Presacral retroperitoneal approach to axial lumbar interbody fusion: a new, minimally invasive technique at L5-S1: Clinical outcomes, complications, and fusion rates in 50 patients at 1-year follow-up

Preoperative evaluation of the sacrum and coccyx for the presacral ALIF procedure. To assess the feasibility of the approach, a line is drawn on the midsagittal MR scan from the probe entry point below the sacrococcygeal joint (red arrow) to the midpoint of the S1 endplate (red line). The optimal trajectory zone (green shaded area) for placement of the implant should be perpendicular to and centered at the midpoint of the superior endplate of S1. MR scan (A) and illustration (B) shows an ideal trajectory for insertion of the screw into the L5-S1 vertebrae. Illustration of the posterior view of the sacrum shows the probe entry point lateral to the coccyx and inferior to the attachments of the sacrospinous and sacrotuberous ligaments. MR scan (C) shows an excessive curvature of the sacrum and coccyx that would result in screw placement at an acute angle to the superior endplate of S1, which is biomechanically suboptimal, and in violation of the spinal canal. This procedure is contraindicated in these patients (with permission from Mayfield Clinic).