Overcoming CT Registration Failures in Robotic Spine Surgery: A Lateral Fiducial Positioning Technique for Obese Patients

Overcoming CT Registration Failures in Robotic Spine Surgery: A Lateral Fiducial Positioning Technique for Obese Patients | 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 Overcoming CT Registration Failures in Robotic Spine Surgery: A Lateral Fiducial Positioning Technique for Obese Patients Abhishek Soni, Vidyadhara S, Balamurugan T, Alia Vidyadhara This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7253011/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Purpose CT registration failure represents a critical barrier excluding severely obese patients from robotic-assisted spine surgery (RASS) benefits. This study validates a novel lateral fiducial positioning technique to overcome field-of-view limitations that cause registration failures in patients with BMI > 40 kg/m², addressing the geometric incompatibility between obese patient size and current imaging constraints. Methods Retrospective analysis of 54 consecutive patients (BMI > 40 kg/m²) undergoing RASS using MazorX Stealth Edition with intraoperative O-arm imaging between October 2023 and November 2024. Lateral fiducial positioning repositioned markers along the patient's flank when standard central positioning demonstrated inadequate visualization on scout images, utilizing O-arm's asymmetric field-of-view (40 cm lateral vs. 15 cm sagittal coverage). Primary outcome was first-attempt registration success rate. Results Mean BMI was 43.6 ± 2.7 kg/m² (range 40.3–51.0). First-attempt registration success was achieved in 45/54 cases (83.3%, 95% CI: 72.1%-91.4%). Lateral positioning was used in 16 cases (29.6%) with significantly higher success rates versus standard positioning (93.8% vs 78.9%, P = 0.043). Ultimate registration success was 100%. Patients requiring reattempts had longer O-arm acquisition times (32.6 vs 19.2 minutes, P < 0.001) and higher radiation exposure (66.6 vs 38.0 units, P < 0.001). Optimal pedicle screw placement (Gertzbein-Robbins Grade A + B) was achieved in 97.6% of 288 screws. Conclusion Lateral fiducial positioning eliminates CT registration failures in severely obese patients undergoing robotic spine surgery, achieving 100% ultimate registration success while maintaining surgical accuracy. This immediately implementable technique expands robotic surgery access to high-BMI patients without requiring additional equipment, ensuring obesity alone does not preclude patients from precision robotic assistance benefits. Thoracolumbar spine Obesity Robotic surgery CT registration Pedicle screw Figures Figure 1 INTRODUCTION Robotic-assisted spine surgery (RASS) has demonstrated superior pedicle screw placement accuracy and reduced radiation exposure since the first FDA-cleared system introduction in 2004 [ 1 – 3 ]. However, CT registration failure represents a critical challenge limiting RASS implementation, with registration errors contributing significantly to failed screws across various robotic platforms [ 3 , 4 ]. The Obesity Challenge in Robotic Spine Surgery The global obesity epidemic has altered the spine surgery practice, with obesity rates creating technical challenges including increased operative complexity, blood loss, and complication rates [ 5 – 7 ]. In obese patients undergoing RASS, CT registration encounters predictable geometric constraints that frequently result in procedure abandonment. The technical challenge stems from asymmetric field-of-view limitations of current imaging systems: the O-arm provides 40 cm lateral coverage versus only 15 cm sagittal coverage for 3D imaging [ 8 ]. When combined patient anterior-posterior diameter plus standard central fiducial marker positioning exceeds this 15 cm sagittal limitation, registration failure is certain. Despite the growing population of obese patients requiring spine surgery, current robotic platforms face technical limitations when treating high-BMI patients. Registration failures due to FOV constraints and imaging quality degradation represent a significant barrier to accessing robotic assistance, creating an unmet clinical need for patients who could benefit most from enhanced surgical precision. Literature Gap and Clinical Need Despite growing numbers of obese patients requiring spine surgery, current robotic platforms face technical limitations when treating high-BMI patients. The clinical consequences of registration failure are: conversion to fluoroscopic-guided or freehand techniques, prolonged operative times, increased radiation exposure, and exclusion of obese patients from the precision and safety benefits of robotic assistance [ 9 ]. This represents an unmet clinical need, as the population most likely to benefit from robotic precision are those with challenging anatomy and higher complication risks, but are deprived of this technology. Innovation and Objectives This study addresses the critical gap by developing and validating a novel lateral fiducial positioning technique designed to overcome the specific geometric constraints causing registration failure in obese patients. This study aims to: (1) systematically evaluate CT registration challenges in consecutive patients with BMI > 40 kg/m² undergoing robotic-assisted spine surgery, (2) validate the efficacy of the lateral fiducial positioning technique in overcoming field-of-view limitations, and (3) provide evidence-based protocols with reproducible technical guidelines that spine surgeons can immediately implement to expand robotic surgery access to high-BMI patients. By addressing the geometric constraints that have historically excluded obese patients from robotic assistance, this research provides a practical solution to a well-known clinical problem, potentially expanding access to precision spine surgery for a rapidly growing patient population. METHODS Study Design and Setting This retrospective single-center consecutive case series was conducted between October 16, 2023, and November 30, 2024, in compliance with the Declaration of Helsinki. The study protocol was approved by the Institutional Ethics Committee (IRB No. ECR/34/Inst/KA/2013/RR-19) with waived informed consent due to retrospective nature and minimal risk. The study adhered to STROBE reporting standards. All procedures utilized the MazorX Stealth Edition robotic system (Medtronic, Minneapolis, MN) with intraoperative O-arm imaging for the Scan-and-Plan workflow. Patient Selection Inclusion criteria comprised consecutive patients undergoing robotic-assisted thoracolumbar fusion procedures with BMI > 40 kg/m², utilizing intraoperative O-arm scanning with the Scan-and-Plan workflow, and having postoperative CT imaging performed. Exclusion criteria included non-robotic surgery, alternative workflows such as CT-fluoroscopy registration, BMI ≤ 40 kg/m², abandoned robotic procedures, and absence of postoperative CT imaging. Surgical Protocol All procedures utilized the MazorX Stealth Edition robotic system (Medtronic, Minneapolis, MN) with O-arm O2 imaging (Medtronic, Minneapolis, MN) following the Scan-and-Plan workflow. Patients were positioned prone on specialized spine tables (Allen Advance Table, Hill-Rom, Chicago, IL) with > 272 kg capacity. A standardized technical protocol was developed for high-BMI patients addressing fiducial marker placement, robotic docking, pre-scan verification, and imaging optimization. Complete technical details are provided in Supplementary Material (S1). Fiducial Marker Positioning Protocol Decision Algorithm for Lateral Positioning The choice between standard central positioning and lateral fiducial positioning was determined intraoperatively using systematic pre-scan verification with orthogonal 2D scout images (anteroposterior and lateral views). Lateral positioning was employed when scout images demonstrated inadequate visualization of fiducial markers, defined as inability to clearly identify all 4 radio-opaque beads in both anteroposterior (AP) and lateral orthogonal views due to FOV limitations. Standard Positioning Fiducial markers were positioned centrally over the midline, positioned as close to skin as possible. Lateral Positioning When scout images indicated FOV limitations, fiducial markers were repositioned laterally along the patient's flank, moving the marker away from the central spine position toward the patient's side. This technique utilizes the O-arm's asymmetric FOV capabilities (40 cm lateral coverage vs. 15 cm sagittal coverage) by positioning the marker laterally while maintaining visualization of both spinal anatomy and fiducial beads within the scan volume. This positioning is shown in Fig. 1 . Technical Specifications