Long-Term Outcomes of Mosaicplasty for Spontaneous Osteonecrosis of the Knee with Varus Alignment: A Retrospective Study with Up to 15 Years of Follow-up"

Background: Spontaneous osteonecrosis of the knee (SONK) commonly affects middle- aged and elderly individuals, and its management varies depending on disease progression. While joint replacement is often required in advanced cases, joint-preserving procedures such as mosaicplasty (Mos) remain an option for early-stage lesions. However, clinical and radiological outcomes of Mos in this population remain unclear. Methods: This retrospective study included 39 knees in 37 patients (mean age 69.1 ± 6.8 years) with SONK and femoro-tibial angle (FTA) <180° who underwent mosaicplasty alone. Patients were followed for a mean of 90 months. Clinical outcomes were assessed using the Lysholm score preoperatively, at 1 year postoperatively, and at final follow-up. MRI at 1 year was evaluated using the MOCART scoring system. Conversion to total knee arthroplasty (TKA) was the primary endpoint, and survivorship analysis was conducted. Univariate and logistic regression analyses were used to identify risk factors for TKA. Results: The mean Lysholm score significantly improved from 60.7 ± 6.4 preoperatively to 89.6 ± 6.6 at 1 year, and remained favorable at final follow-up (83.6 ± 12.7, P < 0.0001). No cases required revision surgery due to graft failure. However, 5 knees (13%) required conversion to TKA at a mean of 136 months. The 10-year and 15-year survival rates were 97% and 50%, respectively, with a median survival time of 188 months. Postoperative MOCART scores did not significantly correlate with clinical improvement. Among female patients, a higher BMI was identified as a significant risk factor for TKA conversion (odds ratio 1.66). Conclusion: Mosaicplasty alone is an effective joint-preserving treatment for SONK in patients with FTA <180°, yielding significant long-term clinical improvement without graft failure. While MRI findings at one year may not predict outcomes, careful postoperative monitoring is warranted, particularly in female patients with higher BMI due to increased risk of late conversion to TKA.