Anatomic relationship between S2 sacroiliac screws' entry points and pelvic external branches of superior gluteal artery.

Objective: To study the relationship between the pelvic external branches of the superior gluteal artery and the entry area of the S2 sacroiliac screw to provide the anatomical basis and technical reference for avoiding the superior gluteal artery injury during the clinical screw placement.

Methods: CTA imaging of superior gluteal artery of 74 healthy adults (37 males and 37 females) was randomly selected. The safe bony entry area ('safe area' for abbreviation) of S2 sacroiliac screw in the standard lateral view of the pelvis three-dimensional reconstruction CT image was determined by the CT auxiliary measurement software. The relationship between the pelvic external branches of the superior gluteal artery and the safe area of S2 sacroiliac screw was observed, and the cases in which the artery intersected the safe area were counted. The distance between the safe area and the superior gluteal artery branches closest to it was measured for the cases in which the artery and the safe area did not intersect.

Results: 21 of the 74 cases did not have a bone channel of horizontal S2 sacroiliac screw, so they were excluded from this study. In the remaining 53 cases, 12 cases had the deep superior branch of the superior gluteal artery through the safe area of S2 screw (22.6%), and 16 cases had the superficial branch of the superior gluteal artery through the safe area of S2 screw (30.2%). There was no obvious overlap feature and law between the safe area and the superficial and deep superior branches. In 20 cases of the 53 cases, the safe area of S2 screw was located between the deep superior branch and the superficial branch of superior gluteal artery (37.7%), and in 5 cases, the safe area of S2 screw was located behind the superficial branch of superior gluteal artery (9.4%). In the cases where the superior gluteal artery did not intersect the screw entry bony safe area, the part of superior gluteal artery closest to the safe area was located in front or back of the widest part of the safe area.

Conclusion: The risk of accidental injury of the deep superior branch and superficial branch of the superior gluteal artery is high during the process of S2 sacroiliac screw placement. Even if the screw entry point is located in the bony safe area, the absolute safety of screw placement cannot be guaranteed. We strongly suggest that a careful and thorough plan is needed before surgery.