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Finite Element Analysis of Ankle-Foot Orthosis (AFO): Influence of Shell and Insole Thickness Across Material Variants

Authors :

Maryam Sheikhi¹ َAisan Rafiei² Nima Jamshidi³

1- University of Isfahan 2- Iran University of Science and Technology 3- University of Isfahan

Keywords :

Ankle-Foot Orthosis،Finite Element Analysis،Shell Thickness،Material Properties،Orthotic Biomechanics

Abstract :

Ankle-Foot Orthoses (AFOs) are essential biomechanical devices designed to enhance gait stability, reduce excessive limb movement, and redistribute load during rehabilitation for individuals with lower limb impairments. To achieve optimal AFO performance, a precise anatomical fit, lightweight construction that does not compromise functionality, mechanical robustness under multi-axial loading, reduced skin pressure, and enhanced user comfort are all required. This study aimed to develop biomechanically optimized, patient-specific AFOs using advanced technologies such as 3D scanning, additive manufacturing, and topology optimization. A finite element analysis (FEA)-based approach was employed to evaluate the effects of orthotic geometry, material properties, shell and insole thickness, and stiffness under dynamic physiological loading conditions. Four geometric configurations were simulated using patient-specific 3D models, varying shell thicknesses (3 mm and 6 mm) and insole thicknesses (6 mm and 9 mm). Two commonly used materials—polylactic acid (PLA) and polypropylene (PP)—were assessed under a vertical load of 350 N to analyze stress distribution, deformation, and plantar pressure. The results demonstrated that both geometry and material selection significantly influence mechanical performance, including displacement, Von Mises stress, and contact pressure. Thicker shell-insole combinations improved load-bearing capacity, while PP exhibited lower stress concentrations compared to PLA. This integrative simulation framework supports the quantitative evaluation of AFO designs and provides clinically relevant insights for personalized orthotic development and optimization.