Design and Initial Validation of a Multiple Degree-of-Freedom Joint for an Ankle-Foot Orthosis

Abstract This paper presents the novel design of a multi-degree-of-freedom joint (M-DOF) for an ankle-foot orthosis (AFO) that aims to improve upon the commercially available double action joint (DAJ). The M-DOF is designed to maintain the functionality of the DAJ, while increasing dorsiflexion stiffness and introducing inversion/eversion. This increase in range of motion is designed to produce greater engagement from lower limb muscles during gait. The M-DOF was experimentally validated with one able-bodied and one stroke subject. Across walking speeds, the M-DOF AFO minimally affected the able-bodied subject's joint kinematics. The stroke subject's ankle dorsiflexion/plantarflexion and knee flexion were not heavily altered when wearing the M-DOF AFO, compared to the DAJ AFO. The new DOF allowed by the M-DOF AFO increased the inversion/eversion of the ankle by ∼3 deg, without introducing any new compensations compared to their gait with the DAJ AFO.