chapter 47, posture & gait

Posture and Gait

VP A R T

835

Chapter 47: Characteristics of Normal Posture and Common Postural

Abnormalities

Chapter 48: Characteristics of Normal Gait and Factors Influencing It

Soleus

Gluteusmaximus

VP A R T

The first part of this textbook presents the basic principles needed to understand the

mechanics and pathomechanics of the musculoskeletal system and presents the me-

chanical 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 knowl-

edge 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 dif-

ficulty in performing a task rather than with complaints of impairments in specific

anatomical structures. Clinicians must be able to observe the activity in question, an-

alyze the biomechanical demands of the activity, and determine what, if any, impair-

ments 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 im-

pairments 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 nor-

mal locomotion and discusses the factors that influence it.

836

Characteristics of NormalPosture and CommonPostural 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 pos-

ture contributes to patients’ complaints and that many impairments within the neuro-

musculoskeletal 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 muscu-

loskeletal 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 im-

portant 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 docu-

mented. The purposes of this chapter are to describe the current understanding of normal

47C H A P T E R

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838 Part V | POSTURE AND GAIT

NORMAL POSTURE

Posture is evaluated by examining its stability and also by de-scribing the relative alignment of adjacent limb segments.

Postural SwayNormal erect standing posture is often compared to themovement of an inverted pendulum in which the base is fixedand the pendulum is free to oscillate over the fixed base(Fig. 47.1). Although erect standing appears static to the ca-sual observer, it is characterized by small oscillations in whichthe body sways anteriorly, posteriorly, and side to side; andthe body’s center of mass, approximately located just ante-rior to the body of the first sacral vertebra, inscribes a smallcircle within the base of support [6,36]. This normal pos-tural sway in erect standing also is described by the move-ment of the center of pressure, which is related to, butdistinct from, the location of the body’s center of mass[25,42]. The center of pressure locates the center of the dis-tributed pressures under both feet. In contrast, a vertical linethrough the center of mass locates the center of mass withinthe entire base of support. The normal sway of the bodyduring quiet standing moves the center of mass and the cen-ter of pressure of the body anteriorly and posteriorly up to7 mm [6,36,42]. Side-to-side excursions of the centers ofmass and pressure are only slightly less than those in theanterior–posterior direction [6].

CLINICAL RELEVANCE: ASSESSING STABILITY INQUIET STANDINGStability in quiet standing is assessed in different popula-tions to better understand why some individuals are atincreased risk for falling. Changes in the magnitude or fre-quency of postural sway determined by the oscillations ofeither center of pressure or center of mass are reported inhealthy elders and in individuals with impairments suchas hemiparesis, sensory deficits, and vestibular dysfunc-tions [6,36,42].

Segmental Alignment inNormal PostureSAGITTAL PLANE ALIGNMENT OF THEBODY IN NORMAL POSTURE

Although both ideal posture and normal posture havebeen described in the clinical literature, the criteria for the

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

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

839Chapter 47 | CHARACTERISTICS OF NORMAL POSTURE AND COMMON POSTURAL ABNORMALITIES

ideal posture remain hypothetical [27,48]. Ideal posture is var-iously described as the posture that requires the least amountof muscular support, the posture that minimizes the stresseson the joints, or the posture that minimizes the loads in thesupporting ligaments and muscles [1,27]. In the absence of aclear understanding of the meaning of the “ideal” posture,careful measurements of the positions assumed by individualswithout known musculoskeletal impairments or complaintsprovide a perspective on the typical, if not ideal, alignmentof limb segments.

Table 47.1 presents the relative orientation of landmarksin the sagittal plane with respect to the ankle joint from twostudies examining the posture of individuals without anyknown musculoskeletal impairment or complaint [6,40]. Fig.47.2 presents the relative location of the landmarks with re-spect to a line through the center of mass, which lies ap-proximately 4 to 6 cm anterior to the ankle joint [6,40]. Thetwo studies report similar relative alignments, and both alsoagree somewhat with the “ideal posture” described by Kendallet al. [27]. The relatively large standard deviations at the su-perior landmarks reported by Danis et al. are consistent withthe normal postural sway that occurs in quiet standing.

