Introduction:
Atlanaxial dislocation is a loss of stability between the axis and atlasaxial, leading to loss of normal articulation. The joint may lose stable circulation due to inflammatory, traumatic, idiopathic, or congenital abnormalities. Several theories are available. Often seen in adolescents.
What Are the Causes of Atlantoaxial Dislocation?
The causes include:
Traumatic Causes:
A traumatic atlantoaxial dislocation is when there is an absence of another predisposing risk factor which is rare. Traumatic atlantoaxial dislocation is caused due to forced displacement of the neck leading to disruption of the transverse ligament. Rarely may this cause simultaneous disruption of the apical and alar ligaments. Such injuries are commonly seen in sports like football and rugby. Traumatic osseous injuries also lead to atlantoaxial instability.
Congenital Causes:
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Down Syndrome: It is a chromosomal disorder caused due to the inflammatory process or an intrinsic defect in collagen fibers that form ligaments. The rate of incidence is 15 % to 20 %.
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Goldenhar Syndrome: It is a skeletal dysplasia caused due to hypoplasia of the dens with atlantoaxial instability. Incidence is three out of eight cases.
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Spondyloepiphyseal Dysplasia: It is a type of skeletal dysplasia caused due to abnormal growth of the spinal vertebrae and epiphysis, hypoplasia of the dens, or ligamentous laxity.
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Morquio Syndrome: It is a type of skeletal dysplasia caused due to autosomal recessive lysosomal storage disease, which leads to odontoid dysplasia. Incidence rates are 42 % to 90 %.
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Occipitalization of the Atlas: It is a congenital osseous abnormality caused due to abnormal motility in the joint region.
Inflammatory Causes:
Atlantoaxial dislocation is commonly seen in individuals with chronic rheumatoid arthritis. The cervical spine may be involved early in the course of rheumatoid arthritis, which leads to different patterns of instability, such as:
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Atlantoaxial dislocation.
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Atlantoaxial impaction.
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Subaxial subluxation.
Chronic systemic inflammation in these individuals leads to chronic synovitis that causes bony erosions and ligamentous laxity, followed by atlantoaxial dislocation. In individuals with chronic atlantoaxial dislocation, anterior atlantoaxial dislocation is common, and it is due to the laxity of ligamentous restraints.
What Is the Clinical Presentation of Atlantoaxial Dislocation?
Atlantoaxial dislocation presentation ranges from minor axial neck pain to death. Approximately 50 % of the individuals complained of neck pain and movement restriction. 70 % of the cases present with weakness or numbness, and 90 % with pyramidal signs. Other presentations include sphincter disturbances, respiratory distress, and lower cranial nerve dysfunction.
Other severe sequelae include respiratory failure, myelopathy, vertebral artery dissection, neurologic compromise, quadriplegia, or death. The differential diagnosis involves atlantoaxial rotatory fixation, torticollis, and odontoid fractures without dislocation. An atlantoaxial dislocation should be considered in children who cannot turn their heads when there is no evidence of torticollis.
In children, congenital atlantoaxial dislocation presents as chronically progressive spinal canal compression associated with neurologic and respiratory symptoms. Atlantoaxial dislocation in adults is mainly seen as a result of rheumatoid arthritis. Some individuals experience few symptoms; others may experience instability and neurologic compromise.
How Is Atlantoaxial Dislocation Classified?
Wang classification for atlantoaxial dislocation:
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Type I: Instability- can be treated by posterior fusion procedure.
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Type II: Reducible- Treated by posterior fusion procedure.
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Type III: Irreducible- Treated by transorally released anteriorly before posterior fusion.
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Type IV: Bony Dislocations- Treated by transoral adenoidectomy.
What Are the Treatment Modalities for Atlantoaxial Dislocation?
Treatment of atlantoaxial dislocation is based on the correction of the upper cervical spine sagittal alignment and the stabilization in the close anatomical alignment. The suggested procedures include posterior occipitocervical or C1 to C2 fusion after transoral odontoidectomy or periodontoid tissue release.
Nonoperative Treatment:
Nonoperative treatment includes cervical halter traction in the supine position and active range of motion exercises for 24 to 48 hours, followed by ambulatory orthotic immobilization and active range of motion exercises. Nonoperative treatment in symptomatic individuals is not recommended without surgical contradictions.
Certain individuals predisposed to atlantoaxial dislocation are advised for preventive treatment and screening. For individuals with rheumatoid arthritis, treatment is aimed at permanent neurologic injury while avoiding potentially dangerous and unnecessary surgery. Strategies include counseling the individual, lifestyle modification, regular radiographic follow-up, and early prompt surgical intervention.
Magnetic resonance imaging is indicated in myelopathic symptoms. Individuals with golden hair syndrome should get cervical flexion-extension films every six months and avoid contact sports.
Surgical Treatment:
A surgical approach for symptomatic individuals is highly recommended to prevent potential respiratory failure, progressive neurologic symptoms, and death. Different recommendations exist for asymptomatic individuals depending on the patient's age and underlying diagnosis. A surgical approach is recommended for adults if the atlantodental interval is greater than 5 mm.
Surgical fusion is indicated in children when the following is present:
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Neurologic involvement.
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Persistent anterior displacement.
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Atlantodental interval greater than 4 mm.
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The deformity was present for more than three months.
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Recurrence of deformity following six weeks of immobilization.
In adults, fusion is recommended when there is moderate displacement seen in flexion and extension of cervical radiographs or instability with or without pain is present. In individuals with rheumatoid arthritis, surgery is considered promptly in an asymptomatic individual with atlantoaxial dislocation for any of the following:
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Chronic neck pain in the setting of radiographic instability that does not respond to pain medication.
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Degree of atlanto axial impaction or cord stenosis.
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Space available for the spinal cord is less than or equal to 14 mm.
There is no clear surgical approach for individuals with Down syndrome or odontoideum. Still, it is monitored with annual lateral flexion or extension due to sudden changes from spinal cord compression. Surgical treatment methods include an attempt at converting irreducible to reducible atlantoaxial dislocation through traction. This involves anterior and posterior methods.
Posterior methods further include:
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Transarticular screw fixation with sublaminar wiring.
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Transarticular screw fixation with C1 hook.
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Transarticular screw fixation with morselized autograft.
Conclusion
Atlantoaxial dislocation is a rare and potentially fatal disturbance to the cervical occipital anatomy. It is a rare but dangerous condition. It involves numerous etiological contributions. Treatment involves surgical and nonsurgical approaches.
