14 analysis of amputee gait

Normal VersionChapter 14 - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles

Analysis of Amputee Gait

Norman Berger, M.S.

*Much of the material in this chapter is taken from the manual Lower-Limb Prosthetics, 1990 Revision,Prosthetics and Orthotics, New York University Post-Graduate Medical School. Permission to reprint isgratefully acknowledged.

With equipment such as force plates, electrogoniome-ters, and electromyographs, a number of research studies havepresented objective, quantified analyses of amputee gait. Clinicians, however, tend to rely on observational gaitanalysis to provide information about prosthetic fit, alignment, and function for the individual patient. This simpler, moreimmediately available procedure requires only the eye, the brain, and sufficient expertise to produce clinically usefulinsights and understanding. Although the future may see sophisticated measurement equipment efficient andinexpensive enough to be used routinely in daily treatment programs, observational gait analysis remains the procedureof choice for the present and is therefore the focus of this chapter.

Basically, observational gait analysis involves the identification of gait deviations and determination of the causesassociated with each deviation. With this accomplished, the treatment team can then plan and recommend correctiveactions to improve the situation. This process works well so long as the clinic team understands normal gait,biomechanics, and prosthetic fit and alignment. The component parts of the gait analysis procedure are as follows:

Observation.-It is essential to observe from at least two vantage points. Sagittal-plane motions are best seenfrom the side, while frontal-plane motions are best seen from the front or rear.

1.

Identification of gait deviations.-The phrase "gait deviation" is defined as any gait characteristic that differs fromthe normal pattern. While all our detailed knowledge of normal locomotion will be useful, keep in mind that thesingle most outstanding characteristic of the normal pattern is symmetry. Thus, for the unilateral amputeedeviations are often identified by observing asymmetry, that is, differences in the patterns of the prosthetic andnormal sides.

2.

Determination of causes.-The obvious place to look is at the prosthesis, and it is certainly true that there aremany prosthetic causes for gait deviations. However, it is equally true that there are many non-prostheticcauses. A particular patient may have restricted range of motion at one or more joints, muscular weakness,concomitant medical conditions, excessive fear, or old habit patterns, any of which may cause deviant gait.Analyze the prosthesis, but do not ignore the patient.

3.

ANALYSIS OF TRANSTIBIAL (BELOW-KNEE) AMPUTEE GAIT

A number of important deviations that may appear in the gait of transtibial amputees are discussed below. To assist inobserving these sometimes subtle characteristics and in understanding their causes, the phase of the walking cycle inwhich each deviation occurs is identified.

Between heel strike and midstanceExcessive knee flexionDuring normal gait the knee is approximately in complete extension at heel strike. Immediately thereafter,the knee begins to flex and continues to do so until just after the sole of the shoe is flat on the ground. Atnormal walking speeds (100 to 120 steps per minute), the average range of knee flexion after heel strikeis from 15 to 20 degrees. The transtibial amputee may exceed this range of knee flexion on theamputated side for any of the following reasons:

Excessive dorsiflexion of the foot or excessive anterior tilt of the socketNormally, foot contact with the floor after heel strike is the result of ankle plantar flexion and kneeflexion. If the prosthetic foot is set in too much dorsiflexion or the socket displays more than theusual 5 degrees of anterior tilt, additional knee flexion is required to allow the foot to reach the

floor after heel strike.

1.

Excessively stiff heel cushion or plantar-flexion bumperIf plantar flexion of the foot is restricted by an overly stiff heel cushion or plantar-flexion bumper,the amputee's knee may have to flex through more than the normal range to allow the sole of thefoot to reach the floor. Also, an overly stiff cushion or bumper will not absorb the impact of the heelstriking the floor, thus tending to produce abrupt and excessive knee flexion.

2.

Excessive anterior displacement of the socket over the footAs illustrated in Fig 14-1., placing the socket forward relative to the prosthetic foot increases thedistance between the lines of action of the force transmitted through the socket (A) and the

3.

A.I.

