Fluoroscopic Confirmation of Sacral Pedicle Screw Placement Utilizing Pelvic Inlet and Outlet Technique

Minimally invasive surgical techniques may decrease length of stay, operative duration and blood loss, and postoperative pain. Numerous technical challenges and concerns surround the placement of percutaneous pedicle screws at the lumbosacral level. Maximization of screw triangulation, bicortical purchase, and rostral bias toward the sacral promontory has been shown repeatedly to stabilize lumbosacral segment instrumentation and maximize pullout strength. Because of the unique anatomy, conventional anteroposterior (AP) and lateral radiographic views are relatively less reliable at determining screw depth and penetration of the sacral cortex. Percutaneous sacral pedicle fixation using AP and lateral 2-dimensional fluoroscopy is complicated by the variable contour of the sacral alae and promontory. The pelvic inlet view is ideal for visualization of the ventral screw extent and is obtained by directing 45-degree cephalad and 0-degree mediolateral, with adjustments aligning the patient's pelvic brim. The modified pelvic outlet view is obtained with the trajectory axis being directed 45-degree caudal from the AP plane. This aligns the pubic symphysis with the second sacral vertebrae providing visualization of the superior boundary of the S1-bony neural foramen and any inferior wall pedicle breaches. The authors describe this reliable fluoroscopic technique and their clinical experience with percutaneous S1-screw placement.