Effects of a Powered Knee–Ankle Prosthesis on Intact Joint Biomechanics Across Sustained Activities of Daily Life: A Case Series

Lower-limb prosthesis users often overuse their intact joints due to the lack of positive work generated by their devices. This overreliance has been shown to increase joint loading, degeneration, and pain. While powered prostheses can generate positive work and therefore reduce this burden, clinical studies of commercialized single-joint devices have demonstrated inconsistent results. Recently, prototype powered knee and ankle prostheses have shown more consistent advantages over passive devices in laboratory settings. Most of the studies, however, focus on the biomechanics of the prosthesis rather than its impact on the user's joints, study isolated activities, and/or do not replicate the demands of continuous real-world use. This case series analyzes the intact joint moments and work for N=3 above-knee amputee subjects using a powered knee-ankle prosthesis vs. their prescribed passive device during a continuous, sustained sequence of the primary activities of daily life. The powered prosthesis decreased peak hip flexion moment (but increased peak extension moment) during level walking, and decreased peak knee extension moment for all other activities. For at least two of the three subjects, the powered prosthesis decreased total positive work across the intact joints during ascent activities (stair ascent, sit-to-stand) and decreased negative total work for descent activities (stair descent, stand-to-sit). This case series suggests that powered knee-ankle prostheses have the potential to reduce overuse of intact joints in emulated real-world conditions.