Development of an upper extremity FES system for individuals with C4 tetraplegia

The application of functional electrical stimulation (FES) to provide upper extremity function for individuals with C4 tetraplegia is under investigation. In this study, a FES system was designed that allowed one individual with complete C4 tetraplegia to coordinate stimulated lateral or palmar prehension with stimulated arm movements using contralateral shoulder position. The system consisted of percutaneous intramuscular electrodes implanted to muscles for hand grasp and release, supination, elbow flexion, and extension and arm adduction. Due to peripheral denervation, transposition and subsequent stimulation of the paralyzed latissimus dorsi muscle provided elbow flexion and transfer and stimulation of the paralyzed extensor carpi ulnaris muscle provided forearm supination. A suspended sling provided shoulder joint stability. The subject controlled stimulation proportionally using contralateral shoulder motion sensed by a position transducer. Control of stimulated hand grasp and release were coupled with stimulated arm motions so that hand-to-mouth activities could be accomplished with one motion of the contralateral shoulder. With this system, the subject was able to grasp a milk carton placed in the hand and lift and lower it from his mouth to drink from a short straw. He could also scoop a semisolid substance with an adapted spoon and lift and lower it from the work surface to his mouth to eat. The subject required assistance to place the milk carton or spoon in his hand and position the plate for scooping. Further investigation is needed to generate the necessary arm movements to make completion of these tasks possible without assistance and to expand the range of activities possible with the FES system.