Medium-term clinical results of unicompartmental knee arthroplasty for the treatment for spontaneous osteonecrosis of the knee with four to 15 years of follow-up

Unicompartmental knee arthroplasty (UKA) is an option for the treatment of spontaneous osteonecrosis of the knee (SONK). However, there are limited studies focusing on this area. This study presents medium-term clinical outcome data of UKA for SONK. We reviewed 50 SONK knees in 48 patients that were treated by UKA. The mean age, height, and body weight were 73 years, 153 cm, and 57 kg, respectively. The mean follow-up was 8.4 years (range, four to 15 years). Preoperatively, we measured the size and the volume (estimated by width × length × depth) of the necrotic bone mass on T1-weighted magnetic resonance imaging. The clinical results were evaluated serially at follow-up visits radiographically and with the Knee Society Scoring (KSS) and Oxford Knee Scoring (OKS) systems. There were no revisions, re-operations, or major complications. The mean sizes of the necrotic lesions were 17.2 mm (14.7–22.3 mm) in width, 28.2 mm (6.2–34.7 mm) in length, and 11.3 mm (3.2–14.5 mm) in depth. The mean volume was approximately 5.4 cm3 (0.7–10.3 cm3). The mean flexion of the knee, KSS Knee Score, Function Score, and OKS increased from a preoperative 128.7–137.5°, 52.3–91.3, 39.7–90.2, and 21.6–40.2, respectively, at the latest follow-up. At the last follow-up, all patients had good or excellent OKS. This study demonstrates that UKA is a good option and is reliable for the treatment of SONK irrespective of necrotic bone mass size.