Biomechanical effects of different intervertebral height reconstructions on the intermediate segment in skip-level ACDF for discontinuous cervical spondylosis: a finite element analysis

Biomechanical effects of different intervertebral height reconstructions on the intermediate segment in skip-level ACDF for discontinuous cervical spondylosis: a finite element analysis | 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 Biomechanical effects of different intervertebral height reconstructions on the intermediate segment in skip-level ACDF for discontinuous cervical spondylosis: a finite element analysis Xulong wang, Zhengqi Bao, Heng Zhang, Yuchen Ye, Wei Gao This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8677951/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 11 You are reading this latest preprint version Abstract Background Skip-level anterior cervical discectomy and fusion (ACDF) has been reported to provide favorable outcomes for discontinuous cervical spondylosis; however, intermediate segment degeneration (ASD) remains a concern. Reconstruction of intervertebral height at fused levels may affect postoperative biomechanics, yet the optimal reconstruction strategy remains unclear. Methods A three-dimensional finite element model of the cervical spine (C2–C7) was developed. Skip-level ACDF was simulated at C4/5 and C6/7. Six models were analyzed: an intact model (M0) and five postoperative models with reconstructed intervertebral heights of 100%, 125%, 150%, 175%, and 200% of a reference height (M1–M5). A 50 N axial preload and a 1.0 N·m pure moment were applied to simulate flexion, extension, left/right lateral bending, and left/right axial rotation. Outcome measures included cervical range of motion (ROM), peak Von Mises stress of vertebrae and implants, and stress in the intermediate disc (C5/6). Results ROM at the fused segments decreased markedly in all postoperative models. During lateral bending and axial rotation, ROM and disc stress at non-fused levels—particularly the intermediate segment—generally increased with greater reconstructed height, whereas disc stress tended to decrease or remain relatively stable during extension and right axial rotation. Across most motion directions, the 100% reconstruction model showed relatively smaller increases in intermediate-segment ROM and disc stress, while the 125% reconstruction model exhibited lower cage and facet joint stresses. Lateral bending produced notably higher cage and screw stresses compared with other motion directions. Conclusions Under finite element conditions, when the cage height was set to 100% of the reference intervertebral height, the intermediate segment exhibited relatively smaller biomechanical changes in most motion scenarios, suggesting that this reconstruction height may have a limited impact on the intermediate segment. Biomechanical responses of the postoperative intermediate segment and the fixation system varied among different motion directions; in particular, load variation patterns during extension and lateral bending suggest that postoperative motion may influence the mechanical environment of the intermediate segment and implant stability. The clinical relevance of these findings requires further investigation. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Cervical spondylosis is a common degenerative disorder. Anterior cervical discectomy and fusion (ACDF), first introduced by Smith–Robinson and Cloward, has become a widely accepted surgical procedure for the treatment of cervical degenerative diseases due to its advantages of direct decompression, reliable neural relief, and high fusion rates [1]. For patients with discontinuous cervical spondylosis, skip-level ACDF has been reported to achieve favorable clinical outcomes and biomechanical performance [2, 3]. Several clinical studies have demonstrated significant postoperative improvement in neurological function and disability scores, with a relatively low incidence of symptomatic adjacent segment degeneration (ASD) during mid- to long-term follow-up [4,5]. However, despite these encouraging results, the occurrence of ASD following skip-level ACDF has not been completely eliminated and remains a clinical concern [5]. ASD is considered a multifactorial process, for example Age; preoperative Cobb angle; change in Cobb angle (ΔCobb, pre- vs. postoperative); and postoperative intervertebral height reconstruction [6]. Among the potential contributing factors, reconstruction of intervertebral height at the fused segments has been suggested to significantly influence load transmission and motion distribution of the cervical spine [7]. Previous studies have indicated that excessive distraction of the intervertebral space may potentially accelerate adjacent segment degeneration [8]. Finite element studies investigating conventional ACDF have shown that increased reconstructed intervertebral height may be associated with elevated intervertebral disc pressure and increased range of motion at adjacent levels. However, the reported optimal reconstruction height varies among studies, and conclusions remain inconsistent [9,10]. At present, there is no consensus regarding the appropriate reconstruction height for the upper and lower fused levels in skip-level ACDF, nor is it fully understood whether increasing reconstruction height may elevate the risk of degeneration at the intermediate segment. With the growing clinical application of skip-level ACDF, further investigation into this issue is warranted. In addition, implant selection may also influence postoperative biomechanics. Previous studies have suggested that zero-profile interbody fusion devices may reduce stress on adjacent discs and endplates compared with traditional anterior plate fixation, potentially decreasing the risk of adjacent segment disease [11]. Therefore, the present study employed a zero-profile fusion system to investigate the biomechanical effects of different intervertebral height reconstructions. Given individual variations in vertebral size and disc degeneration, the average height of the adjacent intervertebral spaces above and below the surgical levels was selected as the reference height in this study, rather than the collapsed surgical disc height. Based on this reference, finite element models with reconstruction heights of 100%, 125%, 150%, 175%, and 200% were established to simulate different clinical distraction strategies. Therefore, the purpose of this study was to investigate the biomechanical effects of different intervertebral height reconstructions in skip-level ACDF on the intermediate segment using a three-dimensional finite element model. The findings of this study may provide biomechanical insights for surgical planning and postoperative management of patients undergoing skip-level ACDF. Methods 1.Finite element model construction A three-dimensional finite element (FE) model of the cervical spine (C2–C7) was constructed based on computed tomography (CT) images of a adult subject. the subject presented with noncontiguous cervical spondylosis in Imaging examinations. The CT data were imported into Mimics software (Materialise, Leuven, Belgium) for segmentation of cortical bone, cancellous bone, intervertebral discs, and posterior elements. Surface reconstruction and smoothing were performed to generate geometric models, which were subsequently imported into ANSA for further processing. The final solid models were assembled and meshed using finite element software. The intervertebral disc was modeled as a composite structure consisting of the nucleus pulposus and annulus fibrosus. The annulus fibrosus was represented with a ground substance reinforced by collagen fibers arranged in concentric layers. Major spinal ligaments, including the anterior longitudinal ligament, posterior longitudinal ligament, ligamentum flavum, interspinous ligament, supraspinous ligament, and capsular ligaments, were simulated using tension-only spring or truss elements. All materials were assumed to be homogeneous, isotropic, and linearly elastic. 2.Material properties Material properties for bone, intervertebral discs, ligaments, and implants were assigned based on values reported in previously published studies. Cortical bone, cancellous bone, posterior elements, endplates, and implants were modeled as linear elastic materials. The nucleus pulposus was assigned a nearly incompressible material property to simulate its hydrostatic behavior, while the annulus fibrosus was modeled with fiber-reinforced characteristics. All material parameters were kept consistent across all models. Material properties are derived from previous studies[12–15].(Table 1 ) Table 1 Material properties assigned in the finite element model Component Material property Young’s modulus (MPa) Poisson’s ratio Cortical bone Linear elastic 12,000 0.30 Cancellous bone Linear elastic 450 0.20 Posterior elements Linear elastic 3,500 0.25 Endplate Linear elastic 500 0.25 Annulus fibrosus (ground substance) Linear elastic 4.2 0.45 Annulus fibrosus fibers Tension-only truss 550 — Nucleus pulposus Nearly incompressible 1.0 0.49 Anterior longitudinal ligament Nonlinear elastic 7.8 — Posterior longitudinal ligament Nonlinear elastic 10.0 — Ligamentum flavum Nonlinear elastic 15.0 — Interspinous ligament Nonlinear elastic 10.0 — Supraspinous ligament Nonlinear elastic 8.0 — Capsular ligament Nonlinear elastic 12.5 — Interbody fusion cage (PEEK) Linear elastic 3,600 0.30 Fixation screws (Titanium alloy) Linear elastic 110,000 0.30 (All materials were assumed to be homogeneous, isotropic, and linearly elastic unless otherwise specified. Ligaments were modeled as tension-only elements.) 3.Surgical simulation and model grouping To simulate skip-level anterior cervical discectomy and fusion (ACDF), intervertebral discs at the C4/5 and C6/7 levels were removed, while the intermediate segment (C5/6) was preserved. A zero-profile interbody fusion device was inserted at the fused levels to represent postoperative conditions. Six FE models were established, including one intact model (M0) and five postoperative models with different intervertebral height reconstructions. The reconstructed heights were defined as 100%, 125%, 150%, 175%, and 200% of the reference height (M1–M5). The reference height was calculated as the average height of the adjacent intervertebral spaces above and below the surgical levels, rather than the collapsed surgical disc height, in order to minimize the influence of individual disc degeneration. 4.Boundary and loading conditions The inferior surface of the C7 vertebra was fully constrained in all degrees of freedom. A compressive preload of 50 N was applied to the superior surface of the C2 vertebra to simulate the weight of the head. Subsequently, a pure moment of 1.0 N·m was applied to generate physiological motions in six directions: flexion, extension, left and right lateral bending, and left and right axial rotation. All loading conditions were applied consistently to each FE model to allow for comparative analysis of biomechanical responses under identical conditions. 