Associations between changes in load-bearing pattern, deformity, and internal stresses at the foot with hammer toe during walking; a finite element approach

Abstract

Over the past decade, Finite Element (FE) modelling has been used as a method to understand the internal stresses within the diabetic foot. Foot deformities such as hammer toe have been associated with increased risk of foot ulcers in diabetic patients. Hence the aim of this study is to investigate the influence of hammer toe deformity on internal stresses during walking. A 3D finite element model of the human foot was constructed based on capturing Magentic Resonance Imaging (MRI) of a diabetic neuropathic volunteer exhibiting hammer toe. 3D gait measurements and a multi-body musculoskeletal model for the same participant were used to define muscle forces; FE simulations were run in five different phases of the stance phase of gait. Peak plantar pressure and pressure distribution results calculated from the model showed a good agreement with the experimental measurement having less than 11% errors. Maximum von Mises internal stresses in the forefoot hard tissue were observed at the 3rd and 5th metatarsals and 4th proximal phalanx. Moreover, presence of hammer toe deformity leads to the location of maximum internal stresses on the soft tissue to be shifted to the forefoot by changing the location of centre of pressure with internal stress more than 1.64 greater than plantar pressure. Hammer toe deformity also showed to reduce the involvement of the first phalanx in internal/external load-bearing during walking. The findings of this study support the association between changes in load-bearing pattern, deformity, and internal stresses in the tissue that lead to foot ulceration.