An investigation of the effect of boundary conditions on the mechanical characteristics of an energy storing and returning prosthetic foot subject to non-destructive testing

It has been recognised that that the mechanical characteristics of Energy Storing and Returning (ESR) prosthetic running feet are not well understood and inconsistent static rating results have been reported elsewhere. The hypothesis that the inconsistent results are due to the varying foot mounting methods used during non-destructive testing was investigated. An ESR prosthetic running foot was rigidly mounted to the load cell of a hydraulic test machine while the metatarsal region of the foot contacted the machine bed. The friction between the foot and the machine bed was varied to create different mounting conditions. For each mounting condition, the foot was displaced vertically and force-displacement data was collected to compare the measured peak force and efficiency of the foot. It is shown that the mounting method affects both the peak measured force (1.2-2.83kN) and efficiency (71-97%) of the foot under test. A novel mounting strategy was then proposed and assessed to overcome the limitations of the previously used mounting methods. The new mounting method produced a linear spring rate across the entire displacement leading to an efficiency of 99.4% and peak measured force of 1.71kN which was in agreement with previously collected data during amputee running. It is concluded that the inconsistencies in reported mechanical characteristics of Energy Storing and Returning prosthetic feet are due to the varying foot mounting methods used during non-destructive testing. A novel foot mounting method has been shown to overcome the limitations of the previous research. Further investigation is needed to fully understand the effect of the prostheses mechanical properties on running performance.