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reaction force from the floor (B).The force couple tending to cause rotation of the prosthesis in a flexion direction thus increases asthe socket is moved farther anteriorly. The effect of this force couple will be somewhat reduced ifthe heel cushion or bumper is soft enough to absorb the impact of the heel striking the floor.Flexion contracture or posterior misplacement of the suspension tabsThe knee cuff used to suspend the prosthesis is attached to the socket posterior to the axis ofmotion of the knee joint. This location causes the suspension tabs to tighten as the knee jointextends and to loosen as the knee flexes. If the attachment points are unduly posterior, thesuspension tabs will tighten to such an extent as to prevent the knee joint from reaching fullextension. The supracondylar/suprapatellar-suspended prosthesis relies on a carefully moldedconvexity above the patella to ensure adequate suspension. If this anterior convexity is excessive,the knee joint will be restricted in extension. These situations are comparable to a flexioncontracture in which tight posterior tissues do not permit full knee extension.

4.

Absent or insufficient knee flexionThe transtibial amputee may walk with absent or insufficient knee flexion on the amputated side for oneor more of the following reasons:

Excessive plantar flexion of the footIn normal walking, contact of the sole of the foot with the floor coincides approximately with theend of knee flexion and the beginning of knee extension. If the prosthetic foot is in an attitude ofplantar flexion, foot flat will occur prematurely and prevent normal knee flexion after heel strike.

1.

Excessively soft heel cushion or plantar-flexion bumperIn the case of a solid-ankle, cushion-heel (SACH) foot with an excessively soft heel cushion, therewill be a momentary delay between heel strike and the initiation of knee flexion. The knee willbegin to flex only after the heel cushion has been fully compressed. With a single-axis ankle, an

excessively soft heel bumper will allow the prosthetic foot to plantar-flex too rapidly and thus slapthe floor. This abrupt contact of the foot with the floor will tend to decrease the range of kneeflexion.

2.

Posterior displacement of the socket over the footAs illustrated in Fig 14-2., posterior displacement of the socket decreases the distance betweenthe lines of action of the force transmitted through the socket (A) and the reaction force from thefloor (B), thus decreasing the tendency of the force couple to rotate the prosthesis in a flexiondirection.If the socket is placed so far posteriorly that the line of force transmission through the socket fallsposterior to the floor reaction, the prosthesis will tend to rotate backward, that is, the knee will beforced toward hyperextension rather than flexion.

3.

Anterodistal discomfortSupporting body weight with the knee in a flexed attitude is possible only if the knee extensors actwith sufficient force to restrain the flexion moment. When the quadriceps muscle contracts,pressure between the anterodistal surface of the tibia and the socket is increased considerably.Consequently, stump discomfort may occur at heel strike.To avoid this pain the amputee may walk so that the forces acting on the knee tend to extendrather than to flex that joint. This can be accomplished by (1) shortening the prosthetic step, (2)digging the heel into the ground by means of increased hip extensor activity, (3) adopting aforward lurch of the head and the shoulder, or (4) some combination of these.

4.

Weakness of the quadriceps muscleIf the quadriceps is not strong enough to control the knee at heel strike, the amputee may

compensate in much the same way as he would if there were anterodistal tibial discomfort. Thesegait maneuvers tend to force the knee into extension and thereby lessen or eliminate the need forquadriceps activity.

5.

HabitAmputees who have established a pattern of walking with the knee held in extension after heelstrike may continue to walk in the same manner when they are making the transition to a patellartendon-bearing prosthesis. A brief period of instruction with adequate follow-up may establish aless deviant walking pattern.

6.

B.

At midstanceExcessive lateral thrust of the prosthesisLateral thrust derives from the tendency of the prosthesis to rotate around the amputated limb. When thisoccurs, the medial socket brim presses against the femoral condyle while the lateral part of the brimtends to gap. A slight amount of this lateral thrust is fairly common, but if it is excessive, the amputee maycomplain of uncomfortable pressure on the medioproximal aspect of his knee, and damage to the skinand to the knee ligaments may result. Excessive lateral thrust may be caused by such factors as thefollowing:

Excessive medial placement of the prosthetic footAt midstance, the sound limb is swinging, so all of the body weight is supported by the prosthetic

1.

