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Summary In order to differentiate between functional and mechanical chronic ankle instability, peroneal muscle function was examined in sudden inversion movements produced by a 30° tilting platform. Surface electromyographic (EMG) signals were recorded from the peroneus brevis and longus, tibialis anterior, and soleus muscles. An electrogoniometer was used to record rearfoot motion. Sixty-five subjects were assigned either to a functional ( n = 35) or a mechanical instability group ( n = 30) based on radiographic and mechanical stability measurements. Mechanical instability was characterized by a greater talar tilt and anterior drawer in the unstable leg. The groups did not differ significantly in the stability characteristics of the unaffected leg. Functional instability was reflected in significantly longer reaction times of the peroneus brevis (65 versus 57 ms, P = 0.002) and longus muscle (60 versus 54 ms, P = 0.01) in comparison with the mechanical instability group. Therefore, in those unstable patients without a clear mechanical insufficiency, the problem appears to be caused by a neuromuscular instability. Peroneal reaction times may help to distinguish between different causes of chronic ankle instability. |
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