Backward tilting of the posterior atlantal arch in rheumatoid arthritis.

In a retrospective survey of 450 patients with rheumatoid arthritis on whom cervical spine radiography was performed, one patient was found with a backward tilting of the posterior arch of the atlas. With preserved relations anteriorly, the posterior arch was rotated downward in front of the spinous process of the axis, encroaching on the space of the spinal canal.