Histological evaluation of spontaneous osteonecrosis of the medial femoral condyle and short-term clinical results of osteochondral autografting: a case series.

Although many surgical modalities for spontaneous osteonecrosis of the knee (SONK) of the medial femoral condyle have been reported, few reports have described these treatment options from the etiological point of view. Recently, osteochondral autografting has gained popularity for use in small cartilage injuries. The aims of this study were to characterize the SONK lesion histopathologically and to report on preliminary clinical results of autogenous osteochondral grafting for SONK. Six patients with SONK of the medial femoral condyle underwent osteochondral autografting. Average age was 54.2 years (range, 50-57 years). Using Koshino's classification, three patients' lesions were classified as stage III and three as stage IV. Classical histological investigation of the lesions was performed in all cases. All the patients achieved favorable pain relief after osteochondral autografts. The mean duration of follow-up was 27.7 months (range, 23-45 months). An increase in the average Lysholm score was found, ranging from 54.7 preoperatively to 92.3 postoperatively. Histological investigation of the lesions revealed articular bone plate fracture with enchondral ossification, reactive cartilage tissue formation, and proliferation of fibrous tissue. An area of osteonecrosis was observed in detached or fragmented osteochondral lesions. Osteochondral autografting was performed on six patients for the SONK and the short-term clinical results were favorable. Histological results give support to subchondral fracture as the etiological mechanism underlying SONK.