole. To prevent breaking cortical bone by the screw head, a plate is sometimes used to distribute over a greater area, or if the cortex the screw can be countersunk (Fig screws are also used to affix plates tical

of the

bone.

When

cortical

opposite

properly

screws

cortex

by

mm

Cancellous Screws.-Cancel!ous (Figs 3, 8) have a wide thread

September

1991

as a

hole.

The

is called of thin washer or the force is thick, 6). Cortical to the con-

positioned,

should 1-2

used

the head is threads so (Figs 4,

the

penetrate (Fig

tip

the

large area between the threads to improve purchase ofthe screw in cancellous bone. These screws are available with different lengths of thread, ranging from fully threaded screws to those with only a few millimeters of thread at the tip. These partially threaded screws have a smooth shank between the screw head and the threads, which facilitates their use as lag screws. Partially threaded cancellous screws can be used as lag screws when the threads gain purchase only in the far fragment. Cancellous screws are used primarily in metaphyseal fractures and in cancellous bone. Malleolar screws (Fig 9) look like partially threaded cancellous screws but have a cortical thread pattern. They have a trocar tip and are self-tapping, which means that the screw cuts its own

thread

path

through

the

bone.

They

were originally designed for the ankle but are no longer used routinely, having been replaced by smaller, less bulky cancellous screws. Current use is limited to unique situations.

7).

screws diameter

and

a

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.

.

.,

..

12. 10-13. (10) Radiograph shows two interfenence (Kurosaka) screws used for an anterior cruciate hgament repair. They are wedge shaped, and there is no typical screw head. (11) Radiograph demonstrates three cannulated screws used to repair a subcapital femoral neck fracture. (12) Diagram ofa Herbert screw shows the difference in thread pitch between the two ends. The two fragments are brought together, achieving static Figures

compression when the screw is turned. (13) shows a Herbert screw used in the treatment oid fracture. A bone graft has been interposed,

coarser

threads

.

Radiograph of a scaphand the

‘it, ,

A .

are in the far fragment.

‘

1.

Special Screws. -Interference screws are used like a wedge or shim to anchor bone on other tissues to bone. They are short, fully threaded screws with self-tapping tips, a cancellous thread pattern, and a recessed head so that they can be placed below the surface of

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the bone. These screws are commonly used cruciate ligament reconstruction for anchoring the bone plugs of bone-tendon-bone grafts (Fig 10). The graft is placed through tunnels drilled in the femur and tibia. The screw

is placed

between

the

Volume

bone

11

block

in

on

Number

5

Figures

15.

14,

in osteopenic

bus

(14) Radiograph (15) Radiograph

bone.

screws

in a sacroiliac

fusion

shows how nuts demonstrates

to prevent

the

splitting

the end of the graft and the “wall of the tunnel,” achieving an interference fit that holds the graft in place. Cannulated screws are hollow screws that are inserted over small-diameter guide pins. The pin is removed after the screws are placed. Both cortical and cancellous screws are available as cannulated screws. A small guide

pin

screw,

or

can

necessary

Kirschner

(K)

be placed

easily

until

it is in the

wire,

unlike

and

redirected

desired

ting

flutes

for

easier

removal.

as

position.

Multiple

By

can screws cutscrews

can be used to provide rotational stability. A common use of cannulated screws is to treat femoral neck fractures (Fig 1 1). The use of guide pins allows accurate placement of the screws, and the smooth shafts of the partially threaded screws cross the fracture line and allow dynamic compression. Contrast material also

can

be

injected

intraoperatively

of thin

ofcortical that were cortical

screws are used to gain purchase used over the head oftwo cancel-

bone.

threads; thus, the ends advance at different rates through the bone. When the screw is turned, the leading end placed in the far fragment moves farther through the bone than the trailing end. When the screw is tightened, static compression is generated and the two fragments are pulled together (Fig 12). Be-

a

following the pin, the cannulated screw be placed accurately. Some cannulated are self-tapping, and some have reverse

on the end flat washers

through

the lumen of the screw to check for screw penetration into the joint. Cannulated screws can be used when accurate placement of screws is essential, such as in juxta-articular

cause both ends of the screw are within the bone, this screw is used in fractures in which a standard screw head would impinge on adjacent tissues, such as in scaphoid or osteoarticular fractures (Fig 13). These screws also can be used for joint fusion in the hands. As with

other

used

to ensure

cannulated

Nuts

screw can

be

a guide

pin

is

placement.

can be threaded on the end of a or threaded pin, creating a bolt.

Nuts.-Nuts

cortical

screws,

accurate

used

to keep

the

screw

or

pin

from pulling out ofosteopenic bone (Fig 14). Bolts are also used to compress bone, as in the case of the tibia! bolt, which is used for displaced, split fractures of the tibial plateau. These devices have been replaced largely by other techniques of fixation or methods of augmenting screw purchase, such as the use of methyl methacrylate cement.

fractures.