Imaging Parameters O-arm radiation settings were standardized at kVp 120.00, mAs 186.25 with Low to Medium dose selection to prevent fiducial marker oversaturation. Field-of-view selection utilized standard 20 cm diameter × 15 cm height for initial attempts, with large 40 cm diameter × 15 cm height when lateral positioning was required. O-arm was positioned centered between spine midline and lateral marker position for optimal coverage. Modifications for High-BMI Patients : The protocol incorporated specific modifications including: (1) fiducial marker positioned as close to skin as possible, (2) intraoperative decision for lateral marker repositioning based on scout image assessment, (3) conservative radiation settings to prevent marker oversaturation, and (4) systematic pre-scan verification using orthogonal 2D scout images. Complete technical details and implementation protocols are provided in Supplementary Material (S1). Outcome Measures Primary Outcome First-attempt O-arm registration success rate, defined as successful automatic fiducial detection and registration on initial 3D scan acquisition. Secondary Outcomes Secondary outcomes included ultimate registration success rate (including successful reattempts), total operative time (skin incision to closure), O-arm acquisition time (from initial scout images to successful registration), pedicle screw accuracy assessed using Gertzbein-Robbins Grade A + B criteria on postoperative CT imaging [ 10 ], radiation exposure (measured in standard institutional units), registration reattempt requirements and failure modes, and perioperative complications. Registration Failure Classification : Primary failure modes were categorized as: (1) inadequate FOV coverage, (2) fiducial marker oversaturation, (3) poor anatomical landmark visualization, or (4) technical/software issues. Statistical Analysis This consecutive case series analysis presents continuous variables as mean ± standard deviation with ranges. Categorical variables are reported as frequencies and percentages with 95% confidence intervals. Comparisons between groups (first-attempt success vs. registration reattempt, standard vs. lateral positioning, BMI categories) were performed using Student's t-test for continuous variables and Fisher's exact test for categorical variables. Spearman rank correlation assessed relationships between BMI and surgical variables. Statistical significance was set at P < 0.05. All analyses were performed using IBM SPSS Statistics for Windows, version 27 (IBM Corp., Armonk, N.Y., USA). Formal sample size calculations were not performed for this consecutive case series. The study period was designed to capture all eligible patients meeting inclusion criteria during the institutional implementation of the lateral positioning technique. Given the exploratory nature of this technical modification and the lack of prior data on registration failure rates in this specific population (BMI > 40 kg/m²), a pragmatic approach was taken to include all consecutive cases over a defined period to establish preliminary efficacy and safety data. The 54 patients represent the complete experience during the study period, providing a representative sample of high-BMI patients undergoing robotic spine surgery at this institution. RESULTS Patient Demographics and Operative Characteristics Between October 2023 and November 2024, 54 consecutive patients with BMI > 40 kg/m² underwent robotic-assisted spine surgery using the MazorX Stealth Edition system with intraoperative O-arm imaging. Patient demographics and operative characteristics are summarized in Table 1 . Table 1 Patient Demographics and Operative Characteristics Variable Value Demographics Total patients, n 54 Age, years (mean ± standard deviation (SD)) 60.9 ± 12.9 Age range, years 15–79 Female sex, n (%) 41 (75.9) Male sex, n (%) 13 (24.1) Anthropometric Data BMI, kg/m² (mean ± SD) 43.6 ± 2.68 BMI range, kg/m² 40.3–51.0 Class III obese (BMI 40-49.9), n (%) 52 (96.3) Super-obese (BMI ≥ 50), n (%) 2 (3.7) Surgical Characteristics Emergency cases, n (%) 3 (5.6) Thoracic fusion, n (%) 4 (7.4) Thoracolumbar fusion, n (%) 3 (5.6) Lumbar fusion, n (%) 47 (87.0) Instrumented levels (mean ± SD) 2.0 ± 1.85 Instrumented levels range 1–9 Total pedicle screws placed 288 Registration Success Outcomes First-attempt O-arm registration was successful in 45 of 54 cases (83.3%, 95% CI: 72.1%-91.4%). Ultimate registration success was achieved in all 54 cases (100%). Registration outcomes stratified by BMI category and fiducial marker positioning are presented in Table 2 . Table 2 Registration Success Outcomes by BMI Category and Lateral Marker Usage Lateral Marker Positioning Standard Positioning (n = 38) Lateral Positioning (n = 16) p-value First-attempt success, n (%) 30 (78.9) 15 (93.8) 0.043 Registration failure, n (%) 8 (21.1) 1 (6.3) 0.043 Ultimate success rate, n (%) 38 (100.0) 16 (100.0) 1.000 Lateral fiducial positioning was employed in 16 of 54 cases (29.6%). No significant difference in first-attempt registration success was observed between BMI categories (P = 0.68). The single registration failure in the lateral positioning group occurred due to inadvertent use of standard 20 cm FOV instead of the required 40 cm FOV protocol. This represents a technical protocol deviation rather than a limitation of the lateral positioning technique itself. Operative Time Metrics and Safety Outcomes Operative time metrics and safety outcomes are detailed in Table 3 . Table 3 Operative Time Metrics and Safety Outcomes Variable First-Attempt Success (n = 45) Registration Reattempt (n = 9) p-value Overall (n = 54) Time Metrics (minutes) Total operative time 192 ± 78.3 151 ± 27.6 0.129 185 ± 73.8 O-arm acquisition time 19.2 ± 8.59 32.6 ± 14.9 < 0.001 21.1 ± 10.9 Safety Outcomes Radiation exposure (units) 38.0 ± 16.1 66.6 ± 21.6 < 0.001 42.3 ± 19.8 Patients requiring registration reattempts had significantly longer O-arm acquisition times (32.6 minutes, 95% CI: 21.4–43.8 vs 19.2 minutes, 95% CI: 16.6–21.8; P = 0.003) and higher radiation exposure (66.6 units, 95% CI: 50.2–83.0 vs 38.0 units, 95% CI: 33.2–42.8; P < 0.001) compared to those achieving first-attempt success. Total operative time showed no significant difference between groups (151.1 minutes, 95% CI: 130.6-171.6 vs 192.1 minutes, 95% CI: 168.6-215.6; P = 0.129). Pedicle Screw Accuracy and Complications Optimal pedicle screw placement (Gertzbein-Robbins Grade A + B) was achieved in 281 of 288 screws (97.6%, 95% CI: 95.4–99.8%). No major intraoperative complications occurred. All 9 cases requiring registration reattempts initially failed with standard central fiducial positioning and achieved successful registration upon reattempt, with 8 cases requiring repositioning to lateral fiducial placement. The single failure in the lateral positioning group was attributed to protocol deviation (use of 20 cm instead of 40 cm FOV). DISCUSSION Solving a Critical Barrier to Robotic Surgery Access This study addresses a technical limitation that has restricted robotic spine surgery access for obese patients. CT registration failure is well known, often due to technical limitations and the need for conversion to alternative techniques in some cases [ 4 ]. Recent systematic reviews demonstrate that while robotic systems generally achieve high accuracy rates, specific patient populations continue to face technical barriers to successful registration [ 11 ]. This lateral fiducial positioning technique provides the first validated solution to overcome the geometric incompatibility between obese patient anatomy and current imaging system limitations and their clinical consequences. The 93.8% vs 78.9% improvement in first-attempt registration success with lateral positioning (P = 0.043) demonstrates the clinical effectiveness of addressing this specific technical barrier. Technical Innovation: Addressing the Core Geometric Problem The O-arm's asymmetric field-of-view (40 cm lateral vs 15 cm sagittal coverage) creates predictable registration failures when combined patient diameter plus central fiducial positioning exceeds the sagittal limitation (15 cm). The lateral positioning technique repositions the marker along the patient's flank, utilizing the full lateral coverage while addressing the geometric incompatibility between obese anatomy and imaging constraints. Clinical Impact: Expanding Robotic Surgery Access Prior to this technique, obese patients experiencing registration failures required conversion to fluoroscopic-guided or freehand techniques, effectively excluding them from robotic assistance benefits. Study’s 100% ultimate registration success rate in 54 consecutive patients eliminates