[Imaging and classification of avascular femoral head necrosis].

Avascular femoral head necrosis (AVNFH) is difficult to diagnose on plain radiographs in early stages of the disease. Since early stages are often clinically occult, early use of MRI is required to rule out or verify a clinical suspicion. MRI and, in some cases, additional CT are the cornerstones of AVNFH diagnosis and classification. Anteroposterior radiography of the pelvis and a second plane of the involved hip remains the primary basic imaging examination for follow-up and to rule out other pathologies. Correct staging of adult disease has been shown to be the key factor in therapeutic decision-making. According to the German S3 guideline on diagnosis and treatment of AVNFH, use of the ARCO classification is recommended for staging. This paper presents the current status of diagnosis and classification of adult AVNFH. The criteria for ascribing disease to a particular ARCO stage are defined and critically discussed.