5.Outcome measurements The primary outcome parameters included the range of motion (ROM) of each cervical segment, peak Von Mises stress of the vertebral bodies, interbody fusion devices, cortical bone, and fixation screws, as well as stress distribution within the intervertebral disc of the intermediate segment (C5/6), including both nucleus pulposus and annulus fibrosus. These parameters were extracted and compared among different models and loading conditions. Results 1.Model validation The intact FE model was validated by comparing its segmental range of motion under physiological loading conditions with previously published experimental and numerical data [13–15]. The simulated ROM values were found to be within the ranges reported in the literature, indicating that the FE model was reasonable for subsequent biomechanical analysis.(Table 2 ) Table 2 Comparison of ROM results of the M0 model under different operating conditions with previous studies(°)[13–15] flexion and extension lateral bending axial rotation panjabi ito Chen This article panjabi ito Chen This article panjabi ito Chen This article C2-C3 6.8 ± 1.4 9 ± 4 8.8 ± 2.1 14.41 9.6 ± 1.8 9.7 ± 4.3 8.4 ± 3.8 4.71 3.3 ± 0.8 6.6 ± 4.8 6.7 ± 3.9 7.98 C3-C4 8.2 ± 4.7 10 ± 4.5 9.7 ± 3.4 12.31 9 ± 1.9 8.6 ± 5.9 8 ± 3.5 4.35 5.1 ± 1.2 9.5 ± 4.9 7.1 ± 2.1 12.06 C4-C5 9.8 ± 4 14.3 ± 5.5 13.8 ± 4.7 6.69 9.3 ± 1.7 8.1 ± 3.8 7.5 ± 3.7 4.98 6.8 ± 1.3 11.5 ± 3.8 9 ± 1.8 8.43 C5-C6 10.4 ± 5.2 14.5 ± 8 14.1 ± 6.1 6.39 6.5 ± 1.5 4.9 ± 2.1 4.8 ± 2.4 4.41 5 ± 1 7.8 ± 4.1 7.7 ± 3.4 7.47 C6-C7 8 ± 4.3 15.2 ± 3.1 14.9 ± 3.5 8.17 5.4 ± 1.5 6.8 ± 3.3 3.9 ± 2.1 4.03 2.9 ± 0.8 6.5 ± 3.3 6 ± 2.1 7.695 2. Maximum segmental range of motion among different models Compared with the intact model (M0), all postoperative models (M1–M5) exhibited a pronounced reduction in ROM at the fused segments (C4/5 and C6/7) under all loading conditions, indicating increased segmental stiffness after implantation. In lateral bending (left and right), ROM increased at the intermediate segment (C5/6) after surgery, and the magnitude of ROM increment generally increased with larger reconstructed intervertebral heights. In combined flexion and extension, the intermediate segment (C5/6) ROM showed a decreasing trend with increasing reconstructed height. For the intermediate segment (C5/6), the ROM increment was relatively smaller in the model with 100% reference height (M1) in axial rotation and lateral bending, and increased progressively as the reconstructed height increased.(Table 3 ) Table 3 .Comparison of intervertebral relative range of motion among different intervertebral disc height groups (°) flexion and extension lateral bending axial rotation M0 M1 M2 M3 M4 M5 M0 M1 M2 M3 M4 M5 M0 M1 M2 M3 M4 M5 C2-C3 9.61 9.91 9.81 9.96 9.85 9.82 3.17 3.14 3.17 3.20 3.22 3.24 5.32 6.71 6.84 6.97 7.08 7.20 C3-C4 8.21 6.93 6.95 6.83 6.92 6.92 2.90 3.25 3.31 3.37 3.42 3.46 8.04 8.85 9.00 9.12 9.25 9.37 C4-C5 4.46 0.56 0.64 0.72 0.78 0.80 3.32 0.79 0.88 0.98 1.11 1.26 5.62 0.51 0.63 0.78 0.95 1.07 C5-C6 4.26 3.45 3.37 3.24 3.12 3.00 2.94 3.19 3.19 3.19 3.19 3.20 4.98 5.86 5.91 5.99 6.07 6.15 C6-C7 3.27 0.30 0.31 0.31 0.29 0.27 2.69 0.86 0.99 1.13 1.24 1.36 5.13 0.63 0.77 0.94 1.09 1.22 3. Peak intervertebral disc stress of the intermediate segment(C5/6) in different models Stress within the intermediate intervertebral disc (C5/6) was evaluated for both the nucleus pulposus and annulus fibrosus. Under flexion, lateral bending, and left axial rotation, disc stress at C5/6 generally increased as the reconstructed height increased. Under extension and right axial rotation, disc stress showed a decreasing trend or remained relatively stable across models. With increasing reconstructed height, disc stress at C5/6 decreased progressively under extension. Among postoperative models, the 100% reference height model (M1) showed a relatively lower increment of disc stress in most loading directions, except for right axial rotation. Right axial rotation produced the highest disc stress among all motion directions in both intact and postoperative models. (Fig. 1. Stress Comparison of the C5/6 intervertebral disc in different models.(MPa)) 4. Peak stress of the interbody fusion cage and screw in different models Peak Von Mises stress of the interbody fusion device (cage) varied across motion directions and reconstructed heights. Stress concentration was mainly observed at the anterior-lateral and posterior regions of the cage, while the central region exhibited relatively lower stress. Across postoperative models, the 125% reference height model (M2) demonstrated lower peak cage stress than the other height conditions over the tested motion directions. In lateral bending, cage stress increased markedly compared with the other motion directions. Screw stress differed among models. The 100% reference height model (M1) exhibited lower screw stress compared with other postoperative models. Screw stress increased substantially during lateral bending and generally increased with larger reconstructed heights. (Fig. 2. Stress Comparison of the cage in different models under six motion directions.(MPa)) 5. Peak cortical bone stress in different models Postoperatively, peak cortical bone stress increased compared with the intact model, with more evident increases under flexion/extension and lateral bending. During lateral bending, cortical bone stress tended to increase as reconstructed height increased. Among postoperative models, the 100% reference height model (M1) showed relatively lower cortical bone stress compared with models with larger reconstructed heights. (Fig. 3. Stress Comparison of cortical bone in different models under six motion directions.(MPa)) 6. Peak facet joint stress of the intermediate segment(C5/6) in different models Facet joint stress of the intermediate segment (C5/6) was assessed under six motion directions. Compared with the intact model, facet joint stress in the postoperative models generally decreased under most loading conditions, whereas an exception was observed under flexion, where facet joint stress did not show the same decreasing pattern. Across postoperative models, the 125% reference height model (M2) exhibited relatively lower average facet joint stress across motion directions. (Fig. 4. Stress Comparison of facet joint in different models under six motion directions.(MPa)) Discussion The present study investigated the biomechanical effects of different intervertebral height reconstructions in skip-level ACDF on the intermediate segment using a three-dimensional finite element model. The main findings were as follows: (1) increasing reconstructed height was associated with distinct changes in cervical kinematics, with progressive increases in ROM at non-fused levels during lateral bending and a decreasing trend in overall C2–C7 ROM during flexion/extension; the intermediate segment (C5/6) demonstrated relatively smaller ROM increments at the 100% reference height condition. (2) Intermediate disc stress exhibited direction-dependent patterns: stresses generally increased with greater reconstructed height under flexion, lateral bending, and left rotation, whereas they decreased or remained stable under extension and right rotation; among the postoperative models, the 100% reference height condition showed relatively lower disc stress increments in most directions except right rotation. (3) Implant-related stresses varied by motion direction and reconstruction height: the 125% reference height condition showed comparatively lower peak cage stress across directions, while the 100% reference height condition showed lower screw stress; lateral bending produced markedly higher cage and screw stresses. (4) Cortical bone stress increased after fusion and tended to increase with reconstructed height during lateral bending, while the 100% reference height condition showed relatively lower cortical bone stress compared with larger-height models. (5) Facet joint stress at the intermediate segment generally decreased after skip-level fusion under most loading conditions, with the 125% reference height condition demonstrating relatively lower average facet stress across directions. (Fig. 5. Stress distribution of the C5/6 intervertebral disc in different models under four motion directions.) These findings highlight that intervertebral height reconstruction and motion direction jointly influence the postoperative biomechanical environment of the intermediate segment and the implant system in skip-level ACDF. Collectively, the 100% reference height condition tended to be associated with smaller changes in intermediate-segment ROM and disc stress in most motion directions, whereas the 125% reference height condition was associated with lower cage stress and facet joint stress. Given that this study was based on a finite element model with standardized loading conditions, the results should be interpreted as biomechanical trends, and further experimental and clinical studies are warranted to validate their clinical relevance. (Fig. 6. Stress distribution map of the fusion device in the M1 model. Figure A: Flexion; Figure B: Extension; Figure C: Left rotation; Figure D: Right rotation;Figure E: Left lateral flexion; Figure F: Right lateral flexion.) 1. Effects of different reconstructed intervertebral heights on range of motion of the intermediate segment Compared with the intact model (M0), all postoperative models (M1–M5) exhibited a marked reduction in range of motion (ROM) at the fused segments (C4/5 and C6/7), indicating increased segmental stability following internal fixation and cage implantation. Under left and right lateral bending, ROM at non-fused segments increased after surgery, and the magnitude of ROM increase progressively rose with increasing reconstructed intervertebral height. In contrast, during combined flexion and extension, the overall C2–C7 ROM demonstrated a continuous decreasing trend as reconstructed height increased. Previous studies have reported that loss of motion at fused segments may lead to increased motion at adjacent segments, potentially accelerating adjacent segment degeneration [16,17]. In the present study, under axial rotation and lateral bending, the smallest increase in ROM at the intermediate segment (C5/6) was observed when the reconstructed height was set to the reference height(100%). As the cage height further increased, ROM at the intermediate segment increased accordingly. These results suggest that excessive reconstruction of intervertebral height may increase the risk of compensatory motion at the intermediate segment, which from a biomechanical perspective could be associated with degenerative trends at this level. 