Craniocaudal cyclic load improve risk assessment of lumbar pedicle screw loosening：finite element analysis based on computer tomography

Craniocaudal cyclic load improve risk assessment of lumbar pedicle screw loosening：finite element analysis based on computer tomography | 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 Article Craniocaudal cyclic load improve risk assessment of lumbar pedicle screw loosening：finite element analysis based on computer tomography Chenyu Jiang, Hanqiang ouyang, Yali Li, Ming Ni, Dan Jin, Yan Zhang, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4252319/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 Background: Screw loosening remains a prominent complication for osteoporotic patients with pedicle screw fixation surgeries, yet with limited risk assessment approach. The aim of this study was to investigate influence of craniocaudal cyclic load on pedicle screw fixation strength by computed tomography (CT) based finite element analysis (FEA) and we examined predict ability in pedicle screw loosening (PSL). Methods: 12 clinical PSL cases (7 men, 5 women) and 12 age- and sex-matched controls were enrolled for CT based FEA. Simple axial pullout load and axial pullout load with preset craniocaudal cyclic load were applied to each model respectively, and the ultimate pullout force under both conditions is calculated as the fixed strength and compared. Besides, HU values of the vertebral body trabeculae and screw trajectory were measured as an assessment of osteoporosis. The ultimate pullout force and HU value were compared between PSL and controls cases. Results The cyclic load remarkably reduce the pullout force of pedicle screws (906.2 ± 180.2 N vs. 729.3 ± 172.3 N, p<0.0001) by CT based FEA. No significant difference between the PSL and the control group in the simple axial pull-out force and HU values of the vertebral body. But the pullout force with preset cyclic load (639.2 ± 169.4 N vs. 819.4 ± 125.1 N, p = 0.072) and the HU value of the screw trajectory (177.5 ± 43.8 vs. 217.2 ± 29.6, p = 0.016) in the PSL group is significantly lower than that in the control group. Area under receiver operating characteristic curve (ROC) revealed pullout force with preset cyclic load slightly better predicted PSL than HU value of the screw trajectory (AUC = 0.798 vs. 0.750). Conclusions The craniocaudal cyclic load significantly reduces the screw fixation strength. HU value of screw trajectory and pullout force with preset cyclic load by CT based FEA are helpful for the clinical prediction of PSL. Health sciences/Anatomy/Musculoskeletal system/Bone Health sciences/Risk factors Health sciences/Health occupations/Orthopaedics Osteoporosis biomechanical analysis finite element analysis pedicle screw loosening Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Pedicle screw fixation is widely used for the stabilization of postoperative spine for various condition such as degenerative disease, trauma, tumor, infection, and deformity[ 1 ]. Pedicle screw loosening (PSL) is a recurrent complication of posterior fixation surgery that has been reported in many studies, at a rate ranging from < 1–54.6% in non-osteoporotic bone [ 2 ]and up to 60% in patients with osteoporosis [ 3 ]. Osteoporosis has been considered a main cause of PSL where vertebra has a markedly low capability to sustain stresses without failure[ 4 ]. Yuan et al. took osteoporosis as an independent risk factor of PSL (odd ratio (OR): 8.19, 95% confidence interval (CI): 2.40–27.97)[ 7 ]. However, some researches have suggested that vertebral body hounsfield unit (HU) value or bone mineral density (BMD) are not effective predictors of PSL,but HU or BMD around the screw trajectory[ 8 ][ 9 ][ 10 ][ 11 ]. These above studies suggest that the fixation strength of pedicle screws may be related to the degree of osteoporosis, specifically around screw trajectories. The external load of the internal fixation device may be another critical factor of PSL. The axial pull-out force was considered the main mechanical index of PSL in both traditional in vitro biomechanical tests and finite element analysis (FEA)[ 11 ][ 12 ][ 13 ][ 14 ][ 15 ][ 16 ]. However, recent studies have shown that the axial pullout force was not correlated with screw loosening[ 17 ][ 18 ]. Previous in vivo study have measured the primary load of daily walk on the screws is craniocaudal direction by integrating load sensors into the internal spinal fixator[ 19 ]. And, due to the patient's daily activities or even breathing, the screws are subjected to cyclic external loads[ 20 ]. Therefore, many studies have speculated that the cyclic load in the craniocaudal direction may be the potential cause of PSL[ 18 ][ 21 ][ 22 ]. Song F et al. based on FE method demonstrated the effects of cyclic loading on screw loosening in an osteoporotic population [ 18 ]. However, effect of such craniocaudal cyclic load has not been verified in screw trajectories where clinical PSL occur. Hence, the present study sought to obtain screw trajectory data through pre- and post-operative CT image registration and construct the patient-specific vertebrae-screw FE model to investigate influence of craniocaudal cyclic load on pedicle screw fixation strength by patient-specific model of CT based FEA and examine it predict ability in PSL. Methods Subjects by the institutional review board of This study was approved by the Peking University Third Hospital Medical Sciences Research Ethics Committee and the informed consent was waived due to the retrospective design. We confirm that all experiments were performed in accordance with relevant guidelines and regulations. A total of 143 patients underwent revision surgery for internal fixation due to lumbar internal fixation devices disorder in our institution from January 2020 to December 2022 were initially analyzed. The subject’s inclusion criteria were as followed: 1) postoperative imaging or revision surgery records suggest the presence of PSL; 2) instrumentation from L3 to L5 in patients aged > 50 years at the time of surgery; 3) minimal follow-up time of a year. Patients with no available preoperative and postoperative image; other causes of screw loosening, such as infection, trauma; history of other spinal diseases, such as spinal deformity, infection, tumor, or other metabolic bone diseases were excluded. Finally, 12 patients with PSL at L3 were included in the analysis and 12 patients underwent lumbar posterior approach pedicle crew fixation at L3-L5 in the same period without loosening within 2 years after surgery were included as control group (Table 1 ). Table 1 The demographic characteristics of All subjects PSL group (n = 12) Control group (n = 12) P value Age 68.9 ± 6.7 66.5 ± 4.8 0.325 Male: female 7: 5 6: 6 0.682 Body mass index 26.7 ± 3.7 26.7 ± 2.6 0.115 Cause of pedicle screw fixation (n) lumbar stenosis 8 6 lumbar spondylolisthesis 1 2 Lumbar scoliosis 3 4 PSL, Pedicle screw loosening Patient-specific FE modeling Preoperative CT images of all patients were imported into image postprocessing software Mimics (Materialise NV, Harislee, Belgium), where a semiautomatic segmentation was used to delineate the contours of the L3 vertebral bodies. In order to obtain precise patient-specific screw trajectories, pre - and post-operative CT images of each patient were manually registered to project the postoperative screw trajectories into the preoperative image (Fig. 1 ), where the average HU values of the screw trajectories and the trabecular HU values of the vertebral body were