Chapter 47, Posture & Gait

P A R T

V Posture and Gait

Gluteus maximus

Soleus

Chapter 47: Characteristics of Normal Posture and Common Postural Abnormalities Chapter 48: Characteristics of Normal Gait and Factors Influencing It

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P A R T

V The first part of this textbook presents the basic principles needed to understand the mechanics and pathomechanics of the musculoskeletal system and presents the mechanical properties of the individual components of the musculoskeletal system. Most of the text then examines the structural and functional properties of the individual joint complexes in the body. This final portion of the textbook applies this knowledge to the analysis of two intrinsically human functions, erect standing and bipedal locomotion. The goals of this final segment are to: ■

discuss the biomechanical demands of these two functions

■

demonstrate how a basic understanding of the structure and function of the components of the musculoskeletal system leads to the ability to analyze functions that involve many different joint complexes

Patients seek help from rehabilitation experts typically for complaints of pain or difficulty in performing a task rather than with complaints of impairments in specific anatomical structures. Clinicians must be able to observe the activity in question, analyze the biomechanical demands of the activity, and determine what, if any, impairments contribute to the pathomechanics producing the complaints. Examination and evaluation of posture and gait require an understanding of the basic biomechanical principles introduced in the first two chapters of this book and use knowledge of muscle and joint function to explain how an individual produces these characteristic human behaviors. Clinicians who can evaluate posture and gait and can identify impairments that contribute to an abnormal movement pattern will be able to apply these same skills to evaluate and treat any abnormal movement, including activities as diverse as lifting boxcar hitches, performing a grand plié, typing at a computer, or operating a cash register at the local supermarket. Chapter 47 describes the current understanding of “correct” posture and discusses the mechanisms to control the posture. Chapter 48 presents the characteristics of normal locomotion and discusses the factors that influence it.

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CHAPTER

47 Characteristics of Normal Posture and Common Postural Abnormalities NORMAL POSTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .838 Postural Sway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .838 Segmental Alignment in Normal Posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .838 Muscular Control of Normal Posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .846 POSTURAL MALALIGNMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .849 Muscle Imbalances Reported in Postural Malalignments . . . . . . . . . . . . . . . . . . . . .849 SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .850 Posture is the relative position of the parts of the body, usually associated with a static position. Clinicians evaluate posture with the underlying assumptions that abnormal posture contributes to patients’ complaints and that many impairments within the neuromusculoskeletal system are reflected in an individual’s posture. Thus clinical interpretation of an individual’s posture requires blending a description of an individual’s posture with an understanding of the person’s physical condition and complaints. Posture in erect standing is the focus of much clinical attention, but postures in sitting and during activities, such as lifting or assembly line work, also may contribute to musculoskeletal complaints. This chapter focuses on standing posture, but the issues considered to understand erect standing posture are applicable to any other posture as well. It is important to recognize that even seemingly static postures such as erect standing exhibit small, random movements, and typically, humans move in and out of several postures. As a result, assessment of a single posture may be insufficient to understand the link between posture and a patient’s complaints. Analysis of posture is a well-established clinical tradition and forms a basic part of the physical examination for many different health disciplines. Despite the frequency with which such evaluations are carried out, there remains a surprising lack of unanimity in the description of “normal” posture. Although faulty posture has been associated with such diverse complaints as headaches, respiratory and digestive problems, and back pain throughout the centuries, the direct consequences of faulty posture are not well documented. The purposes of this chapter are to describe the current understanding of normal

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posture and to describe some common postural faults. Specifically, the objectives of this chapter are to ■

Describe the alignment of the body in erect standing posture and its variability

■

Discuss the current understanding of the muscles needed to control erect standing posture

■

Describe common postural faults

■

Briefly discuss the purported consequences of postural faults

NORMAL POSTURE Posture is evaluated by examining its stability and also by describing the relative alignment of adjacent limb segments.

Postural Sway Normal erect standing posture is often compared to the movement of an inverted pendulum in which the base is fixed and the pendulum is free to oscillate over the fixed base (Fig. 47.1). Although erect standing appears static to the casual observer, it is characterized by small oscillations in which the body sways anteriorly, posteriorly, and side to side; and the body’s center of mass, approximately located just anterior to the body of the first sacral vertebra, inscribes a small circle within the base of support [6,36]. This normal postural sway in erect standing also is described by the movement of the center of pressure, which is related to, but distinct from, the location of the body’s center of mass [25,42]. The center of pressure locates the center of the distributed pressures under both feet. In contrast, a vertical line through the center of mass locates the center of mass within the entire base of support. The normal sway of the body during quiet standing moves the center of mass and the center of pressure of the body anteriorly and posteriorly up to 7 mm [6,36,42]. Side-to-side excursions of the centers of mass and pressure are only slightly less than those in the anterior–posterior direction [6].

CLINICAL RELEVANCE: ASSESSING STABILITY IN QUIET STANDING Stability in quiet standing is assessed in different populations to better understand why some individuals are at increased risk for falling. Changes in the magnitude or frequency of postural sway determined by the oscillations of either center of pressure or center of mass are reported in healthy elders and in individuals with impairments such as hemiparesis, sensory deficits, and vestibular dysfunctions [6,36,42].

