Accuracy of Navigated Pedicle Screw Placement in the Cervical Spine: A comparative Evaluation of a Novel Orthogonal View Evaluation Method (OVEM) Versus other Classification Systems (Neo/Modified Gertzbein-Robbins/Wiesner)

Accuracy of Navigated Pedicle Screw Placement in the Cervical Spine: A comparative Evaluation of a Novel Orthogonal View Evaluation Method (OVEM) Versus other Classification Systems (Neo/Modified Gertzbein-Robbins/Wiesner) | 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 Accuracy of Navigated Pedicle Screw Placement in the Cervical Spine: A comparative Evaluation of a Novel Orthogonal View Evaluation Method (OVEM) Versus other Classification Systems (Neo/Modified Gertzbein-Robbins/Wiesner) Lukas Bobinski, Joel Axelsson, Hassib Lewall, Anders Berglund, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8808729/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 6 You are reading this latest preprint version Abstract Study design: A retrospective, comparison study. Purpose: This study compares different computed tomography (CT)-based methods for evaluating the postoperative position of cervical pedicle screws (CPS). Specifically, our novel Orthogonal View Evaluation Method (OVEM) alongside the Neo, modified Gerzbein-Robbins, and Wiesner classifications to validate a standardized system for postoperative assessment of screw placement in the cervical spine Methods All enrolled patients underwent navigated, posterior stabilization using CPS in the subaxial spine (C3-C6). The intra- and inter-observer assessment was carried out using two statistical methods: the Fleiss Kappa and the Gwet´s agreement coefficient (Gwet´s AC1). Results A total of 90 (60 men and 30 women) patients with total number of screws 275 (median 2, IQR 2 to 4) were enrolled in the study. The OVEM classification demonstrated a statistically significant lower number of screws categorized as correctly placed compared to the other classification across all reviewers (p < 0.001). The reliability analysis showed the highest agreement for OVEM 2 and Neo 2 for Reviewer 1, with Gwet's AC1 (95% CI) of 0.83 (0.77, 0.888) and OVEM for Reviewers 2 and 3 with Gwet's AC1 (95% CI) of 0.87 (0.818, 0.917). Intra-observer agreement was highest for Reviewer 1 in OVEM 2 with Gwet's AC1 (95% CI) of 0.97 (0.943, 1.0), for Reviewer 2 in Neo with 0.97 (0.941, 1.0), and for Reviewer 3 in OVEM with 0.90 (0.829, 0.970). Inter-observer agreement was highest for Neo, with Gwet's AC1 (95% CI) of 0.89 (0.855, 0.927) among Reviewers 1, 2, and 3. Conclusions OVEM evaluation method appears to be more sensitive to detect misplaced screws, has similar reliability and reproducibility in comparison to Neo/modified Gerzbein-Robbins/Wiesner classifications. cervical pedicle screws accuracy Neo classification modified Gerzbein-Robbins classification Figures Figure 1 Figure 2 Figure 3 Introduction Posterior instrumentation is well-established method of stabilizing a wide range of cervical spine pathologies. Cervical pedicle screws (CPS) fixation has gained increasing popularity due to its superior biomechanical properties[ 1 , 2 ]. However, CPS placement technically demanding and controversial, largely because of the small pedicle dimensions, complex angulation, intraoperative cervical mobility, and close proximity of critical neurovascular structures including the vertebral artery, spinal cord, and nerve roots. Postoperative radiological assessment is routinely performed to evaluate screw placement accuracy and ensure patient safety. Plain radiographs are unreliable for this purpose and are inferior to computer tomography (CT)[ 3 ]. Nevertheless, conventional CT assessments relies on two-dimensional (2D), biplanar imaging of a geometrically complex three-dimensional (3D) structure, which may limit the accuracy of CPS evaluation[ 4 ]. Despite several classification systems have been proposed, systemic comparison among them remains challenging[ 5 – 8 ]. The only validated pedicle screw classification system to date is Gertzbein-Robbins classification, originally developed for thoracolumbar instrumentation[ 9 ]. However, it does not differentiate between medial and lateral breaches, accounts for superior and inferior perforations, and lacks the precision required for cervical spine assessment[ 10 ]. A modified version of the Gertzbein-Robbins classification, also referred to as the Wiesner classification, was adopted for evaluation of CPS instrumentations. This system categorizes CPS placement into four grades based on 2 mm incremental pedicle perforations[ 11 – 17 ]. A similar grading framework is employed in another widely recognized and commonly used system, the Neo classification[ 18 ]. The aim of this study is to introduce and validate the OVEM classification, a novel 3D volumetric system for evaluating CPS placement. By assessing screw position within the narrowest portion of the cervical pedicle in three dimensions, this approach may provide greater sensitivity, accuracy and reliability. To our knowledge, no prior validation study has established a gold-standard classification system for CPS placement. Material and methods: This retrospective, single-center study was conducted in accordance with the Declaration of Helsinki and approved by the Ethical Board Authority (Dnr 2023-01288-02). Ninety consecutive patients who underwent posterior stabilization of the subaxial cervical spine between 2015 and 2022 were included. CPS fixation methods included standalone CPS constructs but also hybrid configurations involving CPS with lateral mass screws (LMS) and/or pedicle screws in upper thoracic spine. All procedures used 3D image-guided navigation (O arm TM and Stealth Station, Medtronic Inc., Memphis, TN, USA), and postoperative CT scans (1.25 mm slice thickness) to enable high-quality multiplanar reconstruction and screw assessment. Radiological evaluation and classification of CPS placement were performed using archived digital records (Sectra IDS7) by three reviewers with varying spine experience: reviewer 1 (orthopedic resident, more than three years of experience in spine surgery), reviewer 2 (orthopedics spine surgeon with more than five years post-residency experience in spine surgery), reviewer 3 (fellowship trained, senior consultant neuro-spine surgeon with more than 10 years of post-residency experience). Assessments were performed independently, separated by several weeks to minimize recall bias, with results collected by fourth with results collected by fourth author not involved in evaluation. Orthogonal view evaluation method (OVEM) CT multiplanar reconstruction (CT-MPR) generated images orthogonal to each pedicle´s long axis, allowing detailed 3D assessment of screw placement (Figure 1.). Screws were classified as follows: Grade 1: screw fully contained within pedicle with visible surrounding bone Grade 2: minor cortical engagement, limited to screw thread Grade 3: cortical perforation of the pedicle wall in any direction engaging the internal diameter of the screw without neuro-vascular injury Grade 4: cortical perforation (grade 3 screw) with vertebral artery and/or neural injury Neo/Modified Gerzbein-Robbins /Wiesner classifications Assessed on axial CT images and divided into four grades: Grade 0: screw fully contained Grade 1: breach of the pedicle with less than 2 mm