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

Limitations of CT-Based Planning in Anterior Pelvic Ring Fixation: A Study of Fluoroscopy-Guided Pubic Ramus Screws | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Limitations of CT-Based Planning in Anterior Pelvic Ring Fixation: A Study of Fluoroscopy-Guided Pubic Ramus Screws Guillaume DAVID, Thomas GRIMAUD, Clément MARC, Vincent STEIGER, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9108518/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract 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. Pubic ramus fracture Anterior pelvic ring Percutaneous screw fixation Computed tomography planning Surgical navigation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Percutaneous screw fixation of superior pubic ramus fractures is a widely accepted technique for stabilizing anterior pelvic ring injuries while limiting surgical morbidity.[ 1 – 3 ] Despite its advantages, accurate screw placement remains technically demanding because the intramedullary pathway of the pubic ramus is narrow, curved, and highly variable.[ 4 – 8 ] To assess feasibility and minimize the risk of cortical breach or intra-articular penetration, preoperative CT-based planning is commonly used to identify an osseous corridor suitable for screw insertion.[ 9 – 11 ] Most CT-based planning and navigation systems rely on rectilinear geometric assumptions, defining feasibility by the presence of a straight cylindrical corridor capable of accommodating a screw of predefined diameter. Using this approach, several CT simulation studies have reported limited feasibility rates. Lee et al.[ 9 ] demonstrated that only 35% of patients could accommodate a 6.5-mm screw along a straight corridor and only 21.5% a 7.3-mm screw; notably, 12.9% of women were deemed unable to accept even a 3.5-mm screw. These findings suggest that strict rectilinear CT-based criteria may exclude a substantial proportion of patients from percutaneous anterior pelvic ring fixation. Several methodological and biomechanical factors may contribute to this apparent limitation. First, feasibility is typically assessed using the outer thread diameter of the implant, although the risk of cortical violation is primarily determined by the screw core.[ 9 ] For commonly used 6.5-mm and 7.3-mm cannulated screws, the core diameter remains approximately 5 mm, while the increase in nominal diameter mainly reflects larger thread geometry. In narrow segments of the pubic ramus, particularly near the acetabular joint, planning based on thread diameter may therefore be overly restrictive.[ 12 ] In this context, the use of partially threaded screws allows the most constrained portion of the corridor to be traversed by the core alone, while threads engage wider cancellous regions, a strategy that is not captured by conventional CT planning models. Second, rectilinear CT planning does not account for the intraoperative behavior of flexible guidewires. During fluoroscopy-guided cannulated screws insertion, guidewires may progressively adapt their trajectory within the intramedullary canal, undergoing controlled elastic deformation when encountering areas of denser cortical bone. The definitive screw subsequently follows this guidewire-defined path. Such non-rectilinear trajectories, potentially accentuated by the elastic properties of titanium implants, cannot be represented by straight-line CT-based planning or navigation systems. The clinical relevance of these limitations remains insufficiently quantified. Specifically, it is unclear what proportion of screws successfully inserted under fluoroscopic guidance would have been classified as infeasible using standard CT-based rectilinear analysis, and whether postoperative three-dimensional reconstructions demonstrate screw trajectories that depart from idealized straight paths assumed during planning. The primary objective of this study was therefore to determine the proportion of fluoroscopically inserted pubic ramus screws that could not have been predicted as feasible using conventional CT-based rectilinear planning criteria based on outer thread diameter. Secondary objectives were to assess interobserver reliability for feasibility assessment, to evaluate the impact of core-diameter–based planning on feasibility classification, and to analyze postoperative three-dimensional screw trajectories to determine whether they reflect non-rectilinear pathways incompatible with current CT-based planning and navigation paradigms. We hypothesized that a substantial proportion of accurately positioned pubic ramus screws would not be predicted by standard rectilinear CT planning, highlighting intrinsic limitations of current CT-based planning strategies in anterior pelvic ring fixation. Methods Study Design and Patient Selection A retrospective cohort study was conducted at a Level I trauma center. All consecutive patients who underwent fluoroscopy-guided percutaneous screw fixation of superior pubic ramus fractures between January 2022 and December 2025 were screened for inclusion. Institutional review board approval was obtained. The requirement for informed consent was waived due to the retrospective observational design of the study. Patients were eligible if both a complete preoperative pelvic CT scan and a postoperative CT scan were available, allowing assessment of preoperative feasibility and postoperative screw positioning. Patients with incomplete imaging datasets were excluded. Preoperative CT-Based Planning For each included patient, preoperative CT scans were independently reviewed by two independent fellowship-trained pelvic and acetabular surgeons. Observers were blinded to intraoperative findings and postoperative imaging. Preoperative CT-based planning and postoperative three-dimensional reconstructions were performed using dedicated imaging software (Synapse 3D, Fujifilm, Tokyo, Japan). CT-based feasibility assessment was performed according to the rectilinear planning methodology described in previously published CT simulation studies. Briefly, a straight cylindrical model (6.5 mm and 7.3 mm diameter) was manually positioned along the intramedullary axis of the superior pubic ramus on multiplanar reconstructions and three-dimensional views. Feasibility was defined as the ability to place a straight cylinder corresponding to the outer thread diameter of the intended screw entirely within cancellous bone, without cortical breach or intra-articular penetration along its full length. Each corridor was classified as either feasible or infeasible. Interobserver agreement was subsequently assessed. ( Fig. 1 ) Surgical Technique and Postoperative Assessment All procedures were performed using fluoroscopy-guided percutaneous techniques according to standard institutional practice. Postoperative CT scans were reviewed to assess final screw positioning. Screws were evaluated for cortical breach, intra-articular penetration, or neurovascular compromise. Screws meeting none of these criteria were considered accurately positioned. Analysis of Discrepant Cases Cases in which screws were classified as infeasible on preoperative rectilinear CT planning but demonstrated accurate postoperative positioning were further analyzed to explore potential explanations for this discrepancy. First, postoperative three-dimensional reconstructions were used to compare the actual screw trajectory with a straight cylindrical model corresponding to the same outer thread diameter. This analysis aimed to assess whether the implanted screw deviated from a rectilinear path, suggesting progressive adaptation of the trajectory during fluoroscopic insertion. ( Fig. 2 ) Second, preoperative CT planning was repeated using a straight cylindrical model corresponding to the core diameter of the implanted screw (5 mm) rather than the outer thread diameter. ( Fig. 3 ) Feasibility classification using this alternative criterion was recorded and compared with the original planning results to determine whether core-diameter–based planning improved concordance with postoperative findings. Outcome Measures The primary outcome was the proportion of pubic ramus screws that would have been classified as infeasible based on standard CT-based rectilinear planning using outer thread diameter criteria. Secondary outcomes included interobserver reliability for corridor feasibility assessment, postoperative screw positioning accuracy, and the effect of core-diameter–based planning on feasibility classification. Statistical Analysis Given the descriptive nature of the study, analyses were primarily descriptive. Categorical variables were reported as frequencies and percentages. Interobserver agreement for CT-based feasibility assessment was evaluated using Cohen’s kappa coefficient. Statistical analyses were performed using using R software, version 3.6.1 (R Foundation for Statistical Computing) Results Thirty-three patients with 42 fluoroscopy-guided percutaneous pubic ramus screws were included, including both 6.5-mm and 7.3-mm screws. Using standard CT-based rectilinear planning based on the outer thread diameter corresponding to the implanted screw, 27 screws (64%) were classified as feasible, whereas 15 screws (36%) were deemed infeasible by consensus between the two observers. Interobserver agreement for feasibility assessment was high (κ = 0.89 for the 6.5-mm model and κ = 0.81 for the 7.3-mm model). ( Table 1 ) Table 1 CT-Based Planning Feasibility and Postoperative Outcomes for Pubic Ramus Screws Variable Value Patients, n 33 Screws, n 42 Screw diameter 6.5 mm and 7.3 mm Feasible (CT rectilinear planning) 27 (64%) Not feasible (CT rectilinear planning) 15 (36%) Interobserver agreement κ = 0.89 (6.5 mm); κ = 0.81 (7.3 mm) Accurate postoperative positioning 42 (100%) Cortical breach 0 Intra-articular penetration 0 Neurovascular complication 0 Fixation-related revision surgery 0 Legend table 1 : CT-based feasibility was assessed using rectilinear planning models corresponding to the outer thread diameter of the implanted screw (6.5 or 7.3 mm). Accurate positioning was defined as the absence of cortical breach, intra-articular penetration, or neurovascular complication on postoperative CT imaging. Postoperative CT imaging demonstrated accurate screw positioning in all cases (100%), with no cortical breach, intra-articular penetration, neurovascular complication, or fixation-related revision surgery. All screws classified as infeasible on preoperative CT planning were successfully inserted and correctly positioned postoperatively. ( Table 2 ) Table 2 Effect of Core-Diameter–Based Planning in Screws Classified as Infeasible on Standard CT Planning Variable Value Screws classified as infeasible (thread diameter) 15 Core diameter used for reassessment 5 mm Reclassified as feasible with core planning 14 (93%) Remaining infeasible with core planning 1 (7%) Postoperative positioning accuracy in this subgroup 100% Legend table 2 : Among screws initially classified as infeasible using standard CT-based rectilinear planning based on outer thread diameter, feasibility was reassessed using a straight cylindrical model corresponding to the screw core diameter (5 mm). Fourteen of fifteen screws were reclassified as feasible. One screw remained infeasible despite accurate postoperative intramedullary positioning, reflecting a markedly non-rectilinear trajectory. Among the 15 screws initially classified as infeasible using thread-diameter–based rectilinear planning, all were partially threaded implants. Reassessment using a core-diameter–based (5 mm) cylindrical model reclassified 14 screws (93%) as feasible. One screw, implanted with a 6.5-mm diameter, remained classified as infeasible even with core-diameter–based planning despite accurate postoperative intramedullary positioning. In this case, postoperative three-dimensional reconstruction demonstrated a markedly non-rectilinear screw trajectory that could not be encompassed by any straight cylindrical model, illustrating an extreme example of guidewire-driven trajectory adaptation. ( Figs. 4 and 5 ) Discussion The present study demonstrates that standard CT-based rectilinear planning substantially underestimates the feasibility of fluoroscopy-guided pubic ramus screw fixation. More than one third of screws in this cohort would have been classified as infeasible using conventional CT planning criteria based on outer thread diameter, yet all were accurately positioned postoperatively without complication. These findings highlight intrinsic limitations of current planning paradigms and suggest that feasibility is governed by additional geometric and implant-related factors that are not captured by straight-line CT analysis. A first key finding is the impact of implant geometry on feasibility assessment. Conventional CT planning relies on the outer thread diameter of the screw, implicitly assuming that the entire threaded portion must remain fully intramedullary along the narrowest segment of the corridor. However, between 6.5-mm and 7.3-mm screws, the increase in nominal diameter is primarily related to the size of the threads rather than the core, which remains constant at approximately 5 mm. From a biomechanical and anatomical standpoint, cortical violation risk is determined by the position of the core rather than the thread crests.[ 13 ] In corridors that are narrow or closely adjacent to the acetabular joint, especially near the most constrained portions of the superior pubic ramus, planning based on thread diameter may therefore be overly restrictive. In such situations, the use of partially threaded screws allows the narrowest segment of the corridor to be traversed by the core alone, while the threaded portion is positioned in wider cancellous regions. This consideration is particularly relevant for 7.3-mm screws, for which thread diameter disproportionately increases relative to the core. In the present study, reassessment using a core-diameter–based planning model improved concordance between preoperative feasibility assessment and postoperative outcomes in the vast majority of cases, supporting the concept that planning based on the screw core better reflects clinical reality. Based on these observations, our current practice has shifted toward preferential use of partially threaded screws, except in cases where preoperative planning demonstrates a sufficiently wide intramedullary corridor. In both antegrade and retrograde fixation, this strategy allows the narrowest and highest-risk segment of the corridor, adjacent to the joint and neurovascular structures, to be traversed by the 5-mm core alone. ( Fig. 6 ) A second major mechanism underlying the discrepancy between CT planning and intraoperative feasibility relates to screw trajectory geometry. Standard CT-based planning assumes a rigid, rectilinear trajectory, whereas fluoroscopy-guided insertion relies on a flexible guidewire that can progressively adapt its path within the intramedullary canal.[ 14 ] As demonstrated by postoperative three-dimensional reconstructions in this study, several screws followed non-rectilinear trajectories that could not be fully encompassed by a straight cylindrical model corresponding to the outer thread diameter. Notably, in one case, even core-diameter–based rectilinear planning failed to predict feasibility, despite accurate intramedullary screw placement. In this instance, the implanted 6.5-mm screw demonstrated a markedly curved trajectory on postoperative three-dimensional reconstruction, reflecting substantial guidewire deformation within the corridor. ( Figs. 4 and 5 ) This extreme example illustrates that feasibility may occasionally depend on trajectories that cannot be approximated by any straight cylindrical model, regardless of diameter, further emphasizing the intrinsic limitations of rectilinear planning assumptions. This phenomenon likely reflects guidewire behavior at the bone–implant interface. When encountering areas of denser cortical bone, the guidewire may undergo controlled elastic deformation, gradually redirecting its trajectory toward available cancellous pathways.