Oppenheimer ossicles are accessory ossicles, result of the non-union of a secondary ossification center of the articular process. They predominantly occur as a single, unilateral ossicle of the inferior articular processes of the lumbar spine. Usually asymptomatic and discovered incidentally on imaging.

On imaging, the main differential diagnosis is a fracture of the articular process: an Oppenheimer ossicle will demonstrate regular, well-defined corticated margins.