Atlanto-Occipital Dislocation

Atlanto-occipital dislocation is one of the most lethal spinal injuries. The majority of patients die at the scene from brainstem transection or vascular disruption. Those who reach hospital require immediate recognition because inappropriate traction or delayed diagnosis converts a potentially survivable injury into a fatal one. Paediatric patients have a higher relative incidence due to ligamentous laxity and larger head-to-body ratio.

The Anderson-Montesano Type III occipital condyle fracture is an alar-ligament avulsion - because the alar ligament is a craniocervical-junction stabiliser, a displaced or bilateral type III (or one with associated ligamentous injury) is unstable and may need halo immobilisation or occipitocervical fusion, whereas types I and II are usually stable and treated in a collar. Like AOD, occipital condyle fractures are frequently missed on plain films and need CT.

The unconscious polytrauma patient cannot report neck pain. AOD must be excluded by CT in every high-energy mechanism patient who arrives intubated or with Glasgow Coma Scale less than 8. A normal lateral cervical X-ray does not rule out AOD; up to half of cases are missed on plain films.

The other craniocervical injuries competing for this diagnosis are developed in full elsewhere: atlantoaxial rotatory subluxation, Jefferson fracture, and — for the chronic and congenital instability that reaches clinic rather than the resuscitation room — craniocervical junction instability.

Plain lateral cervical radiographs are unreliable for AOD. The Powers ratio requires precise identification of the basion and opisthion, which are often obscured. CT with multiplanar reconstructions is mandatory. Document the exact measurements in the radiology report and communicate abnormal values immediately to the trauma and spine teams.

Add the Wackenheim line (the clivus extended should touch the dens tip) and the Harris rule of 12s (BDI and BAI each under 12 mm) to the Powers ratio and CCI, because each catches a pattern the others can miss and any one of them being abnormal is enough to stop and call the spine team. What none of them can do is exclude the injury: the classic lines run at 25 to 50 percent sensitivity, and on CT the 12 mm cut-off is itself too generous. Measure the CCI bilaterally on the reformats before the craniocervical junction is called normal.

Best prognosis: Early recognition, Type I or III injury, successful closed reduction, rigid occipitocervical fusion within 72 hours, absence of vertebral artery injury. Poor prognosis: Type II distraction pattern, unconscious at scene, associated severe head injury, delayed diagnosis beyond 24 hours. Two cautions about the numbers. First, type-specific survival figures in circulation ("20-30% for Type I/III, under 10% for Type II") have no source that separates survivorship by Traynelis type - quote overall survival to hospital (15-30%) and mechanism instead. Second, early fusion is credited with "improving survival" only by selection: it is performed on patients who have already survived to theatre, and no series compares it against non-fusion in matched patients. What early stabilisation changes is the neurological outcome and the security of the junction in a survivor - not the probability of surviving. Saying it improves survival is a common and unearned extrapolation.

There is no dedicated international registry for atlanto-occipital dislocation because of its rarity and high pre-hospital mortality. Evidence is drawn from case series and expert consensus. The consistent message across all guidelines is: maintain neutral rigid immobilisation, obtain CT with measurements immediately, avoid traction in distraction injuries, and proceed to occipitocervical fusion as soon as the patient is medically stable.