Segmental Alignment in Normal Posture SAGITTAL PLANE ALIGNMENT OF THE BODY IN NORMAL POSTURE Although both ideal posture and normal posture have been described in the clinical literature, the criteria for the

Figure 47.1: Standing posture often is modeled as an inverted pendulum in which the body sways over the fixed feet.

Chapter 47 | CHARACTERISTICS OF NORMAL POSTURE AND COMMON POSTURAL ABNORMALITIES

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TABLE 47.1 Alignment in the Sagittal Plane of Body Landmarks with Respect to the Ankle during Erect Standing Opila et al. [40]a Description of Landmark

Danis [6]b Locationc (cm)

Description of Landmark

Locationc (cm)

Ankle

Lateral malleolus

Calculated joint center

Knee

Lateral epicondyle of femur

5.1

Calculated joint center

4.24
2.14

Hip

Greater trochanter

5.4

Calculated joint center

5.42
2.86

Shoulder

Acromioclavicular joint

3.0

Acromion process

1.89
3.01

Head/neck

Just inferior to the external auditory meatus

5.4

Approximately the atlanto-occipital joint

4.84
4.03

a

Based on 19 unimpaired males and females aged 21 to 43 years. Originally reported with respect to the body’s center of gravity. b Based on 26 unimpaired males and females aged 22 to 88 years. Originally referenced to the ankle joint. c Positive numbers indicate that the landmark is anterior to the ankle joint.

ideal posture remain hypothetical [27,48]. Ideal posture is variously described as the posture that requires the least amount of muscular support, the posture that minimizes the stresses on the joints, or the posture that minimizes the loads in the supporting ligaments and muscles [1,27]. In the absence of a clear understanding of the meaning of the “ideal” posture, careful measurements of the positions assumed by individuals without known musculoskeletal impairments or complaints provide a perspective on the typical, if not ideal, alignment of limb segments. Table 47.1 presents the relative orientation of landmarks in the sagittal plane with respect to the ankle joint from two studies examining the posture of individuals without any known musculoskeletal impairment or complaint [6,40]. Fig. 47.2 presents the relative location of the landmarks with respect to a line through the center of mass, which lies approximately 4 to 6 cm anterior to the ankle joint [6,40]. The two studies report similar relative alignments, and both also agree somewhat with the “ideal posture” described by Kendall et al. [27]. The relatively large standard deviations at the superior landmarks reported by Danis et al. are consistent with the normal postural sway that occurs in quiet standing.

Acromion

Greater trochanter

Trunk and Pelvic Alignment The data presented in Table 47.1 describe the sagittal plane orientation of many body parts in erect standing but provide little information regarding the normal alignment of the spine and pelvis. The adult spine is characterized by a kyphosis in the thoracic and sacral regions in which the curves are convex posteriorly and a lordosis in the cervical and lumbar regions in which the curves are concave posteriorly. At birth, the spine is entirely kyphotic, and consequently, the thoracic and sacral curves are primary curves. Development of head control by approximately 4 months of age induces the development of a cervical lordosis, and a child’s progression to upright standing and bipedal ambulation lead to the formation of the lumbar lordosis. Hence these curves are known as secondary curves and do not develop in the absence of acquisition of the respective skill. The most common means of characterizing the curvatures of the spine use a radiographic method to assess the total

Axis of knee

Ankle joint

Figure 47.2: In erect standing, the body is aligned approximately so that a line through the body’s center of mass passes very close to the ear, slightly anterior to the acromion process of the scapula, close to the greater trochanter, slightly anterior to the knee joint, and anterior to the ankle joint.

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T1

Thoracic Cobb angle T12 L1 Lumbar Cobb angle

L5

Figure 47.3: Cobb angles in the thoracic and lumbar spines are determined radiographically by determining the angles formed between the superior surface of the most superior vertebra of the region and the inferior surface of the most inferior vertebra of the region.

curve of a region. The Cobb angle describes the angle formed by the surfaces of the superior and inferior vertebrae of a spinal region (Fig. 47.3). Mean Cobb angles of 20 to 70 are reported for the lumbar region and 20 to 50 for the thoracic region [16,24,54,57]. These data demonstrate wide disparities and are influenced by the measurement procedures used in each investigation, but also reflect the wide spectrum of spinal curvatures found in a population with no known pathology. Despite the differences reported in the literature, some

Figure 47.4: Surface methods to assess spinal curves. A. Clinicians use inclinometers to measure the curvature of spinal regions from surface palpations. B. Flexible rulers are used to trace the curvature in a spinal region, and the tracing can be quantified mathematically.

Chapter 47 | CHARACTERISTICS OF NORMAL POSTURE AND COMMON POSTURAL ABNORMALITIES

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observation of head posture, assessing head alignment as normal or noting a “mild,” “moderate,” or “severe” forward head. In the presence of an abnormal forward-head posture, the clinician typically initiates an intervention to improve or normalize the posture. However, without operational definitions of the postural deviations, it is difficult to identify changes in posture objectively and to associate any changes in the patient’s complaints with changes in posture. Third-party payers are challenging the value of interventions to alter posture. Well-controlled outcome studies to measure the effectiveness of postural interventions are needed, and these studies demand more precise and more objective measures of postural alignment.