Trunk and Pelvic Alignment

The data presented in Table 47.1 describe the sagittal planeorientation of many body parts in erect standing but providelittle information regarding the normal alignment of the spineand pelvis. The adult spine is characterized by a kyphosis inthe thoracic and sacral regions in which the curves are con-vex posteriorly and a lordosis in the cervical and lumbar re-gions in which the curves are concave posteriorly. At birth,the spine is entirely kyphotic, and consequently, the thoracicand sacral curves are primary curves. Development of headcontrol by approximately 4 months of age induces the devel-opment of a cervical lordosis, and a child’s progression to up-right standing and bipedal ambulation lead to the formationof the lumbar lordosis. Hence these curves are known as sec-ondary curves and do not develop in the absence of acqui-sition of the respective skill.

The most common means of characterizing the curvaturesof the spine use a radiographic method to assess the total

TABLE 47.1 Alignment in the Sagittal Plane of Body Landmarks with Respect to the Ankleduring Erect Standing

Opila et al. [40]a Danis [6]b

Description of Landmark 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 � 4.03a 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.

Acromion

Greatertrochanter

Axis ofknee

Anklejoint

Figure 47.2: In erect standing, the body is aligned approximatelyso that a line through the body’s center of mass passes veryclose to the ear, slightly anterior to the acromion process of thescapula, close to the greater trochanter, slightly anterior to theknee joint, and anterior to the ankle joint.


curve of a region. The Cobb angle describes the angle formedby the surfaces of the superior and inferior vertebrae ofa spinal region (Fig. 47.3). Mean Cobb angles of 20 to 70� arereported for the lumbar region and 20 to 50� for the thoracicregion [16,24,54,57]. These data demonstrate wide dispari-ties and are influenced by the measurement procedures usedin each investigation, but also reflect the wide spectrum ofspinal curvatures found in a population with no known pathol-ogy. Despite the differences reported in the literature, some

LumbarCobb angle

ThoracicCobb angle

T1

T12

L1

L5

Figure 47.3: Cobb angles in the thoracic and lumbar spines aredetermined radiographically by determining the angles formedbetween the superior surface of the most superior vertebra ofthe region and the inferior surface of the most inferior vertebraof the region.

Figure 47.4: Surface methods to assess spinal curves. A. Cliniciansuse inclinometers to measure the curvature of spinal regionsfrom surface palpations. B. Flexible rulers are used to trace thecurvature in a spinal region, and the tracing can be quantifiedmathematically.


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

θ

α

Figure 47.6: Sacral alignments determined from radiographstypically measure the angle between the superior surface of thesacrum and the horizontal (�) or an angle between the posteriorsurface of the sacrum and the vertical (�).

consistent findings are found. The studies that examine boththe thoracic and lumbar curves consistently report a largerlumbar lordosis than thoracic kyphosis [2,16,53]. Also thereis general agreement that the peak or apex of the thoraciccurve occurs at approximately the midthoracic region, mostoften at T7, and the apex of the lumbar curve typically islocated at either L3 or L4 [2,16,53].

Although the Cobb method is the most frequently usedmethod of quantifying spinal curves, it requires radiographicassessment and is not part of a routine physical examination.Methods to evaluate the spinal curves from surface assessmentinclude the use of inclinometers to define the angulation andflexible rulers to trace the shape of the spinal curvature[15,52,64] (Fig. 47.4). The surface curvature methods yielddifferent measures from radiographic methods and lack nor-mative data defining the range of curvature values found in ahealthy population [49]. Based on current knowledge, clini-cians lack well-accepted criteria for normal curvatures of thespine in the sagittal plane using surface methods and continueto rely on qualitative assessments of the spinal curves [34].

CLINICAL RELEVANCE: MONITORING CHANGES INFORWARD-HEAD POSTUREForward-head posture is associated with a wide range ofpatient complaints including headaches, vertigo, temporo-mandibular joint pain, and neck and shoulder pain. A typ-ical physical examination of a patient with any of thesecomplaints includes assessment of postural alignment(Fig. 47.5). Although objective procedures to quantify headposition exist [15,21], the clinician often resorts to visual

observation of head posture, assessing head alignment asnormal or noting a “mild,” “moderate,” or “severe” forwardhead. In the presence of an abnormal forward-head pos-ture, the clinician typically initiates an intervention toimprove or normalize the posture. However, without oper-ational definitions of the postural deviations, it is difficultto identify changes in posture objectively and to associateany changes in the patient’s complaints with changes inposture. Third-party payers are challenging the value of in-terventions to alter posture. Well-controlled outcome stud-ies to measure the effectiveness of postural interventionsare needed, and these studies demand more precise andmore objective measures of postural alignment.