The Herbert screw is a unique type of cannulated screw that is threaded on both ends and does not have a screw head. The threads run in the same direction on each end but have different pitches. The leading end has coarser threads, and the trailing end has finer

September

1991

Wasbers.-Washers heads of screws.

Flat

are used washers

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16.

----

-.

_tateralviewsshowa,iic

--

compression

plate

side ofa femoral

16, 17. (16) Diagram ofa serrated shows how the washer is used to affix soft

tissues

to bone.

washer

on a cancellous

(17)

Radiograph

screw

tissues in an anterior cruciate serrations are not radiopaque

crease

the

distributed

surface and

area are

over

used

shows

a serrated soft ligament repair. The and cannot be seen.

used

which

to prevent

fects

to anchor

the thin

force

pull

830

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out

of the

U

bone,

Slone

can become or break if subjected

is

corti-

et a!

loose, to

in the

bone,

of fracture, removed.

cal bone from splitting. Serrated washers (Figs 16, 17) have spiked edges and are used for affixing avulsed ligaments and for compressing small avulsion or comminuted fractures. The spikes may not be radiopaque, and therefore serrated washers may be impossible to differentiate nadiographically from other washers. Complications-Screws

on the tension

(lateral)

excess loads. Screws that are incorrectly placed can actually displace fracture fragments and prevent or delay healing. Protruding screws can cause symptoms from irritation of the soft tissues adjacent to bone and, in rare instances, may erode into nerves or blood vessels. Screw holes create stress de-

17. Figures washer

placed fracture.

which

especially

can

when

increase

the

the

screws

risk

are

#{149} Plates Plates come in various sizes and shapes, and each can be used in several different ways. Plates are identified by their shape and function.

The

three

basic

compress, neutralize, Compression plates fractures

that

are

stable

plate

functions

and buttress. (Fig 18) are in compression.

are

used

to

for The

plate may be used in combination with lag screws. The shape of the bone and the location of the mechanical axis give some bones, such as the femur, compression (medial cortex) and tension (lateral cortex) sides. A plate placed on the tension side (tension-band plating) absorbs the tensile forces, resulting in dynamic compression of the fracture.

Volume

11

Number

5

Figures

the various wrist.

(20)

19, 20. (19a) AP lengths of screws Radiograph

Neutralization faces from normal ial-loading forces.

view

shows

ofa

chosen small

custom

straight

to optimize straight

plate

purchase

plate

and

plates protect fracture sunbending, rotation, and axA neutralization plate is

shows

five small

Straight variety

maining

clinical

screws

in the

plate

to the bone and on the fracture to both compress

simply

anchor

the

neutralize the loading site. It is possible for a the fracture site and

neutralize the loading forces. Buttress plates support bone that is unstable in compression or axial loading. These plates are used for fractures in which impacted fragments must be elevated to restore the articular surface (eg, distal radius and tibial plateau fractures) A buttress or support plate is then used to hold these elevated frag-

round

holes.

(19b)

in a resection

cortical

ments

often Plates those

often used in combination with lag screws, which are placed separately from the plate or through one of the holes in the plate to provide interfragmentary compression. The replate forces plate

the

in the cortex

screws

in the

used

desired

Lateral arthrodesis

in the

view shows of the

hand.

position.

Their

use

is

supplemented with cancellous screws. can be grouped by shape generally into with straight and special shapes. Plates.-Straight oflengths and application.

on the shaft, to fit complex of straight

holes,

dynamic

plates, Straight

and

They

although surfaces.

types

are

plates:

those

reconstruction with

most

often

used

they can be contoured There are four general

compression

plates

plates come in a depending on the

sizes,

with

round

plates,

tubular

plates. round

holes

(Figs

19,

20) consist of a flat metal strip with a single row of round holes and represent an earlier

.

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a. 21. Diagrams show the plate as they enter the the fragments are beginning toward the center, bringing Figure in

Figure

namic

how

22.

(a)APviewofrwody-

compression

they

the use ofa dynamic compression plate. (a) The screws are placed eccentrically cortex. (b) Screw heads have just reached the beveled edges of the holes, and to move together. (C) When the screws are tightened, the screw head is forced the two fragments together.

are used

plates

shows

to repair

frac-

tures

of the distal radius and ulna. The two lag screws are placed in the ulna outside the plate. (b) Lateral view shows two lag screws across

the ulnar fracture and good chase of the cortical screws the plates.

punaffixing

plate design. They are still used today under certain circumstances. Dynamic compression plates (Figs 21, 22) have unique oval holes with inclined edges. The plates are slightly concave and replace

the original screws are holes with the tapered screw head

round-hole design. When the placed at the outer ends of the oval a special guide and are tightened, contour of the hole forces the toward the center of the hole (Fig

2 1). This moves tive to the bone, careful placement

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the plate for each of the

about screw screws

Volume

1 mm, placed. in the

11

relaWith plate,

Number

5

[o.ooo1)

Figures

23-25.

the thin profile

(23)

Diagram ofa tubular designed to grip a one-third tubular

and curve

(24) Radiograph shows repair a distal fibula fracture. Two cannulated screws are also seen in the medial malleolus.

plate shows cortical bone. plate used to

cancellous (25) Radioplate used on

graph reveals a malleable reconstruction the posterior column of the acetabulum. An osteotomy of the greater trochanter was performed to better visualize the fracture, and two partially threaded cancellous screws with flat washers were used for reattachment. Assorted screws were chosen to affix the plate.

