Increasing prosthetic foot energy return affects whole-body mechanics during walking on level ground and slopes

Abstract

Prosthetic feet are designed to store energy during early stance and then release a portion of that energy during late stance. The usefulness of providing more energy return depends on whether or not that energy transfers up the lower limb to aid in whole body propulsion. This research examined how increasing prosthetic foot energy return affected walking mechanics across various slopes. Five people with a uni-lateral transtibial amputation walked on an instrumented treadmill at 1.1 m/s for three conditions (level ground, +7.5°, -7.5°) while wearing a prosthetic foot with a novel linkage system and a traditional energy storage and return foot. The novel foot demonstrated greater range of motion (p = 0.0012), and returned more energy (p = 0.023) compared to the traditional foot. The increased energy correlated with an increase in center of mass (CoM) energy change during propulsion from the prosthetic limb (p = 0.012), and the increased prosthetic limb propulsion correlated to a decrease in CoM energy change (i.e., collision) on the sound limb (p < 0.001). These data indicate that this novel foot was able to return more energy than a traditional prosthetic foot and that this additional energy was used to increase whole body propulsion.

Figure 1

The Pro-Flex foot (left) has a linkage system on the upper portion of the foot that is designed to non-linearly load the heel and forefoot sections. This is a departure from conventional energy storage and return type prosthetic feet like the Vari-Flex (right).

Figure 2

Angle between the prosthetic shank and foot segments demonstrate that the Pro-Flex foot (black solid line) was able to dorsiflex more throughout stance phase than the Vari-Flex foot (yellow dashed line) across all conditions. Shaded regions represent ± one standard deviation. The steeper slope of these lines indicate the Pro-Flex foot was able to more rapidly dorsiflex and this may have helped to increase the amount of energy that was stored in the forefoot.

Figure 3

CoM energy change during propulsion (open symbols) and collision (closed symbols) for the Pro-Flex foot (panel a) and the Vari-Flex foot (panel b) compared with energy absorbed by the foot/ankle complex (closed symbols) and returned/generated (open symbols) by the Pro-Flex foot (panel c) and the Vari-Flex foot (panel d). Data trends for the amputated limb (solid black line) and the sound limb (dashed blue line) show that the storage and return of energy in the passive prosthetic is more constant than the sound limb across terrains, the Pro-Flex foot does return more energy than the Vari-Flex foot, and the CoM energy change during propulsion is larger with the Pro-Flex foot. Error bars represent ± one standard deviation.

Figure 4

CoM rate of energy change (rows 1 & 3) and foot/ankle power (rows 2 & 4) throughout the gait cycle for downhill (column 1), level (column 2), and uphill (column 3) for the amputated limb (rows 1 & 2) and the sound limb (rows 3 & 4). The Pro-Flex foot (solid black line) demonstrated higher peak powers than the Vari-Flex foot (dashed yellow line) and this resulted in a trend to reduce the absorption of energy by the sound limb during the step-to-step transition.

Figure 5

Vertical (rows 1 & 3) and horizontal (rows 2 & 4) components of the ground reaction force throughout the gait cycle for downhill (column 1), level (column 2), and uphill (column 3) for the amputated limb (rows 1 & 2) and the sound limb (rows 3 & 4). The Pro-Flex foot (solid black line) demonstrated a trend to reduce the first peak of the vertical ground reaction force on the sound limb compared to the Vari-Flex foot (dashed yellow line). There were no discernable differences between feet associated with lowering the loading rate and no changes in the horizontal components.