Limitations of CT-Based Planning in Anterior Pelvic Ring Fixation: A Study of Fluoroscopy-Guided Pubic Ramus Screws

Purpose Current CT-based planning for pubic ramus screw fixation uses rectilinear geometric models based on the outer thread diameter to define intraosseous corridors. This method may underestimate feasibility by failing to incorporate implant geometry and non-rectilinear screw trajectories achievable under fluoroscopic guidance. This study aimed to determine the proportion of fluoroscopically inserted pubic ramus screws that would have been classified as infeasible using standard CT-based rectilinear planning and to explore mechanisms for this discrepancy. Methods We conducted a retrospective cohort study at a Level I trauma center including all patients who underwent fluoroscopy-guided percutaneous pubic ramus screw fixation from January 2022 to December 2025 with complete pre- and postoperative pelvic CT imaging. The primary outcome was the proportion of screws judged infeasible under standard CT-based rectilinear planning using outer thread diameter. Secondary outcomes were interobserver reliability for feasibility assessment, postoperative screw positioning accuracy, complications, and the impact of core-diameter-based planning on feasibility classification. Results Thirty-three patients (42 screws) were analysed. Standard CT-based rectilinear planning classified 15 screws (36%) as infeasible by consensus of two observers. Postoperative CT demonstrated accurate positioning of all screws (100%) with no cortical breach, intra-articular penetration, neurovascular injury, or fixation-related revision. Core-diameter-based planning reclassified 14 of the 15 screws as feasible. In one case, three-dimensional postoperative reconstruction revealed a markedly non-rectilinear trajectory not approximable by any straight cylindrical model. Conclusion Standard CT-based rectilinear planning underestimates the feasibility of fluoroscopically guided pubic ramus screw fixation. Core-diameter-based planning improves prediction but may still fail with pronounced trajectory curvature, highlighting limitations of rectilinear models for preoperative planning and navigation systems. Level of Evidence Level IV, therapeutic study.