Impact of ankle locking on gait implications for the design of hip and knee exoskeletons

Patients affected by spinal cord injury cannot usually regain unassisted walking. This is why several research groups and companies have developed exoskeletons which enable these people to regain mobility in a standing position. The simplest joint configuration for exoskeletons is to actuate the knees and the hips in the sagittal plane. The ankles and feet are then unactuated and their range of motion is limited. In this paper we investigate the impact of locking the ankle joint on gait. We therefore recorded gait trajectories on seven subjects whose ankles and feet were restrained. This pilot study demonstrates that hip and knee trajectories change when the subjects cannot move their ankles. The implications for the design and control of exoskeletons with active degrees of freedom at the hips and knees are discussed.