Occipitocervical Dissociation

Occipitocervical Dissociation are high-energy injuries resulting from a combination of hyperextension, distraction and rotation at the craniocervical junction. It’s also known as craniovertebral dissociations.

It is twice as common in children, owing to the inclination and shallowness of the condyles and the large head. The incidence of this injury is 8% and represents around 20% of the fatal cervical spine injuries

The most common mechanism of Occipitocervical Dissociation is sudden deceleration after high-energy trauma, such as in motor vehicle collisions, pedestrian versus automobile accidents, or falls from great heights.

Most instances of traumatic occipito-cervical dislocation are lethal and survivors may demonstrate a wide range of neurological injuries.

See Also: Cranial Nerves

Occipitocervical Dissociation Diagnosis

Diagnosis of occipitocervical dislocation is frequently missed on initial lateral cervical spinal radiographs mainly due to inadequate visualization of radiological landmarks and low degree of suspicion. The most frequently described measurement is the Powers ratio, which divides the basion to posterior arch distance by the anterior arch to opisthion distance.

A ratio greater than 1 suggests possible anterior dissociation. The Harris basion–axial interval (BAI)/ basion–dental interval (BDI) method measures the distance from the basion to a line drawn tangentially to the posterior border of C2 (a distance greater than 12 mm or less than 4 mm is abnormal) and the distance from the basion to the odontoid (greater than 12 mm is abnormal). This is considered by some to be the most sensitive measurement.

Overall, the sensitivity of plain radiographs for occipitocervical dislocation is approximately 57%. The sensitivity of CT and MRI has been estimated to be 84% and 86%, respectively, and one or both of these adjunctive studies is recommended for patients with suspected occipitocervical dissociation injuries.

See Also: Occipital Condyle Fractures

Classification

Occipitocervical dislocation injuries have been classified by Traynelis, based on the position of the occiput in relation to C1.

1. Type I, occipital condyles anterior to the atlas; most common.
2. Type II, condyles longitudinally dissociated from atlas without translation (result of pure distraction).
3. Type III, occipital condyles posterior to the atlas.

Occipitocervical dislocation Treatment

Immediate treatment includes halo vest application with strict avoidance of traction.

Early surgical stabilization of the atlanto-occipital joint is recommended as ligamentous healing in a halo vest is unpredictable, and many of these injuries are so unstable that displacement may occur even in the halo vest.

References & More

1. Kasliwal MK, Fontes RB, Traynelis VC. Occipitocervical dissociation-incidence, evaluation, and treatment. Curr Rev Musculoskelet Med. 2016 Sep;9(3):247-54. doi: 10.1007/s12178-016-9347-6. PMID: 27255101; PMCID: PMC4958379. Pubmed
2. Tavolaro C, Bransford R, Yerrapragada A, Bellabarba C, Zhou H. Occipitocervical Dislocation in Low-Energy Trauma. Case Rep Orthop. 2018 Nov 29;2018:3931525. doi: 10.1155/2018/3931525. PMID: 30631620; PMCID: PMC6304856. Pubmed
3. Mercer’s Textbook of Orthopaedics and Trauma, Tenth edition.