[ 15 ] The definitive screw subsequently follows the established guidewire path. This effect is expected to be more pronounced with titanium screws compared with stainless steel implants, given their greater elasticity. The superposition of curved implanted screw trajectories and rectilinear cylindrical models in this study visually illustrates this limitation of straight-line planning and supports the concept of non-rectilinear “functional corridors” during fluoroscopy-guided fixation. These observations also support the concept of implants designed to better accommodate curved intramedullary pathways. By allowing controlled implant curvature along a guidewire-defined trajectory, such devices may better adapt to the complex anatomy of the pubic ramus and expand the indications for percutaneous fixation in anatomically constrained corridors. These findings have important implications for the development and clinical use of navigation systems in anterior pelvic ring fixation. Current navigation platforms are fundamentally based on rectilinear trajectories defined on intraoperative CT scans.[ 16 ] While such systems may accurately identify optimal entry points and reduce variability in starting position for anterior column screw, they are inherently unable to account for curved or progressively adjusted trajectories enabled by guidewire flexibility. As a result, navigation may falsely classify certain corridors as infeasible, potentially discouraging percutaneous fixation in cases that are technically achievable under fluoroscopic guidance. Rather than negating the value of navigation, the present results suggest that future planning and navigation tools should integrate more flexible geometric models, incorporating core-diameter–based constraints and allowing for non-rectilinear trajectories. Such developments could improve feasibility prediction while preserving the advantages of navigation for entry-point selection and spatial orientation. This study has several limitations. Its retrospective design may introduce selection bias, and the analysis was performed at a single Level I trauma center with surgeons experienced in fluoroscopy-guided pelvic fixation. The absence of complications limits comparative statistical analysis but reflects the safety of the technique in this cohort. Finally, non-rectilinear trajectories were assessed qualitatively rather than quantified by curvature metrics, although three-dimensional reconstructions clearly demonstrated deviations from straight-line planning assumptions. Conclusions Standard CT-based rectilinear planning underestimates the feasibility of fluoroscopy-guided pubic ramus screw fixation. Planning based on outer thread diameter and rigid trajectories fails to account for implant geometry, partial threading strategies, and guidewire-driven non-rectilinear pathways. Core-diameter–based planning and consideration of functional screw trajectories may better reflect intraoperative realities and should be integrated into future planning and navigation systems for anterior pelvic ring fixation. Declarations Funding Declaration: The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. References de Ridder VA, Whiting PS, Balogh ZJ et al (2023) Pelvic ring injuries: recent advances in diagnosis and treatment. OTA Int 6:e261. https://doi.org/10.1097/OI9.0000000000000261 Koval KJ, Aharonoff GB, Schwartz MC et al (1997) Pubic rami fracture: a benign pelvic injury? J Orthop Trauma 11:7–9. https://doi.org/10.1097/00005131-199701000-00003 Hill RM, Robinson CM, Keating JF (2001) Fractures of the pubic rami. Epidemiology and five-year survival. J Bone Joint Surg Br 83:1141–1144. https://doi.org/10.1302/0301-620x.83b8.11709 Eastman JG, Chip Routt ML (2018) Intramedullary Fixation Techniques for the Anterior Pelvic Ring. J Orthop Trauma 32:S4–S13. https://doi.org/10.1097/BOT.0000000000001250 Mosheiff R, Liebergall M (2002) Maneuvering the Retrograde Medullary Screw in Pubic Ramus Fractures. J Orthop Trauma 16:594–596. https://doi.org/10.1097/00005131-200209000-00009 Weatherby DJ, Chip Routt ML, Eastman JG (2017) The Retrograde-Antegrade-Retrograde Technique for Successful Placement of a Retrograde Superior Ramus Screw. J Orthop Trauma 31:e224–e229. https://doi.org/10.1097/BOT.0000000000000849 Yoon Y-C, Tucker NJ, Kim YJ et al (2024) Surgical complications after fixation of minimally displaced lateral compression type 1 pelvic ring injuries. Eur J Orthop Surg Traumatol Orthop Traumatol 34:3583–3590. https://doi.org/10.1007/s00590-024-03915-9 Starr AJ, Nakatani T, Reinert CM, Cederberg K (2008) Superior Pubic Ramus Fractures Fixed With Percutaneous Screws: What Predicts Fixation Failure? J Orthop Trauma 22:81–87. https://doi.org/10.1097/BOT.0b013e318162ab6e Lee C, Tilan J, Foster BD et al (2025) Determinants for successful medullary fixation of the superior ramus. Injury 56:112170. https://doi.org/10.1016/j.injury.2025.112170 Puchwein P, Enninghorst N, Sisak K et al (2012) Percutaneous fixation of acetabular fractures: computer-assisted determination of safe zones, angles and lengths for screw insertion. Arch Orthop Trauma Surg 132:805–811. https://doi.org/10.1007/s00402-012-1486-7 Boudissa M, Kerschbaumer G, Tonetti J (2025) Computer-assisted surgery and planning in percutaneous pelvic screw fixation. Orthop Traumatol Surg Res OTSR 104392. https://doi.org/10.1016/j.otsr.2025.104392 Suzuki T, Soma K, Shindo M et al (2008) Anatomic Study for Pubic Medullary Screw Insertion. J Orthop Surg 16:321–325. https://doi.org/10.1177/230949900801600311 Hadeed MM, Woods D, Koerner J et al (2022) Risk factors for screw breach and iatrogenic nerve injury in percutaneous posterior pelvic ring fixation. J Clin Orthop Trauma 33:101994. https://doi.org/10.1016/j.jcot.2022.101994 Scolaro JA, Routt ML (2013) Intraosseous correction of misdirected cannulated screws and fracture malalignment using a bent tip 2.0 mm guidewire: technique and indications. Arch Orthop Trauma Surg 133:883–887. https://doi.org/10.1007/s00402-013-1740-7 David G, Rony L, Moullac D et al (2024) The Metaizeau trick to facilitate medullary pubic ramus screw insertion: A technical note. Orthop Traumatol Surg Res OTSR 110:103879. https://doi.org/10.1016/j.otsr.2024.103879 Timmer RA, van der Zwaal P, Meylaerts SAG (2025) Accuracy of 3D-navigated screw fixation in pelvic ring fractures: a single-centre consecutive observational case series. Eur J Orthop Surg Traumatol 35:429. https://doi.org/10.1007/s00590-025-04541-9 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 13 Apr, 2026 Reviews received at journal 12 Apr, 2026 Reviews received at journal 01 Apr, 2026 Reviewers agreed at journal 22 Mar, 2026 Reviewers agreed at journal 19 Mar, 2026 Reviewers invited by journal 16 Mar, 2026 Editor assigned by journal 15 Mar, 2026 Submission checks completed at journal 13 Mar, 2026 First submitted to journal 12 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9108518","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":607195784,"identity":"15b8a77d-86ec-4fcb-86b7-a715afbdbc36","order_by":0,"name":"Guillaume DAVID","email":"data:image/png;base64,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","orcid":"","institution":"Centre Hospitalier Universitaire d'Angers","correspondingAuthor":true,"prefix":"","firstName":"Guillaume","middleName":"","lastName":"DAVID","suffix":""},{"id":607195785,"identity":"54a155a9-3dbf-4a87-92cf-7801d499d169","order_by":1,"name":"Thomas GRIMAUD","email":"","orcid":"","institution":"Centre