Lateral wedge shoe insoles decrease medial knee loading, but trials have shown no effect on pain in medial knee osteoarthritis (OA). However, loading effects of insoles are inconsistent, and they can increase patellofemoral loading. We undertook this study to investigate the hypothesis that insoles would reduce pain in preselected patients.
Among patients with painful medial knee OA, we excluded those with patellofemoral OA and those with a pain rating of <4 of a possible 10. We further excluded participants who, in a gait analysis using lateral wedges, did not show at least a 2% reduction in knee adduction moment (KAM), compared to wearing their shoes and a neutral insole. We then randomized subjects to lateral wedge versus neutral insole for 8-week periods, separated by an 8-week washout. The primary outcome measure was knee pain (0-10 scale) during the past week, and secondary outcome measures included activity pain and pain rated in the Knee Injury and Osteoarthritis Outcome Score questionnaire. We carried out mixed model analyses adjusted for baseline pain.
Of 83 participants, 21 (25.3%) were excluded from analysis because of insufficient reduction in KAM. In the 62 patients included in analysis, the mean ± SD age was 64.2 ± 9.1 years, and 37.1% were women. Lateral wedge insoles produced a greater reduction in knee pain than neutral insoles (mean difference of 0.7 on 0-10 scale [95% confidence interval 0.1, 1.2]) (P = 0.02). Findings for secondary outcome measures were mixed.
In participants prescreened to eliminate those with patellofemoral OA and biomechanical nonresponders, lateral wedge insoles reduced knee pain, but the effect of treatment was small and is likely of clinical significance in only a minority of patients. Targeting patients may identify those who respond to this treatment.