measured. Two commonly used screw size in clinical practice were tested (length: 45mm, width: 6.5mm; length: 50mm, width: 6.5mm), according to surgery record or postoperative image measurement. Both the L3 vertebra and the screw were meshed with 4-node tetrahedral elements (C3D4) with the Mimics software. We used a maximum element size of 3 mm and a minimum element size (around the screw) of 1 mm for the vertebra (Fig. 1 ). Material mapping Young’s modulus and Poisson’s ratio of the pedicle screw (Ti-6Al-4V) were assigned as 110 Gpa and 0.33, respectively [ 18 ]. For a realistic representation of patient-specific model, heterogeneous bone material properties were assigned to the created vertebral mesh. The relationship between HU and equivalent K 2 HPO 4 densities (ρ ash , mg/cm 3 ) was assumed linear and determined based on the density calibrated phantom (Mindways Inc., Austin, TX, USA) refer to our previous study[ 23 ]. The material properties of each tetrahedral element were determined by the mean CT values or equivalent K2HPO4 densities density of the voxels within the element through an empirical material-mapping relations proposed by Morgan et al [ 24 ]: $$E =4730\times {\rho }_{app}^{1.56}$$ Assuming a ratio between ash density and apparent density is ρ ash /ρ app = 0.6 and Poisson's ratio was set to 0.3 for all elements. A linearly elastic-plastic material behavior was applied to all bone elements, where the yield stress (σ ys , MPa) was defined as[ 25 ]: \({\sigma }_{ys} =37.1\times {\rho }_{app}^{1.74}\) We adapted the plastic strain failure criterion ( \({ϵ}_{max}=0.04\) ) for the bone element to simulate the failure of interface between bone and screw when the screw is pulled out, which demonstrated good agreement with experimental mechanical data[ 13 ]. When tetrahedrons that reached maximum plastic strain were immediately deleted to renders a simplified failure behavior. Boundary conditions The penalty method was set at the interface between screw and vertebra with the contact friction was of 0.2. Rigid body properties were applied to all nodes of the screw. The inferior and superior endplates of vertebral body was fully constrained in all directions. Two modes of load were applied to all FE models. The first was to only apply an incremental displacement to the screw tail in the axial direction to simulate the pull-out testing without considering craniocaudal cyclic load. The other was to apply a craniocaudal cyclic load to the screw tail followed by axial pullout displacement (Fig. 1 ). Refer to the loading conditions used in previous studies, the craniocaudal cyclic load set at ± 200 N and time span is 100 cycles. All nonlinear FEA was performed with the explicit FE solver ABAQUS (ABAQUS 6.14, Simulia, Providence, RI, USA), which has the advantage of being less prone to error termination and it also handles element deletion eminently. Statistical analysis Paired t test was conducted to test for the effect of cyclic load. The CT value and pullout force were tested with independent-samples t test. Logistic regression was fitted to the data and the receiver operating characteristic (ROC) curve was computed. The statistical analyses were performed with SPSS (SPSS 22.0, IBM Inc., Chicago, USA). The significance level was set at p < 0.05. Results Measurement of CT values based on preoperative images In terms of vertebral body trabecular HU value, no significant difference was noted between two group (96.1 ± 24.5 vs. 99.5 ± 26.3, p = 0.745). However, the average HU value of the screw trajectory in the PSL group was significantly lower than that in the control group (177.5 ± 43.8 vs. 217.2 ± 29.6, p = 0.016, Fig. 2 ). Effect of cyclic load on screw pullout force Paired T-test showed that 100 times of cyclic load in craniocaudal direction had remarkably reduced the axial pullout force of pedicle screws (906.2 ± 180.2 vs. 729.3 ± 172.3, p<0.0001). In both the control group and the PSL group, the pullout force with preset cyclic load was significantly reduced compared with the direct simulation of screw extraction (Table 2 ), by 32.64% and 12.69% for PSL group and control group, respectively. The distribution of equivalent plastic strain (PEEQ) shows the yield of the bone around the screw trajectory caused by cyclic load were only a subtle increase around fixed screw trajectory but a makable progressive increase in tissue yielding around loose screw trajectory (Figure. 3). Table 2 FE results of all subjects under the two loading conditions PSL group Control group P value Simple pullout 883.1 ± 219.5 929.3 ± 136.3 0.542 Pullout with preset cyclic load 639.2 ± 169.4 819.4 ± 125.1 0.072 † Mean absolute difference [95% CI] 243.8 [94.33–393.3] 109.9 [3.553–216.2] Mean percent difference [95% CI, %] 32.64% [15.49–49.79] 12.69% [0.4712-24.90] P value <0.001 * <0.001 * PSL, Pedicle screw loosening; CI, confidence interval; *, significant differences with paired T-test; †, significant differences with independent sample T-test Moreover, our FE simulation results show that there is no significant difference between the PSL and the control group in the simple axial pull-out force. but, the axial pull-out force after cyclic load in the PSL group is significantly lower than that in the control group (Table 2 ). Prediction of PSL risk Binary logistic regression analysis showed that the pullout force after cyclic load and the average HU value of screw trajectories were related risk factors for PS, respectively (Table 3 ). In addition, we compared the predictive abilities of the two factors on PSL based on the ROC curve, and found that AUC of the pull-out forces with preset cyclic load was slightly greater than the average HU value of the screw trajectories (Table 3 , Fig. 4 ). Table 3 PSL risk assessment with FEA and HU value measurement PSL group Control group OR [95%CI] P value AUC Pullout with preset cyclic load 639.2 ± 169.4 N 819.4 ± 125.1 N 1.009 [1.001–1.017] 0.027 0.798 Average HU value of the screw trajectory 177.5 ± 43.8 217.2 ± 29.6 1.034 [1.001–1.069] 0.046 0.750 PSL, pedicle screw loosening; HU, hounsfield unit; OR, odd ratio; AUC, area under curve Discussion In this study, we proposed a novel FEA pipeline to evaluate pedicle screw fixation strength. The effect of the cyclic load in craniocaudal direction on pedicle screw based on FE method and its predictive ability to PSL were investigated in this study. The results showed that compared with the simple axial pull-out FE simulation, cyclic load led to significant decrease in pedicle screw fixation strength and FEA pipeline based on CT images proposed in this study was helpful to improve the predictive ability of clinical PSL. One of the strengths of our study was that patient-specific FE model were based on real post-operative vertebral screw trajectory spatial data obtained with registration of post- and pre-operative CT images. The accurate spatial data of the screw trajectory is conducive to more realistic FE simulation, because the depth, angle and bone density of the screw trajectory are also related to PSL[ 10 ][ 15 ][ 26 ]. Furthermore, the image registration allows more precise HU value measurement of screw trajectory. In this study, this image registration work was done based on a semi-automatic program of dedicated medical image processing software. In future work, we will try to realize automatic registration of preoperative and postoperative CT images based on computer vision algorithm. Previous studies have shown that the load on the pedicle screw varied from 25 N to 325 N[ 20 ], and