Anatomy
- Pseudosubluxation is physiological anterior translation of C2 on C3, less often C3 on C4
- Seen in up to 40% of children under 8 years, measuring up to 4 mm
- Due to ligamentous laxity and horizontal facets, and reduces in extension
- Dentocentral synchondrosis, below the adult type II level, fuses around 6 to 7 years
- Os odontoideum is a smooth ossicle above a hypoplastic dens, from unrecognised early fracture or developmental anomaly
- Large heads, shallow occipital condyles and lax ligaments predispose children to atlanto-occipital dissociation
Clinical Features
- SCIWORA mainly affects children under 8 years, as the elastic spine stretches further than the cord
- SCIWORA neurology may be delayed, and transient symptoms at the scene are a warning sign
- Atlantoaxial rotatory subluxation presents with torticollis and cock robin posture
- Rotatory subluxation follows minor trauma, URTI or head and neck surgery (Grisel syndrome)
- Os odontoideum may cause atlantoaxial instability and myelopathy
Classification
Fielding and Hawkins
| Type | Description |
|---|---|
| I | Rotatory fixation, no anterior displacement, ligament intact, most common |
| II | Anterior displacement 3 to 5 mm, one lateral mass acting as pivot |
| III | Anterior displacement more than 5 mm |
| IV | Posterior displacement |
Original publication Fielding JW, Hawkins RJ. Atlanto-axial rotatory fixation. (Fixed rotatory subluxation of the atlanto-axial joint). J Bone Joint Surg Am. 1977;59(1):37-44.
Investigations
- Swischuk line from C1 to C3 spinous process cortices should pass within about 2 mm of C2
- Greater deviation suggests a hangman’s fracture
- Dynamic CT in neutral and maximal rotation each way confirms rotatory fixation
- Powers ratio greater than 1 indicates anterior atlanto-occipital dissociation
- Condyle to C1 interval is more reliable in children
Management
- SCIWORA, collar for up to 12 weeks and no contact activity for several months
- Rotatory subluxation, soft collar early, halter traction at a week or more, halo traction if chronic
- C1 to C2 fusion for failed reduction, recurrence or instability
- Synchondrosis fracture, closed reduction in extension and Minerva cast or halo
- Os odontoideum, posterior C1 to C2 fusion for instability or neurological signs
- Atlanto-occipital dissociation, no traction, halo then occipitocervical fusion
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.