A Right
3. If the socket is uncomfortable, the subject may be reluctant to apply large forces to the prosthetic limb
Pathological Gait 121 fitted, the mechanical coupling between the femur and the prosthetic limb can never be as good as in the normal individual, for three reasons:
1. The lever arm between the hip joint and the socket is relatively small,
122 Gait Analysis: An Introduction
decreased cadence. The stride length was close to normal, but the decreased cadence led to a decreased velocity. Lateral trunk bending was often present; they attributed this partly to a compensation for a wider walking base, which was used to improve stability, and partly to a compensation for a decreased efficiency of the hip abductors, due to movement of the femoral stump within the socket. Heel rise took place earlier in the stance phase than in normal individuals, because of a reduction in the ability to dorsiflex the ankle. The magnitude of the heel rise in early swing was increased, especially at higher walking speeds - it is very sensitive to the frictional properties of the knee mechanism.
There was a tendency to vault on the normal leg during the swing phase of the prosthetic leg. Since the prosthetic leg shortened adequately during the swing phase, this vaulting was probably not necessary. It may have been used to gain added security, since the ground clearance of the prosthetic limb cannot be judged in the absence of proprioception.
Figure 3.23 shows plots of the hip, knee and ankle angles in a 17-year- old female AK amputee with a hydraulic knee mechanism. It should be compared with Fig. 2.5, which shows comparable data from a normal subject. The knee moves into a few degrees of hyperextension before the
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Fig. 3.23 Hip, knee and ankle angles dunng walking in an above knee amputee.
The main abnormality is hyperextension of the knee (c/Fig. 2.5).
Pathological Gait 123 end of the swing phase, and remains hyperextended until near the end of the stance phase, which is a little shorter than normal. The swing phase knee flexion is almost normal. The hip movement is also almost normal, except for a sudden increase in flexion late in the swing phase, as the knee mechanism reaches its extension stop. Flexibility in the foot mechanism leads to a normal pattern of ankle motion, although the magnitudes of these movements are less than normal.
A BK amputation deprives the user of the ability to plantarflex and dorsiflex the ankle, although the artificial foot normally provides some flexibility in this axis, and its shape provides partially functioning initial and terminal rockers. The loss of active plantarflexion at the end of the stance phase means that muscle power cannot be used to provide an active 'push off,' and the effective length of the leg is shorter than normal, so that it has to be lifted clear of the ground sooner (Breakey, 1976).
According to Saunders et al. (1953), the path of the center of gravity is essentially normal after a BK amputation, since the hip and knee together can largely compensate for the loss of the ankle joint. If both ankle and knee are lost, as in an AK amputation, the compensation is incomplete.
Figure 3.24 shows the hip, knee and ankle angles of a 47-year-old male
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Fig. 3.24 Hip, knee and ankle angles dwring walking in a below knee amputee.
The ankle angle shows slight abnormalities (c/Fig. 2.5).
124 Gait Analysis: An Introduction
BK amputee using a 'multiflex' foot, walking with a cadence of 95 steps/min, stride length 1.45 m and velocity 1.15 m/s, all of which are towards the lower end of the normal range. The hip and knee angles are entirely normal. The ankle angle is also just within normal limits, although the movement into plantarflexion at the end of the stance phase is of relatively low magnitude and occurs a little late. This is because it is a passive movement, resulting from the removal of loading from the elastic foot mechanism, rather than the active plantarflexion seen in normal subjects.
There are considerable differences between subjects in amputee gait.
The subject whose gait is illustrated in Fig. 3.24 walks almost normally.
However, according to Breakey (1976), the 'typical' gait pattern of the BK amputee includes:
1. Delayed foot flat
2. Reduced stance phase knee flexion 3. Early heel off
4. Early toe off
5. Reduced stance phase duration 6. Reduced swing phase knee flexion.
Common pathologies affecting gait
While many pathological conditions can cause an abnormal gait, a group of neurological conditions stand out as being particularly important. If the basic defect is in the brain, the gait abnormality is often very complex and accurate diagnosis may only be possible using the techniques of modern gait analysis. In contrast, gait abnormalities due to more 'peripheral' disorders, such as diseases of the joints, tend to be much easier to identify and interpret. The following sections outline the gait disorders which may result from some relatively common conditions that affect the brain.
Cerebral palsy
One of the most important current applications of gait analysis is in the assessment of patients with cerebral palsy (CP). Cerebral palsy usually follows brain damage around the time of birth. It involves a loss of the selective control of muscles by the motor cortex, and the emergence of spasticity and primitive patterns of contraction. As a general rule, the muscles are not weak, but they may be unable to contract adequately at
Pathological Gait 125 the appropriate times in the gait cycle, due to a loss of coordination.
Muscular contraction cannot be turned on or off rapidly, and there is commonly a co-contraction of antagonists.
The characteristics of CP are given by Gage as follows:
1. Abnormal tone which varies with position and/or movement 2. In a growing child, a propensity to develop muscle contractures 3. Loss of selective control of muscles
4. The necessity to use primitive reflexes to accomplish ambulation 5. Difficulty with balance.
There is considerable variation between one patient and another in the way in which cerebral palsy affects the positions and movements of the joints. The clinical picture depends on which muscles are affected, and on the timing of their contraction during the gait cycle. Since the neurological deficit is permanent and irreparable, the timing of muscular contraction cannot be altered by treatment. However, four basic methods of treatment can be employed:
1. Muscles can be made stronger by training
2. Muscles can be made weaker or non-functional by cutting or lengthening their tendons
3. The mode of action of muscles can be changed by tendon transplantation
4. Orthoses can be used to limit the movement of a joint, or to apply a force in a particular direction.
The two main varieties of cerebral palsy which affect the gait are spastic hemiplegia and spastic diplegia. The use of gait analysis to plan and monitor the treatment of cerebral palsy is discussed further in Chapter 5.
Spastic hemiplegia
Spastic hemiplegia is the commonest neurological cause of an abnormal gait. As well as occurring in cerebral palsy, it is also frequently seen in elderly people who have suffered a cerebro vascular accident ('stroke'). It may also occur following traumatic brain damage. It is characterized by spasticity and loss of function in some or all of the muscles of one leg, the other leg being normal or nearly normal. A hémiplégie patient usually possesses a mixture of normal motor control, spasticity and 'patterned responses,' the exact combination depending on the severity and location of the brain damage (Perry, 1969). As well as problems with moving and controlling their limbs, many hémiplégie patients also experience difficulty in maintaining balance, because a defect in the 'body image'
126 Gait Analysis: An Introduction
causes them to ignore the affected side. Winters et al. (1987) showed that the gait pattern of children and young adults with this condition could be divided into four groups. These are numbered I to IV, in order of increasing severity, each group having all the neurological deficits of the preceding one, with some addition. In general, the results of this study of young people agreed with other publications on the gait of elderly subjects who had suffered a cerebrovascular accident.
Group I subjects essentially suffer from a single problem - a foot drop