Above-Knee Amputees' Balance and Recovery Strategies After Mediolateral Perturbations from a Cable-Driven System

This study aims to analyze the balance responses and foot placement strategies of above-knee amputees following controlled mediolateral perturbations and to compare these responses with those of non-amputee individuals.

We recruited eight above-knee amputees and eight non-amputee participants to walk on an instrumented treadmill while a cable-driven system delivered mediolateral perturbations to the waist. We applied perturbations at three gait timings (heel strike, late swing, and late single support), two directions (prosthesis and sound side, left and right for non-amputees), and two force magnitudes (7.5 and 15% of body weight), for a total of twelve conditions. We applied each condition once per trial and recorded five trials. We randomized the order and timing of perturbations within each trial and recorded full-body motion capture to quantify balance and recovery behavior.

Above-knee amputees fell 16 times when pulled toward their sound side and 29 times when pulled toward their prosthesis side, whereas non-amputee participants never fell. Instability increased for both groups with higher perturbation magnitudes and later gait timings. Amputees showed significantly greater instability than non-amputees during late single support and high-force pulls. Their recovery strategies also diverged during late single support, varying by pull direction. The recovery time and number of steps required to regain balance depended on both direction and magnitude.

Above-knee amputees demonstrated distinct recovery strategies and greater instability than non-amputee participants. These findings highlight the need for advancements in assistive technology to improve balance and reduce fall risk for above-knee amputees.