Study design: Dissection of 37 human cadavers was performed to assess the variability in the vascular anatomy anterior to the L5-S1 disc space.
Objectives: To determine the variability of the anterior vascular anatomy at the L5-S1 disc space, and to assess its reliability as an anatomic landmark for the placement of anterior interbody fusion devices.
Summary of background data: Although multiple studies have defined both the lumbar spinal anatomy and the anatomy of the great vessels, the relation of the great vessels to the anterior L5-S1 disc space has not been quantified directly.
Methods: This study investigated 35 human cadavers (17 males and 18 females). The anterior L5-S1 disc space and great vessel bifurcation were exposed through a transabdominal approach. Two independent observers each obtained 10 measurements in each specimen.
Results: The middle sacral artery was present in 100% of the specimens, averaging 2.5 mm in width. Its location in relation to the midline was quite variable, with a range greater than 2 cm in both the top and bottom of the disc. The distance from the bifurcation to the top of the L5-S1 disc averaged 18 mm (range, 7-36 mm). The total width between the left common iliac vein and the right common iliac artery averaged 33.5 mm (range, 12-50 mm).
Conclusions: The middle sacral artery, present in 100% of the specimens, is a poor anatomic landmark for locating the midline at L5-S1. Because the average space available between the left common iliac vein and the right common iliac artery is 33.5 mm, and because the left common iliac vein averages only 12 mm from midline, the surgeon must be prepared to mobilize the local vasculature in most cases to expose the L5-S1 disc space adequately.