2. Effects of different reconstructed intervertebral heights on disc stress of the intermediate segment The intervertebral disc consists primarily of the annulus fibrosus and nucleus pulposus. The nucleus pulposus plays a critical role in absorbing spinal loads and distributing them evenly to the surrounding annulus fibrosus and cartilaginous endplates. Increased nucleus pulposus pressure has been reported to impair cellular activity and promote apoptosis [18], while excessive intradiscal pressure may also contribute to annular rupture and subsequent disc herniation [19]. Moreover, elevated stress in either the nucleus pulposus or annulus fibrosus has been associated with disc cell apoptosis and degenerative processes [20]. Long-term mechanical loading is therefore considered an important contributor to intervertebral disc degeneration. Previous studies have demonstrated that anterior cervical fusion can lead to increased stress at adjacent segments [21]. In the present study, disc stress at the intermediate segment (C5/6) exhibited a progressive increasing trend under flexion, lateral bending, and left axial rotation as reconstructed intervertebral height increased, which is consistent with findings from previous investigations. These results suggest that greater reconstruction height may be associated with increased shear and compressive loading at the intermediate segment under these motion directions. In contrast, under extension and right axial rotation, stress in both the annulus fibrosus and nucleus pulposus decreased or remained relatively stable, indicating that increased construct rigidity may partially attenuate load transmission in these directions.With increasing reconstructed height, disc stress at the intermediate segment gradually decreased during extension, which may be associated with reduced segmental mobility in this motion direction. Among the postoperative models, when the reconstructed height was set to the reference height(100%), the increase in disc stress at the intermediate segment was relatively smaller than that observed in the other reconstruction conditions in most motion directions, except for right axial rotation. Across both intact and postoperative models, right axial rotation consistently produced higher disc stress compared with other motion directions. These findings indicate that axial rotation may impose greater mechanical loading on the intervertebral disc and therefore warrants attention in postoperative motion considerations. 3, Effects of different reconstructed intervertebral heights on cage and screw stress Previous study have reported that excessive stress on interbody fusion cages may accelerate implant damage, whereas insufficient stress may delay fusion and compromise fusion efficiency. Increased implant stress may also induce stress shielding in the surrounding bone tissue, potentially reducing bone density and, over time, contributing to implant subsidence or osteoporotic changes [22]. In the present study, cage stress exhibited distinct patterns across different motion directions and reconstructed height conditions. As shown in Fig. 2, the magnitude of cage stress varied with both motion direction and reconstruction height. Stress distribution maps demonstrated that stress was primarily concentrated at the anterior–lateral and posterior regions of the cage, while the central region experienced relatively lower stress, which is considered favorable for bone graft fusion. This distribution pattern is consistent with previous finite element findings reported by Huang et al. [23]. Among the postoperative models, the 125% reference height model (M2) demonstrated lower peak cage stress compared with the other reconstruction conditions, with peak values ranging from 77.34 to 221.30 MPa. These findings indicate that reconstruction at 125% of the reference height may be associated with more favorable stress conditions for the cage structure under finite element conditions. In contrast, cage stress increased markedly during left and right lateral bending, suggesting that this motion direction may impose higher mechanical demands on the cage. Screw stress also varied among models. The 100% reference height model (M1) exhibited lower screw stress than the other postoperative models. Under lateral bending, screw stress increased substantially and showed a progressive rise with increasing reconstructed height. Elevated screw stress has been associated with an increased risk of screw loosening, migration, or fracture, which may adversely affect fusion stability and, in severe cases, necessitate revision surgery. The present findings suggest that lateral bending conditions may increase screw-related mechanical loading and associated structural risk under finite element conditions. 4. Effects of different reconstructed intervertebral heights on cortical bone stress In the present study, cortical bone stress increased markedly after fusion compared with the intact model, with more pronounced increases observed during flexion–extension and left and right lateral bending. From a biomechanical perspective, elevated cortical bone stress may be associated with an increased risk of bone overload under these motion conditions. Similar findings were reported by Xu et al. [11], who demonstrated that zero-profile fusion systems produced higher cortical bone stress than conventional anterior plate fixation, particularly during flexion–extension and lateral bending, suggesting a potential increase in mechanical demand on the fused vertebrae. With increasing reconstructed intervertebral height, cortical bone stress exhibited a progressive increase during lateral bending. In contrast, when the reconstructed height was set to the reference height, cortical bone stress was relatively lower than that observed in models with greater reconstruction heights. These findings suggest that moderate intervertebral height reconstruction may help limit peak cortical bone stress and thereby reduce excessive load concentration on the cortical bone under finite element conditions. 5. Effects of different reconstructed intervertebral heights on facet joint stress of the intermediate segment Previous studies have reported that facet joint stress at adjacent segments increases after cervical fusion, accompanied by a higher load rate, which may accelerate degenerative processes [24]. In contrast, the present study demonstrated a different biomechanical response. Except for the flexion condition, facet joint stress at the intermediate segment (C5/6) was generally reduced after skip-level ACDF compared with the intact model. A possible explanation for this discrepancy may be related to the unique biomechanical characteristics of skip-level fusion. Following fusion of the segments above and below C5/6, loss of motion at the fused levels and increased construct rigidity may indirectly reduce the motion demand at the intermediate segment. Consequently, shear and compressive loads transmitted to the facet joints at C5/6 may be reduced. Among the postoperative models, the 125% reference height model (M2) exhibited the lowest average facet joint stress across motion directions. Overall, the present findings suggest that skip-level ACDF may be associated with reduced facet joint loading at the intermediate segment under finite element conditions, which from a biomechanical perspective could indicate a potential protective effect on the intermediate facet joints. However, the clinical relevance of these observations requires further investigation. Limitations Several limitations of the present study should be acknowledged. First, the finite element model of the cervical spine was constructed based on CT data from a single individual, and the postoperative fusion models were derived from this baseline geometry. Therefore, the biomechanical results may not fully represent population-level variability. Future studies incorporating models with different sexes, ages, and bone mineral densities are warranted to reduce potential selection bias. Nevertheless, the overall biomechanical trends observed in finite element analysis are considered to be reliable. Second, muscle forces and other soft tissues were not included in the present finite element model. The absence of dynamic muscular stabilization may influence cervical kinematics and load distribution, potentially affecting the accuracy of the simulated results. Third, simplifications were applied to the fusion cage and model geometry, which may limit precise reproduction of the in vivo biomechanical environment, particularly with respect to motion at the implant levels. Fourth, the present study lacked validation through cadaveric or animal experiments, and no direct experimental data were available for comparison. Consequently, further experimental investigations, including cadaveric testing, animal studies, or clinical outcome analyses, are required to validate the biomechanical findings of this study. Future research should integrate diversified finite element models, dynamic muscle loading, and clinical outcome data to further verify and refine the conclusions. In addition, currently available interbody fusion cages are typically manufactured with predefined heights, which limits the degree of individualization in clinical practice. Future studies may benefit from incorporating patient-specific implant designs, potentially enabled by three-dimensional printing technologies, to explore personalized reconstruction strategies and their biomechanical implications. Declarations Clinical trial number Not applicable. Ethics approval and consent to participate Not applicable. Consent for publication Not applicable Competing interests The authors declare that they have no competing interests. Funding This study was supported by the Third Batch of Excellent Young Scientific Research Projects of the First Affiliated Hospital of Bengbu Medical College(Grant No. 2025BYYFYYQ08);Key Natural Science Projects of Universities in Anhui Province༈Grant No.2022AH051487༉;Anhui Province Clinical Medicine Research and Translation Special Project(Grant No.202527C10020128);Key Natural Science Project of Bengbu Medical University(Grant No.2021BYZD082) and Youth Project of Anhui Provincial Health and Medical Research Programme༈Grant No.AHWJ2023A30150༉(AnHui China) Author Contribution Wang and Bao designed the study ，constructed the finite element models.and performed the data analysis and interpretation.Wang and Gao drafted the manuscript.Bao 、Zhang and Ye critically revised the manuscript.All authors read and approved the final manuscript. Acknowledgements The authors would like to thank all contributors who provided technical support for this study. 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Sun Z, Mi C. Biomechanics of annulus fibrosus: elastic fiber simplification and degenerative impact on damage initiation and propagation. J Mech Behav Biomed Mater. 2024;157:106628. Wu TK, Meng Y, Liu H, et al. Biomechanical effects on the intermediate segment of noncontiguous hybrid surgery with cervical disc arthroplasty and anterior cervical discectomy and fusion: a finite element analysis. Spine J. 2019;19(7):1254–63. Cao L, Chen Q, Jiang LB, et al. Bioabsorbable self-retaining PLA/nano-sized β-TCP cervical spine interbody fusion cage in goat models: an in vivo study. Int J Nanomedicine. 2017;12:7197–205. Huang DA, Liu C. Three-dimensional finite element analysis of a novel height-adjustable cervical fusion cage. Chin J Tissue Eng Res. 2023;27(18):2797–803. Li H, Pei BQ, Yang JC, et al. Load rate of facet joints at the adjacent segment increased after fusion. Chin Med J (Engl). 2015;128(8):1042–6. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 03 Mar, 2026 Reviews received at journal 01 Mar, 2026 Reviews received at journal 24 Feb, 2026 Reviewers agreed at journal 11 Feb, 2026 Reviews received at journal 10 Feb, 2026 Reviewers agreed at journal 09 Feb, 2026 Reviewers agreed at journal 09 Feb, 2026 Reviewers invited by journal 09 Feb, 2026 Editor assigned by journal 24 Jan, 2026 Submission checks completed at journal 24 Jan, 2026 First submitted to journal 23 Jan, 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-8677951","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":588963965,"identity":"461611f4-980a-4ee5-90c7-c5fc17450b4f","order_by":0,"name":"Xulong wang","email":"","orcid":"","institution":"First Affiliated Hospital of Bengbu Medical College","correspondingAuthor":false,"prefix":"","firstName":"Xulong","middleName":"","lastName":"wang","suffix":""},{"id":588963966,"identity":"f0dc7a1b-9a14-4aab-8ae7-3ac7f1348e87","order_by":1,"name":"Zhengqi Bao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA00lEQVRIiWNgGAWjYBACAyBmBrOYmQ8c+PCDNC1siQdn9pCkhYHH+DAHGxFazNkPH/5cUHHHru84z4fDDDwM8vxiB/BrsexJSzCeceZZ8szDvBsOF1gwGM6cnUDAYQdyDJJ52w4nG4C0zOBhSDC4TUjL+TdAxf9AWngeHOZhI0bLjRzDZt6Gw3ZALQzEabGc8SyZmefY4QTJw2wGwECWIOwXc/7kw595ag7b850//PjDhx828vzSBLTAQGLDATAtQZxyELBnOEC84lEwCkbBKBhhAADyfEkukkYtHwAAAABJRU5ErkJggg==","orcid":"","institution":"First Affiliated Hospital of Bengbu Medical College","correspondingAuthor":true,"prefix":"","firstName":"Zhengqi","middleName":"","lastName":"Bao","suffix":""},{"id":588963967,"identity":"64eae44d-ac7e-4562-8a30-fe17d9a94b96","order_by":2,"name":"Heng Zhang","email":"","orcid":"","institution":"First Affiliated Hospital of Bengbu Medical College","correspondingAuthor":false,"prefix":"","firstName":"Heng","middleName":"","lastName":"Zhang","suffix":""},{"id":588963968,"identity":"bf08fd5e-3008-4744-ae56-6c7423518af8","order_by":3,"name":"Yuchen Ye","email":"","orcid":"","institution":"First Affiliated Hospital of Bengbu Medical College","correspondingAuthor":false,"prefix":"","firstName":"Yuchen","middleName":"","lastName":"Ye","suffix":""},{"id":588963969,"identity":"559f9998-29b0-4f1f-9ee0-c72077645183","order_by":4,"name":"Wei Gao","email":"","orcid":"","institution":"First Affiliated Hospital of Bengbu Medical College","correspondingAuthor":false,"prefix":"","firstName":"Wei","middleName":"","lastName":"Gao","suffix":""}],"badges":[],"createdAt":"2026-01-23 10:12:05","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8677951/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8677951/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102379892,"identity":"0dec99af-7ee2-45d1-afde-34358010ce16","added_by":"auto","created_at":"2026-02-11 06:28:34","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":153364,"visible":true,"origin":"","legend":"\u003cp\u003eStress Comparison of the C5/6 intervertebral disc in different models.（MPa）\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8677951/v1/a5d0444b626d7b58c2ca22de.png"},{"id":102398104,"identity":"606d6920-8043-412f-a219-7b277f4b9b3a","added_by":"auto","created_at":"2026-02-11 10:21:00","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":129527,"visible":true,"origin":"","legend":"\u003cp\u003eStress Comparison of the cage in different models under six motion directions.（MPa）\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8677951/v1/d4e908b4a9ad37ffe4c2b58d.png"},{"id":102379894,"identity":"dfa87738-e296-4814-b7dc-328691bbbd70","added_by":"auto","created_at":"2026-02-11 06:28:34","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":121895,"visible":true,"origin":"","legend":"\u003cp\u003eStress Comparison of cortical bone in different models under six motion directions.（MPa）\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8677951/v1/105324f129da4cf99de733c9.png"},{"id":102379896,"identity":"c750bb83-3c0a-4ee9-b132-bb8ee1b3f790","added_by":"auto","created_at":"2026-02-11 06:28:34","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":163058,"visible":true,"origin":"","legend":"\u003cp\u003eStress Comparison of facet joint in different models under six motion directions.（MPa）\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8677951/v1/490ac6f0e3e625d3924debe9.png"},{"id":102379898,"identity":"6efbdce9-307c-4e7e-b6dd-6a5b30908c25","added_by":"auto","created_at":"2026-02-11 06:28:35","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":478291,"visible":true,"origin":"","legend":"\u003cp\u003eStress distribution of the C5/6 intervertebral disc in different models under four motion directions.）\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8677951/v1/80e5be4630faf7066648a6af.png"},{"id":102398234,"identity":"4d87b13e-9c89-4fb1-b725-eb4b1d29ecb5","added_by":"auto","created_at":"2026-02-11 10:21:52","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":302244,"visible":true,"origin":"","legend":"\u003cp\u003eStress distribution map of the fusion device in the M1 model. Figure A: Flexion; Figure B: Extension; Figure C: Left rotation; Figure D: Right rotation;Figure E: Left lateral flexion; Figure F: Right lateral flexion.)\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8677951/v1/f6fe4c813d1423d1d4914b58.png"},{"id":102399143,"identity":"b7d4a74e-b016-4733-b373-386c632ba501","added_by":"auto","created_at":"2026-02-11 10:33:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2577585,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8677951/v1/475b0ef4-6a43-4f9c-9388-86bf769ff959.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Biomechanical effects of different intervertebral height reconstructions on the intermediate segment in skip-level ACDF for discontinuous cervical spondylosis: a finite element analysis","fulltext":[{"header":"Introduction","content":"\u003cp\u003eCervical spondylosis is a common degenerative disorder. Anterior cervical discectomy and fusion (ACDF), first introduced by Smith\u0026ndash;Robinson and Cloward, has become a widely accepted surgical procedure for the treatment of cervical degenerative diseases due to its advantages of direct decompression, reliable neural relief, and high fusion rates [1].\u003c/p\u003e \u003cp\u003eFor patients with discontinuous cervical spondylosis, skip-level ACDF has been reported to achieve favorable clinical outcomes and biomechanical performance [2, 3]. Several clinical studies have demonstrated significant postoperative improvement in neurological function and disability scores, with a relatively low incidence of symptomatic adjacent segment degeneration (ASD) during mid- to long-term follow-up [4,5]. However, despite these encouraging results, the occurrence of ASD following skip-level ACDF has not been completely eliminated and remains a clinical concern [5].\u003c/p\u003e \u003cp\u003eASD is considered a multifactorial process, for example Age; preoperative Cobb angle; change in Cobb angle (ΔCobb, pre- vs. postoperative); and postoperative intervertebral height reconstruction [6]. Among the potential contributing factors, reconstruction of intervertebral height at the fused segments has been suggested to significantly influence load transmission and motion distribution of the cervical spine [7]. Previous studies have indicated that excessive distraction of the intervertebral space may potentially accelerate adjacent segment degeneration [8]. Finite element studies investigating conventional ACDF have shown that increased reconstructed intervertebral height may be associated with elevated intervertebral disc pressure and increased range of motion at adjacent levels. However, the reported optimal reconstruction height varies among studies, and conclusions remain inconsistent [9,10].\u003c/p\u003e \u003cp\u003eAt present, there is no consensus regarding the appropriate reconstruction height for the upper and lower fused levels in skip-level ACDF, nor is it fully understood whether increasing reconstruction height may elevate the risk of degeneration at the intermediate segment. With the growing clinical application of skip-level ACDF, further investigation into this issue is warranted.\u003c/p\u003e \u003cp\u003eIn addition, implant selection may also influence postoperative biomechanics. Previous studies have suggested that zero-profile interbody fusion devices may reduce stress on adjacent discs and endplates compared with traditional anterior plate fixation, potentially decreasing the risk of adjacent segment disease [11]. Therefore, the present study employed a zero-profile fusion system to investigate the biomechanical effects of different intervertebral height reconstructions.\u003c/p\u003e \u003cp\u003eGiven individual variations in vertebral size and disc degeneration, the average height of the adjacent intervertebral spaces above and below the surgical levels was selected as the reference height in this study, rather than the collapsed surgical disc height. Based on this reference, finite element models with reconstruction heights of 100%, 125%, 150%, 175%, and 200% were established to simulate different clinical distraction strategies.\u003c/p\u003e \u003cp\u003eTherefore, the purpose of this study was to investigate the biomechanical effects of different intervertebral height reconstructions in skip-level ACDF on the intermediate segment using a three-dimensional finite element model. The findings of this study may provide biomechanical insights for surgical planning and postoperative management of patients undergoing skip-level ACDF.\u003c/p\u003e"},{"header":"Methods","content":"\u003ch3\u003e1.Finite element model construction\u003c/h3\u003e\n\u003cp\u003eA three-dimensional finite element (FE) model of the cervical spine (C2\u0026ndash;C7) was constructed based on computed tomography (CT) images of a adult subject. the subject presented with noncontiguous cervical spondylosis in Imaging examinations. The CT data were imported into Mimics software (Materialise, Leuven, Belgium) for segmentation of cortical bone, cancellous bone, intervertebral discs, and posterior elements. Surface reconstruction and smoothing were performed to generate geometric models, which were subsequently imported into ANSA for further processing. The final solid models were assembled and meshed using finite element software.\u003c/p\u003e \u003cp\u003eThe intervertebral disc was modeled as a composite structure consisting of the nucleus pulposus and annulus fibrosus. The annulus fibrosus was represented with a ground substance reinforced by collagen fibers arranged in concentric layers. Major spinal ligaments, including the anterior longitudinal ligament, posterior longitudinal ligament, ligamentum flavum, interspinous ligament, supraspinous ligament, and capsular ligaments, were simulated using tension-only spring or truss elements. All materials were assumed to be homogeneous, isotropic, and linearly elastic.\u003c/p\u003e\n\u003ch3\u003e2.Material properties\u003c/h3\u003e\n\u003cp\u003eMaterial properties for bone, intervertebral discs, ligaments, and implants were assigned based on values reported in previously published studies. Cortical bone, cancellous bone, posterior elements, endplates, and implants were modeled as linear elastic materials. The nucleus pulposus was assigned a nearly incompressible material property to simulate its hydrostatic behavior, while the annulus fibrosus was modeled with fiber-reinforced characteristics. All material parameters were kept consistent across all models. Material properties are derived from previous studies[12\u0026ndash;15].