The Anderson and D'Alonzo classification is the most commonly used classification of fractures of the odontoid process of C2 ¹.

Another classification system is the Roy-Camille classification, which aids more in the management of odontoid fractures.

Classification

• type I

  • rare

  • fracture of the upper part of the odontoid peg (generally oblique)

  • above the level of the transverse band of the cruciform ligament

  • usually considered stable

• type II

  • most common

  • transverse course fracture at the base of the odontoid

  • below the level of the transverse band of the cruciform ligament

  • unstable

  • high risk of non-union

• type IIa

  • ​type II fractures with comminution at the odontoid base

  • Hadley ² described this type of fracture which has a significantly increased risk of nonunion when treated non-operatively compared with classical type II fractures

  • represents 5-10% of type II fractures

• type III

  • through the odontoid and into the lateral masses of C2

  • relatively stable if not excessively displaced

  • best prognosis for healing because of the larger surface area of the fracture

Grauer classification of type II fractures

Grauer et al. ³ published a revised subclassification of type II fractures based on the management of odontoid process fractures:

• type IIa

  • undisplaced

  • conservative management with external immobilisation

• type IIb

  • ​anterosuperior to posteroinferior and displaced transverse fractures

  • operative management with anterior screw fixation

• type IIc

  • ​​anteroinferior to posterosuperior or comminuted fractures

  • operative management with posterior atlantoaxial fusion