[Atraumatic and aseptic osteonecrosis of large joints]

Subchondral osteonecrosis of large weight-bearing joints (hip and knee joints) represents a severe and joint-threatening disease. Apart from idiopathic forms, glucocorticoid medication and alcohol abuse have been identified as major causative factors for atraumatic osteonecrosis. In addition to direct cytotoxic factors, a critically reduced perfusion of the subchondral osseous space will eventually lead to bone marrow ischemia and osseous necrosis. Magnetic resonance imaging (MRI) is capable of visualizing a reactive border-like zone in this early, already irreversible and often asymptomatic stage I according to the Association of Research Circulation Osseous (ARCO) staging system. Later in the course, osteonecrosis progresses to form serpiginous sclerotic lines, enclosing the necrotic bone area (stage II ARCO). Repair mechanisms of osteonecrosis are mostly unsuccessful and depending on the size of the osteonecrosis result in biomechanical failure and ultimately subchondral insufficiency fractures (crescent sign), thus marking the transition to stage III ARCO (joint surface collapse).