Orientation of the pelvis is a common postural evaluationperformed in conjunction with the assessment of spinalcurves. Pelvic alignment is determined from the orientationof the sacrum or by the orientation of pelvic landmarks. Mostmeasurements based on sacral alignment derive from radi-ographic assessment and report the angle made betweena vertical or horizontal reference line and either the supe-rior or posterior surface of the sacrum [24,54] (Fig. 47.6).


Orientation of the pelvis from surface landmarks is reportedas the angle formed between the horizontal and a line con-necting the posterior superior iliac spine with the anteriorsuperior iliac spine [3,14,64] (Fig. 47.7). Typical measure-ments of sacral and pelvic orientation are reported in Table47.2. Measurements based on the orientation of the sacrumare larger than those based on the pelvis, and the two meas-urement procedures show only slight-to-moderate correla-tions with each other [17].

Clinical literature suggests interdependence among thespinal curves and pelvic alignment [27]. An increased lordosis

θ

ASIS

PSIS

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

TABLE 47.2 Measurements of Pelvic Orientation Reported in the Literature

Sacral Orientation ASIS–PSIS Angle

Voutsinas and MacEwen [54] 56.5 � 9.3a

During et al. [11] 40.4 � 8.8b

Jackson and McManus [24] 50.4 � 7.7c

Levine and Whittle [30] 11.3 � 4.3

Crowell et al. [3] 12.4 � 4.5a 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.

purportedly accompanies an increased thoracic kyphosis.Similarly, an anterior pelvic tilt reportedly accompanies an in-creased lumbar lordosis, while a decreased lumbar lordosisis reportedly associated with a posterior pelvic tilt. Thereis limited evidence to support these purported relationships,and the existing relationships may be more complex thanthose reflected by the popular beliefs. The assessment pro-cedures as well as the populations studied appear to affectthe strength of the associations reported. A study of 100 adultsover the age of 40 years reports a correlation between thethoracic kyphosis measured between T5 and T12 and the totallumbar lordosis but finds no association between the kypho-sis in the upper thorax and the lumbar lordosis [16]. A studyof 88 adolescents reports no relationship between the tho-racic kyphosis from T3 to T12 and the total lumbar lordosis[53]. However, the same study does find correlations betweenthe thoracic kyphosis and the lordosis between L5 and S1.Although additional research is required, these data suggestsome association between the thoracic and lumbar curves, buttheir interdependence may be a function of age and the spe-cific morphology of an individual’s spine.

Studies investigating the relationship of pelvic alignmentand lumbar lordosis also yield conflicting results. Studies thatuse radiographic measures consistently demonstrate an asso-ciation between pelvic tilt as measured by sacral alignmentand lumbar lordosis measured by the Cobb method[11,16,53]. These studies demonstrate the expected positiveassociations between an anterior tilt of the sacrum and an in-creased lordosis and between posterior tilting and a flatteningof the lordosis (Fig. 47.8). Yet studies using surface methodsto assess pelvic and spinal alignment in static posture fail todemonstrate any significant correlation between pelvic align-ment using pelvic landmarks and the amount of lumbarlordosis using inclinometers or flexible rulers [55,62,63]. Incontrast, studies using surface methods to assess the associa-tion between pelvic tilt and lumbar position during activemovement demonstrate that posterior pelvic rotations doappear to decrease the lumbar lordosis [8,30]. Controversycontinues regarding the effect of an active anterior pelvic tiltand the lordosis, with studies showing an increased lordosiswith an anterior tilt [7,30] and others showing no change [8].


The studies reported here present confusing results forclinicians. On the one hand, radiographic data support thegenerally accepted clinical impression that pelvic alignmentand spinal curves are related, but assessments of those rela-tionships using the evaluation procedures typically applied inthe clinic reveal weak or absent relationships. What do theseconflicts mean to the clinician? Existing evidence appears suf-ficient to justify the continued belief that pelvic and spinalalignments are interdependent. However, current clinicalassessment tools may be influenced enough by soft tissueoverlying the skeleton that they do not reflect true bonyalignment. The larger question that clinicians and researchersmust answer is whether knowing the alignment of the pelvisand the spine, regardless of measurement technique, affectstreatment outcomes.