penetration Grade 2: breach of the pedicle with more than 2 mm and less than 4 mm penetration Grade 3: breach of the pedicle with more than 4 mm penetration (i.e., complete misplacement) As these three classifications share methodology and design, only the Neo system was used for statistical comparison. Table 1 summarizes OVEM and Neo classifications. Correct placement was defined as follows: OVEM/Neo: grades 1-2 and 0-1, respectively OVEM 2/Neo 2 modification: only grade 1 and 0, respectively Statistical analysis Descriptive statistics summarized screw placement ratings for all reviewers. McNemar’s test compared the number of correctly placed screws between Neo and OVEM. Accuracy was calculated in three distinctive and consecutive steps: first, based on initial grades for OVEM and Neo classifications assessed by reviewer 1, 2 and 3. Thereafter, both classifications were dichotomized and assigned as OVEM and Neo with two initial grades in both classifications were assessed as “non-misplaced screws” and grade 3 and 4 for OVEM and grade 2 and 3 for Neo as “misplaced screws”. Following this, both OVEM and Neo classification were dichotomized into second model and assigned as OVEM 2 and NEO 2 in which only first grade in each classification was regarded as “non-misplaced” with following grades as “misplaced screws”. Accuracy comparisons between OVEM and Neo, as well as OVEM 2 and Neo 2, were performed using cross-tabulations for reviewers 1, 2, and 3 to determine sensitivity and specificity. Intraobserver reliability was evaluated via repeated assessment of three separated batches of 30 patients per reviewer. Interobserver agreement was analyzed first across all three reviewers, then between senior reviewers 2 and 3 using the Fleiss Kappa as well as the Gwet´s agreement coefficient (Gwet´s AC1), the latter preferred for symmetrical data imbalance. All analyses were performed using R version 4.2.1. Results A total of 90 patients (60 men and 30 women) were enrolled in this study. The total number of analyzed CPS was 275 with median of 2 (IQR 2 to 4) and range 7. C6 was the most common instrumented vertebra (36%) followed by C5 (28%), C4 (19%) and C3 (17%). The number of correctly placed screws was statistically significantly higher with the Neo classification compared to OVEM for all reviewers (p < 0.001). See Figure 2. Sensitivity and Specificity of OVEM, OVEM 2, Neo, and Neo 2 classification models: Reviewer 1: The highest sensitivity was observed in the OVEM 2 compared to Neo model, while the highest specificity was noted in the OVEM compared to Neo 2 model. Reviewers 2 and 3: The highest sensitivities were found in the OVEM compared to Neo and OVEM 2 compared to Neo models. The highest specificity was again observed in the OVEM compared Neo 2 model. The results are summarized in Table 2 . Reliability testing: Reviewer 1: The highest reliability was observed in the OVEM 2 compared to Neo 2, with Gwet’s AC1 (95% CI) of 0.83 (0.775, 0.888). Reviewers 2 and 3: The highest reliability were observed in the OVEM compared to Neo, with Gwet’s AC1 (95% CI) of 0.87 (0.818, 0.917) for reviewer 2 and 0.62 (0.528, 0.714) for reviewer 3. The results are summarized in Table 3 . Intra-observer agreement: Reviewer 1: Highest Fleiss’ Kappa (95% CI) value for Neo classification: 0.73 (0.529, 0.921) Highest Gwet’s AC1 (95% CI) value for OVEM 2: 0.93 (0.868, 0.983) Reviewer 2: Highest Fleiss’ Kappa (95% CI) value for OVEM: 0.88 (0.748, 1) Highest Gwet’s AC1 (95% CI) value for OVEM and Neo: both 0.97 (0.927, 1) and 0.97 (0.941, 1), respectively Reviewer 3: Highest values for both Fleiss’ Kappa and Gwet’s AC1 (95% CI) for OVEM: 0.86 (0.762, 0.955) and 0.90 (0.829, 0.97) The results are summarized in Table 4 . Inter-rater agreement (all reviewers): Highest values for Neo classification with Fleiss’ Kappa (95% CI): 0.40 (0.26, 0.538) and Gwet’s AC1 (95% CI): 0.89 (0.855, 0.927) respectively. The results are summarized in Table 5 . Inter-rater agreement (senior reviewers 2 and 3): Highest values for Neo classification with Fleiss’ Kappa (95% CI): 0.37 (0.154, 0.592) and Gwet’s AC1 (95% CI): 0.92 (0.88, 0.955) respectively The results are summarized in Table 6 . Analysis of misplaced screw trajectories: An additional review of trajectories of screws classified as misplaced according to OVEM (grades 3 and 4), revealed that the most common trajectory was in the lateral-upper direction, accounting for 33% of all misplaced screws. See figure 3. Discussion We found that the OVEM classification identified a higher number of misplaced CPS compared to the Neo classification, indicating greater sensitivity but lower specificity. The introduction and implementation of intraoperative image navigation have enhanced the accuracy and precision of CPS placement, which has translated into improved clinical outcomes[ 19 ]. Optimal screw placement is defined as complete containment within the cancellous bone of the pedicle, without any cortical breaches or protrusions of the screw. The absence of a consensus about a gold-standard classification is underscored by the fact that three systems: Neo, modified Gertzbein-Robbins and Wiesner classification, share the evaluation methodology, yet none have been formally validated. The OVEM classification was developed to provide a 3D based model for CPS position assessment. The findings of our current study corroborate OVEM’s superior sensitivity in detecting even minor deviations of the screw within the pedicle’s bony corridor along its axis, thereby enhancing its clinical utility and lying the foundation for future advancements, such as artificial intelligence (AI)-driven automated radiological assessment. Moreover, it incorporates clinical outcomes by introducing a specific grade (G.4) to describe neurovascular complication. 2D evaluation, although traditionally utilized, can fail to detect screw misplacements, particularly when the screw follows pedicle’s anatomical axis, which is more likely to occur due to its smaller bone volume in the cervical spine. Medial, superior and inferior screw perforations are well described in the literature[ 5 , 7 , 20 , 21 ]. However, the most common type, accounting for up to 84%, is lateral perforation[ 5 , 7 , 18 , 22 ]. This is postulated to occur due to diminished cortical bone thickness of the pedicle contiguous with the vertebral artery [ 23 , 24 ]. Our findings corroborate this observation, revealing that lateral-high and lateral-low misplacements constituted for more than 60% of all recorded displacements, underscoring their predominance in the overall misplacement pattern. Thus, reliance on the Neo classification, which permits a certain degree of misplacement (e.g., up to 2mm), may foster a false sense of security. To put it in the perspective, given that the most common diameter of CPS is 3.5 mm, a 2 mm misplacement translates to over half of the screw being outside the intended bony corridor. It is crucial to interpret these findings from clinical perspective. Misplaced screws may lead to devastating consequences, including permanent neurological deficit, chronic neuropathic pain, vascular and/or visceral injury. Nonetheless, several studies showed that the CPS placement is generally safe, with vertebral artery injury being rare (0.2 to 0.4%), and nerve root and spinal cord injury occurring in 0.9% and 