Hospitalier Universitaire de Bordeaux","correspondingAuthor":false,"prefix":"","firstName":"Thomas","middleName":"","lastName":"GRIMAUD","suffix":""},{"id":607195786,"identity":"9b9dd3a0-95c4-4d53-8385-88e830ccaccf","order_by":2,"name":"Clément MARC","email":"","orcid":"","institution":"Centre Hospitalier Universitaire d'Angers","correspondingAuthor":false,"prefix":"","firstName":"Clément","middleName":"","lastName":"MARC","suffix":""},{"id":607195787,"identity":"91e6ee75-1e69-47bf-ac04-dbfea4698513","order_by":3,"name":"Vincent STEIGER","email":"","orcid":"","institution":"Centre Hospitalier Universitaire d'Angers","correspondingAuthor":false,"prefix":"","firstName":"Vincent","middleName":"","lastName":"STEIGER","suffix":""},{"id":607195788,"identity":"51a4c07b-3076-44d7-9b28-cac490dd2e7a","order_by":4,"name":"Louis RONY","email":"","orcid":"","institution":"Centre Hospitalier Universitaire d'Angers","correspondingAuthor":false,"prefix":"","firstName":"Louis","middleName":"","lastName":"RONY","suffix":""}],"badges":[],"createdAt":"2026-03-12 22:23:41","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9108518/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9108518/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104996454,"identity":"2e3980ea-9c2c-41f0-a9f6-de052fed80ac","added_by":"auto","created_at":"2026-03-19 16:14:40","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":8712360,"visible":true,"origin":"","legend":"\u003cp\u003eExample of CT-based rectilinear planning using a 6.5-mm cylindrical model. No safe trajectory could be identified, with simulated cortical breach along the medial aspect of the superior pubic ramus (white arrows) and intra-articular penetration of the acetabulum, as demonstrated on three-dimensional reconstruction (black arrow).\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-9108518/v1/efad245b3180ac59cbd5d556.png"},{"id":104996451,"identity":"3ba23d15-2720-4172-8445-99ed3560e259","added_by":"auto","created_at":"2026-03-19 16:14:40","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":5108710,"visible":true,"origin":"","legend":"\u003cp\u003eAnteroposterior fluoroscopic view showing a retrograde pubic ramus screw with progressive curvature after crossing the acetabular region. On the right, postoperative three-dimensional CT reconstruction of the same screw with superimposition of a straight 6.5-mm cylindrical model. A marked divergence between the implanted screw and the rectilinear model is observed distal to the acetabulum (white arrow), illustrating guidewire-driven trajectory adaptation within the intramedullary corridor.\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-9108518/v1/ab792932f2a1b854d77a3186.png"},{"id":105034995,"identity":"26d40410-199a-4a58-974c-66335af0e93e","added_by":"auto","created_at":"2026-03-20 07:25:09","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":7346484,"visible":true,"origin":"","legend":"\u003cp\u003eSame patient as in Figure 1. On the left, anteroposterior fluoroscopic view demonstrating bilateral superior pubic ramus screws accurately positioned. In the center, postoperative CT scan showing the screw located within the intramedullary corridor at a safe distance from the acetabular joint, without cortical breach. On the right, CT-based planning using a 5-mm cylindrical model corresponding to the screw core diameter, demonstrating a feasible intramedullary corridor despite the absence of a feasible trajectory using a 6.5-mm rectilinear model.\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-9108518/v1/cc1d278958f598a7f7e3d8bc.png"},{"id":105035045,"identity":"796895d9-0071-472f-b4ba-2fb669b8771f","added_by":"auto","created_at":"2026-03-20 07:25:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":7654982,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative LC-1 pelvic injury, illustrating the unique case in which no rectilinear corridor could be identified even using a core-diameter model.\u003cbr\u003e\nTop left: CT-based rectilinear planning on the uninjured left side using a 6.5-mm cylindrical model, demonstrating absence of a safe intramedullary corridor.\u003cbr\u003e\nTop center: Preoperative anteroposterior pelvic radiograph.\u003cbr\u003e\nTop right: CT-based planning on the uninjured side using a 5-mm cylindrical model corresponding to the screw core diameter, again demonstrating no feasible rectilinear corridor.\u003cbr\u003e\nBottom: Postoperative anteroposterior (left) and inlet (right) radiographs showing accurate reduction and stable fixation despite the absence of a rectilinear corridor on preoperative planning.\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-9108518/v1/b827aee5d3342d454bf8baa4.png"},{"id":104996452,"identity":"1f199dc7-ac0b-46b3-bd79-b12ebaf111de","added_by":"auto","created_at":"2026-03-19 16:14:40","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1908265,"visible":true,"origin":"","legend":"\u003cp\u003ePostoperative CT analysis of the same patient as in Figure 4, illustrating a markedly non-rectilinear screw trajectory.\u003cbr\u003e\nTop left: Axial CT slice through the right superior pubic ramus demonstrating a curved intramedullary screw trajectory.\u003cbr\u003e\nBottom left: Series of orthogonal CT cross-sections obtained along the axis of the superior pubic ramus from the pubic symphysis to the acetabular roof, showing the screw entirely contained within a narrow intramedullary corridor, at a safe distance from the joint and without cortical breach.\u003cbr\u003e\nRight: Three-dimensional reconstruction of the implanted screw with superimposition of a straight 6.5-mm cylindrical model. A pronounced divergence between the actual screw trajectory and the rectilinear model is observed distal to the symphysis (white arrow), illustrating a degree of trajectory curvature that cannot be approximated by any straight cylindrical planning model.\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-9108518/v1/f6f351c8d205ae5213be6f9f.png"},{"id":104996453,"identity":"ba52a85a-0d14-49b4-bb94-fb82669ec933","added_by":"auto","created_at":"2026-03-19 16:14:40","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":5190203,"visible":true,"origin":"","legend":"\u003cp\u003eIllustration of partial-threaded screw strategy in a fluoroscopy-guided retrograde pubic ramus \u0026nbsp;fixation. Left: Anteroposterior radiograph showing a retrograde 7.3-mm partially threaded screw, with the threaded portion positioned in the acetabular roof, well away from the joint. Top right: CT-based rectilinear planning using a 7.3-mm cylindrical model demonstrating the absence of a feasible intramedullary corridor, with simulated cortical breach.\u003cbr\u003e\nBottom right: CT-based planning using a 5-mm cylindrical model corresponding to the screw core diameter, demonstrating a feasible intramedullary corridor without cortical violation or false passage. This example illustrates that partial threading allows the narrowest and highest-risk segment of the corridor to be traversed by the screw core alone, while the larger-diameter threaded portion is positioned in a wider, cancellous and safer region of the ramus.\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-9108518/v1/c5a697d805a8228d5e2dfa60.png"},{"id":105036868,"identity":"137b2574-33a0-4a12-997a-64b3a5626cf6","added_by":"auto","created_at":"2026-03-20 07:36:27","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":33663186,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9108518/v1/93588c3b-2ecc-42c6-8bd1-f1fb6b150768.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Limitations of CT-Based Planning in Anterior Pelvic Ring Fixation: A Study of Fluoroscopy-Guided Pubic Ramus Screws","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePercutaneous screw fixation of superior pubic ramus fractures is a widely accepted technique for stabilizing anterior pelvic ring injuries while limiting surgical morbidity.