Goel's classification of atlantoaxial “facetal” dislocation

Th e facets of atlas and axis are strong in their material content and larger in size when compared to all the other facets of the spine.[1] Two large superior articular facets of axis fl ank the odontoid process. Superior facet of C2 vertebra diff ers from the facets of all other vertebrae in two important characters. First is that the superior facet of C2 is present in proximity to the body when compared to other facets, which are located in proximity to the lamina. Th e second is that the vertebral artery foramen is present partially or completely in the inferior aspect of the superior facet of C2, while in other cervical vertebrae, vertebral artery foramen is located entirely in relationship with the transverse process. Unlike superior facets of all other vertebrae, they do not form a pillar with the inferior facets, being considerably anterior to these. Th e course of the vertebral artery in relationship to the inferior aspect of the superior articular facet of the C2 makes its susceptible to injury during Magerl’s transarticular and Goel’s inter-facetal screw implantation techniques.[2-5] Th e inferior facet of the atlas is almost circular in most of the vertebrae without any signifi cant diff erence in the mean anteroposterior and transverse (15 mm) dimensions.