Modulation of internal tissue stresses of the knee via control of variable-stiffness properties in a 3D-printed footwear: A combined experimental and finite element analysis
Wen‐Ming Chen, Yue Yu, Xiang Geng, Chen Wang, Li Chen, Xin Ma
Abstract
AIMS: Therapeutic footwear with variable-stiffness properties has been shown to be effective in reducing the external knee adduction moment. However, the exact changes of internal tissue stresses following intervention with variable-stiffness footwear remains unknown. The objective of this study is to construct a finite element model of the foot-ankle-knee complex to investigate the therapeutic efficacy of the variable-stiffness footwear in modulating internal knee joint stress distributions. METHODS: Footwear with lateral-to-medial stiffness ratio of 1.00, 1.33, 1.49 and 1.77 were designed and 3D-printed as lattice structures at different porosity levels. A three-dimensional finite element model of the foot-ankle-knee complex was constructed with cartilage-meniscus structures characterized by magnetic resonance imaging. Ground reaction forces and muscular loads estimated from gait experiments with 3D-printed variable-stiffness footwear were used to drive the model, and effects of footwear intervention with four stiffness ratios on tibiofemoral joint loads were evaluated during the simulated instant in gait. RESULTS: Compared with the constant-stiffness design, the variable-stiffness footwear reached a maximum reduction of the first peak knee adduction moment up to 17.1%. As the lateral-to-medial stiffness ratio increases, the peak stresses at the meniscus in the medial compartment of the knee were reduced by 5.0%, 7.9%, and 16.4%, respectively. The stress-modifying effects were less pronounced for the lateral compartment of the knee. CONCLUSION: The variable-stiffness footwear design produced stress relieving to the cartilage and meniscus structures, and the fact that lower stiffness ratio had reached significantly less effects, suggesting a favourable stress-relief effect should consider footwear with a higher lateral-to-medial stiffness ratio.