Design of a Hydraulic Prosthetic Knee with Control Moment for Adjustable Stance-Phase Knee Flexion

Abstract

Lower-limb amputees worldwide have been increasing continuously in recent years. Hydraulic knees are suitable for active transfemoral amputees in developing countries due to their adaptability to various walking speeds and greater accessibility compared to high-end prosthetics. However, most hydraulic prosthetic knees operate via ground reaction force control, which exhibits a double-peak characteristic, causing slight flexion during the early stance phase, leading to unnatural and asymmetrical gait patterns for amputees. This study proposes a novel technique that expands the concept of the two-axis for application in a hydraulic prosthetic knee, utilizing the control moment to achieve stance-phase control (CMSPC knee). The control moment exhibits only one positive peak during the stance phase, allowing for adjustment of suitable stance-phase knee flexion by varying the spring stiffness. The single-subject walking experiment was conducted in the gait laboratory with one transfemoral amputee to evaluate the conceptual design. The subject walked on a treadmill at a constant velocity of 0.9 m/s, a self-selected walking speed, for 30 seconds, repeated four times for each spring stiffness. The results showed that the CMSPC knee can adjust the maximum stance-phase knee flexion from approximately 4.15° to 13.89°, which is roughly the same range observed in non-disabled individuals. Finally, most gait symmetry in temporal variables was significantly improved, with comparable results between the best condition, at a spring stiffness of 12.2 N/mm, and the condition without a spring (Mann-Whitney, p < 0.05). The condition without a spring is represented by hydraulic knees that offer slight stance-phase knee flexion.