Investigations of roll-over shape: implications for design, alignment, and evaluation of ankle-foot prostheses and orthoses

Abstract

Purpose. The purpose of this article is to provide an overview of our previous work on roll-over shapes, which are the effective rocker shapes that the lower limb systems conform to during walking.

Method. This article is a summary of several recently published articles from the Northwestern University Prosthetics Research Laboratory and Rehabilitation Engineering Research Program on the topic of roll-over shapes. The roll-over shape is a measurement of centre of pressure of the ground reaction force in body-based coordinates. This measurement is interpreted as the effective rocker shape created by lower limb systems during walking.

Results. Our studies have shown that roll-over shapes in able-bodied subjects do not change appreciably for conditions of level ground walking, including walking at different speeds, while carrying different amounts of weight, while wearing shoes of different heel heights, or when wearing shoes with different rocker radii. In fact, results suggest that able-bodied humans will actively change their ankle movements to maintain the same roll-over shapes.

Conclusions. 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.

Keywords:

• Artificial limbs
• prostheses
• orthoses
• gait

Acknowledgements

The authors are grateful to the many investigators and research subjects who were involved in the projects summarised in this article. The authors also thank Stefania Fatone, PhD, BPO (Honors) and R.J. Garrick, PhD for their careful proof-reading of the article. The opinions expressed in this paper are those of the authors and not necessarily those of the funding agencies.

Declaration of interest

The work described in this paper was supported by grants from the Department of Veterans Affairs (Pre-doctoral fellowship, A2676I, and A4325R), the National Institutes of Health (R03-HD050428-01A2), the National Institute on Disability and Rehabilitation Research (NIDRR) of the Department of Education (H133E980023, H133E030030, and H133E080009), and a subcontract from the Center for International Rehabilitation (CIR).