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Atlantoaxial subluxation

Atlantoaxial subluxation (AAS) is a disorder of C1-C2 causing impairment in rotation of the neck. The anterior facet of C1 is fixed on the facet of C2. It may be associated with dislocation of the lateral mass of C1 on C2.

Atlantoaxial instability (AAI) is characterized by excessive movement at the junction between the atlas (C1) and axis (C2) as a result of either a bony or ligament abnormality.

Atlantoaxial instability with and without basilar invagination poses a considerable challenge in management regarding reduction, surgical approach, decompression, instrumentation choice, and extent of fusion. A variety of strategies have been described to reduce and stabilize cranial settling with basilar invagination.


Atlantoaxial dislocation (AAD) is the most common bony craniovertebral junction (CVJ) anomaly followed by basilar invagination (BI) and assimilation of the atlas.

Atlantoaxial dislocation in children is a very rare condition.

see Atlantoaxial subluxation.


Antero-posterior subluxation

Atlantoaxial rotatory subluxation


May be due to:

Disruption of the transverse ligament and increase of the atlantodental interval.

The causes of AAI are varied. AAI sometimes results from trauma. Other cases occur secondary to an upper respiratory infection or infection following head and neck surgery.

Atlantoaxial subluxation in rheumatoid arthritis

see Atlantoaxial subluxation in rheumatoid arthritis.

As a manifestation of ankylosing spondylitis (juvenile and adult onset), reactive arthritis, juvenile idiopathic arthritis.

Craniocervical malformation

Congenital os odontoideum

Odontoid fracture

Disruption of transverse ligament

Atlantoaxial fracture

Chiari malformation and herniation of the cerebellar tonsils into the foramen magnum appears to the natural protective phenomenon in the face of atlantoaxial instability 1).

Upper cervical spinal epidural abscess (UCEA) (occiput to C2) is an uncommon condition. In upper cervical spine infections, degradation of the odontoid ligaments with subsequent atlantoaxial subluxation or dislocation is a risk.

Clinical Features

Neurologic symptoms occur when the spinal cord is involved.


Distance between the anterior surface of the dens and the posterior surface of the tubercle of C1 is usually 3 mm or less in adults and 5 mm or less in children This space is called by many names: predentate space, predental space, atlantodental distance.

The distance may increase slightly on flexion in children but is usually unchanged between flexion and extension in adults

Forward movement of the atlas on the axis is normally restricted by the transverse ligament.

Atlantoaxial instability is defined by an increase in the predentate space of greater then 3 mm in adults and 5 mm in children

Radiographic features

Plain film (C spine)

In a non traumatic setting flexion and extension views may be performed. The expected distance between anterior arch of C1 and the dens in the fully flexed position should be <3 mm in an adult (~5 mm in a child).

In a vertical subluxation the dens is often above the McGregor line by over 8 mm in men and 9.7 mm in women


On CT, C1 is not oriented in line with the head. The head may be pointed anteriorly, C1 is turned. If this is a fixed defect, C2 is rotated in conjunction with C1.

Predisposing factors


os odontoideum

Down syndrome (20%)

Morquio syndrome

spondyloepiphyseal dysplasia

Osteogenesis imperfecta

Marfan disease

neurofibromatosis type 1 (NF1)


rheumatoid arthritis

psoriatic arthritis

Reiter syndrome (reactive arthritis)

ankylosing spondylitis

systemic lupus erythematosus (SLE)



retropharyngeal abscess/Grisel syndrome

Differential diagnosis

odontoid fracture


The earlier treatment paradigms focused on transoral excision of the dens followed by posterior instrumented fusion.

The more recent therapies have focused on a single stage correction using joint distraction or more recently using corrective motions in both the vertical and horizontal axis, thus shifting the attention to the joints.

The shift in philosophy in treatment has also encouraged studies, which have examined various joint parameters (in both cases and controls) and have defined normal and abnormal parameters.

Sagittal joint inclination and craniocervical tilt significantly correlated with both BI and AAD (P < .01). Coronal joint inclination correlated with BI (P = .2). The mean sagittal joint inclination value in control subjects was 87.15 ± 5.65° and in patients with BI and AAD was 127.1 ± 22.05°. The mean craniocervical tilt value in controls was 60.2 ± 9.2° and in patients with BI and AAD was 84.0 ± 15.1°. The mean coronal joint inclination value in control subjects was 110.3 ± 4.23° and in patients with BI and AAD was 121.15 ± 14.6°.

It is a important role of joint orientation and its correlation with the severity of BI and AAD and has described new joint indexes 2).