[\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] Despite its advantages, accurate screw placement remains technically demanding because the intramedullary pathway of the pubic ramus is narrow, curved, and highly variable.[\u003cspan additionalcitationids=\"CR5 CR6 CR7\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] To assess feasibility and minimize the risk of cortical breach or intra-articular penetration, preoperative CT-based planning is commonly used to identify an osseous corridor suitable for screw insertion.[\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eMost CT-based planning and navigation systems rely on rectilinear geometric assumptions, defining feasibility by the presence of a straight cylindrical corridor capable of accommodating a screw of predefined diameter. Using this approach, several CT simulation studies have reported limited feasibility rates. Lee et al.[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] demonstrated that only 35% of patients could accommodate a 6.5-mm screw along a straight corridor and only 21.5% a 7.3-mm screw; notably, 12.9% of women were deemed unable to accept even a 3.5-mm screw. These findings suggest that strict rectilinear CT-based criteria may exclude a substantial proportion of patients from percutaneous anterior pelvic ring fixation.\u003c/p\u003e \u003cp\u003eSeveral methodological and biomechanical factors may contribute to this apparent limitation. First, feasibility is typically assessed using the outer thread diameter of the implant, although the risk of cortical violation is primarily determined by the screw core.[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] For commonly used 6.5-mm and 7.3-mm cannulated screws, the core diameter remains approximately 5 mm, while the increase in nominal diameter mainly reflects larger thread geometry. In narrow segments of the pubic ramus, particularly near the acetabular joint, planning based on thread diameter may therefore be overly restrictive.[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] In this context, the use of partially threaded screws allows the most constrained portion of the corridor to be traversed by the core alone, while threads engage wider cancellous regions, a strategy that is not captured by conventional CT planning models.\u003c/p\u003e \u003cp\u003eSecond, rectilinear CT planning does not account for the intraoperative behavior of flexible guidewires. During fluoroscopy-guided cannulated screws insertion, guidewires may progressively adapt their trajectory within the intramedullary canal, undergoing controlled elastic deformation when encountering areas of denser cortical bone. The definitive screw subsequently follows this guidewire-defined path. Such non-rectilinear trajectories, potentially accentuated by the elastic properties of titanium implants, cannot be represented by straight-line CT-based planning or navigation systems.\u003c/p\u003e \u003cp\u003eThe clinical relevance of these limitations remains insufficiently quantified. Specifically, it is unclear what proportion of screws successfully inserted under fluoroscopic guidance would have been classified as infeasible using standard CT-based rectilinear analysis, and whether postoperative three-dimensional reconstructions demonstrate screw trajectories that depart from idealized straight paths assumed during planning.\u003c/p\u003e \u003cp\u003eThe primary objective of this study was therefore to determine the proportion of fluoroscopically inserted pubic ramus screws that could not have been predicted as feasible using conventional CT-based rectilinear planning criteria based on outer thread diameter. Secondary objectives were to assess interobserver reliability for feasibility assessment, to evaluate the impact of core-diameter\u0026ndash;based planning on feasibility classification, and to analyze postoperative three-dimensional screw trajectories to determine whether they reflect non-rectilinear pathways incompatible with current CT-based planning and navigation paradigms. We hypothesized that a substantial proportion of accurately positioned pubic ramus screws would not be predicted by standard rectilinear CT planning, highlighting intrinsic limitations of current CT-based planning strategies in anterior pelvic ring fixation.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy Design and Patient Selection\u003c/h2\u003e \u003cp\u003eA retrospective cohort study was conducted at a Level I trauma center. All consecutive patients who underwent fluoroscopy-guided percutaneous screw fixation of superior pubic ramus fractures between January 2022 and December 2025 were screened for inclusion. Institutional review board approval was obtained. The requirement for informed consent was waived due to the retrospective observational design of the study. Patients were eligible if both a complete preoperative pelvic CT scan and a postoperative CT scan were available, allowing assessment of preoperative feasibility and postoperative screw positioning. Patients with incomplete imaging datasets were excluded.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePreoperative CT-Based Planning\u003c/h3\u003e\n\u003cp\u003eFor each included patient, preoperative CT scans were independently reviewed by two independent fellowship-trained pelvic and acetabular surgeons. Observers were blinded to intraoperative findings and postoperative imaging. Preoperative CT-based planning and postoperative three-dimensional reconstructions were performed using dedicated imaging software (Synapse 3D, Fujifilm, Tokyo, Japan). CT-based feasibility assessment was performed according to the rectilinear planning methodology described in previously published CT simulation studies. Briefly, a straight cylindrical model (6.5 mm and 7.3 mm diameter) was manually positioned along the intramedullary axis of the superior pubic ramus on multiplanar reconstructions and three-dimensional views. Feasibility was defined as the ability to place a straight cylinder corresponding to the outer thread diameter of the intended screw entirely within cancellous bone, without cortical breach or intra-articular penetration along its full length. Each corridor was classified as either feasible or infeasible. Interobserver agreement was subsequently assessed. \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eSurgical Technique and Postoperative Assessment\u003c/h3\u003e\n\u003cp\u003eAll procedures were performed using fluoroscopy-guided percutaneous techniques according to standard institutional practice. Postoperative CT scans were reviewed to assess final screw positioning. Screws were evaluated for cortical breach, intra-articular penetration, or neurovascular compromise. Screws meeting none of these criteria were considered accurately positioned.\u003c/p\u003e\n\u003ch3\u003eAnalysis of Discrepant Cases\u003c/h3\u003e\n\u003cp\u003eCases in which screws were classified as infeasible on preoperative rectilinear CT planning but demonstrated accurate postoperative positioning were further analyzed to explore potential explanations for this discrepancy.\u003c/p\u003e \u003cp\u003eFirst, postoperative three-dimensional reconstructions were used to compare the actual screw trajectory with a straight cylindrical model corresponding to the same outer thread diameter. This analysis aimed to assess whether the implanted screw deviated from a rectilinear path, suggesting progressive adaptation of the trajectory during fluoroscopic insertion. \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSecond, preoperative CT planning was repeated using a straight cylindrical model corresponding to the core diameter of the implanted screw (5 mm) rather than the outer thread diameter. \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e Feasibility classification using this alternative criterion was recorded and compared with the original planning results to determine whether core-diameter\u0026ndash;based planning improved concordance with postoperative findings.