Imaging modalities for early diagnosis of osteonecrosis of the hip

Abstract

Abstract Avascular necrosis frequently affects young adults, with a high morbidity, often necessitating joint replacement. There is evidence suggesting that early surgical intervention may prevent progression of the disease; hence, there has been widespread interest in increasing our sensitivity for early diagnosis. Plain x-ray film findings are often subtle or absent in the early stages of disease, and scintigraphy had been the most sensitive diagnostic modality until the advent of magnetic resonance imaging. Several studies have now confirmed the sensitivity of magnetic resonance imaging for early avascular necrosis as better than that of plain x-ray films, computed tomography, and nuclear medicine. In rare instances, biopsy-proven cases have had normal magnetic resonance imaging results. Avascular necrosis most commonly appears as a focal defect in the anterosuperior portion of the femoral head bounded by a low signal margin. This margin correlates well histologically with the reactive interface between viable and nonviable bone and the margin of peripheral sclerosis noted by computed tomography. Although this low signal rim is a characteristic sign of avascular necrosis, it is not pathognomonic. Another characteristic finding, on T2WI, is the double-line sign, which consists of a high signal intensity rim within the low signal margin. It has been described in 65% to 80% of cases and seems to be less common in early disease. It is thought to represent a zone of hyperemia and granulation tissue at the reactive interface between viable and nonviable bone, although chemical shift artifact may create similar findings in some instances.