Avascular necrosis of the femoral head (AVN) is an increasingly common cause of musculoskeletal disability, and it poses a major diagnostic and therapeutic challenge. Although patients are initially asymptomatic, AVN usually progresses to joint destruction, requiring total hip replacement (THR), usually before the fifth decade. It is estimated that almost 10% of the nearly 500,000 THRs performed each year in the United States are intended to treat AVN; at a cost of more than 1 billion dollars, THRs performed to treat AVN constitute approximately 25% of the total national costs for THR.
Axial CT in a patient without avascular necrosis of the femoral head shows prominent and thickened but normal trabeculae (arrow) within the femoral head. Note the delicate, sclerotic, raylike branchings emanating in a radial fashion from the central dense band. This is the asterisk sign.
Avascular necrosis, femoral head. Anteroposterior view of the pelvis shows flattening of the outer portion of the right femoral head from avascular necrosis (arrow), with adjacent joint space narrowing, juxta-articular sclerosis, and osteophytes representing degenerative joint disease.
Avascular necrosis, femoral head. Coronal T1-weighted MRI in a patient showing hypointense signal within the proximal femoral neck and intertrochanteric regions (arrows) representing hematopoietic marrow. Increased signal is present within the greater trochanters and femoral capital epiphysis representing normal fatty marrow .