Therapeutic Footwear for Medial Knee Osteoarthritis: Individualizing Midsole Stiffness Enhances Intended Kinetic Changes

Progression of medial knee osteoarthritis (OA) has been associated with walking biomechanics, specifically with the knee adduction (KAM) and flexion (KFM) moments. Lower medial stiffness shoes (LMSS), that are shoes with the sole made of softer material medially than laterally, were proposed for disease management through KAM reductions. This study primarily tested the hypothesis that larger pKAM reductions can be achieved with stiffness ratios selected individually than with the smallest ratios of the LMSS. Secondarily, the proportions of individuals reducing the KAM or reducing the KAM without increasing the KFM were compared between the individualized and smallest ratios conditions. The two LMSS conditions were also compared with lateral wedge insoles. Walking biomechanics were recorded for 15 OA patients (8 males; 62.3 ± 9.6 years old) and 14 asymptomatic individuals (5 males; 53.6 ± 3.6 years old) wearing LMSS with various stiffness ratios and wedges. Larger decreases in KAM were obtained with individualized stiffness ratios (14.0%-16.4%) than with the two other interventions (6.7%-12.5%) (p < 0.001). The percentage of participants reducing the KAM without increasing the KFM was larger with individualized ratios compared to the smallest ratios in the OA group (14 vs. 6; p = 0.001) and compared to wedges in the asymptomatic group (13 vs. 6; p = 0.015). This exploratory study showed the potential of individualizing the stiffness ratios, particularly in terms of KAM reduction amplitude, percentage of individuals achieving specific modifications, and possibility to aim for more complex kinetic changes. Further work is necessary to assess the effect of individualized stiffness ratios on clinical outcomes.