Design Changes in Ankle-Foot Orthosis Intended to Alter Stiffness Also Alter Orthosis Kinematics

The specific aim of the present research was to determine whether kinematics of an ankle-foot orthosis (AFO) are dependent on design changes made to alter stiffness. Four AFOs of different design were loaded in plantaiflexion/dorsiflexion. The applied moment, coupled moments, and screw axis were determined. Increased trim resulted in decreased stiffness and a posterior shift in the location of the screw axis. The flexible-hinge design exhibited a substantial increase in the variability of the screw axis location compared to the locked-hinge design. Results indicate that design changes intended to alter stiffness also alter the kinematics of the orthoses.