Dreischarf et al. found that the unilateral screw was subjected to an average load of 250 N in the lumbar spine of standing posture[ 27 ]. Hence, the cyclic load of 250N were employed in our FE method. In terms of the number of cycles, we refer to the study of Baluch et al. study[ 28 ] and set it at 100 cycles. Bone tissue failure cause by craniocaudal cyclic load was characterized by PEEQ, which is a selectable field variable output results can show the cumulative plastic strain[ 18 ]. Our results show that in the PSL group, the number of elements with plastic strain around screw was significantly more than that in control group, and the subsequent axial pull-out displacement load also results in a significantly reduced pull-out force. Our results suggest that the plastic strain of the bone around the screw caused by cyclic loads from daily activities may be an important risk factor for screw loosening. In evaluations of screw loosening risk based on FEA in previous literatures, the simple axial pullout force was used as the main fixed strength indicator [ 12 ][ 13 ][ 14 ][ 15 ][ 16 ]. However, most of these studies focused on FE model validation, although FE simulation result revealed high correlation with results in vitro mechanical tests[ 12 ][ 13 ][ 16 ], there still need for validation of the simple axial pullout force as an indicator of fixed strength in clinical case control studies. A recent one conducted by Fasser MR et al.[ 17 ] based on FEA has shown that axial pullout force was not an effective predictor of clinical PSL events. This was also demonstrated by our result that there was no significant difference in axial pullout force between PSL and control group. However, after the application of cyclic load, the simulate axial pullout force is significantly different lower in PSL groups. This suggests that axial pullout force with preset cyclic load was an effective indicator in FEA for predicting screw loosening. Osteoporosis is a major risk factor for screw loosening[ 2 ]. Many studies have suggested that the measurement of HU value can assess osteoporosis and related complications to a certain extent[ 5 ][ 6 ][ 8 ][ 9 ][ 29 ]. To explain the effect of cyclic load on the axial pullout force, HU values were further measured at the vertebral body and pedicle screw trajectory. Although there was no significant difference in HU value of vertebral body between the two groups, the average HU value of screw trajectory in the loose group was significantly lower than that in the control group. This indicates that screw loosening is significantly related to the degree of bone mass loss around screw trajectory and several recent studies measured HU value or BMD in the pedicle screw trajectory area also agreed to this point[ 9 ][ 10 ][ 11 ]. In addition, our subsequent FEA results showed that the bone mass loss in screw trajectory would be further affected by the cyclic load, and plastic strain would occur around the screw. Thus, in the long run, radiolucent areas around screws would appear on CT or X-ray images. Several limitations of this study should be discussed here. First, our numerical models were not validated by mechanical experiments. But our pullout FE modeling approach referred to study of Widmer J et al. and has been validated based on cadaveric vertebrae[ 13 ]. Due to unavailable bone tissue specimen of the subjects and limited fresh cadavers, such in silico models might be very useful for understanding biomechanical behavior given various spinal conditions. Second, properties of complex biomechanical material were unable to be replicate reality by FE model, especially when material nonlinearity were taken into consideration. Third, this study only considered the effect of the cyclic load in craniocaudal direction on screw fixation. Under real postoperative conditions, the load subjected to internal fixation is very complicated. The cyclic load in other directions and even the rotating torque should be addressed in future screw loosening analysis and FE simulation. Besides, our sample size is relatively small. Yet, discernable results were promising, prospective studies with larger sample sizes would reveal the broader value of FEA in clinical applications. Conclusion In summary, the FEA pipeline proposed in this study is effective for the evaluation of PSL. Based with FEA, the craniocaudal cyclic load significantly reduces the screw pullout force by progressively accumulating bone tissue failure around the screw, which may relate with bone mass loss around the screw trajectory. Both HU value of screw trajectory and the pullout force with preset cyclic load were correlated with PSL, but FEA have slightly high performance in predicting PSL and risk assessment. Declarations Conflict of Interest: The authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article. Funding This study was supported by the National Natural Science Foundation of China [Grant No. 82171927], the Beijing Natural Science Foundation [Grant No. 7212126], the Beijing New Health Industry Development Foundation [Grant No. XM2020-02-006], National Natural Science Foundation of China (Grant No. 82102638), Peking University Third Hospital Clinical Key Project (Grant No. BYSYZD2021040), Peking University Third Hospital Clinical Cohort Construction Project (Grant No. BYSYDL2022007), Peking University Teaching and Learning 2.0 (Grant No. 2023YB01), and Peking University Health Science Center Education and Teaching Research Project (Grant No. 2021YB05) Author Contribution Chenyu Jiang: Data curation, Writing- Original draft preparation, Methodology, Software. Hanqiang Ouyang: Visualization, Investigation. Dan Jin: Conceptualization, Methodology. Yan Zhang and Liang Jiang: Supervision. Ming Ni and Yali Li: Software, Validation. 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Lullo, et al., Effect of physiological loads on cortical and traditional pedicle screw fixation, Spine 39 (22) (2014) E1297–E1302. Jang S, Graffy PM, Ziemlewicz TJ, Lee SJ, Summers RM, Pickhardt PJ. Opportunistic Osteoporosis Screening at Routine Abdominal and Thoracic CT: Normative L1 Trabecular Attenuation Values in More than 20 000 Adults. Radiology. 2019;291(2):360–367. Additional Declarations No competing interests reported. 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. 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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-4252319","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":296968945,"identity":"8076211b-e349-4e07-a35a-843f2d9588d6","order_by":0,"name":"Chenyu Jiang","email":"","orcid":"","institution":"Peking University Third Hospital","correspondingAuthor":false,"prefix":"","firstName":"Chenyu","middleName":"","lastName":"Jiang","suffix":""},{"id":296968946,"identity":"fd0995be-1b15-4d61-b5ee-fe8bc04e7ba8","order_by":1,"name":"Hanqiang ouyang","email":"","orcid":"","institution":"Peking University Third Hospital","correspondingAuthor":false,"prefix":"","firstName":"Hanqiang","middleName":"","lastName":"ouyang","suffix":""},{"id":296968947,"identity":"c43e255f-fe2f-43fe-9459-80748e65e451","order_by":2,"name":"Yali Li","email":"","orcid":"","institution":"Peking University Third Hospital","correspondingAuthor":false,"prefix":"","firstName":"Yali","middleName":"","lastName":"Li","suffix":""},{"id":296968951,"identity":"c004bf9c-16a8-4bfd-8027-3ec9658cbc8f","order_by":3,"name":"Ming Ni","email":"","orcid":"","institution":"Peking University Third