0.3% of cases, respectively[ 25 , 26 ]. However, s construct incorporating misplaced screws, may exhibit significantly compromised biomechanical integrity, predisposing development of pseudarthrosis and screw dislodgment. This can precipitate development of cervical deformity, and theoretically, neurological deterioration. We strongly believe that this leniency may hinder the advancement of accurate and reliable CPS planning and insertion techniques. Postoperative assessment and classification of CPS placement are essential, as they indirectly evaluate the screw placement method employed during surgery. The adoption, of 2 mm threshold (Neo grade 1 or modified Gertzbein-Robbins/Wiesner grade 2) as a margin of acceptable error likely accounts for the discrepancies between accuracy of CPS in the current study and the literature[ 10 , 17 , 19 ]. We encountered a statistically significant lower number of correctly placed screws in the OVEM classification compared to the Neo system across all reviewers. OVEM’s rigorous criteria enhance sensitivity but reduce specificity. CPS deemed by OVEM would often be considered acceptable by Neo or other similar 2D-based systems. This indicates that most misplacements detected by OVEM were minor and clinically insignificant. Inter-observer agreement was highest for the Neo classification, likely due to its tolerance for minor errors. In contrast, eliminating the margin of error (e.g., Neo vs Neo 2) resulted in a five- to seven-fold increase in identified misplacements and a corresponding drop in inter-observer agreement. Interestingly, applying of stricter criteria in OVEM (e.g., OVEM vs OVEM 2) resulted in much higher inter-observer agreement, suggesting that the model’s robustness improves with greater rigor. When comparing only senior reviewers (reviewers 2 and 3), the inter-observer agreement dropped by nearly a half for OVEM 2, while for the Neo 2 classification demonstrated a threefold decrease. That reaffirms that eliminating accepted error margin increases the sensitivity in Neo classification but consequently reduces apparent sensitivity of the OVEM in comparison. In contrast, the OVEM 2 model demonstrated the highest sensitivity among all of the reviewers compared to Neo model. We postulate that the differences between the junior and both senior reviewers can be attributed to two key factors: first, the OVEM’s classification unique learnings curve, which initially seems demanding and time-consuming for less experienced reviewers, and second, discrepancy in clinical experience with planning of CPS instrumentation utilizing CT-MPR. Our findings indicate that, despite its lower specificity, the OVEM classification provides superior sensitivity, rendering it a more reliable and robust tool for assessment and classification of CPS placement. This explains the consistently higher misplacement rates identified by the OVEM across all reviewers. Furthermore, the OVEM exhibited greater intra-observer reproducibility among experienced clinicians, irrespective of the error tolerance specified in the Neo models. This study has important limitations. Its retrospective design resulted in screw assessment performed on non-anonymized images, which might be a source of confirmation bias. Secondary, we did not included assessment of neuro-radiologist due to local routines in which 2D assessment is performed on post-operative images (similar to Neo/modified Gertzbein-Robbins/Wisener classifications) and therefore we wanted to avoid evaluation bias with skewed results caused by this practice. The study did not consider pedicle screws intentionally placed with a violation of the pedicle i.e. due to small size of the pedicles pre-operatively. The present study does not investigate the clinical significance of implant placement or its impact on neurological outcome and complication rates in patients treated with navigated CPS fixation. These aspects were investigated in separate study that has been submitted to a different peer-reviewed international spine journal. Conclusions The OVEM classification system demonstrates greater robustness and sensitivity, providing more reliable information about screw displacement and potential risk for neurovascular injury. In contrast, the inherent margin of error in the Neo classification and its modified variants, limits their reliability and reproducibility, regardless of the evaluator’s experience. Although OVEM classification may require greater clinical experience and a steeper learning curve, it offers improved accuracy. We conclude that a robust, reproducible classification system is essential for accurate evaluation of the cervical pedicle screw placement. Such system ca enhance assessment of clinical and radiological outcomes, improve surgical technique, and support higher-quality research in cervical spine surgery. Declarations Competing Interests The first author has received teaching honoraria and a research grand from industry in connection with a separate, published study. These relationships however are unrelated to the present work. Declaration of Conflict of Interest The first author of this manuscript has received teaching honoraria and a research grand from industry in connection with a separate study. These relationships are unrelated to the present work. The remaining authors declare no potential conflicts of interest related the research, authorship, and/or publication of this article. Contribution All listed authors have actively contributed to the preparation of the manuscript. Author Contribution All listed authors have actively contributed to the preparation of the manuscript. All listed authors made substantial contributions to the preparation of this manuscript. L.B. and J.M.D. conceived and designed the study. J.A., H.L., and L.B. collected data from available medical records. A.B. provided consultation on the selection of appropriate statistical analyses, performed all statistical calculations, and prepared Figure 1. J.A. drafted the initial version of the manuscript under the supervision of L.B. Tables 1 and 2–6 were prepared by L.B. Figure 2 was designed and prepared by J.W. Interpretation of the results was undertaken through collaborative discussions among L.B., J.W., J.M.D., and L.-O.K. All authors contributed to the writing of the manuscript. The final manuscript was critically reviewed and revised by J.W., J.M.D., L.-O.K., and L.B Data Availability The data is only available internally by the authors due to ethical reasons. For external researchers, ethical approval may be obtained via formal application to the Ethical Board Authority. Founding The study has received no founding. References Duff J, Hussain MM, Klocke N, Harris JA, Yandamuri SS, Bobinski L, Daniel RT, Bucklen BS (2018) Does pedicle screw fixation of the subaxial cervical spine provide adequate stabilization in a multilevel vertebral body fracture model? An in vitro biomechanical study. 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Neurosurg Rev 45:1941–1950. 10.1007/s10143-022-01750-2 Founding The study has received no founding Tables Tables 1 to 6 are available in the Supplementary Files section. Additional Declarations Competing interest reported. The first author has received teaching honoraria and a research grand from industry in connection with a separate, published study. These relationships however are unrelated to the present work. Supplementary Files Table4final.docx Table5final.docx Table2final.docx Table3final.docx Table6final.docx Table1.