Classification of Traumatic Spondylolisthesis of the Axis (Hangman’s Fracture) (According to Effendi, Modified by Levine). Type I: Nondisplaced Fracture of the Pars Interarticularis. Type IA: Atypical Unstable Fracture that are Obliquely Displaced Extending Anterior to Pars and into Body on Contralateral Side. Type II: Displaced Fracture of the Pars Interarticularis. Type IIA: Displaced Fracture of the Pars Interarticularis with Disruption of the C2–c3 Discoligamentous Complex. Type III: Dislocation of C2–c3 Facets Joints with Fractured Pars Interarticularis.

(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.)