.,

compression at the fracture site can be achieved. In current usage, dynamic compression plate refers to a plate with oval holes. This causes some confusion, since this plate can be used to compress, neutralize, or buttress, depending on its application. Tubular plates are thin and have a concave inner surface that conforms to the curvature ofthe bone surface (Fig 23). They are pliable and easy to contour. They are available in one-half-, one-third-, and one-quarter-round profiles and are used most commonly as neutralization plates or to achieve compression in non-weight-bearing

be achieved centrically

September

bones.

when within

1991

the the

Compression

screws oval

are holes.

placed

.

they lack beveled edges, the effect is similar to that achieved with dynamic compression plates. The one-third tubular plate is commonly used on the distal fibula (Fig 24) and the one-quarter tubular plate on the small bones of the hands and feet. Reconstruction plates (Fig 25) are designed to allow bending, twisting, and contouring to accommodate bones with unusual shapes, such as the acetabulum, distal humerus, and mandible. These plates are thin and very phiable because the edges are scored.

can

cc-

Although

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833

I-

Figure 26. sion device

fracture screws.

Diagrams of an intraoperative in use. (a) A plate is applied

and is attached The compression

opposite

end

of the

compresto span the

to one fragment with device is attached to the

plate

and

to the

bone

with

a sin-

gle screw.

(b) Compression device is tightened, bringing the two fragments together. (C) Screws are placed in the other side of the plate when the fragments are in the proper position. (d) Device is then removed. Site of attachment can be seen as a defect beyond the end of the plate.

F1

%

4

d.

Compression of these straight

also can be obtained with plates by using a compres-

sion

26).

device

(Fig

A plate

is applied

any

to span

the fracture and is anchored to only one side of the fracture with one or more screws. The compression device is then applied to the opposite end of the plate and anchored to the bone with a single screw. The device is tightened, pulling the plate toward the device and compressing the fracture. The remaining holes of the plate are filled with screws, and the compression device is removed. The compression

device,

radiographs; it may

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be

therefore,

is not

seen

however,

the

hole

used

seen

beyond

one

end

of the

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on

the

to attach plate.

plates have a shape that makes them uniquely suited for specific types of intra-articular and juxta-articular fractures. Several special plates are available that are used at the ends of bones. Most of these are buttress-type plates because they provide

SpecialPlates.-Special

support intra-articular

and

prevent and

settling metaphyseal

of comminuted fractures.

These plates often are used in combination with both cancellous and cortical screws because the plate spans both types of bone. T- and L-shaped plates (Figs 27-29) frequently are used to repair tibia! plateau fractures. When seen on profile, they are curved to follow the contour of the proximal tibia. T-shaped plates are also used for fractures of the distal radius (Figs 28, 29), proximal hu-

Volume

11

Number

5

Figures

There (2Th) with

plate

27-29. (27a) AP view shows is a double bend in the buttress Lateral view shows the L-shaped the cancellous screw impinging is used to better accommodate

September

1991

an L-shaped

plate, plate.

plate

used

and two cancellous (28) Radiograph

on the ulna and the distal radius.

causing

to repair a fracture of the proximal tibia. lag screws and four cortical screws are

shows

a T-shaped

a mechanical

erosion.

plate

seen.

on the distal radius, (29) Oblique T-shaped

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merus, and distal tibia. Cloverleaf plates (Fig 30) are a special type of buttress plate designed for use on the medial distal tibia. Their shape can be modified by removing one or more of the “petals” with cutting forceps. The clovenleafend appears rounded on profile.

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Other specially shaped plates include spoon plates (Fig 31), which have a flared end that is rounded and is used primarily on the distal tibia. Y-shaped plates are used to accommodate unusual anatomy such as that encountered in the repair of fractures of the calcaneus (Fig 32). Cobra plates are used for hip arthrodesis and have a widened proximal end that is used for placing multiple screws in

Volume

11

Number

5

33, 34. (33) Radiograph a blade plate used for fixa-

gures

nows tion

of an osteotomy

in the

proxi-

mal femur. Various screws are used to affix the plate (from the top lown): two partially threaded cancellous screws, a malleolar screw, and nine fully threaded cortical screws. (34) Radiograph shows a r blade plate in a commituted fracture of the distal femur. A -

ingle

lag screw

seen

in the distal

with

a flat washer

is

metaphysis.

the pelvis and a straight distal end for attachment to the femur. Condylar blade plates (Figs 33, 34) have a U-shaped blade that is designed to enter cancellous bone. The blade is at a fixed angle with the side plate, which is attached to the proximal or distal femur with cortical screws. This

0 0 0 0 35.