A.II.


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foot on the floor. If this supporting foot is too far medial to the line of action of forces transmittedthrough the socket, as illustrated in Fig 14-3., a force couple is created that tends to rotate thesocket around the stump. In almost all instances, this lateral thrust can be minimized or eliminatedby "out-setting" the prosthetic foot slightly.Abducted socketIf a socket that has been set in excessive abduction (brim tilted medially, simulating genu valgum)is placed on the vertically positioned residual limb, the distal end of the prosthesis shifts medially,and the patient's weight tends to be borne on the lateral border of the foot. This, in turn, increasesthe lateral thrust of the socket brim.

2.

Between midstance and toe-offEarly knee flexion (drop-off) Just prior to heel-off during normal gait, the knee is extending. At heel-off orimmediately thereafter, knee motion reverses, and flexion begins. This knee flexion coincides with thepassing of the center of gravity over the metatarsophalangeal joints. If the body weight is carried overthese joints too soon, the resulting lack of anterior support would allow premature knee flexion or drop-off.Possible causes for this lack of anterior support are as follows:

Excessive anterior displacement of the socket over the footThe farther forward the socket is placed, the closer is the line of action of forces transmittedthrough the socket to the end of the keel in a SACH foot or to the toe-break in a wood foot. Thedistance that the center of gravity must move forward to pass over these prosthetic equivalents ofthe metatarsophalangeal joints is thus minimized and allows knee flexion to occur too early.

1.

Posterior displacement of the toe-break or the keel2.Excessive dorsiflexion of the foot or excessive anterior tilt of the socket3.Soft dorsiflexion bumperThese conditions also minimize the distance that the body weight must move forward before

anterior support is lost. The shorter this distance, the earlier and more abrupt will be the kneeflexion.

4.

A.

Delayed knee flexionThe reverse of the situation described above occurs if the body weight must be carried forward anunusually long distance before anterior support is lost. Under such circumstances, the knee joint wouldremain in extension during the latter part of the stance phase, and the amputee might complain of a"walking-uphill" sensation since his center of gravity would be carried up and over the extended knee.This excessive anterior support can be brought about by the following:

Excessive posterior displacement of the socket over the foot1.Anterior displacement of the toe-break or the keel2.Excessive plantar flexion of the foot or excessive posterior tilt of the socket3.Hard dorsiflexion bumper4.

B.

III.

Some of the gait deviations discussed below in relation to the transfemoral amputee may also be noted in the transtibialpatient. However, the incidence is small, and no separate discussion is warranted.

ANALYSIS OF TRANSFEMORAL (ABOVE-KNEE) AMPUTEE GAIT

Eleven common transfemoral deviations and their usual causes are presented. The sequence of presentation is basedon the preferred vantage point for observation, with the first 6 deviations best viewed from the rear or the front and theremaining 5 best seen from the side.

LATERAL TRUNK BENDING

Description: The amputee leans toward the amputated side when the prosthesis is in stance phase (Fig 14-4.).


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Fig 14-4. Lateral trunk bending.

When to observe: From just after heel strike to mid-stance.

How to observe: From behind the patient.

Causes:

Weak hip abductors. By shifting the center of gravity toward the prosthesis, lateral bending counteracts thetendency toward pelvic drop on the sound side.

1.

Abducted socket. This alignment fault reduces the effectiveness of the hip abductors in stabilizing the pelvis. Theresulting tendency of the pelvis to drop on the sound side is counteracted by lateral trunk bending.

2.

Insufficient support by the lateral socket wall. If the lateral wall does not block lateral movement of the femur, thepelvis will tend to drop on the sound side when the prosthesis is in stance phase. To check this tendency, theamputee leans toward the prosthesis.

3.

Pain or discomfort, particularly on the lateral distal aspect of the femur. By bending to the prosthetic side, the

amputee relieves pressure on the lateral aspect.

4.

Lateral trunk bending. This is usually present when an amputee walks with an abducted gait. Most of the causesof abducted gait can be responsible for lateral bending.

5.

Short prosthesis.6.

