The impact of insole wedge height on knee alignment, joint space width, and patient-reported outcomes in medial knee OA

INTRODUCTION: Lateral wedge insoles (LWIs) are a recommended conservative treatment for medial knee osteoarthritis (OA), yet the optimal wedge height remains unclear. This randomized controlled trial evaluated the effects of different LWI heights on radiographic outcomes in patients with medial knee OA. METHODS: This study employed a randomized, controlled, parallel-arm design with a sequential, within-subject dose-escalation intervention arm. Thirty-four participants with mild-to-moderate medial knee OA (Kellgren- Lawrence grade <3) were randomized into a case group (n = 17) receiving custom LWIs (4 mm, 8 mm,12 mm, 16 mm) and a control group (n = 17) receiving standard care. Radiographic assessments (femorotibial angle [FTA], medial joint space width [MJSW]) and patient-reported outcomes (WOMAC) were performed at baseline and follow-up. Mixed ANOVA analyzed group and time effects. RESULTS: The 12 mm LWI significantly reduced varus alignment (FTA: 177.3° ± 2.8 vs. 178.1° ± 2.7 with 4 mm, p < 0.05) in the non-dominant limb. No significant FTA change was observed in the dominant limb, suggesting that limb-specific loading history may modulate biomechanical responsiveness to orthotic correction. No significant FTA changes occurred in the dominant limb. MJSW remained stable in the case group but narrowed in controls (3.04 ± 0.7 mm vs. 3.16 ± 0.8 mm, p < 0.05). The 16 mm LWI was discontinued due to poor tolerability (11/17 participants). The LWI group also showed significant improvements in WOMAC total and pain scores compared to controls. CONCLUSION: Among the clinically tolerable LWI heights tested, the 12 mm wedge provided the best balance between biomechanical efficacy and patient tolerability. It significantly improved varus alignment (in the non-dominant limb), halted joint space narrowing, and reduced pain and overall symptoms. The 16 mm wedge was poorly tolerated (11/17 participants) and was therefore deemed clinically impractical. Future studies should explore personalized height selection and long-term outcomes.