Rehabilitation Engineering Research Center on Prosthetics and Orthotics
Study purpose or goal:
The data is used to evaluate the roll-over shape of prosthetic feet as compared to non-disabled feet and ankle systems to improve the design of the prosthesis
Who administers this tool?:
Prosthetic engineers, designers, and manufacturers
The direct method requires a force platform, weights to simulate and acquire body loads, and a motion analysis system. The quasi-static method requires a prosthetic foot loading apparatus.
How is it administered?:
This tool records roll-over shapes of prosthetic feet. For quasi-static roll-over shape measurements: Prosthetic feet, attached orthogonally to an instrumented pylon, are mechanically loaded at 5 orientations (60 degrees, 75 degrees, 90 degrees, 97 degree.
What is the scope or what areas does it cover?:
The tool could be used to measure any prosthetic shape that is deformable or with passive or active articulation(s).
The original concept of modeling prosthetic feet as rockers was shown by Stein and Flowers in the _Journal of Biomechanics_ (Vol. 20, pp. 19-28, 1987) for the SACH (solid ankle cushioned heel) prosthetic foot. Erick Knox, PhD, while at the Rehabilitation Engineering Program, expanded the concept and examined many kinds of feet as rockers as part of his doctoral thesis. Knox developed the direct method for measuring roll-over shapes of prosthetic feet during his studies at Northwestern University.
Use of this tool requires knowledge of prosthetic engineering and design. Low forces on the force platform are fairly “noisy” which impedes the view of the heel shape.
Analysis is ongoing. This system is applied to new feet as they are developed. The test requires the use of two markers to define the attachment surface of the foot and the foot is rolled over a force platform while maintaining a specified load (equal to .
For quasi-static roll-over shape measurements: Prosthetic feet, attached orthogonally to an instrumented pylon, are mechanically loaded at 5 orientations (60o, 75o, 90o, 97o, and 105o) in a prosthetic foot loading apparatus. Center of pressure (COP), force, and deflection data are collected while gradually loading and unloading each foot. Although most feet show hysteresis in the loading/unloading cycle, only data associated with the loading part of the cycle are used. For direct roll-over shape measurements: Sagittal plane kinematic data of two markers, one at the fibular head (knee) and one at the lateral malleolus (ankle), and the forward progression component of the COP are used to create the roll-over shape directly. Markers are placed at approximations of these anatomical locations when directly measuring prosthetic foot roll-over shapes
Impact of these findings on the field:
Roll over shapes give a goal of design of feet – a way to evaluate a foot to see how close it is to a non-disabled foot. The collected and analyzed data simplifies the design process. The improved design may lead to reduced cost in manufacture, which may influence clinical outcomes
Peer review status:
 Hansen, A.H., Childress, D.S., Knox, E.H. (2000) Prosthetic Foot Roll-over Shapes with Implications for Alignment of Trans-tibial Prostheses. Prosthetics and Orthotics International, Vol. 24, No. 3, December, 205-215
Dudley S. Childress, PhD; Resource Unit Help Line
312/238-6524 (V), 312/238-6530 (TTY)