Figure 47.5: Forward-head alignment observed in the clinic is often assessed qualitatively as mild, moderate, or severe.

consistent findings are found. The studies that examine both the thoracic and lumbar curves consistently report a larger lumbar lordosis than thoracic kyphosis [2,16,53]. Also there is general agreement that the peak or apex of the thoracic curve occurs at approximately the midthoracic region, most often at T7, and the apex of the lumbar curve typically is located at either L3 or L4 [2,16,53]. Although the Cobb method is the most frequently used method of quantifying spinal curves, it requires radiographic assessment and is not part of a routine physical examination. Methods to evaluate the spinal curves from surface assessment include the use of inclinometers to define the angulation and flexible rulers to trace the shape of the spinal curvature [15,52,64] (Fig. 47.4). The surface curvature methods yield different measures from radiographic methods and lack normative data defining the range of curvature values found in a healthy population [49]. Based on current knowledge, clinicians lack well-accepted criteria for normal curvatures of the spine in the sagittal plane using surface methods and continue to rely on qualitative assessments of the spinal curves [34]. CLINICAL RELEVANCE: MONITORING CHANGES IN FORWARD-HEAD POSTURE Forward-head posture is associated with a wide range of patient complaints including headaches, vertigo, temporomandibular joint pain, and neck and shoulder pain. A typical physical examination of a patient with any of these complaints includes assessment of postural alignment (Fig. 47.5). Although objective procedures to quantify head position exist [15,21], the clinician often resorts to visual

Orientation of the pelvis is a common postural evaluation performed in conjunction with the assessment of spinal curves. Pelvic alignment is determined from the orientation of the sacrum or by the orientation of pelvic landmarks. Most measurements based on sacral alignment derive from radiographic assessment and report the angle made between a vertical or horizontal reference line and either the superior or posterior surface of the sacrum [24,54] (Fig. 47.6).

α

θ

Figure 47.6: Sacral alignments determined from radiographs typically measure the angle between the superior surface of the sacrum and the horizontal () or an angle between the posterior surface of the sacrum and the vertical ().

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PSIS

θ

ASIS

Figure 47.7: Pelvic alignment from surface landmarks is defined by the angle between a line drawn through the anterior superior iliac spine (ASIS) and the posterior superior iliac spine (PSIS) and the horizontal ().

Orientation of the pelvis from surface landmarks is reported as the angle formed between the horizontal and a line connecting the posterior superior iliac spine with the anterior superior iliac spine [3,14,64] (Fig. 47.7). Typical measurements of sacral and pelvic orientation are reported in Table 47.2. Measurements based on the orientation of the sacrum are larger than those based on the pelvis, and the two measurement procedures show only slight-to-moderate correlations with each other [17]. Clinical literature suggests interdependence among the spinal curves and pelvic alignment [27]. An increased lordosis

TABLE 47.2

purportedly accompanies an increased thoracic kyphosis. Similarly, an anterior pelvic tilt reportedly accompanies an increased lumbar lordosis, while a decreased lumbar lordosis is reportedly associated with a posterior pelvic tilt. There is limited evidence to support these purported relationships, and the existing relationships may be more complex than those reflected by the popular beliefs. The assessment procedures as well as the populations studied appear to affect the strength of the associations reported. A study of 100 adults over the age of 40 years reports a correlation between the thoracic kyphosis measured between T5 and T12 and the total lumbar lordosis but finds no association between the kyphosis in the upper thorax and the lumbar lordosis [16]. A study of 88 adolescents reports no relationship between the thoracic kyphosis from T3 to T12 and the total lumbar lordosis [53]. However, the same study does find correlations between the thoracic kyphosis and the lordosis between L5 and S1. Although additional research is required, these data suggest some association between the thoracic and lumbar curves, but their interdependence may be a function of age and the specific morphology of an individual’s spine. Studies investigating the relationship of pelvic alignment and lumbar lordosis also yield conflicting results. Studies that use radiographic measures consistently demonstrate an association between pelvic tilt as measured by sacral alignment and lumbar lordosis measured by the Cobb method [11,16,53]. These studies demonstrate the expected positive associations between an anterior tilt of the sacrum and an increased lordosis and between posterior tilting and a flattening of the lordosis (Fig. 47.8). Yet studies using surface methods to assess pelvic and spinal alignment in static posture fail to demonstrate any significant correlation between pelvic alignment using pelvic landmarks and the amount of lumbar lordosis using inclinometers or flexible rulers [55,62,63]. In contrast, studies using surface methods to assess the association between pelvic tilt and lumbar position during active movement demonstrate that posterior pelvic rotations do appear to decrease the lumbar lordosis [8,30]. Controversy continues regarding the effect of an active anterior pelvic tilt and the lordosis, with studies showing an increased lordosis with an anterior tilt [7,30] and others showing no change [8].

