Design and Evaluation of a Powered Four-Bar Prosthetic Hip Joint

Abstract

Hip-level amputees face challenges in ambulation due to the lack of residuum musculature and prosthetic hip actuator power. A powered four-bar hip, providing augmenting hip flexion-extension moments, was successfully designed, prototyped, and tested. The powered hip contains the Össur Power Knee 2 harmonic drive DC motor, providing up to 96 N-m of torque. Additionally, the powered hip contains a four-bar linkage to guide hip flexion-extension, and a torque transmission linkage to convert motor torque to a hip flexion-extension moment. Link lengths were optimized to balance size, weight, range of motion, mechanical advantage, and component forces. The powered hip prototype has mostly met the design criteria and has passed all ISO 15032:2000 A100 static compression tests. Furthermore, three able-bodied individuals, with an average weight of 96 kg, walked successfully with the powered hip by means of a hip-knee-ankle-foot prosthesis simulator. No prototype cracking or deformation were observed during testing. The powered hip would benefit from a supplementary bearing to reduce output bearing loading. Moreover, future design optimization could reduce device weight, improve cosmesis, and provide more mechanical advantage at larger hip flexion angles to improve device performance beyond level walking. Future powered hip evaluation with hip-level amputees will further inform device performance.