Vertebral artery in relationship to C1-C2 vertebrae: an anatomical study.

BACKGROUND Ten randomly selected adult cadaveric specimens were dissected to analyse the anatomy of the vertebral artery during its course from the C3 transverse process to its entry into the spinal dural canal at the level of C1. In addition, 10 dry cadaveric C1-C2 bones were studied. The course of the artery and the parameters relevant during surgery in the region are evaluated. METHODS Ten adult cadaveric specimens and 10 adult dry cadaveric C1 and C2 bones were studied. In five cadaveric specimens, the arteries and veins were injected with coloured silicon. The artery during its course from the transverse process of C3 to the transverse process of C2 was labelled as V1 segment, the artery during its course from the C2 transverse process to the C1 transverse process was labelled as V2 segment and the segment of the artery after its exit from the transverse foramen of C1 to the point of its dural entry was labelled as V3 segment. The relationship of the artery to the C1-2 joint and facets, distance of the location of the artery from the midline, from the C2 ganglion and from the other surgery related landmarks were evaluated. The extent of occupancy of the artery into the vertebral artery groove on the inferior surface of the superior facet of the C2 vertebra, and over the posterior arch of the atlas was studied. RESULTS The V1 segment of the vertebral artery takes a varying degree of loop inside the vertebral artery foramen on the inferior aspect of the superior facet of the C2 vertebra. The loop extends towards the midline and was at an average distance of 14.6 mm from the midline of the vertebral body. The V2 segment of the artery takes an initial lateral loop after its exit from the transverse process of the C2 vertebra. The average distance of the artery from the lateral end of the C2 ganglion was 7.2 mm and from the dural tube was 15.3 mm. The vertebral artery groove in the superior facet of C2 and the groove over the posterior arch of the atlas were completely occupied by the vertebral artery only in six sides and in none respectively, suggesting the possibility of the dynamic nature of the relationship of the artery to the bone. CONCLUSIONS The vertebral artery adopts a serpentine course in relationship to the C2 vertebra, making it susceptible to injury during the surgical procedures in the region. The multiple loops of the artery and a buffer space within the vertebral artery groove on the inferior surface of the superior facet of the C2 vertebra and over the posterior arch of atlas provide the artery an extra length and space, probably essential to avoid any stretch during neck movements.