Effect of variable-stiffness walking shoes on knee adduction moment, pain, and function in subjects with medial compartment knee osteoarthritis after 1 year

This study investigated the load-modifying and clinical efficacy of variable-stiffness shoes after 12 months in subjects with medial compartment knee osteoarthritis. Subjects who completed a prior 6-month study were asked to wear their assigned constant-stiffness control or variable-stiffness intervention shoes during the remainder of the study. Changes in peak knee adduction moment, total Western Ontario and McMaster Universities (WOMAC), and WOMAC pain scores were assessed. Seventy-nine subjects were enrolled, and 55 completed the trial. Using an intention-to-treat analysis, the variable-stiffness shoes reduced the within-day peak knee adduction moment (-5.5%, p<0.001) in the intervention subjects, while the constant-stiffness shoes increased the peak knee adduction moment in the control subjects (+3.1%, p=0.015) at the 12-month visit. WOMAC pain and total scores for the intervention group were significantly reduced from baseline to 12 months (-32%, p=0.002 and -35%, p=0.007, respectively). The control group had a reduction of 27% in WOMAC pain score (p=0.04) and no significant reduction in total WOMAC score. Reductions in WOMAC pain and total scores were similar between groups (p=0.8 and p=0.47, respectively). In the intervention group, reductions in adduction moment were related to improvements in pain and function (R2=0.11, p=0.04). Analysis by disease severity revealed greater efficacy in adduction moment reduction in the less severe intervention group. While the long-term effects of the intervention shoes on pain and function did not differ from control, the data suggest wearing the intervention shoe reduces the within-day adduction moment after long-term wear, and thus should reduce loading on the affected medial compartment of the knee. (C) 2011 Orthopaedic Research Society. (C) 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:514521, 2012