Vertical mobile and reducible atlantoaxial dislocation

Clinical article

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The authors' experience with treatment of 8 patients with “vertical mobile and reducible” atlantoaxial dislocation is reviewed. The probable pathogenesis, radiological and clinical features, and management issues in such cases are discussed.


Between January 2006 and March 2008, 8 patients who presented with vertical mobile and reducible atlantoaxial dislocations were treated at the Department of Neurosurgery at King Edward Memorial Hospital in Mumbai, India. The vertical atlantoaxial dislocation/basilar invagination reduced completely on extension of the neck, with no need of any cervical traction. According to the extent of superior migration of the odontoid process, and measurements based on the vertical atlantoaxial instability index, the dislocation was graded as mild, moderate, or severe. All patients were treated using the C-1 lateral mass and C-2 pars plate and screw method of fixation.


The study group was composed of 5 male and 3 female patients (mean age 24 years, age range 8–54 years). All patients presented with the physical features of short neck, torticollis, pain in the nape of the neck, and varying degrees of quadriparesis. In 6 patients there was a history of trauma prior to the onset of major neurological symptoms. The dislocation was mild in 3 cases, moderate in 1, and severe in 4. All patients had clinical neurological improvement following surgery. The follow-up duration ranged from 4 to 30 months (mean 18 months).


Vertical mobile and reducible atlantoaxial dislocation is a discrete clinical entity. Abnormal inclination and incompetence of the facet joint appears to be the primary causative factor that resulted in vertical dislocation or basilar invagination. Posterior fixation in the reduced dislocation position forms the basis of treatment.

Abbreviation used in this paper:VA = vertebral artery.

Article Information

Address correspondence to: Atul Goel, M.Ch., Department of Neurosurgery, King Edward VII Memorial Hospital and Seth G. S. Medical College, Parel, Mumbai 400012, India. email:

© AANS, except where prohibited by US copyright law.



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    Neuroimages obtained in a 54-year-old woman with unstable basilar invagination. A: Sagittal CT scan reconstruction with head in flexion, showing vertical dislocation (or basilar invagination). B: Sagittal CT scan obtained with the head in extension, showing reduction of the dislocation. C: Radiograph of the craniovertebral junction with the head in flexion, showing evidence of basilar invagination and atlantoaxial dislocation. D: Radiograph obtained with the head in extension, showing reduction of the dislocation. E: Postoperative CT scan showing fixation of the atlantoaxial dislocation in reduced position. F: Postoperative radiograph showing fixation with plate and screws.

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    Neuroimages obtained in an 8-year-old girl with unstable basilar invagination. A: Sagittal T2-weighted MR image showing extensive basilar invagination and cervicomedullary spinal cord compression. B: A CT scan reconstruction with the head in flexed position showing severe basilar invagination and vertical atlantoaxial dislocation. The Wackenheim clival line (A – – – B) and the McRae foramen magnum line (C – – – D) show the relationship with the odontoid process. C: A CT scan with head in extension showing reduction of dislocation. Note the altered relationship of the odontoid process with the McRae line and the Wackenheim line. D: A CT scan with the sagittal cut passing through the atlantoaxial joint. An abnormal oblique orientation of the joint can be appreciated. E: Postoperative CT scan showing fixation of the dislocation by using the lateral mass plate and screw fixation method. Reduction of the vertical dislocation can be appreciated. F: Postoperative sagittal CT scan showing plate and screw fixation and realignment of the joint.

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    Neuroimages obtained in a 12-year-old boy with unstable basilar invagination. A: Sagittal CT scan with the head in flexion, showing the presence of basilar invagination. B: A CT scan with the head in extension position showing reduction of the basilar invagination. C: A CT scan with the cut traversing the atlantoaxial joint. An abnormal configuration of the joint can be appreciated. D: Postoperative CT scan showing fixation in a partially reduced position.

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    Algorithm for management of basilar invagination cases.



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