The effect of patient positioning on the relative position of the aorta to the thoracic spine.

Purpose: Detailed knowledge of the anatomy of the thoracic aorta is crucial for thoracolumbar spinal surgery. The purpose of the present study is to describe the relative displacement of the aorta to the spine in supine, prone and prone position with padding. Improved understanding of the magnitude and direction of this often-overlooked change could benefit preoperative planning and decision-making.

Methods: A total of 200 patients underwent CT scan of the thoracic spine in the standard supine, prone and prone position with padding. Axial CT images from T4 to T12, in all three different positions, were selected and the following parameters were measured: (a) distance B connecting left pedicle entry point to the edge of the aortic wall and (b) projections Bx and By, representing the minimum AP depth and horizontal displacement of the aortic wall relative to the left pedicle entry point O.

Results: There was a significant difference in the distance B between the three different positions across all thoracic vertebrae levels, confirming that positioning significantly affects aorta's relative position. Moreover, in the prone position with padding at the level of T6, the aortic wall lies at a minimum distance from the left pedicular axis and thus from the typical screw trajectory.

Conclusion: The results of this study show that prone positioning for posterior thoracolumbar approach affects significantly the anatomic relationship of the aorta to the spine. Surgeons should be aware that standard supine CT evaluation represents a static technique, which can differ considerably from surgical reality. These slides can be retrieved from electronic supplementary material.