Figure hip

screw

sliding

Diagram the

shows lag

screw,

and

I”

of a dynamic side

plate

a smaller

and

0 0 0 or sliding

type

of plate

is used

primarily

for

frac-

tunes of the proximal or distal femur. The dynamic compression screw system (Figs 35-38) consists of a plate that has a sleeve or barrel at one end, through which a large-diameter lag screw can be placed (Fig 35). The threads of the lag screw are placed in the proximal fragment. The smooth shaft crosses the fracture site and is placed into the barrel of the side plate and held by a compressing

screw.

This

side

plate

is then

fixed

to

barrel,

compressing

screw.

September

1991

Sloneeta!

U

RadioGraphics

U

837

838

U

Radic

r-

-,

40.

I

.

-

41. .

.

:ti.

k

. .

..

.

..

‘

.

,.

.

. . .

,. .

.-7’l’

.‘

,

Figures

40-42.

triple

arthrodesis

view.

(41)

used

in fixation

.

‘.

I

:

.,

tendon.

42a. reveals

Radiograph

of the foot. shows

of a proximal

designed to accommodate of a Stone or table staple patellar

:

(40)

Radiograph

,

..

The barbs

are seen

a stepped

osteotomy

tibial

such shows

(42b)

fixation

Lateral

valgus

staples only or

osteotomy.

shows

all four

in a

in the en face Coventry

staple

The shape

a bone configuration. how it is used to repair view

used

(42a) an

prongs

is

AP view avulsed

of the

sta-

pie.

rr: .

‘r‘

42b.

the

bone

bearing

with and

cortical muscle

screws. forces,

With the

weight-

fracture

is

compressed and the screw can slide down the sleeve as compression is achieved. Thus, duning treatment, the compressing screw may seem to “back out” of the sleeve (Fig 37). The plate and barrel are available in different lengths and angles (range, 90#{176}-150#{176}) so that they

can

be

used

in either

the

distal

or

proxi-

mal femur. This is the most common type of device used for fixation of intertrochanteric and some femoral neck fractures. Many types and brands of hip fixation devices are available. Some of the devices used before the dynamic or sliding hip screw, such as the Jewett nail

(Fig

39),

may

still

Complications.-Plate

vascularity influences

September

of the bone the biologic

1991

be

seen.

fixation alters the beneath the plate and mechanisms by which

the fracture heals. An incorrect technique of plating or premature removal may prevent healing or lead to refracture of the bone. The plates also can fracture. Regardless of size or strength,

bone I

all

does

plates

not

will

eventually

fail

if the

heal.

Staples

staples (Fig 40) are also referred to as bone staples, epiphyseal staples, on fracture staples. They are available with either smooth or barbed surfaces. The barbed surface prevents the staple from backing out of the bone. Stepped osteotomy on Coventry staples (Fig Fixation

41)

have

a stepped

most commonly teotomies. The has four prongs ligaments.

cross

member

and

are

used in proximal tibia! osStone or table staple (Fig 42) and is used to repair avulsed

Sloneeta!

U

RadioGraphics

U

839

43, 44. (43a) AP view shows K wires used The small cross section of the wire minimizes

Figures

bow. protruding

bone

ends,

which

fragments

are

bent

in a fracture

to

prevent

around

injury.

the stem

ofa

#{149} Wires

(44)

femoral

a fracture to

the

are unthreaded

wire

ofvariable

into

bone

segments

thickness.

by placing a drill

bility

when

wires

are

bit. more

often

stabilization

They

the They

used during

wire provide

than

one

wire

to provide the

of extruded

course

tion.

are into

drilled a drill

as if

notational is used.

staK

temporary of an

medial

shows

epicondyle in the ciLateral view shows the wiring used to contain

(43b)

plate.

cerclage

prosthesis.

to the

plate.

