RESTORATION OF PRONOSUPINATION CONTROL BY FNS IN TETRAPLEGIA - EXPERIMENTAL AND BIOMECHANICAL EVALUATION OF FEASIBILITY

Individuals with C5/C6 tetraplegia lack voluntary control of the forea rm pronators. We evaluated the feasibility of restoring forearm pronat ion/supination control using an electrically activated pronator oppose d by voluntary supination. To this end, we measured the electrically p roduced pronation moments of subjects with tetraplegia. The maximal pr onation moment achieved by stimulating the pronator quadratus ranged f rom 30 to 100 N cm in three forearms of two subjects. These moments we re sufficient to produce forearm pronation in all three forearms. Volu ntary control of pronosupination during constant pronator stimulation was achieved by having the subject voluntarily supinate or relax to ch ange the balance of rotational torques acting on the forearm. In all c ases, the subjects were able to supinate voluntarily against the conti nuously stimulated pronator, producing intermediate angles between ful l pronation and full supination. We also observed under some condition s that subjects could voluntarily pronate and supinate even without pr onator stimulation. Using a biomechanical model, we show how pronation can be initiated from a supinated position using the brachioradialis, with gravity completing the pronation. This method of pronation witho ut stimulation is extremely sensitive to the orientation of the forear m in the gravitational field, and thus is not a widely applicable tech nique. We conclude that forearm pronosupination via Functional Neuromu scular Stimulation is feasible, and would provide subjects the ability to pronate without the assistance of gravity.