CLINICAL RELEVANCE: IS POSTURE REEDUCATION AUSEFUL INTERVENTION STRATEGY FOR A PATIENTWITH LOW BACK PAIN?A patient with low back pain provides a good model toexamine the role posture plays in some treatment strate-gies. The patient reports pain with lumbar extensionand in quiet standing and decreased pain with forwardbending and sitting. Radiographs demonstrate a spondy-lolisthesis at L4–L5. Spondylolisthesis is an anterior dis-placement of one vertebra on the vertebra below, anddecreasing the lumbar curve would decrease the forcesthat tend to increase the displacement. Although the ev-idence regarding the effect of pelvic alignment on lumbarcurvature is conflicting, the clinician chooses to proceedwith a program to teach the patient to stand maintaininga posterior pelvic tilt to flatten the lumbar curve. Theclinician teaches the patient abdominal strengtheningexercises and posterior pelvic tilts. The patient learns tostand while contracting the abdominal muscles and thegluteus maximus, rotating the pelvis posteriorly. The pa-tient reports pain relief.

This case provides an example of the commonly re-ported anecdotal evidence supporting the use of posturaleducation to treat patients’ complaints. Anecdotal evi-dence by itself, however, is insufficient to determine theeffectiveness of the intervention, since many factors be-sides pelvic alignment may contribute to the reductionin symptoms, including the placebo effect. Without well-controlled biomechanical studies to determine the me-chanical effects of pelvic alignment on low back postureand without similarly well-controlled effectiveness stud-ies, the role of postural interventions in rehabilitationremains a firmly held belief.

FRONTAL AND TRANSVERSE PLANE ALIGNMENT INNORMAL ERECT POSTURE

In the frontal and transverse planes, normal posture suggestsa right–left symmetry, with the head and vertebral columnaligned vertically, hips and shoulders at an even height, theknees exhibiting symmetrical genu valgum within normallimits, and symmetrical placement of the upper and lower ex-tremities in the transverse plane (Fig. 47.9). Scoliosis de-scribes a postural deformity of the vertebral column that ismost apparent in the frontal plane but includes both frontaland transverse plane deviations. The curve is named accord-ing to its location in the spine and the side of its frontal planeconvexity. For example, a right thoracic curve indicates thatthe curve is located in the thoracic region of the spine and itsconvexity is on the right side.

Scolioses can be either structural or functional. A func-tional scoliosis results from soft tissue imbalances, but astructural scoliosis includes bony changes as well as soft

φ

φ

A B

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


tissue asymmetries. As noted in Chapter 29, idiopathicscoliosis is the most common form of scoliosis. It is a struc-tural scoliosis that is found most frequently in adolescent girls.The curve usually involves at least two spinal regions, and thecurves typically are compensated, so that adjacent regionshave opposite convexities (Fig. 47.10). A structural scoliosisin the thoracic region is accompanied by a rib hump on thesame side as the convexity as a result of the coupled move-ments of the thoracic spine and their effects on the joints ofthe ribs. (Chapter 29 reviews the mechanics producing a ribhump.)

A popular theory in rehabilitation suggests that hand dom-inance induces muscle imbalances that lead to functionalscolioses and asymmetry in shoulder and hip alignment [27].Few objective studies exist that test this hypothesis, but a studyof 15 females aged 19 to 21 years reports no statistically sig-nificant differences in frontal plane alignment of the scapulabetween the dominant and nondominant sides, although 11 of15 subjects demonstrated a lower right shoulder [47]. Hori-zontal distances between the medial border of the scapula andthe vertebral column range from 5 to 9 cm [5,44,47]. Althoughasymmetry in hip height, or pelvic obliquity, also is allegedly

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

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


associated with hand dominance, there is no known directevidence to support or refute the contention [27].

