Rotatory subluxation is classifed into four types depending upon the degree of separation of the dens from the anterior arch of atlas:

Type I : Atlanto-dens distance <3 mm; transverse ligament intact

Type II: Atlanto-dens distance 3–5 mm; transverse ligament ruptured

Type III: Atlanto-dens distance >5 mm; alar ligaments ruptured

Type IV: Posterior subluxations of C1 on C2 (usually signifies an odontoid fracture or hypoplasia)


Provide an explanation for key principles and pertinent aspects of the classification


Insert figures illustrating the classification


Provide the citation for the landmark article and recent review articles describing the classification