[Osteonecrosis].

In orthopedic pathology, the pathologist is most commonly faced with the study of resected femoral heads for osteonecrosis. Such a study necessitates a knowledge of clinical findings, of physiopathology and chiefly of radiological findings. Osteonecrosis of the femoral head following fracture has been reported with four morphological stages which are very precisely described. In the same way, idiopathic, non traumatic, or primary osteonecrosis is covered, stressing the putative etiological factors and the most important findings of imaging. The review includes also the skeletal manifestations of decompression sickness as well as bone infarctions not associated with caisson disease, and spontaneous osteonecrosis of the knee. From the recruitment of the Hospital for Special Surgery, NY, it has been recently reported that a significant number of patients regarded as cases of osteonecrosis, either in the femoral head or in the knee, are actually cases of subchondral insufficiency fractures.