Anderson and D'Alonzo classification of odontoid fractures, fractures of dens axis (C2)

Odontoid fractures are classified into three types. Type III is not an odontoid fracture but rather fracture of the vertebral body.

Type Description
Type I avulsion fracture of the tip of dens (rare)
Type II fracture at the base of dens - most common (cca 2/3)
Type III fracture extends into the body of the vertebra, does not involve dens (cca 1/3)


1. Anderson LD, D’Alonzo RT. Fractures of the odontoid process of the axis. J Bone Joint Surg Am. 1974 Dec;56(8):1663–74.
2. Chi Y-L, Wang X-Y, Xu H-Z, Lin Y, Huang Q-S, Mao F-M, et al. Management of odontoid fractures with percutaneous anterior odontoid screw fixation. Eur Spine J. 2007 Aug;16(8):1157–64