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 24 Apr, 2026 Reviewers agreed at journal 15 Apr, 2026 Reviewers invited by journal 13 Apr, 2026 Editor assigned by journal 08 Feb, 2026 Submission checks completed at journal 08 Feb, 2026 First submitted to journal 06 Feb, 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. 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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-8808729","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":623917960,"identity":"4afa2b21-dfb3-48f5-af5a-2fbffe3a2130","order_by":0,"name":"Lukas Bobinski","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA20lEQVRIiWNgGAWjYBACPgY2EHWAwYCZgYGxwcCGsBY2NC1ppGhhAGlhOEyEFom0xI8/GO7ImbPzHv44o+B84toZCcwfPuDXcliah+GZsWUzX5rkBoPbidtuJLBJzsCrJb1BmoHhcOKGwzxmjA+gWph58Gtp/vkDosX44wODcyAtzJ//4HfYMQkeiBYDoMMOgLQwSOP1Ps+zNGseA5BfeMwkZxgkG28787BNsgePFn72NOObPyqAIcZ/xvhjzx872W3Hkw9/+IHPGjAwQOEBo2cUjIJRMApGAWUAACZFTidaPUfHAAAAAElFTkSuQmCC","orcid":"","institution":"Umeå University","correspondingAuthor":true,"prefix":"","firstName":"Lukas","middleName":"","lastName":"Bobinski","suffix":""},{"id":623917961,"identity":"778bede7-5199-4774-b38f-5d04216fa831","order_by":1,"name":"Joel Axelsson","email":"","orcid":"","institution":"University Hospital of Umeå","correspondingAuthor":false,"prefix":"","firstName":"Joel","middleName":"","lastName":"Axelsson","suffix":""},{"id":623917962,"identity":"d85bdc33-e093-4060-a429-2f0bbf8e8ffc","order_by":2,"name":"Hassib Lewall","email":"","orcid":"","institution":"University Hospital of Umeå","correspondingAuthor":false,"prefix":"","firstName":"Hassib","middleName":"","lastName":"Lewall","suffix":""},{"id":623917963,"identity":"8132bb90-0752-4879-a8c9-9ea5fbf92d07","order_by":3,"name":"Anders Berglund","email":"","orcid":"","institution":"Epistat AB, Statistical analysis","correspondingAuthor":false,"prefix":"","firstName":"Anders","middleName":"","lastName":"Berglund","suffix":""},{"id":623917964,"identity":"62351385-6ba9-4844-bf99-ce83a7260ab7","order_by":4,"name":"Duff John Michael Duff","email":"","orcid":"","institution":"Mediclinic City Hospital","correspondingAuthor":false,"prefix":"","firstName":"Duff","middleName":"John Michael","lastName":"Duff","suffix":""},{"id":623917965,"identity":"575da754-6559-4938-a163-490288579284","order_by":5,"name":"Lars-Owe Koskinen","email":"","orcid":"","institution":"Umeå University","correspondingAuthor":false,"prefix":"","firstName":"Lars-Owe","middleName":"","lastName":"Koskinen","suffix":""},{"id":623917966,"identity":"617dc32b-b6d1-4dc6-8637-411ed6f001f5","order_by":6,"name":"Johan Wänman","email":"","orcid":"","institution":"Umeå University","correspondingAuthor":false,"prefix":"","firstName":"Johan","middleName":"","lastName":"Wänman","suffix":""}],"badges":[],"createdAt":"2026-02-06 15:23:39","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8808729/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8808729/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107705987,"identity":"be960a30-c62a-460b-bbd1-9132e22f126a","added_by":"auto","created_at":"2026-04-24 09:17:03","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":94009,"visible":true,"origin":"","legend":"\u003cp\u003eDemonstration of multiplanar reconstruction (MPR) on computer tomography images (CT)\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8808729/v1/dde586ee7b1aa3b709a80a16.jpg"},{"id":107499938,"identity":"74985989-8a54-4670-8ad4-53d47f99faba","added_by":"auto","created_at":"2026-04-22 05:43:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":13191,"visible":true,"origin":"","legend":"\u003cp\u003eDirect comparison of correctly placed screws between OVEM and Neo classification among the reviewers 1, 2 and 3.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-8808729/v1/4dd4d8a36b996aef447456c7.png"},{"id":107705740,"identity":"13686998-049e-4014-b3b7-2f8128d6d94a","added_by":"auto","created_at":"2026-04-24 09:14:56","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":58499,"visible":true,"origin":"","legend":"\u003cp\u003eType and percentage of CPS misplacement trajectories\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8808729/v1/711dec16a67781b3226af84f.jpg"},{"id":107709035,"identity":"0bd5ea2c-d268-4a0e-9a25-3b9498adc881","added_by":"auto","created_at":"2026-04-24 09:34:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":374483,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8808729/v1/4c3aca17-6c69-42ed-bb9b-00bdb5d66a4f.pdf"},{"id":107499936,"identity":"970c159e-b0ca-46e7-8c15-100f144ad973","added_by":"auto","created_at":"2026-04-22 05:43:23","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":14279,"visible":true,"origin":"","legend":"","description":"","filename":"Table4final.docx","url":"https://assets-eu.researchsquare.com/files/rs-8808729/v1/bd941a9d797ef78f1837d749.docx"},{"id":107705871,"identity":"0f2a569e-9e3c-48ca-9727-4f910f3a8fef","added_by":"auto","created_at":"2026-04-24 09:15:34","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":13669,"visible":true,"origin":"","legend":"","description":"","filename":"Table5final.docx","url":"https://assets-eu.researchsquare.com/files/rs-8808729/v1/512dd2cdfee47422a30b4f0f.docx"},{"id":107499939,"identity":"df8e94c0-cb02-43a1-846b-373615d9c1d6","added_by":"auto","created_at":"2026-04-22 05:43:23","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":14306,"visible":true,"origin":"","legend":"","description":"","filename":"Table2final.docx","url":"https://assets-eu.researchsquare.com/files/rs-8808729/v1/d79767f1ef26d1aeefa3ba45.docx"},{"id":107705706,"identity":"32f04759-379e-469f-a4fa-9015d2e6ea9c","added_by":"auto","created_at":"2026-04-24 09:14:42","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":14417,"visible":true,"origin":"","legend":"","description":"","filename":"Table3final.docx","url":"https://assets-eu.researchsquare.com/files/rs-8808729/v1/37bf528492e8b880f5e2effc.docx"},{"id":107499942,"identity":"6da6e364-2d7b-42dc-9d40-f2e08a5f38ac","added_by":"auto","created_at":"2026-04-22 05:43:23","extension":"docx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":13703,"visible":true,"origin":"","legend":"","description":"","filename":"Table6final.docx","url":"https://assets-eu.researchsquare.com/files/rs-8808729/v1/78cb80b9773504dda8467572.docx"},{"id":107705377,"identity":"4818f768-ca35-4f68-baf2-16c60165f756","added_by":"auto","created_at":"2026-04-24 09:12:05","extension":"docx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":689039,"visible":true,"origin":"","legend":"","description":"","filename":"Table1.docx","url":"https://assets-eu.researchsquare.com/files/rs-8808729/v1/39212aa53053ad74f1cb5deb.docx"}],"financialInterests":"Competing interest reported. The first author has received teaching honoraria and a research grand from industry in connection with a separate, published study. These relationships however are unrelated to the present work.","formattedTitle":"Accuracy of Navigated Pedicle Screw Placement in the Cervical Spine: A comparative Evaluation of a Novel Orthogonal View Evaluation Method (OVEM) Versus other Classification Systems (Neo/Modified Gertzbein-Robbins/Wiesner)","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePosterior instrumentation is well-established method of stabilizing a wide range of cervical spine pathologies. Cervical pedicle screws (CPS) fixation has gained increasing popularity due to its superior biomechanical properties[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. However, CPS placement technically demanding and controversial, largely because of the small pedicle dimensions, complex angulation, intraoperative cervical mobility, and close proximity of critical neurovascular structures including the vertebral artery, spinal cord, and nerve roots.