Cervical vertebral erosions and subluxations in rheumatoid arthritis and ankylosing spondylitis

Atlanto‐axial and lower cervical subluxations are frequently present in rhematoid arthritis and ankylosing spondylitis. Vertebral erosions, particularly of the odontoid process, can often be demonstrated. Rheumatoid involvement of the occipito‐atlanto‐axial joints may cause a vertical translation of the cervical spine with respect to the skull; at times, this is associated with true basilar invagination.