Natural history of osteonecrosis

Osteonecrosis is an incapacitating disorder of bone circulation that is insidious in onset and affects predominantly the younger population in the second to sixth decade of their lives. In about 75 % of cases, the disease occurs between the third and the sixth decade and is bilateral in about 50 % of the cases. Various terms have been used in literature to describe this condition, such as aseptic necrosis, avascular necrosis, subchondral avascular necrosis, and avascular necrosis. Although both traumatic and nontraumatic disorders have been associated with its development, the fi nal common pathway involves interruption in the vascular supply. This disruption in the blood fl ow causes bone cell death, leading to collapse of the bony architecture (Table 20.1 ). Although cell death is a nonspecifi c marker of major cell stress and is found to occur in a variety of conditions such as fractures, tumors, infections, and osteoarthritis, it is only in osteonecrosis that the predominant abnormality is massive necrosis of the bone and its marrow.