Pathogenetic mechanism and prevalence of the stable atlantoaxial subluxation in rheumatoid arthritis.

Objective: To study the pathogenetic mechanisms responsible for and prevalence of stable atlantoaxial subluxation (AAS).
Methods: Lateral view cervical spine radiographs during flexion and extension were studied in 262 patients with rheumatoid arthritis (RA).
Results: AAS was found in 130 patients, 42 (32%) of whom had a stable deformity; in a population based subseries, stable AAS was seen in 16% of the patients with ASS. Atlantoaxial impaction (AAI) was diagnosed in 98 cases and in 37 (88%) of the 42 patients with stable AAS.
Conclusion: The main cause of the spontaneous stabilization and occasional ankylosis of the atlantoaxial area is the development of erosions and collapse in the lateral facet joints leading to AAI.