O&P Library > Atlas of Limb Prosthetics > Chapter 14

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:

1. 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.
2. 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.
3. 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.

1. Between heel strike and midstance
2. At midstance
3. Between midstance and toe-off

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:

1. Weak hip abductors. By shifting the center of gravity toward the prosthesis, lateral bending counteracts the tendency toward pelvic drop on the sound side.
2. 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.
3. 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.
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 the causes 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 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:

1. 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.
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.

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:

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.

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:

1. 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.
2. 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:

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:

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:

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:

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.

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:

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 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:

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 be reflected 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 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:

1. 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.
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 cause increased lordosis. In addition, the amputee may roll his pelvis forward to assist the weak extensors to control knee stability.
5. 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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