9. Spina bifida 10. Multiple sclerosis.
Only a small part of the clinical research on these conditions currently involves gait analysis.
When a patient suffers from some condition which affects the locomotor system, their usual response is to make a series of compensations in an attempt to continue walking as well as possible under the circumstances. The difficulties in distinguishing between the original condition and the patient's compensations have already been referred to. The use of gait analysis techniques, particularly the more advanced methods involving the measurement of moments, forces and powers, gives a better insight into the exact nature of the deficit and the way in which the patient is able to compensate for it. This may lead to a better understanding of the pathological condition itself, and may also suggest improved methods of treatment. For example, if a patient is compensating for weakness of one muscle group by using other muscles, physical therapy could be aimed at strengthening those muscles, and perhaps at increasing the patient's skill in using these slightly unnatural movements.
The use of gait analysis in cerebral palsy has already been discussed at length. It is used not only for the management of individual patients, but also in an attempt to improve our understanding of the condition, by dividing it into different diagnostic groups, and by monitoring objectively the results of different forms of treatment. Of particular
Applications of Gait Analysis 189 importance is the production of general hypotheses on the interaction between the neurological deficit, the patient's compensations, and the results of any treatment they might have received (Rose, 1983). An example of this was seen in Chapter 3, where a hypothesis was described which sought to explain the development of crouch gait following Achilles tendon lengthening (see Fig. 3.26). Gait analysis may also be used to classify those patients who have not undergone Achilles tendon lengthening, but who develop a crouch gait as a direct result of muscle imbalance. The classification is made according to the degree of spasticity of the hip flexors and the hamstrings, and aids in the selection of the best form of treatment.
An examination of the moments of force about the joints may also explain some of the gait abnormalities in CP, since deformity may reduce the muscle lever arms, requiring very high muscle forces to be produced in order to produce modest joint moments.
Hemiplegia due to a cerebrovascular accident ('stroke') is a common condition in the elderly, which often severely affects gait. Brandstater et al. (1983) related the temporal parameters of gait, measured using foot-switches, to the clinical severity of the condition, measured on a six point scale. They found that both the walking speed and the symmetry of the gait were strongly correlated with the clinical severity. A number of other measured parameters also correlated with the clinical condition, but these were thought to have changed because of the reduction in walking speed, rather than as a direct result of the stroke. They found, not unexpectedly, that the motor deficit was more important than the sensory deficit in affecting the walking pattern. They also noted that although the relative time spent in single-leg stance on the affected side correlated strongly with the clinical severity, the absolute time spent on that leg did not, because of the slower walking speed in the more severely affected patients. They regarded the measurement of walking speed, in particular, as an 'extremely useful component' of the evaluation of a hémiplégie patient.
Investigation of forms of treatment
For pathological conditions that affect the locomotor system, gait analysis provides an excellent way to compare the results of different forms of treatment, because it is able to provide objective data.
Reviewers of scientific publications have started to insist that claims about clinical results should be supported by evidence, making the methods of gait analysis increasingly valuable as a tool for research.
There is often a reluctance to use gait analysis for this purpose, since
190 Gait Analysis: An Introduction
many clinicians associate the term with the use of the complicated and expensive combined kinetic/kinematic systems, of which there are relatively few in the world. However, clinical trials seldom need the detailed data on the functioning of the locomotor system of which these systems are capable. More commonly, simpler methods are perfectly adequate to measure the improvement which takes place after a particular form of treatment. Insufficient use is made of the general gait parameters, yet they are simple to measure and the results are readily amenable to statistical analysis.
One of the commonest ways in which gait analysis is used in clinical research is to perform a direct comparison between two or more methods of treatment. This type of research normally takes the form either of a prospective study, which is planned in advance and follows the patients over a period of time, or a retrospective study, which examines the consequences of some form of treatment, after the event. As a general rule, prospective studies give more accurate results, since clearly defined procedures can be laid down before the study begins, and the patient's condition is known both before and after treatment. Retrospective studies may suffer from uncertainties as to the pre-treatment condition of the patient, and sometimes as to the exact details of the treatment given. Nevertheless, they may still provide valuable data on the results of a particular form of treatment.
In cerebral palsy, both prospective and retrospective studies may be used to compare different forms of treatment, although retrospective studies may be somewhat more unreliable than usual, because the clinical features of the condition are so variable. A typical way in which gait analysis can be used in cerebral palsy research is to study two groups of patients who undergo different surgical procedures for the same condition. Parameters such as joint angles and general gait parameters may be measured before and after surgery. If the differences between the techniques are small, it would very difficult to demonstrate that one surgical technique was superior without the benefit of objective methods of measurement. The routine follow-up of the results of surgery in cerebral palsy also constitutes clinical research, particularly if the reasons for past successes and failures are analyzed and used as a guide to future treatment.
