Anterior subluxation of C1 on C2 in rheumatoid arthritis with cord indentation on MRI

A T2-weighted image of the cervical spine in the sagittal plain (A) shows a 5 mm separation (arrows) between the posterior border of C1 arch (anterior arrow) and the anterior border of the dens (posterior arrow). Multilevel spondylosis is also present between C3 and C7. Image B is a magnified view of image A, and shows the C1 to C2 separation (arrows), pannus formation posterior to the dens (asterisk), with impingement on the cord and the anterior CSF space (dashed arrow), and the cord (arrowhead).