Atlantoaxial subluxation is a common cervical manifestation of rheumatoid arthritis and results from erosive synovitis in the atlantoaxial and atlanto-odontoid joints and the bursa between the dens and Ligamentum transversum. Since mobility in the atlantoaxial segment is primarily controlled by the joint capsules and ligaments, destruction of the restraining structures in this highly mobile region of the cervical spine causes instability. This progressively increases and can lead over time to compression of the caudal portions of the medulla oblongata in the upper cervical canal. Additional pannus formation at the dens leads to further motion-independent compression of the cervical spinal cord.
Etiology
Patients are particularly at risk in flexion injuries of the cervical spine[^2], since destruction of the Ligamentum transversum eliminates the posterior restraint to the Dens [^1]. Atlantoaxial subluxation may also be associated with rheumatoid arthritis or tonsillitis (Grisel syndrome)[^2].