Medial Unicompartmental Knee Arthroplasty in Patients with Spontaneous Osteonecrosis of the Knee

Background: We analyzed the clinical and radiologic results of patients with spontaneous osteonecrosis of the knee treated by minimally invasive medial unicompartmental arthroplasty using Oxford Uni. Methods: We reviewed 22 knees in 21 patients which were treated for spontaneous osteonecrosis between 2002 and 2006. Patients included one male and 20 females. The mean age was 70.8 years (range, 53 to 82 years). The mean follow-up period was 70.3 months (range, 48 to 93 months). The clinical results were evaluated using the Hospital for Special Surgery (HSS) knee score and the range of motion of the knee preoperatively and at the final follow-up. Preoperative plain radiographs and magnetic resonance images were analyzed to determine the size and stage of osteonecrotic lesions. Results: The mean HSS knee score was 64.3 (range, 54 to 75) preoperatively and 92.0 (range, 71 to 100) at the final follow-up. The mean preoperative flexion contracture was 8.9o (range, 0 to 15 degrees) and 0.2 degrees (range, 0 to 5 degrees) at the final follow-up. The mean further flexion increased from 138.6 inverted perpendicular (range, 100 to 145 degrees) preoperatively to 145.6 degrees (range, 140 to 150 degrees) at the final follow-up. Active full flexion was possible within 2 months of the operation. The squatting position was possible in 16 patients (84.2%) out of 19, except one case of bronchiectasis and one case of spine fracture. The cross-leg posture was possible in 19 patients (90.5%) out of 21. The mean tibiofemoral angle was improved from varus 0.98o to valgus 3.22o. Meniscal bearing dislocation occurred in 2 cases and femoral component loosening occurred in 1 case. Conclusions: Unicompartmental knee arthroplasty using Oxford Uni could be an alternative treatment option in spontaneous osteonecrosis of the knee.