Measurements of Pelvic Orientation Reported in the Literature Sacral Orientation

Voutsinas and MacEwen [54]

56.5
9.3a

During et al. [11]

40.4
8.8b

Jackson and McManus [24]

50.4
7.7c

ASIS–PSIS Angle

Levine and Whittle [30]

11.3
4.3

Crowell et al. [3]

12.4
4.5

a

Based on the angle made by the superior surface of the sacrum and the horizontal. b Based on the angle made by the posterior surface of the sacrum and the vertical. c Based on the angle made by the superior surface of the sacrum and the horizontal.

Chapter 47 | CHARACTERISTICS OF NORMAL POSTURE AND COMMON POSTURAL ABNORMALITIES

φ φ

A

B

Figure 47.8: An anterior pelvic tilt, which enlarges the angle () formed by the horizontal and a line through the anterior superior iliac spine, is believed to lead to an increased lumbar lordosis (A) and a posterior pelvic tilt in which the angle () decreases and produces a decreased lumbar lordosis (B). Data supporting these beliefs conflict.

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CLINICAL RELEVANCE: IS POSTURE REEDUCATION A USEFUL INTERVENTION STRATEGY FOR A PATIENT WITH LOW BACK PAIN? A patient with low back pain provides a good model to examine the role posture plays in some treatment strategies. The patient reports pain with lumbar extension and in quiet standing and decreased pain with forward bending and sitting. Radiographs demonstrate a spondylolisthesis at L4–L5. Spondylolisthesis is an anterior displacement of one vertebra on the vertebra below, and decreasing the lumbar curve would decrease the forces that tend to increase the displacement. Although the evidence regarding the effect of pelvic alignment on lumbar curvature is conflicting, the clinician chooses to proceed with a program to teach the patient to stand maintaining a posterior pelvic tilt to flatten the lumbar curve. The clinician teaches the patient abdominal strengthening exercises and posterior pelvic tilts. The patient learns to stand while contracting the abdominal muscles and the gluteus maximus, rotating the pelvis posteriorly. The patient reports pain relief. This case provides an example of the commonly reported anecdotal evidence supporting the use of postural education to treat patients’ complaints. Anecdotal evidence by itself, however, is insufficient to determine the effectiveness of the intervention, since many factors besides pelvic alignment may contribute to the reduction in symptoms, including the placebo effect. Without wellcontrolled biomechanical studies to determine the mechanical effects of pelvic alignment on low back posture and without similarly well-controlled effectiveness studies, the role of postural interventions in rehabilitation remains a firmly held belief.

FRONTAL AND TRANSVERSE PLANE ALIGNMENT IN NORMAL ERECT POSTURE The studies reported here present confusing results for clinicians. On the one hand, radiographic data support the generally accepted clinical impression that pelvic alignment and spinal curves are related, but assessments of those relationships using the evaluation procedures typically applied in the clinic reveal weak or absent relationships. What do these conflicts mean to the clinician? Existing evidence appears sufficient to justify the continued belief that pelvic and spinal alignments are interdependent. However, current clinical assessment tools may be influenced enough by soft tissue overlying the skeleton that they do not reflect true bony alignment. The larger question that clinicians and researchers must answer is whether knowing the alignment of the pelvis and the spine, regardless of measurement technique, affects treatment outcomes.

In the frontal and transverse planes, normal posture suggests a right–left symmetry, with the head and vertebral column aligned vertically, hips and shoulders at an even height, the knees exhibiting symmetrical genu valgum within normal limits, and symmetrical placement of the upper and lower extremities in the transverse plane (Fig. 47.9). Scoliosis describes a postural deformity of the vertebral column that is most apparent in the frontal plane but includes both frontal and transverse plane deviations. The curve is named according to its location in the spine and the side of its frontal plane convexity. For example, a right thoracic curve indicates that the curve is located in the thoracic region of the spine and its convexity is on the right side. Scolioses can be either structural or functional. A functional scoliosis results from soft tissue imbalances, but a structural scoliosis includes bony changes as well as soft

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Figure 47.9: Normal alignment of the head and trunk in the frontal plane is characterized by a vertically aligned head and vertebral column, with shoulder, pelvis, hips, and knees at the same height, and the knees and feet exhibiting valgus and subtalar neutral positions within normal limits.

tissue asymmetries. As noted in Chapter 29, idiopathic scoliosis is the most common form of scoliosis. It is a structural scoliosis that is found most frequently in adolescent girls. The curve usually involves at least two spinal regions, and the curves typically are compensated, so that adjacent regions have opposite convexities (Fig. 47.10). A structural scoliosis in the thoracic region is accompanied by a rib hump on the same side as the convexity as a result of the coupled movements of the thoracic spine and their effects on the joints of the ribs. (Chapter 29 reviews the mechanics producing a rib hump.)

Part V | POSTURE AND GAIT

Figure 47.10: A. An individual exhibits a right thoracic left lumbar idiopathic scoliosis. B. When flexed forward, the individual exhibits a rib hump on the right, the side of the thoracic convexity.