(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\u003eMaterial properties assigned in the finite element model\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 \u003cp\u003eComponent\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMaterial property\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYoung\u0026rsquo;s modulus (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePoisson\u0026rsquo;s ratio\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCortical bone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12,000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCancellous bone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e450\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePosterior elements\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3,500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEndplate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnnulus fibrosus (ground substance)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnnulus fibrosus fibers\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTension-only truss\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e550\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNucleus pulposus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNearly incompressible\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.49\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnterior longitudinal ligament\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNonlinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePosterior longitudinal ligament\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNonlinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLigamentum flavum\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNonlinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInterspinous ligament\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNonlinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSupraspinous ligament\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNonlinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCapsular ligament\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNonlinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInterbody fusion cage (PEEK)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3,600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFixation screws (Titanium alloy)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLinear elastic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e110,000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e(All materials were assumed to be homogeneous, isotropic, and linearly elastic unless otherwise specified. Ligaments were modeled as tension-only elements.)\u003c/p\u003e\n\u003ch3\u003e3.Surgical simulation and model grouping\u003c/h3\u003e\n\u003cp\u003eTo simulate skip-level anterior cervical discectomy and fusion (ACDF), intervertebral discs at the C4/5 and C6/7 levels were removed, while the intermediate segment (C5/6) was preserved. A zero-profile interbody fusion device was inserted at the fused levels to represent postoperative conditions.\u003c/p\u003e \u003cp\u003eSix FE models were established, including one intact model (M0) and five postoperative models with different intervertebral height reconstructions. The reconstructed heights were defined as 100%, 125%, 150%, 175%, and 200% of the reference height (M1\u0026ndash;M5). The reference height was calculated as the average height of the adjacent intervertebral spaces above and below the surgical levels, rather than the collapsed surgical disc height, in order to minimize the influence of individual disc degeneration.\u003c/p\u003e\n\u003ch3\u003e4.Boundary and loading conditions\u003c/h3\u003e\n\u003cp\u003eThe inferior surface of the C7 vertebra was fully constrained in all degrees of freedom. A compressive preload of 50 N was applied to the superior surface of the C2 vertebra to simulate the weight of the head. Subsequently, a pure moment of 1.0 N\u0026middot;m was applied to generate physiological motions in six directions: flexion, extension, left and right lateral bending, and left and right axial rotation.\u003c/p\u003e \u003cp\u003eAll loading conditions were applied consistently to each FE model to allow for comparative analysis of biomechanical responses under identical conditions.\u003c/p\u003e\n\u003ch3\u003e5.Outcome measurements\u003c/h3\u003e\n\u003cp\u003eThe primary outcome parameters included the range of motion (ROM) of each cervical segment, peak Von Mises stress of the vertebral bodies, interbody fusion devices, cortical bone, and fixation screws, as well as stress distribution within the intervertebral disc of the intermediate segment (C5/6), including both nucleus pulposus and annulus fibrosus. These parameters were extracted and compared among different models and loading conditions.\u003c/p\u003e"},{"header":"Results","content":"\n\u003ch3\u003e1.Model validation\u003c/h3\u003e\n\u003cp\u003eThe intact FE model was validated by comparing its segmental range of motion under physiological loading conditions with previously published experimental and numerical data [13\u0026ndash;15]. The simulated ROM values were found to be within the ranges reported in the literature, indicating that the FE model was reasonable for subsequent biomechanical analysis.(Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of ROM results of the M0 model under different operating conditions with previous studies(\u0026deg;)[13\u0026ndash;15]\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"13\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003eflexion and extension\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c9\" namest=\"c6\"\u003e \u003cp\u003elateral bending\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c13\" namest=\"c10\"\u003e \u003cp\u003eaxial rotation\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003epanjabi\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eito\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eChen\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eThis\u003c/p\u003e \u003cp\u003earticle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003epanjabi\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eito\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eChen\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eThis\u003c/p\u003e \u003cp\u003earticle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003epanjabi\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eito\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003eChen\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003eThis\u003c/p\u003e \u003cp\u003earticle\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC2-C3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e6.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e9\u0026thinsp;\u0026plusmn;\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e8.8\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e14.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e9.6\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e9.7\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c8\"\u003e \u003cp\u003e8.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c10\"\u003e \u003cp\u003e3.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c11\"\u003e \u003cp\u003e6.6\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c12\"\u003e \u003cp\u003e6.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e7.98\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC3-C4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e8.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e10\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e9.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e8.6\u0026thinsp;\u0026plusmn;\u0026thinsp;5.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c8\"\u003e \u003cp\u003e8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c10\"\u003e \u003cp\u003e5.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c11\"\u003e \u003cp\u003e9.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c12\"\u003e \u003cp\u003e7.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e12.06\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC4-C5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e9.8\u0026thinsp;\u0026plusmn;\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e14.3\u0026thinsp;\u0026plusmn;\u0026thinsp;5.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e13.8\u0026thinsp;\u0026plusmn;\u0026thinsp;4.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e6.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e9.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e8.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c8\"\u003e \u003cp\u003e7.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c10\"\u003e \u003cp\u003e6.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c11\"\u003e \u003cp\u003e11.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c12\"\u003e \u003cp\u003e9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e8.43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC5-C6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e10.4\u0026thinsp;\u0026plusmn;\u0026thinsp;5.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e14.5\u0026thinsp;\u0026plusmn;\u0026thinsp;8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e14.1\u0026thinsp;\u0026plusmn;\u0026thinsp;6.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e6.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e6.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e4.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c8\"\u003e \u003cp\u003e4.8\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c10\"\u003e \u003cp\u003e5\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c11\"\u003e \u003cp\u003e7.8\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c12\"\u003e \u003cp\u003e7.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e7.47\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC6-C7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e8\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e15.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e14.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e5.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e6.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c8\"\u003e \u003cp\u003e3.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c10\"\u003e \u003cp\u003e2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c11\"\u003e \u003cp\u003e6.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c12\"\u003e \u003cp\u003e6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e7.695\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003e2. Maximum segmental range of motion among different models\u003c/h3\u003e\n\u003cp\u003eCompared with the intact model (M0), all postoperative models (M1\u0026ndash;M5) exhibited a pronounced reduction in ROM at the fused segments (C4/5 and C6/7) under all loading conditions, indicating increased segmental stiffness after implantation.\u003c/p\u003e \u003cp\u003eIn lateral bending (left and right), ROM increased at the intermediate segment (C5/6) after surgery, and the magnitude of ROM increment generally increased with larger reconstructed intervertebral heights. In combined flexion and extension, the intermediate segment (C5/6) ROM showed a decreasing trend with increasing reconstructed height.\u003c/p\u003e \u003cp\u003eFor the intermediate segment (C5/6), the ROM increment was relatively smaller in the model with 100% reference height (M1) in axial rotation and lateral bending, and increased progressively as the reconstructed height increased.(Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003e.Comparison of intervertebral relative range of motion among different intervertebral disc height groups (\u0026deg;)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"19\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c15\" colnum=\"15\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c16\" colnum=\"16\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c17\" colnum=\"17\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c18\" colnum=\"18\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c19\" colnum=\"19\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"6\" nameend=\"c7\" namest=\"c2\"\u003e \u003cp\u003eflexion and extension\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"6\" nameend=\"c13\" namest=\"c8\"\u003e \u003cp\u003elateral bending\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"6\" nameend=\"c19\" namest=\"c14\"\u003e \u003cp\u003eaxial rotation\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eM0\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eM1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eM2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eM3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eM4\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eM5\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eM0\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eM1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eM2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eM3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c12\"\u003e \u003cp\u003eM4\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c13\"\u003e \u003cp\u003eM5\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c14\"\u003e \u003cp\u003eM0\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c15\"\u003e \u003cp\u003eM1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c16\"\u003e \u003cp\u003eM2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c17\"\u003e \u003cp\u003eM3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c18\"\u003e \u003cp\u003eM4\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c19\"\u003e \u003cp\u003eM5\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC2-C3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e9.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e9.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e9.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e9.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e9.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e3.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e3.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e3.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e3.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e3.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e3.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c14\"\u003e \u003cp\u003e5.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c15\"\u003e \u003cp\u003e6.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c16\"\u003e \u003cp\u003e6.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c17\"\u003e \u003cp\u003e6.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c18\"\u003e \u003cp\u003e7.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c19\"\u003e \u003cp\u003e7.20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC3-C4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e6.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e6.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e2.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e3.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e3.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e3.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e3.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e3.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c14\"\u003e \u003cp\u003e8.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c15\"\u003e \u003cp\u003e8.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c16\"\u003e \u003cp\u003e9.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c17\"\u003e \u003cp\u003e9.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c18\"\u003e \u003cp\u003e9.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c19\"\u003e \u003cp\u003e9.37\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC4-C5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e3.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e0.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e1.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e1.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c14\"\u003e \u003cp\u003e5.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c15\"\u003e \u003cp\u003e0.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c16\"\u003e \u003cp\u003e0.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c17\"\u003e \u003cp\u003e0.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c18\"\u003e \u003cp\u003e0.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c19\"\u003e \u003cp\u003e1.07\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC5-C6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e3.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e2.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e3.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e3.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e3.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e3.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e3.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c14\"\u003e \u003cp\u003e4.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c15\"\u003e \u003cp\u003e5.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c16\"\u003e \u003cp\u003e5.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c17\"\u003e \u003cp\u003e5.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c18\"\u003e \u003cp\u003e6.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c19\"\u003e \u003cp\u003e6.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC6-C7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e2.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e1.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e1.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e1.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c14\"\u003e \u003cp\u003e5.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c15\"\u003e \u003cp\u003e0.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c16\"\u003e \u003cp\u003e0.77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c17\"\u003e \u003cp\u003e0.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c18\"\u003e \u003cp\u003e1.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c19\"\u003e \u003cp\u003e1.22\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003e3. Peak intervertebral disc stress of the intermediate segment(C5/6) in different models\u003c/h3\u003e\n\u003cp\u003eStress within the intermediate intervertebral disc (C5/6) was evaluated for both the nucleus pulposus and annulus fibrosus. Under flexion, lateral bending, and left axial rotation, disc stress at C5/6 generally increased as the reconstructed height increased. Under extension and right axial rotation, disc stress showed a decreasing trend or remained relatively stable across models.\u003c/p\u003e \u003cp\u003eWith increasing reconstructed height, disc stress at C5/6 decreased progressively under extension. Among postoperative models, the 100% reference height model (M1) showed a relatively lower increment of disc stress in most loading directions, except for right axial rotation. Right axial rotation produced the highest disc stress among all motion directions in both intact and postoperative models.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(Fig.\u0026nbsp;1. Stress Comparison of the C5/6 intervertebral disc in different models.(MPa))\u003c/p\u003e\n\u003ch3\u003e4. Peak stress of the interbody fusion cage and screw in different models\u003c/h3\u003e\n\u003cp\u003ePeak Von Mises stress of the interbody fusion device (cage) varied across motion directions and reconstructed heights. Stress concentration was mainly observed at the anterior-lateral and posterior regions of the cage, while the central region exhibited relatively lower stress.\u003c/p\u003e \u003cp\u003eAcross postoperative models, the 125% reference height model (M2) demonstrated lower peak cage stress than the other height conditions over the tested motion directions. In lateral bending, cage stress increased markedly compared with the other motion directions.\u003c/p\u003e \u003cp\u003eScrew stress differed among models. The 100% reference height model (M1) exhibited lower screw stress compared with other postoperative models. Screw stress increased substantially during lateral bending and generally increased with larger reconstructed heights.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(Fig.\u0026nbsp;2. Stress Comparison of the cage in different models under six motion directions.(MPa))\u003c/p\u003e\n\u003ch3\u003e5. Peak cortical bone stress in different models\u003c/h3\u003e\n\u003cp\u003ePostoperatively, peak cortical bone stress increased compared with the intact model, with more evident increases under flexion/extension and lateral bending. During lateral bending, cortical bone stress tended to increase as reconstructed height increased.\u003c/p\u003e \u003cp\u003eAmong postoperative models, the 100% reference height model (M1) showed relatively lower cortical bone stress compared with models with larger reconstructed heights.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(Fig.\u0026nbsp;3. Stress Comparison of cortical bone in different models under six motion directions.(MPa))\u003c/p\u003e\n\u003ch3\u003e6. Peak facet joint stress of the intermediate segment(C5/6) in different models\u003c/h3\u003e\n\u003cp\u003eFacet joint stress of the intermediate segment (C5/6) was assessed under six motion directions. Compared with the intact model, facet joint stress in the postoperative models generally decreased under most loading conditions, whereas an exception was observed under flexion, where facet joint stress did not show the same decreasing pattern.\u003c/p\u003e \u003cp\u003eAcross postoperative models, the 125% reference height model (M2) exhibited relatively lower average facet joint stress across motion directions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(Fig.\u0026nbsp;4. Stress Comparison of facet joint in different models under six motion directions.(MPa))\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe present study investigated the biomechanical effects of different intervertebral height reconstructions in skip-level ACDF on the intermediate segment using a three-dimensional finite element model. The main findings were as follows: (1) increasing reconstructed height was associated with distinct changes in cervical kinematics, with progressive increases in ROM at non-fused levels during lateral bending and a decreasing trend in overall C2\u0026ndash;C7 ROM during flexion/extension; the intermediate segment (C5/6) demonstrated relatively smaller ROM increments at the 100% reference height condition. (2) Intermediate disc stress exhibited direction-dependent patterns: stresses generally increased with greater reconstructed height under flexion, lateral bending, and left rotation, whereas they decreased or remained stable under extension and right rotation; among the postoperative models, the 100% reference height condition showed relatively lower disc stress increments in most directions except right rotation. (3) Implant-related stresses varied by motion direction and reconstruction height: the 125% reference height condition showed comparatively lower peak cage stress across directions, while the 100% reference height condition showed lower screw stress; lateral bending produced markedly higher cage and screw stresses. (4) Cortical bone stress increased after fusion and tended to increase with reconstructed height during lateral bending, while the 100% reference height condition showed relatively lower cortical bone stress compared with larger-height models. (5) Facet joint stress at the intermediate segment generally decreased after skip-level fusion under most loading conditions, with the 125% reference height condition demonstrating relatively lower average facet stress across directions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(Fig.