Iliosacral Screw Placement: Are Uniplanar Changes Realistic Based on Standard Fluoroscopic Imaging?

Abstract

We commonly work in orthogonal systems. Within these systems, it is possible to make a uniplanar correction by moving perpendicular to one plane or radiographic view. The ideal views to image the safe zone for iliosacral screw placement do not create an orthogonal system. When this average angle arc is placed on a graphic model of the pelvis, it becomes clear that the plane of the radiographic beam of the ideal inlet view is collinear with the anterior aspect of the upper two sacral bodies. The outlet view is oblique to the upper sacral bodies. Surgeons must keep this in mind when using fluoroscopic views to insert iliosacral screws.

Fluoroscopic Views for a More Accurate Placement of Iliosacral Screws

“…Many authors have suggested the equivalent of our outlet 2 view as the best outlet view for IS screw placement. 21,23 Contrary to expectations, our study found that the outlet 1 view demonstrated partial penetration through the proximal part of the S1 foramen more precisely than the outlet 2 view (Fig. 5).…”

Pedicle axis view combined by sacral mapping can decrease fluoroscopic shot count in percutaneous iliosacral screw placement

“…A quite common scenario in percutaneous iliosacral screwing is unconscious manipulation of the guide-wire in a wrong direction [16]. Graves and Routt [20] have reported that current standard inlet and outlet images are not based on orthogonal coordinates, and therefore any starting point and aim changes made by moving perpendicular to the C-arm beam will not preclude the trajectory changing on both inlet and outlet views. With the use of orthogonal intracutaneous K-wires, which indicate up, down, cranial and caudal, it is easy to match the position of the sacrum with the image of the sacrum by simply rotating the image on the screen.…”

Anatomic Determinants of Sacral Dysmorphism and Implications for Safe Iliosacral Screw Placement

“…A change in trajectory of only 4°can result in cortical perforation 22 . Concise understanding of this aspect of sacral anatomy and its corresponding fluoroscopic landmarks enables safe placement of percutaneous iliosacral screws 2,[23][24][25][26] .…”