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 atla s vertebra using dry bony vertebrae. Objectives. To measure the dimens ion of the vertebral artery groove of the atlas and to define its rela tion to the posterior midline. Summary of Background Data. Anatomic de scriptions of the vertebral artery groove of the atlas exist, but very little quantitative data focused on this groove have been reported. M ethods. Fifty dry atlas vertebrae were obtained for this study. Anatom ic evaluation focused on the vertebral artery groove and its relation to the midline. A total of eight linear and two angular measurements w ere made bilaterally. The mean, range, and standard deviation were cal culated for all of the specimens and for male and female specimens sep arately. Results. Differences in dimensions of male and female specime ns were found to be statistically significant in one linear and two an gular parameters. The average depths of the medial and lateral entranc es, lengths of the axis, and thicknesses of the vertebral artery groov e for male and female specimens were 9 mm, 6 mm, 14 mm, and 4 mm, resp ectively. The average angle of the vertebral artery groove axis for bo th genders was 64 degrees lateral to the sagittal plane. The distances from the midline to the medial-most edge of the vertebral artery groo ve on the inner and outer cortexes for male and female specimens avera ged 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 dis section on the posterior aspect of the posterior ring should remain wi thin 12 mm lateral to the midline, and dissection on the superior aspe ct of the posterior ring should remain within 8 mm of the midline.