Osteonecrosis is a disease process characterized by the ischemic death of subchondral bone, that is, bone under the cartilage near the joint surface, culminating in the possible collapse of the bone and damage to the joint. Osteonecrosis is distinguished from “bone infarction,” which is also characterized by ischemic death of bone – but in the diaphyseal shaft, and thus not associated with a risk of arthritis. Osteonecrosis is also known as “avascular necrosis” or “aseptic necrosis,” older terms that are no longer preferred. Osteonecrosis has many causes, including trauma, sickle cell disease, corticosteroid use, and excessive alcohol intake, though in many instances a cause is not identified. In those cases, the osteonecrosis is labeled “idiopathic.” Osteonecrosis is frequently encountered in the femoral head, proximal humerus, medial femoral condyle, talus, scaphoid, and lunate.
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