Clinical and radiological features of atlantoaxial joints in rheumatoid arthritis

Atlantoaxial(AA) instability is frequent radiological finding in patients w ith 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 a ccording to Steel's rule of third and its relationship to clinical symptoms . Radiological and clinical evaluation was performed in 65 in-patients with R A. Fifty four patients complained of neck pain, 39 had vertebrobasilar symp toms, and 25 mild neurological disorders. A hyperreflexy tendon responses w ere registered in 16 patients. Only 1 patient had extensor plantar response . Forward AA dislocation was verified in 28 (43%) cases with a mean Value o f 8.3 mm (4-17 mm). Still free space for spinal cord in spinal canal was ob tained in 62 (95%) of patients, which can explain such a low incidence of s erious 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 patie nts on the basis of radiological analysis at C1 level according to Steel's rule of third and recognize when "safe zone" has exceeded and enters the ar ea of impending spinal cord compression.