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eOutcome Measures\u003c/h3\u003e\n\u003cp\u003eThe primary outcome was the proportion of pubic ramus screws that would have been classified as infeasible based on standard CT-based rectilinear planning using outer thread diameter criteria. Secondary outcomes included interobserver reliability for corridor feasibility assessment, postoperative screw positioning accuracy, and the effect of core-diameter\u0026ndash;based planning on feasibility classification.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eStatistical Analysis\u003c/h2\u003e \u003cp\u003eGiven the descriptive nature of the study, analyses were primarily descriptive. Categorical variables were reported as frequencies and percentages. Interobserver agreement for CT-based feasibility assessment was evaluated using Cohen\u0026rsquo;s kappa coefficient. Statistical analyses were performed using using R software, version 3.6.1 (R Foundation for Statistical Computing)\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eThirty-three patients with 42 fluoroscopy-guided percutaneous pubic ramus screws were included, including both 6.5-mm and 7.3-mm screws. Using standard CT-based rectilinear planning based on the outer thread diameter corresponding to the implanted screw, 27 screws (64%) were classified as feasible, whereas 15 screws (36%) were deemed infeasible by consensus between the two observers. Interobserver agreement for feasibility assessment was high (κ = 0.89 for the 6.5-mm model and κ = 0.81 for the 7.3-mm model). \u003cstrong\u003e(\u003c/strong\u003eTable\u0026nbsp;1\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 1\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eCT-Based Planning Feasibility and Postoperative Outcomes for Pubic Ramus Screws\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"2\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eVariable\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eValue\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePatients, n\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e33\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eScrews, n\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e42\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eScrew diameter\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.5 mm and 7.3 mm\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFeasible (CT rectilinear planning)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27 (64%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot feasible (CT rectilinear planning)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15 (36%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eInterobserver agreement\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eκ = 0.89 (6.5 mm); κ = 0.81 (7.3 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAccurate postoperative positioning\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e42 (100%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCortical breach\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eIntra-articular penetration\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNeurovascular complication\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFixation-related revision surgery\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003eLegend table 1\u003c/strong\u003e: \u0026nbsp;CT-based feasibility was assessed using rectilinear planning models corresponding to the outer thread diameter of the implanted screw (6.5 or 7.3 mm). Accurate positioning was defined as the absence of cortical breach, intra-articular penetration, or neurovascular complication on postoperative CT imaging.\u003c/p\u003e\n\u003cp\u003ePostoperative CT imaging demonstrated accurate screw positioning in all cases (100%), with no cortical breach, intra-articular penetration, neurovascular complication, or fixation-related revision surgery. All screws classified as infeasible on preoperative CT planning were successfully inserted and correctly positioned postoperatively. \u003cstrong\u003e(\u003c/strong\u003eTable\u0026nbsp;2\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 2\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eEffect of Core-Diameter–Based Planning in Screws Classified as Infeasible on Standard CT Planning\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"2\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eVariable\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eValue\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eScrews classified as infeasible (thread diameter)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCore diameter used for reassessment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5 mm\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eReclassified as feasible with core planning\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14 (93%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRemaining infeasible with core planning\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePostoperative positioning accuracy in this subgroup\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e100%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003eLegend table 2\u003c/strong\u003e: Among screws initially classified as infeasible using standard CT-based rectilinear planning based on outer thread diameter, feasibility was reassessed using a straight cylindrical model corresponding to the screw core diameter (5 mm). Fourteen of fifteen screws were reclassified as feasible. One screw remained infeasible despite accurate postoperative intramedullary positioning, reflecting a markedly non-rectilinear trajectory.\u003c/p\u003e\n\u003cp\u003eAmong the 15 screws initially classified as infeasible using thread-diameter–based rectilinear planning, all were partially threaded implants. Reassessment using a core-diameter–based (5 mm) cylindrical model reclassified 14 screws (93%) as feasible. One screw, implanted with a 6.5-mm diameter, remained classified as infeasible even with core-diameter–based planning despite accurate postoperative intramedullary positioning. In this case, postoperative three-dimensional reconstruction demonstrated a markedly non-rectilinear screw trajectory that could not be encompassed by any straight cylindrical model, illustrating an extreme example of guidewire-driven trajectory adaptation. \u003cstrong\u003e(\u003c/strong\u003eFigs.\u0026nbsp;4 and 5\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe present study demonstrates that standard CT-based rectilinear planning substantially underestimates the feasibility of fluoroscopy-guided pubic ramus screw fixation. More than one third of screws in this cohort would have been classified as infeasible using conventional CT planning criteria based on outer thread diameter, yet all were accurately positioned postoperatively without complication. These findings highlight intrinsic limitations of current planning paradigms and suggest that feasibility is governed by additional geometric and implant-related factors that are not captured by straight-line CT analysis.\u003c/p\u003e \u003cp\u003eA first key finding is the impact of implant geometry on feasibility assessment. Conventional CT planning relies on the outer thread diameter of the screw, implicitly assuming that the entire threaded portion must remain fully intramedullary along the narrowest segment of the corridor. However, between 6.5-mm and 7.3-mm screws, the increase in nominal diameter is primarily related to the size of the threads rather than the core, which remains constant at approximately 5 mm. From a biomechanical and anatomical standpoint, cortical violation risk is determined by the position of the core rather than the thread crests.