Femoral head avascular necrosis: CT assessment with multiplanar reconstruction

Thirty-two patients with avascular necrosis (AVN) of the femoral head underwent imaging studies using computed tomography with multiplanar reconstructions (CT/MPR). Staging of the disease by means of CT/MPR images was compared with traditional staging by means of routine frontal and frog-leg lateral radiographs. CT/MPR examination upgraded staging in 30% of the hips studied and made significant contributions to patient management in 14 (54%) of 26 patients for whom both CT scans and plain-film radiographs were available for comparison. Asymptomatic and radiographically normal contralateral hips were found at CT study to have stage II or stage III AVN in four patients. Subtle alterations in trabecular patterns, joint spaces, femoral-head contours, and acetabula were well defined on CT/MPR studies in many cases; previously undetected or ill-defined abnormalities were frequently visualized. The major weight-bearing components of the hip (anterior and posterior acetabular columns, acetabular dome, and superior pole of the femur), which may be poorly defined on CT scans due to partial volume effects on the transaxial images, were best seen on the sagittal and coronal reconstructions. A new system for staging AVN is suggested.