scholarly journals Partial Threading of Pedicle Screws in a Standard Construct Increases Fatigue Life: A Biomechanical Analysis

2021 ◽  
Vol 11 (4) ◽  
pp. 1503
Author(s):  
Fon-Yih Tsuang ◽  
Chia-Hsien Chen ◽  
Lien-Chen Wu ◽  
Yi-Jie Kuo ◽  
Yueh-Ying Hsieh ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Pedicle Screw ◽  
Pedicle Screws ◽  
Biomechanical Analysis ◽  
Von Mises Stress ◽  
Shaft Length ◽  
Element Analysis ◽  
Screw Design ◽  
Screw Length

This study proposed a pedicle screw design where the proximal 1/3 of the screw is unthreaded to improve fixation in posterior spinal surgery. This design was also expected to reduce the incidence of mechanical failure often observed when an unsupported screw length is exposed outside the vertebra in deformed or degenerated segments. The aim of this study was to evaluate the fatigue life of the novel pedicle screw design using finite element analysis and mechanical testing in a synthetic spinal construct in accordance with American Society for Testing and Materials (ASTM) F1717. The following setups were evaluated: (i) pedicle screw fully inserted into the test block (EXP-FT-01 and EXP-PU-01; full thread (FT), proximal unthread (PU)) and (ii) pedicle screw inserted but leaving an exposed shaft length of 7.6 mm (EXP-FT-02 and EXP-PU-02). Corresponding finite element models FEM-FT-01, FEM-FT-02, FEM-PU-01, and FEM-PU-02 were also constructed and subjected to the same loading conditions as the experimental groups. The results showed that under a 220 N axial load, the EXP-PU-01 group survived the full 5 million cycles, the EXP-PU-02 group failed at 4.4 million cycles on average, and both EXP-FT-01 and EXP-FT-02 groups failed after less than 1.0 million cycles on average, while the fatigue strength of the EXP-FT-02 group was the lowest at 170 N. The EXP-FT-01 and EXP-FT-02 constructs failed through fracture of the pedicle screw, but a rod fractured in the EXP-PU-02 group. In comparison to the FEM-FT-01 model, the maximum von Mises stress on the pedicle screw in the FEM-PU-01 and FEM-PU-02 models decreased by −43% and −27%, respectively. In conclusion, this study showed that having the proximal 1/3 of the pedicle screw unthreaded can reduce the risk of screw fatigue failure when used in deformed or degenerated segments.

Modeling NiTi Superelastic-Shape Memory Antagonistic Beams: A Finite Element Analysis

2009 ◽  
Author(s):  
Majid Tabesh ◽  
Mohammad Elahinia ◽  
Mehdi Pourazady
Keyword(s):  
Finite Element ◽  
Body Temperature ◽  
Shape Memory ◽  
Pedicle Screws ◽  
Experimental Tests ◽  
Element Analysis ◽  
Major Drawback ◽  
Screw Design ◽  
Finite Element Software ◽  
Engineering Sciences

Shape memory alloys (SMA) have received widespread attention from researchers in various fields of engineering sciences due to their exceptional properties of shape memory and superelasticity. NiTi equiatomic alloys among other SMA, show acceptable biocompatibility to be implemented in biomedical applications. Applications of NiTi in biomedical areas specifically orthopedics, demonstrate its unique performance which is not achievable with conventional materials. Pedicle screws, which are used as an anchoring point for implanting spinal instrumentations in spinal fracture and deformity treatments, entail a major drawback; i.e. loosening and back-out. The strength of screw contact with the surrounding bone diminishes as the bone degrades due to osteoporosis. A “Smart” pedicle screw design was developed to address this issue which uses NiTi superelastic-shape memory coils wrapped around it. The smart assembly consists of external superelastic tubing which is responsible for expanding the designed protrusions when they reach body temperature; also an internal shape memory wire inserted into the tubing is sought to retract the assembly when locally heated to above body temperature. The whole assembly was modeled as a beam structure in COMSOL Multiphysics Finite Element software. The behavior of shape memory alloy was defined in the software via its Partial Differential Equation (PDE) module. The SMA model has is a Tanaka-based model and is capable of capturing shape memory effect, superelasticity and hysteresis behavior, and partial transformation in both positive and negative directions. This 1D model was further modified to be included in a 3D framework such that it makes it possible for simulation of a beam under bending. The functionality of the smart screw design can be studied via this FEM model as a future work and the outcomes of the simulation can be compared with experimental tests on the prepared sample of the screw comprising NiTi tubing and wires.

