Spontaneous osteonecrosis of the medial compartment of the knee: a MRI follow-up after conservative and operative treatment, preliminary results

Symptoms in patients suffering from spontaneous osteonecrosis of the knee ( SONK) may be reduced by high tibial osteotomy (HTO). However, the fare of t he necrotic lesion is unknown and needs further investigation. We conducted a prospective study to evaluate magnetic resonance imaging (MRI) changes a fter operative and nonoperative treatment. Ten consecutive patients sufferi ng from SONK of the medial compartment were given two treatment options: ei ther HTO (n = 6) or conservative treatment with partial weight bearing for 3 months (n = 4). We measured the greatest extent of well-defined subchondr al low signal intensity abnormality, considered to represent necrosis, and the surrounding area of intermediate signal intensity, considered to repres ent perifocal bone marrow edema, on T1-weighted coronal MRI images before a nd after treatment. The MRI follow-up period was 17.5 months (range 12-27) in the HTO group and 14.5 months (range 8-25) in the nonoperative group. At follow-up the MRI evaluation revealed a decrease in the low signal intense areas (necrosis) in five of the six patients in the HTO group. Only one of the four nonoperative patients showed a decrease in the low signal intense area. The intermediate intense areas (edema) decreased in all patients in the HTO group and in three of four in the nonoperative group. The mean decr ease in the area of perifocal edema was significantly greater in the HTO gr oup than in the nonoperative group (P = 0.019). No statistically significan t difference was found for the area of necrosis between the two groups (P = 0.171). A clinical improvement was observed in all patients of the HTO gro up but in only two of the four patients of the nonoperative group. We concl ude that the decrease in perifocal bone marrow edema seems to be associated with improved patient comfort. The MRI appearance of the necrotic lesion d oes not alter with either treatment mode.