Comparative Study of S2-Alar-Iliac Screw Trajectories between Males and Females Using Three-Dimensional Computed Tomography Analysis: The True Lateral Angulation of the S2-Alar-Iliac Screw in the Axial Plane

Abstract

The S2 alar-iliac screw (S2AIS) is commonly used for long spinal fusion as a rigid distal foundation in spinal deformity surgeries, and it is also used in percutaneous sacropelvic fixation for providing an in-line connection to the proximal spinal constructs without using offset connectors. Although the pelvic shape is different between males and females, reports on S2AIS trajectories according to gender have been scarce in the literature. In this paper, S2AIS trajectories are compared between males and females using pelvic three-dimensional computed tomography (3D-CT) in a normal Japanese population. After resetting the caudal angulation in CT-imaging plane manipulation, the angulation of S2AIS was more lateral in the axial plane and more horizontal in the coronal plane in females. Mean distances from the midline to starting points of S2AIS tended to be shorter in females, whereas mean distances from the midline to the posterior superior iliac spine was significantly longer in females. We also found that there were positive correlations between the patients’ height and the maximal lengths of S2AISs, and the patients’ height and minimal areas of S2AIS pathways. Our results are useful not only for conventional open spinal surgery, but also for minimally invasive spine surgery.

Safe Optimal Tear Drop View for Spinopelvic Fixation Using a Three-Dimensional Reconstruction Model of the Pelvis

“…These results are consistent with those of previous studies. In Funao et al’s report 24) using 3D CT analysis, the maximum length and minimal intraosseous area on the perpendicular plane of the S2AIS pathway were significantly longer and larger in men and women. Wang et al 25) also indicated that the modified sacroiliac screws, measured on the 3D pelvis model, were thicker and longer in men than in women, suggesting that it would stem from the anatomical differences between the sexes.…”

“…Zhu et al 23) reported that the trajectory of S2AIS in women was 5° more caudal than that in men in the Asian population. Funao et al 24) also documented that the insertion angle of S2AIS was significantly different between men and women. Thus, we suggest that the anatomical differences between the sexes should be considered when determining the screw size and insertion angle pre- and intraoperatively.…”

“… 26) Several authors have utilized a 3D pelvis model or CT images to analyze the parameters and angles for various SPF techniques. 23 24 25 27 28) In addition, Bow et al 16) reported the efficacy of a 3D-printed simulator and teaching module for S2AIS. It is meaningful that the results of our study can be utilized not only in preoperative planning, but also intuitively in the actual surgical field, since we simulated the situation of the SPF procedure with intraoperative C-arm fluoroscopy.…”

Advancements and Updates on Operative Techniques in Spinal Deformity

“…Similar to new technology outside of the operating room, advancements in intraoperative techniques have been utilized to improve the success rates of spinal deformity surgery. In a study conducted by Funao et al, sacropelvic fixation with S2-alar-iliac screws (S2AI) based on patient sex was evaluated in adults, given the innate difference in pelvic size and shape between males and females [ 9 ]. Three-dimensional pelvic computed tomography was used to determine ideal trajectory pathways for S2AI screw placement, which was determined to be more laterally angled in the axial plane in females (right 47.7°, left 46.1°) than in males (right 45.3°, left 44.3°), and more horizontally angled in the coronal plane in females (right 33.7°, left 34.5°) than in males (right 36.5°, left 37.0°).…”