Clinical and radiological features of atlantoaxial joints in rheumatoid arthritis.

Atlantoaxial (AA) instability is frequent radiological finding in patients with rheumatoid arthritis (RA). Mostly no serious neurological disorders are expected in such patients. The purpose of the study was to assess the sagittal spinal canal diameter according to Steel's rule of third and its relationship to clinical symptoms. Radiological and clinical evaluation was performed in 65 in-patients with RA. Fifty four patients complained of neck pain, 39 had vertebrobasilar symptoms, and 25 mild neurological disorders. Hyperreflexy tendon responses were registered in 16 patients. Only 1 patient had extensor plantar response. Forward AA dislocation was verified in 28 (43%) cases with a mean value of 8.3mm (4-17 mm). Still free space for spinal cord in spinal canal was obtained in 62 (95%) of patients, which can explain such a low incidence of serious neurological disorders. Our results suggest an association among duration of disease, atlantodental distance, and sagittal spinal canal diameter. We consider that it is important to detect early the most jeopardized patients on the basis of radiological analysis at C1 level according to Steel's rule of third and recognize when rising dbl quote, left (low)safe zone" has exceeded and enters the area of impending spinal cord compression.