Advancing Conservative Treatment of Knee Osteoarthritis: 3D-Printed Shoe Soles for Passive Toe-Out Gait Modification

To evaluate whether a 3D-printed shoe sole can passively replicate toe-out gait biomechanics and reduce the knee adduction moment (KAM) and knee adduction angular impulse (KAAI), addressing limitations of traditional gait retraining.

Custom shoe soles were 3D-printed using gyroid infill structures to create a rotational hind-sole and a variable stiffness fore-sole ('RVS' shoes). Twenty-one healthy adults completed three baseline gait trials in control shoes, followed by randomised biofeedback-based gait retraining at toe-out angles of 5°, 10° and 15°. After each retraining session, motion capture was used during overground walking. Participants then walked wearing RVS shoes for three trials. Gait biomechanics were analysed using repeated measures ANOVA and multiple linear regression.

Compared to baseline, KAM's second peak was significantly reduced after toe-out retraining: 5° (13.6%, p = 0.002), 10° (20.2%, p < 0.001) and 15° (31.7%, p < 0.001). RVS shoes alone reduced it by 16.3% (p < 0.001), and KAAI by 8.6% (p < 0.001)-a reduction not achieved by retraining. Regression analysis showed that changes in KAM were strongly predicted (95%) by knee centre-of-pressure offset and mediolateral ground reaction force.

3D-printed RVS shoes passively replicated or exceeded the biomechanical effects of active toe-out gait retraining, offering a promising, low-effort intervention for managing knee osteoarthritis.