Atlanto-Occipital Dislocation (AOD)
What is the Occipitoatlantal Joint?
Atlanto-occipital joint is formed between facets of atlas (the first cervical vertebra, also known as C1), and occipital condyles (two oval shaped, bony parts on the underside of the skull’s base).
The atlanto-occipital joint permits flexion (forward bending the head) and extension (bending the head backwards e.g. to look up) movement at craniocervical junction.
Video of the anatomy of the atlanto-occipital joint.
What is Atlanto-Occipital Dislocation?
Although once considered an invariably fatal injury, improvements in diagnosis and management have made atlanto-occipital dislocation (also called atlanto-occipital dissociation) (AOD) a survivable injury. The injury occurs mainly due to tear of ligaments at cervico-occipital junction due to hyper extension, hyperflexion, lateral flexion, or combination of these. AOD is a specific, severe type of craniocervical instability that requires urgent, immediate life-saving care.
On the other hand, craniocervical instability (CCI) is the excessive movement of the atlanto-occipital joint and possibly down to the C2 vertebrae. CCI is similar to AOD but considered life-threatening.
What is the cause of AOD?
Trauma is the main cause of atlanto-occipital instability, however, congenital abnormalities and inflammatory conditions can also lead to instability / hypermobility and injury.
What are the types of AOD?
AOD is classified into three main types (Trayneli’s Classification), however, they can occur in combination as well.
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- Anterior dislocation of occiput over atlas : The atlanto-occipital joint has slipped forward relative to the C2 vertebrae below the joint.
- Posterior Dislocation: The atlanto-occipital joint has slipped backwards relative to the C2 vertebrae below the joint.
- Traction / Longitudinal Dislocation: The atlanto-occipital joint separates vertically from the top of the spine.
What are the symptoms of AOD?
The dislocation or instability can be asymptomatic, or can present with symptoms of compression to brainstem, nerves or cervical cord. The symptoms can include neck pain, motor or neurological deficits, numbness and tingling (paresthesia) of the arms, hands, legs and feet, as well as damage or irritation of the cranial nerve (nerves from the brain) .
What are the conservative and surgical treatments for AOD?
Immediate urgent care or neurosurgical management may include cervical spine immobilization using halo cervical collar. Although some medical articles state halo immobilization and traction are contraindicated in the management of AOD because of the risk of displacement of the injured atlanto-occipital joint. Most articles agree that cervical traction is never applied, but again, others state to apply cervical traction.
Surgical fusion is later done, when indicated. Postoperative hydrocephalus is frequent and should be suspected when neurologic decline occurs after fixation. Those who survive AOD will likely have residual neurologic deficits.
Medical-level information video.
Additional References:
- Fiester P, Rao D, Soule E, Orallo P, Rahmathulla G. Anatomic, functional, and radiographic review of the ligaments of the craniocervical junction. J Craniovertebr Junction Spine. 2021 Jan-Mar;12(1):4-9. doi: 10.4103/jcvjs.JCVJS_209_20. Epub 2021 Mar 4. PMID: 33850375; PMCID: PMC8035576.
- Atlantooccipital joint. radiopaedia.org. Updated November 25, 2022. Accessed: December 21, 2022. Atlanto-axial subluxation | Radiology Reference Article | Radiopaedia.org
- Hall GC, Kinsman MJ, Nazar RG, Hruska RT, Mansfield KJ, Boakye M, Rahme R. Atlanto-occipital dislocation. World journal of orthopedics. 2015 Mar 18;6(2):236.