WIDE WALKING BASE (ABDUCTED GAIT)

Description: Throughout the gait cycle, the width of the walking base is significantly greater than the normal range of 5to 10 cm (2 to 4 in.). There is exaggerated displacement of the pelvis and trunk (Fig 14-5.).


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Fig 14-5. Width of walking gait is significantly greater than

normal, with exaggerated displacement of the pelvis and

trunk.

When to observe: During the period of double support.


Causes:

Pain or discomfort in the crotch area. The discomfort may be due to such factors as skin infection, adductor roll,or pressure from the medial socket brim. The amputee tries to gain relief by abducting his prosthesis, thusmoving the medial part of the brim away from the painful area.

1.

Contracted hip abductors.2.Prosthesis too long. Excessive length makes it difficult to place the limb directly under the hip during stance andto clear the floor during swing. Widening the base helps to solve these problems.

3.

Shank aligned in the valgus position with respect to the thigh section.4.Mechanical hip joint set so that the socket is abducted.5.Feeling of insecurity. The amputee compensates by widening his walking base.6.

CIRCUMDUCTION

Description: The prosthesis follows a laterally curved line as it swings (Fig 14-6.).


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Fig 14-6. Circumduction: prosthesis swings in laterallycurved line.

When to observe: Throughout swing phase.


Causes: The basic cause of this deviation is a prosthesis that is too long, thus forcing the amputee to swing it to theside to clear the ground. The following are among the factors tending to produce excessive length:

Insufficient flexion of the knee because of insecurity or fear.1.Manual knee lock, excessive friction, or a tight extension aid preventing the knee from flexing.2.

Inadequate suspension allowing the prosthesis to drop (piston action).3.Too small a socket. The ischial tuberosity is above its proper location.4.Foot set in excessive plantar flexion.5.

VAULTING

Description: The amputee raises his entire body by early and excessive plantar flexion of the sound foot (Fig 14-7.).


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Fig 14-7. Vaulting: early and excessive plantar flexion of

sound foot raises entire body.

When to observe: During swing phase of the prosthesis.

How to observe: From behind or from the side of patient.

Causes:

Insufficient friction in the prosthetic knee. In the normal pattern, maximum elevation of the body occurs when thesupporting limb is in the middle of stance phase and the other limb swings alongside it. When there is insufficientfriction, heel rise is excessive, and the shank takes a longer time to swing forward. Because of this time lag, thebody is no longer at maximum elevation as the prosthetic foot is at its lowest point in swinging through, and theprosthetic foot would fail to clear the ground unless the amputee gained additional time and clearance byvaulting.

1.

Excessive length of the prosthesis. The amputee vaults to gain additional clearance so that the prosthetic foot

will clear the ground as it swings through. The following are among the factors that may produce excessivelength:

Insufficient flexion of the knee because of insecurity or fear.A.Manual knee lock, excessive friction, or too tight an extension aid.B.Inadequate suspension allowing the prosthesis to slip off the stump (piston action).C.Too small a socket. The ischial tuberosity is above its proper location.D.Foot set in excessive plantar flexion.E.

2.

SWING-PHASE WHIPS

Description: Medial whip-At toe-off the heel moves medially (Fig 14-8.). Lateral whip-At toe-off the heel moves laterally(Fig 14-8.).


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Fig 14-8. Left, medial whip. Right, lateral whip.

When to observe: At and just after toe-off.


Causes:

Improper alignment of the knee bolt in the transverse plane.1.With a suction socket and no auxiliary suspension, whips may be seen because of the following:

Weak and flabby musculature that rotates freely around the femur.A.A socket that is too tight or improperly contoured to accommodate muscles. Pressure from contractingmuscle bellies causes the prosthesis to rotate around its long axis.

B.

2.

FOOT ROTATION AT HEEL STRIKE

Description: As the heel contacts the ground, the foot rotates laterally, sometimes with a vibratory motion (Fig 14-9.).


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Fig 14-9. Foot rotation at heel strike.

When to observe: At heel strike. How to observe: From in front of the patient.

Cause: Too hard a heel cushion or plantar-flexion bumper.

