A predictive nomogram for treatment response in osteonecrosis patients receiving denosumab with UKA: integrating bone turnover markers and functional parameters.

Background: Primary spontaneous osteonecrosis of the knee (SONK) is a debilitating condition that primarily affects elderly patients with an unknown etiology. Denosumab has emerged as a novel therapeutic agent for osteoporosis treatment. This study aimed to investigate whether denosumab improves knee function and osteoporosis in SONK patients undergoing unicompartmental knee arthroplasty (UKA). Methods: Between January 1, 2018, and December 31, 2022, patients with knee osteonecrosis undergoing UKA were enrolled. Thirty-five patients (Group A) received vitamin D3 and calcium supplements only, while 36 patients (Group B) received subcutaneous denosumab (60 mg every 6 months) plus supplements. Patients were evaluated through serum biomarkers, clinical examination, radiography, and MRI. A predictive model was developed using the least absolute shrinkage and selection operator (LASSO) regression. Results: The mean follow-up was 2.11 ± 0.99 years. One patient developed tibial plateau collapse and fibular head fracture. At 24 months, Group B showed significantly better HSS scores (T = 15.07, P = 0.04), VAS scores (T = 1.11, P = 0.04), and ROM (T = 15.07, P = 0.02) compared to Group A. Group B exhibited higher PTH levels at 12, 18, and 24 months, and higher OCN levels at 18 and 24 months. At 24 months, Group B had lower CTX but higher T-scores and BMD. Radiographic analysis revealed component malposition in some cases, with a mean postoperative femoral angle of 176.1° ± 2.3°. The prediction nomogram incorporating CTX, BMD, and ROM showed excellent discrimination (C-index = 0.925, 95% CI: 0.881-0.969), confirmed by internal validation (C-index = 0.97). Conclusion: Clinically, the 7-point improvement in HSS scores observed in Group B corresponds to a transition from 'poor' to 'good' knee function, while the 0.8-unit increase in femoral neck T-score translates into a 30% reduction in major-fracture risk over 10 years (FRAX-adjusted), indicating meaningful gains in patient mobility, pain relief, and long-term skeletal protection.