Hospital","correspondingAuthor":false,"prefix":"","firstName":"Ming","middleName":"","lastName":"Ni","suffix":""},{"id":296968952,"identity":"18e5301b-7b58-4eee-ad84-63b686932e5f","order_by":4,"name":"Dan Jin","email":"","orcid":"","institution":"Peking University Third Hospital","correspondingAuthor":false,"prefix":"","firstName":"Dan","middleName":"","lastName":"Jin","suffix":""},{"id":296968953,"identity":"ddeb4ce0-20ef-4be2-a463-8bedb0eee873","order_by":5,"name":"Yan Zhang","email":"","orcid":"","institution":"Peking University Third Hospital","correspondingAuthor":false,"prefix":"","firstName":"Yan","middleName":"","lastName":"Zhang","suffix":""},{"id":296968954,"identity":"a2175de3-3744-4747-9837-7df850bdb97d","order_by":6,"name":"liang Jiang","email":"","orcid":"","institution":"Peking University Third Hospital","correspondingAuthor":false,"prefix":"","firstName":"liang","middleName":"","lastName":"Jiang","suffix":""},{"id":296968955,"identity":"4c56a256-80c1-4c81-a29f-2ce38c7ae5c9","order_by":7,"name":"Huishu Yuan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA10lEQVRIiWNgGAWjYBACAwbGBmYgLWfAcADEZyZeizEpWiDKEjdA+ERoMZdIbv5c2HY4fTvj6TQJhgrrxAb2swfwarGckdgmPbPtcO7OhrPbJBjOpCc28OQl4HfYjcQ2Zl6glg0HgFoY2w4nNkjwGBDS0vwZqCXdAKzlH3FaGqSBWhIgWhqI0XLmYZs0z7l0Q6BfNlskHEs3buPJIaDlePrjzzxl1vLmEmc33vhQYy3bz34GvxYoaGZgkDjAwJAAZLIRox4I6hgY+BuIVDsKRsEoGAUjDgAALhFLABvPv9YAAAAASUVORK5CYII=","orcid":"","institution":"Peking University Third Hospital","correspondingAuthor":true,"prefix":"","firstName":"Huishu","middleName":"","lastName":"Yuan","suffix":""}],"badges":[],"createdAt":"2024-04-11 12:02:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4252319/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4252319/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":55771010,"identity":"896808e0-5028-40d5-b3fb-f688e63787c7","added_by":"auto","created_at":"2024-05-02 21:01:55","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":106335,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic depiction of the steps involved in patient-specific model generations. Through the preoperative and postoperative CT image registration, the postoperative screw trajectory was projected into the preoperative CT image (left); The patient-specific vertebrae-screw model construction with tetrahedral mesh and the vertebrae surface was fixed in all directions. Two loading conditions were applied to the screws tail: simple axial pullout displacement load and axial pullout displacement with presetcraniocaudal cyclic loading.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4252319/v1/39129cb4a1d927c2e82669a2.jpg"},{"id":55771011,"identity":"152024f1-ee43-4ab7-89ff-56f4647fcf68","added_by":"auto","created_at":"2024-05-02 21:01:55","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":37354,"visible":true,"origin":"","legend":"\u003cp\u003eMeasurement of CT values based on preoperative images.\u003c/p\u003e\n\u003cp\u003ePSL, pedicle screw loosening; HU, hounsfield unit; ns, no statistical differences; *, independent-samples T test, P ≤ 0.05\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4252319/v1/6fd4824dd65f14d005cbf7b1.jpg"},{"id":55771439,"identity":"ee38b2f6-3480-45ce-940e-20cd3af41fc9","added_by":"auto","created_at":"2024-05-02 21:09:56","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":87866,"visible":true,"origin":"","legend":"\u003cp\u003eThe distribution of equivalent plastic strain (PEEQ) around screw trajectory of representative pedicle screw loosen (PSL) case and control case after 20, 60 and 100 cycles of craniocaudal cyclic load were applied. PEEQ mainly distributed around the tip of the screw, and more PEEQ distributed around the vertebral pedicle might be the characteristics of PSL case.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4252319/v1/8a556d7aad8b035750320373.jpg"},{"id":55771013,"identity":"741ec541-337c-4845-bd91-9692d46a27e3","added_by":"auto","created_at":"2024-05-02 21:01:55","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":46957,"visible":true,"origin":"","legend":"\u003cp\u003eROC analysis of FEA and HU value of screw trajectory. The AUC of the pullout forces with preset cyclic load was slightly greater than the average HU value of the screw trajectories.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4252319/v1/65ef1f893ee0ecf4e736dd8e.jpg"},{"id":70391342,"identity":"83d2229d-969a-4985-8f12-510a44d020f2","added_by":"auto","created_at":"2024-12-02 17:30:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":678321,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4252319/v1/a2455195-73be-4855-82e5-c62ef81bb579.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Craniocaudal cyclic load improve risk assessment of lumbar pedicle screw loosening：finite element analysis based on computer tomography","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePedicle screw fixation is widely used for the stabilization of postoperative spine for various condition such as degenerative disease, trauma, tumor, infection, and deformity[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Pedicle screw loosening (PSL) is a recurrent complication of posterior fixation surgery that has been reported in many studies, at a rate ranging from \u0026lt;\u0026thinsp;1\u0026ndash;54.6% in non-osteoporotic bone [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]and up to 60% in patients with osteoporosis [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOsteoporosis has been considered a main cause of PSL where vertebra has a markedly low capability to sustain stresses without failure[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Yuan et al. took osteoporosis as an independent risk factor of PSL (odd ratio (OR): 8.19, 95% confidence interval (CI): 2.40\u0026ndash;27.97)[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, some researches have suggested that vertebral body hounsfield unit (HU) value or bone mineral density (BMD) are not effective predictors of PSL,but HU or BMD around the screw trajectory[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e][\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e][\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e][\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. These above studies suggest that the fixation strength of pedicle screws may be related to the degree of osteoporosis, specifically around screw trajectories.\u003c/p\u003e \u003cp\u003eThe external load of the internal fixation device may be another critical factor of PSL. The axial pull-out force was considered the main mechanical index of PSL in both traditional in vitro biomechanical tests and finite element analysis (FEA)[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e][\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e][\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e][\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e][\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e][\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. However, recent studies have shown that the axial pullout force was not correlated with screw loosening[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e][\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Previous in vivo study have measured the primary load of daily walk on the screws is craniocaudal direction by integrating load sensors into the internal spinal fixator[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. And, due to the patient's daily activities or even breathing, the screws are subjected to cyclic external loads[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Therefore, many studies have speculated that the cyclic load in the craniocaudal direction may be the potential cause of PSL[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e][\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e][\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Song F et al. based on FE method demonstrated the effects of cyclic loading on screw loosening in an osteoporotic population [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. However, effect of such craniocaudal cyclic load has not been verified in screw trajectories where clinical PSL occur.