Osteonecrosis is defined as bone death due to inadequate vascular supply. It is sometimes also called "avascular necrosis" and "aseptic necrosis" when involving epiphysis, or "bone infarct" when involving metadiaphysis. Common sites include femoral head, humeral head, tibial metadiaphysis, femoral metadiaphysis, scaphoid, lunate, and talus. Osteonecrosis is thought to be a common condition most commonly affecting adults in third to fifth decades of life. 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. Epiphyseal osteonecrosis can lead to subchondral fracture and secondary osteoarthritis whereas metadiaphyseal cases do not, likely explaining their lack of long-term sequelae. Early diagnosis of osteonecrosis is important: 1) to exclude other causes of patient's pain and 2) to allow for possible early surgical prevention to prevent articular collapse and need for joint replacements. Imaging is also important for preoperative planning. The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer-reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances in which peer-reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.
