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Roll-over shape is introduced as a significant characteristic of prosthetic feet. The roll-over shapes of the Flexwalk, Quantum, SACH, and SAFE prosthetic feet were determined using three methods; two involving quasi-static loading and one dynamic loading. The results show that foot roll-over shape properties obtained by quasi-static and by dynamic methods are similar.Relationships between foot roll-over shape and the alignment of trans-tibial prostheses are introduced that suggest ways to align trans-tibial prostheses without walking trials and iterations. The relationships may explain what prosthetists attempt to accomplish when they dynamically align a trans-tibial limb. They also explain why prosthetic feet with different mechanical properties usually necessitate different alignments, and may explain why a number of gait studies of trans-tibial amputees do not show major gait differences when walking is executed on various kinds of prosthetic feet.

This study investigated the effects of shoe heel height on the rollover characteristics of the biologic ankle-foot system. Ten nondisabled adult female volunteers walked using three pairs of shoes with varying heel heights and at three walking speeds with each pair of shoes. Kinematic and kinetic data needed to calculate the rollover shapes of the ankle-foot systems of the participants were collected. Rollover shapes are the effective rocker geometries that ankle-foot systems conform to between heel contact and opposite heel contact. Parameters of the best-fit circular arcs to the rollover shapes were used in an examination of the effects of shoe heel height on the ankle-foot system. The results support the notion that nondisabled humans automatically adapt their ankle-foot systems to accommodate a range of shoe heel heights, resulting in rollover shapes that do not change appreciably. Given physiologic constraints, this adaptation may not be possible for very high heels.

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The Shape&Roll prosthetic foot was used to examine the effect of roll-over shape arc length on the gait of 14 unilateral trans-tibial prosthesis users. Simple modifications to the prosthetic foot were used to alter the effective forefoot rocker length, leaving factors such as alignment, limb length, and heel and mid-foot characteristics unchanged. Shortening the roll-over shape arc length caused a significant reduction in the maximum external dorsiflexion moment on the prosthetic side at all walking speeds (p 5 0.001 for main effect of arc length), due to a reduction in forefoot leverage (moment arm) about the ankle. Roll-over shape arc length significantly affected the initial loading on the sound limb at normal and fast speeds (p ¼ 0.001 for the main effect of arc length), with participants experiencing larger first peaks of vertical ground reaction forces on their sound limbs when using the foot with the shortest effective forefoot rocker arc length. Additionally, the difference between step lengths on the sound and prosthetic limbs was larger with the shortest arc length condition, although this difference was not statistically significant (p ¼ 0.06 for main effect). It appears that prosthesis users may experience a dropoff effect at the end of single limb stance on prosthetic feet with short roll-over shape arc lengths, leading to increased loading and/or a shortened step on the contralateral limb.

The consistency of the roll-over shapes to level surface walking conditions has provided insight for design, alignment and evaluation of lower limb prostheses and orthoses. Changes to ankle-foot and knee-ankle-foot roll-over shapes for ramp walking conditions have suggested biomimetic (i.e. mimicking biology) strategies for adaptable ankle-foot prostheses and orthoses.

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