Editing Atlas (anatomy) (section)

=== Variations ===
[[File:Posterior arch defect.png|thumb|An axial [[CT scan]] showing a posterior arch defect]]
Accessory transverse foramen of the atlas is present in 1.4–12.5% across the population.<ref>{{Cite journal |last1=Paraskevas |first1=George |last2=Mavrodi |first2=Alexandra |last3=Natsis |first3=Konstantinos |date=2015-06-01 |title=Accessory mental foramen: an anatomical study on dry mandibles and review of the literature |url=https://doi.org/10.1007/s10006-014-0474-1 |journal=Oral and Maxillofacial Surgery |language=en |volume=19 |issue=2 |pages=177–181 |doi=10.1007/s10006-014-0474-1 |pmid=25394607 |s2cid=32194827 |issn=1865-1569}}</ref>

[[Arcuate foramen|Foramen arcuale]] or a bony bridge above the vertebral artery on the posterior arch of the atlas may be present. This foramen has an overall prevalence of 9.1%.<ref>{{Cite journal |last1=Pękala |first1=Przemysław A. |last2=Henry |first2=Brandon M. |last3=Pękala |first3=Jakub R. |last4=Hsieh |first4=Wan Chin |last5=Vikse |first5=Jens |last6=Sanna |first6=Beatrice |last7=Walocha |first7=Jerzy A. |last8=Tubbs |first8=R. Shane |last9=Tomaszewski |first9=Krzysztof A. |date=2017 |title=Prevalence of foramen arcuale and its clinical significance: a meta-analysis of 55,985 subjects |url=https://pubmed.ncbi.nlm.nih.gov/28621616/ |journal=Journal of Neurosurgery. Spine |volume=27 |issue=3 |pages=276–290 |doi=10.3171/2017.1.SPINE161092 |issn=1547-5646 |pmid=28621616|doi-access=free }}</ref> [[Arch defects]] refer to the condition where a gap or cleft exists at the anterior arch or posterior arch of the atlas. The prevalence of the posterior arch defect and anterior arch defect was 0.95% and 0.087%, respectively.<ref>{{Cite journal |last1=Kwon |first1=Jong Kyu |last2=Kim |first2=Myoung Soo |last3=Lee |first3=Ghi Jai |date=2009 |title=The Incidence and Clinical Implications of Congenital Defects of Atlantal Arch |journal=Journal of Korean Neurosurgical Society |volume=46 |issue=6 |pages=522–527 |doi=10.3340/jkns.2009.46.6.522 |issn=2005-3711 |pmc=2803266 |pmid=20062566}}</ref> The anterior arch defect may be presented along with posterior arch defect, a condition known as combined arch defect or bipartite atlas.<ref>{{Cite journal |last1=Hummel |first1=Edze |last2=Groot |first2=Jan C. de |date=2013-05-01 |title=Three cases of bipartition of the atlas |url=https://www.thespinejournalonline.com/article/S1529-9430(13)00080-6/abstract |journal=The Spine Journal |language=English |volume=13 |issue=5 |pages=e1–e5 |doi=10.1016/j.spinee.2013.01.024 |issn=1529-9430 |pmid=23415018}}</ref>