The relative alignment of the hip, knee, and foot in thefrontal and transverse planes during erect standing is dis-cussed in some detail in the respective chapters dealing witheach joint (Chapters 38, 41, and 44, respectively). Figure47.11 provides a brief review of the characteristic alignments.Because the lower extremities participate in a closed chainduring erect standing, lower extremity malalignments mayindicate local deformities but also may reflect compensa-tions for more remote malalignments. Findings from a pos-tural assessment lead a clinician to hypothesize underlyingimpairments. Direct assessment of joints can identify theimpairments that contribute to or explain the posturalmalalignments. A single contracture at either the hip, knee,or ankle may produce the same posture as the individual com-pensates for the functional limb length discrepancy producedby the contracture (Fig. 47.12). An understanding of themechanisms contributing to faulty posture requires carefulassessment of each joint.

CLINICAL RELEVANCE: RELATING POSTURAL FINDINGS TOIMPAIRMENTS OF THE NEUROMUSCULOSKELETALSYSTEM: A CASE REPORTA 45-year-old male with rheumatoid arthritis was evaluatedin the clinic with hip, knee, and foot pain bilaterally. Anevaluation of his standing posture revealed a pelvic obliq-uity, right side higher than left, a slightly plantarflexed rightankle, 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 structuralleg length discrepancy and a plantarflexion contracture. Athorough examination of all of the joints of the lowerextremities was required before an explanation for theposture emerged. The patient demonstrated bilateral hip

A B

Lateral Medial

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

Figure 47.12: Flexion contractures of the hip or kneefunctionally shorten the lower extremity, and a commoncompensation is plantarflexion to lengthen the limb so thatthe individual can stand with the pelvis level. A plantarflexioncontracture produces a functionally lengthened lower extremityso that an individual with a plantarflexion contracture maystand with a flexed hip and/or knee to restore symmetry andstand with a level pelvis. The resulting postures lookapproximately the same although the precipitating factorsdiffer.


flexion contractures. In addition, range of motion assess-ments revealed that the patient had a complex contractureof the left hip, holding it flexed, laterally rotated, and ab-ducted. The patient stood with an anterior pelvic tilt andincreased lordosis, consistent with the hip flexion contrac-tures, but the lateral rotation and abduction contractureson the left effectively shortened the left lower extremitywhile turning the toes outward. The patient stood with theleft hip in obligatory abduction secondary to the abductioncontracture, while the right hip was adducted, and conse-quently, the pelvis was higher on the right. Correction ofstanding posture required reduction of the contractures ofboth the left and right hip. Although conservative treat-ment failed to reduce the contractures on the left, a totalhip replacement on the left restored normal joint alignment,and standing posture was immediately improved.

Muscular Control of Normal PostureExamples throughout this textbook demonstrate that groundreaction forces and body segment weights apply external

moments to the joints, which are balanced by internal mo-ments supplied by the surrounding muscles and noncontrac-tile connective tissue. The alignment of the body’s center ofmass relative to joint axes in quiet standing defines the exter-nal moments applied to the joints during erect standing. Theseexternal moments then are balanced by either active or pas-sive support to maintain the upright posture against the ever-present gravitational forces tending to press the body into theground. Examination of the external moments applied to thejoints of the lower extremities, trunk, and head by the groundreaction forces helps explain the forces needed to supportthese joints (Fig. 47.14). Using the data from the studies pre-sented in Table 47.1, the sagittal plane external moments on

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

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

Add

Abd Hip joint axis

Knee axis

Anklejoint axis


TABLE 47.3 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.b 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.

many joints of the body are presented in Table 47.3. Biome-chanical analysis of these moments and electromyographic(EMG) studies combine to help explain the mechanisms usedto maintain upright posture.

Although the external moments described in Table 47.3are the predominant moments applied during quiet standing,it is important to recall that standing posture is dynamic andthat even so-called quiet standing is characterized by oscilla-tions of the body over the fixed feet. Panzer et al. report thatduring quiet standing, the EMG activity of muscle groups isless than 10% of each group’s activity during a maximum vol-untary contraction (MVC) [42]. These investigators also notethat many of these muscle groups exhibit sudden, brief ac-tivity levels of 30–45% of their MVC and suggest that thesesudden bursts may reflect a muscle group’s response to thesway of the body’s center of mass.

Because the body’s center of mass generates a dorsiflexionmoment on the ankle during quiet standing, the plantar flexormuscles generate a plantarflexion moment to maintain staticequilibrium. EMG data demonstrate activity of both thesoleus and the gastrocnemius during quiet standing [1,42].Brief, intermittent, and slight EMG activity is also found inthe dorsiflexor muscles, apparently in response to posturalsway [1,42].