scholarly journals The Influence of Pelvic Tilt on Stress Distribution in the Acetabulum: Finite Element Analysis

2020 ◽  
Author(s):  
Kazuhiro Hasegawa ◽  
Tamon Kabata ◽  
Yoshitomo Kajino ◽  
Daisuke Inoue ◽  
Jiro Sakamoto ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Distribution ◽  
Hip Joint ◽  
Tilt Angle ◽  
Pelvic Tilt ◽  
Biomechanical Analysis ◽  
Von Mises Stress ◽  
Element Analysis ◽  
Von Mises

Abstract Background Finite element analysis (FEA) has been previously applied for the biomechanical analysis of acetabular dysplasia and osteotomy. However, until now, there have been little reports on the use of FEA to evaluate the effects of pelvic tilt on stress distribution in the acetabulum. Methods We used the Mechanical Finder Ver. 7.0 (RCCM, Inc., Japan) to construct finite element models based on 3D-CT data of patients, and designed dysplasia, borderline, and normal pelvic models. For analysis, body weight was placed on the sacrum and the load of the flexor muscles of the hip joint was placed on the ilium. The pelvic tilt was based on the anterior pelvic plane, and the pelvic tilt angles were -20°, 0°, and 20°. The load of the flexor muscle of the hip joint was calculated using the moment arm equation.Results All three models showed the highest values of von Mises stress in the -20° pelvic tilt angle, and the lowest in the 20° angle. Stress distribution concentrated in the load-bearing area. The maximum values of von Mises stress in the borderline at pelvic tilt angles of -20° was 3.5Mpa, and in the dysplasia at pelvic tilt angles of 0° was 3.1Mpa. Conclusions The pelvic tilt angle of -20° of the borderline model showed equal maximum values of von Mises stress than the dysplasia model of pelvic tilt angle of 0°, indicating that pelvic retroversion of -20° in borderline is a risk factor for osteoarthritis of the hip joints, similar to dysplasia.

Biomechanical comparison of stand-alone and bilateral pedicle screws fixation for oblique lumbar inter-body fusion surgery – a finite element analysis

2019 ◽  
Author(s):  
guofang Fang ◽  
yunzhi lin ◽  
wenggang cui ◽  
lili guo ◽  
shihao Zhang ◽  
...  
Keyword(s):  
Finite Element ◽  
Pedicle Screw ◽  
Screw Fixation ◽  
Pedicle Screws ◽  
Element Model ◽  
Axial Rotation ◽  
Pedicle Screw Fixation ◽  
Element Analysis ◽  
Intact Group ◽  
Flexion Extension

