Simplifying the Orientation of S1 Iliosacral Screws for Placement in the Dysmorphic Sacrum

Background: Determining the proper iliosacral screw orientation in a dysmorphic S1 sacral segment using a C-arm is difficult, and pelvic computed tomography (CT) is often necessary for the preoperative planning. On the preoperative pelvic axial CT section, the intended screw trajectory can be delineated intraosseously along the axis of the oblique osseous corridor. An inherently accurate orientation would be determined by 2 factors: (1) the trajectory is in the pelvic transverse plane, and (2) it is oriented relative to the coronal plane at a patient-specific angle, which should be measured preoperatively. Based on the above reasoning, we aimed to simplify and verify the orientation. Methods: After establishing the starting point on the sacral lateral view, we tested a method of simplifying the guidewire orientation: placing the guidewire in the pelvic transverse plane and then manipulating it to be angled relative to the coronal plane at the preoperatively measured patient-specific angle. The guidewire orientation should then be reproducibly accurate on the pelvic outlet and inlet views. The feasibility and safety of our method were verified through computer-simulated virtual surgical procedures in 95 dysmorphic sacra and clinical surgical procedures in 12 patients. The primary outcome parameters were the guidewire orientation and screw placement accuracy. Results: Using our method, the S1 guidewire orientation was reproducibly accurate on the pelvic outlet and inlet views in all of the virtual and clinical surgical procedures. Ninety-five virtual S1 screws (1 screw in each left hemipelvis) were placed intraosseously in the pelvic transverse plane. Fourteen unilateral S1 screws were placed intraosseously in the pelvic transverse plane in the 12 patients (2 patients had double screws) without iatrogenic injuries. Conclusions: The guidewire orientation can be simplified by placing the guidewire in the pelvic transverse plane and replicating the preoperatively measured patient-specific angle between the guidewire and the coronal plane. After establishing the starting point on the sacral lateral view, our simplified manipulation yields a reproducibly accurate orientation on the pelvic outlet and inlet views. Level of Evidence: Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.