Retrotransverse foramen in atlas vertebrae of the late 17th and 18th centuries

Anatomical variations of the atlas vertebra are of particular importance because of their possible repercussions on the vertebral vessels. In view of the extensive articular mobility of the atlas, any anomaly where the vertebral artery and veins run through the transverse foramen could impair blood flow. However, in spite of the possible effect of this anomaly on the vertebral artery and veins, there are few data on the presence of an abnormal accessory transverse foramen, termed retrotransverse foramen, which is smaller and located behind the transverse foramen of the atlas. The aim of this research was to analyse the prevalence of retrotransverse foramen in a sample of 88 dry C1 vertebrae from a Spanish rural population of the late 17th and the early 18th centuries, as well as to study the possible repercussions of the presence of this anatomical variant on the size of the transverse foramen. The anteroposterior diameter and the lateral diameter of the transverse foramen of all the atlas vertebrae and retrotransverse foramina were measured using digital calibres. Two atlases with retrotransverse foramina (2.27%) were found in which the presence of the anatomical variant caused a larger anteroposterior diameter and a smaller lateral diameter than those of the transverse foramina of the normal 86 C1 vertebrae that were analysed. Our results show that a thorough study should be performed on the prevalence of this anatomical variant in the current population, as well as its possible clinical repercussion on the vertebral artery.

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