Atlanto-occipital dissociation injuries
Updates to Article Attributes
Body
was changed:
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 the most 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 joints is by 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
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 (AARF) will cause C1 lateral masses asymmetry relative to the dens
- down Syndrome: atlantooccipital instability due to laxity of alar ligament
- rheumatoid arthritis: CT/MRI will show atlantooccipital instability due to pannus destabilizesation of joints and ligaments and x-ray will show erosions
- +</ul><h4>Differential diagnosis</h4><ul>
- +<li><a href="/articles/occipital-condyle-fracture">occipital condyle fracture</a></li>
- +<li>
- +<a href="/articles/jefferson-fracture">jefferson fracture</a>: anterior and posterior c1 ring fracture, possible lateral masses displacement</li>
- +<li>
- +<a href="/articles/odontoid-fracture">odontoid fracture</a>: type 2 will cause posterior dens displacement and will disrupt Powers ratio</li>
- +<li>
- +<a href="/articles/atlanto-axial-subluxation">Atlanto-axial subluxation</a>: atlantoaxial rotatory fixation (AARF) will cause C1 lateral masses asymmetry relative to the dens</li>
- +<li>
- +<a href="/articles/down-syndrome">down Syndrome</a>: atlantooccipital instability due to laxity of alar ligament</li>
- +<li>
- +<a href="/articles/rheumatoid-arthritis-musculoskeletal-manifestations-1">rheumatoid arthritis</a>: CT/MRI will show atlantooccipital instability due to pannus destabilizesation of joints and ligaments and x-ray will show erosions</li>