Deformation of prosthetic foot: A contributing factor to leg length discrepancy in unilateral amputees

For unilateral amputee (UA) dynamic leg length discrepancy (LLD) is a kind of asymmetry between the intact side and prosthetic side at toe-off and heel strike. The aim of this study is to assess whether the deformation of prosthetic foot is one of the contributing factors of dynamic LLD in UAs. It helps to choose or design prosthetic foot to reduce LLD, which may be one of the causations of low back pain in UAs. The forefoot and heel deformations of normal person were measured by motion capture system to represent normal foot result of UA. Following ISO 10328:2006 Prosthetics-Structural testing of lower-limb prostheses-requirements and test methods, the deformations of seven types of prosthetic feet (including two types of conventional prosthetic feet and five types of energy-storing-and-returning feet) were tested and served as the prosthetic foot result of UA. There was significant difference in forefoot deformations between normal foot and each type of prosthetic foot (P < 0.05), as well as heel deformations. The forefoot deformations of all the seven types prosthetic foot were greater than normal foot at toe-off. The heel deformations at heel strike suffered from the similar problem, but heel deformations of four types of prosthetic foot were close to normal foot. For UA, the difference values of foot deformation between the intact side and the prosthetic side were supposed to cause the dynamic LLD at toe-off and heel strike. It had better choose prosthetic foot with less deformation and high stiffness in forefoot, and deformation closed to normal foot in heel.