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 aft er 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 classifica tion, and plain radiographs, Band images were observed 2 months after surge ry in eight patients and ii months in 12 patients (39% of all patients). Ac cording to the location and extent of the band image on magnetic resonance imaging, one patient was classified in the B1 Group (lateral type), four pa tients in the B2 Group (surface type), three patients in the B3 Group (inte rmediate type), and four patients in the B4 Group (extended type), Band ima ges appeared in all patients in the B4 Group 5 months after surgery, Femora l heads of the patients in the B3 and B4 Groups by magnetic resonance imagi ng classification all were collapsed, On plain radiographs, osteonecrosis o f the femoral head could be diagnosed in eight patients between 11 and 24 m onths after injury. The interval giving the greatest sensitivity, specifici ty, and accuracy of the diagnosis of osteonecrosis of the femoral head by m agnetic resonance imaging was 6 months after surgery.