Relationship between assistive torque and knee biomechanics during exoskeleton walking in individuals with crouch gait

Crouch or "flexed knee" gait is a pathological gait pattern affecting many individuals with cerebral palsy. One proposed method to alleviate crouch is to provide robotic assistance to knee extension during walking. The purpose of this study was to evaluate how the magnitude of knee extensor torque affects knee kinematics, kinetics, and muscle activity. Motion capture, ground reaction force and electromyography data were collected while four participants with crouch gait from cerebral palsy walked with assistance from a novel robotic exoskeleton on an instrumented treadmill. Different magnitudes of knee extensor torque were provided during the stance (range: 0.09-0.38 Nm/kg) and swing (range: 0.09-0.29 Nm/kg) phases of the gait cycle. Using a linear regression analysis, we found that greater torque from the exoskeleton was positively associated with increased knee extension (reduction in crouch) at foot contact and mid-stance, negatively associated with the biological knee extensor moment, and positively associated with knee flexor muscle activity. Determining the relationships between exoskeleton assistance and knee kinematics and kinetics will benefit the continued investigation of robotic treatment strategies for treating crouch gait. Our findings indicate the importance of properly tuned robotic control strategies for gait rehabilitation.