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Atlanto Occipital Dissociation

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Other Names

  • Atlanto-Occipital Dissociation (AOD)
  • Orthopedic decapitation
  • Internal decapitation
  • Occipitocervical dissociation
  • Craniocervical Dissociation (CCD)
  • Atlantao-occipital subluxation
  • Occipitocervical Instability
  • Occipitoatlantal Dissociation


  • This pages describes dissociation (dislocation or subluxation) or instability of C1 (Atlas) and the Occiput
    • This is a rare clinically entity that is considered an internal decapitation
  • Instability of C1-C2 is discussed elsewhere: Atlantoaxial Instability


  • First described by blackwood in 1908[1]


  • General
    • Up to 30% of traumatic injuries to the cervical spine occur between the occiput, C1 and C2[2]
  • AOD is a rare clinical entity
    • Mueller et al: In a prospective study of all traumatic CT scans of the skull or cervical spine, incidence was 0.2%[3]
    • Bucholz and Burkhead: 8% incidence following motor vehicle fatalities[4]
    • Likely overestimates due to retrospective nature and inclusion criteria
  • May be the most common cause of cervical spine injury fatalities in motor vehicle accidents (need citation)
  • More common in children than adults[4]
    • Postulated to be due to increased ratio of cranium to body ratio


  • AOD is a highly unstable craniocervical injury
  • Associated with significantly neurologic deficits and high mortality


  • Associated with high energy trauma
  • Including MVC, fall from heights
  • Typically involves a component of acceleration-deceleration
  • Forces vectors can be flexion-extension, side bending (lateral flexion) or rotational


Associated Injuries

Risk Factors

Differential Diagnosis

Clinical Features

  • General: Physical Exam Neck
  • History
    • History of significant trauma
    • Alert patients will often complain of neck pain
  • Physical Exam
    • Presentations can vary wildly requiring a thorough neurovascular exam
    • Up to 20% patients may have normal neurological exam on initial presentation
    • Patients may have unilateral or bilateral weakness, quadriplegia
    • Most patients present unconscious, GCS 15 and in respiratory failure or arrest



  • Findings on cervical spine films
  • Sensitivity 57% (need citation)
  • Increase in basion-dens interval, basion-axial interval and atlanto-dental interval


  • Gold standard for evaluating cervical spine in the setting of trauma
  • Can be helpful in children
  • Will demonstrate increase ion C1-Condyle interval


  • Useful in suspcted or occult cases
  • Or with neuro deficits


Traynelis Classification

  • Describes direction of displacement[6]
  • Type I: anterior displacement of the occiput relative to the atlas
  • Type II: distraction of the occiput from the atlas
  • Type III: posterior displacement of the occiput relative to the atlas

Harbourview Classification System

  • Describes degree of instability
  • Stage I: stable, minimal or non-displaced, unilateral injury to craniocervical ligaments
  • Stage II: stable or unstable, minimally displaced, but MRI demonstrates significant soft-tissue injuries
  • Stage III: unstable, gross craniocervical misaligment (BAI or BDI > 2mm beyond normal limits)

Other radiographic classification measurements

  • Powers’ ratio
  • X-line method
  • Harris lines (Basion-dens interval (BDI) and basion-axis interval (BAI))
  • Occipital condyle-C1 interval (CCI)



  • Outcome analysis and prognostication limited by heterogeneity of published data, diagnostic bias
  • Associated with a high level of mortality, especially pre-hospital
  • Not universally fatal
  • Untreated
    • Arabi et al: 54% neurologically worsening, 15% mortality among untreated patients[7]
  • Nonsurgical
    • Hadley et al: Amomng 40 AOD injuries treated conservatively with external immoblization, 30% had continued worsening neurologic symptoms on follow up[8]
  • Internal stabilization
    • Among 19 patients with early fusion, neurologic improvement seen in 15 patients, stable in 3, 1 with new cranial nerve palsy[8]
    • Among 8 patients with delayed fusion, no new or worsening neuro symptoms [8]


  • Field treatment
    • Address ABCs
    • Hemodynamic stability
    • In line stabilization, application of cervical collar
  • Emergency Department
    • Thorough and rapid assessment
    • Appropriate imaging
    • Neurosurgical consultation


  • Technique
    • Initial: Halo immobilization (falling out of favor)
    • Follow up: open reduction, internal fixation of atlanto-occipital joint

Rehab and Return to Play


  • Per Neurosurgery

Return to Play

  • No return to sports


  • Cardiac Arrest in the field or hospital
  • Severe neurological disability
  • Nonunion
  • Bleeding (carotid or vertebral artery)

See Also


  1. Blackwood NJ. III. Atlo-Occipital Dislocation: A Case of Fracture of the Atlas and Axis, and Forward Dislocation of the Occiput on the Spinal Column, Life being Maintained for Thirty-four Hours and Forty Minutes by Artificial Respiration, during which a Laminectomy was Performed upon the Third Cervical Vertebra. Ann Surg. 1908;47:654–658
  2. Bohlman HH. Acute fractures and dislocations of the cervical spine. An analysis of three hundred hospitalized patients and review of the literature. J Bone Joint Surg Am. 1979;61:1119–1142
  3. Mueller, Franz Josef, et al. "Incidence and outcome of atlanto-occipital dissociation at a level 1 trauma centre: a prospective study of five cases within 5 years." European Spine Journal 22.1 (2013): 65-71.
  4. 4.0 4.1 Bucholz RW, Burkhead WZ (1979) The pathological anatomy of fatal atlanto-occipital dislocations. J Bone Surg Am 61:248–250
  5. Riascos R, Bonfante E, Cotes C et-al. Imaging of Atlanto-Occipital and Atlantoaxial Traumatic Injuries: What the Radiologist Needs to Know. Radiographics. 2015;35 (7): 2121-2134. doi:10.1148/rg.2015150035
  6. Traynelis VC, Marano GD, Dunker RO, Kaufman HH. Traumatic atlanto-occipital dislocation. Case report. J Neurosurg. 1986;65:863–870
  7. Theodore N, Aarabi B, Dhall SS, Gelb DE, Hurlbert RJ, Rozzelle CJ, Ryken TC, Walters BC, Hadley MN. The diagnosis and management of traumatic atlanto-occipital dislocation injuries. Neurosurgery. 2013;72 Suppl 2:114–126
  8. 8.0 8.1 8.2 Hadley, M. N., et al. "Diagnosis and management of traumatic atlanto-occipital dislocation injuries." Neurosurgery 50.3 Suppl (2002): S105-13.
Created by:
John Kiel on 4 July 2019 09:22:30
Last edited:
6 October 2022 23:10:36