A popular theory in rehabilitation suggests that hand dominance induces muscle imbalances that lead to functional scolioses and asymmetry in shoulder and hip alignment [27]. Few objective studies exist that test this hypothesis, but a study of 15 females aged 19 to 21 years reports no statistically significant differences in frontal plane alignment of the scapula between the dominant and nondominant sides, although 11 of 15 subjects demonstrated a lower right shoulder [47]. Horizontal distances between the medial border of the scapula and the vertebral column range from 5 to 9 cm [5,44,47]. Although asymmetry in hip height, or pelvic obliquity, also is allegedly

Chapter 47 | CHARACTERISTICS OF NORMAL POSTURE AND COMMON POSTURAL ABNORMALITIES

associated with hand dominance, there is no known direct evidence to support or refute the contention [27]. The relative alignment of the hip, knee, and foot in the frontal and transverse planes during erect standing is discussed in some detail in the respective chapters dealing with each joint (Chapters 38, 41, and 44, respectively). Figure 47.11 provides a brief review of the characteristic alignments. Because the lower extremities participate in a closed chain during erect standing, lower extremity malalignments may indicate local deformities but also may reflect compensations for more remote malalignments. Findings from a postural assessment lead a clinician to hypothesize underlying impairments. Direct assessment of joints can identify the impairments that contribute to or explain the postural malalignments. A single contracture at either the hip, knee, or ankle may produce the same posture as the individual compensates for the functional limb length discrepancy produced by the contracture (Fig. 47.12). An understanding of the mechanisms contributing to faulty posture requires careful assessment of each joint.

Lateral

A

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CLINICAL RELEVANCE: RELATING POSTURAL FINDINGS TO IMPAIRMENTS OF THE NEUROMUSCULOSKELETAL SYSTEM: A CASE REPORT A 45-year-old male with rheumatoid arthritis was evaluated in the clinic with hip, knee, and foot pain bilaterally. An evaluation of his standing posture revealed a pelvic obliquity, right side higher than left, a slightly plantarflexed right ankle, and increased out-toeing on the left (Fig. 47.13). Many possible impairments could explain these findings, and the clinician’s initial hypotheses included a structural leg length discrepancy and a plantarflexion contracture. A thorough examination of all of the joints of the lower extremities was required before an explanation for the posture emerged. The patient demonstrated bilateral hip

Medial

B

Figure 47.11: In normal alignment, the femoral condyles are aligned in the frontal plane so that the hip is in neutral rotation and the feet exhibit out-toeing of approximately 15–25ⴗ. A. Frontal view. B. Superior view.

Figure 47.12: Flexion contractures of the hip or knee functionally shorten the lower extremity, and a common compensation is plantarflexion to lengthen the limb so that the individual can stand with the pelvis level. A plantarflexion contracture produces a functionally lengthened lower extremity so that an individual with a plantarflexion contracture may stand with a flexed hip and/or knee to restore symmetry and stand with a level pelvis. The resulting postures look approximately the same although the precipitating factors differ.

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flexion contractures. In addition, range of motion assessments revealed that the patient had a complex contracture of the left hip, holding it flexed, laterally rotated, and abducted. The patient stood with an anterior pelvic tilt and increased lordosis, consistent with the hip flexion contractures, but the lateral rotation and abduction contractures on the left effectively shortened the left lower extremity while turning the toes outward. The patient stood with the left hip in obligatory abduction secondary to the abduction contracture, while the right hip was adducted, and consequently, the pelvis was higher on the right. Correction of standing posture required reduction of the contractures of both the left and right hip. Although conservative treatment failed to reduce the contractures on the left, a total hip replacement on the left restored normal joint alignment, and standing posture was immediately improved.

moments to the joints, which are balanced by internal moments supplied by the surrounding muscles and noncontractile connective tissue. The alignment of the body’s center of mass relative to joint axes in quiet standing defines the external moments applied to the joints during erect standing. These external moments then are balanced by either active or passive support to maintain the upright posture against the everpresent gravitational forces tending to press the body into the ground. Examination of the external moments applied to the joints of the lower extremities, trunk, and head by the ground reaction forces helps explain the forces needed to support these joints (Fig. 47.14). Using the data from the studies presented in Table 47.1, the sagittal plane external moments on

Muscular Control of Normal Posture Examples throughout this textbook demonstrate that ground reaction forces and body segment weights apply external

Add Abd

Hip joint axis

Knee axis

Figure 47.13: A patient with an abduction contracture of the left hip stands with the left hip abducted. To maintain an upright posture with the feet close together, the individual adducts the right hip, producing a pelvic obliquity in the frontal plane. The left hip is abducted and the right hip is adducted. The right ankle plantarflexes to equalize limb length.

Ankle joint axis

Figure 47.14: In quiet standing, the ground reaction force applies a dorsiflexion moment at the ankle, extension moments at the knee and hip, and flexion moments on the spine.

