To study the pathogenetic mechanisms responsible for and prevalence of stable atlantoaxial subluxation (AAS).
Lateral view cervical spine radiographs during flexion and extension were studied in 262 patients with rheumatoid arthritis (RA).
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.
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.