[Measurement and clinical validation of safe distance for LC-

Objective: To define a safe distance range from the LC-Ⅱ screw trajectory to the apex of the greater sciatic notch based on pelvic CT measurements, and to clinically assess the feasibility of using this range under iliac oblique view combined with iliac tangential view fluoroscopy to guide screw insertion. Methods: CT scans of 104 normal pelvises collected between January 2022 and February 2025 were analyzed. There were 52 males and 52 females, with a median age of 45.8 years (range, 19-76 years). The RadiAnt DICOM Viewer software was used to reconstruct coronal, sagittal, and axial sections of the potential LC-Ⅱ screw trajectory. The maximum safety distance (Dmax) and the optimal safety distance (Dopt) from this trajectory to the greater sciatic notch were measured on the coronal and sagittal views. A retrospective analysis was conducted on 21 patients with LC-Ⅱ type pelvic fractures treated with the LC-Ⅱ screws fixation. And the screws were placed within the pre-defined safe distance under guidance from the iliac oblique view and iliac tangential view. Postoperative CT scans were obtained to evaluate the accuracy of screw placement. Results: Radiographic measurements from the 104 cases showed that Dmax ranged from 1.87 to 3.87 cm (mean, 2.79 cm), and Dopt ranged from 1.01 to 2.92 cm (mean, 1.84 cm). Both Dmax and Dopt were significantly greater in the males than in the females ( Conclusion: Utilizing a CT-defined safe distance range from the screw trajectory to the greater sciatic notch, and adhering to this range under iliac oblique view combined with iliac tangential view fluoroscopy, enables the accurate and precise placement of LC-Ⅱ screws.