this, providing predictable access to robotic spine surgery for high-BMI patients. The technique's clinical significance extends beyond technical feasibility. Patients achieving first-attempt registration success experienced 41% shorter O-arm acquisition times (19.2 vs 32.6 minutes, P < 0.001) and 43% lower radiation exposure (38.0 vs 66.6 units, P < 0.001), demonstrating that solving the registration challenge improves overall procedural efficiency. The 97.6% optimal screw placement rate (Gertzbein-Robbins Grade A + B) demonstrates that accuracy is maintained despite the technical challenges posed by obesity. Comparison to Alternative Approaches While emerging solutions like ultrasound-based registration offer radiation-free alternatives, they require specialized equipment and extended validation periods [ 12 ]. Deep learning approaches show promise but require extensive computational resources and large training datasets that limit immediate clinical applicability [ 13 ]. Cone-beam CT systems demonstrate higher revision rates compared to O-arm CT systems (4.0% vs 2.8%, p = 0.0081) [ 14 ]. The lateral positioning technique provides an immediately implementable solution using existing robotic platforms and imaging systems without additional capital investment, specialized equipment, or extended validation periods, offering significant practical advantages over emerging alternatives. Radiation Considerations and Safety Profile Failed registrations requiring multiple attempts constitute the primary source of excessive exposure in this patient population. Notably, despite registration challenges in some cases, total operative times showed no significant difference between first-attempt success and reattempt groups (P = 0.129), indicating that the surgical workflow remains robust even when imaging obstacles arise. The zero major complication rate across all 54 procedures demonstrates that the technique maintains safety standards while solving technical challenges. Clinical Implementation and Generalizability The systematic protocol developed for this technique provides reproducible guidelines for implementation across robotic spine surgery centers. Key elements include systematic pre-scan verification using orthogonal 2D scout images, proactive lateral positioning when FOV limitations are anticipated, and conservative radiation settings to prevent marker oversaturation. Technical Consideration : The single lateral positioning failure resulted from human error (selecting 20 cm vs 40 cm FOV), emphasizing success rates with this protocol. This finding underscores that when the lateral positioning protocol is followed precisely, registration failures can be eliminated entirely. This represents a crucial learning point for surgical teams: the lateral positioning technique is only effective when coupled with appropriate FOV selection (40 cm), emphasizing the importance of strict protocol adherence and team education during implementation. Limitations Single-center experience represents both a limitation and a strength of this study. While generalizability to other institutions remains to be demonstrated, these results provide a realistic assessment of what can be achieved when these technical protocols are consistently implemented. The study period encompasses the institutional learning curve, offering authentic guidance for centers beginning to treat similar patient populations. The study focused specifically on patients with BMI > 40 kg/m², limiting applicability to lower BMI ranges where standard positioning may be adequate. Additionally, the technique was developed for the MazorX/O-arm platform, though the geometric principles should apply to other robotic systems with similar FOV constraints. CONCLUSIONS Current technique implementation with lateral fiducial positioning achieves 83.3% first-attempt CT registration success in robotic spine surgery for patients with BMI > 40 kg/m², providing spine surgeons with a reproducible technical solution to overcome registration difficulties in obese patients. The lateral positioning technique addresses the geometric incompatibility between obese patient anatomy and current imaging systems, demonstrating that technical innovation can overcome challenges that have historically excluded high-BMI patients from robotic assistance. These findings provide evidence-based protocols that spine surgeons can immediately implement to expand robotic-assisted surgery access to high-BMI patients with predictable outcomes. The technique reduces the need for conversion to alternative surgical approaches, ensuring that obesity alone does not preclude patients from benefiting from the precision and safety advantages of robotic spine surgery. Declarations Ethics approval: This study was conducted in compliance with the principles of the Declaration of Helsinki. The study protocol was approved by the Institutional Ethics Committee (approval number: ECR/34/Inst/KA/2013/RR-19). Consent to participate: Written informed consent was waived by the Institutional Ethics Committee due to the retrospective nature of the study and minimal risk to participants. Consent for publication: Not applicable. This study does not contain any individual patient data that would require specific consent for publication. Competing interests: The authors declare no conflicts of interest with respect to the research, authorship, and/or publication of this article. Funding: No external funding was received for this study. The authors received no financial support for the research, authorship, and/or publication of this article. Author Contribution A.S. and V.S. conceived and designed the study. V.S. performed all surgical procedures and developed the lateral fiducial positioning technique. A.S. and A.V. collected and analyzed the data. A.S. performed statistical analysis and wrote the main manuscript text. V.S. and A.S. prepared figures and tables. B.T. provided technical expertise and critical revision of the methodology. V.S. and B.T. reviewed and edited the manuscript for important intellectual content. V.S. supervised the overall project. All authors reviewed and approved the final manuscript. A.S. and V.S. contributed equally to this work. Data availability: The datasets generated and analysed during the current study are not publicly available due to patient privacy considerations but are available from the corresponding author on reasonable request and with appropriate institutional approval. References D’Souza M, Gendreau J, Feng A et al (2019) Robotic-Assisted Spine Surgery: History, Efficacy, Cost, And Future Trends. Robot Surg Res Rev Volume 6:9–23. https://doi.org/10.2147/RSRR.S190720 Fatima N, Massaad E, Hadzipasic M et al (2021) Safety and accuracy of robot-assisted placement of pedicle screws compared to conventional free-hand technique: a systematic review and meta-analysis. Spine J 21:181–192. https://doi.org/10.1016/j.spinee.2020.09.007 Ha B-J, Lee J-M, Yoon S-J et al (2023) Three-Dimensional Quantitative Assessment of Pedicle Screw Accuracy in Clinical Utilization of a New Robotic System in Spine Surgery: A Multicenter Study. Neurospine 20:1028–1039. https://doi.org/10.14245/ns.2346552.276 Keric N, Doenitz C, Haj A et al (2017) Evaluation of robot-guided minimally invasive implantation of 2067 pedicle screws. Neurosurg Focus 42:E11. https://doi.org/10.3171/2017.2.FOCUS16552 Boutari C, Mantzoros CS (2022) A 2022 update on the epidemiology of obesity and a call to action: as its twin COVID-19 pandemic appears to be receding, the obesity and dysmetabolism pandemic continues to rage on. Metabolism 133:155217. https://doi.org/10.1016/j.metabol.2022.155217 Hirahata M, Yasui Y, Fujita M et al (2022) Overweight increases perioperative spinal surgery complications. a single-center retrospective study Jiang J, Teng Y, Fan Z et al (2014) Does Obesity Affect the Surgical Outcome and Complication Rates of Spinal Surgery? A Meta-analysis. Clin Orthop 472:968–975. https://doi.org/10.1007/s11999-013-3346-3 Sembrano JN, Polly DW, Ledonio CGT, Santos ERG (2012) Intraoperative 3-dimensional imaging (O-arm) for assessment of pedicle screw position: Does it prevent unacceptable screw placement? Int J Spine Surg 6:49–54. https://doi.org/10.1016/j.ijsp.2011.11.002 Peng Y-N, Tsai L-C, Hsu H-C, Kao C-H (2020) Accuracy of robot-assisted versus conventional freehand pedicle screw placement in spine surgery: a systematic review and meta-analysis of randomized controlled trials. Ann Transl Med 8:824–824. https://doi.org/10.21037/atm-20-1106 Gertzbein SD, Robbins SE (1990) Accuracy of Pedicular Screw Placement. Vivo: Spine 15:11–14. https://doi.org/10.1097/00007632-199001000-00004 Matur AV, Palmisciano P, Duah HO