Acetabular ossicles: normal variant or disease entity?

Ossicles located in the acetabular fossa may confuse diagnostic and therapeutic work-up. An accessory ossification centre may persist unfused as an os acetabuli centrale which is surrounded by intact hyaline cartilage representing an anatomic variant. Bone islands located in the pillars of the acetabulum can project into the acetabular fossa simulating acetabular ossicles. Osteochondrosis dissecans, posttraumatic articular bodies, degenerative disease and other rare lesions may be responsible for clinical symptoms and are of similar appearance than anatomic variants. Plain film radiography, X-ray tomography, CT and MRI are used to categorize these lesions. MRI is very valuable to assess cartilage integrity in a noninvasive way, but arthro-CT or arthro-MRI have to be used in unclear cases. Therefore the purpose of this presentation is to discuss the appearance, the possible etiology and the differential diagnosis of acetabular ossicles and how they can be evaluated to avoid an unnecessary arthrotomy.