In contrast to the ankle, the knee exhibits minimal mus-cle activity during quiet standing [1,42]. In erect posture, theground reaction force applies an extension moment to theknee allowing it to maintain extension using its passive con-straints, including the collateral and anterior cruciate liga-ments. Reports of slight electrical activity in the quadricepsmuscles (4–7% of MVC) and hamstrings (1% of MVC) areconsistent with the use of passive supports to sustain the ex-tended knee during quiet standing [42]. However, like themuscle activity at the ankle, larger brief bursts of activity inthe quadriceps and hamstrings muscles may reflect the mus-cles’ response to sway.

Few studies examine activity of the hip musculature dur-ing erect posture. The ground reaction force produces anextension moment at the hip, and EMG data reveal activityof the iliacus in quiet standing, exerting a stabilizing flexion

moment [1]. Understanding the role of muscles and ligamentsin generating the internal moments needed to balance the ex-ternal moments exerted by body weight and ground reactionforces allows the clinician to intervene to provide postural sta-bility in the absence of muscular support.

CLINICAL RELEVANCE: MAINTAINING ERECT POSTURE INTHE PRESENCE OF MUSCLE WEAKNESS: A PATIENT WITHPARAPLEGIAA patient with a spinal cord injury resulting in loss of mus-cle function from the level of L2 is beginning rehabilita-tion. Functional goals include standing for stimulation ofbone growth and limited ambulation. Weakness second-ary to the spinal cord injury begins at the hip flexors andextends throughout the rest of the lower extremities. Toteach the individual safe and efficient standing, the clini-cian uses an understanding of the effects of externalmoments on the joints of the lower extremities and arecognition of the passive structures that are available tosupport the joints.

The individual lacks muscular support at the hip, knee,and ankle, but the astute clinician knows that the hippossesses strong anterior ligaments, the iliofemoral,pubofemoral, and ischiofemoral ligaments. By maintain-ing the hip in hyperextension, the individual can “hangon” these anterior ligaments, even in the absence of thehip flexors. Similarly, the knee normally maintains ex-tension in erect standing without muscular support,since the body’s center of mass falls anterior to the kneejoint and exerts an extension moment on the knee. Aslong as the knee remains extended, no additional mus-cular support is needed. Thus the individual can stand inhip and knee hyperextension using passive supports atthese joints.

Stable erect posture requires that the body’s center ofmass remain over the base of support. To maintain hip andknee hyperextension while keeping the body’s center ofmass over the base of support, the individual’s ankles as-sume a dorsiflexed position, and the ground reaction force


applies an external dorsiflexion moment (Fig. 47.15). Withno muscle support at the ankle, the individual with weak-ness from the hips distally requires external support froman orthosis to exert a plantarflexion moment at the an-kle, balancing the external dorsiflexion moment. Thus theindividual can stand with minimal external support to sta-bilize the lower extremity by using the external momentsgenerated by the ground reaction force to apply externalmoments at the knee and hip that can be balanced by pas-sive joint structures.

For the individual described in this case to stand withminimal external support, he or she must be able to as-sume a position of hip and knee hyperextension. Flexioncontractures at the hips or knees or plantarflexion con-tractures at the ankle produce disastrous results, prevent-ing the individual from positioning the joints to usepassive supports (Fig. 47.16).

The weight of the trunk exerts an external flexion momenton the back, requiring an extension moment to maintain erectposture. EMG data show low-level activity of the erectorspinae and multifidus with intermittent bursts of increasedactivity [1,42,56]. The cervical region also sustains an exter-nal flexion moment because the head’s center of mass is an-terior to the joints of the cervical spine. Active contraction ofcervical extensors maintains upright posture of the head andneck, but as in the trunk, EMG data reveal that only slightactivity is required to hold the head erect. Although few stud-ies examine activity in the cervical muscles during quiet stand-ing, data show activity in the semispinalis muscles with noactivity in the splenius muscles [51].

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

Figure 47.16: Effect of sagittal plane contractures on standingposture and the external moments applied to the hip, knees,and ankles. A. Flexion contractures at either the hip or kneecause an individual to stand in a flexed position at both thehips and knees, generating external flexion moments at bothjoints. Consequently, the individual is unable to use the passivesupports at the hip and knee joints. B. Plantarflexioncontractures at the ankles prevent an individual from movingthe center of mass over the base of support while stillmaintaining hip and knee hyperextension. To relocate thecenter of mass over the base of support, the patient flexesthe hip joints, thus requiring muscular support to supportthe hip joints.

