Increased joint line obliquity is associated with lateral cartilage degeneration after medial opening wedge high tibial osteotomy: a quantitative MRI analysis

BACKGROUND: Joint line obliquity (JLO) often increases after medial opening wedge high tibial osteotomy (MOWHTO), and excessive JLO may adversely affect the lateral compartment. However, its effects on cartilage tissue and postoperative outcomes remain unclear. This study investigated whether increased postoperative JLO is associated with early cartilage changes on quantitative MRI T2 mapping and differences in clinical outcomes. METHODS: A total of 33 knees undergoing MOWHTO were retrospectively reviewed. Radiographic parameters-hip-knee-ankle angle (HKA), medial proximal tibial angle (MPTA), and JLO-were assessed preoperatively and at 6 months. Based on postoperative radiographic measurements, patients were classified as increased JLO/MPTA (Group I: JLO > 5° and/or MPTA > 94°) or acceptable range JLO/MPTA (Group A: JLO < 5° and MPTA < 94°). Quantitative MRI T2 mapping was performed preoperatively and at 12 months to measure T2 relaxation times (T2 values) and ΔT2 values (postoperative-preoperative) in the patella, trochlea, lateral femoral condyle (LFC), and lateral tibial plateau (LTP), analyzing superficial, deep, and total cartilage layers. Knee Injury and Osteoarthritis Outcome Score (KOOS) was assessed at both time points. RESULTS: Group I included 13 patients and group A included 20 patients. Postoperative HKA was similar between groups (p = 0.326). No significant intergroup differences were observed in preoperative or postoperative T2 values in the patellofemoral or lateral compartments. However, ΔT2 values in the LTP were significantly higher in group I than in group A in the superficial (3.3 ± 6.5 versus -1.7 ± 5.9 ms, p = 0.022) and total (4.5 ± 5.7 versus - 0.6 ± 5.0 ms, p = 0.012) layers. Group I also had worse KOOS-Symptoms (p = 0.016), QOL (p = 0.022), and Sport/Rec (p = 0.040). CONCLUSIONS: Even with similar postoperative limb alignment, increased JLO/MPTA was associated with early degenerative changes in lateral tibial cartilage and worse clinical outcomes. Maintaining postoperative JLO within the acceptable range during MOWHTO may help maintain lateral compartment cartilage health and optimize clinical outcomes. LEVEL OF EVIDENCE: Level IV.