et al (2023) Robotic and navigated pedicle screws are safer and more accurate than fluoroscopic freehand screws: a systematic review and meta-analysis. Spine J 23:197–208. https://doi.org/10.1016/j.spinee.2022.10.006 Gueziri H-E, Rabau O, Santaguida C, Collins DL (2021) Evaluation of an Ultrasound-Based Navigation System for Spine Neurosurgery: A Porcine Cadaver Study. Front Oncol 11:619204. https://doi.org/10.3389/fonc.2021.619204 Fan X, Duke RB, Ji S et al (2021) Stereovision surface stitching for image updating in open spine surgery. In: Linte CA, Siewerdsen JH (eds) Medical Imaging 2021: Image-Guided Procedures, Robotic Interventions, and Modeling. SPIE, Online Only, United States, p 10 Ille S, Baumgart L, Obermueller T et al (2021) Clinical efficiency of operating room-based sliding gantry CT as compared to mobile cone-beam CT-based navigated pedicle screw placement in 853 patients and 6733 screws. Eur Spine J 30:3720–3730. https://doi.org/10.1007/s00586-021-06981-3 Additional Declarations No competing interests reported. Supplementary Files SupplementaryMaterialNew.docx Cite Share Download PDF Status: Posted Version 1 posted 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-7253011","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":499731725,"identity":"be9cccd3-a46f-422a-998d-34c9d54a1617","order_by":0,"name":"Abhishek Soni","email":"","orcid":"","institution":"Manipal Institute of Robotic Spine Surgery","correspondingAuthor":false,"prefix":"","firstName":"Abhishek","middleName":"","lastName":"Soni","suffix":""},{"id":499731726,"identity":"8e650019-cb47-4c2b-90d0-b420d8c3a7d0","order_by":1,"name":"Vidyadhara S","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3ElEQVRIiWNgGAWjYDACZgYDBgYDifp+ECehgGgtFTaMMxtAWgyIsweo7Ewa44YDUDZh9ceZt0n8bDvMbHx+deKHBwYM8vxiBwhoOcxWJtnbdpjN7MbbzRJAhxnOnJ2AX4tkM4+ZBG/bYR6zG2c3gLQkGNwmQovk37bDEsYzzm7+QZQWfmYeM2meM2kGBvy924izhZ+ZrdhapsImQeIG7zaLBAMJwn5h4z+88eYbA4kE/v6zm2/+qLCR55cmoAUIWCTAlARYpQRB5SDA/AHixANEqR4Fo2AUjIIRCAD01UGlsFmPXQAAAABJRU5ErkJggg==","orcid":"","institution":"Manipal Institute of Robotic Spine Surgery","correspondingAuthor":true,"prefix":"","firstName":"Vidyadhara","middleName":"","lastName":"S","suffix":""},{"id":499731727,"identity":"27e74e84-afd3-44bb-9ecf-8d8beadf02e7","order_by":2,"name":"Balamurugan T","email":"","orcid":"","institution":"Manipal Institute of Robotic Spine Surgery","correspondingAuthor":false,"prefix":"","firstName":"Balamurugan","middleName":"","lastName":"T","suffix":""},{"id":499731728,"identity":"8862bc29-cc3f-406c-a508-9e2901b99bff","order_by":3,"name":"Alia Vidyadhara","email":"","orcid":"","institution":"Manipal Institute of Robotic Spine Surgery","correspondingAuthor":false,"prefix":"","firstName":"Alia","middleName":"","lastName":"Vidyadhara","suffix":""}],"badges":[],"createdAt":"2025-07-30 12:38:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7253011/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7253011/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":89233672,"identity":"39d6f4e9-10cd-4237-bb15-1abf888e3b79","added_by":"auto","created_at":"2025-08-17 14:40:18","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":3323208,"visible":true,"origin":"","legend":"\u003cp\u003eLateral Fiducial Marker Positioning Technique for Obese Patients in Robotic Spine Surgery. (A) Fiducial marker placed in the lateral position along the flank of the patient, allowing it to move closer to the spine in the sagittal plane. (B) Lateral scout image from O-arm showing visualization of all 4 fiducial marker beads (red arrows), note the proximity to the spine. (C) AP scout image showing partial coverage of both the marker and spine, representing an incomplete view; red arrows indicate fiducial marker beads. (D) The 3D CT volume reconstruction after the scan with 40 cm FOV demonstrates complete coverage of the spine along with the fiducial marker and both ilia\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-7253011/v1/3c66669cb8d86a85a61869e5.png"},{"id":94472106,"identity":"8169639e-3922-43c5-a6e4-7059b4f89550","added_by":"auto","created_at":"2025-10-27 15:40:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4866399,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7253011/v1/91a888cf-426c-42b5-a8cd-4bd34929fff1.pdf"},{"id":89233258,"identity":"bd68cad3-6c27-4d8a-b598-783042402439","added_by":"auto","created_at":"2025-08-17 14:32:18","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":22074,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterialNew.docx","url":"https://assets-eu.researchsquare.com/files/rs-7253011/v1/481db39ee21b00e704a4c854.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eOvercoming CT Registration Failures in Robotic Spine Surgery: A Lateral Fiducial Positioning Technique for Obese Patients\u003c/p\u003e","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eRobotic-assisted spine surgery (RASS) has demonstrated superior pedicle screw placement accuracy and reduced radiation exposure since the first FDA-cleared system introduction in 2004 [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e–\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eHowever, CT registration failure represents a critical challenge limiting RASS implementation, with registration errors contributing significantly to failed screws across various robotic platforms [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003cb\u003eThe Obesity Challenge in Robotic Spine Surgery\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe global obesity epidemic has altered the spine surgery practice, with obesity rates creating technical challenges including increased operative complexity, blood loss, and complication rates [\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e–\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In obese patients undergoing RASS, CT registration encounters predictable geometric constraints that frequently result in procedure abandonment. The technical challenge stems from asymmetric field-of-view limitations of current imaging systems: the O-arm provides 40 cm lateral coverage versus only 15 cm sagittal coverage for 3D imaging [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. When combined patient anterior-posterior diameter plus standard central fiducial marker positioning exceeds this 15 cm sagittal limitation, registration failure is certain.\u003c/p\u003e\u003cp\u003eDespite the growing population of obese patients requiring spine surgery, current robotic platforms face technical limitations when treating high-BMI patients. Registration failures due to FOV constraints and imaging quality degradation represent a significant barrier to accessing robotic assistance, creating an unmet clinical need for patients who could benefit most from enhanced surgical precision.\u003c/p\u003e\u003cp\u003e\u003cb\u003eLiterature Gap and Clinical Need\u003c/b\u003e\u003c/p\u003e\u003cp\u003eDespite growing numbers of obese patients requiring spine surgery, current robotic platforms face technical limitations when treating high-BMI patients. The clinical consequences of registration failure are: conversion to fluoroscopic-guided or freehand techniques, prolonged operative times, increased radiation exposure, and exclusion of obese patients from the precision and safety benefits of robotic assistance [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. This represents an unmet clinical need, as the population most likely to benefit from robotic precision are those with challenging anatomy and higher complication risks, but are deprived of this technology.\u003c/p\u003e\u003cp\u003e\u003cb\u003eInnovation and Objectives\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThis study addresses the critical gap by developing and validating a novel lateral fiducial positioning technique designed to overcome the specific geometric constraints causing registration failure in obese patients.\u003c/p\u003e\u003cp\u003eThis study aims to: (1) systematically evaluate CT registration challenges in consecutive patients with BMI \u0026gt; 40 kg/m² undergoing robotic-assisted spine surgery, (2) validate the efficacy of the lateral fiducial positioning technique in overcoming field-of-view limitations, and (3) provide evidence-based protocols with reproducible technical guidelines that spine surgeons can immediately implement to expand robotic surgery access to high-BMI patients. By addressing the geometric constraints that have historically excluded obese patients from robotic assistance, this research provides a practical solution to a well-known clinical problem, potentially expanding access to precision spine surgery for a rapidly growing patient population.