Abstract Objectives: The aim of this study was to evaluate the biomechanical stability and safety in patients undergoing oblique lumbar inter-body fusion (OLIF) surgery with stand-alone (SA) and Bilateral pedicle screw fixation (BPSF). Methods: A finite element model of L4-L5 spinal unit was established and validated. Based on the validated model technique, function surgical models corresponding to SA, BPSF were created. Simulations employing the models were performed to investigate the OLIF surgery. A bending moment of 7.5 Nm and a 500 N follower load were applied to the models in flexion, extension, axial rotation and lateral bending. Finite element(FE) models were developed to compare the biomechanics of the intact group, SA, BPSF group. Results: Compared with the Range of motion (ROM) of the intact lumbar model, SA model decreased by 79.5% in flexion, 54.2% in extension, BPSF model decreased by 86.4% in flexion, 70.8% in extension. Compared with the BPSF, the maximum stresses of L4 inferior endplate (IEP) and L5 superior endplate (SEP) increased significantly in SA model, L4 IEP increased to 49.7MPa in extension, L5 SEP increased to 47.7MPa in flexion. Conclusions: OLIF surgery with BPSF could reduce the max stresses of the endplate which may reduce cage sedimentation incidence. However, OLIF surgery with SA could not provide enough rigidity for the fusion segment in osteoporosis patients which may increase the cage sedimentation incidence. Keywords: OLIF; Pedicle screw fixation; spinal fusion; finite element

scholarly journals STUDI NUMERIK UMUR KELELAHAN (FATIGUE LIFE) PADA PROPELLER KAPAL PENANGKAP IKAN DENGAN KAPASITAS MESIN 24 HP

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Rizqi Ilmal Yaqin ◽  
Angger Bagus Prasetiyo ◽  
Pritiansyah Pritiansyah ◽  
Muhammad Haritsah Amrullah ◽  
Binsar Maruli Tua Pakpahan
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Fatigue Life ◽  
Rapid Development ◽  
Von Mises Stress ◽  
Element Analysis ◽  
Fishing Boat ◽  
Finite Element Analysis Simulation ◽  
Von Mises ◽  
Model Affect

Propeller is part of a key component in fishing boat propulsion. Propeller can provide momentum to the fluid which can be a thrust on the ship. However, The failure of the propeller found prematurely. The failure of the propeller maybe because of overload on the propeller model so the fatigue life of the propeller becomes low. On the other hand, the rapid development of technology can simulate a design model to look for failures that occur. Finite Element Analysis is one of the designer solutions to determine the age of failure of a model and failure-prone areas in a model. This study uses propeller model data from fishing boat with engine 24HP in Dumai City TPI that always fail prematurely. The material used is copper alloy. While the drawing model uses Autodesk Inventor and Finite Element Analysis simulation using ANSYS R17.2 software with the number of model nodes is 51108 and the number of elements of the model is 26268. The results obtained from this study are Von Mises stress on the simulation model that is equal to 613.33 MPa to 0.01164 MPa. While the deformation value due to the effect of loading on the model is 5,3657 mm to 0 mm. These results affect the age of fatigue (fatigue life) on the model with the highest value 109 and the lowest 0. The results of the fatigue life value on the model affect the results of the level of damage and the safety number of the model with successive values of 1032 to 1 and 15 to 0.32446. The conclusion of the result is the propeller will fail prematurely.

scholarly journals Biomechanical Analysis of the Forces Exerted during Different Occlusion Conditions following Bilateral Sagittal Split Osteotomy Treatment for Mandibular Deficiency

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Yuan-Han Chang ◽  
Man-Yee Chan ◽  
Jui-Ting Hsu ◽  
Han-Yu Hsiao ◽  
Kuo-Chih Su
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
High Stress ◽  
Biomechanical Analysis ◽  
Von Mises Stress ◽  
Intermaxillary Fixation ◽  
Element Analysis ◽  
Sagittal Split Osteotomy ◽  
Bilateral Sagittal Split Osteotomy ◽  
External Forces

