Special Consideration: Atlanto-occipital Subluxation

Atlanto-occipital dislocation is usually a fatal injury. Rarely, however, there may be subluxation at the atlanto-occipital joint without such devastating effects. This is a potentially life-threatening injury which can be difficult to detect.

There should be no more than 12 mm between:

1. The tip of the basion and the tip of the dens (i.e. the basion-dental interval – see caption)
2. The tip of the basion to the posterior axial line [6] (i.e. the basion-posterior axial line interval – see caption)

Image: Harris' measurements – basion-dental interval and basion-posterior axial line interval are both 12 mm [6]. Also known as the 'rule of twelve'