Targeted muscle reinnervation for improved myoelectric prosthesis control

A novel method for the control of myoelectric upper limb prostheses has been developed. By transferring the residual nerves of amputees to spare muscles in or near the residual limb, additional myoelectric control signals are made that allow the simultaneous control of multiple degrees-of-freedom in the prostheses. Since the nerve function correlates physiologically to the function it is controlling in the prosthesis, operation is more natural and thus easier than current control paradigms. The procedure has been successfully employed in two amputees. A patient with traumatic bilateral shoulder disarticulation amputations had four brachial plexus nerves transferred onto denervated pectoralis muscle segments. Four independent new myosites were created that allowed for simulataneous control of two degrees-of-freedom with shoulder movement still available for a third degree-of-freedom. Objective testing showed a doubling of blocks moved with a box and blocks test and a 26% increase in speed with a clothes pin moving test. Furthermore, the skin of the anterior chest was reinnervated with sensory fibers from the patient's hand and arm. A second patient with a long transhumeral amputation had his median nerve transferred on to a denervated medial biceps and his distal radial nerve transferred on to his brachialis muscle. Both nerves successfully reinnervated the respective muscles. This patient was then also able to simultaneously use myoelectric control for a powered elbow and hand, and simultaneously controlled wrist rotation with shoulder motion for a total of three degrees-of-freedom. Objective testing showed over a three-fold improvement of speed with the block and box test and significant improvement with AMPS testing. Skin sensory reinnervation did not occur. These patients demonstrate the potential for targeted muscle reinnervation to improve the function of powered artificial limbs and possibly provide unique and valuable sensory feedback to the amputee.