\u003c/p\u003e"},{"header":"METHODS","content":"\u003cp\u003e\u003cb\u003eStudy Design and Setting\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThis retrospective single-center consecutive case series was conducted between October 16, 2023, and November 30, 2024, in compliance with the Declaration of Helsinki. The study protocol was approved by the Institutional Ethics Committee (IRB No. ECR/34/Inst/KA/2013/RR-19) with waived informed consent due to retrospective nature and minimal risk. The study adhered to STROBE reporting standards. All procedures utilized the MazorX Stealth Edition robotic system (Medtronic, Minneapolis, MN) with intraoperative O-arm imaging for the Scan-and-Plan workflow.\u003c/p\u003e\u003cp\u003e\u003cb\u003ePatient Selection\u003c/b\u003e\u003c/p\u003e\u003cp\u003eInclusion criteria comprised consecutive patients undergoing robotic-assisted thoracolumbar fusion procedures with BMI \u0026gt; 40 kg/m², utilizing intraoperative O-arm scanning with the Scan-and-Plan workflow, and having postoperative CT imaging performed.\u003c/p\u003e\u003cp\u003eExclusion criteria included non-robotic surgery, alternative workflows such as CT-fluoroscopy registration, BMI ≤ 40 kg/m², abandoned robotic procedures, and absence of postoperative CT imaging.\u003c/p\u003e\u003cp\u003e\u003cb\u003eSurgical Protocol\u003c/b\u003e\u003c/p\u003e\u003cp\u003eAll procedures utilized the MazorX Stealth Edition robotic system (Medtronic, Minneapolis, MN) with O-arm O2 imaging (Medtronic, Minneapolis, MN) following the Scan-and-Plan workflow. Patients were positioned prone on specialized spine tables (Allen Advance Table, Hill-Rom, Chicago, IL) with \u0026gt; 272 kg capacity.\u003c/p\u003e\u003cp\u003eA standardized technical protocol was developed for high-BMI patients addressing fiducial marker placement, robotic docking, pre-scan verification, and imaging optimization. Complete technical details are provided in Supplementary Material (S1).\u003c/p\u003e\u003cp\u003e\u003cb\u003eFiducial Marker Positioning Protocol\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eDecision Algorithm for Lateral Positioning\u003c/strong\u003e\u003c/p\u003e\u003cp\u003eThe choice between standard central positioning and lateral fiducial positioning was determined intraoperatively using systematic pre-scan verification with orthogonal 2D scout images (anteroposterior and lateral views). Lateral positioning was employed when scout images demonstrated inadequate visualization of fiducial markers, defined as inability to clearly identify all 4 radio-opaque beads in both anteroposterior (AP) and lateral orthogonal views due to FOV limitations.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eStandard Positioning\u003c/strong\u003e\u003c/p\u003e\u003cp\u003eFiducial markers were positioned centrally over the midline, positioned as close to skin as possible.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eLateral Positioning\u003c/strong\u003e\u003c/p\u003e\u003cp\u003eWhen scout images indicated FOV limitations, fiducial markers were repositioned laterally along the patient's flank, moving the marker away from the central spine position toward the patient's side. This technique utilizes the O-arm's asymmetric FOV capabilities (40 cm lateral coverage vs. 15 cm sagittal coverage) by positioning the marker laterally while maintaining visualization of both spinal anatomy and fiducial beads within the scan volume. This positioning is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eTechnical Specifications\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eImaging Parameters\u003c/strong\u003e\u003c/p\u003e\u003cp\u003eO-arm radiation settings were standardized at kVp 120.00, mAs 186.25 with Low to Medium dose selection to prevent fiducial marker oversaturation. Field-of-view selection utilized standard 20 cm diameter × 15 cm height for initial attempts, with large 40 cm diameter × 15 cm height when lateral positioning was required. O-arm was positioned centered between spine midline and lateral marker position for optimal coverage.\u003c/p\u003e\u003cp\u003e\u003cb\u003eModifications for High-BMI Patients\u003c/b\u003e: The protocol incorporated specific modifications including: (1) fiducial marker positioned as close to skin as possible, (2) intraoperative decision for lateral marker repositioning based on scout image assessment, (3) conservative radiation settings to prevent marker oversaturation, and (4) systematic pre-scan verification using orthogonal 2D scout images. Complete technical details and implementation protocols are provided in Supplementary Material (S1).\u003c/p\u003e\u003cp\u003e\u003cb\u003eOutcome Measures\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003ePrimary Outcome\u003c/strong\u003e\u003c/p\u003e\u003cp\u003eFirst-attempt O-arm registration success rate, defined as successful automatic fiducial detection and registration on initial 3D scan acquisition.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eSecondary Outcomes\u003c/strong\u003e\u003c/p\u003e\u003cp\u003eSecondary outcomes included ultimate registration success rate (including successful reattempts), total operative time (skin incision to closure), O-arm acquisition time (from initial scout images to successful registration), pedicle screw accuracy assessed using Gertzbein-Robbins Grade A + B criteria on postoperative CT imaging [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], radiation exposure (measured in standard institutional units), registration reattempt requirements and failure modes, and perioperative complications.\u003c/p\u003e\u003cp\u003e\u003cb\u003eRegistration Failure Classification\u003c/b\u003e: Primary failure modes were categorized as: (1) inadequate FOV coverage, (2) fiducial marker oversaturation, (3) poor anatomical landmark visualization, or (4) technical/software issues.\u003c/p\u003e\u003ch2\u003eStatistical Analysis\u003c/h2\u003e\u003cp\u003eThis consecutive case series analysis presents continuous variables as mean ± standard deviation with ranges. Categorical variables are reported as frequencies and percentages with 95% confidence intervals. Comparisons between groups (first-attempt success vs. registration reattempt, standard vs. lateral positioning, BMI categories) were performed using Student's t-test for continuous variables and Fisher's exact test for categorical variables. Spearman rank correlation assessed relationships between BMI and surgical variables. Statistical significance was set at P \u0026lt; 0.05. All analyses were performed using IBM SPSS Statistics for Windows, version 27 (IBM Corp., Armonk, N.Y., USA).\u003c/p\u003e\u003cp\u003eFormal sample size calculations were not performed for this consecutive case series. The study period was designed to capture all eligible patients meeting inclusion criteria during the institutional implementation of the lateral positioning technique. Given the exploratory nature of this technical modification and the lack of prior data on registration failure rates in this specific population (BMI \u0026gt; 40 kg/m²), a pragmatic approach was taken to include all consecutive cases over a defined period to establish preliminary efficacy and safety data. The 54 patients represent the complete experience during the study period, providing a representative sample of high-BMI patients undergoing robotic spine surgery at this institution.\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cp\u003e\u003cb\u003ePatient Demographics and Operative Characteristics\u003c/b\u003e\u003c/p\u003e\u003cp\u003eBetween October 2023 and November 2024, 54 consecutive patients with BMI\u0026thinsp;\u0026gt;\u0026thinsp;40 kg/m\u0026sup2; underwent robotic-assisted spine surgery using the MazorX Stealth Edition system with intraoperative O-arm imaging. Patient demographics and operative characteristics are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePatient Demographics and Operative Characteristics\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVariable\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eValue\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDemographics\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal patients, n\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e54\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAge, years (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD))\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e60.9\u0026thinsp;\u0026plusmn;\u0026thinsp;12.