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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, 1990 Revision, Prosthetics and Orthotics, New York University Post-Graduate Medical School. Permission to reprint is gratefully acknowledged.
With equipment such as force plates, electrogoniome-ters, and electromyographs, a number of research studies have presented objective, quantified analyses of amputee gait. Clinicians, however, tend to rely on observational gait analysis to provide information about prosthetic fit, alignment, and function for the individual patient. This simpler, more immediately available procedure requires only the eye, the brain, and sufficient expertise to produce clinically useful insights and understanding. Although the future may see sophisticated measurement equipment efficient and inexpensive enough to be used routinely in daily treatment programs, observational gait analysis remains 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 causes associated with each deviation. With this accomplished, the treatment team can then plan and recommend corrective actions 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 seen from the side, while frontal-plane motions are best seen from the front or rear.
- Identification of gait deviations.-The phrase "gait deviation" is defined as any gait characteristic that differs from the normal pattern. While all our detailed knowledge of normal locomotion will be useful, keep in mind that the single most outstanding characteristic of the normal pattern is symmetry. Thus, for the unilateral amputee deviations are often identified by observing asymmetry, that is, differences in the patterns of the prosthetic and normal sides.
- Determination of causes.-The obvious place to look is at the prosthesis, and it is certainly true that there are many prosthetic causes for gait deviations. However, it is equally true that there are many non-prosthetic causes. 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 GAIT
A number of important deviations that may appear in the gait of transtibial amputees are discussed below. To assist in observing these sometimes subtle characteristics and in understanding their causes, the phase of the walking cycle in which each deviation occurs is identified.
- Between heel strike and midstance
- Excessive knee flexion
During 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.
At normal walking speeds (100 to 120 steps per minute), the average range of knee flexion after heel strike is from 15 to 20
degrees. The transtibial amputee may exceed this range of knee flexion on the amputated side for any of the following reasons:
- 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 and knee flexion. If the prosthetic foot is set in too much
dorsiflexion or the socket displays more than the usual 5 degrees of anterior tilt, additional knee flexion is required to
allow the foot to reach the floor after heel strike. - Excessively stiff heel cushion or plantar-flexion bumper
If 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 the foot to reach the floor. Also, an overly stiff cushion
or bumper will not absorb the impact of the heel striking the floor, thus tending to produce abrupt and excessive knee
flexion. - Excessive anterior displacement of the socket over the foot
As illustrated in Fig 14-1., placing the socket forward relative to the prosthetic foot
increases the distance between the lines of action of the force transmitted through the socket (A) and the reaction
force from the floor (B).
The force couple tending to cause rotation of the prosthesis in a flexion direction thus increases as the socket is moved
farther anteriorly. The effect of this force couple will be somewhat reduced if the 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 tabs
The knee cuff used to suspend the prosthesis is attached to the socket posterior to the axis of motion of the knee joint. This
location causes the suspension tabs to tighten as the knee joint extends and to loosen as the knee flexes. If the attachment
points are unduly posterior, the suspension tabs will tighten to such an extent as to prevent the knee joint from reaching full
extension. The supracondylar/suprapatellar-suspended prosthesis relies on a carefully molded convexity 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 flexion contracture in which tight posterior tissues do not permit full knee extension.
- Absent or insufficient knee flexion
The transtibial amputee may walk with absent or insufficient knee flexion on the amputated side for one or more of the following
reasons:
- Excessive plantar flexion of the foot
In normal walking, contact of the sole of the foot with the floor coincides approximately with the end of knee flexion and the
beginning of knee extension. If the prosthetic foot is in an attitude of plantar flexion, foot flat will occur prematurely and
prevent normal knee flexion after heel strike. - Excessively soft heel cushion or plantar-flexion bumper
In 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. The knee 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 too
rapidly and thus slap the floor. This abrupt contact of the foot with the floor will tend to decrease the range of knee
flexion. - Posterior displacement of the socket over the foot
As illustrated in Fig 14-2., posterior displacement of the socket decreases the distance
between the lines of action of the force transmitted through the socket (A) and the reaction force from the floor
(B), thus decreasing the tendency of the force couple to rotate the prosthesis in a flexion direction.
If the socket is placed so far posteriorly that the line of force transmission through the socket falls posterior to the
floor reaction, the prosthesis will tend to rotate backward, that is, the knee will be forced toward hyperextension rather than
flexion. - Anterodistal discomfort
Supporting body weight with the knee in a flexed attitude is possible only if the knee extensors act with 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 extend rather 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 a forward lurch of the head and the shoulder, or (4) some combination of
these. - Weakness of the quadriceps muscle
If 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. These gait maneuvers tend to force the knee into extension and thereby
lessen or eliminate the need for quadriceps activity. - Habit
Amputees who have established a pattern of walking with the knee held in extension after heel strike may continue to walk in
the same manner when they are making the transition to a patellar tendon-bearing prosthesis. A brief period of instruction with
adequate follow-up may establish a less deviant walking pattern.
- At midstance
- 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 part of 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 by such factors as the
following:
- Excessive medial placement of the prosthetic foot
At midstance, the sound limb is swinging, so all of the body weight is supported by the prosthetic foot on the floor. If this
supporting foot is too far medial to the line of action of forces transmitted through the socket, as illustrated in Fig 14-3., a force couple is created that tends to rotate the socket around the stump. In almost all
instances, this lateral thrust can be minimized or eliminated by "out-setting" the prosthetic foot slightly. - Abducted socket
If 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, increases the lateral thrust of the socket brim.