The comparison of different surgical procedures is also frequently used in studies of joint replacement. A number of studies have shown that, in mechanical terms, the functioning of a prosthetic hip or knee joint tends to be very different from that of a normal joint. Newer designs, and newer methods of surgical implantation, may be tested by the methods of gait analysis to determine how close to 'normal' they are,
Applications of Gait Analysis 191
100
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Preoperative Postoperative
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Fig. 5.2 Change in coronal plane external knee moment from abduction (abnor- mal) to adduction (normal), following total knee replacement surgery.
and how much they have improved on earlier designs. The alignment of prostheses plays a large part in determining the stresses to which the prosthesis and the prosthesis-bone interface are subjected. Gait analysis can demonstrate the change in alignment following surgery, as in Fig. 5.2, which shows the change in the knee moment, measured in the coronal plane, before and after a total joint replacement. Gait analysis can also be used to examine different operative techniques. For example, total hip joint replacement may be performed using a number of different approaches, and gait analysis may be used to look for any functional deficits which result, for example, from cutting particular muscles.
As well as its use in comparative trials between two or more forms of treatment, gait analysis is also commonly used simply to quantify the benefit which a patient receives from a particular type of treatment. In such cases, a comparison may be made with pre-treatment data values for that patient, and with comparable results from normal individuals.
Figure 5.3 shows the elimination of an excessively high external adduction moment at the knee by the operation of high tibial osteotomy (Jefferson and Whittle, 1989).
The design and prescription of orthose tends to be based much more on art than science, and a significant proportion of orthotic devices are
192 Gait Analysis: An Introduction
£
100
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Preoperative ,__ Postopei 3tiv6
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Fig. 5.3 Change in coronal plane external knee moment from excessive adduction moment to abnormally low biphasic moment, following high tibial osteotomy (Jefferson and Whittle, 1989).
regrettably not used by the patients for whom they are made. Gait analysis is able to provide an insight into the functioning of orthoses, and to compare different designs. It may also permit improvements to be made to existing designs, such as the Saltiel anterior floor reaction orthosis (Harrington el al., 1984). Some objective studies of orthoses have failed to demonstrate that they have any significant mechanical effects. It then becomes arguable whether the devices really do have no effect, or whether their mode of action is too subtle for the methods of measurement being used.
Gait analysis can be used for the assessment of new or modified forms of lower limb pros theses. It may be used to examine the effects of changing the design of a prosthetic limb, such as by altering the mass distribution (Tashman et al., 1985), or using knee joints with different types of braking mechanism (Hicks et al., 1985). Two types of measurement are of particular value in this type of assessment - the kinematics of motion and the muscle forces the amputee has to produce in order to walk.
Measurement of the power output across the ankle joint is very valuable when comparing different prosthetic foot mechanisms. One of
Applications of Gait Analysis 193 the major differences between the prosthetic foot and the natural foot is the inability of the prosthetic foot to generate power during the push off phase of walking. However, it is able to store energy earlier during the stance phase, and to release it during push off, which may lead to a more natural gait pattern. Gait analysis can be used to examine the energy storage and recovery by prosthetic foot mechanisms, and to determine how well particular types of foot suit different categories of patient. For example, a young subject who has suffered a traumatic amputation is much better able to take advantage of an energy-storing foot mechanism than an elderly subject who has received an amputation for vascular disease.
Electrical stimulation of muscle is becoming increasingly important as a method of treatment in a number of different conditions. It may be used either as a rehabilitation aid, to build up strength in weakened or paralyzed muscles, or as a method of producing useful muscle contraction. The latter is referred to as functional electrical stimulation (FES). Electrical stimulation has been used in cerebral palsy to build up strength in paretic muscles, and gait analysis has been used to monitor the resulting improvements. One important use of FES is to act as an 'electronic orthosis' (Muccio et al., 1989), for example for the control of foot-drop by the stimulation of the anterior tibial muscles. The monitoring of the functioning of such a device, and its comparison with mechanical orthoses, would be difficult to do without the use of some form of gait analysis.
Another important use for FES is to enable paralyzed people to walk.
The three methods currently under investigation for this purpose are:
1. A purely mechanical approach, using an orthosis