\u003c/p\u003e \u003cp\u003ePostoperative radiological assessment is routinely performed to evaluate screw placement accuracy and ensure patient safety. Plain radiographs are unreliable for this purpose and are inferior to computer tomography (CT)[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Nevertheless, conventional CT assessments relies on two-dimensional (2D), biplanar imaging of a geometrically complex three-dimensional (3D) structure, which may limit the accuracy of CPS evaluation[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Despite several classification systems have been proposed, systemic comparison among them remains challenging[\u003cspan additionalcitationids=\"CR6 CR7\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The only validated pedicle screw classification system to date is Gertzbein-Robbins classification, originally developed for thoracolumbar instrumentation[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. However, it does not differentiate between medial and lateral breaches, accounts for superior and inferior perforations, and lacks the precision required for cervical spine assessment[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eA modified version of the Gertzbein-Robbins classification, also referred to as the Wiesner classification, was adopted for evaluation of CPS instrumentations. This system categorizes CPS placement into four grades based on 2 mm incremental pedicle perforations[\u003cspan additionalcitationids=\"CR12 CR13 CR14 CR15 CR16\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. A similar grading framework is employed in another widely recognized and commonly used system, the Neo classification[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe aim of this study is to introduce and validate the OVEM classification, a novel 3D volumetric system for evaluating CPS placement. By assessing screw position within the narrowest portion of the cervical pedicle in three dimensions, this approach may provide greater sensitivity, accuracy and reliability.\u003c/p\u003e \u003cp\u003eTo our knowledge, no prior validation study has established a gold-standard classification system for CPS placement.\u003c/p\u003e"},{"header":"Material and methods:","content":"\u003cp\u003eThis retrospective, single-center study was conducted in accordance with the Declaration of Helsinki and approved by\u0026nbsp;the Ethical Board Authority (Dnr 2023-01288-02). Ninety consecutive patients who underwent posterior stabilization of the subaxial cervical spine between 2015 and 2022 were included.\u0026nbsp;CPS\u0026nbsp;fixation methods included \u0026nbsp;standalone CPS constructs but also hybrid configurations involving CPS with lateral mass screws (LMS) and/or pedicle screws in upper thoracic spine.\u003c/p\u003e\n\u003cp\u003eAll procedures used 3D image-guided navigation (O arm\u003csup\u003eTM\u003c/sup\u003e and Stealth Station, Medtronic Inc., Memphis, TN, USA), and postoperative CT scans (1.25 mm slice thickness) to enable high-quality multiplanar reconstruction and screw assessment.\u0026nbsp;Radiological evaluation and classification of CPS placement were performed using archived digital records (Sectra IDS7) by three reviewers with varying spine experience: reviewer 1 (orthopedic resident, more than three years of experience in spine surgery), reviewer 2 (orthopedics spine surgeon with more than five years post-residency experience in spine surgery), reviewer 3 (fellowship trained, senior consultant neuro-spine surgeon with more than 10 years of post-residency experience). Assessments were performed independently, separated by several weeks to minimize recall bias, with results collected by fourth with results collected by fourth author not involved in evaluation.\u003c/p\u003e\n\u003ch2\u003e\u003cstrong\u003eOrthogonal view evaluation method (OVEM)\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eCT multiplanar reconstruction (CT-MPR) generated images orthogonal to each pedicle\u0026acute;s long axis, allowing detailed 3D assessment of screw placement (Figure 1.). Screws were classified as follows:\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eGrade 1: screw fully contained within pedicle with visible surrounding bone\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eGrade 2: minor cortical engagement, limited to screw thread\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eGrade 3: cortical perforation of the pedicle wall in any direction engaging the internal diameter of the screw without neuro-vascular injury\u003c/li\u003e\n \u003cli\u003eGrade 4: cortical perforation (grade 3 screw) with vertebral artery and/or neural injury \u0026nbsp;\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003e\u003cstrong\u003eNeo/Modified Gerzbein-Robbins /Wiesner classifications\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAssessed on axial CT images and divided into four grades:\u0026nbsp;\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eGrade 0: \u0026nbsp;screw fully contained\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eGrade 1: breach of the pedicle with less than 2 mm penetration\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eGrade 2: breach of the pedicle with more than 2 mm and less than 4 mm penetration\u003c/li\u003e\n \u003cli\u003eGrade 3: breach of the pedicle with more than 4 mm penetration (i.e., complete misplacement)\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eAs these three classifications share methodology and design, only the Neo system was used for statistical comparison.\u0026nbsp;Table 1 summarizes OVEM and Neo classifications. Correct placement was defined as follows:\u0026nbsp;\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eOVEM/Neo: grades 1-2 and 0-1, respectively\u003c/li\u003e\n \u003cli\u003eOVEM 2/Neo 2 modification: only grade 1 and 0, respectively\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003e\u003cstrong\u003eStatistical analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDescriptive statistics summarized screw placement ratings for all reviewers. McNemar\u0026rsquo;s test compared the number of correctly placed screws between Neo and OVEM. Accuracy was calculated in three distinctive and consecutive steps: first, based on initial grades \u0026nbsp;for OVEM and Neo classifications assessed by reviewer 1, 2 and 3. Thereafter, both classifications were \u0026nbsp;dichotomized and assigned as OVEM and Neo with two initial grades in both classifications were assessed as \u0026ldquo;non-misplaced screws\u0026rdquo; and grade 3 and 4 for OVEM and grade 2 and 3 for Neo as \u0026ldquo;misplaced screws\u0026rdquo;. Following this, both OVEM and Neo classification were dichotomized into second model and assigned as OVEM 2 and NEO 2 in which only first grade in each classification was regarded as \u0026ldquo;non-misplaced\u0026rdquo; with following grades as \u0026ldquo;misplaced screws\u0026rdquo;.