The injury is a result of disruption of the stabilizing ligaments between the occiput, or posterior skull base, and the C1 vertebral body, otherwise known as the atlas.
The diagnosis is usually suspected by history and physical exam, but confirmed by imaging, typically by CT due to its faster speed in the acute trauma setting, although MRI can also help with assessment in equivocal cases.
The injury is more likely in children due to the large size of their heads relative to their bodies, and more horizontal orientation of the occipital condyles.
The basion to axion interval, or BAI, is also used, which is determined by measuring the distance between an imaginary vertical line at the anterior skull base, or basion, at the foramen magnum, and the axis of the cervical spine along its posterior margin, which should measure 12 mm, an assessment more reliable on radiograph than CT.
The distance between the atlas and the occipital condyles, the atlanto-occipital interval (AOI), should measure less than 4 mm, and is better assessed on coronal images.
[6] Treatment involves fixation of the cervical spine to the skull base, or occipitocervical fusion, using paramedian rods and transpedicular screws with cross-links for stabilization.
[8] The injury is immediately fatal in 70% of cases, with an additional 15% surviving to the emergency room but dying during the subsequent hospital stay.
[9] Most deaths result from mechanical damage to the spinal cord and lower brainstem, ranging from localized contusion to diffuse axonal injury to complete transection.
[13] In Michael Connelly's 2020 thriller novel Fair Warning, protagonist Jack McEvoy investigates occurrences of atlanto-occipital dislocation.