Hand opening by electrical stimulation in patients with spastic hemiplegia

Spasticity is a motor control disorder common after stroke, which can cause the fingers to involuntarily flex and form a fist. Even in the presence of strong spasticity, functional electrical stimulation can provide hand opening in hemiplegics with spastic finger flexor muscles through stimulation of the extensor digitorum communis muscle and the ulnar nerve. Stimulation of these sites did not reduce the activity in spastic finger flexor muscles, as hypothesized initially, and as might occur through a reciprocal inhibitory mechanism. In fact, flexor activity generally increased during extensor stimulation. In spite of increased flexor activity, the extension force was sufficient to fully extend the fingers. Similarly, stimulation of the finger extensors in able-bodied subjects did not reduce the EMG in the finger flexors, and could even increase it. The influence of voluntary effort on finger extension achieved by stimulation was also studied, since a neuroprosthesis for stroke patients might combine voluntary effort with stimulation. Finger extension was generally diminished when the subject attempted to assist the stimulated extension voluntarily or when stimulation followed voluntary flexion as might occur when trying to open the hand following a voluntary grasp. The largest extension was achieved when the subject remained relaxed. Since voluntary effort influences the degree of hand opening achieved by stimulation, some method of adjusting stimulation levels during task performance would be desirable in a clinically deployed neuroprosthesis