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAge range, years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15\u0026ndash;79\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFemale sex, n (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e41 (75.9)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMale sex, n (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e13 (24.1)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eAnthropometric Data\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBMI, kg/m\u0026sup2; (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e43.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.68\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBMI range, kg/m\u0026sup2;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e40.3\u0026ndash;51.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eClass III obese (BMI 40-49.9), n (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e52 (96.3)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSuper-obese (BMI\u0026thinsp;\u0026ge;\u0026thinsp;50), n (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2 (3.7)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eSurgical Characteristics\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEmergency cases, n (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3 (5.6)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eThoracic fusion, n (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4 (7.4)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eThoracolumbar fusion, n (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3 (5.6)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLumbar fusion, n (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e47 (87.0)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInstrumented levels (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.85\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInstrumented levels range\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u0026ndash;9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal pedicle screws placed\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e288\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"2\"\u003e\u003cb\u003eRegistration Success Outcomes\u003c/b\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFirst-attempt O-arm registration was successful in 45 of 54 cases (83.3%, 95% CI: 72.1%-91.4%). Ultimate registration success was achieved in all 54 cases (100%). Registration outcomes stratified by BMI category and fiducial marker positioning are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eRegistration Success Outcomes by BMI Category and Lateral Marker Usage\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLateral Marker Positioning\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eStandard Positioning (n\u0026thinsp;=\u0026thinsp;38)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eLateral Positioning (n\u0026thinsp;=\u0026thinsp;16)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ep-value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFirst-attempt success, n (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e30 (78.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e15 (93.8)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.043\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRegistration failure, n (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e8 (21.1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1 (6.3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.043\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eUltimate success rate, n (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e38 (100.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e16 (100.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eLateral fiducial positioning was employed in 16 of 54 cases (29.6%). No significant difference in first-attempt registration success was observed between BMI categories (P\u0026thinsp;=\u0026thinsp;0.68).\u003c/p\u003e\u003cp\u003eThe single registration failure in the lateral positioning group occurred due to inadvertent use of standard 20 cm FOV instead of the required 40 cm FOV protocol. This represents a technical protocol deviation rather than a limitation of the lateral positioning technique itself.\u003c/p\u003e\u003cp\u003e\u003cb\u003eOperative Time Metrics and Safety Outcomes\u003c/b\u003e\u003c/p\u003e\u003cp\u003eOperative time metrics and safety outcomes are detailed in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eOperative Time Metrics and Safety Outcomes\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVariable\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFirst-Attempt Success (n\u0026thinsp;=\u0026thinsp;45)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eRegistration Reattempt (n\u0026thinsp;=\u0026thinsp;9)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ep-value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eOverall (n\u0026thinsp;=\u0026thinsp;54)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime Metrics (minutes)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal operative time\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e192\u0026thinsp;\u0026plusmn;\u0026thinsp;78.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e151\u0026thinsp;\u0026plusmn;\u0026thinsp;27.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.129\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e185\u0026thinsp;\u0026plusmn;\u0026thinsp;73.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eO-arm acquisition time\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e19.2\u0026thinsp;\u0026plusmn;\u0026thinsp;8.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e32.6\u0026thinsp;\u0026plusmn;\u0026thinsp;14.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e21.1\u0026thinsp;\u0026plusmn;\u0026thinsp;10.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eSafety Outcomes\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRadiation exposure (units)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e38.0\u0026thinsp;\u0026plusmn;\u0026thinsp;16.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e66.6\u0026thinsp;\u0026plusmn;\u0026thinsp;21.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e42.3\u0026thinsp;\u0026plusmn;\u0026thinsp;19.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003ePatients requiring registration reattempts had significantly longer O-arm acquisition times (32.6 minutes, 95% CI: 21.4\u0026ndash;43.8 vs 19.2 minutes, 95% CI: 16.6\u0026ndash;21.8; P\u0026thinsp;=\u0026thinsp;0.003) and higher radiation exposure (66.6 units, 95% CI: 50.2\u0026ndash;83.0 vs 38.0 units, 95% CI: 33.2\u0026ndash;42.8; P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) compared to those achieving first-attempt success. Total operative time showed no significant difference between groups (151.1 minutes, 95% CI: 130.6-171.6 vs 192.1 minutes, 95% CI: 168.6-215.6; P\u0026thinsp;=\u0026thinsp;0.129).\u003c/p\u003e\u003cp\u003e\u003cb\u003ePedicle Screw Accuracy and Complications\u003c/b\u003e\u003c/p\u003e\u003cp\u003eOptimal pedicle screw placement (Gertzbein-Robbins Grade A\u0026thinsp;+\u0026thinsp;B) was achieved in 281 of 288 screws (97.6%, 95% CI: 95.4\u0026ndash;99.8%). No major intraoperative complications occurred. All 9 cases requiring registration reattempts initially failed with standard central fiducial positioning and achieved successful registration upon reattempt, with 8 cases requiring repositioning to lateral fiducial placement. The single failure in the lateral positioning group was attributed to protocol deviation (use of 20 cm instead of 40 cm FOV).\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003e\u003cb\u003eSolving a Critical Barrier to Robotic Surgery Access\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThis study addresses a technical limitation that has restricted robotic spine surgery access for obese patients. CT registration failure is well known, often due to technical limitations and the need for conversion to alternative techniques in some cases [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Recent systematic reviews demonstrate that while robotic systems generally achieve high accuracy rates, specific patient populations continue to face technical barriers to successful registration [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. This lateral fiducial positioning technique provides the first validated solution to overcome the geometric incompatibility between obese patient anatomy and current imaging system limitations and their clinical consequences. The 93.8% vs 78.9% improvement in first-attempt registration success with lateral positioning (P\u0026thinsp;=\u0026thinsp;0.043) demonstrates the clinical effectiveness of addressing this specific technical barrier.