Atlas posterior arch and vertebral artery’s groove variants: a classification, morphometric study, clinical and surgical implications
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The third part of the vertebral artery (VA) coursing in vertebral artery groove (VAG) may be injured during posterior craniocervical junction approaches.
The current study classifies all possible variants of the posterior arch (PA) of the atlas vertebra (C1), focusing on VAG and calculates their incidence. PA and VAG morphometry is studied in correlation with gender and age. Clinical and surgical implications of recorded variants are provided in an effort to explain associated pathology. The usefulness of three-dimensional computed tomography (3D-CT) in detecting PA variants is highlighted.
Materials and methods
Two hundred and forty-four Greek adult dry C1 were classified in types according to PA morphology [i.e. presence of an imprint or a distinct VAG and occurrence of a partially or completely ossified dorsal (PDP or CDP) or lateral (PLP or CLP) ponticle unilaterally or bilaterally]. Combined variants were also included.
A VAG and an imprint were detected in 42.62% and 15.16%. A PDP and CDP were observed in 18.03% and 15.98%, while a CLP and PLP in 2.05% and 1.64%, respectively. Combined PDP and PLP were detected in 2.05%, a CDP and CLP similarly to a CDP and PLP in 1.23% and a PDP and CLP in 0.40%.
Variants’ classification will contribute to an in depth understanding of the complex C1 anatomy and may explain cases of VA entrapment and injury during PA fixation. Surgeons should carefully study 3D-CT imaging to ensure type, location, size and shape of C1 ponticles in combination with VAG morphology and VA course before screw insertion.
KeywordsAtlas vertebra Posterior arch Posterior ponticle Lateral ponticle Vertebral artery groove Variation Ossification
Vertebral artery groove
Partially ossified dorsal ponticle
Completely ossified dorsal ponticle
Partially ossified lateral ponticle
Completely ossified lateral ponticle
Linear distance of vertebral artery groove from the posterior midline to the most medial edge of vertebral artery groove on the inner cortex
Linear distance of vertebral artery groove from the posterior midline to the most medial edge of vertebral artery groove on the outer cortex
Linear distances of vertebral artery groove from the posterior midline to the most lateral edge of vertebral artery groove to the inner cortex
Linear distances of vertebral artery groove from the posterior midline to the most lateral edge of vertebral artery groove to the outer cortex
Technical error of measurement
Relative technical error of measurement
Coefficient of reliability
KN: project development, data analysis, classification system, manuscript editing and final approval, ETP: data collection, data analysis, schematic drawings, PPT, MF and NL: manuscript editing, AS: data analysis, manuscript editing, MK: data analysis, and MP: project development, data collection, data analysis and manuscript editing.
Compliance with ethical standards
Conflict of interest
There is no conflict of interest.
The authors of the current study express their gratitude to the body donors who donated their bodies before death (written informed consent) and throughout this act; their vertebrae were used for this study.
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