A Comparative Study of Fixed-Bearing Unicompartmental Knee Arthroplasty for Spontaneous Osteonecrosis and Osteoarthritis of the Knee.

Abstract

The purpose of the study was to investigate the two-year clinical efficacy differences between fixed-bearing unicompartmental knee arthroplasty (FB-UKA) for treating spontaneous osteonecrosis of the knee (SONK) and medial knee osteoarthritis (MKOA). A retrospective cohort study was conducted, enrolling 25 patients who had SONK and underwent FB-UKA performed by the same senior surgeon at our institution between January 2023 and December 2024. Patients who had SONK were matched 1:1 with 25 contemporaneous MKOA patients who underwent FB-UKA, based on age, sex, and body mass index (BMI). The usage rates of intraoperative fixation aids for femoral components were recorded in both groups of patients, as well as Visual Analog Scale (VAS), Knee Society Score (KSS), Oxford Knee Score (OKS), range of motion (ROM), and hip-knee-ankle angle (HKA) at preoperative and final follow-up, as well as the incidence of postoperative complications. In the SONK group, the mean volume of necrotic lesions was 6.1 ± 6.7 cm³ (95% confidence interval [CI], 3.4 to 8.9). Among these, the number and proportion of cases with small, medium, and large necrotic lesions were 19 (76%), four (16%), and two (8%), respectively. The SONK group exhibited significantly higher preoperative VAS scores and greater VAS score improvement compared to the MKOA group (6 versus 4, P < 0.001; 4 versus 3, P < 0.001). However, HKA improvement was significantly lower in the SONK group than in the MKOA group (3 versus 5.3, P = 0.03). There were no statistically significant differences observed between the two groups in other aspects (P > 0.05). A FB-UKA yields comparable and satisfactory two-year clinical outcomes for both SONK and MKOA. However, for patients who have medium-to-large SONK necrotic areas, it is essential to prepare auxiliary fixation supports for the femoral component. Ⅲ, Retrospective Cohort Study.