Abstract:
Foot orientation is a significant variable affecting barefoot plantar pressures, a standard measure used in biomechanics for assessing the risk of ulceration, particularly in patients with diabetic neuropathy. The modeling of plantar pressure distribution is also invaluable for the design of therapeutic footwear. Recent three-dimensional finite element (FE) models of the foot have often approximated foot orientation and relative bone alignment based on unloaded imaging positions or kinematic information. The present study addresses this by performing a detailed biomechanical sensitivity analysis focused on two critical variables: i) foot orientation in the frontal plane and ii) the relative metatarsal (MT) alignment, and their influence on plantar pressure distribution. Magnetic resonance images were acquired from the right foot of a male subject to obtain subject-specific bone (MT, phalanges, and sesamoids) and soft-tissue (ST) contours. These contours were digitized using custom Matlab code, and a high-fidelity FE mesh, comprising 57,544 eight-noded hexahedral elements, was generated using TrueGrid software. In this biomechanical model, bones were simulated as rigid bodies, while soft tissues were modeled as an incompressible hyperelastic material. Frictional contact was established between the plantar surface of the foot and a rigid floor. The foot was initially positioned in a neutral stance, with metatarsal heads approximately parallel to the floor. Subsequent loading involved displacing the floor towards the foot, applying horizontal and vertical forces of 500 N and 90 N respectively. To assess sensitivity, the frontal plane orientation of the foot was systematically varied by ±1° from the neutral position. An additional simulation explored the effect of specific bone alignment changes, such as plantarflexing the second MT by 1.5 degrees and dorsiflexing the first MT by 1.5 degrees within a rotated model (neutral +1°). The results indicate that the finite element model's prediction of plantar pressures is acutely sensitive to variations in foot orientation and bone alignment. This sensitivity is potentially greater than observed in vivo. These findings suggest that an optimization protocol could be developed to configure bone alignment and foot orientation in FE models to better represent experimental barefoot pressures, thereby enhancing the accuracy of simulations for footwear design and other biomechanical applications.
