Description of a transosseous approach to the L5-S1 disc and 2 clinical case reports

BACKGROUND The lumbosacral disc with the adjacent iliac crest and its relationships to neurologic, visceral, and vascular structures is difficult to approach with cannula-based retractor systems. Previous, less invasive approaches have been described to access this space. Anterior, presacral, and transforaminal approaches each have approach-related complications that have prevented their widespread adoption. A laterally based approach to this disc between the exiting L5 nerve root and traversing S1 nerve root would theoretically eliminate visceral and vascular complications but would necessarily course through the adjacent iliac crest. Our objective was to determine the feasibility of placing an interbody device into the L5-S1 disc space through a lateral transosseous approach. METHODS Six transosseous pathways were created from the iliac crest, laterally through the sacral ala, and entering the L5-S1 intervertebral disc space (3 cadavers). The positions of the portals in relation to the local anatomy were evaluated anatomically and with computed tomographic sagittal, coronal, and axial planes. We measured the lengths, heights, and widths of the pathways; distance between the L5 and S1 nerve roots; endplate diameters; and angles necessary to access the space. In addition, 2 clinical cases using the transosseous pathway are presented. RESULTS Computed tomographic scans and anatomic evaluations showed that there was an average 22-mm distance between the L5 and S1 nerve roots available to enter the L5-S1 disc space. The mean length of the pathway was 69 mm, and the mean height was 27 mm. The mean angle of the approach was 45° off the posterior-anterior axis, and there was a 25° upward angle from true lateral in the frontal plane. CONCLUSIONS A lateral, transosseous approach to the L5-S1 disc space for placing an interbody device is feasible. A closed cannula-based technique may offer reduced approach-related complications. Further studies will be required to determine the reproducibility and utility of this pathway.