[Idiopathic osteonecrosis of the medial femoral condyle. Treatment with tibial osteotomy or unicompartmental arthroplasty].

Thirty-three patients, with a mean age of 72 years, were treated for idiopathic osteonecrosis of the medial femoral condyle by a valgus upper tibial osteotomy in 18 cases and by a unicompartmental arthroplasty in 15 cases. The site of the osteonecrosis was in the medial femoral condyle alone in 27 knees and in the medial femoral condyle and the medial tibial plateau in six knees. Pre-operatively, the two groups were comparable with involvement localised to the medial compartment and with no changes in the lateral compartment or the patello-femoral joint. The mean age of the unicompartmental arthroplasties was higher. At follow-up at the present time, which was nine years for the osteotomies and five years for the prostheses, no knee has had to have a further operation. All the knees were improved by the operation. The functional results were the same in both groups. The necrotic nature of the medial femoral condyle did not affect the cementing of the femoral component in the arthroplasties and no loosening occurred. After osteotomy, no further depression of the osteochondral fragment developed. When the knee did not show osteoarthritic change before operation, the valgus tibial osteotomy was not able to prevent narrowing of the medial compartment in this series unless the correction obtained exceeded two degrees of valgus.