- Between midstance and toe-off
- 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 coincides with the passing of the center of gravity over the metatarsophalangeal joints. If the
body weight is carried over these 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 foot
The farther forward the socket is placed, the closer is the line of action of forces transmitted through 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 prosthetic equivalents of the metatarsophalangeal joints is thus minimized and allows knee flexion to occur too
early. - Posterior displacement of the toe-break or the keel
- Excessive dorsiflexion of the foot or excessive anterior tilt of the socket
- Soft dorsiflexion bumper
These 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 knee flexion.
- Delayed knee flexion
The reverse of the situation described above occurs if the body weight must be carried forward an unusually long distance before
anterior support is lost. Under such circumstances, the knee joint would remain 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 foot
- Anterior displacement of the toe-break or the keel
- Excessive plantar flexion of the foot or excessive posterior tilt of the socket
- Hard dorsiflexion bumper
Some of the gait deviations discussed below in relation to the transfemoral amputee may also be noted in the transtibial patient. 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 based on the preferred vantage point for observation, with the first 6 deviations best viewed from the rear or the front and the remaining 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.).
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 the tendency toward pelvic drop on the sound side.
- Abducted socket. This alignment fault reduces the effectiveness of the hip abductors in stabilizing the pelvis. The resulting tendency of the pelvis to drop on the sound side is counteracted by lateral trunk bending.
- Insufficient support by the lateral socket wall. If the lateral wall does not block lateral movement of the femur, the pelvis will tend to drop on the sound side when the prosthesis is in stance phase. To check this tendency, the amputee leans toward the prosthesis.
- 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.
- Lateral trunk bending. This is usually present when an amputee walks with an abducted gait. Most of the causes of abducted gait can be responsible for lateral bending.
- Short prosthesis.
WIDE WALKING BASE (ABDUCTED GAIT)
Description: Throughout the gait cycle, the width of the walking base is significantly greater than the normal range of 5 to 10 cm (2 to 4 in.). There is exaggerated displacement of the pelvis and trunk (Fig 14-5.).
When to observe: During the period of double support.
How to observe: From behind the patient.
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, thus moving the medial part of the brim away from the painful area.
- Contracted hip abductors.
- 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.
- Shank aligned in the valgus position with respect to the thigh section.
- Mechanical hip joint set so that the socket is abducted.
- Feeling of insecurity. The amputee compensates by widening his walking base.
CIRCUMDUCTION
Description: The prosthesis follows a laterally curved line as it swings (Fig 14-6.).
When to observe: Throughout swing phase.
How to observe: From behind the patient.
Causes: The basic cause of this deviation is a prosthesis that is too long, thus forcing the amputee to swing it to the side 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.
- Manual knee lock, excessive friction, or a tight extension aid preventing the knee from flexing.
- Inadequate suspension allowing the prosthesis to drop (piston action).
- Too small a socket. The ischial tuberosity is above its proper location.
- Foot set in excessive plantar flexion.
VAULTING
Description: The amputee raises his entire body by early and excessive plantar flexion of the sound foot (Fig 14-7.).
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 the supporting limb is in the middle of stance phase and the other limb swings alongside it. When there 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 lowest point in swinging through, and the prosthetic foot would fail to clear the ground unless the amputee gained additional time and clearance by vaulting.
- 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 excessive length:
- Insufficient flexion of the knee because of insecurity or fear.
- Manual knee lock, excessive friction, or too tight an extension aid.
- Inadequate suspension allowing the prosthesis to slip off the stump (piston action).
- Too small a socket. The ischial tuberosity is above its proper location.
- Foot set in excessive plantar flexion.
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.).
When to observe: At and just after toe-off.
How to observe: From behind the patient.
Causes:
- Improper alignment of the knee bolt in the transverse plane.
- 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 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 STRIKE
Description: As the heel contacts the ground, the foot rotates laterally, sometimes with a vibratory motion (Fig 14-9.).
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.).
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 is transferred to the prosthesis.
UNEVEN HEEL RISE
Description: 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.).
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.
- Insufficient tension or absence of an extension aid.
- 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.
- Too tight an extension aid.
- Fear and insecurity. The amputee walks with little or no knee flexion.
- Manual knee lock.
TERMINAL IMPACT
Description: The prosthetic shank comes to a sudden stop with a visible and possibly audible impact as the knee reaches full extension (Fig 14-12.).
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.
- Too tight an extension aid.
- 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.
- Absent or worn resilient extension bumper in the knee unit.
UNEVEN STEP LENGTH
Description: The length of the step [*The term step refers to the distance between successive positions of the sound 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 the length of the step taken with the sound leg.
When to observe: During successive periods of double support.
How to observe: From the side.
Causes:
- 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.
- Hip flexion contracture or insufficient socket flexion. Any restriction of the hip extension range must be reflected by a shorter step length on the sound side.
- Insufficient friction at the prosthetic knee or too loose an extension aid. The pendular swing of the shank produces a prosthetic step length that is longer than the step length on the sound side.
EXAGGERATED LORDOSIS
Description: The lumbar lordosis is exaggerated when the prosthesis is in stance phase, and the trunk may lean posteriorly (Fig 14-13.).
When to observe: Throughout stance phase.
How to observe: From the side.
Causes:
- Hip flexion contracture. The pelvis tends to tilt downward and forward because the center of gravity is anterior to the support point (a theoretical point around which the supporting forces are balanced). A flexion contracture aggravates the tendency of the pelvis to tilt anteriorly because the shortened hip flexor muscles exert a downward and forward pull on the pelvis when the femur is at the limit of its extension range.
- Insufficient socket flexion.
- Insufficient support from the anterior socket brim.
- 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 cause increased lordosis. In addition, the amputee may roll his pelvis forward to assist the weak extensors to control knee stability.
- Weak abdominal muscles. The abdominal muscles restrain the tendency of the pelvis to tilt forward. If the abdominal muscles are weak, some of this restraint is lost, and the amputee will show increased lordosis.
Chapter 14 - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles
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