analysis of amputee gait

17/11/2014 14: Analysis of Amputee Gait | O&P Virtual Library

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Chapter 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, 1990Revision, Prosthetics and Orthotics, New York University Post-Graduate Medical School. Permissionto reprint is gratefully acknowledged.

With equipment such as force plates, electrogoniome-ters, and electromyographs, a number of research studieshave presented objective, quantified analyses of amputee gait. Clinicians, however, tend to rely on observationalgait analysis to provide information about prosthetic fit, alignment, and function for the individual patient. Thissimpler, more immediately available procedure requires only the eye, the brain, and sufficient expertise to produceclinically useful insights and understanding. Although the future may see sophisticated measurement equipmentefficient and inexpensive enough to be used routinely in daily treatment programs, observational gait analysisremains the procedure of 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 recommendcorrective actions to improve the situation. This process works well so long as the clinic team understands normalgait, biomechanics, and prosthetic fit and alignment. The component parts of the gait analysis procedure are asfollows:

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

2. Identification of gait deviations.-The phrase "gait deviation" is defined as any gait characteristic that differsfrom the normal pattern. While all our detailed knowledge of normal locomotion will be useful, keep in mindthat the single most outstanding characteristic of the normal pattern is symmetry. Thus, for the unilateralamputee deviations are often identified by observing asymmetry, that is, differences in the patterns of theprosthetic and normal sides.

3. 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.

ANALYSIS OF TRANSTIBIAL (BELOW-KNEE) AMPUTEE GAITA number of important deviations that may appear in the gait of transtibial amputees are discussed below. Toassist in observing these sometimes subtle characteristics and in understanding their causes, the phase of thewalking cycle in which each deviation occurs is identified.

I. Between heel strike and midstanceA. Excessive knee flexion

During normal gait the knee is approximately in complete extension at heel strike. Immediatelythereafter, the knee begins to flex and continues to do so until just after the sole of the shoe is flaton the ground. At normal walking speeds (100 to 120 steps per minute), the average range of kneeflexion after heel strike is from 15 to 20 degrees. The transtibial amputee may exceed this range ofknee flexion on the amputated side for any of the following reasons:

1. Excessive dorsiflexion of the foot or excessive anterior tilt of the socket Normally, foot contact with the floor after heel strike is the result of ankle plantar flexion andknee flexion. If the prosthetic foot is set in too much dorsiflexion or the socket displays morethan the usual 5 degrees of anterior tilt, additional knee flexion is required to allow the foot toreach the floor after heel strike.

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

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3. Excessive anterior displacement of the socket over the footAs illustrated in Fig 14-1., placing the socket forward relative to the prosthetic foot increasesthe distance between the lines of action of the force transmitted through the socket (A) andthe reaction force from the floor (B).The force couple tending to cause rotation of the prosthesis in a flexion direction thusincreases as the socket is moved farther anteriorly. The effect of this force couple will besomewhat reduced if the heel cushion or bumper is soft enough to absorb the impact of theheel striking the floor.

4. 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 isexcessive, the knee joint will be restricted in extension. These situations are comparable to aflexion contracture in which tight posterior tissues do not permit full knee extension.

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

1. Excessive plantar flexion of the footIn normal walking, contact of the sole of the foot with the floor coincides approximately withthe end of knee flexion and the beginning of knee extension. If the prosthetic foot is in anattitude of plantar flexion, foot flat will occur prematurely and prevent normal knee flexionafter heel strike.

2. Excessively soft heel cushion or plantar-flexion bumperIn the case of a solid-ankle, cushion-heel (SACH) foot with an excessively soft heel cushion,there will be a momentary delay between heel strike and the initiation of knee flexion. Theknee will begin 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 toorapidly and thus slap the floor. This abrupt contact of the foot with the floor will tend todecrease the range of knee flexion.

