T1-weighted MR images of the cervical spine in 42 rheumatoid arthritis patients with cervical spine involvement were obtained and analyzed prospectively. We assessed changes between images obtained in the neutral position and following active flexion, especially horizontal atlantoaxial and subaxial motion, presence or absence of brainstem compression, subarachnoid space involvement at the atlantoaxial and subaxial level and the cervicomedullary angle