Preoperative Medial Meniscus Extrusion Predicts Varus Correction Loss After 5 Years Despite Stable Bony Alignment After Medial Opening‐Wedge High Tibial Osteotomy

PURPOSE: To determine if medial meniscus extrusion (MME) impacts postoperative alignment and varus correction loss after medial opening-wedge high tibial osteotomy. METHODS: We retrospectively reviewed patients who underwent medial opening-wedge high tibial osteotomy for medial compartment osteoarthritis with ≥5 years of follow-up. Patients were categorized using a 3-mm cutoff for preoperative MME on magnetic resonance imaging (≥3 mm defined pathological). Serial standing radiographs were obtained preoperatively and at 3 months, 1 year, and ≥5 years postoperatively, and the weight-bearing line (WBL) ratio, hip-knee-ankle angle, mechanical lateral distal femoral angle, medial proximal tibial angle, and joint line convergence angle were evaluated by an independent blinded observer. Alignment changes were analyzed using repeated-measures analysis of variance. Varus correction loss was defined as a final WBL ratio <50%, and predictors were identified using multivariate logistic regression including demographic and radiographic variables. Knee Injury and Osteoarthritis Outcome Score values (mean ± standard deviation) were evaluated preoperatively and at the final follow-up. Minimal clinically important difference achievement rates (defined as one-half of the standard deviation of the pre-to-post change) were compared between groups using Fisher's exact tests. RESULTS: Fifty-five knees (44 patients; mean age, 59.3 years; mean follow-up, 6.9 [5.0-10.4] years) were included. Forty knees (72.7%) showed pathological MME. The pathological group had a significantly lower final WBL ratio (55.8% vs 65.7%, P = .008) and hip-knee-ankle (1.9° vs 3.9°, P = .025), whereas mechanical lateral distal femoral angle and medial proximal tibial angle did not differ. MME ≥3 mm (P = .004), lower 3-month WBL ratio (P < .001), and greater preoperative mechanical lateral distal femoral angle (P = .005) independently predicted varus correction loss. Knee Injury and Osteoarthritis Outcome Score significantly improved from preoperative to final follow-up in both groups (all P < .001). At final follow-up, there were no significant differences between the groups (MME ≥3 mm vs <3 mm): pain, 70.3 ± 24.3 vs 73.7 ± 25.4 (P = .667); symptoms, 70.9 ± 22.3 vs 80.7 ± 12.3 (P = .139); activities of daily living, 76.8 ± 22.8 vs 76.7 ± 20.4 (P = .992); sports, 45.3 ± 27.4 vs 53.8 ± 21.4 (P = .313); and quality of life, 53.2 ± 25.8 vs 55.8 ± 22.2 (P = .751). Minimal clinically important difference achievement rates were lower in the pathological group (57.5%-65.0% vs 80.0%-86.7%), although not statistically significant. CONCLUSIONS: Pathological MME was associated with greater varus correction loss despite stable bony alignment and tended to show lower minimal clinically important difference achievement rates. LEVEL OF EVIDENCE: Level III, retrospective comparative case series.