Recent work suggests that a prosthetic ankle-foot component's roll-over shape - the effective rocker it conforms to between initial contact and opposite initial contact (the 'roll-over' interval of walking) - is closely linked to its final alignment in the prosthesis (as determined by a skilled prosthetist using heuristic techniques). If true, this information may help to determine the appropriate alignment for a lower limb prosthesis before it is built, or a priori. Knowledge is needed for future models that will incorporate the roll-over shape including the relative effect of alignment on the roll-over shape's radius of curvature and arc length. The purpose of this study was to evaluate the hypotheses that: (i) Changes in prosthesis alignment alter the position and orientation of a foot's roll-over shape in prosthesis-based coordinates, and (ii) these changes occur without changing the radius of curvature or arc length of the roll-over shape. To examine the hypotheses, this study examined the effects of nine alignment settings on the roll-over shapes of two prosthetic feet. The idea that alignment changes move and rotate roll-over shapes of prosthetic feet in prosthesis coordinates is supported by this work, but the hypothesis that the radius of curvature and arc length do not change for different alignments is not strongly supported by the data. A revised approach is presented that explains some of the changes to the roll-over shape parameters due to changes in rotational alignment.
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The author thanks Dr. Sujatha Srinivasan for her questions about roll-over shapes and alignment. Her questions triggered this work. The author also thanks Ms. Rebecca Stine, Ms. Sara Koehler, and Mr. Brian Ruhe for their assistance with this project, and Drs. Dudley Childress, Steven Gard, Michael Dillon, and Stefania Fatone for proofreading the manuscript. The author would like to acknowledge the use of the VA Chicago Motion Analysis Research Laboratory of the Jesse Brown VA Medical Center, Chicago, Illinois. This work was funded by the National Institute on Disability and Rehabilitation Research (NIDRR) of the U.S. Department of Education under grant No. H133E030030. The opinions contained in this publication are those of the grantee and do not necessarily reflect those of the Department of Education.
- Biomechanics of prosthetic/orthotic devices
- Prosthetic design
- Prosthetic feet
- Testing of prosthetic and orthotic components