K wires

left

in place

may

be cut off beneath the skin, left protruding through the skin where the tip is bent (Fig 43b), or covered with a protective cap to prevent injury. Complications include migration, backing

out,

breaking,

bending,

and

infec-

tion.

opera-

After the fracture is reduced, it is held with K wires until the reduction can be confirmed nadiographically. The final fixation can then be applied, and the K wires are either left in place or removed. If the wire is removed at the end of the procedure, the resultant hole may be seen. K wires can serve as guide pins for the placement of cannulated screws. K wires also are used for fixation of small fragments and for pediatric fractures, such as supracondylar fractures of the elbow and fractures involving the epiphyseal plate (Fig 43a) Because these wires are smooth and have a small cross-sectional area, they can be placed across the epiphyseal plate without .

of the

growth

Radiograph

injury

K wires

it were

to repair trauma

Cerciage Wiring.-Cenclage wiring (Fig 44) refers to the use ofwires placed around the bone to hold fracture fragments. A single on double strand ofwire is placed around the bone, and then the ends are twisted together. The bone fragments are held together by the wires. Metal or plastic bands have been used in the past but have mostly been replaced by other techniques of fixation because they interfene with the periosteal blood supply of the bone. Cenclage wines usually are used in cornbination with other types of fixation devices, such as plates or intramedullary nails, but can be used alone in special situations. Complications

include

fracture

of the

wires;

irritation

of the

adjacent soft tissues, especially by the twisted ends of the wire; problems with fracture healing if the fixation is unstable; bone resorption

bone

840

U

RadioGraphics

U

Slone

et a!

under

formation

the

over

wires;

the

and,

occasionally,

wire.

Volume

11

Number

5

Figures 45-47. (45) chanics of tension-band verse patellar fracture. tional

stability

and

wire

is placed When normal resists the compressive

.

Diagram shows the biomewiring applied to a transTwo K wires provide rota-

prevent

shearing.

Figure-of-eight

on the tension side of the fracture. physiologic load is applied, the wire

tension forces

on the fracture and on the compression

increases side of the

bone. (46a) AP view shows tension-band wiring and K wires used in a fusion of the first metacarpophalangeal joint. (46b) Lateral view shows figureof-eight wire on the tension side. (47) Lateral radiograph shows tension-band wiring used to repair an oiecranon fracture. The figure-of-eight wire passes around the K wires and through a hole in the ulna to resist tension.

Tension Band Wiring.-The tension band technique (Figs 45-47) is used to provide dynamic compression for the treatment of avulsion-type fractures, such as those involving the olecranon and patella, and also for fusion of small joints. Parallel K wines are placed to provide notational stability and reduce shearing forces between the fragments. A figure-of-

(1). Tension with screw

eight

pair

wine

bone.

This

it around

by passing bone and

September

is placed

wire

on

the

side

of the

47).

An

eccentrically

loaded

bone

is sub-

transmitting

compressive

band fixation

of olecranon

forces

to the

bone

wiring also can be used devices, such as in the and

malleolar

re-

fractures.

by passing (Fig 45) on it through a drilled hole in the around one end of the K wires (Figs

both

is anchored

tension

46,

ject to bending stresses, resulting in a tension and compression side. When physiologic forces pull on the bone, the wire carries the tensile force, which prevents separation,

ends

1991

of the

either

K wines

Sloneeta!

U

RadioGraphics

U

841

Figures graph wires shows

48-50.

(48)

AP view

U EXTERNAL External fixation vidual

bone

FIXATION

three

smooth

DEVICES

is a technique

fragments

are

percutaneous wires or external frame. External versatile and allow for ization, or distraction and some devices can time

shows

to improve

the

in which held

mdi-

in place

by

pins attached to an fixation devices are compression, neutralof fracture fragments, even be adjusted over

reduction.

External

fixa-

tion is sometimes used in patients with multipIe injuries because it can be applied rapidly. It is used for fractures associated with severe soft-tissue

mize

injury

the

vation sues,

and for

or contamination,

surgical

trauma,

treatment example,

and

of the in cases

to mini-

to allow

obsen-

overlying ofopen

soft

tis-

fractures,

burns requiring skin grafts, and vascular injunies (1,3,4). External fixation may be used instead of casts or internal fixation in some dinical situations (5). External fixation devices may be used to provide temporary stabilization

and

are

replaced

with

another

device when the soft tissues gun to heal, when the risk of infection or when the condition of the patient fixation

842

U

RadioGraphics

Steinman

shows a smooth Steinman pin used as an intramedullary used for arthrodesis of the metacarpophalangeal joint two Schanz screws used to attach an external fixation

U

Slone

et a!

type

of

have beis less, permits

pins

in a distal

humerus

fracture.

rod in a wrist fusion. Also seen of the thumb. (50) AP view of the device.

(49)

Radio-

are two K distal tibia

additional surgery. In some situations, such as fractures of the distal radius, external fixation may be used as definitive fixation until the fracture heals. External fixation also is used in special cases, such as limb lengthening, arthrodesis, fractures requiring distraction, infected fractures, and nonunions (1,4). There are many different types of external fixation frames that are assembled by the surgeon to meet specific fixation needs. Some frames have bars to connect the pins, others have rings that partially or completely sunround the limb (eg, Ilizarov), and others have a combination of clamps, bars, and rings. External fixation devices usually are classified according to the type of pins and the configunation of the frame. Often only a portion of the fixation device is visible on radiographs, making identification difficult. #{149} Pins Pins nology

can

be smooth is not

exact

on threaded. and

refers

The more

termito

the

name that was originally given to the device than to its function. Steinman pins (Fig 48) are large-caliber wires used for fixation of fractures or as traction pins. They have pointed tips and are cut to the desired length.