\u0026nbsp;Accuracy comparisons between OVEM and Neo, as well as OVEM 2 and Neo 2, were performed using cross-tabulations for reviewers 1, 2, and 3 to determine sensitivity and specificity.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIntraobserver reliability was evaluated via repeated assessment of three separated batches of 30 patients per reviewer. Interobserver agreement was analyzed first across all three reviewers, then between senior reviewers 2 and 3 using the Fleiss Kappa as well as the Gwet\u0026acute;s agreement coefficient (Gwet\u0026acute;s AC1), the latter preferred for symmetrical data imbalance. All analyses were performed using R version 4.2.1.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 90 patients (60 men and 30 women) were enrolled in this study. The total number of analyzed CPS was 275 with median of 2 (IQR 2 to 4) and range 7. C6 was the most common instrumented vertebra (36%) followed by C5 (28%), C4 (19%) and C3 (17%).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;The number of correctly placed screws was statistically significantly higher with the Neo classification compared to OVEM for all reviewers (p \u0026lt; 0.001). See Figure 2.\u003c/p\u003e\n\u003ch3\u003eSensitivity and Specificity of OVEM, OVEM 2, Neo, and Neo 2 classification models:\u003c/h3\u003e\n\u003cp\u003e\u003cstrong\u003eReviewer 1:\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;The highest sensitivity was observed in the OVEM 2 compared to Neo model, while the highest specificity was noted in the OVEM compared to Neo 2 model.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReviewers 2 and 3:\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;The highest sensitivities were found in the OVEM compared to Neo and OVEM 2 compared to Neo models. The highest specificity was again observed in the OVEM compared Neo 2 model.\u003c/p\u003e\n\u003cp\u003eThe results are summarized in \u003cstrong\u003eTable 2\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eReliability testing:\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReviewer 1:\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;The highest reliability was observed in the OVEM 2 compared to Neo 2, with Gwet\u0026rsquo;s AC1 (95% CI) of 0.83 (0.775, 0.888).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReviewers 2 and 3:\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;The highest reliability were observed in the OVEM compared to Neo, with Gwet\u0026rsquo;s AC1 (95% CI) of 0.87 (0.818, 0.917) for reviewer 2 and 0.62 (0.528, 0.714) for reviewer 3.\u003c/p\u003e\n\u003cp\u003eThe results are summarized in \u003cstrong\u003eTable 3\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eIntra-observer agreement:\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReviewer 1:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHighest Fleiss\u0026rsquo; Kappa (95% CI) value for Neo classification: 0.73 (0.529, 0.921)\u003c/p\u003e\n\u003cp\u003eHighest Gwet\u0026rsquo;s AC1 (95% CI) value for OVEM 2: 0.93 (0.868, 0.983)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReviewer 2:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHighest \u0026nbsp;Fleiss\u0026rsquo; Kappa (95% CI) value for OVEM: 0.88 (0.748, 1)\u003c/p\u003e\n\u003cp\u003eHighest Gwet\u0026rsquo;s AC1 (95% CI) value for OVEM and Neo: both 0.97 (0.927, 1) and 0.97 (0.941, 1), respectively\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReviewer 3:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHighest values for both Fleiss\u0026rsquo; Kappa and Gwet\u0026rsquo;s AC1 (95% CI) for OVEM: 0.86 (0.762, 0.955) and 0.90 (0.829, 0.97)\u003c/p\u003e\n\u003cp\u003eThe results are summarized in \u003cstrong\u003eTable 4\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eInter-rater agreement (all reviewers):\u003c/p\u003e\n\u003cp\u003eHighest values for Neo classification with Fleiss\u0026rsquo; Kappa (95% CI): 0.40 (0.26, 0.538) and Gwet\u0026rsquo;s AC1 (95% CI): 0.89 (0.855, 0.927) respectively.\u003c/p\u003e\n\u003cp\u003eThe results are summarized in \u003cstrong\u003eTable 5\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eInter-rater agreement (senior reviewers 2 and 3):\u003c/p\u003e\n\u003cp\u003eHighest values for Neo classification with Fleiss\u0026rsquo; Kappa (95% CI): 0.37 (0.154, 0.592) and Gwet\u0026rsquo;s AC1 (95% CI): 0.92 (0.88, 0.955) respectively\u003c/p\u003e\n\u003cp\u003eThe results are summarized in \u003cstrong\u003eTable 6\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eAnalysis of misplaced screw trajectories:\u003c/p\u003e\n\u003cp\u003eAn additional review of trajectories of screws classified as misplaced according to OVEM \u0026nbsp;(grades 3 and 4), revealed that the most common trajectory was in the lateral-upper direction, accounting for 33% of all misplaced screws. See figure 3.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eWe found that the OVEM classification identified a higher number of misplaced CPS compared to the Neo classification, indicating greater sensitivity but lower specificity.\u003c/p\u003e \u003cp\u003eThe introduction and implementation of intraoperative image navigation have enhanced the accuracy and precision of CPS placement, which has translated into improved clinical outcomes[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Optimal screw placement is defined as complete containment within the cancellous bone of the pedicle, without any cortical breaches or protrusions of the screw.\u003c/p\u003e \u003cp\u003eThe absence of a consensus about a gold-standard classification is underscored by the fact that three systems: Neo, modified Gertzbein-Robbins and Wiesner classification, share the evaluation methodology, yet none have been formally validated. The OVEM classification was developed to provide a 3D based model for CPS position assessment. The findings of our current study corroborate OVEM\u0026rsquo;s superior sensitivity in detecting even minor deviations of the screw within the pedicle\u0026rsquo;s bony corridor along its axis, thereby enhancing its clinical utility and lying the foundation for future advancements, such as artificial intelligence (AI)-driven automated radiological assessment. Moreover, it incorporates clinical outcomes by introducing a specific grade (G.4) to describe neurovascular complication. 2D evaluation, although traditionally utilized, can fail to detect screw misplacements, particularly when the screw follows pedicle\u0026rsquo;s anatomical axis, which is more likely to occur due to its smaller bone volume in the cervical spine.