Staying in dynamic balance on a prosthetic limb: A leg to stand on?

• We examined single-leg stance on prosthesis vs. sound limb balancing on narrow ridges.
• When balancing, amputees compensate lack of ankle strategy through counter-rotation.
• Single-leg stance on a prosthesis involves same mechanism as balancing on 20–40 mm ridge.
• Balancing on ridges was a weak predictor for ability to stand on a prosthesis.

With the loss of a lower limb, amputees lack the active muscle empowered control of the ankle that is important for balance control. We examined single-leg stance on prosthesis vs. sound limb balancing on narrow ridges in transtibial amputees. When balancing on the prosthetic limb, the lateral displacement of the center of pressure was reduced and was compensated by an increase in counter-rotation. We show that single-leg stance on a prosthetic limb can be compared to balancing on a narrow ridge. Standing on a prosthetic limb involves the same balance mechanisms as balancing on narrow ridges of 40-mm to 20-mm width. Yet, the ability to balance on a narrow ridge with the sound limb was only a weak predictor for an amputee's ability to stand on the prosthetic limb. Balancing in single-leg stance on a prosthetic limb is not a common activity. The ability to compensate with the sound limb may therefore be functionally more important than the ability to stay in dynamic balance on the prosthetic limb.