Design factors of lumbar pedicle screws under bending load: A finite element analysis

Biswas, Jayanta Kumar; Sahu, Tikeshwar Prasad; Rana, Masud; Roy, Sandipan; Karmakar, Santanu Kumar; Majumder, Santanu; Roy-Chowdhury, Amit K.

doi:10.1016/j.bbe.2018.10.003

Cited by 28 publications

(14 citation statements)

References 50 publications

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“…Therefore, finding the compromise between the largest diameter of the screws by avoiding iatrogenic fractures is crucial to provide a good anchorage on the cortical bone, which results in lower micromotions at the screw-vertebra interface and better distribution of stress, thus preventing postoperative complications. Our results are in line with most experimental and numerical studies in the literature, that showed the predominant effect of the diameter of the screws compared to their length (Zindrick et al, 1986;Chen et al, 2003;Cho et al, 2010;Matsukawa et al, 2016Matsukawa et al, , 2020Bianco et al, 2019;Biswas et al, 2019). Matsukawa et al (2016) evaluated the effect of different screw sizes on fixation with a cortical bone trajectory, where screws are inserted pointing laterally in the transverse plane during superior screw angulation in the sagittal plane, and anchor only on cortical bone in the pedicle without the contribution of trabecular bone in the vertebral body (Santoni et al, 2009), by using an FE model including bone heterogeneities and realistic screw design.…”

Section: Discussionsupporting

confidence: 92%

“…The screw was considered isotropic and homogeneous with Young's modulus and Poisson's ratio of Titanium: E screw = 102 GPa, ν screw = 0.36 (Niinomi and Boehlert, 2015). The model was loaded with a quasi-static uniformly distributed force of 200 N (100 N per screw) applied to the head of the screw in a direction perpendicular to the longitudinal axis of the screw and perpendicular to the superior endplate, toward the caudal direction (Chen et al, 2003;Biswas et al, 2019; Figure 1). The force was equally distributed between the two surfaces of the head of the screw that would interact with the rod (50 N on each surface) ( Figure 1).…”

Section: Generation Of the Fe Modelmentioning

confidence: 99%

“…Other studies focused on the vertebra-screws interactions and proposed FE models validated with experimental measures: FE models were found to be good predictors of pull-out strength and stiffness obtained by experimental tests better than apparent density estimated from CT images ( Abbeele et al, 2018 ; Chevalier et al, 2018 ; Widmer et al, 2020 ). The screw size and other insertion-related parameters have been tested with linear FE models ( Qi et al, 2011 ; Newcomb et al, 2017 ), with non-linear FE models (material non-linearities, contact mechanics) ( Chen et al, 2003 ; Bianco et al, 2017 , 2019 ; Molinari et al, 2021 ), or assuming the bone as heterogeneous material with elastic properties driven by the local bone mineral density (BMD) ( Matsukawa et al, 2016 , 2020 ; Biswas et al, 2019 ; Molinari et al, 2021 ). In most cases a realistic screw geometry was used and only in a few studies the simplified geometry of the screw was modeled ( Li et al, 2014 ; Su et al, 2018 ).…”

Section: Introductionmentioning

confidence: 99%

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Patient-Specific Finite Element Models of Posterior Pedicle Screw Fixation: Effect of Screw’s Size and Geometry

Sensale

Vendeuvre

Schilling³

et al. 2021

Front. Bioeng. Biotechnol.

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Pedicle screw fixation is extensively performed to treat spine injuries or diseases and it is common for thoracolumbar fractures. Post-operative complications may arise from this surgery leading to back pain or revisions. Finite element (FE) models could be used to predict the outcomes of surgeries but should be verified when both simplified and realistic designs of screws are used. The aim of this study was to generate patient-specific Computed Tomography (CT)-based FE models of human vertebrae with two pedicle screws, verify the models, and use them to evaluate the effect of the screws’ size and geometry on the mechanical properties of the screws-vertebra structure. FE models of the lumbar vertebra implanted with two pedicle screws were created from anonymized CT-scans of three patients. Compressive loads were applied to the head of the screws. The mesh size was optimized for realistic and simplified geometry of the screws with a mesh refinement study. Finally, the optimal mesh size was used to evaluate the sensitivity of the model to changes in screw’s size (diameter and length) and geometry (realistic or simplified). For both simplified and realistic models, element sizes of 0.6 mm in the screw and 1.0 mm in the bone allowed to obtain relative differences of approximately 5% or lower. Changes in screw’s length resulted in 4–10% differences in maximum deflection, 1–6% differences in peak stress in the screws, 10–22% differences in mean strain in the bone around the screw; changes in screw’s diameter resulted in 28–36% differences in maximum deflection, 6–27% differences in peak stress in the screws, and 30–47% differences in mean strain in the bone around the screw. The maximum deflection predicted with realistic or simplified screws correlated very well (R2 = 0.99). The peak stress in screws with realistic or simplified design correlated well (R2 = 0.82) but simplified models underestimated the peak stress. In conclusion, the results showed that the diameter of the screw has a major role on the mechanics of the screw-vertebral structure for each patient. Simplified screws can be used to estimate the mechanical properties of the implanted vertebrae, but the systematic underestimation of the peak stress should be considered when interpreting the results from the FE analyses.