Chapter 47 | CHARACTERISTICS OF NORMAL POSTURE AND COMMON POSTURAL ABNORMALITIES

TABLE 47.3

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External Moments Applied to the Joints Based on the Center of Mass Line Opila et al. [40]a External Moment

Danis [6]b External Moment

Ankle

Dorsiflexion

Dorsiflexionc

Knee

Extension

Extension

Hip

Extension

Extension

Back

Flexion

Flexion

Head/neck

Flexion

Approximately zerod

a

Based on 19 unimpaired males and females aged 21 to 43 years. Originally reported with respect to the body’s center of gravity. Based on 26 unimpaired males and females aged 22 to 88 years. Referenced to the ankle joint. c Moment is reported directly in the study but is derived from the available data. d Although the moment arm is 0.03 cm, the standard deviation is almost 4 cm, suggesting that some individuals sustain a flexion moment, and others sustain an extension moment. b

many joints of the body are presented in Table 47.3. Biomechanical analysis of these moments and electromyographic (EMG) studies combine to help explain the mechanisms used to maintain upright posture. Although the external moments described in Table 47.3 are the predominant moments applied during quiet standing, it is important to recall that standing posture is dynamic and that even so-called quiet standing is characterized by oscillations of the body over the fixed feet. Panzer et al. report that during quiet standing, the EMG activity of muscle groups is less than 10% of each group’s activity during a maximum voluntary contraction (MVC) [42]. These investigators also note that many of these muscle groups exhibit sudden, brief activity levels of 30–45% of their MVC and suggest that these sudden bursts may reflect a muscle group’s response to the sway of the body’s center of mass. Because the body’s center of mass generates a dorsiflexion moment on the ankle during quiet standing, the plantar flexor muscles generate a plantarflexion moment to maintain static equilibrium. EMG data demonstrate activity of both the soleus and the gastrocnemius during quiet standing [1,42]. Brief, intermittent, and slight EMG activity is also found in the dorsiflexor muscles, apparently in response to postural sway [1,42]. In contrast to the ankle, the knee exhibits minimal muscle activity during quiet standing [1,42]. In erect posture, the ground reaction force applies an extension moment to the knee allowing it to maintain extension using its passive constraints, including the collateral and anterior cruciate ligaments. Reports of slight electrical activity in the quadriceps muscles (4–7% of MVC) and hamstrings (1% of MVC) are consistent with the use of passive supports to sustain the extended knee during quiet standing [42]. However, like the muscle activity at the ankle, larger brief bursts of activity in the quadriceps and hamstrings muscles may reflect the muscles’ response to sway. Few studies examine activity of the hip musculature during erect posture. The ground reaction force produces an extension moment at the hip, and EMG data reveal activity of the iliacus in quiet standing, exerting a stabilizing flexion

moment [1]. Understanding the role of muscles and ligaments in generating the internal moments needed to balance the external moments exerted by body weight and ground reaction forces allows the clinician to intervene to provide postural stability in the absence of muscular support.

CLINICAL RELEVANCE: MAINTAINING ERECT POSTURE IN THE PRESENCE OF MUSCLE WEAKNESS: A PATIENT WITH PARAPLEGIA A patient with a spinal cord injury resulting in loss of muscle function from the level of L2 is beginning rehabilitation. Functional goals include standing for stimulation of bone growth and limited ambulation. Weakness secondary to the spinal cord injury begins at the hip flexors and extends throughout the rest of the lower extremities. To teach the individual safe and efficient standing, the clinician uses an understanding of the effects of external moments on the joints of the lower extremities and a recognition of the passive structures that are available to support the joints. The individual lacks muscular support at the hip, knee, and ankle, but the astute clinician knows that the hip possesses strong anterior ligaments, the iliofemoral, pubofemoral, and ischiofemoral ligaments. By maintaining the hip in hyperextension, the individual can “hang on” these anterior ligaments, even in the absence of the hip flexors. Similarly, the knee normally maintains extension in erect standing without muscular support, since the body’s center of mass falls anterior to the knee joint and exerts an extension moment on the knee. As long as the knee remains extended, no additional muscular support is needed. Thus the individual can stand in hip and knee hyperextension using passive supports at these joints. Stable erect posture requires that the body’s center of mass remain over the base of support. To maintain hip and knee hyperextension while keeping the body’s center of mass over the base of support, the individual’s ankles assume a dorsiflexed position, and the ground reaction force

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applies an external dorsiflexion moment (Fig. 47.15). With no muscle support at the ankle, the individual with weakness from the hips distally requires external support from an orthosis to exert a plantarflexion moment at the ankle, balancing the external dorsiflexion moment. Thus the individual can stand with minimal external support to stabilize the lower extremity by using the external moments generated by the ground reaction force to apply external moments at the knee and hip that can be balanced by passive joint structures. For the individual described in this case to stand with minimal external support, he or she must be able to assume a position of hip and knee hyperextension. Flexion contractures at the hips or knees or plantarflexion contractures at the ankle produce disastrous results, preventing the individual from positioning the joints to use passive supports (Fig. 47.16).

A

B

Figure 47.16: Effect of sagittal plane contractures on standing posture and the external moments applied to the hip, knees, and ankles. A. Flexion contractures at either the hip or knee cause an individual to stand in a flexed position at both the hips and knees, generating external flexion moments at both joints. Consequently, the individual is unable to use the passive supports at the hip and knee joints. B. Plantarflexion contractures at the ankles prevent an individual from moving the center of mass over the base of support while still maintaining hip and knee hyperextension. To relocate the center of mass over the base of support, the patient flexes the hip joints, thus requiring muscular support to support the hip joints.

