Quantitative anatomy of vertebral artery groove on the posterior arch of atlas in relation to spinal surgical procedures

The location of the vertebral artery on a groove on the superior surface of the posterior arch of atlas makes it vulnerable to injury during surgical procedures in this region. Knowledge of the quantitative anatomy of the vertebral artery groove is therefore necessary. In 55 dry adult atlas vertebrae, the distance of the medial edges of the vertebral artery groove were measured from the posterior midline at both the inner and outer cortices of the posterior arch of atlas. In addition, the distance between the vertebral artery grooves on either side as well as the length of the vertebral artery groove was also measured. It was found that a minimum of 1.5 cm of the posterior arch could be safely exposed at both the outer and inner cortices. In addition, with mobilization of the vertebral artery from its groove on both the sides, an additional 1 cm of posterior arch could be exposed on either side. Exposure of the posterior arch of the atlas is an important step in surgical procedures for treatment of diverse conditions of the upper spinal cord and foramen magnum region. Injury to the vertebral artery in its position on the vertebral groove may lead to disastrous complications. The present study reveals that the neurosurgeon can safely expose up to 3.5 cm of the posterior arch of atlas and knowledge of this anatomic fact may help in planning surgical approaches.