The quantitative anatomy of the vertebral artery groove of the atlas and its relation to the posterior atlantoaxial approach.

STUDY DESIGN: An evaluation of the vertebral artery groove of the atlas vertebra using dry bony vertebrae.

OBJECTIVES: To measure the dimension of the vertebral artery groove of the atlas and to define its relation to the posterior midline.

SUMMARY OF BACKGROUND DATA: Anatomic descriptions of the vertebral artery groove of the atlas exist, but very little quantitative data focused on this groove have been reported.

METHODS: Fifty dry atlas vertebrae were obtained for this study. Anatomic evaluation focused on the vertebral artery groove and its relation to the midline. A total of eight linear and two angular measurements were made bilaterally. The mean, range, and standard deviation were calculated for all of the specimens and for male and female specimens separately.

RESULTS: Differences in dimensions of male and female specimens were found to be statistically significant in one linear and two angular parameters. The average depths of the medial and lateral entrances, lengths of the axis, and thicknesses of the vertebral artery groove for male and female specimens were 9 mm, 6 mm, 14 mm, and 4 mm, respectively. The average angle of the vertebral artery groove axis for both genders was 64 degrees lateral to the sagittal plane. The distances from the midline to the medial-most edge of the vertebral artery groove on the inner and outer cortexes for male and female specimens averaged 10 mm, with a minimum of 8 mm, and 18 mm, with a minimum of 12 mm, respectively.

CONCLUSIONS: The results of this study suggest that dissection on the posterior aspect of the posterior ring should remain within 12 mm lateral to the midline, and dissection on the superior aspect of the posterior ring should remain within 8 mm of the midline.