Atlanto-occipital dislocation

Atlanto-occipital dislocation, orthopedic decapitation, or internal decapitation describes ligamentous separation of the spinal column from the skull base. It is possible for a human to survive such an injury, however only 30% of cases do not result in death.

Mechanism

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 treatment is initial stabilization with a cervical spine collar, and then surgical intervention in cases in which reversal of paralysis is possible. The most common mechanism of injury is high-speed motor vehicle accidents. 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. It represents <1% of all cervical spine injuries.[1]

Imaging

Several indirect measurements on CT can be used to assess ligamentous integrity at the craniocervical junction. The Wackenheim line, a straight line extending from the clivus at the skull base through the dens, normally intersects its posterior margin of the tip of the dens on plain film. 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.[2]

The distances between the dens and surrounding structures are also key features that can suggest the diagnosis, with the normal distance between the dens and basion (BDI) measuring less than 9 mm on CT, and the distance between the dens and atlas (ADI) measuring less than 3 mm on CT, although this can be increased in cases of rheumatoid arthritis due to pannus formation. Lastly, the atlanto-occipital interval can be measured.[3]

The Powers ratio was formerly used, which was the tip of the basion to the spinolaminar line, divided by the distance from the tip of the opisthion to the midpoint of the posterior aspect of the anterior arch of C1. It is no longer recommended due to low sensitivity and difficulty identifying landmarks. It also will miss vertical or posterior displacement of the cervical spine.[4]

Treatment

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. The patient is subsequently unable to rotate his or her head in the horizontal plane.[5] If there is obstructive hydrocephalus, a pseudomeningocele can form, which is decompressed at the time of surgery.[6]

Prognosis

The injury is immediately fatal in 70% of cases, with an additional 15% surviving to the emergency room, but perishing during their hospital stay. A basion-dental interval of 16mm or greater is associated with mortality. In those with neurologic deficits, survival is unlikely.[7]

Proximal cervical fractures associated with injury

The Jefferson fracture can be associated with this injury, with the C1 ring, or atlas, being fractured in several places, allowing the spine to shift forward relative to the skull base. The Hangman's fracture which is a fracture of the C2 vertebral body or dens of the cervical spine upon which the skull base sits to allow the head to rotate, can also be associated with atlanto-occipital dislocation. Despite its eponym, the fracture is not usually associated with a hanging mechanism of injury.[8]

References

  1. ↑ Theodore, N; Aarabi, B; Dhall, SS; Gelb, DE; Hurlbert, RJ; Rozzelle, CJ; Ryken, TC; Walters, BC; Hadley, MN (March 2013). "The diagnosis and management of traumatic atlanto-occipital dislocation injuries". Neurosurgery. 72 Suppl 2: 114–26. doi:10.1227/NEU.0b013e31827765e0. PMID 23417184.
  2. ↑ Chaput, CD; Walgama, J; Torres, E; Dominguez, D; Hanson, J; Song, J; Rahm, M (20 April 2011). "Defining and detecting missed ligamentous injuries of the occipitocervical complex.". Spine 36 (9): 709–14. doi:10.1097/brs.0b013e3181de4ec1. PMID 21192303.
  3. ↑ Bisson, E; Schiffern, A; Daubs, MD; Brodke, DS; Patel, AA (15 April 2010). "Combined occipital-cervical and atlantoaxial disassociation without neurologic injury: case report and review of the literature.". Spine 35 (8): E316–21. doi:10.1097/brs.0b013e3181c41d2c. PMID 20308946.
  4. ↑ Hanson, JA; Deliganis, AV; Baxter, AB; Cohen, WA; Linnau, KF; Wilson, AJ; Mann, FA (May 2002). "Radiologic and clinical spectrum of occipital condyle fractures: retrospective review of 107 consecutive fractures in 95 patients.". AJR. American journal of roentgenology 178 (5): 1261–8. doi:10.2214/ajr.178.5.1781261. PMID 11959743.
  5. ↑ Theodore, N; Aarabi, B; Dhall, SS; Gelb, DE; Hurlbert, RJ; Rozzelle, CJ; Ryken, TC; Walters, BC; Hadley, MN (March 2013). "The diagnosis and management of traumatic atlanto-occipital dislocation injuries". Neurosurgery. 72 Suppl 2: 114–26. doi:10.1227/NEU.0b013e31827765e0. PMID 23417184.
  6. ↑ Gutiérrez-González, R; Boto, GR; Pérez-Zamarrón, A; Rivero-Garvía, M (September 2008). "Retropharyngeal pseudomeningocele formation as a traumatic atlanto-occipital dislocation complication: case report and review". European spine journal : official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society. 17 Suppl 2: S253–6. doi:10.1007/s00586-007-0531-7. PMC 2525892. PMID 17973127.
  7. ↑ Cooper, Z; Gross, JA; Lacey, JM; Traven, N; Mirza, SK; Arbabi, S (1 May 2010). "Identifying survivors with traumatic craniocervical dissociation: a retrospective study.". The Journal of surgical research 160 (1): 3–8. doi:10.1016/j.jss.2009.04.004. PMID 19765722.
  8. ↑ Chaput, CD; Torres, E; Davis, M; Song, J; Rahm, M (August 2011). "Survival of atlanto-occipital dissociation correlates with atlanto-occipital distraction, injury severity score, and neurologic status.". The Journal of trauma 71 (2): 393–5. doi:10.1097/ta.0b013e3181eb6a31. PMID 21206289.

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