Figure 47.15: Standing posture of an individual with weakness at the hip, knees, and ankles. By hyperextending the hip joints, the individual uses the passive restraint of the anterior ligaments of the hip joint to support the hip. Hyperextension of the knee increases the extension moment at the knee that is supported by passive structures of the knee. To maintain hyperextension of the hip and knees while keeping the center of mass over the base of support, the ankles dorsiflex, producing a dorsiflexion moment that is withstood by an externally applied plantarflexion moment using an orthotic device.

The weight of the trunk exerts an external flexion moment on the back, requiring an extension moment to maintain erect posture. EMG data show low-level activity of the erector spinae and multifidus with intermittent bursts of increased activity [1,42,56]. The cervical region also sustains an external flexion moment because the head’s center of mass is anterior to the joints of the cervical spine. Active contraction of cervical extensors maintains upright posture of the head and neck, but as in the trunk, EMG data reveal that only slight activity is required to hold the head erect. Although few studies examine activity in the cervical muscles during quiet standing, data show activity in the semispinalis muscles with no activity in the splenius muscles [51].

Chapter 47 | CHARACTERISTICS OF NORMAL POSTURE AND COMMON POSTURAL ABNORMALITIES

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The role of the abdominal muscles during quiet standing continues to be debated. EMG studies of the abdominal muscles identify activity, particularly in the internal oblique muscle, with some activity in the external oblique muscle during quiet standing [1,12,43,46]. Yet studies that investigate the association between abdominal muscle strength as measured by leg-lowering maneuvers and postural alignment of the pelvis report either no association [55] or weak associations in females and no association in males [63]. The leg-lowering exercise recruits the rectus abdominis more than the oblique abdominal muscles in most individuals and, consequently, may not reflect the ability of the oblique abdominal muscles to participate in postural support [43]. Chapter 34 discusses the role of the abdominal muscles in stabilizing the spine. The data presented here suggest that the oblique abdominal muscles are important in erect posture, although their role may be to function with the transversus abdominis muscle to stabilize the spine rather than to position the pelvis. The role played by muscles to maintain shoulder position during quiet standing also lacks definitive conclusions. Inman et al. demonstrate active contraction of the levator scapulae along with the upper trapezius and upper portion of the serratus anterior muscles in quiet standing, suggesting that these muscles are providing upward support for the shoulder girdle and upper extremity [23]. However, Johnson et al. note that only the levator scapulae and the rhomboid major and minor muscles can directly suspend the scapula [26]. EMG studies show that in the presence of voluntary relaxation of the upper trapezius in quiet standing, there is an increase in EMG activity of the two rhomboid muscles but a decrease in activity in the levator scapulae [41]. These data support the notion that the rhomboid muscles can and do support the upright position of the shoulder girdle, at least under certain circumstances. Whether the levator scapulae contributes additional support remains debatable.

[21,27]. Complaints attributed to postural deviations of the head and spine include circulatory, respiratory, digestive, and excretory dysfunctions; headaches; backaches; depression; and a generalized increased susceptibility to disease [4,21,38,39]. Pain in the back and lower extremities also is attributed to abnormal alignment in the hips, knees, and feet [10,28,29,32,59]. Despite the presumption of associations between postural abnormalities and patients’ complaints, studies examining these associations vary in their findings. Correlations between the incidence of reported head, neck, and shoulder pain are reported in people with forward head, rounded shoulders, and increased thoracic kyphoses [21]. Studies investigating the association between low back postural deviations and low back pain draw variable conclusions, with some reporting little or no difference in posture between those with and without low back pain [7,11,62], and others finding differences between the two groups [24]. Malalignments of the patellofemoral joint are associated with a variety of pain syndromes at the knee [22,35,45]. Considerably more research is required to determine the role that postural abnormalities play in musculoskeletal complaints and to determine the effectiveness of treatments directed toward improving posture to reduce pain. Typical postural deviations are listed and defined in Tables 47.4 and 47.5. These postural abnormalities are presumed to produce excessive or abnormally located stresses (force/area) on joint surfaces or to contribute to altered muscle mechanics by putting some muscles on slack while stretching others [27]. Although evidence supports these effects in some cases, evidence is lacking for others [9,29,32]. Determining the role posture plays in the pathomechanics of musculoskeletal disorders requires continued research in basic anatomy and biomechanics, as well as well-controlled outcome studies examining the effectiveness of treatments directed toward posture reeducation.

