Prediction of osteonecrosis by magnetic resonance imaging after femoral neck fractures.

Thirty-one patients undergoing internal fixation for femoral neck fractures who were examined by magnetic resonance imaging at 2, 6, and 12 months after surgery and who could be followed up more than 2 years were enrolled in the current study. The items investigated were timing of the appearance of the band image on T1 weighted images, magnetic resonance imaging classification, and plain radiographs. Band images were observed 2 months after surgery in eight patients and 6 months in 12 patients (39% of all patients). According to the location and extent of the band image on magnetic resonance imaging, one patient was classified in the B1 Group (lateral type), four patients in the B2 Group (surface type), three patients in the B3 Group (intermediate type), and four patients in the B4 Group (extended type). Band images appeared in all patients in the B4 Group 6 months after surgery. Femoral heads of the patients in the B3 and B4 Groups by magnetic resonance imaging classification all were collapsed. On plain radiographs, osteonecrosis of the femoral head could be diagnosed in eight patients between 11 and 24 months after injury. The interval giving the greatest sensitivity, specificity, and accuracy of the diagnosis of osteonecrosis of the femoral head by magnetic resonance imaging was 6 months after surgery.