\u0026nbsp;5. Stress distribution of the C5/6 intervertebral disc in different models under four motion directions.)\u003c/p\u003e \u003cp\u003eThese findings highlight that intervertebral height reconstruction and motion direction jointly influence the postoperative biomechanical environment of the intermediate segment and the implant system in skip-level ACDF. Collectively, the 100% reference height condition tended to be associated with smaller changes in intermediate-segment ROM and disc stress in most motion directions, whereas the 125% reference height condition was associated with lower cage stress and facet joint stress. Given that this study was based on a finite element model with standardized loading conditions, the results should be interpreted as biomechanical trends, and further experimental and clinical studies are warranted to validate their clinical relevance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(Fig.\u0026nbsp;6. Stress distribution map of the fusion device in the M1 model. Figure A: Flexion; Figure B: Extension; Figure C: Left rotation; Figure D: Right rotation;Figure E: Left lateral flexion; Figure F: Right lateral flexion.)\u003c/p\u003e\n\u003ch3\u003e1. Effects of different reconstructed intervertebral heights on range of motion of the intermediate segment\u003c/h3\u003e\n\u003cp\u003eCompared with the intact model (M0), all postoperative models (M1\u0026ndash;M5) exhibited a marked reduction in range of motion (ROM) at the fused segments (C4/5 and C6/7), indicating increased segmental stability following internal fixation and cage implantation. Under left and right lateral bending, ROM at non-fused segments increased after surgery, and the magnitude of ROM increase progressively rose with increasing reconstructed intervertebral height. In contrast, during combined flexion and extension, the overall C2\u0026ndash;C7 ROM demonstrated a continuous decreasing trend as reconstructed height increased.\u003c/p\u003e \u003cp\u003ePrevious studies have reported that loss of motion at fused segments may lead to increased motion at adjacent segments, potentially accelerating adjacent segment degeneration [16,17]. In the present study, under axial rotation and lateral bending, the smallest increase in ROM at the intermediate segment (C5/6) was observed when the reconstructed height was set to the reference height(100%). As the cage height further increased, ROM at the intermediate segment increased accordingly.\u003c/p\u003e \u003cp\u003eThese results suggest that excessive reconstruction of intervertebral height may increase the risk of compensatory motion at the intermediate segment, which from a biomechanical perspective could be associated with degenerative trends at this level.\u003c/p\u003e\n\u003ch3\u003e2. Effects of different reconstructed intervertebral heights on disc stress of the intermediate segment\u003c/h3\u003e\n\u003cp\u003eThe intervertebral disc consists primarily of the annulus fibrosus and nucleus pulposus. The nucleus pulposus plays a critical role in absorbing spinal loads and distributing them evenly to the surrounding annulus fibrosus and cartilaginous endplates. Increased nucleus pulposus pressure has been reported to impair cellular activity and promote apoptosis [18], while excessive intradiscal pressure may also contribute to annular rupture and subsequent disc herniation [19]. Moreover, elevated stress in either the nucleus pulposus or annulus fibrosus has been associated with disc cell apoptosis and degenerative processes [20]. Long-term mechanical loading is therefore considered an important contributor to intervertebral disc degeneration. Previous studies have demonstrated that anterior cervical fusion can lead to increased stress at adjacent segments [21].\u003c/p\u003e \u003cp\u003eIn the present study, disc stress at the intermediate segment (C5/6) exhibited a progressive increasing trend under flexion, lateral bending, and left axial rotation as reconstructed intervertebral height increased, which is consistent with findings from previous investigations. These results suggest that greater reconstruction height may be associated with increased shear and compressive loading at the intermediate segment under these motion directions. In contrast, under extension and right axial rotation, stress in both the annulus fibrosus and nucleus pulposus decreased or remained relatively stable, indicating that increased construct rigidity may partially attenuate load transmission in these directions.With increasing reconstructed height, disc stress at the intermediate segment gradually decreased during extension, which may be associated with reduced segmental mobility in this motion direction.\u003c/p\u003e \u003cp\u003eAmong the postoperative models, when the reconstructed height was set to the reference height(100%), the increase in disc stress at the intermediate segment was relatively smaller than that observed in the other reconstruction conditions in most motion directions, except for right axial rotation. Across both intact and postoperative models, right axial rotation consistently produced higher disc stress compared with other motion directions. These findings indicate that axial rotation may impose greater mechanical loading on the intervertebral disc and therefore warrants attention in postoperative motion considerations.\u003c/p\u003e\n\u003ch3\u003e3, Effects of different reconstructed intervertebral heights on cage and screw stress\u003c/h3\u003e\n\u003cp\u003ePrevious study have reported that excessive stress on interbody fusion cages may accelerate implant damage, whereas insufficient stress may delay fusion and compromise fusion efficiency. Increased implant stress may also induce stress shielding in the surrounding bone tissue, potentially reducing bone density and, over time, contributing to implant subsidence or osteoporotic changes [22].\u003c/p\u003e \u003cp\u003eIn the present study, cage stress exhibited distinct patterns across different motion directions and reconstructed height conditions. As shown in Fig.\u0026nbsp;2, the magnitude of cage stress varied with both motion direction and reconstruction height. Stress distribution maps demonstrated that stress was primarily concentrated at the anterior\u0026ndash;lateral and posterior regions of the cage, while the central region experienced relatively lower stress, which is considered favorable for bone graft fusion. This distribution pattern is consistent with previous finite element findings reported by Huang et al. [23].\u003c/p\u003e \u003cp\u003eAmong the postoperative models, the 125% reference height model (M2) demonstrated lower peak cage stress compared with the other reconstruction conditions, with peak values ranging from 77.34 to 221.30 MPa. These findings indicate that reconstruction at 125% of the reference height may be associated with more favorable stress conditions for the cage structure under finite element conditions. In contrast, cage stress increased markedly during left and right lateral bending, suggesting that this motion direction may impose higher mechanical demands on the cage.\u003c/p\u003e \u003cp\u003eScrew stress also varied among models. The 100% reference height model (M1) exhibited lower screw stress than the other postoperative models. Under lateral bending, screw stress increased substantially and showed a progressive rise with increasing reconstructed height. Elevated screw stress has been associated with an increased risk of screw loosening, migration, or fracture, which may adversely affect fusion stability and, in severe cases, necessitate revision surgery. The present findings suggest that lateral bending conditions may increase screw-related mechanical loading and associated structural risk under finite element conditions.\u003c/p\u003e\n\u003ch3\u003e4. Effects of different reconstructed intervertebral heights on cortical bone stress\u003c/h3\u003e\n\u003cp\u003eIn the present study, cortical bone stress increased markedly after fusion compared with the intact model, with more pronounced increases observed during flexion\u0026ndash;extension and left and right lateral bending. From a biomechanical perspective, elevated cortical bone stress may be associated with an increased risk of bone overload under these motion conditions. Similar findings were reported by Xu et al. [11], who demonstrated that zero-profile fusion systems produced higher cortical bone stress than conventional anterior plate fixation, particularly during flexion\u0026ndash;extension and lateral bending, suggesting a potential increase in mechanical demand on the fused vertebrae.\u003c/p\u003e \u003cp\u003eWith increasing reconstructed intervertebral height, cortical bone stress exhibited a progressive increase during lateral bending. In contrast, when the reconstructed height was set to the reference height, cortical bone stress was relatively lower than that observed in models with greater reconstruction heights. These findings suggest that moderate intervertebral height reconstruction may help limit peak cortical bone stress and thereby reduce excessive load concentration on the cortical bone under finite element conditions.\u003c/p\u003e\n\u003ch3\u003e5. Effects of different reconstructed intervertebral heights on facet joint stress of the intermediate segment\u003c/h3\u003e\n\u003cp\u003ePrevious studies have reported that facet joint stress at adjacent segments increases after cervical fusion, accompanied by a higher load rate, which may accelerate degenerative processes [24]. In contrast, the present study demonstrated a different biomechanical response. Except for the flexion condition, facet joint stress at the intermediate segment (C5/6) was generally reduced after skip-level ACDF compared with the intact model.\u003c/p\u003e \u003cp\u003eA possible explanation for this discrepancy may be related to the unique biomechanical characteristics of skip-level fusion. Following fusion of the segments above and below C5/6, loss of motion at the fused levels and increased construct rigidity may indirectly reduce the motion demand at the intermediate segment. Consequently, shear and compressive loads transmitted to the facet joints at C5/6 may be reduced.\u003c/p\u003e \u003cp\u003eAmong the postoperative models, the 125% reference height model (M2) exhibited the lowest average facet joint stress across motion directions. Overall, the present findings suggest that skip-level ACDF may be associated with reduced facet joint loading at the intermediate segment under finite element conditions, which from a biomechanical perspective could indicate a potential protective effect on the intermediate facet joints. However, the clinical relevance of these observations requires further investigation.