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Fielding and Hawkins classified atlantoaxial rotatory subluxation into 4 types:
- Type I: Simple rotatory displacement without anterior shift. The transverse ligament is intact and the dens acts as a pivot point.
- Type II: Rotatory and anterior displacement between 3-5 mm. The transverse ligament is injured and the opposite facet acts as the pivot point.
- Type III: Rotatory and anterior displacement greater than 5 mm with both lateral atlantoaxial joints anteriorly subluxed. The transverse ligament and facet capsules are injured.
- Type IV: Posterior subluxation of both lateral atlantoaxial joints. Rare and described in adult patients with rheumatoid arthritis and destruction of the dens.