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An odontoid fracture is a break involving the odontoid process (dens) of C2 (axis), one of the most common cervical spine fractures, accounting for ~10–15% of all cervical spine fractures.
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It is particularly important due to its risk of instability, non-union, and spinal cord injury.
Anderson & D’Alonzo (1974) classification:
| Type | Key features | Stability |
|---|---|---|
| Type I | Avulsion of tip of dens (rare, stable) | |
| • Mechanism: alar ligament avulsion. | Stable, but may mimic os odontoideum. | |
| Type II | Fracture at the base of dens (junction with body of C2) | |
| • Most common (~60%). | ||
| • Management often surgical (odontoid screw fixation or fusion). | Unstable with high risk of non-union due to poor vascular supply. | |
| Type III | Fracture line extends into body of axis | |
| • Better healing potential due to cancellous bone involvement. | ||
| More stable compared to Type II. |
Anderson and D'Alonzo's classification of odontoid fractures. Note that Type I injuries are at the tip of the odontoid. Type II injuries are at the base of the odontoid. And, Type III injuries extend into the cancellous C2 body
Grauer JN, Shafi B, Hilibrand AS, et al. Proposal of a modified, treatment-oriented classification of odontoid fractures. The Spine Journal. 2005;5(2):123-129. doi:10.1016/j.spinee.2004.09.014