RadEssentialReading-room reference
Odontoid fracture (Anderson–D’Alonzo)
Classified by level of the fracture through C2.
| Type | Level | Stability |
|---|---|---|
| I | Avulsion of the dens tip (alar ligament) | Usually stable Exclude occipitocervical dissociation |
| II | Base of the dens, at junction with C2 body | Unstable Highest non-union risk |
| IIA | Comminuted type II at the base (Hadley) | Unstable |
| III | Extends into the C2 vertebral body | Usually stable Good healing potential |
Non-union risk in type II rises with displacement ≥5 mm, posterior displacement, age >50 and fracture gap. Report displacement and angulation.
Sources
- Anderson LD, D’Alonzo RT. Fractures of the odontoid process of the axis. J Bone Joint Surg Am. 1974;56:1663–1674.PubMed ↗
Radessential summarizes published classification systems for practicing radiologists. Summaries are condensed; confirm details against the cited source before relying on them for patient care.