musculoskeletal and connective tissue disorders
Osteonecrosis (ON)
Pathophysiology of Osteonecrosis
Osteonecrosis involves the death of cellular elements of the bone marrow. Mechanisms of nontraumatic osteonecrosis may include embolization by blood clots or lipid droplets, intravascular thrombosis, and extravascular compression. After the vascular insult, the repair processes attempt to remove necrotic bone and marrow and replace them with viable tissue. For example, if an infarct in the hip is small, particularly if it is not subject to major weight bearing, these processes may succeed and the femoral head remains round. However, in approximately 80% of patients, especially if the infarct is large and in the weight-bearing area, collapse of the infarcted area outstrips attempts at repair, and the infarcted area collapses. The femoral head is no longer round. Because osteonecrosis usually affects the ends (epiphysis and metaphysis) of long bones, the overlying articular cartilage surface becomes flattened and irregular, with areas of collapse that may eventually lead to Osteoarthritis (OA) and increased pain. For more information about the pathophysiology of osteonecrosis, seeOsteonecrosis: Overview of New Paradigms in the Etiology and Treatment. 