Computational modelling of foot orthosis for midfoot arthritis: a Taguchi approach for design optimization.

Purpose: Evaluation of the internal biomechanics of the foot-and-ankle complex is challenging for the prescription of orthosis particularly for midfoot arthritis patients in which the joint condition is crucial.
Methods: Using computational modeling and design optimization techniques, the objective of this study was to compare the biomechanical functions among different combinations of design factors using computer simulation. A finite element foot model was reconstructed from a midfoot arthritis patient. Orthotic designs with 3 levels for each of the 3 design factors (arch height, lateral wedge angle, and insole stiffness) contributed to 9 configurations using a fractional factorial design were tested.
Results: An increase in peak plantar stress of the midfoot was facilitated by a medium arch height and wedge angle, and stiffest insole material, notwithstanding the combination neither reduced the peak plantar stress of other foot regions nor was consistent with the combination that minimized the stress of the articular cartilage.
Conclusions: Insole with high arch (H = 30 mm), low stiffness (E = 1.0 MPa), and medium wedge angle (A = 5°) could minimize the stress of the cartilage at the arthritic joint (primary outcome) and could be beneficial to the patients. Also, insole stiffness predominantly influenced cartilage stress. However, secondary outcomes including the stress of the navicular and medial cuneiform and the regional plantar stress did not produce the same solution. Future studies can consider a patient-specific loading profile to further the investigation on the stabilizing effect and the attenuation of load transfer induced by the insole.