 Osteonecrosis is thought to be a common condition most commonly affecting adults in third to fifth decades of life, with femoral head osteonecrosis incidence reported to be 10,000 to 20,000 new symptomatic cases per year in the United States [4,5]. True prevalence of osteonecrosis is likely quite underestimated because many patients are asymptomatic, especially the metadiaphyseal cases. Recent studies have shown that MR-proven cases of femoral osteonecrosis can be retrospectively visualized on CT abdomen/pelvis with intravenous (IV) contrast performed for other clinical purposes and were originally vastly underreported [6,7]. Risk factors for osteonecrosis are numerous and include trauma, corticosteroid therapy, alcohol use, HIV, lymphoma/leukemia, blood dyscrasias, chemotherapy, radiation therapy, Gaucher disease, and Caisson disease [8-10]. In nontraumatic cases, femoral head osteonecrosis is often bilateral (70%-80%) [5]. Other locations of osteonecrosis (eg, talus, humeral head) are often involved in cases of multifocal osteonecrosis [11,12]. In a long-term follow-up of patients on steroids, Nawata et al [12] found osteonecrosis in the hip (68%), knee (44%), ankle (17%), and shoulder (15%). Many staging systems have been developed for femoral osteonecrosis and often adapted for the humeral head. Ficat and Arlet, developed in the 1960s, does not account for size or location of the necrotic lesion but remains the most commonly used system. Other systems, University of Pennsylvania (Steinberg), Association Research Circulation Osseous (ARCO), and Japanese Orthopedic Association systems, may also be used [15]. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through representation of such organizations on expert panels. Participation on the expert panel does not necessarily imply endorsement of the final document by individual contributors or their respective organization.
Osteonecrosis PCAs.  Osteonecrosis is thought to be a common condition most commonly affecting adults in third to fifth decades of life, with femoral head osteonecrosis incidence reported to be 10,000 to 20,000 new symptomatic cases per year in the United States [4,5]. True prevalence of osteonecrosis is likely quite underestimated because many patients are asymptomatic, especially the metadiaphyseal cases. Recent studies have shown that MR-proven cases of femoral osteonecrosis can be retrospectively visualized on CT abdomen/pelvis with intravenous (IV) contrast performed for other clinical purposes and were originally vastly underreported [6,7]. Risk factors for osteonecrosis are numerous and include trauma, corticosteroid therapy, alcohol use, HIV, lymphoma/leukemia, blood dyscrasias, chemotherapy, radiation therapy, Gaucher disease, and Caisson disease [8-10]. In nontraumatic cases, femoral head osteonecrosis is often bilateral (70%-80%) [5]. Other locations of osteonecrosis (eg, talus, humeral head) are often involved in cases of multifocal osteonecrosis [11,12]. In a long-term follow-up of patients on steroids, Nawata et al [12] found osteonecrosis in the hip (68%), knee (44%), ankle (17%), and shoulder (15%). Many staging systems have been developed for femoral osteonecrosis and often adapted for the humeral head. Ficat and Arlet, developed in the 1960s, does not account for size or location of the necrotic lesion but remains the most commonly used system. Other systems, University of Pennsylvania (Steinberg), Association Research Circulation Osseous (ARCO), and Japanese Orthopedic Association systems, may also be used [15]. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through representation of such organizations on expert panels. Participation on the expert panel does not necessarily imply endorsement of the final document by individual contributors or their respective organization.