Os odontoideum with associated multidirectional atlantoaxial instability: imaging and clinical considerations.

Acquired anomalies of the craniovertebral junction although rare, may result in serious clinical sequella. The prevalence of craniovertebral anomalies remains unknown since they may remain clinically silent. Os odontoideum is one such anomaly. The etiology remains controversial over whether it is a post-traumatic or congenital condition but the clinical considerations of os odontoideum remain the same. Chiropractors may encounter os odontoideum in the subclinical patient with the potential for deleterious effects with manipulation. Radiography is essential to its detection.