There are no pharmacologic interventions for atlantoaxial instability (AAI). Because of the chronicity of the instability at the time of presentation in most cases, corticosteroids have little, if any, impact on neurologic findings and may present many undesirable outcomes. In the acute traumatic setting, corticosteroids remain controversial in the literature. Current guidelines provided by the American Academy of Neurological Surgeons (AANS) include level I evidence against the use of corticosteroids or gangliosides in the acute trauma patient.

Unless symptoms of spinal cord compression occur, AAI requires no treatment. Once symptoms arise, cervical spine stabilization is indicated until surgical stabilization is performed.

In persons with rotatory displacement, the time of presentation dictates the treatment. Most of these patients' conditions resolve spontaneously, and additional care is not sought.

Patients presenting with subluxation of less than 1 week's duration are treated with a soft collar and rest for a week. If close follow-up fails to document reduction, a period of halter traction with analgesics and muscle relaxants is warranted. If this fails, halo bracing can be undertaken.

In patients with rotatory displacement of more than 1 month's duration, a period of halo traction for 3 weeks is tried. Usually, two types of patients are in this group: (1) those whose subluxation resolves with bracing but recurs when bracing stops and (2) those who usually present with a fixed deformity.

Traumatic atlantoaxial dislocation

Posterior atlantoaxial dislocation (AAD) is rare and mostly follows trauma to the craniovertebral junction (CVJ).

Biomechanics include a significant force with severe hyperextension and cranial traction at CVJ. This is known to be associated with extensive facial injuries 3) 4).

Traumatic posterior atlantoaxial dislocation without fracture of odontoid process usually presents without a severe neurological deficit. Even if it presents with mild or transient neurological deficit, it would be restored without any residual deficits. Closed reduction is usually successful and safe. The need for fusion after successful closed reduction depends on the integrity of the transverse ligament and the stability of cervical spine. If anatomic reduction is not achieved by closed reduction, open reduction and fusion should be performed.

Clinical features

AAD commonly present with progressive neurologic deficits due to compression of high cervical cord, lower brainstem and lower cranial nerves. Less commonly patient's with AAD may also present with neurologic symptoms attributable to vascular compromise at the CVJ 5).

Case series

Case reports

A 30-year-old woman presented with neck pain and spastic quadriparesis. Her imaging revealed atlantoaxial dislocation and bony segmentation defects. Three-dimensional computed tomography angiography showed bilateral anomalous vertebral arteries (V3 segment) and an incidental aneurysm on the arterial segment that crossed the right C1-C2 joint posteriorly. Because the artery bearing the aneurysm was non-dominant, it was ligated, and successful C1-C2 posterior reduction and fusion could be performed.

The association of an incidental aneurysm with an anomalous VA in congenital atlantoaxial dislocation (AAD) is unusual. The etiology could be an underlying collagen defect or repeated shearing-trauma to the vessel wall due to C1-C2 instability. It would be less risky to proceed with endovascular embolization followed by occipitocervical fusion without opening the joints in case the aneurysm is present on dominant aberrant V3 segment. Ventral decompression can be supplemented for irreducible AAD. On the contrary if the aneurysm is present on the non-dominant aberrant V3 segment, the C1-2 joint can be opened and manipulated following an initial endovascular treatment of the aneurysm. If the circumstances demand, the non-dominant artery can be ligated and sacrificed although there is a small risk of formation of stump aneurysm 6).

A case of a dislocation happened during a break-dance maneuver. The purpose of this report is describing dangers of break-dancing and discussing the treatment we chose. The patient was followed up until 12 months after surgery. Magnetic resonance imaging and computed tomography of the cervical spine were evaluated. Translaminar fixation of C1/C2 had been performed after manual reposition under X-ray illumination. After a 12-month follow-up, the patient shows a stable condition without neurological dysfunction. He is not allowed to perform any extreme sports 7).

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Chandra PS, Goyal N, Chauhan A, Ansari A, Sharma BS, Garg A. The severity of basilar invagination and atlantoaxial dislocation correlates with sagittal joint inclination, coronal joint inclination, and craniocervical tilt: a description of new indexes for the craniovertebral junction. Neurosurgery. 2014 Dec;10 Suppl 4:621-30. doi: 10.1227/NEU.0000000000000470. PubMed PMID: 25320950.
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Petridis AK, Kinzel A, Blaeser K, Thissen J, Maslehaty H, Scholz M. Can Break-Dance Break Your Neck? C1/C2 Luxation with a Combined Dens Fracture Without Neurological Deficits in an 11-Year Old Boy After a Break-Dance Performance. Clin Pract. 2015 Sep 28;5(3):781. eCollection 2015 Sep 28. PubMed PMID: 26664716.
atlantoaxial_subluxation.txt · Last modified: 2019/08/18 11:22 by administrador