Atlanto-occipital dissociation


  • Unstable spine fractures
  • Tectorial membrane and alar ligaments provide stability to atlanto-occipital joint
    • Injury or laxity of these ligaments can lead to subluxation or dislocation
  • Also referred to as internal decapitation
  • Down syndrome predisposes to atlanto-occipital dislocation

Vertebral fractures and dislocations types

Vertebral anatomy.
Numbering order of vertebrae.

Clinical Features

  • Pure flexion injury involving C1-C2, with or without odontoid fracture
  • Often associated with brain injury, which predicts mortality[1]

Differential Diagnosis

Neck Trauma


Atlanto-occipital Dissociation
  • Evaluate with the Powers ratio
    • Ratio of BC:OA > 1 suggests anterior subluxation
    • BC = distance between basion and midpoint of C2 post laminar line
    • OA = Distance between opisthion and ant arch of C2
  • Basion to dens interval of > 10mm [2]


Prehospital Immobilization

See the NAEMSP National Guidelines for Spinal Immobilization


  • C-collar
  • Consult ortho or spine as needed


  • Admit

See Also

External Links


  1. Mendenhall, S. K., Sivaganesan, A., Mistry, A., Sivasubramaniam, P., McGirt, M. J. and Devin, C. J. (2015) ‘Traumatic atlantooccipital dislocation: Comprehensive assessment of mortality, neurologic improvement, and patient-reported outcomes at a level 1 trauma center over 15 years’, The Spine Journal, 15(11), pp. 2385–2395
  2. 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