Adapting Biomimetic Kinematics for Controlling a Powered-Knee, Passive-Ankle Prosthesis Across Inclines

Abstract

Despite promising benefits for people with limb loss, powered multi-joint prostheses from the research field have not been translated into the clinical space. Commercial powered knee prostheses like the Össur Power Knee ${ }^{\text{TM}}$ are paired with passive feet which lack the range of motion of biological ankle joints, especially on steep inclines. This discrepancy prevents the direct translation of emerging biomimetic control methods for powered knee-ankle prostheses, which implicitly assume both joints exhibit normative biomechanics. To enable commercial prostheses to benefit from biomimetic control methods on inclines, this paper adapts a continuous knee kinematic model to minimize the difference in global foot angle compared to able-bodied reference data, under the assumption that the ankle joint is locked. In a pilot experiment with an above-knee amputee participant, our adapted controller produced substantial benefits compared to a baseline controller that only tracks ablebodied knee trajectories. Level-ground walking performance is similar to existing methods despite the change of objective, and on steep inclines, prosthesis load-bearing and center of pressure progression are restored to near-normative levels. These results show a promising pathway towards translation of biomimetic control methods onto existing commercial hardware, allowing near-term impacts with tangible benefits for prosthesis users.