[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eIn corridors that are narrow or closely adjacent to the acetabular joint, especially near the most constrained portions of the superior pubic ramus, planning based on thread diameter may therefore be overly restrictive. In such situations, the use of partially threaded screws allows the narrowest segment of the corridor to be traversed by the core alone, while the threaded portion is positioned in wider cancellous regions. This consideration is particularly relevant for 7.3-mm screws, for which thread diameter disproportionately increases relative to the core. In the present study, reassessment using a core-diameter\u0026ndash;based planning model improved concordance between preoperative feasibility assessment and postoperative outcomes in the vast majority of cases, supporting the concept that planning based on the screw core better reflects clinical reality. Based on these observations, our current practice has shifted toward preferential use of partially threaded screws, except in cases where preoperative planning demonstrates a sufficiently wide intramedullary corridor. In both antegrade and retrograde fixation, this strategy allows the narrowest and highest-risk segment of the corridor, adjacent to the joint and neurovascular structures, to be traversed by the 5-mm core alone. \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA second major mechanism underlying the discrepancy between CT planning and intraoperative feasibility relates to screw trajectory geometry. Standard CT-based planning assumes a rigid, rectilinear trajectory, whereas fluoroscopy-guided insertion relies on a flexible guidewire that can progressively adapt its path within the intramedullary canal.[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] As demonstrated by postoperative three-dimensional reconstructions in this study, several screws followed non-rectilinear trajectories that could not be fully encompassed by a straight cylindrical model corresponding to the outer thread diameter. Notably, in one case, even core-diameter\u0026ndash;based rectilinear planning failed to predict feasibility, despite accurate intramedullary screw placement. In this instance, the implanted 6.5-mm screw demonstrated a markedly curved trajectory on postoperative three-dimensional reconstruction, reflecting substantial guidewire deformation within the corridor. \u003cb\u003e(\u003c/b\u003eFigs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e This extreme example illustrates that feasibility may occasionally depend on trajectories that cannot be approximated by any straight cylindrical model, regardless of diameter, further emphasizing the intrinsic limitations of rectilinear planning assumptions.\u003c/p\u003e \u003cp\u003eThis phenomenon likely reflects guidewire behavior at the bone\u0026ndash;implant interface. When encountering areas of denser cortical bone, the guidewire may undergo controlled elastic deformation, gradually redirecting its trajectory toward available cancellous pathways.[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] The definitive screw subsequently follows the established guidewire path. This effect is expected to be more pronounced with titanium screws compared with stainless steel implants, given their greater elasticity. The superposition of curved implanted screw trajectories and rectilinear cylindrical models in this study visually illustrates this limitation of straight-line planning and supports the concept of non-rectilinear \u0026ldquo;functional corridors\u0026rdquo; during fluoroscopy-guided fixation. These observations also support the concept of implants designed to better accommodate curved intramedullary pathways. By allowing controlled implant curvature along a guidewire-defined trajectory, such devices may better adapt to the complex anatomy of the pubic ramus and expand the indications for percutaneous fixation in anatomically constrained corridors.\u003c/p\u003e \u003cp\u003eThese findings have important implications for the development and clinical use of navigation systems in anterior pelvic ring fixation. Current navigation platforms are fundamentally based on rectilinear trajectories defined on intraoperative CT scans.[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] While such systems may accurately identify optimal entry points and reduce variability in starting position for anterior column screw, they are inherently unable to account for curved or progressively adjusted trajectories enabled by guidewire flexibility. As a result, navigation may falsely classify certain corridors as infeasible, potentially discouraging percutaneous fixation in cases that are technically achievable under fluoroscopic guidance.\u003c/p\u003e \u003cp\u003eRather than negating the value of navigation, the present results suggest that future planning and navigation tools should integrate more flexible geometric models, incorporating core-diameter\u0026ndash;based constraints and allowing for non-rectilinear trajectories. Such developments could improve feasibility prediction while preserving the advantages of navigation for entry-point selection and spatial orientation.\u003c/p\u003e \u003cp\u003eThis study has several limitations. Its retrospective design may introduce selection bias, and the analysis was performed at a single Level I trauma center with surgeons experienced in fluoroscopy-guided pelvic fixation. The absence of complications limits comparative statistical analysis but reflects the safety of the technique in this cohort. Finally, non-rectilinear trajectories were assessed qualitatively rather than quantified by curvature metrics, although three-dimensional reconstructions clearly demonstrated deviations from straight-line planning assumptions.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eStandard CT-based rectilinear planning underestimates the feasibility of fluoroscopy-guided pubic ramus screw fixation. Planning based on outer thread diameter and rigid trajectories fails to account for implant geometry, partial threading strategies, and guidewire-driven non-rectilinear pathways. Core-diameter\u0026ndash;based planning and consideration of functional screw trajectories may better reflect intraoperative realities and should be integrated into future planning and navigation systems for anterior pelvic ring fixation.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding Declaration:\u0026nbsp;\u003c/strong\u003eThe authors declare that no funds, grants, or other support were received during the preparation of this manuscript.\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003ede Ridder VA, Whiting PS, Balogh ZJ et al (2023) Pelvic ring injuries: recent advances in diagnosis and treatment. OTA Int 6:e261. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1097/OI9.0000000000000261\u003c/span\u003e\u003cspan address=\"10.1097/OI9.0000000000000261\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKoval KJ, Aharonoff GB, Schwartz MC et al (1997) Pubic rami fracture: a benign pelvic injury? J Orthop Trauma 11:7\u0026ndash;9. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1097/00005131-199701000-00003\u003c/span\u003e\u003cspan address=\"10.1097/00005131-199701000-00003\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHill RM, Robinson CM, Keating JF (2001) Fractures of the pubic rami. Epidemiology and five-year survival. J Bone Joint Surg Br 83:1141\u0026ndash;1144. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1302/0301-620x.83b8.11709\u003c/span\u003e\u003cspan address=\"10.1302/0301-620x.83b8.11709\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEastman JG, Chip Routt ML (2018) Intramedullary Fixation Techniques for the Anterior Pelvic Ring. J Orthop Trauma 32:S4\u0026ndash;S13. