Implanted Neuro-Prostheses for Bipedal and Seated Mobility After Paralysis

Implanted motor system neuroprostheses can restore standing, stepping, and seated posture and balance to individuals with hemiplegia or paraplegia due to spinal cord injuries or stroke and represent powerful new interventions for central nervous system disorders. Surgically implanted pulse generators (IPGs) deliver small electric currents to excite the peripheral nerves coordinate contractions of the otherwise paralyzed muscles to generate functional movements of the entire limb. Implanted technologies offer numerous advantages over stimulation applied externally through the skin surface, including strong and repeatable stimulated responses, access to anatomically deep nerves and muscles, donning and doffing convenience, and continuous availability for spontaneous use. While systems based on surface stimulation have widely been used for exercise after paralysis with stationary rowing machines or cycles, implanted technologies developed to restore independent standing, stepping and seated function have rarely been adapted for such applications. Our research group at Case Western Reserve University and the Center for Advanced Platform Technology based at the Cleveland VA Medical Center is attempting to interface surgically implanted neuroprostheses to both commercially available stationary exercise cycles, and a specially instrumented recumbent trike for over ground pedaling. The system represents another option for recreation and independent mobility previously unavailable to implanted neuroprosthesis recipients, and may offer the potential for health benefits from exercising the large paralyzed muscles of the lower extremities and trunk.

Approximately 30 individuals with paralysis have received such implanted neuroprostheses for standing, walking or trunk control at our Center over the past 15 years. IPGs are sutured to the subcutaneous fascia and connected to stimulating electrodes inserted near or wrapped around the peripheral motor nerves to the target muscles. A transmitting and receiving coil taped to the surface of the skin over the IPG powers and communicates with the implant. The coil connects to an external control unit which is worn on a belt or affixed to the walker or wheelchair.  Users select the desired movement patterns from a menu of options with a wireless finger switch.  The resulting motions can be monitored by wireless wearable sensors to control progression through the movement pattern or react to applied disturbances. For cycling, the pilot is secured to the trike through appropriate custom adaptations to ensure bone and joint safety. The external controller processes sensor signals from the bike and instructs the IPG to deliver customized patterns of stimulation to the appropriate muscles at the proper time and intensity required to smoothly and continuously pedal over ground, thus seamlessly coordinating actions of the biological and mechanical systems.