FOOT SLAP

Description: The foot plantar-flexes too rapidly and strikes the floor with a slap (Fig 14-10.).

Fig 14-10. Foot slap.

When to observe: Just after heel strike.

How to observe: From the side. Listen for slap.


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Cause: The plantar-flexion bumper is too soft and does not offer enough resistance to foot motion as weight istransferred to the prosthesis.

UNEVEN HEEL RISE

Description: Usually the prosthetic heel rises higher than the sound heel. However, the reverse may also be seen, thatis, the prosthetic heel rises less than the sound heel (Fig 14-11.).

Fig 14-11. Uneven heel rise.

When to observe: During first part of swing phase.

How to observe: From the side.

Causes: Excessive heel rise results when the following are present:

Insufficient friction at the prosthetic knee.1.Insufficient tension or absence of an extension aid.2.Forceful hip flexion to ensure that the prosthetic knee will be extended fully at heel strike.Insufficient heel rise results when the following are present:

Excessive friction at the prosthetic knee.1.Too tight an extension aid.2.Fear and insecurity. The amputee walks with little or no knee flexion.3.Manual knee lock.4.

3.

TERMINAL IMPACT

Description: The prosthetic shank comes to a sudden stop with a visible and possibly audible impact as the kneereaches full extension (Fig 14-12.).


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Fig 14-12. Terminal impact.

When to observe: At the end of swing phase.

How to observe: From the side. Listen for the impact.

Causes:

Insufficient friction at the prosthetic knee.1.Too tight an extension aid.2.The amputee's fear of buckling causing him to extend the hip abruptly as the knee approaches full extension.This maneuver snaps the shank forward into full extension.

3.

Absent or worn resilient extension bumper in the knee unit.4.

UNEVEN STEP LENGTH

Description: The length of the step [*The term step refers to the distance between successive positions of the soundfoot and prosthetic foot. The total length of the stride taken with each foot will be the same ("stride" signifies thedistance between successive positions of the same foot.) taken with the prosthesis differs from the length of the steptaken with the sound leg.

When to observe: During successive periods of double support.


Causes:

Pain or insecurity causing the amputee to transfer his weight quickly from the prosthesis to his sound leg. To dothis he takes a short, rapid step with his sound foot.

1.

Hip flexion contracture or insufficient socket flexion. Any restriction of the hip extension range must be reflectedby a shorter step length on the sound side.

2.

Insufficient friction at the prosthetic knee or too loose an extension aid. The pendular swing of the shankproduces a prosthetic step length that is longer than the step length on the sound side.

3.

EXAGGERATED LORDOSIS

Description: The lumbar lordosis is exaggerated when the prosthesis is in stance phase, and the trunk may leanposteriorly (Fig 14-13.).


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Fig 14-13. Exaggerated lordosis.

When to observe: Throughout stance phase.


Causes:

Hip flexion contracture. The pelvis tends to tilt downward and forward because the center of gravity is anterior tothe support point (a theoretical point around which the supporting forces are balanced). A flexion contractureaggravates the tendency of the pelvis to tilt anteriorly because the shortened hip flexor muscles exert adownward and forward pull on the pelvis when the femur is at the limit of its extension range.

1.

Insufficient socket flexion.2.Insufficient support from the anterior socket brim.3.Weak hip extensors. The extensors help to restrain the tendency of the pelvis to tilt forward. When thisrestraining force is lost, the resulting forward pelvic tilt and compensatory backward trunk bending causeincreased lordosis. In addition, the amputee may roll his pelvis forward to assist the weak extensors to controlknee stability.

4.

Weak abdominal muscles. The abdominal muscles restrain the tendency of the pelvis to tilt forward. If theabdominal muscles are weak, some of this restraint is lost, and the amputee will show increased lordosis.

5.

Fig 14-1. Excessive anterior displacement of the socket over the foot.


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Fig 14-2. Posterior displacement of the socket over the foot.

Fig 14-3. Excessivemedial placement of the

prosthetic foot.

Chapter 14 - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles

Normal Version


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14 analysis of amputee gait

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