Preservation of Residual Foot Length in Partial Foot Amputation: A Biomechanical Analysis

Abstract

Background: Partial foot amputation may be preferred to more proximal amputation because of the perceived improvement in function associated with preserving foot length and the ankle joint complex, thus enabling normal gait and push-off. Clinically, partial foot amputees display significant wasting of the triceps surae musculature, strongly indicative of disuse. This investigation aimed to examine the belief that preserving residual foot length should be the primary operative objective necessary to maintain normal foot and ankle function. Method: The gait patterns of eight partial foot amputees and a cohort of matched nonamputee control subjects were analyzed using a peak three-dimensional (3D) motion analysis system incorporating an AMTI force platform (Advanced Mechanical Technology Inc., Waterton, MA). Amputee subjects used their own prostheses for the evaluation. Results: Amputations disarticulating the metatarsophalangeal (MTP) joint had little impact on the normal pattern of ankle power generation. However, amputation proximal to the MTP joint level resulted in virtually negligible power generation across the ankle, regardless of residual foot length. Subjects compensated for the lack of ankle power generation by adopting strategies in which the hip became the primary source of power to advance the body forward. Conclusions: The primary reason for a partial foot amputation is to preserve the normal function of the foot and ankle complex associated with push-off. As such, surgery should strive to preserve the metatarsal heads to allow amputees to use the ankle's contribution to walking. Given that amputation proximal to the metatarsal heads compromised the normal propulsive function of the foot and ankle, surgery should not strive to preserve residual foot length to maintain function but should instead aim to achieve good distal tissue coverage and healing, particularly given that the hip joint(s), not the ankle, become the primary source of power for walking.