\u003c/p\u003e \u003cp\u003eMedial, superior and inferior screw perforations are well described in the literature[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. However, the most common type, accounting for up to 84%, is lateral perforation[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. This is postulated to occur due to diminished cortical bone thickness of the pedicle contiguous with the vertebral artery [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Our findings corroborate this observation, revealing that lateral-high and lateral-low misplacements constituted for more than 60% of all recorded displacements, underscoring their predominance in the overall misplacement pattern. Thus, reliance on the Neo classification, which permits a certain degree of misplacement (e.g., up to 2mm), may foster a false sense of security. To put it in the perspective, given that the most common diameter of CPS is 3.5 mm, a 2 mm misplacement translates to over half of the screw being outside the intended bony corridor.\u003c/p\u003e \u003cp\u003eIt is crucial to interpret these findings from clinical perspective. Misplaced screws may lead to devastating consequences, including permanent neurological deficit, chronic neuropathic pain, vascular and/or visceral injury. Nonetheless, several studies showed that the CPS placement is generally safe, with vertebral artery injury being rare (0.2 to 0.4%), and nerve root and spinal cord injury occurring in 0.9% and 0.3% of cases, respectively[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. However, s construct incorporating misplaced screws, may exhibit significantly compromised biomechanical integrity, predisposing development of pseudarthrosis and screw dislodgment. This can precipitate development of cervical deformity, and theoretically, neurological deterioration.\u003c/p\u003e \u003cp\u003eWe strongly believe that this leniency may hinder the advancement of accurate and reliable CPS planning and insertion techniques. Postoperative assessment and classification of CPS placement are essential, as they indirectly evaluate the screw placement method employed during surgery. The adoption, of 2 mm threshold (Neo grade 1 or modified Gertzbein-Robbins/Wiesner grade 2) as a margin of acceptable error likely accounts for the discrepancies between accuracy of CPS in the current study and the literature[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. We encountered a statistically significant lower number of correctly placed screws in the OVEM classification compared to the Neo system across all reviewers. OVEM\u0026rsquo;s rigorous criteria enhance sensitivity but reduce specificity. CPS deemed by OVEM would often be considered acceptable by Neo or other similar 2D-based systems. This indicates that most misplacements detected by OVEM were minor and clinically insignificant. Inter-observer agreement was highest for the Neo classification, likely due to its tolerance for minor errors. In contrast, eliminating the margin of error (e.g., Neo vs Neo 2) resulted in a five- to seven-fold increase in identified misplacements and a corresponding drop in inter-observer agreement. Interestingly, applying of stricter criteria in OVEM (e.g., OVEM vs OVEM 2) resulted in much higher inter-observer agreement, suggesting that the model\u0026rsquo;s robustness improves with greater rigor.\u003c/p\u003e \u003cp\u003eWhen comparing only senior reviewers (reviewers 2 and 3), the inter-observer agreement dropped by nearly a half for OVEM 2, while for the Neo 2 classification demonstrated a threefold decrease. That reaffirms that eliminating accepted error margin increases the sensitivity in Neo classification but consequently reduces apparent sensitivity of the OVEM in comparison. In contrast, the OVEM 2 model demonstrated the highest sensitivity among all of the reviewers compared to Neo model. We postulate that the differences between the junior and both senior reviewers can be attributed to two key factors: first, the OVEM\u0026rsquo;s classification unique learnings curve, which initially seems demanding and time-consuming for less experienced reviewers, and second, discrepancy in clinical experience with planning of CPS instrumentation utilizing CT-MPR.\u003c/p\u003e \u003cp\u003eOur findings indicate that, despite its lower specificity, the OVEM classification provides superior sensitivity, rendering it a more reliable and robust tool for assessment and classification of CPS placement. This explains the consistently higher misplacement rates identified by the OVEM across all reviewers. Furthermore, the OVEM exhibited greater intra-observer reproducibility among experienced clinicians, irrespective of the error tolerance specified in the Neo models.\u003c/p\u003e \u003cp\u003eThis study has important limitations. Its retrospective design resulted in screw assessment performed on non-anonymized images, which might be a source of confirmation bias. Secondary, we did not included assessment of neuro-radiologist due to local routines in which 2D assessment is performed on post-operative images (similar to Neo/modified Gertzbein-Robbins/Wisener classifications) and therefore we wanted to avoid evaluation bias with skewed results caused by this practice. The study did not consider pedicle screws intentionally placed with a violation of the pedicle i.e. due to small size of the pedicles pre-operatively. The present study does not investigate the clinical significance of implant placement or its impact on neurological outcome and complication rates in patients treated with navigated CPS fixation. These aspects were investigated in separate study that has been submitted to a different peer-reviewed international spine journal.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe OVEM classification system demonstrates greater robustness and sensitivity, providing more reliable information about screw displacement and potential risk for neurovascular injury. In contrast, the inherent margin of error in the Neo classification and its modified variants, limits their reliability and reproducibility, regardless of the evaluator\u0026rsquo;s experience.\u003c/p\u003e \u003cp\u003eAlthough OVEM classification may require greater clinical experience and a steeper learning curve, it offers improved accuracy. We conclude that a robust, reproducible classification system is essential for accurate evaluation of the cervical pedicle screw placement. Such system ca enhance assessment of clinical and radiological outcomes, improve surgical technique, and support higher-quality research in cervical spine surgery.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe first author has received teaching honoraria and a research grand from industry in connection with a separate, published study. These relationships however are unrelated to the present work.\u003c/p\u003e\n\u003ch2\u003eDeclaration of Conflict of Interest\u003c/h2\u003e\n\u003cp\u003eThe first author of this manuscript has received teaching honoraria and a research grand from industry in connection with a separate study. These relationships are unrelated to the present work. The remaining authors declare no potential conflicts of interest related the research, authorship, and/or publication of this article.\u003c/p\u003e\n\u003ch2\u003eContribution\u003c/h2\u003e\n\u003cp\u003eAll listed authors have actively contributed to the preparation of the manuscript.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eAll listed authors have actively contributed to the preparation of the manuscript. All listed authors made substantial contributions to the preparation of this manuscript. L.B. and J.M.D. conceived and designed the study. J.A., H.L., and L.B. collected data from available medical records. A.B. provided consultation on the selection of appropriate statistical analyses, performed all statistical calculations, and prepared Figure 1. J.A. drafted the initial version of the manuscript under the supervision of L.B. Tables 1 and 2\u0026ndash;6 were prepared by L.B. Figure 2 was designed and prepared by J.W. Interpretation of the results was undertaken through collaborative discussions among L.B., J.W., J.M.D., and L.