POSTURAL MALALIGNMENTS

Muscle Imbalances Reported in Postural Malalignments

Health care providers evaluate posture on the premise that postural malalignments contribute to altered joint and muscle mechanics, producing impairments that lead to pain TABLE 47.4

A commonly held clinical perception is that postural malalignments produce adaptive changes in the muscles surrounding

Common Postural Abnormalities in the Sagittal Plane

Postural Deviation

Description

Forward head

The mastoid process lies anterior to the body of C7

Forward shoulders

The acromion process lies anterior to the body of C7, or the scapula tilts anteriorly

Excessive/flattened thoracic kyphosis

The sagittal plane curve of the thorax is excessive or inadequate

Excessive/flattened lumbar lordosis

The sagittal plane curve of the lumbar spine is excessive or inadequate

Anterior/posterior pelvic tilt

The angle made by a line through the ASIS and PSIS and the horizontal increases/decreases from an angle of approximately 10–15

Forward/backward translation of the pelvis

Determined by the location of the greater trochanter with respect to the vertical line through the center of mass, which in normal alignment passes approximately through the trochanter

Genu recurvatum

Angle between the mechanical axes of the leg and thigh in the sagittal plane is greater than 0

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TABLE 47.5

Part V | POSTURE AND GAIT

Common Postural Abnormalities in the Frontal and Transverse Planes

Postural Deviation

Description

Head tilt

The line through the center of the head deviates from the midsagittal plane

Asymmetrical shoulder height

Measured by the height of the acromions or the inferior angles of the scapulae

Scoliosis

Frontal plane deviation of the vertebral column as assessed by the spinous processes

Pelvic obliquity

Asymmetrical height of the pelvis as measured by the iliac crests

Asymmetrical hip height

Measured by the height of the greater trochanters or gluteal folds

Genu varum/valgus

Angle between the mechanical axes of the leg and thigh in the frontal plane

Foot pronation/supination

Indicated by several different measures including (1) the frontal plane alignment of the heel and leg, (2) the height of the navicular relative to the medial malleolus and the head of the first metatarsal, and (3) the subtalar neutral position

In-toeing/out-toeing

The angle between the long axis of the foot and the malleoli is less than/greater than approximately 20

the malaligned joints. Specifically, it is believed that muscles on one side of the joint are held in a lengthened position and the antagonistic muscles are maintained in a shortened position. Clinicians also suggest that these length changes produce joint impairments including weakness and limited range of motion that contribute to a patient’s complaints. Although these hypotheses are logical and may still prove true, studies to date have failed to identify clear associations between malalignments and joint impairments [9,37]. As noted in Chapter 4, studies in animals demonstrate that prolonged length changes in muscles produce structural changes in muscle, although those changes depend upon many factors besides length. These additional mitigating factors include age, fiber arrangement within the muscles, and fiber type within the muscle [31,33]. In general, prolonged stretch of a muscle induces protein synthesis and the production of additional sarcomeres [18,19,50,58,60]. The lengthened muscle hypertrophies, and as a result, peak contractile force increases with prolonged stretch [31,33]. The structural remodeling that accompanies prolonged lengthening appears to maintain the muscle’s original length–tension relationship so that, although the muscle has a larger peak torque, it generates the peak torque at a different joint position. The clinical literature describes stretch weakness in which a muscle that has been held in a stretched position long enough to remodel appears weak when tested in the traditional test position [20,27]. For example, at the shoulder, stretch weakness suggests that a posture characterized by rounded shoulders applies a prolonged stretch to the middle trapezius, which undergoes the structural adaptations that lead to weakness when assessed in the traditional manual muscle test position. Although the changes described here are logical and plausible, they remain unproved. Animal studies examining prolonged shortening reveal that shortening produced by immobilization appears to accelerate atrophy, and muscles demonstrate a loss of sarcomeres [18,50,60]. Studies examining the effect of prolonged length changes in muscle reveal that the relationship between muscle length and muscle performance is complex, requiring

independent investigation of the relationship with each muscle. The complexity of the association helps explain the absence of clearly defined associations. Attempts to confirm the expected muscle impairments with postural abnormalities have failed to yield clear relationships. Individuals with idiopathic scoliosis exhibit atrophy of the muscles of the posterior thorax, particularly on the concave side, and a higher percentage of type I muscle fibers than normal on the convex side of the deformity [13,61,65]. The muscles of the thorax on the concave side of the curve are likely shortened, while those on the convex side are lengthened; yet both muscle groups exhibit atrophy. Although this atrophy may precede the development of the scoliosis, the expected adaptive changes with prolonged lengthening apparently are lacking. Similarly, attempts to relate scapular alignment and muscle performance fail to reveal associations [9]. However, the scapula moves in a complex, three-dimensional way, and studies so far may not accurately reflect the effects of scapular malalignment on muscle length. These data demonstrate the need for careful anatomical, biomechanical, and clinical studies to identify and explain any detrimental effects of postural malalignment.

SUMMARY This chapter describes the relative alignment of body segments identified in healthy adults during quiet standing. In the absence of a validated description of “ideal posture,” the documented alignments provide clinicians with a view of the variability of alignments found in individuals without musculoskeletal complaints. Although individuals demonstrate a wide spectrum of alignments, the overall image of upright posture shows a head well balanced over the pelvis, which in turn is well balanced over the feet. Using these alignments, the chapter also demonstrates the external moments applied to the joints of the lower extremities and trunk during upright standing. The external moments are balanced by internal moments generated by muscle contractions and noncontractile

Chapter 47 | CHARACTERISTICS OF NORMAL POSTURE AND COMMON POSTURAL ABNORMALITIES

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