Technical Tricks to Improve Iliosacral Screw Safety Using Three-dimensional Computed Tomography Imaging

This technical note describes a method used to facilitate iliosacral screw fixation with three-dimensional (3D) computed tomography (CT) imaging. Preoperative pelvis CT scans were used to generate 3D reconstructions, which were then manipulated into inlet and outlet orientations. The inlet position for S1 was achieved when the anterior cortex of the S1 body became superimposed on itself; the outlet position was when the S1 nerve root tunnel was viewed en face. On the fluoroscopic inlet view of S1, multiple cortical densities were often visible and could be difficult to distinguish as S1 versus other sacral segments. 3D CT helped distinguish the position and shape of the anterior cortical limit of S1 by referencing preoperative 3D CT inlet images that were reproduced intraoperatively on fluoroscopy using the appearance of the anterior pelvic ring and the relative obliquity of the obturator foramen. This technique was especially valuable in the setting of common posterior pelvic anatomic variations-including asymmetry, degenerative osteophytes, severe sacral slope, and dramatic cortical recesses of the upper sacral segment. These variations were often difficult to anticipate with conventional plain film or standard CT imaging alone, underscoring the potential clinical utility of this technique.