\u003c/p\u003e\u003cp\u003e\u003cb\u003eTechnical Innovation: Addressing the Core Geometric Problem\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe O-arm's asymmetric field-of-view (40 cm lateral vs 15 cm sagittal coverage) creates predictable registration failures when combined patient diameter plus central fiducial positioning exceeds the sagittal limitation (15 cm). The lateral positioning technique repositions the marker along the patient's flank, utilizing the full lateral coverage while addressing the geometric incompatibility between obese anatomy and imaging constraints.\u003c/p\u003e\u003cp\u003e\u003cb\u003eClinical Impact: Expanding Robotic Surgery Access\u003c/b\u003e\u003c/p\u003e\u003cp\u003ePrior to this technique, obese patients experiencing registration failures required conversion to fluoroscopic-guided or freehand techniques, effectively excluding them from robotic assistance benefits. Study\u0026rsquo;s 100% ultimate registration success rate in 54 consecutive patients eliminates this, providing predictable access to robotic spine surgery for high-BMI patients.\u003c/p\u003e\u003cp\u003eThe technique's clinical significance extends beyond technical feasibility. Patients achieving first-attempt registration success experienced 41% shorter O-arm acquisition times (19.2 vs 32.6 minutes, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and 43% lower radiation exposure (38.0 vs 66.6 units, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001), demonstrating that solving the registration challenge improves overall procedural efficiency. The 97.6% optimal screw placement rate (Gertzbein-Robbins Grade A\u0026thinsp;+\u0026thinsp;B) demonstrates that accuracy is maintained despite the technical challenges posed by obesity.\u003c/p\u003e\u003cp\u003e\u003cb\u003eComparison to Alternative Approaches\u003c/b\u003e\u003c/p\u003e\u003cp\u003eWhile emerging solutions like ultrasound-based registration offer radiation-free alternatives, they require specialized equipment and extended validation periods [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Deep learning approaches show promise but require extensive computational resources and large training datasets that limit immediate clinical applicability [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Cone-beam CT systems demonstrate higher revision rates compared to O-arm CT systems (4.0% vs 2.8%, p\u0026thinsp;=\u0026thinsp;0.0081) [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe lateral positioning technique provides an immediately implementable solution using existing robotic platforms and imaging systems without additional capital investment, specialized equipment, or extended validation periods, offering significant practical advantages over emerging alternatives.\u003c/p\u003e\u003cp\u003e\u003cb\u003eRadiation Considerations and Safety Profile\u003c/b\u003e\u003c/p\u003e\u003cp\u003eFailed registrations requiring multiple attempts constitute the primary source of excessive exposure in this patient population. Notably, despite registration challenges in some cases, total operative times showed no significant difference between first-attempt success and reattempt groups (P\u0026thinsp;=\u0026thinsp;0.129), indicating that the surgical workflow remains robust even when imaging obstacles arise. The zero major complication rate across all 54 procedures demonstrates that the technique maintains safety standards while solving technical challenges.\u003c/p\u003e\u003cp\u003e\u003cb\u003eClinical Implementation and Generalizability\u003c/b\u003e\u003c/p\u003e\u003cp\u003e The systematic protocol developed for this technique provides reproducible guidelines for implementation across robotic spine surgery centers. Key elements include systematic pre-scan verification using orthogonal 2D scout images, proactive lateral positioning when FOV limitations are anticipated, and conservative radiation settings to prevent marker oversaturation.\u003c/p\u003e\u003cp\u003e\u003cb\u003eTechnical Consideration\u003c/b\u003e: The single lateral positioning failure resulted from human error (selecting 20 cm vs 40 cm FOV), emphasizing success rates with this protocol. This finding underscores that when the lateral positioning protocol is followed precisely, registration failures can be eliminated entirely. This represents a crucial learning point for surgical teams: the lateral positioning technique is only effective when coupled with appropriate FOV selection (40 cm), emphasizing the importance of strict protocol adherence and team education during implementation.\u003c/p\u003e\u003cp\u003e\u003cb\u003eLimitations\u003c/b\u003e\u003c/p\u003e\u003cp\u003eSingle-center experience represents both a limitation and a strength of this study. While generalizability to other institutions remains to be demonstrated, these results provide a realistic assessment of what can be achieved when these technical protocols are consistently implemented. The study period encompasses the institutional learning curve, offering authentic guidance for centers beginning to treat similar patient populations.\u003c/p\u003e\u003cp\u003eThe study focused specifically on patients with BMI\u0026thinsp;\u0026gt;\u0026thinsp;40 kg/m\u0026sup2;, limiting applicability to lower BMI ranges where standard positioning may be adequate. Additionally, the technique was developed for the MazorX/O-arm platform, though the geometric principles should apply to other robotic systems with similar FOV constraints.\u003c/p\u003e"},{"header":"CONCLUSIONS","content":"\u003cp\u003eCurrent technique implementation with lateral fiducial positioning achieves 83.3% first-attempt CT registration success in robotic spine surgery for patients with BMI\u0026thinsp;\u0026gt;\u0026thinsp;40 kg/m\u0026sup2;, providing spine surgeons with a reproducible technical solution to overcome registration difficulties in obese patients. The lateral positioning technique addresses the geometric incompatibility between obese patient anatomy and current imaging systems, demonstrating that technical innovation can overcome challenges that have historically excluded high-BMI patients from robotic assistance.\u003c/p\u003e\u003cp\u003eThese findings provide evidence-based protocols that spine surgeons can immediately implement to expand robotic-assisted surgery access to high-BMI patients with predictable outcomes. The technique reduces the need for conversion to alternative surgical approaches, ensuring that obesity alone does not preclude patients from benefiting from the precision and safety advantages of robotic spine surgery.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval:\u003c/strong\u003e\u003cp\u003e This study was conducted in compliance with the principles of the Declaration of Helsinki. The study protocol was approved by the Institutional Ethics Committee (approval number: ECR/34/Inst/KA/2013/RR-19).\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eConsent to participate:\u003c/strong\u003e\u003cp\u003e Written informed consent was waived by the Institutional Ethics Committee due to the retrospective nature of the study and minimal risk to participants.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eConsent for publication:\u003c/strong\u003e\u003cp\u003eNot applicable. This study does not contain any individual patient data that would require specific consent for publication.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eCompeting interests:\u003c/strong\u003e\u003cp\u003eThe authors declare no conflicts of interest with respect to the research, authorship, and/or publication of this article.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e\u003cp\u003eNo external funding was received for this study. The authors received no financial support for the research, authorship, and/or publication of this article.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eA.S. and V.S. conceived and designed the study. V.S. performed all surgical procedures and developed the lateral fiducial positioning technique. A.S. and A.V. collected and analyzed the data. A.S. performed statistical analysis and wrote the main manuscript text. V.S. and A.S. prepared figures and tables. B.T. provided technical expertise and critical revision of the methodology. V.S. and B.T. reviewed and edited the manuscript for important intellectual content. V.S. supervised the overall project. All authors reviewed and approved the final manuscript. A.S. and V.S. contributed equally to this work.\u003c/p\u003e\u003ch2\u003eData availability:\u003c/h2\u003e\u003cp\u003eThe datasets generated and analysed during the current study are not publicly available due to patient privacy considerations but are available from the corresponding author on reasonable request and with appropriate institutional approval.