Osteonecrosis is defined as cell death in the marrow fat and mineralized tissue of the bone. It represents the final common pathway of several disease entities, which result in impaired blood supply to the bone tissue – causing necrosis or death of the bone. The most common sites are the hip, the knees and shoulders, as well as the wrist bones and feet.
Young males are more commonly affected. Usually the patient is less than age 50. The male : female ratio is 8:1. It is a disease of divers who have suffered from "the bends" (Caisson's disease).