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1097/BOT.0000000000001250\u003c/span\u003e\u003cspan address=\"10.1097/BOT.0000000000001250\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMosheiff R, Liebergall M (2002) Maneuvering the Retrograde Medullary Screw in Pubic Ramus Fractures. J Orthop Trauma 16:594\u0026ndash;596. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1097/00005131-200209000-00009\u003c/span\u003e\u003cspan address=\"10.1097/00005131-200209000-00009\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWeatherby DJ, Chip Routt ML, Eastman JG (2017) The Retrograde-Antegrade-Retrograde Technique for Successful Placement of a Retrograde Superior Ramus Screw. J Orthop Trauma 31:e224\u0026ndash;e229. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1097/BOT.0000000000000849\u003c/span\u003e\u003cspan address=\"10.1097/BOT.0000000000000849\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYoon Y-C, Tucker NJ, Kim YJ et al (2024) Surgical complications after fixation of minimally displaced lateral compression type 1 pelvic ring injuries. Eur J Orthop Surg Traumatol Orthop Traumatol 34:3583\u0026ndash;3590. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00590-024-03915-9\u003c/span\u003e\u003cspan address=\"10.1007/s00590-024-03915-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStarr AJ, Nakatani T, Reinert CM, Cederberg K (2008) Superior Pubic Ramus Fractures Fixed With Percutaneous Screws: What Predicts Fixation Failure? J Orthop Trauma 22:81\u0026ndash;87. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1097/BOT.0b013e318162ab6e\u003c/span\u003e\u003cspan address=\"10.1097/BOT.0b013e318162ab6e\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee C, Tilan J, Foster BD et al (2025) Determinants for successful medullary fixation of the superior ramus. Injury 56:112170. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.injury.2025.112170\u003c/span\u003e\u003cspan address=\"10.1016/j.injury.2025.112170\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePuchwein P, Enninghorst N, Sisak K et al (2012) Percutaneous fixation of acetabular fractures: computer-assisted determination of safe zones, angles and lengths for screw insertion. Arch Orthop Trauma Surg 132:805\u0026ndash;811. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00402-012-1486-7\u003c/span\u003e\u003cspan address=\"10.1007/s00402-012-1486-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBoudissa M, Kerschbaumer G, Tonetti J (2025) Computer-assisted surgery and planning in percutaneous pelvic screw fixation. Orthop Traumatol Surg Res OTSR 104392. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.otsr.2025.104392\u003c/span\u003e\u003cspan address=\"10.1016/j.otsr.2025.104392\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSuzuki T, Soma K, Shindo M et al (2008) Anatomic Study for Pubic Medullary Screw Insertion. J Orthop Surg 16:321\u0026ndash;325. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1177/230949900801600311\u003c/span\u003e\u003cspan address=\"10.1177/230949900801600311\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHadeed MM, Woods D, Koerner J et al (2022) Risk factors for screw breach and iatrogenic nerve injury in percutaneous posterior pelvic ring fixation. J Clin Orthop Trauma 33:101994. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jcot.2022.101994\u003c/span\u003e\u003cspan address=\"10.1016/j.jcot.2022.101994\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eScolaro JA, Routt ML (2013) Intraosseous correction of misdirected cannulated screws and fracture malalignment using a bent tip 2.0 mm guidewire: technique and indications. Arch Orthop Trauma Surg 133:883\u0026ndash;887. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00402-013-1740-7\u003c/span\u003e\u003cspan address=\"10.1007/s00402-013-1740-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDavid G, Rony L, Moullac D et al (2024) The Metaizeau trick to facilitate medullary pubic ramus screw insertion: A technical note. Orthop Traumatol Surg Res OTSR 110:103879. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.otsr.2024.103879\u003c/span\u003e\u003cspan address=\"10.1016/j.otsr.2024.103879\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTimmer RA, van der Zwaal P, Meylaerts SAG (2025) Accuracy of 3D-navigated screw fixation in pelvic ring fractures: a single-centre consecutive observational case series. Eur J Orthop Surg Traumatol 35:429. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00590-025-04541-9\u003c/span\u003e\u003cspan address=\"10.1007/s00590-025-04541-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"european-journal-of-orthopaedic-surgery-and-traumatology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ejos","sideBox":"Learn more about [European Journal of Orthopaedic Surgery \u0026 Traumatology](http://link.springer.com/journal/590)","snPcode":"590","submissionUrl":"https://submission.springernature.com/new-submission/590/3","title":"European Journal of Orthopaedic Surgery \u0026 Traumatology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Pubic ramus fracture, Anterior pelvic ring, Percutaneous screw fixation, Computed tomography planning, Surgical navigation","lastPublishedDoi":"10.21203/rs.3.rs-9108518/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9108518/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eCurrent 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.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eWe 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.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThirty-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.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eStandard 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.\u003c/p\u003e\u003ch2\u003eLevel of Evidence\u003c/h2\u003e \u003cp\u003eLevel IV, therapeutic study.\u003c/p\u003e","manuscriptTitle":"Limitations of CT-Based Planning in Anterior Pelvic Ring Fixation: A Study of Fluoroscopy-Guided Pubic Ramus Screws","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-19 16:14:35","doi":"10.21203/rs.3.rs-9108518/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-13T09:36:42+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-12T06:55:52+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-01T14:12:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"35327738069211569954845889716703519804","date":"2026-03-22T15:40:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"41270220112868659813211988883846415378","date":"2026-03-19T09:58:48+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-16T22:01:03+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-15T17:40:36+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-13T14:39:22+00:00","index":"","fulltext":""},{"type":"submitted","content":"European Journal of Orthopaedic Surgery \u0026 Traumatology","date":"2026-03-12T22:05:47+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"european-journal-of-orthopaedic-surgery-and-traumatology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ejos","sideBox":"Learn more about [European Journal of Orthopaedic Surgery \u0026 Traumatology](http://link.springer.com/journal/590)","snPcode":"590","submissionUrl":"https://submission.springernature.com/new-submission/590/3","title":"European Journal of Orthopaedic Surgery \u0026 Traumatology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"d44e95bd-799a-4f54-bb71-fe0ec62e3b75","owner":[],"postedDate":"March 19th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-13T12:25:24+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-19 16:14:35","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9108518","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9108518","identity":"rs-9108518","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}