Powered Knee-Ankle Prostheses Can Improve Hip Compensations

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People with transfemoral amputations often exhibit gait compensations due to the lack of ankle push-off power and control over swing foot position using passive prostheses. Powered prostheses can restore this functionality, but their effects on compensatory behaviors, specifically at the residual hip, have not been well understood, according to a recent study.

Researchers investigated residual hip compensations through walking experiments with three people with transfemoral amputations using a low-impedance powered knee-ankle prosthesis compared to their passive prostheses.

The powered prosthesis used impedance control during stance for compliant interaction with the ground, a time-based push-off controller to deliver high torque and power, and phase-based trajectory tracking during swing to provide user control over foot placement.

Experiments showed that when the subjects utilized the powered ankle push-off, less mechanical pull-off power was required from the residual hip to progress the limb forward. Overall, positive work at the residual hip was reduced for two of the three subjects, and negative work was reduced for all subjects. Moreover, all subjects displayed increased step length, increased propulsive impulses on the prosthetic side, and improved impulse symmetries, the study found. Hip circumduction also improved for subjects who had previously exhibited this compensation on their passive prosthesis.

These improvements in gait, especially reduced residual hip power and work, have the potential to reduce fatigue and overuse injuries in persons with transfemoral amputations, the study found.

The study "Effects of a Powered Knee-Ankle Prothesis on Amputee Hip Compensations: A Case Series," was published in IEEE Xplore.