Sensor-Based Stance Control With Orthosis and Functional Neuromuscular Stimulation for Walking After Spinal Cord Injury

ABSTRACT An isocentric reciprocal gait orthosis (IRGO) was combined with a multichannel functional neuromuscular stimulation (FNS) in a prototype hybrid neuroprosthesis (HNP) to take advantage of each subsystem in providing stability and power for forward progression for walking in paraplegia, respectively. In this HNP, a hydraulic stance control knee mechanism (SCKM) was combined with a sensor-based FNS controller to provide knee stability during stance and foot-ground clearance during swing while minimizing knee extensor stimulation. The feasibility of reducing both the upper limb loading applied to a walking aid and muscle stimulation duty cycle was examined in an individual with paraplegia using this HNP. The SCKM supported the user during stance while the FNS controller deactivated stimulation to the knee extensor muscles once the knee was constrained in extension by the SCKM. The HNP reduced the average vertical upper limb forces on the walking aid by 36% and 17% as compared with walking with FNS only and IRGO, respectively. The HNP was also capable of reducing the stimulation duty cycle of the knee extensor muscles by 68% of the preprogrammed baseline levels used in FNS-only walking. Furthermore, the additional mass and internal friction of the SCKM was shown to have minimal effect on knee angle trajectory during swing. These results show that the HNP can significantly reduce the user’s upper limb loading and the amount of muscle stimulation, potentially enabling individuals with paraplegia to walk longer distances and with less effort than with either bracing or FNS alone.