Fact-sheet: Atlantooccipital dislocation
Updated on 09/17/2021 at 12:16 PM
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Definition
Loss of joint contact between the occiput and the atlas. Rare lesion, most often fatal, 2.5 times more common in children due to favorable anatomical factors, notably horizontal cervical facet joints. Highly unstable lesion. Follows the Traynelis classification. Injury mechanisms: Hyperextension, Hyperflexion +++, Axial compression
Clinical features
Occurs in severe, high-energy trauma, often in the setting of polytrauma (motor vehicle accidents...).
- respiratory distress
- sensorimotor deficit up to tetraplegia
- cardiac disturbances
Radiography
Cervical spine X-ray, AP + lateral:
- spontaneous visibility of the atlas on an AP radiograph
- dislocation of the occipital condyles, anterior, above, or posterior to the C1 facet joints
- basion-dens distance greater than 12 mm
CT
Many findings to look for: Kaufman occipito-atlantal distance > 5 mm. Odontoid process displaced downward relative to Chamberlain's line, and backward relative to Wackenheim's clivus-canal line. A ratio of the distance between the inferior border of the posterior arch of C1 and the superior border of the spinous process of C2, to the distance between the spinous processes of C2 and C3, greater than 2.5, indicates rupture of the tectorial membrane and therefore atlanto-axial dislocation. Absence of any bony structure on two consecutive slices at the cervico-occipital junction. Look for associated lesions ++++++: Soft tissue hematoma. Epidural hematoma. Cervicocephalic artery dissection.
MRI
Assessment of ligamentous injuries.
Search for epidural hematoma.
Assessment of associated lesions.
Vascular intervention
X-Ray Angiography is routinely proposed by some teams.
Management
Emergency surgical treatment by occipitocervical fixation.
Initial fixation with a Halo vest may be performed (orthosis).
Classification
Traynelis classification:
I = anterior displacement of the occiput relative to the atlas.
II = longitudinal separation between the occiput and the atlas.
III = posterior displacement of the occiput relative to the atlas