\u003c/p\u003e\n\u003ch3\u003eLimitations\u003c/h3\u003e\n\u003cp\u003eSeveral limitations of the present study should be acknowledged. First, the finite element model of the cervical spine was constructed based on CT data from a single individual, and the postoperative fusion models were derived from this baseline geometry. Therefore, the biomechanical results may not fully represent population-level variability. Future studies incorporating models with different sexes, ages, and bone mineral densities are warranted to reduce potential selection bias. Nevertheless, the overall biomechanical trends observed in finite element analysis are considered to be reliable.\u003c/p\u003e \u003cp\u003eSecond, muscle forces and other soft tissues were not included in the present finite element model. The absence of dynamic muscular stabilization may influence cervical kinematics and load distribution, potentially affecting the accuracy of the simulated results. Third, simplifications were applied to the fusion cage and model geometry, which may limit precise reproduction of the in vivo biomechanical environment, particularly with respect to motion at the implant levels.\u003c/p\u003e \u003cp\u003eFourth, the present study lacked validation through cadaveric or animal experiments, and no direct experimental data were available for comparison. Consequently, further experimental investigations, including cadaveric testing, animal studies, or clinical outcome analyses, are required to validate the biomechanical findings of this study. Future research should integrate diversified finite element models, dynamic muscle loading, and clinical outcome data to further verify and refine the conclusions.\u003c/p\u003e \u003cp\u003eIn addition, currently available interbody fusion cages are typically manufactured with predefined heights, which limits the degree of individualization in clinical practice. Future studies may benefit from incorporating patient-specific implant designs, potentially enabled by three-dimensional printing technologies, to explore personalized reconstruction strategies and their biomechanical implications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eClinical trial number\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003ch2\u003eCompeting interests\u003c/h2\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003ch2\u003eFunding\u003c/h2\u003e\n\u003cp\u003eThis study was supported by the Third Batch of Excellent Young Scientific Research Projects of the First Affiliated Hospital of Bengbu Medical College(Grant No. 2025BYYFYYQ08);Key Natural Science Projects of Universities in Anhui Province༈Grant No.2022AH051487༉;Anhui Province Clinical Medicine Research and Translation Special Project(Grant No.202527C10020128);Key Natural Science Project of Bengbu Medical University(Grant No.2021BYZD082) and Youth Project of Anhui Provincial Health and Medical Research Programme༈Grant No.AHWJ2023A30150༉(AnHui China)\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eWang and Bao designed the study ，constructed the finite element models.and performed the data analysis and interpretation.Wang and Gao drafted the manuscript.Bao 、Zhang and Ye critically revised the manuscript.All authors read and approved the final manuscript.\u003c/p\u003e\n\u003ch2\u003eAcknowledgements\u003c/h2\u003e\n\u003cp\u003eThe authors would like to thank all contributors who provided technical support for this study.\u003c/p\u003e\n\u003ch2\u003eData Availability\u003c/h2\u003e\n\u003cp\u003eThe datasets used and analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWhitecloud TS 3rd. Anterior surgery for cervical spondylotic myelopathy: Smith\u0026ndash;Robinson, Cloward, and vertebrectomy. Spine (Phila Pa 1976). 1988;13(7):861\u0026ndash;3.\u003c/li\u003e\n\u003cli\u003eFinn MA, Samuelson MM, Bishop F, et al. Two-level noncontiguous versus three-level anterior cervical discectomy and fusion: a biomechanical comparison. Spine (Phila Pa 1976). 2011;36(6):448\u0026ndash;53.\u003c/li\u003e\n\u003cli\u003eBaumann AN, Fiorentino A, Sidlowski K, et al. Clinical outcomes and complication rates for noncontiguous anterior cervical discectomy and fusion, cervical disc arthroplasty, and hybrid cervical surgery: a systematic review. World Neurosurg. 2024;189:55\u0026ndash;69.\u003c/li\u003e\n\u003cli\u003eBaram A, Riva M, Franzini A, et al. Outcomes of non-contiguous two-level anterior cervical discectomy and fusion in patients with degenerative cervical myelopathy: a retrospective study. Acta Neurochir (Wien). 2024;166(1):347.\u003c/li\u003e\n\u003cli\u003eQizhi S, Peijia L, Lei S, et al. Anterior cervical discectomy and fusion for noncontiguous cervical spondylotic myelopathy. Indian J Orthop. 2016;50(4):390\u0026ndash;6.\u003c/li\u003e\n\u003cli\u003eWu Z, Wang W, Zhou F, et al. Comparative analysis of risk factors associated with degeneration of adjacent segments: zero-profile anchored spacer versus anterior cervical plate and cage construct. Front Med (Lausanne). 2024;11:1375554.\u003c/li\u003e\n\u003cli\u003eCheng CH, Chiu PY, Chen HB, et al. The influence of over-distraction on biomechanical response of the cervical spine after anterior interbody fusion: a comprehensive finite element study. Front Bioeng Biotechnol. 2023;11:1217274.\u003c/li\u003e\n\u003cli\u003eLi J, Li Y, Kong F, et al. Adjacent segment degeneration after single-level anterior cervical decompression and fusion: disc space distraction and its impact on clinical outcomes. 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Biomechanical effects on the intermediate segment of noncontiguous hybrid surgery with cervical disc arthroplasty and anterior cervical discectomy and fusion: a finite element analysis. Spine J. 2019;19(7):1254\u0026ndash;63.\u003c/li\u003e\n\u003cli\u003eCao L, Chen Q, Jiang LB, et al. Bioabsorbable self-retaining PLA/nano-sized \u0026beta;-TCP cervical spine interbody fusion cage in goat models: an in vivo study. Int J Nanomedicine. 2017;12:7197\u0026ndash;205.\u003c/li\u003e\n\u003cli\u003eHuang DA, Liu C. Three-dimensional finite element analysis of a novel height-adjustable cervical fusion cage. Chin J Tissue Eng Res. 2023;27(18):2797\u0026ndash;803.\u003c/li\u003e\n\u003cli\u003eLi H, Pei BQ, Yang JC, et al. Load rate of facet joints at the adjacent segment increased after fusion. Chin Med J (Engl). 2015;128(8):1042\u0026ndash;6.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-musculoskeletal-disorders","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmsd","sideBox":"Learn more about [BMC Musculoskeletal Disorders](http://bmcmusculoskeletdisord.biomedcentral.com/)","snPcode":"","submissionUrl":"https://author-welcome.nature.com/12891","title":"BMC Musculoskeletal Disorders","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-8677951/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8677951/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eSkip-level anterior cervical discectomy and fusion (ACDF) has been reported to provide favorable outcomes for discontinuous cervical spondylosis; however, intermediate segment degeneration (ASD) remains a concern. Reconstruction of intervertebral height at fused levels may affect postoperative biomechanics, yet the optimal reconstruction strategy remains unclear.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eA three-dimensional finite element model of the cervical spine (C2\u0026ndash;C7) was developed. Skip-level ACDF was simulated at C4/5 and C6/7. Six models were analyzed: an intact model (M0) and five postoperative models with reconstructed intervertebral heights of 100%, 125%, 150%, 175%, and 200% of a reference height (M1\u0026ndash;M5). A 50 N axial preload and a 1.0 N\u0026middot;m pure moment were applied to simulate flexion, extension, left/right lateral bending, and left/right axial rotation. Outcome measures included cervical range of motion (ROM), peak Von Mises stress of vertebrae and implants, and stress in the intermediate disc (C5/6).\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eROM at the fused segments decreased markedly in all postoperative models. During lateral bending and axial rotation, ROM and disc stress at non-fused levels\u0026mdash;particularly the intermediate segment\u0026mdash;generally increased with greater reconstructed height, whereas disc stress tended to decrease or remain relatively stable during extension and right axial rotation. Across most motion directions, the 100% reconstruction model showed relatively smaller increases in intermediate-segment ROM and disc stress, while the 125% reconstruction model exhibited lower cage and facet joint stresses. Lateral bending produced notably higher cage and screw stresses compared with other motion directions.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eUnder finite element conditions, when the cage height was set to 100% of the reference intervertebral height, the intermediate segment exhibited relatively smaller biomechanical changes in most motion scenarios, suggesting that this reconstruction height may have a limited impact on the intermediate segment. Biomechanical responses of the postoperative intermediate segment and the fixation system varied among different motion directions; in particular, load variation patterns during extension and lateral bending suggest that postoperative motion may influence the mechanical environment of the intermediate segment and implant stability. The clinical relevance of these findings requires further investigation.\u003c/p\u003e","manuscriptTitle":"Biomechanical effects of different intervertebral height reconstructions on the intermediate segment in skip-level ACDF for discontinuous cervical spondylosis: a finite element analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-11 06:28:29","doi":"10.21203/rs.3.rs-8677951/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-03T10:02:06+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-02T02:28:42+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-24T16:30:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"215225134511544730380323468786031289019","date":"2026-02-11T15:21:34+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-10T12:12:39+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"204801277527529940648122987357468514157","date":"2026-02-09T23:53:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"74036087994947016174232241896161772698","date":"2026-02-09T12:28:08+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-09T11:59:33+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-24T10:23:08+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-01-24T10:19:17+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Musculoskeletal Disorders","date":"2026-01-23T09:45:23+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-musculoskeletal-disorders","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmsd","sideBox":"Learn more about [BMC Musculoskeletal Disorders](http://bmcmusculoskeletdisord.biomedcentral.com/)","snPcode":"","submissionUrl":"https://author-welcome.nature.com/12891","title":"BMC Musculoskeletal Disorders","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"fc485713-dbc5-4baa-8139-e36118aa9274","owner":[],"postedDate":"February 11th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-17T07:10:53+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-11 06:28:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8677951","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8677951","identity":"rs-8677951","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}