Finite Element-Based Biomechanical Evaluation of Patient-Specific Insoles for a Pediatric Patient with Hereditary Spastic Paraplegia Using the Taguchi Method

Abstract

Customized foot orthoses are widely used to manage plantar pressure and improve structural support in children with hereditary spastic paraparesis. However, the combined biomechanical effects of insole design parameters remain insufficiently quantified. This study employed a patient-specific three-dimensional finite element model to evaluate the influence of four design factors (arch height, heel cup depth, insole thickness, and material type, namely ethylene-vinyl acetate [EVA], thermoplastic polyurethane [TPU], and rubber) on four biomechanical metrics: plantar pressure distribution, von Mises stress, strain, and total deformation. Nine orthotic configurations, defined by a Taguchi L9 orthogonal array, were simulated under a vertical ground reaction force equal to 1.1x body weight. The configuration with an arch height of 42 mm, heel cup depth of 20 mm, thickness of 10 mm, and EVA material achieved the lowest peak plantar pressure (0.087 MPa). Arch height was the dominant factor for plantar pressure (79.4% of variance), deformation (68.1%), and strain (48.2%), while heel cup depth was most influential for stress (40.2%). Material type contributed minimally to plantar pressure and deformation but had a greater effect on stress (11.6%) and strain (15.0%). Thickness played a secondary role, particularly in deformation (19.9%) and strain (22.3%). These findings demonstrate the feasibility of using finite element modeling combined with the Taguchi method to systematically evaluate and optimize orthotic design parameters. Specifically, the study demonstrates that optimized personalized insoles can substantially reduce peak plantar pressure and improve load distribution in a pediatric patient with HSP, pes planovalgus, and flexed-knee gait, providing a potentially effective noninvasive intervention to prevent secondary complications and improve gait mechanics.