3. Posterior displacement of the socket over the footAs illustrated in Fig 14-2., posterior displacement of the socket decreases the distancebetween the lines of action of the force transmitted through the socket (A) and the reactionforce from the floor (B), thus decreasing the tendency of the force couple to rotate theprosthesis in a flexion direction.If the socket is placed so far posteriorly that the line of force transmission through the socketfalls posterior to the floor reaction, the prosthesis will tend to rotate backward, that is, theknee will be forced toward hyperextension rather than flexion.

4. Anterodistal discomfortSupporting body weight with the knee in a flexed attitude is possible only if the kneeextensors act with sufficient force to restrain the flexion moment. When the quadricepsmuscle contracts, pressure between the anterodistal surface of the tibia and the socket isincreased 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) adoptinga forward lurch of the head and the shoulder, or (4) some combination of these.

5. Weakness of the quadriceps muscleIf the quadriceps is not strong enough to control the knee at heel strike, the amputee maycompensate in much the same way as he would if there were anterodistal tibial discomfort.These gait maneuvers tend to force the knee into extension and thereby lessen or eliminatethe need for quadriceps activity.

6. HabitAmputees who have established a pattern of walking with the knee held in extension afterheel strike may continue to walk in the same manner when they are making the transition to apatellar tendon-bearing prosthesis. A brief period of instruction with adequate follow-up mayestablish a less deviant walking pattern.

II. At midstanceA. Excessive lateral thrust of the prosthesis

Lateral thrust derives from the tendency of the prosthesis to rotate around the amputated limb.When this occurs, the medial socket brim presses against the femoral condyle while the lateral partof the brim tends to gap. A slight amount of this lateral thrust is fairly common, but if it is excessive,the amputee may complain of uncomfortable pressure on the medioproximal aspect of his knee, and



damage to the skin and to the knee ligaments may result. Excessive lateral thrust may be caused bysuch factors as the following:

1. Excessive medial placement of the prosthetic footAt midstance, the sound limb is swinging, so all of the body weight is supported by theprosthetic foot on the floor. If this supporting foot is too far medial to the line of action offorces transmitted through the socket, as illustrated in Fig 14-3., a force couple is createdthat tends to rotate the socket around the stump. In almost all instances, this lateral thrustcan be minimized or eliminated by "out-setting" the prosthetic foot slightly.

2. Abducted socketIf a socket that has been set in excessive abduction (brim tilted medially, simulating genuvalgum) is placed on the vertically positioned residual limb, the distal end of the prosthesisshifts medially, and the patient's weight tends to be borne on the lateral border of the foot.This, in turn, increases the lateral thrust of the socket brim.

III. Between midstance and toe-offA. Early knee flexion (drop-off) Just prior to heel-off during normal gait, the knee is extending. At heel-

off or immediately thereafter, knee motion reverses, and flexion begins. This knee flexion coincideswith the passing of the center of gravity over the metatarsophalangeal joints. If the body weight iscarried over these joints too soon, the resulting lack of anterior support would allow premature kneeflexion or drop-off. Possible causes for this lack of anterior support are as follows:

1. 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.The distance that the center of gravity must move forward to pass over these prostheticequivalents of the metatarsophalangeal joints is thus minimized and allows knee flexion tooccur too early.

2. Posterior displacement of the toe-break or the keel3. Excessive dorsiflexion of the foot or excessive anterior tilt of the socket4. Soft dorsiflexion bumper

These conditions also minimize the distance that the body weight must move forward beforeanterior support is lost. The shorter this distance, the earlier and more abrupt will be the kneeflexion.

B. 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 jointwould remain in extension during the latter part of the stance phase, and the amputee mightcomplain of a "walking-uphill" sensation since his center of gravity would be carried up and over theextended knee. This excessive anterior support can be brought about by the following:

1. Excessive posterior displacement of the socket over the foot2. Anterior displacement of the toe-break or the keel3. Excessive plantar flexion of the foot or excessive posterior tilt of the socket4. Hard dorsiflexion bumper

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

ANALYSIS OF TRANSFEMORAL (ABOVE-KNEE) AMPUTEE GAITEleven common transfemoral deviations and their usual causes are presented. The sequence of presentation isbased on the preferred vantage point for observation, with the first 6 deviations best viewed from the rear or thefront and the remaining 5 best seen from the side.