Volume

11

Number

5

51.

Figure Knowles

Radiograph

pins

used

shows

to

repair

neck fracture. The pointed that they are self-tapping.

Large Steinman tramedullary pins

are

ens

are

pins fixation

threaded smooth

may be used for in(Fig 49). Some types

and and

function

are

of

as screws;

used

for

oth-

and

are placed

below Unilateral

tissues

and

on

one

thread

threads

in each

major

the fracture or one-half side end

fragment

enter

through

directly at one

(6). pins

a small

into

the

that

engage

Many surgeons now use partially cannulated screws instead of these

pins.

bone.

above

the

soft

incision

They the

have

cortex

and

#{149} Traction Traction is a directional force applied to the extremities with transfixing wires or pins attached to the soft tissues on placed through the metaphysis, perpendicular to the long axis ofbones (1,8). Traction is used for imrnobilizing and reducing fractures, correcting deformities,

and

ment

elevating

#{149} Complications External fixation

that

uncommon.

smooth

cortex.

This

caused

by

increases

shank

reduces the

the

threads stiffness

also

the

engages

soft-tissue

outside and

the strength

the

near

irritation bone of the

pin.

Transfixing pins and wires pass through the entire extremity and are supported on both ends by the fixation or traction frame. Transfixing pins used with bilateral or Hoffmantype devices usually are threaded in the centen of the pin, and ideally the threaded section should be equal to the bone diameter (7). Transfixing pins are also used with the circular-

or

ring-type

external

fixation

devices,

such as the Ilizarov frame. They are more commonly called transfixing wires because they are small in diameter and unthreaded. Many types of pins were developed for treating femoral neck fractures or for pinning slipped

capital

femoral

epiphyses.

These

injuries, ing,

and

extremities

of soft-tissue

a smooth shank that connects with the external fixation frame. These pins are also referred to as Schanz screws (Fig 50). Many of these pins now have threads only at the tip so the

tips indicate

intramedul-

lary fixation, such as the Rush pin. Two types of pins are used with external fixation: unilateral and transfixing pins. Usually two or more pins

Deyerle. threaded

four

a femoral

and, or

injuries

is often therefore,

They cutting

include

out

of the

for

the

treat-

(6).

used

with

complex

complications

are

infection,

loosen-

fixation

pins

not

or

wires, and fracture distraction (1,6). Problems with fracture healing are often related more to the nature of the original injury than to the use of the external fixation device. Pin-track infection is the most common complication and is related to the technique of pin insertion,

care

pin-bone this

interface

site,

and

interface.

of the

pin

Both

increased

and

infection

loosening. Inaccurate pin result in injury to the soft the neurovascular bundle.

stresses can

result

on

the

stress

at

in pin

placement can also tissues, especially

usu-

ally have a smooth shank with a threaded end. The smooth shank crosses the fracture line and allows dynamic compression. These pins include Knowles (Fig 51), Hagie, Guffon, and

September

1991

Slone

et a!

U

RadioGrapbks

U

843

52-55. (52a) AP view shows two Rush mntramedullary pins in a fracture ofthe proximal third of (52b) Lateral view shows the preshaped curved and beveled ends. (53) Radiograph demonstrates Sampson rod used for fixation of a proximal humeral osteoarticular allograft. (There is no entry site. First, the rod is driven into the allograft and then as a unit into the distal humerus.) (54) Composite image shows Figures

the ulna.

Sampson

an ankle

rod

used

shows

in a knee

arthrodesis.

the characteristic

end

(Reproduced,

of the Sampson

U INTRAMEDULLARY FIXATION DEVICES There are many devices designed for intramedullary fixation and many different techniques for their application. Intramedullary devices can be solid or hollow; circular, thangular, or cloverleaf in cross section; and flexible

to extremely

rigid.

They

can

be

placed

in

either reamed or unreamed channels, can be used with or without interlocking screws, and confer different degrees of fixation stability to the fracture. The intramedullary nail can be inserted without opening or exposing the fracture

site.

The

nail

is considered

a load-

sharing device because the central position of the nail allows the bone to carry some of the load. Intramedullary nails are used most cornmonly to treat fractures of the femonal, tibia!, and humenal shafts. The terms rod, nail, andpin have specific biomechanical implications, but clinically they are used interchangeably and often represent

with

permission,

U

RadioGraphics

U

Slone

et a!

reference

9.) (55)

AP view

a of

rod.

the original name of the device (eg, Rush pin, Ender nails, Sampson rod, KUntscher nail). Many early nails were solid and designed to be driven into the bone without reaming (eg, diamond-shaped

term

Hansen-Street

nail).

