Abstract

Atlantoaxial instability frequently causes extrinsic cervical myelopathy via anterior displacement of the posterior arch of the atlas. However, upper cervical myelopathy resulting from atlantodental osteoarthritis with the hypertrophic dens due to atlantoaxial instability is very rare. We present a case of upper cervical myelopathy secondary to atlantoaxial instability and atlantodental osteoarthritis. Although there was no atlantoaxial subluxation on the flexion and extension radiographies, hypertrophic changes of the anterior arch of the atlas with the dens axis and a fusion of the atlanto-dental joint resulting from atlantoaxial instability were determined on computed tomography and magnetic resonance imaging.