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



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:

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

2. Abducted socket. This alignment fault reduces the effectiveness of the hip abductors in stabilizing thepelvis. The resulting tendency of the pelvis to drop on the sound side is counteracted by lateral trunkbending.

3. Insufficient support by the lateral socket wall. If the lateral wall does not block lateral movement of thefemur, the pelvis will tend to drop on the sound side when the prosthesis is in stance phase. To check thistendency, the amputee leans toward the prosthesis.

4. 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.

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

6. Short prosthesis.

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



Fig 14-5. Width of walking gait is significantly greater thannormal, with exaggerated displacement of the pelvis andtrunk.

When to observe: During the period of double support.


Causes:

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

2. Contracted hip abductors.3. Prosthesis too long. Excessive length makes it difficult to place the limb directly under the hip during stance

and to clear the floor during swing. Widening the base helps to solve these problems.4. Shank aligned in the valgus position with respect to the thigh section.5. Mechanical hip joint set so that the socket is abducted.6. Feeling of insecurity. The amputee compensates by widening his walking base.

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



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 tothe side to clear the ground. The following are among the factors tending to produce excessive length:

1. Insufficient flexion of the knee because of insecurity or fear.2. Manual knee lock, excessive friction, or a tight extension aid preventing the knee from flexing.3. Inadequate suspension allowing the prosthesis to drop (piston action).4. Too small a socket. The ischial tuberosity is above its proper location.5. Foot set in excessive plantar flexion.

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



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

1. Insufficient friction in the prosthetic knee. In the normal pattern, maximum elevation of the body occurswhen the supporting limb is in the middle of stance phase and the other limb swings alongside it. Whenthere is insufficient friction, heel rise is excessive, and the shank takes a longer time to swing forward.Because of this time lag, the body is no longer at maximum elevation as the prosthetic foot is at its lowestpoint in swinging through, and the prosthetic foot would fail to clear the ground unless the amputee gainedadditional time and clearance by vaulting.

2. Excessive length of the prosthesis. The amputee vaults to gain additional clearance so that the prostheticfoot will clear the ground as it swings through. The following are among the factors that may produceexcessive length:

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

SWING-PHASE WHIPSDescription: Medial whip-At toe-off the heel moves medially (Fig 14-8.). Lateral whip-At toe-off the heel moveslaterally (Fig 14-8.).



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

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


Causes:

1. Improper alignment of the knee bolt in the transverse plane.2. With a suction socket and no auxiliary suspension, whips may be seen because of the following:

A. Weak and flabby musculature that rotates freely around the femur.B. A socket that is too tight or improperly contoured to accommodate muscles. Pressure from

contracting muscle bellies causes the prosthesis to rotate around its long axis.

FOOT ROTATION AT HEEL STRIKEDescription: As the heel contacts the ground, the foot rotates laterally, sometimes with a vibratory motion (Fig 14-9.).



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 SLAPDescription: 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.

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 RISEDescription: Usually the prosthetic heel rises higher than the sound heel. However, the reverse may also be seen,that is, 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:

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

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



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:

1. Insufficient friction at the prosthetic knee.2. Too tight an extension aid.3. 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.4. Absent or worn resilient extension bumper in the knee unit.

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

When to observe: During successive periods of double support.


Causes:

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

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

3. 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.

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



Fig 14-13. Exaggerated lordosis.

When to observe: Throughout stance phase.


Causes:

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

2. Insufficient socket flexion.3. Insufficient support from the anterior socket brim.4. Weak hip extensors. The extensors help to restrain the tendency of the pelvis to tilt forward. When this

restraining 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 tocontrol knee stability.

5. 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.

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



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

Fig 14-3. Excessivemedial placement of theprosthetic foot.

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analysis of amputee gait

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