The early diagnosis of idiopathic femoral osteonecrosis

Idiopathic osteonecrosis of the femoral head presents many problems of diagnosis and treatment during the early stages of the disease due to the paucity of clinical manifestations and the absence of radiographic evidence. By the time that the radiographic and clinical evidence are sufficient for a reliable diagnosis, the disease is so advanced that treatment is a problem. Early diagnosis is therefore the key issue and, in this context, instrumental tests, CT scanning and the measurement of blood flow velocity play an ever-increasing role. In the early stages of the disease CT scanning shows characteristic changes in the socalled "asterisk sign" of Dihlmann, and this has proved useful not only in terms of diagnosis, but also in order to initiate early treatment of the disease. Although radioisotope methods with double tracer do not allow for direct visualisation of the circulation in the femoral head, they have proved to be extremely reliable in evaluating the perfusion index of the femoral heads by providing activity/time curves which are a reliable estimate of regional blood flow.