The bilateral sagittal split osteotomy (BSSO) technique is commonly used to correct mandibular deficiency. If the patient is exposed to excessive external forces after the procedure, occlusal changes or nonunion may occur. However, previous studies only focused on single external forces on the mandible and did not conduct relevant research on the forces exerted by different occlusion conditions. The main purpose of this study was to use finite element analysis methods to determine the biomechanics of four common occlusion conditions after BSSO surgical treatment. This study constructed a finite element analysis computer model of a miniplate implanted in the lower jaw. The structure of the model consisted of the mandible, miniplate, and screws. In addition, external forces were applied to the superficial masseter, deep masseter, medial pterygoid, anterior temporalis, middle temporalis, and posterior temporalis muscles to simulate the incisal clench, intercuspal position (ICP), right unilateral molar clench (RMOL), and right group function occlusion conditions. Subsequently, this study observed the effects of these conditions on the miniplate, screws, and mandible, including the von Mises stress values. The results showed that all of the different occlusion conditions that this study evaluated placed high stress on the miniplate. In the ICP and RMOL occlusion conditions, the overall mandibular structure experienced very high stress. The screw on the proximal segment near the bone gap experienced high stress, as did the screw on the buccal side. According to the present analysis, although the data were not directly obtained from clinical practice, the finite element analysis could evaluate the trend of results under different external forces. The result of this study recommended that patients without intermaxillary fixation avoid the ICP and RMOL occlusion conditions. It can be used as a pilot study in the future for providing clinicians more information on the biomechanics of implantation.

Selection of suitable pedicle screw for degenerated cortical and cancellous bone of human lumbar spine: A finite element study

2020 ◽  
pp. 039139882096448
Author(s):  
Pushpdant Jain ◽  
David Chua Sing Ngie ◽  
Soh Fong Lim ◽  
Bee Huah Lim
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Pedicle Screw ◽  
Cancellous Bone ◽  
Body Movement ◽  
Pedicle Screws ◽  
Element Analysis ◽  
Moment Conditions ◽  
Bone Screw ◽  
Selection Of

Pedicular arthrodesis is the traditional procedure in terms of increase in the biomechanical stability with higher fixation rate. The current work aims to identify the effect of three spinal pedicle screws considering cortical and cancellous degeneracy condition. Lumbar section L2-L3 is utilized and various load and moment conditions were applied to depict the various biomechanical parameters for selection of suitable screw. Three dimensional model is considered in finite element analysis to identify the various responses of pedicle screw at bone screw juncture. Computed tomography (CT) images of a healthy male were considered to generate the finite element vertebral model. Generated intact model was further utilized to develop the other implanted models of degenerated cortical and cancellous bone models. The three fused instrumented models with different cortical and cancellous degeneracy conditions were analyzed in finite element analysis. The results were obtained as stress pattern at bone screw boundary and intervertebral disc stress. FE simulated results represents significant changes in the von Mises stress due to various load and moment conditions on degenerated bones during different body movement conditions. Results have shown that among all pedicle screws, the 6.0 mm diameter screw reflects very less stress values at the juncture. Multiple results on biomechanical aspects obtained during the FE study can be considered to design a new stabilization device and may be helpful to plan surgery of critical sections.

scholarly journals Influence of cement-augmented pedicle screws with different volumes of polymethylmethacrylate in osteoporotic lumbar vertebrae over the adjacent segments: A 3D finite element analysis

2020 ◽  
Author(s):  
Hui-zhi Guo ◽  
Shun-cong Zhang ◽  
Dan-qing Guo ◽  
Yan-huai Ma ◽  
Kai yuan ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Pedicle Screw ◽  
Thoracolumbar Spine ◽  
Lumbar Vertebrae ◽  
Pedicle Screws ◽  
Adjacent Segment Degeneration ◽  
Adjacent Segment ◽  
Element Analysis ◽  
Adjacent Segments

