Atlanto-occipital dissociation injuries

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Atlanto-occipital dissociation (AOD) injuries are severe and include both atlanto-occipital dislocations and atlanto-occipital subluxations.

Pathology

The tectorial membrane and alar ligaments provide most of the stability to the atlanto-occipital joint, and injury to these ligaments results in instability due to low inherent osseous stability ³.

Radiographic features

The key to the diagnosis, in addition to visualising gross disruption of the normal alignment of the atlanto-occipital joint, hinges on using a number of lines on the lateral horizontal shoot-through cervical spine film ¹:

basion-dens interval (BDI) >10 mm in adults ³
basion-axial interval (BAI) >12 mm in adults
Powers ratio >1 (insensitive to a vertical distraction injury or posterior dissociation)
atlantodental interval (ADI)
- >3 mm in adult males
- >2.5 mm in adult females

CT

For pediatric patients the condyle-C1 interval (CCI) has been shown to provide the highest diagnostic accuracy⁴.

condyle-C1 interval (CCI) > 4 mm in children

Differential diagnosis

occipital condyle fracture
Jefferson fracture: anterior and posterior C1 ring fracture, possible lateral masses displacement
odontoid fracture: type 2 will cause posterior dens displacement and will disrupt Powers ratio
atlanto-axial subluxation: atlantoaxial rotatory fixation will cause C1 lateral mass asymmetry relative to the dens
Down syndrome: atlanto-occipital instability due to laxity of alar ligament
rheumatoid arthritis: CT/MRI will show atlantooccipital instability due to pannus destabilisation of joints and ligaments, and x-ray will show erosions

-<p><strong>Atlanto-occipital dissociation</strong> <strong>injuries</strong> are severe and include both atlanto-occipital dislocations and atlanto-occipital subluxations.</p><h4>Pathology</h4><p>The <a href="/articles/tectorial-membrane-of-the-spine">tectorial membrane</a> and <a href="/articles/alar-ligament">alar ligaments</a> provide most of the stability to the atlanto-occipital joint, and injury to these ligaments results in instability due to low inherent osseous stability <sup>3</sup>.</p><h4>Radiographic features</h4><p>The key to the diagnosis, in addition to visualising gross disruption of the normal alignment of the atlanto-occipital joint, hinges on using a number of lines on the lateral horizontal shoot-through cervical spine film <sup>1</sup>:</p><ul>
+<p><strong>Atlanto-occipital dissociation (AOD)</strong> <strong>injuries</strong> are severe and include both atlanto-occipital dislocations and atlanto-occipital subluxations.</p><h4>Pathology</h4><p>The <a href="/articles/tectorial-membrane-of-the-spine">tectorial membrane</a> and <a href="/articles/alar-ligament">alar ligaments</a> provide most of the stability to the atlanto-occipital joint, and injury to these ligaments results in instability due to low inherent osseous stability <sup>3</sup>.</p><h4>Radiographic features</h4><p>The key to the diagnosis, in addition to visualising gross disruption of the normal alignment of the atlanto-occipital joint, hinges on using a number of lines on the lateral horizontal shoot-through cervical spine film <sup>1</sup>:</p><ul>

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