-O.K. All authors contributed to the writing of the manuscript. The final manuscript was critically reviewed and revised by J.W., J.M.D., L.-O.K., and L.B\u003c/p\u003e\n\u003ch2\u003eData Availability\u003c/h2\u003e\n\u003cp\u003eThe data is only available internally by the authors due to ethical reasons. For external researchers, ethical approval may be obtained via formal application to the Ethical Board Authority.\u003c/p\u003e\n\u003ch2\u003e\u003cstrong\u003eFounding\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe study has received no founding.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDuff J, Hussain MM, Klocke N, Harris JA, Yandamuri SS, Bobinski L, Daniel RT, Bucklen BS (2018) Does pedicle screw fixation of the subaxial cervical spine provide adequate stabilization in a multilevel vertebral body fracture model? An in vitro biomechanical study. 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Surg Radiol Anat 35:181\u0026ndash;189. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s00276-012-1013-0\u003c/span\u003e\u003cspan address=\"10.1007/s00276-012-1013-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSoliman MAR, Aguirre AO, Khan S, Kuo CC, Ruggiero N, Mariotti BL, Fritz AG, Sharma S, Nezha A, Levy BR, Khan A, Salem AA, Jowdy PK, Zeeshan Q, Ghannam MM, Starling RV, Rho K, Pollina J, Mullin JP (2023) Complications associated with subaxial placement of pedicle screws versus lateral mass screws in the cervical spine (C2-T1): systematic review and meta-analysis comprising 4,165 patients and 16,669 screws. Neurosurg Rev 46:61. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s10143-023-01968-8\u003c/span\u003e\u003cspan address=\"10.1007/s10143-023-01968-8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSoliman MAR, Khan S, Ruggiero N, Mariotti BL, Aguirre AO, Kuo CC, Fritz AG, Sharma S, Nezha A, Levy BR, Khan A, Salem AA, Jowdy PK, Zeeshan Q, Ghannam MM, Starling RV, Pollina J, Mullin JP (2022) Complications associated with subaxial placement of pedicle screws versus lateral mass screws in the cervical spine: systematic review and meta-analysis comprising 1768 patients and 8636 screws. Neurosurg Rev 45:1941\u0026ndash;1950. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s10143-022-01750-2\u003c/span\u003e\u003cspan address=\"10.1007/s10143-022-01750-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFounding\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eThe study has received no founding\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 6 are available in the Supplementary Files section.\u003c/p\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-spine-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"esjo","sideBox":"Learn more about [European Spine Journal](http://link.springer.com/journal/586)","snPcode":"586","submissionUrl":"https://submission.springernature.com/new-submission/586/3","title":"European Spine Journal","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"cervical pedicle screws, accuracy, Neo classification, modified Gerzbein-Robbins classification","lastPublishedDoi":"10.21203/rs.3.rs-8808729/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8808729/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eStudy design:\u003c/strong\u003e A retrospective, comparison study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePurpose:\u003c/strong\u003e This study compares different computed tomography (CT)-based methods for evaluating the postoperative position of cervical pedicle screws (CPS). Specifically, our novel Orthogonal View Evaluation Method (OVEM) alongside the Neo, modified Gerzbein-Robbins, and Wiesner classifications to validate a standardized system for postoperative assessment of screw placement in the cervical spine\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll enrolled patients underwent navigated, posterior stabilization using CPS in the subaxial spine (C3-C6). The intra- and inter-observer assessment was carried out using two statistical methods: the Fleiss Kappa and the Gwet´s agreement coefficient (Gwet´s AC1).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA total of 90 (60 men and 30 women) patients with total number of screws 275 (median 2, IQR 2 to 4) were enrolled in the study. The OVEM classification demonstrated a statistically significant lower number of screws categorized as correctly placed compared to the other classification across all reviewers (p \u0026lt; 0.001).\u003c/p\u003e\n\u003cp\u003eThe reliability analysis showed the highest agreement for OVEM 2 and Neo 2 for Reviewer 1, with Gwet's AC1 (95% CI) of 0.83 (0.77, 0.888) and OVEM for Reviewers 2 and 3 with Gwet's AC1 (95% CI) of 0.87 (0.818, 0.917).\u003c/p\u003e\n\u003cp\u003eIntra-observer agreement was highest for Reviewer 1 in OVEM 2 with Gwet's AC1 (95% CI) of 0.97 (0.943, 1.0), for Reviewer 2 in Neo with 0.97 (0.941, 1.0), and for Reviewer 3 in OVEM with 0.90 (0.829, 0.970). Inter-observer agreement was highest for Neo, with Gwet's AC1 (95% CI) of 0.89 (0.855, 0.927) among Reviewers 1, 2, and 3.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOVEM evaluation method appears to be more sensitive to detect misplaced screws, has similar reliability and reproducibility in comparison to Neo/modified Gerzbein-Robbins/Wiesner classifications.\u003c/p\u003e","manuscriptTitle":"Accuracy of Navigated Pedicle Screw Placement in the Cervical Spine: A comparative Evaluation of a Novel Orthogonal View Evaluation Method (OVEM) Versus other Classification Systems (Neo/Modified Gertzbein-Robbins/Wiesner)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-22 05:43:17","doi":"10.21203/rs.3.rs-8808729/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-04-24T08:56:57+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"30042014308061726261466590851281583400","date":"2026-04-16T00:00:01+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-13T17:02:57+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-09T02:16:10+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-09T02:16:07+00:00","index":"","fulltext":""},{"type":"submitted","content":"European Spine Journal","date":"2026-02-06T15:03:04+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"european-spine-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"esjo","sideBox":"Learn more about [European Spine Journal](http://link.springer.com/journal/586)","snPcode":"586","submissionUrl":"https://submission.springernature.com/new-submission/586/3","title":"European Spine Journal","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"2c210d2b-163b-4e02-9937-f27a1836fc50","owner":[],"postedDate":"April 22nd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-22T05:43:18+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-22 05:43:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8808729","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8808729","identity":"rs-8808729","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}