Atlantoaxial Subluxation

Radiographs of the cervical spine showing atlantoaxial subluxation and subaxial subluxation in a patient with rheumatoid arthritis. The lateral views of the cervical spine were taken in neck extension (on left) and flexion (on right). In flexion, the anterior arch of C1 is far anterior to the dens of C2 (posterior to the black arrow), indicating anterior subluxation. This finding is not evident in extension (black arrow), indicating that atlantoaxial subluxation is dynamic. Anterolisthesis (slipping forward of the upper vertebral body, shown by white arrowheads) is also present at C2-C3 and C3-C4 in extension and at C3-C4 and C4-C5 in flexion.