UKA after spontaneous osteonecrosis of the knee: a retrospective analysis.

PURPOSE: Safety and efficacy of unicompartmental knee arthroplasty (UKA) in unicompartmental osteoarthritis (OA) has been shown in large patient series. It has been matter of discussion whether or not spontaneous osteonecrosis of the knee (SONK) can successfully be treated with UKA.

PATIENTS AND METHODS: A retrospective approach included 52 cases of UKA for SONK of the femoral condyles. Four implants were revised (7.7%), and seven patients had died. Nine patients were interviewed by telephone, 28 followed the invitation for clinical examination including clinical scores (KSS and WOMAC) and radiographs. Satisfaction of patients was recorded in four categories. Four patients (7.7%) were lost to follow-up.

RESULTS: Average follow-up was 10.9 ± 4.8 years (4-25). Average age at operation was 66.6 ± 9.7 years. The KSS score increased from a preoperative 85 ± 30 to 173 ± 27 (p < 0.0001) at latest follow-up. WOMAC was 7.7 ± 11.4 at latest follow-up. Of the patients with implants still in place, most patients were satisfied (21.6%) or very satisfied (75.7%) with the outcome of this surgical procedure. One patient was dissatisfied (2.7%). Kaplan-Meier analysis with implant revision as endpoint revealed a survival rate of 93.1% at 10 years and 90.6% at 15 years.

DISCUSSION: This study shows that spontaneous osteonecrosis of the knee (SONK) can successfully be treated with UKA at a good mid- to long-term follow-up.