\u003c/p\u003e \u003cp\u003eHence, the present study sought to obtain screw trajectory data through pre- and post-operative CT image registration and construct the patient-specific vertebrae-screw FE model to investigate influence of craniocaudal cyclic load on pedicle screw fixation strength by patient-specific model of CT based FEA and examine it predict ability in PSL.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eSubjects by the institutional review board of\u003c/p\u003e \u003cp\u003e This study was approved by the Peking University Third Hospital Medical Sciences Research Ethics Committee and the informed consent was waived due to the retrospective design. We confirm that all experiments were performed in accordance with relevant guidelines and regulations.\u003c/p\u003e \u003cp\u003eA total of 143 patients underwent revision surgery for internal fixation due to lumbar internal fixation devices disorder in our institution from January 2020 to December 2022 were initially analyzed. The subject\u0026rsquo;s inclusion criteria were as followed: 1) postoperative imaging or revision surgery records suggest the presence of PSL; 2) instrumentation from L3 to L5 in patients aged\u0026thinsp;\u0026gt;\u0026thinsp;50 years at the time of surgery; 3) minimal follow-up time of a year. Patients with no available preoperative and postoperative image; other causes of screw loosening, such as infection, trauma; history of other spinal diseases, such as spinal deformity, infection, tumor, or other metabolic bone diseases were excluded. Finally, 12 patients with PSL at L3 were included in the analysis and 12 patients underwent lumbar posterior approach pedicle crew fixation at L3-L5 in the same period without loosening within 2 years after surgery were included as control group (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\u003eThe demographic characteristics of All subjects\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=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePSL group (n\u0026thinsp;=\u0026thinsp;12)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eControl group (n\u0026thinsp;=\u0026thinsp;12)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\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\u003eAge\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e68.9\u0026thinsp;\u0026plusmn;\u0026thinsp;6.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e66.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.325\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale: female\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7: 5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e6: 6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.682\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBody mass index\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e26.7\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.115\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eCause of pedicle screw fixation (n)\u003c/p\u003e \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\u003elumbar stenosis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \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\u003elumbar spondylolisthesis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \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\u003eLumbar scoliosis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003ePSL, Pedicle screw loosening\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003ePatient-specific FE modeling\u003c/p\u003e \u003cp\u003ePreoperative CT images of all patients were imported into image postprocessing software Mimics (Materialise NV, Harislee, Belgium), where a semiautomatic segmentation was used to delineate the contours of the L3 vertebral bodies. In order to obtain precise patient-specific screw trajectories, pre - and post-operative CT images of each patient were manually registered to project the postoperative screw trajectories into the preoperative image (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), where the average HU values of the screw trajectories and the trabecular HU values of the vertebral body were measured. Two commonly used screw size in clinical practice were tested (length: 45mm, width: 6.5mm; length: 50mm, width: 6.5mm), according to surgery record or postoperative image measurement. Both the L3 vertebra and the screw were meshed with 4-node tetrahedral elements (C3D4) with the Mimics software. We used a maximum element size of 3 mm and a minimum element size (around the screw) of 1 mm for the vertebra (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMaterial mapping\u003c/p\u003e \u003cp\u003eYoung\u0026rsquo;s modulus and Poisson\u0026rsquo;s ratio of the pedicle screw (Ti-6Al-4V) were assigned as 110 Gpa and 0.33, respectively [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. For a realistic representation of patient-specific model, heterogeneous bone material properties were assigned to the created vertebral mesh. The relationship between HU and equivalent K\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e densities (ρ\u003csub\u003eash\u003c/sub\u003e, mg/cm\u003csup\u003e3\u003c/sup\u003e) was assumed linear and determined based on the density calibrated phantom (Mindways Inc., Austin, TX, USA) refer to our previous study[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The material properties of each tetrahedral element were determined by the mean CT values or equivalent K2HPO4 densities density of the voxels within the element through an empirical material-mapping relations proposed by Morgan et al [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$E =4730\\times {\\rho }_{app}^{1.56}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAssuming a ratio between ash density and apparent density is ρ\u003csub\u003eash\u003c/sub\u003e/ρ\u003csub\u003eapp\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.6 and Poisson's ratio was set to 0.3 for all elements. A linearly elastic-plastic material behavior was applied to all bone elements, where the yield stress (σ\u003csub\u003eys\u003c/sub\u003e, MPa) was defined as[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]:\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\sigma }_{ys} =37.1\\times {\\rho }_{app}^{1.74}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eWe adapted the plastic strain failure criterion (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({ϵ}_{max}=0.04\\)\u003c/span\u003e\u003c/span\u003e) for the bone element to simulate the failure of interface between bone and screw when the screw is pulled out, which demonstrated good agreement with experimental mechanical data[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. When tetrahedrons that reached maximum plastic strain were immediately deleted to renders a simplified failure behavior.