Medullary compression in rheumatoid atlanto-axial subluxation evaluated by computerized tomography.

CT examination of rheumatoid dislocation in the C1-C2 region was performed in 20 patients with advanced disease. The patients were classified in three grades according to the degree of medullary compression caused by the odontoid process in the extended position of the neck. Five patients showed no dural or medullary compression (grade 1), nine dural compression (grade 2), and six medullary compression (grade 3). CT grading was found to correlate best with long tract symptoms. These were present in 4/6 grade 3 and 0/5 grade 1 patients, while 3/9 grade 2 patients had long tract symptoms. Tissue attenuation values over the anterior atlanto-axial joint indicated interposing firm connective tissue in patients showing no reduction of the subluxation on extension of the neck.