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eD\u0026rsquo;Souza M, Gendreau J, Feng A et al (2019) Robotic-Assisted Spine Surgery: History, Efficacy, Cost, And Future Trends. Robot Surg Res Rev Volume 6:9\u0026ndash;23. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2147/RSRR.S190720\u003c/span\u003e\u003cspan address=\"10.2147/RSRR.S190720\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFatima N, Massaad E, Hadzipasic M et al (2021) Safety and accuracy of robot-assisted placement of pedicle screws compared to conventional free-hand technique: a systematic review and meta-analysis. Spine J 21:181\u0026ndash;192. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.spinee.2020.09.007\u003c/span\u003e\u003cspan address=\"10.1016/j.spinee.2020.09.007\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHa B-J, Lee J-M, Yoon S-J et al (2023) Three-Dimensional Quantitative Assessment of Pedicle Screw Accuracy in Clinical Utilization of a New Robotic System in Spine Surgery: A Multicenter Study. Neurospine 20:1028\u0026ndash;1039. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.14245/ns.2346552.276\u003c/span\u003e\u003cspan address=\"10.14245/ns.2346552.276\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKeric N, Doenitz C, Haj A et al (2017) Evaluation of robot-guided minimally invasive implantation of 2067 pedicle screws. Neurosurg Focus 42:E11. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3171/2017.2.FOCUS16552\u003c/span\u003e\u003cspan address=\"10.3171/2017.2.FOCUS16552\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBoutari C, Mantzoros CS (2022) A 2022 update on the epidemiology of obesity and a call to action: as its twin COVID-19 pandemic appears to be receding, the obesity and dysmetabolism pandemic continues to rage on. Metabolism 133:155217. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.metabol.2022.155217\u003c/span\u003e\u003cspan address=\"10.1016/j.metabol.2022.155217\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHirahata M, Yasui Y, Fujita M et al (2022) Overweight increases perioperative spinal surgery complications. a single-center retrospective study\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJiang J, Teng Y, Fan Z et al (2014) Does Obesity Affect the Surgical Outcome and Complication Rates of Spinal Surgery? A Meta-analysis. Clin Orthop 472:968\u0026ndash;975. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11999-013-3346-3\u003c/span\u003e\u003cspan address=\"10.1007/s11999-013-3346-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSembrano JN, Polly DW, Ledonio CGT, Santos ERG (2012) Intraoperative 3-dimensional imaging (O-arm) for assessment of pedicle screw position: Does it prevent unacceptable screw placement? Int J Spine Surg 6:49\u0026ndash;54. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijsp.2011.11.002\u003c/span\u003e\u003cspan address=\"10.1016/j.ijsp.2011.11.002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePeng Y-N, Tsai L-C, Hsu H-C, Kao C-H (2020) Accuracy of robot-assisted versus conventional freehand pedicle screw placement in spine surgery: a systematic review and meta-analysis of randomized controlled trials. Ann Transl Med 8:824\u0026ndash;824. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.21037/atm-20-1106\u003c/span\u003e\u003cspan address=\"10.21037/atm-20-1106\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGertzbein SD, Robbins SE (1990) Accuracy of Pedicular Screw Placement. Vivo: Spine 15:11\u0026ndash;14. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1097/00007632-199001000-00004\u003c/span\u003e\u003cspan address=\"10.1097/00007632-199001000-00004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMatur AV, Palmisciano P, Duah HO et al (2023) Robotic and navigated pedicle screws are safer and more accurate than fluoroscopic freehand screws: a systematic review and meta-analysis. Spine J 23:197\u0026ndash;208. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.spinee.2022.10.006\u003c/span\u003e\u003cspan address=\"10.1016/j.spinee.2022.10.006\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGueziri H-E, Rabau O, Santaguida C, Collins DL (2021) Evaluation of an Ultrasound-Based Navigation System for Spine Neurosurgery: A Porcine Cadaver Study. Front Oncol 11:619204. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3389/fonc.2021.619204\u003c/span\u003e\u003cspan address=\"10.3389/fonc.2021.619204\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFan X, Duke RB, Ji S et al (2021) Stereovision surface stitching for image updating in open spine surgery. In: Linte CA, Siewerdsen JH (eds) Medical Imaging 2021: Image-Guided Procedures, Robotic Interventions, and Modeling. SPIE, Online Only, United States, p 10\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eIlle S, Baumgart L, Obermueller T et al (2021) Clinical efficiency of operating room-based sliding gantry CT as compared to mobile cone-beam CT-based navigated pedicle screw placement in 853 patients and 6733 screws. Eur Spine J 30:3720\u0026ndash;3730. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00586-021-06981-3\u003c/span\u003e\u003cspan address=\"10.1007/s00586-021-06981-3\" 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":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Thoracolumbar spine, Obesity, Robotic surgery, CT registration, Pedicle screw","lastPublishedDoi":"10.21203/rs.3.rs-7253011/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7253011/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e\u003cp\u003eCT registration failure represents a critical barrier excluding severely obese patients from robotic-assisted spine surgery (RASS) benefits. This study validates a novel lateral fiducial positioning technique to overcome field-of-view limitations that cause registration failures in patients with BMI\u0026thinsp;\u0026gt;\u0026thinsp;40 kg/m\u0026sup2;, addressing the geometric incompatibility between obese patient size and current imaging constraints.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eRetrospective analysis of 54 consecutive patients (BMI\u0026thinsp;\u0026gt;\u0026thinsp;40 kg/m\u0026sup2;) undergoing RASS using MazorX Stealth Edition with intraoperative O-arm imaging between October 2023 and November 2024. Lateral fiducial positioning repositioned markers along the patient's flank when standard central positioning demonstrated inadequate visualization on scout images, utilizing O-arm's asymmetric field-of-view (40 cm lateral vs. 15 cm sagittal coverage). Primary outcome was first-attempt registration success rate.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eMean BMI was 43.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7 kg/m\u0026sup2; (range 40.3\u0026ndash;51.0). First-attempt registration success was achieved in 45/54 cases (83.3%, 95% CI: 72.1%-91.4%). Lateral positioning was used in 16 cases (29.6%) with significantly higher success rates versus standard positioning (93.8% vs 78.9%, P\u0026thinsp;=\u0026thinsp;0.043). Ultimate registration success was 100%. Patients requiring reattempts had longer O-arm acquisition times (32.6 vs 19.2 minutes, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and higher radiation exposure (66.6 vs 38.0 units, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Optimal pedicle screw placement (Gertzbein-Robbins Grade A\u0026thinsp;+\u0026thinsp;B) was achieved in 97.6% of 288 screws.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e\u003cp\u003eLateral fiducial positioning eliminates CT registration failures in severely obese patients undergoing robotic spine surgery, achieving 100% ultimate registration success while maintaining surgical accuracy. This immediately implementable technique expands robotic surgery access to high-BMI patients without requiring additional equipment, ensuring obesity alone does not preclude patients from precision robotic assistance benefits.\u003c/p\u003e","manuscriptTitle":"Overcoming CT Registration Failures in Robotic Spine Surgery: A Lateral Fiducial Positioning Technique for Obese Patients","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-17 14:32:13","doi":"10.21203/rs.3.rs-7253011/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"61823cdb-2a85-4707-b321-57057426b107","owner":[],"postedDate":"August 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-10-27T14:22:12+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-17 14:32:13","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7253011","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7253011","identity":"rs-7253011","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}