The

was generally used for intramedullary devices that were driven into reamed or unreamed channels. They are, in a sense, wedged into position, which makes them selfretaining. Some of these nails are stifi being used. A rod was a solid or hollow intramedullary device with a blunt tip that was larger than that of a nail and that was usually placed in reamed channels. Intramedullary pins are nail

smaller,

usually Rods,

solid,

circular

in cross

section,

and

the canal without reaming. a lesser degree-pins neutralize shearing and bending forces but allow axial compression and rotation. Most intramedullary rods and nails used now are hollow, and almost all have a unique cross-sectional pattern designed to reduce or prevent rotation. The hollow designs have either an open on a closed section. They provide stability by an interference fit along the medullary

844

from

a

driven into nails, and-to

canal.

However,

Volume

the

availability

11

Number

and

5

Figures

56-60.

(56a)

Lateral

view

shows

a custom

nail used

in the placement

of a proximal

tibial

osteoar-

ticular allograft with an interlocking screw inserted distally, allowing compression. (56b) AP view shows that the interlocking screw could he missed on a single projection. (57) Radiograph shows a Seidel humeral nail with interlocking screws placed proximally. The distal end can be expanded by turning a screw in the proximal end, which provides some rotational stability. (58) Radiograph depicts a tibial interlocking intramedulIan’ nail in a comminuted fracture of the humerus. The interlocking screws placed at both ends prevent rotation and shortening. (59) Lateral view shows a tibial interlocking intramedullary nail used in large segmental defect. A single cerclage wire can be seen. (60) Radiograph shows a femoral intramedullary nail used in a femoral fracture. The interlocking screws above and below the prevent apposition of the fracture after the fracture has begun to heal. This can be remedied either the upper or lower interlocking screws.

success

of interlocking

most

surgeons

interference

of fractures.

vices

are

quite

cally

apparent,

The

Rush

52).

may

end

prevents

many

the

migration

#{149} Interlocking

differ-

other and

placement

nail. in

is hooked,

facilitates

re-

moval (3). Ender nails arc solid, oval in cross section, and flexible. They were originally developed for the treatment of femoral fractunes, including intertnochanteric and femoral neck fractures. Usually, multiple nails are driven into the medullary canal through drill holes at the end ofthe bone. They are less able to resist rotational and axial loading forces. The Sampson mntramedullary rod (Figs 53-55) (9) is a thick-walled, very rigid rod that

is slightly

to prevent constructive

September

curved

and

has

a fluted

rotation. It is used primarily procedures, such as knee

1991

refers

to the

placement

of acces-

sory pins, screws, or deployable Brooker-Wilhis nail) through the

difficult.

end

Nails

Interlocking

radiographi-

for

KUntscher nails are hollow and cloverin cross section, with a rounded tip and open section, allowing for a press fit (5). leaf

desmall

he

an

pin may be used tubular long bones

is beveled

channels;

for

identification

intramedullary smaller

One

only not

of the

unreamed which

with

making

in fractures (Fig

similar, that

only

intramedullary

a

deses.

made

on

stability

Many

in design

have

to depend

fit to provide

types ences

techniques

reluctant

a patient with interlocking fracture may by removing

They

are

tioned and shortening, tunes.

One

terlocked, tion stability

60).

placed

after

or both fracture

needed

In the

nail

is posi-

are used to prevent rotation particularly in comminuted ends

depending

of the

the

fins (eg, shaft of the

femur,

of the

on and

the

to treat

the

the

nail

type

can

and

amount

the

be

in-

loca-

of fixation

patient

proximal

and frac-

(Figs

56-

interlocking

surface

in rearthno-

Slone

et a!

U

RadioGrapbics

U

845

61, 62.

Figures

(61) Lateral view intramedullary recon-

of a femoral struction

vided (62)

nail

shows

the

for interlocking AP view shows

pro-

a Zickel nail fracture. Several

subtrochanteric

cerclage

slots

screws.

wires

in a

are also seen.

screws can be placed in the subtrochanteric bone or into the femoral head, depending the design of the nail. The locking screws the distal femur and for nails used in the and humerus are usually placed traversing metaphysis.

should

The

engage

Tibial

Static

femoral

interlocking

screws

are

is achieved placed

in both

intramedullary

when

846

U

RadioGraphics

U

Sloneeta!

of malrotation fractures can

terlocking

and shortening in be minimized with in-

techniques.

