CT analysis of the upper end of the femur: the asterisk sign and ischaemic bone necrosis of the femoral head.

In computed tomography (CT) of the head of the femur, a star-shaped structure can be seen which we refer to as the asterisk or asterisk sign. The asterisk is formed by thickened weight-bearing bone trabeculae. It can be shown by CT that the asterisk exhibits a characteristic change in ischaemic bone necrosis of the femoral head, even when the disease is in an early stage. CT of the hip joint is therefore an important examination for early diagnosis of ischaemic disease of the femoral head.