EMG-based control for a C5/C6 spinal cord injury upper extremity neuroprosthesis

The goal of this project is to enhance the benefits of functional electrical stimulation (FES) for individuals with cervical mid-level spinal cord injury (C5-C6 SCI) by providing upper arm function that complements the hand function provided by current FES systems. As a result of stimulation to selected shoulder and elbow muscles, individuals are able to increase their range of motion, their reaching ability, and improve their overall shoulder stability. An approach that provides a natural way of controlling arm stimulation is proposed. The controller extracts information from recorded EMG activity of muscles under retained voluntary control and processes these signals to generate the appropriate stimulation levels for the stimulated paralyzed muscles. One subject with complete C5 paralysis has been implemented with this advanced neuroprosthesis which includes four implanted EMG electrodes and 24 channels of stimulation. Eight of these channels were used for hand grasp and six were used for trunk stimulation to provide posture control, trunk stability and weight relief. The shoulder and elbow implanted stimulation channels include the suprascapular, thoracodorsal and radial nerves (via nerve-cuff electrodes) and the pectoralis major, rhomboids and pronator quadratus muscles (via muscle-based electrodes). The thoracic portion of the pectoralis major was transferred to the scapula to restore the actions of the denervated serratus anterior muscle, essential for reaching tasks and shoulder stability. The four EMG channels implanted include the trapezius, biceps, deltoids and extensor carpi radialis longus. Currently, the EMG control strategy is being refined and tested with the subject including evaluation of the functional benefits of the intervention.