The Odontoid Fracture Classification of Anderson and D’alonzo.

Type I: fractures of the odontoid tip represent alar ligament avulsions. Type II: occur at the odontoid waist, above the C2 lateral masses. Type III: extend below the odontoid waist to involve the body and lateral masses of C2.

(From SchoenfeldAJ, LeHV, BonoCM. Cervical spine fractures and dislocations. In: TornettaP III, RicciWM, OstrumRF, et al., eds. Rockwood and Green’s Fractures in Adults. Vol 2. 9th ed. Philadelphia: Wolters Kluwer; 2020:1817–1899.)