Prognostic features of atlantoaxial subluxation in rheumatoid arthritis patients.

The clinical and radiographic findings of 194 patients with rheumatoid arthritis and atlantoaxial (C1-C2) subluxation and/or atlantoaxial impaction (AAI) were reviewed. The condition of most patients with C1-C2 alignment abnormalities remained unchanged or became worse with time (i.e., the misalignment became fixed, subluxation increased, or AAI developed). The chance of developing upper cervical cord compression was not related to worsening per se, but to the degree of deformity. Upper spinal cord compression developed more often in men; when C1-C2 subluxation was greater than 9 mm; and in the presence of atlantoaxial impaction. The presence of lateral C1-C2 subluxation probably also contributes to the development of upper spinal cord compression. Settling of the skull and C1 onto C2 (AAI) were considered to be present when the anterior arch of C1 was abnormally low in relation to C2.