Technical

with nail insertion fractures, bending, Other complications on irritation

problems

can result or breaking include of soft

too long or one that can occur as a result tal end of a rod that

nails

allowing anterior

in additional of the nail. protrusion into

tissues

by a nod

that

a is

has migrated. Fractures of stress around the disis too short (10).

inter-

ends. nail

The (Figs

60, 61) is a hollow nail with prednilled holes proximally and distally for interlocking screws. The Zickel intramedullary nail (Fig 62) is a solid nail that is very stiff and is used for the treatment of subtrochanteric femoral fractures. The nail has a predrilled hole to accommodate a pin placed into the femoral neck (Smith-Peterson tniflanged pin). #{149} Complications The current techniques ing generally produce

problems unstable

joint

a curved end, the proximal

fixation

screws

or

mntrameduhlary

59) have through

locking

pins

cortices.

interlocking

(Figs 58, placement tibia.

interlocking

both

on for tibia the

U IMPLANT FAILURE #{149} Implant Failure Implant failure is usually

AND

the

nailThe

result

of techni-

cal errors or failure of the bone to heal. Hardware implants are designed to be used for specific indications, and injudicious modifications of these indications can result in failure. Tremendous stress is imparted to internal devices by normal musculoskeletal activities, and this can result in fractures of the implant. Fatigue

fractures

motion

and

repetitive

are

the

result

stress

of excessive and

Volume

occur in to prolonged called the fatigue failure in the imthe elastic will

implants if they are subjected cyclic loading (1 1). This often is race between bone healing and of the implant. Plastic deformity plant results from loads exceeding all

of intramedullary very good results.

REMOVAL

11

Number

5

range of the implant the result of a defect uncommon (5).

(1). Brittle fractures in the implant and

. Implant Removal Implant removal is controversial. plants

should

be

removed

are are

when

imparted

and

principles vices.

of the

U Ideally, the

im-

bone

by the

implant

2.

3.

and

can lead to fractures. Examples include fractunes of the bone just above or below a plate and fractures at the site of screws. Rarely, irnplants can serve as a nidus for infection, harboring organisms that are inaccessible to the immune system. The greatest concern is the long-term effect of the metal on the tissue,

4.

particularly

6.

tion.

This

the risk

risk

of malignant

appears

to be

transformalow

with

tion,

the are This

time

patient usually permits

of recovery,

and

overall

also must be considered. not removed before 1-2 time

for

bone

remodeling

benefit

1991

fixation

de-

orthopedic

and indications. 22.

Clin

Winquist

Complications ed. Philadelphia: Pierce RO Jr.

devices.

and

In: Epp

appliances.

180:15-

SA.

Compli-

CH Jr, ed.

surgery. 2nd 1986; 149-178. of traction, In: Epp

in orthopaedic

Philadelphia:

F.

Green

VH,

use.

1983;

in orthopaedic Lippincott, Complications

casts,

Behrens

Orthop

RA, Frankel of implant

2nd ed. 102. 7.

fixation

1987; 7:685-70 1. Weissman BNW, Sledge CB. Orthopedic radiology. Philadelphia: Saunders, 1986; 33-49. Sisk TD. External fixation: historical review, advantages, disadvantages, complications,

ed. Complications

CH Jr,

surgery.

Lippincott,

1986;

81-

A primer

of fixation devices and 1989; 24 1:5-14. F. General theory and principles of fixation. Chin Orthop 1989; 241:15-

configurations.

Clin

Orthop

8.

Behrens external

9.

10.

Vander Gniend RA. Arthrodesis ofthe knee with intramedullary fixation. Chin Orthop 1983; 181:146-150. Ordway CB. Complications of intramedul-

1 1.

cepts in intramedullary nailing. Orlando, Grune & Stratton, 1985; 165-186. SchatzkerJ. Principles ofstable internal

23.

and

U SUMMARY We have attempted to simplify a complex topic and have discussed the most commonly used types of screws, plates, washers, wires, pins, staples, and intramedullary nods. Ideally, this information will help radiologists better

biomechanical

common

ation ofmodern RadioGraphics

cations

to

Implants years.

the

most

Weissman BN, Reilly DT. Diagnostic imaging evaluation ofthe postoperative patient following musculoskeletal trauma. Radiol Clin NorthAm 1989; 27: 1035-1052. Richardson ML, Kilcoyne RF, Mayo KA, LamontJG, Hastrup W. Radiographic evalu-

plaster

revascularization. Bones also are susceptible to fracture at the site of screws and screw holes, and protection should be provided for at least 6 weeks after implant removal to decrease the risk of nefracture (1,3,5).

September

5.

the

metal alloys now being used, but there is concern. Implant removal is not without risk, as infection, injury to the soft tissues, and nefractune of the bone may occur as a result of irnplant removal. The cost of a second opera-

understand

REFERENCES

1.

is

healed and the hardware is no longer needed. Internal fixation devices alter the normal distribution of stress on the cortex and trabecuiae, resulting in areas of relative strength and weakness. Stress risers are focused areas of increased stress resulting from the altered biomechanics

recognize

hary fracture

fixation.

tion.

In: The

rationale

care.

New York:

In: Sehigson

D, ed.

ofoperative

et a!

F14: ftxa-

fracture 1987; 3-12.

Springer-Verlag,

Slone

Con-

U

RadioGrapbks

U

847