Neuroradiology

Dislocation, atlantoaxial

relatively common post-traumatic finding usually resulting from flexion and less frequently from extension traumatic forces. Flexion and extension are responsible for anterior and posterior dislocation, respectively. Rotary dislocation resulting from rotational forces is also possible but is much less common. Anterior and posterior dislocation are usually associated with odontoid fractures, unless a tear in the transverse and alar ligament is produced, which is very uncommon in normal individuals and is usually only observed over pre-existing ligamentous weakness.

Atlantoaxial dislocation may be diagnosed on X-ray and should be suspected in particular with the loss of normal articular relations between C1 and C2 (the most common evidence is an increased distance between the odontoid and the anterior atlas arch that should not exceed 3 mm). It can be confirmed by CT that should be performed with thin slices and sagittal and coronal reformations.

FS