Atlanto-occipital assimilation associated with atlanto-axial rotatory fixation
Presentation
Torticollis; no history of trauma.
Patient Data
CT reveals the fusion and pseudo articulation of the right anterior arch of the atlas with the occipital bone. Finding suggestive of incomplete atlanto-occipital assimilation.
There is atlantoaxial rotation, the left inferior articular facet of the C1 vertebra is rotated posteriorly relative to the left superior facet of the C2.
There is also closure defect of the posterior elements of the C1 and C2 vertebrae.
The ossification centers of the C1 and C2 vertebrae are open.
Case Discussion
The atlanto-occipital assimilation is one of the transitional vertebrae and fusion of the atlas with the occipital bone. Atlanto-axial rotatory fixation is also known as an atlantoaxial rotatory subluxation. In atlantoaxial rotatory fixation, the C1 vertebra is rotated relative to the odontoid process.