A B


The role of the abdominal muscles during quiet standingcontinues to be debated. EMG studies of the abdominal mus-cles identify activity, particularly in the internal oblique mus-cle, with some activity in the external oblique muscle duringquiet standing [1,12,43,46]. Yet studies that investigate the as-sociation between abdominal muscle strength as measured byleg-lowering maneuvers and postural alignment of the pelvisreport either no association [55] or weak associations in fe-males and no association in males [63]. The leg-lowering ex-ercise recruits the rectus abdominis more than the obliqueabdominal muscles in most individuals and, consequently,may not reflect the ability of the oblique abdominal musclesto participate in postural support [43]. Chapter 34 discussesthe role of the abdominal muscles in stabilizing the spine. Thedata presented here suggest that the oblique abdominal mus-cles are important in erect posture, although their role maybe to function with the transversus abdominis muscle to sta-bilize the spine rather than to position the pelvis.

The role played by muscles to maintain shoulder positionduring quiet standing also lacks definitive conclusions. Inmanet al. demonstrate active contraction of the levator scapulaealong with the upper trapezius and upper portion of the ser-ratus anterior muscles in quiet standing, suggesting that thesemuscles are providing upward support for the shoulder gir-dle and upper extremity [23]. However, Johnson et al. notethat only the levator scapulae and the rhomboid major andminor muscles can directly suspend the scapula [26]. EMGstudies show that in the presence of voluntary relaxation ofthe upper trapezius in quiet standing, there is an increase inEMG activity of the two rhomboid muscles but a decrease inactivity in the levator scapulae [41]. These data support thenotion that the rhomboid muscles can and do support the up-right position of the shoulder girdle, at least under certaincircumstances. Whether the levator scapulae contributes ad-ditional support remains debatable.

POSTURAL MALALIGNMENTS

Health care providers evaluate posture on the premise thatpostural malalignments contribute to altered joint and mus-cle mechanics, producing impairments that lead to pain

[21,27]. Complaints attributed to postural deviations of thehead and spine include circulatory, respiratory, digestive, andexcretory dysfunctions; headaches; backaches; depression;and a generalized increased susceptibility to disease[4,21,38,39]. Pain in the back and lower extremities also is at-tributed to abnormal alignment in the hips, knees, and feet[10,28,29,32,59].

Despite the presumption of associations between posturalabnormalities and patients’ complaints, studies examiningthese associations vary in their findings. Correlations betweenthe incidence of reported head, neck, and shoulder pain arereported in people with forward head, rounded shoulders, andincreased thoracic kyphoses [21]. Studies investigating the as-sociation between low back postural deviations and low backpain draw variable conclusions, with some reporting little orno difference in posture between those with and without lowback pain [7,11,62], and others finding differences betweenthe two groups [24]. Malalignments of the patellofemoral jointare associated with a variety of pain syndromes at the knee[22,35,45]. Considerably more research is required to deter-mine the role that postural abnormalities play in muscu-loskeletal complaints and to determine the effectiveness oftreatments directed toward improving posture to reduce pain.

Typical postural deviations are listed and defined in Tables47.4 and 47.5. These postural abnormalities are presumed toproduce excessive or abnormally located stresses (force/area)on joint surfaces or to contribute to altered muscle mechan-ics 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 roleposture plays in the pathomechanics of musculoskeletal dis-orders requires continued research in basic anatomy andbiomechanics, as well as well-controlled outcome studiesexamining the effectiveness of treatments directed towardposture reeducation.

Muscle Imbalances Reported inPostural MalalignmentsA commonly held clinical perception is that postural malalign-ments produce adaptive changes in the muscles surrounding

TABLE 47.4 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 froman 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 thecenter 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�


the malaligned joints. Specifically, it is believed that muscleson one side of the joint are held in a lengthened position andthe antagonistic muscles are maintained in a shortened posi-tion. Clinicians also suggest that these length changes pro-duce joint impairments including weakness and limited rangeof motion that contribute to a patient’s complaints. Althoughthese hypotheses are logical and may still prove true, studiesto date have failed to identify clear associations betweenmalalignments and joint impairments [9,37].