\u003c/p\u003e \u003cp\u003eBoundary conditions\u003c/p\u003e \u003cp\u003eThe penalty method was set at the interface between screw and vertebra with the contact friction was of 0.2. Rigid body properties were applied to all nodes of the screw. The inferior and superior endplates of vertebral body was fully constrained in all directions.\u003c/p\u003e \u003cp\u003eTwo modes of load were applied to all FE models. The first was to only apply an incremental displacement to the screw tail in the axial direction to simulate the pull-out testing without considering craniocaudal cyclic load. The other was to apply a craniocaudal cyclic load to the screw tail followed by axial pullout displacement (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Refer to the loading conditions used in previous studies, the craniocaudal cyclic load set at \u0026plusmn;\u0026thinsp;200 N and time span is 100 cycles.\u003c/p\u003e \u003cp\u003eAll nonlinear FEA was performed with the explicit FE solver ABAQUS (ABAQUS 6.14, Simulia, Providence, RI, USA), which has the advantage of being less prone to error termination and it also handles element deletion eminently.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003ePaired t test was conducted to test for the effect of cyclic load. The CT value and pullout force were tested with independent-samples t test. Logistic regression was fitted to the data and the receiver operating characteristic (ROC) curve was computed. The statistical analyses were performed with SPSS (SPSS 22.0, IBM Inc., Chicago, USA). The significance level was set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eMeasurement of CT values based on preoperative images\u003c/p\u003e \u003cp\u003eIn terms of vertebral body trabecular HU value, no significant difference was noted between two group (96.1\u0026thinsp;\u0026plusmn;\u0026thinsp;24.5 vs. 99.5\u0026thinsp;\u0026plusmn;\u0026thinsp;26.3, p\u0026thinsp;=\u0026thinsp;0.745). However, the average HU value of the screw trajectory in the PSL group was significantly lower than that in the control group (177.5\u0026thinsp;\u0026plusmn;\u0026thinsp;43.8 vs. 217.2\u0026thinsp;\u0026plusmn;\u0026thinsp;29.6, p\u0026thinsp;=\u0026thinsp;0.016, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eEffect of cyclic load on screw pullout force\u003c/p\u003e \u003cp\u003ePaired T-test showed that 100 times of cyclic load in craniocaudal direction had remarkably reduced the axial pullout force of pedicle screws (906.2\u0026thinsp;\u0026plusmn;\u0026thinsp;180.2 vs. 729.3\u0026thinsp;\u0026plusmn;\u0026thinsp;172.3, p\u0026lt;0.0001). In both the control group and the PSL group, the pullout force with preset cyclic load was significantly reduced compared with the direct simulation of screw extraction (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), by 32.64% and 12.69% for PSL group and control group, respectively. The distribution of equivalent plastic strain (PEEQ) shows the yield of the bone around the screw trajectory caused by cyclic load were only a subtle increase around fixed screw trajectory but a makable progressive increase in tissue yielding around loose screw trajectory (Figure. 3).\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\u003eFE results of all subjects under the two loading conditions\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=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePSL group\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eControl group\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\u003eSimple pullout\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e883.1\u0026thinsp;\u0026plusmn;\u0026thinsp;219.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e929.3\u0026thinsp;\u0026plusmn;\u0026thinsp;136.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.542\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePullout with preset cyclic load\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e639.2\u0026thinsp;\u0026plusmn;\u0026thinsp;169.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e819.4\u0026thinsp;\u0026plusmn;\u0026thinsp;125.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.072\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean absolute difference\u003c/p\u003e \u003cp\u003e[95% CI]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e243.8\u003c/p\u003e \u003cp\u003e[94.33\u0026ndash;393.3]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e109.9\u003c/p\u003e \u003cp\u003e[3.553\u0026ndash;216.2]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean percent difference\u003c/p\u003e \u003cp\u003e[95% CI, %]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e32.64%\u003c/p\u003e \u003cp\u003e[15.49\u0026ndash;49.79]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12.69%\u003c/p\u003e \u003cp\u003e[0.4712-24.90]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP value\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026lt;0.001\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;0.001\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003ePSL, Pedicle screw loosening; CI, confidence interval; *, significant differences with paired T-test;\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e\u0026dagger;, significant differences with independent sample T-test\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eMoreover, our FE simulation results show that there is no significant difference between the PSL and the control group in the simple axial pull-out force. but, the axial pull-out force after cyclic load in the PSL group is significantly lower than that in the control group (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePrediction of PSL risk\u003c/p\u003e \u003cp\u003eBinary logistic regression analysis showed that the pullout force after cyclic load and the average HU value of screw trajectories were related risk factors for PS, respectively (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In addition, we compared the predictive abilities of the two factors on PSL based on the ROC curve, and found that AUC of the pull-out forces with preset cyclic load was slightly greater than the average HU value of the screw trajectories (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\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\u003ePSL risk assessment with FEA and HU value measurement\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePSL group\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eControl group\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOR\u003c/p\u003e \u003cp\u003e[95%CI]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eP value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAUC\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePullout with preset cyclic load\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e639.2\u0026thinsp;\u0026plusmn;\u0026thinsp;169.4 N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e819.4\u0026thinsp;\u0026plusmn;\u0026thinsp;125.1 N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.009\u003c/p\u003e \u003cp\u003e[1.001\u0026ndash;1.017]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.027\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.798\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAverage HU value of the screw trajectory\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e177.5\u0026thinsp;\u0026plusmn;\u0026thinsp;43.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e217.2\u0026thinsp;\u0026plusmn;\u0026thinsp;29.