Can partial foot prostheses effectively restore foot length?

Our understanding of how partial foot prostheses function stems from static force analyses, where assumptions about the location of the ground reaction force during terminal stance have been made. While such assumptions seemed reasonably based on an understanding of normal gait, they are often illogical based on what is observed clinically. As such, the aim of this work was to evaluate the belief that partial foot prostheses are able to restore the effective foot length. Centre of pressure (CoP) excursion data were collected as part of a complete gait analysis incorporating an Advanced Mechanical Technology Inc. force platform. The CoP excursion patterns, observed in a cohort of eight partial foot amputees and matched control subjects, highlight the inability of toe fillers and slipper sockets to restore the 'effective' foot length in transmetatarsal and Lisfranc amputees, whereas clamshell prostheses fitted to the Chopart amputees were able to restore the effective foot length. In the transmetatarsal and Lisfranc amputees, the observed CoP excursion patterns could indicate a learned gait strategy necessary to reduce the requirement of the weak triceps surae musculature as well as spare the sensitive distal stump from extreme forces. The toe fillers and slipper sockets fitted to these amputees may not be stiff enough to support the amputee's body weight or the device may not be designed appropriately to assist the weakened triceps musculature to resist the external moments caused by loading the forefoot. The clamshell prostheses restored the 'effective' foot length due to the rigid toe lever and clamshell socket, which could allow and comfortably support the generation of substantial external moments during terminal stance.