In-silico simulations to study the effects of ankle-joint misalignments in Ankle-Foot-Orthoses during level walking

Exoskeletons and orthotic devices are commonly used in physical rehabilitation. However, these devices, fitting intimately with the human body, often lead to skin-related issues amongst users. Misalignments between orthotic and anatomical joints cause relative sliding motion between the limb and orthosis and also cause pressure points on the limb, which may contribute to these skin problems. This research quantifies the effects of sagittal plane ankle-joint misalignments for an ankle-foot orthosis (AFO) user during walking. A 2D mathematical model that simulates the effects of sagittal plane ankle-joint misalignments in terms of relative motion between the limb and the orthosis was developed using MATLAB software. The orthotic ankle-joint was systematically misaligned against the anatomical ankle-joint to generate various misalignment conditions. Published gait data of 5 healthy subjects was used to generate walking kinematics which was then superimposed with an articulated AFO. The simulations showed that Anterior-Posterior misalignments resulted in greater pistoning motion than Proximal-Distal misalignments. Combined misalignments (Posterior-Distal, Anterior-Proximal, Posterior-Proximal, and Anterior-Distal) resulted in higher overall relative motions between the limb and AFO. The model also predicted pressure points on the shank and foot caused by misalignments. This study demonstrates that misaligned ankle-joints in AFOs lead to relative sliding motion and pressure points during walking.