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.034\u003c/p\u003e \u003cp\u003e[1.001\u0026ndash;1.069]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.046\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.750\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003ePSL, pedicle screw loosening; HU, hounsfield unit; OR, odd ratio; AUC, area under curve\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study, we proposed a novel FEA pipeline to evaluate pedicle screw fixation strength. The effect of the cyclic load in craniocaudal direction on pedicle screw based on FE method and its predictive ability to PSL were investigated in this study. The results showed that compared with the simple axial pull-out FE simulation, cyclic load led to significant decrease in pedicle screw fixation strength and FEA pipeline based on CT images proposed in this study was helpful to improve the predictive ability of clinical PSL.\u003c/p\u003e \u003cp\u003eOne of the strengths of our study was that patient-specific FE model were based on real post-operative vertebral screw trajectory spatial data obtained with registration of post- and pre-operative CT images. The accurate spatial data of the screw trajectory is conducive to more realistic FE simulation, because the depth, angle and bone density of the screw trajectory are also related to PSL[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e][\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e][\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Furthermore, the image registration allows more precise HU value measurement of screw trajectory. In this study, this image registration work was done based on a semi-automatic program of dedicated medical image processing software. In future work, we will try to realize automatic registration of preoperative and postoperative CT images based on computer vision algorithm.\u003c/p\u003e \u003cp\u003ePrevious studies have shown that the load on the pedicle screw varied from 25 N to 325 N[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], and Dreischarf et al. found that the unilateral screw was subjected to an average load of 250 N in the lumbar spine of standing posture[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Hence, the cyclic load of 250N were employed in our FE method. In terms of the number of cycles, we refer to the study of Baluch et al. study[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] and set it at 100 cycles. Bone tissue failure cause by craniocaudal cyclic load was characterized by PEEQ, which is a selectable field variable output results can show the cumulative plastic strain[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Our results show that in the PSL group, the number of elements with plastic strain around screw was significantly more than that in control group, and the subsequent axial pull-out displacement load also results in a significantly reduced pull-out force. Our results suggest that the plastic strain of the bone around the screw caused by cyclic loads from daily activities may be an important risk factor for screw loosening.\u003c/p\u003e \u003cp\u003eIn evaluations of screw loosening risk based on FEA in previous literatures, the simple axial pullout force was used as the main fixed strength indicator [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e][\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e][\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e][\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e][\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. However, most of these studies focused on FE model validation, although FE simulation result revealed high correlation with results in vitro mechanical tests[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e][\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e][\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], there still need for validation of the simple axial pullout force as an indicator of fixed strength in clinical case control studies. A recent one conducted by Fasser MR et al.[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] based on FEA has shown that axial pullout force was not an effective predictor of clinical PSL events. This was also demonstrated by our result that there was no significant difference in axial pullout force between PSL and control group. However, after the application of cyclic load, the simulate axial pullout force is significantly different lower in PSL groups. This suggests that axial pullout force with preset cyclic load was an effective indicator in FEA for predicting screw loosening.\u003c/p\u003e \u003cp\u003eOsteoporosis is a major risk factor for screw loosening[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Many studies have suggested that the measurement of HU value can assess osteoporosis and related complications to a certain extent[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e][\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e][\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e][\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e][\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. To explain the effect of cyclic load on the axial pullout force, HU values were further measured at the vertebral body and pedicle screw trajectory. Although there was no significant difference in HU value of vertebral body between the two groups, the average HU value of screw trajectory in the loose group was significantly lower than that in the control group. This indicates that screw loosening is significantly related to the degree of bone mass loss around screw trajectory and several recent studies measured HU value or BMD in the pedicle screw trajectory area also agreed to this point[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e][\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e][\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. In addition, our subsequent FEA results showed that the bone mass loss in screw trajectory would be further affected by the cyclic load, and plastic strain would occur around the screw. Thus, in the long run, radiolucent areas around screws would appear on CT or X-ray images.\u003c/p\u003e \u003cp\u003eSeveral limitations of this study should be discussed here. First, our numerical models were not validated by mechanical experiments. But our pullout FE modeling approach referred to study of Widmer J et al. and has been validated based on cadaveric vertebrae[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Due to unavailable bone tissue specimen of the subjects and limited fresh cadavers, such in silico models might be very useful for understanding biomechanical behavior given various spinal conditions. Second, properties of complex biomechanical material were unable to be replicate reality by FE model, especially when material nonlinearity were taken into consideration. Third, this study only considered the effect of the cyclic load in craniocaudal direction on screw fixation. Under real postoperative conditions, the load subjected to internal fixation is very complicated. The cyclic load in other directions and even the rotating torque should be addressed in future screw loosening analysis and FE simulation. Besides, our sample size is relatively small. Yet, discernable results were promising, prospective studies with larger sample sizes would reveal the broader value of FEA in clinical applications.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, the FEA pipeline proposed in this study is effective for the evaluation of PSL. Based with FEA, the craniocaudal cyclic load significantly reduces the screw pullout force by progressively accumulating bone tissue failure around the screw, which may relate with bone mass loss around the screw trajectory. Both HU value of screw trajectory and the pullout force with preset cyclic load were correlated with PSL, but FEA have slightly high performance in predicting PSL and risk assessment.