An anatomic study on the placement of the second sacral screw and its clinical applications

The fixation of lumbosacral and sacral pelvis can be performed on the ilium and the Second Sacrum Vertebrae (S2). Although several studies on the anatomical and biomechanical features of S2 screw fixation have been published, little clinical application has been reported, especially combination of anatomical investigation and clinical study. This study was performed to design and optimize the method of pedicle screw placement for S2.

Fifteen adult dry sacrum specimens were prepared and truncated from the S1-S2 and S2-S3 vertebral fusion remnants, and the morphology of the S2 vertebral body was observed from this section. The intersection of the horizontal line through the lowest point of the inferior edge of the first posterior sacral foramen and the lateral sacral crest was the entry point (Point X). The screws were inserted anterolaterally or anteromedially at Point X in 10 cadavers, with all of the screws penetrating the sacrum. Finally, the S2 sacral screw fixation technique was applied to a total of 13 patients with lumbosacral lesions, and the clinical outcome was evaluated at a minimum follow-up of 1 year.

Two S2 sacral screw placement methods were developed, i.e., the anterolateral and anteromedial insertions. Seven patients had complete preoperative, postoperative, and follow-up data. In all cases, the bilateral S2 screws were placed in good position and the fixation was firm. There was no surgical wound infection or internal fixation loosening. All the patients achieved partial bone graft healing, which was verified by computed tomography.

The intersection of the horizontal line through the lowest point of the inferior edge of the first posterior sacral foramen and the lateral sacral crest can be used as the entry point for S2 sacral screw fixation. The S2 pedicle screw fixation shows good clinical effectiveness and safety for stable reconstruction of lumbosacral lesions.