The effective foot length ratio: A potential tool for characterization and evaluation of prosthetic feet

The purpose of this technical note is to introduce the effective foot length ratio (EFLR) as a possible measurement tool for evaluation of prosthetic feet. The EFLR multiplied by 100 provides the percentage of a foot that is effectively used during a walking step and may have clinical implications for step length and limb loading on the contralateral side. Prosthetic feet were manually rolled over a force platform while maintaining a constant level of force representative of a user's weight. Effective foot lengths were measured by finding the distance from the heel of each prosthetic foot to the center of pressure in foot-based coordinates at a loading angle that represented the approximate shank angle at opposite heel contact during walking. The effective foot lengths were then normalized by overall foot length to determine the EFLR. EFLRs from 15 prosthetic feet used clinically during the 1990s are presented along with an estimate of the EFLR of the physiologic ankle-foot system. All prosthetic feet had EFLRs lower than the corresponding physiologic system, although some had ratios close to the physiologic system. The EFLRs for the prosthetic feet were between 0.63 and 0.81, whereas the EFLR estimated for the physiologic system was 0.83.