Design of a two degree-of-freedom ankle-foot orthosis for robotic rehabilitation

An ankle-foot orthosis (AFO) is commonly used to help subjects with weakness of ankle dorsiflexor muscles due to peripheral or central nervous system disorders. Both these disorders are due to the weakness of the tibialis anterior muscle which results in lack of dorsiflexion assist moment. The deformity and muscle weakness of one joint in the lower extremity influences the stability of the adjacent joints, thereby requiring compensatory adaptations. We present an innovative ankle-foot orthosis (AFO) that was designed to allow two degree-of-freedom motion while serving to maintain proper foot position for subjects. The prototype AFO would introduce greater functionality over currently marketed devices by means of its inversion-eversion degree-of-freedom in addition to flexion/extension. The flexion/extension is controlled with the help of an actuator and inversion/eversion with a spring and a damper.