Introduction: The data reporting clinical and radiological outcomes after modern unicompartmental knee arthroplasty (UKA) for spontaneous avascular osteonecrosis are limited. We hypothesized that UKA for spontaneous osteonecrosis may be as reliable and durable as it is for osteoarthritis.

Materials and Methods: We retrospectively reviewed 40 cemented UKA operated for spontaneous osteonecrosis of the knee in two different centers between 1989 and 2004. Twenty-six patients were women and 14 men, mean patient age was 67 years (range, 45 to 84) and mean body mass index was 27.4 Kg/m2 (range, 18 to 44). Clinical and radiological evaluations were performed by an independent observer in each center according to the same protocol at a minimum follow-up of 3 years (mean 8 years; range, 3–17.5 years).

Results: The mean Knee Society Knee score improved from 60 preoperatively to 95 post-operatively. The mean Knee Society Function score improved from 50 preoperatively to 89 post-operatively. Restoration of an appropriate lower-limb mechanical axis was achieved for 36 knees (90%). Two knees were revised for aseptic loosening. The Kaplan–Meier survivorship was 95% at 12 years.

Discusssion and conclusion: Our data suggest UKA is a reasonable solution for restoring clinical function and radiological lower-limb alignment for spontaneous osteonecrosis of the knee, with a durable survivorship.