As noted in Chapter 4, studies in animals demonstrate thatprolonged length changes in muscles produce structuralchanges in muscle, although those changes depend uponmany factors besides length. These additional mitigating fac-tors include age, fiber arrangement within the muscles, andfiber type within the muscle [31,33]. In general, prolongedstretch of a muscle induces protein synthesis and the pro-duction of additional sarcomeres [18,19,50,58,60]. Thelengthened muscle hypertrophies, and as a result, peak con-tractile force increases with prolonged stretch [31,33]. Thestructural remodeling that accompanies prolonged lengthen-ing appears to maintain the muscle’s original length–tensionrelationship so that, although the muscle has a larger peaktorque, it generates the peak torque at a different joint posi-tion. The clinical literature describes stretch weakness inwhich a muscle that has been held in a stretched position longenough to remodel appears weak when tested in the tradi-tional test position [20,27]. For example, at the shoulder,stretch weakness suggests that a posture characterized byrounded shoulders applies a prolonged stretch to the middletrapezius, which undergoes the structural adaptations thatlead to weakness when assessed in the traditional manual mus-cle test position. Although the changes described here arelogical and plausible, they remain unproved.

Animal studies examining prolonged shortening reveal thatshortening produced by immobilization appears to accelerateatrophy, and muscles demonstrate a loss of sarcomeres[18,50,60]. Studies examining the effect of prolonged lengthchanges in muscle reveal that the relationship between mus-cle length and muscle performance is complex, requiring

independent investigation of the relationship with each mus-cle. The complexity of the association helps explain the ab-sence of clearly defined associations.

Attempts to confirm the expected muscle impairments withpostural abnormalities have failed to yield clear relationships.Individuals with idiopathic scoliosis exhibit atrophy of the mus-cles of the posterior thorax, particularly on the concave side,and a higher percentage of type I muscle fibers than normalon the convex side of the deformity [13,61,65]. The musclesof the thorax on the concave side of the curve are likely short-ened, while those on the convex side are lengthened; yet bothmuscle groups exhibit atrophy. Although this atrophy may pre-cede the development of the scoliosis, the expected adaptivechanges with prolonged lengthening apparently are lacking.Similarly, attempts to relate scapular alignment and muscleperformance fail to reveal associations [9]. However, thescapula moves in a complex, three-dimensional way, and stud-ies so far may not accurately reflect the effects of scapularmalalignment on muscle length. These data demonstrate theneed for careful anatomical, biomechanical, and clinical stud-ies to identify and explain any detrimental effects of posturalmalalignment.

SUMMARY

This chapter describes the relative alignment of body seg-ments identified in healthy adults during quiet standing. Inthe absence of a validated description of “ideal posture,” thedocumented alignments provide clinicians with a view of thevariability of alignments found in individuals without muscu-loskeletal complaints. Although individuals demonstrate awide spectrum of alignments, the overall image of upright pos-ture shows a head well balanced over the pelvis, which in turnis well balanced over the feet. Using these alignments, thechapter also demonstrates the external moments applied tothe joints of the lower extremities and trunk during uprightstanding. The external moments are balanced by internal mo-ments generated by muscle contractions and noncontractile

TABLE 47.5 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) theheight of the navicular relative to the medial malleolus and the head of the first metatarsal, and (3) thesubtalar 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�


connective tissue support. EMG data are consistent withthe mechanical data, demonstrating low levels of activity in theplantar flexors, hip flexors, and erector spinae muscles ofthe lumbar and cervical regions. Additional activity in theoblique abdominal muscles is consistent with their role as sta-bilizers of the spine. In addition, other muscle groups such asthe dorsiflexor muscles, the quadriceps, and the hamstringsdemonstrate very brief bursts of activity that may be requiredto control the small, but persistent sway of the body that occursthroughout quiet stance.

Postural alignment is commonly assessed clinically, andsome abnormal postures are associated with musculoskeletalabnormalities and clinical complaints. However, many of thecommonly held beliefs regarding the associations betweenpostural abnormalities and musculoskeletal impairments lackobjective evidence. Although these associations may well exist,additional research is required to identify such relationshipsand to demonstrate the effectiveness of treating posturaldeviations to reduce pain or other impairments.

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chapter 47, posture & gait

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