Part 2 book “Imaging of bones and joints” has contents: Osteonecroses of the skeletal system, osteochondroses, metabolic, hormonal, and toxic bone disorders, congenital disorders of bone and joint development, rheumatic disorders, miscellaneous bone, joint, and soft tissue disorders, and other contents. | 6 Osteonecroses of the Skeletal System Anatomy, Etiology, and Pathogenesis Anatomy. Bone varies significantly in its composition, depending on age and location. It has an organic matrix, comprised of primarily collagen (osteoid), into which inorganic mineral components (especially calcium hydroxyapatite) are incorporated. The mineralized matrix is subject to constant resorption and formation by specific cells (osteoblasts and osteoclasts). This matrix harbors both red (hematopoietic) and yellow (fatty) marrow. These are the components that, together with the mineralized bony matrix, constitute the organ “bone.” Survival of the bone is not possible, however, without arterial inflow and venous drainage. For purposes of clarification. Osteonecrosis takes place at a cellular level and only histopathology can identify the cellular alterations. Fat cells and hematopoietic marrow are always involved where ischemia is present. Cellular death in bone is a nonspecific, commonly subclinical, process that occurs more often when bone cells are subjected to abnormal stress. Therefore, histopathology will reveal small areas of necrosis along with severe osteoarthritis, stress or insufficiency fracture, an acute fracture, tumor, or infection. This chapter addresses clinically relevant forms of osteonecrosis which can be readily demonstrated by imaging studies. Imaging reflects macroscopic anatomy and reveals the effects of cell death on the bone (or parts of it). Common terms such as “osteonecrosis,”“bone infarction,”“avascular necrosis,” and “aseptic necrosis” are poorly defined and are applied inconsistently. These terms do not provide information about prognosis or etiology. Note In everyday language, the term “osteonecrosis” generally refers to bone necrosis located in the epiphysis or apophysis or involving the entire bone ( Fig. ). If the osteonecrosis is located in the metaphysis or diaphysis, then this is referred to as “bone infarct.” A task for the future is to
