Effects of prosthetic ankle power and foot stiffness category on biomechanical asymmetry and knee moment during walking at different speeds

People with unilateral transtibial amputation (uTTA) using a passive-elastic prosthesis typically walk with contact time (tc) and first and second peak vertical ground reaction force (F1 and F2) asymmetry and greater first peak external knee adduction moment in their unaffected versus affected leg. A previous study found that use of stance-phase powered prosthesis (BiOM) at a recommended power setting compared to a passive-elastic prosthesis can reduce tc asymmetry at self-selected speed and unaffected leg first peak external knee adduction moment at 1.50–1.75 m/s. However, the BiOM includes a passive-elastic prosthesis that can have different stiffness categories and can be tuned to different power settings, which may affect tc and F1 and F2 asymmetry and unaffected leg first peak external knee adduction moment. Thirteen people with uTTA used 16 different passive-elastic prosthetic foot stiffness categories and BiOM power settings to walk at 0.75–1.75 m/s. We found that use of the stiffest compared to least stiff category reduced F2 asymmetry. Use of the BiOM reduced tc asymmetry compared to a passive-elastic prosthesis and the effects of power setting on F1 and F2 asymmetry depended on walking speed. To minimize biomechanical asymmetry during walking at 1.25 m/s, people with uTTA should use the BiOM with power settings up to 20% greater than those that match biological ankle joint biomechanics. Such prosthetic settings could potentially reduce unaffected leg joint pain and/or osteoarthritis risk.