A pinboard by
Victor Prost

PhD candidate, Massachussets Institute of Technology


In India alone, there are about one million people with lower limb amputation who require significantly more effort to walk, and are subject to social stigmas preventing them from employment and independent living, by using limbs that do not facilitate able-bodied walking motions. There is a gap between the high performance prosthetic feet in the United States that come at a cost of thousands of dollars and the affordable prosthesis in the developing world that lack quality, durability and performance.

The aim of this study is to design a high performance, mass-manufacturable passive prosthetic foot for Indian amputees that complies with international standards at an affordable cost. Through a novel quantitative method, developed in our group, called Lower Leg Trajectory Error (LLTE) which maps the mechanical design of a prosthetic foot to its biomechanical performance, we can optimize the shape and material properties of the passive prosthesis to replicate natural gait and loading on the foot using affordable materials such as injection molding plastics. This exact same design tool (LLTE) can also be used to create highly customized prosthetic feet for high end markets.

By validating this design tool through clinical testing, it will enable us to create a tailored compliant structures that deform under the amputee's weight allowing him to walk in a natural fashion.


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

Abstract: 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.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.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.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.

Pub.: 16 Jul '10, Pinned: 30 Jun '17

Effective rocker shapes used by able-bodied persons for walking and fore-aft swaying: implications for design of ankle-foot prostheses.

Abstract: The use of rocker models to understand functional tasks of the human lower limb is attractive because of their simplicity. Recent studies have determined a consistent feature of able-bodied walking termed the roll-over shape (ROS), which is the effective rocker shape that the lower limb system conforms to between initial contact and contralateral initial contact during walking. However, it is unclear what effective rocker shapes are used for fore-aft swaying. A better understanding of these shapes could be used to develop improved prostheses for this task, perhaps improving balance and balance confidence, and reducing the occurrence of falling in lower limb prosthesis users. We measured effective rocker shapes used by 11 able-bodied persons during walking and fore-aft swaying. We hypothesized that the curvature of the swaying shapes would be smaller (radius larger) than that of the walking shapes, providing a more stable interface with the ground during swaying. The radius (measured as the inverse of the curvature of the shape) was found to be about 1/3 of the leg length for walking, but over two times the leg length for swaying. A model examining the effective ankle stiffness necessary to achieve these curvatures suggests that the stiffness of a biomimetic prosthetic ankle would need to be over three times higher for fore-aft swaying than for walking. These results suggest that two separate modes would be needed in an ankle-foot prosthesis to mimic the physiologic system for walking and swaying.

Pub.: 18 May '10, Pinned: 30 Jun '17

Roll-over characteristics of human walking on inclined surfaces.

Abstract: Roll-over characteristics of able-bodied human subjects walking on ramped surfaces were examined in this study. Ten subjects walked at their normal self-selected speed on a level surface, a 5-deg ramp, and a 10-deg ramped surface. Ramps were designed such that ground reaction forces and center of pressure of the ground reaction forces could be measured on their surfaces. This set-up facilitated calculation of the effective rockers that the ankle-foot (AF) and knee-ankle-foot (KAF) systems conformed to during single-limb stance (contralateral toe off to contralateral heel contact). Since our original "roll-over shapes" were characterized between heel contact and opposite heel contact, we label the shapes found during single-limb stance as "truncated roll-over shapes". We hypothesized that the ankle-foot system would adapt to the various surfaces, creating a roll-over shape that would change in orientation with different levels of inclination. The truncated AF roll-over shapes supported this hypothesis for uphill walking but did not support the hypothesis for downhill walking. However, truncated roll-over shapes of the KAF system did adjust their orientation to match both the positive and negative levels of surface inclination. In general, the ankle appears to be the main adapting joint when walking up inclined surfaces while the knee becomes important for the overall adaptation in downhill walking. Knowledge of physiological lower-limb roll-over characteristics on ramped surfaces may help in the development of biomimetic prostheses and orthoses that will automatically adapt to changes in walking surface inclination.

Pub.: 25 Jan '05, Pinned: 30 Jun '17