The effects of prosthetic ankle dorsiflexion and energy return on below-knee amputee leg loading

Prosthetic devices are intended to return lower limb amputees to their pre-amputation functional status. However, prosthetic devices designed for unilateral below-knee amputees have yet to completely restore the biomechanical functions normally provided by the ankle muscles, leading to gait asymmetries and increased reliance on their intact leg. In an effort to improve amputee gait, energy storage and return feet have been developed that store mechanical energy in elastic structures in early to mid-stance and return it in late stance. However, little is known regarding how ankle compliance and the level of energy return influences walking mechanics. The purpose of this study was to identify the influence of prosthetic ankle dorsiflexion and energy storage and return on leg loading during steady-state walking.

Compliant ankles with different stiffness levels were attached to a Seattle Lightfoot2 in different orientations (forward- and reverse-facing).

The ankles decreased residual leg vertical ground reaction forces in late stance, increased residual leg propulsive ground reaction force impulses and increased residual leg knee joint extensor moments. The reverse-facing ankles increased residual leg vertical ground reaction forces in early stance, and the compliant forward-facing ankle increased residual leg braking impulses. In contrast to previous studies, increased energy storage and return from compliant ankles did not decrease hip joint powers or the intact leg vertical ground reaction forces.

These results provide insight into the relationships between ankle dorsiflexion, energy storage and return, and leg loading, which may lead to more effective prosthetic devices to improve amputee gait.