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Section: Discussionsupporting

confidence: 92%

Section: Generation Of the Fe Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Patient-Specific Finite Element Models of Posterior Pedicle Screw Fixation: Effect of Screw’s Size and Geometry

Sensale

Vendeuvre

Schilling³

et al. 2021

Front. Bioeng. Biotechnol.

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“…Friction contact pair is generated between bone-implant surfaces, and frictional coefficient (µ) was set 0.3 and for the sliding spacer-rod, µ was set to be 0.1. 14,19…”

Section: Methodsmentioning

confidence: 99%

Design and development of a novel expanding flexible rod device (FRD) for stability in the lumbar spine: A finite-element study

et al. 2020

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The aim of this study is to design a novel expanding flexible rod device, for pedicle screw fixation to provide dynamic stability, based on strength and flexibility. Three-dimensional finite-element models of lumbar spine (L1-S) with flexible rod device on L3-L4-L5 levels are developed. The implant material is taken to be Ti-6Al-4V. The models are simulated under different boundary conditions, and the results are compared with intact model. In natural model, total range of motion under 10 Nm moment were found 66.7°, 24.3° and 13.59°, respectively during flexion–extension, lateral bending and axial rotation. The von Mises stress at intact bone was 4 ± 2 MPa and at bone, adjacent to the screw in the implanted bone, was 6 ± 3 MPa. The von Mises stress of disc of intact bone varied from 0.36 to 2.13 MPa while that of the disc between the fixed vertebra of the fixation model reduced by approximately 10% for flexion and 25% for extension compared to intact model. The von Mises stresses of pedicle screw were 120, 135, 110 and 90 MPa during flexion, extension, lateral bending, and axial rotation, respectively. All the stress values were within the safe limit of the material. Using the flexible rod device, flexibility was significantly increased in flexion/extension but not in axial rotation and lateral bending. The results suggest that dynamic stabilization system with respect to fusion is more effective for homogenizing the range of motion of the spine.

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“…First, FE analysis was performed only on the implant without considering any bone, but stress or strain generation on the bone after surgery is also an important factor to be studied. 39 However, since our surgery induces fusion between the articular processes of the posterior column, the original biomechanical environment is changed, the bone bridge formed by fusion varies and its imaging data can be obtained only after the end of animal experiments. The optimization of the NDFS after bone graft fusion by the FE model will be addressed in our future work.…”

Section: Limitationsmentioning

confidence: 99%

A novel dynamic fixation system with biodegradable components on lumbar fusion between articular processes in a canine model

Zheng

Chen

et al. 2020

Proc Inst Mech Eng H

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The objective of this study was to design a novel dynamic fixation system with biodegradable components, apply it for lumbar fusion between articular processes and compare the fusion results and biomechanical changes to those of conventional rigid fixation. The novel dynamic fixation system was designed using a finite element model, stress distributions were compared and 24 mongrel dogs were randomly assigned to two groups and subjected to either posterior lumbar fusion surgery with a novel dynamic fixation system or titanium rods at the L5-L6 segments. Lumbar spines were assessed in both groups to detect radiographic, manual palpation and biomechanical changes. Histological examination was performed on organs and surrounding tissues. In the novel dynamic fixation system, stress was mainly distributed on the meshing teeth of the magnesium alloy spacer. The magnesium alloy components maintained their initial shape 8 weeks after the operation, but the meshing teeth were almost completely degraded at 16 weeks. The novel dynamic fixation system revealed an increased lateral bending range of motion at 8 weeks; however, both groups showed similar radiographic grades, fusion stiffness, manual palpation and histological results. The novel dynamic fixation system design is suitable, and its degradation in vivo is safe. The novel dynamic fixation system can be applied for posterior lumbar fusion between articular processes and complete the fusion like titanium rods.

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Design factors of lumbar pedicle screws under bending load: A finite element analysis

Cited by 28 publications

References 50 publications

Patient-Specific Finite Element Models of Posterior Pedicle Screw Fixation: Effect of Screw’s Size and Geometry

Patient-Specific Finite Element Models of Posterior Pedicle Screw Fixation: Effect of Screw’s Size and Geometry

Design and development of a novel expanding flexible rod device (FRD) for stability in the lumbar spine: A finite-element study

A novel dynamic fixation system with biodegradable components on lumbar fusion between articular processes in a canine model

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