The effect of wrist angle on electrically evoked hand opening in patients with spastic hemiplegia

This paper studied the effect of wrist angle on the amount of hand opening achieved by electrical stimulation in people with spastic hemiplegia. With their forearm in pronation, subjects were asked to relax while their affected wrist was passively moved in steps of about 15 degrees from full flexion into extension. Trains of stimuli were applied to the long finger extensor muscles through surface electrodes on the forearm. At each wrist position stimulation was turned on for a few seconds until hand opening equilibrated. Wrist angle and fingertip positions were recorded using a three-dimensional (3-D) motion analysis system. Maximal displacements between thumbtip and each fingertip occurred when the wrist was fully flexed. As the wrist was extended, hand aperture achieved by electrical stimulation progressively declined, reaching zero at 40 degrees of wrist extension. We conclude that electrical stimulation can significantly increase the grasp aperture of the hemiplegic hand, but this is strongly dependent on wrist posture and accompanying voluntary effort.