Shoe torsional resistance related to medial knee oa

Abstract

Purpose: Recent evidence suggests that footwear can significantly affect dynamic knee loading and that flat, flexible shoes may result in lower knee loads compared to more supportive, stiff-soled shoes. Here, we evaluate the torsional stiffness of the shoe compared longitudinal effects on knee loading over 6 months. Methods: Subjects with radiographic (KL grades ≥ 2) and symptomatic (at least 30mm pain of 100mm scale while walking) medial compartment knee OA were recruited and randomized to receive a flexible soled shoe (mobility shoe) or identical appearing “control” shoe with stiffer sole. The frontal plane torsional stiffness of the shoe was evaluated using a biomaterial testing system. Investigators and participants were blinded to shoe assignment. Baseline gait analyses were performed using an optoelectronic camera system and multi-component force plate in subjects’ “own shoes”, study shoes, and barefoot. Subjects were instructed to wear the study shoes at least 6 hours/day for 6 days/week. Gait analysis was repeated at 6, 12 and 24 weeks. The peak knee adduction moment (KAM), a validated marker of medial compartment loading, was evaluated. An intent-to-treat analysis was performed with imputation of missing data using a hot deck method (Rubin, 1987). Repeated measures analysis of variance compared the two arms and planned contrasts were used to further analyze the data and load reductions at various time points. Results: 22 participants (13 women, mean age 55±7 years) were assigned to the mobility shoe and 28 (21 women, mean age 55±8 years) to the control shoe. The median modulus of elasticity of the treatment group shoes was 0.25±0.07 compared to the control shoe 0.94±1.05 (p=0.009). There was a strong correlation between the reduction in the KAM and torsional stiffness from baseline to 24 months in treatment group and control group (0.88 and 0.89 respectively p=0.03) There were differences in Peak KAM over time in the treatment group vs. control with the more flexible shoe producing reductions while the control increased moments (-0.25 ±0.95 and 0.09 ±0.95 %BW*ht respectively, rmANOVA, p=0.002). Conclusions: This double-blind randomized controlled trial suggests that loading of the medial knee is directly related to the torsional stiffness the shoe. The use of shoes with flexibility in the frontal plane over 6 months results in significant reductions in medial knee loading compared to stiffer shoes with greater torsional resistance. Thus, evaluating the shoe for torsional resistance may help determine which shoe would be an effective biomechanical intervention for the management of knee OA.