Iliosacral Screws Can Be Placed With Precision by Adjusting the Pelvic Inlet Between S1 and S2.

OBJECTIVES

To determine (1) the natural incidence of sacral inlet angle differences between S1 and S2 and (2) implications for iliosacral screw placement with a technique to improve the accuracy of the intraoperative fluoroscopic inlet for S1 and S2.

DESIGN

Combined retrospective and prospective cohort reviews.

SETTING

Regional Level 1 trauma center.

PATIENTS/PARTICIPANTS: After exclusion criteria, 300 patients with uninjured pelvic rings to determine the natural incidence of S1-S2 angle differences and 33 patients treated with iliosacral screws over the study period.

INTERVENTION

None in the retrospective cohort. In the prospective cohort, all patients underwent fluoroscopically assisted iliosacral screw fixation.

MAIN OUTCOME MEASUREMENTS

Radiographic determination of S1-S2 angle differences above 10 degrees in a natural population for the retrospective cohort. In the prospective, operative cohort, the outcome of interest was the safety of iliosacral screws in S1 and S2 as determined on intraoperative fluoroscopy and postoperative CT scan.

RESULTS

In the retrospective cohort, 180 of 300 (60.0%) had S1-S2 inlet angle differences above 10 degrees. In the operative cohort, 19 of 33 (57.6%) had S1-S2 inlet angle differences above 10 degrees. Of the iliosacral screws in S1 and S2 placed using the described imaging technique, all (69/69, 100%) were safe.

CONCLUSIONS

A normal population determined that differences in the inlet angle between S1 and S2 are common. An operative cohort was treated using preoperative CT-based planning to define different intraoperative fluoroscopic inlet views for S1 and S2, if a larger difference existed. Using this technique, 69 of 69 (100%) iliosacral screws were safe.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.