Effects of shoe heel height on the roll-over shapes of prosthetic ankle-foot systems: Implications for heel-height-adjustable components

When wearing shoes of different heel heights, able-bodied persons alter their ankle flexion in a way that keeps their ankle-foot roll-over shapes (i.e., their effective rockers) similarly oriented (parallel) in the shank-reference frame. The purpose of this study was to examine the effects of shoe heel height on the roll-over shapes of prosthetic ankle-foot systems. The hypothesis was that the orientation of the roll-over shapes of these systems would be altered with even small changes in shoe heel height. Seven prosthetic ankle-foot systems were mechanically loaded to determine their roll-over shapes while using a no-heel shoe and a low-heel shoe (20-mm heel height). One of the seven systems tested had a feature that allowed the prosthesis-user the ability to alter the alignment of the ankle without the need for tools. This system was developed specifically to allow users the ability to switch between shoes of different heel heights (i.e., it is a heel-height-adjustable system). Additional loading trials were performed with the heel-height-adjustable system in which the ankle alignment was altered to accommodate the change in heel height between shoes. Roll-over shapes of all seven prosthetic ankle-foot systems had noticeable changes in orientation when going from the no-heel shoe to the low-heel shoe (without alignment adjustments). The roll-over shapes of the heel-height-adjustable system were approximately parallel (i.e., no change in orientation) when alignment changes were made to accommodate the low-heel shoe. The results suggest that heel-height-adjustable systems could allow more biomimetic function for lower limb prosthesis users who want to use a variety of shoe heel heights and who understand how to properly adjust them for their different shoes.