Abstract Background: Polymethylmethacrylate (PMMA) is commonly used for cement-augmented pedicle screw instrumentation (CAPSI) to improve the fixation stability and reduce the risk of screw loosening in the osteoporotic thoracolumbar spine. Biomechanical researches have shown that various dose of cement (1-3ml) can be injected to enhance screw stability. To date, there have been no studies on the relationship between adjacent segment degeneration and the volume of PMMA. This study aimed to explore the influence of CAPSI with different volumes of PMMA in osteoporotic lumbar vertebrae over adjacent segments by using finite element analysis.Methods: Seven different finite element models were reconstructed and simulated under different loading conditions, including (1) an intact model, (2) three single-level CAPSI models with different volumes of PMMA (1, 1.73, and 2.5 ml), and (3) three double-level CAPSI models with different volumes of PMMA (1, 1.73, and 2.5 ml). To improve the accuracy of the finite element analysis, the models of the injectable pedicle screw and bone cement were created by using a three-dimensional scanning machine and the CAPSI patient’s CT data, respectively. The range of motion (ROM), the stress of intervertebral discs, and the stress of facet in the adjacent segment were comparatively analysed among the different models.Results: The ROMs of the different segments were compared with experimental data, with good agreement under the different load conditions. Compared with the intact model, the ROM, disc stresses, and facet stress in adjacent segments were found to be higher in the six operative models. Otherwise, with a larger volume of PMMA injected, the ROM, disc stresses, and facet stress slightly increased at the adjacent segment. However, the differences among the augmented models were insignificant for all loading cases.Conclusions: CAPSI could increase the incidence of disk degeneration in the adjacent segment, while within a certain range, different volumes of PMMA provided an approximate impact over the adjacent segment degeneration.

scholarly journals Influence of Different Fixed System in Osteoporotic Lumbar Vertebrae in Fusion：A 3D Finite Element Analysis

2021 ◽  
Author(s):  
Han Ye ◽  
Wu Jincheng ◽  
Wang Xiaodong ◽  
Gao Wenshan ◽  
Sun Shaosong ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Pedicle Screw ◽  
Maximum Stress ◽  
Pedicle Screws ◽  
Cement Augmentation ◽  
Normal Model ◽  
Element Analysis ◽  
Normal Bone ◽  
Flexion Extension

Abstract Background：Posterior lumbar interbody fusion(PLIF) is the most common surgical method for lumbar fusion surgery, and pedicle screws（PS）can provide effective fixation strength in normal bone. However, pedicle screws are prone to loosening in osteoporotic patients. cortical bone trajectory (CBT) screw fixation and cement augmentation pedicle screw（CAPS） fixation are often used to reduce the risk of loosening. Although several studies are reported that the pullout strength of CBT screws or CAPS screws are higher than PS，There are no relevant studies on different internal fixation stress analysis. The purpose of this study was to compare the stresses of different fixation methods and analyze the stresses of different internal fixation systems through finite element analysis.Methods: Five finite element models were established and tested by simulating PLIF surgery at L4/5. They included: (1) normal model (2) osteoporosis model (3) pedicle screw model; (4) cement augmentation pedicle screw（CAPS）model; (5) cortical bone trajectory (CBT) model. The range of motion (ROM), stress of fusion cage and screw-rod system of different models were analyzed by simulating flexion, extension, left bending, right bending, left rotation and right rotation movements through software.Results: The ROM of the osteoporosis model was increased compared with the normal bone, and the osteoporosis was increased by 5.3%, 17.6%, 11.5%, 11.3%, 7.5%, and 8.3% compared with the normal model during flexion, extension, left bending, right bending, left rotation, and right rotation. After fixation, the ROM decreased, but the difference was not significant between the different fixation models. The stress of the screw-rods is the minimum one in the CAPS group. the PS group is the middle one, and stress of the CBT group is max. The cage stress is the minimum in the CAPS group which is slightly smaller than the cage stress in the PS group. the cage stress was the max in the CBT group.Conclusion: PLIF can decrease the ROM of lumbar vertebra and fusion segment in osteoporosis, but different fixation methods have little effect on ROM. However, there was a great difference in the stress of implant, with the least stress in the CAPS group, the second in the PS group, and the greatest stress in the CBT. The same is true for Cage stress. At the same time, the maximum stress zone to occur at the screw-rod junction, while the maximum stress of cage occurs at the position in contact with the endplate. The study has guiding significance for clinical practice.

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