Case study evaluation of stability and mobility in a length-actuated transfemoral prosthesis

Unilateral transfemoral prosthesis users experience increased gait compensations, possibly because of their inability to produce sufficient knee flexion resistance during stance, ankle plantar flexion for forward progression, and leg shortening for toe clearance. This case study evaluates a novel kneeless prosthesis with powered length actuation (lengthening for push-off and shortening for toe clearance), which was hypothesized to result in greater stability, easier toe clearance, and assisted-forward progression, toward improving compensatory mechanisms of prosthesis users. Two persons with unilateral transfemoral amputation walked with both their habitual devices and the length-actuated prosthesis. Quantitative metrics of knee stability (thigh velocity and hip flexion/extension moment), mobility (ankle power, pelvis obliquity, hip abduction, toe clearance) and qualitative rankings were collected for both devices. Stability-related results showed increased confidence in the length-actuated prosthesis’ knee buckling avoidance with decreased prosthetic-side early stance hip extension and swing hip flexion angle/velocity. Mobility-related metrics showed decreased confidence in the length-actuated prosthesis’ toe clearance with increased frontal plane compensations and push-off ankle power (vaulting). Although both participants were encouraging of the overall concept, the user with higher mobility and a microprocessor knee preferred his own device, whereas the user with lower mobility and a passive knee preferred the length-actuated prosthesis. Both users had increased confidence (and decreased compensations) in knee stability during stance but continued to have compensations during swing to ease toe clearance. The device received positive feedback and was well received by the participant with a more recent amputation, knee buckling difficulty, and lower mobility level.