Atlantoaxial anomalies with particular emphasis on os odontoideum.

Anomalies of the atlantoaxial articulation are discussed with emphasis on os odontoideum. Normal and abnormal embryological and anatomical characteristics are described, as is their relevance upon stability of the upper cervical segments. This paper further discusses and reviews theories pertaining to the congenital and acquired forms of os odontoideum and a case report is presented. Some conclusions are drawn from the presented case report.