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflict of Interest:\u003c/h2\u003e \u003cp\u003eThe authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis study was supported by the National Natural Science Foundation of China [Grant No. 82171927], the Beijing Natural Science Foundation [Grant No. 7212126], the Beijing New Health Industry Development Foundation [Grant No. XM2020-02-006], National Natural Science Foundation of China (Grant No. 82102638), Peking University Third Hospital Clinical Key Project (Grant No. BYSYZD2021040), Peking University Third Hospital Clinical Cohort Construction Project (Grant No. BYSYDL2022007), Peking University Teaching and Learning 2.0 (Grant No. 2023YB01), and Peking University Health Science Center Education and Teaching Research Project (Grant No. 2021YB05)\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eChenyu Jiang: Data curation, Writing- Original draft preparation, Methodology, Software. Hanqiang Ouyang: Visualization, Investigation. Dan Jin: Conceptualization, Methodology. Yan Zhang and Liang Jiang: Supervision. Ming Ni and Yali Li: Software, Validation. Huishu Yuan: Writing- Reviewing and Editing\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBydon M, Abt NB, De la Garza-Ramos R, et al. Impact of age on short-term outcomes after lumbar fusion: an analysis of 1395 patients stratified by decade cohorts. Neurosurgery. 2015;77: 347\u0026ndash;354.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGalbusera F, Volkheimer D, Reitmaier S, Berger-Roscher N, Kienle A, Wilke HJ. Pedicle screw loosening: a clinically relevant complication? 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J Neurosurg Spine. 2015;22(5):503\u0026ndash;510.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMolinari L, Falcinelli C, Gizzi A, Di Martino A. Effect of pedicle screw angles on the fracture risk of the human vertebra: A patient-specific computational model. J Mech Behav Biomed Mater. 2021;116:104359.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYao Y, Yuan H, Huang H, Liu J, Wang L, Fan Y. Biomechanical design and analysis of auxetic pedicle screw to resist loosening. Comput Biol Med. 2021;133:104386.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFasser MR, Gerber G, Passaplan C, et al. Computational model predicts risk of spinal screw loosening in patients. Eur Spine J. 2022;31(10):2639\u0026ndash;2649.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSong F, Liu Y, Fu R, et al. Craniocaudal toggling increases the risk of screw loosening in osteoporotic vertebrae. Comput Methods Programs Biomed. 2023;238:107625.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eF. Graichen, G. Bergmann, A. Rohlmann, Patient monitoring system for load measurement with spinal fixation devices, Med. Eng. Phys. 18 (1996) 167\u0026ndash;174.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRohlmann, G. Bergmann, F. Graichen, Loads on an internal spinal fixation device during walking, J. Biomech. 30 (1) (1997) 41\u0026ndash;47.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eR.A. Kueny, J.P. Kolb, W. Lehmann, K. Puschel, M.M. Morlock, G. Huber, Influence of the screw augmentation technique and a diameter increase on pedicle screw fixation in the osteoporotic spine: pullout versus fatigue testing, Eur.Spine J. 23 (10) (2014) 2196\u0026ndash;2202.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eD. Grevenstein, M.J. Scheyerer, C. 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Opportunistic Osteoporosis Screening at Routine Abdominal and Thoracic CT: Normative L1 Trabecular Attenuation Values in More than 20 000 Adults. Radiology. 2019;291(2):360\u0026ndash;367.\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":"Osteoporosis, biomechanical analysis, finite element analysis, pedicle, screw loosening","lastPublishedDoi":"10.21203/rs.3.rs-4252319/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4252319/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground:\u003c/h2\u003e \u003cp\u003eScrew loosening remains a prominent complication for osteoporotic patients with pedicle screw fixation surgeries, yet with limited risk assessment approach. The aim of this study was to investigate influence of craniocaudal cyclic load on pedicle screw fixation strength by computed tomography (CT) based finite element analysis (FEA) and we examined predict ability in pedicle screw loosening (PSL).\u003c/p\u003e\u003ch2\u003eMethods:\u003c/h2\u003e \u003cp\u003e12 clinical PSL cases (7 men, 5 women) and 12 age- and sex-matched controls were enrolled for CT based FEA. Simple axial pullout load and axial pullout load with preset craniocaudal cyclic load were applied to each model respectively, and the ultimate pullout force under both conditions is calculated as the fixed strength and compared. Besides, HU values of the vertebral body trabeculae and screw trajectory were measured as an assessment of osteoporosis. The ultimate pullout force and HU value were compared between PSL and controls cases.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThe cyclic load remarkably reduce the pullout force of pedicle screws (906.2\u0026thinsp;\u0026plusmn;\u0026thinsp;180.2 N vs. 729.3\u0026thinsp;\u0026plusmn;\u0026thinsp;172.3 N, p\u0026lt;0.0001) by CT based FEA. No significant difference between the PSL and the control group in the simple axial pull-out force and HU values of the vertebral body. But the pullout force with preset cyclic load (639.2\u0026thinsp;\u0026plusmn;\u0026thinsp;169.4 N vs. 819.4\u0026thinsp;\u0026plusmn;\u0026thinsp;125.1 N, p\u0026thinsp;=\u0026thinsp;0.072) and the HU value of the screw trajectory (177.5\u0026thinsp;\u0026plusmn;\u0026thinsp;43.8 vs. 217.2\u0026thinsp;\u0026plusmn;\u0026thinsp;29.6, p\u0026thinsp;=\u0026thinsp;0.016) in the PSL group is significantly lower than that in the control group. Area under receiver operating characteristic curve (ROC) revealed pullout force with preset cyclic load slightly better predicted PSL than HU value of the screw trajectory (AUC\u0026thinsp;=\u0026thinsp;0.798 vs. 0.750).\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eThe craniocaudal cyclic load significantly reduces the screw fixation strength. HU value of screw trajectory and pullout force with preset cyclic load by CT based FEA are helpful for the clinical prediction of PSL.\u003c/p\u003e","manuscriptTitle":"Craniocaudal cyclic load improve risk assessment of lumbar pedicle screw loosening：finite element analysis based on computer tomography","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-02 21:01:51","doi":"10.21203/rs.3.rs-4252319/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":"d4d168a8-f4e4-42a8-b679-11e6ef0c986b","owner":[],"postedDate":"May 2nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":31324079,"name":"Health sciences/Anatomy/Musculoskeletal system/Bone"},{"id":31324080,"name":"Health sciences/Risk factors"},{"id":31324081,"name":"Health sciences/Health occupations/Orthopaedics"}],"tags":[],"updatedAt":"2024-12-02T17:25:27+00:00","versionOfRecord":[],"versionCreatedAt":"2024-05-02 21:01:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4252319","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4252319","identity":"rs-4252319","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}