Comparison of Fatigue Behaviors of Spinal Implants Under Physiological Spinal Loads: A Finite Element Pilot Study

2017 ◽  
Author(s):  
Ming Xu ◽  
James Yang ◽  
Isador H. Lieberman ◽  
Ram Haddas
Keyword(s):  
Pedicle Screw ◽  
Axial Rotation ◽  
Von Mises Stress ◽  
Fe Model ◽  
Fusion Surgery ◽  
Spinal Loads ◽  
Spinal Implants ◽  
Exact Geometry ◽  
Von Mises ◽  
Biomechanical Tests

The fusion surgery is a standard treatment for scoliosis. Fatigue-related failure is one common cause for the fusion surgery implant. Due to the high cost of revision surgery, it is of clinical value to study the fatigue behaviors of the spinal implants under physiological spinal loads. In the literature, biomechanical tests and finite element (FE) methods have been used to study the fatigue of the spinal implants. Compared with biomechanical tests, FE analysis has the advantage of low cost and high efficiency. Due to the high computational cost, no FE study has been modeled the exact geometry of the pedicle screw (including the thread) in the screw-bone connection within the multi-level spine FE model. This study introduced a feasible FE-based method to predict the fatigue behaviors of the spinal implants with exact geometry of pedicle screw. One previously-validated FE spine model was utilized to provide physiological spinal loads and was bilaterally fused with pedicle screws and rods at L3-L4 spine levels. The exact geometry of the pedicle screw was simulated in this study for accurate stress prediction. The fused spine FE model was subjected to six loading directions (flexion/extension, left/right lateral bending, and left/right axial rotation). For each loading direction, a pure bending moment of 10 Nm was tested. First, FE analysis was performed for one loading cycle. Range of motion, maximum von Mises stress values of the spinal implants were recorded and compared for the six tested loading conditions. Then, based on the stress/strain history of the spinal implants for one loading cycle provided by the FE simulation, fatigue life cycles of the spinal implants were calculated using strain-based Smith-Watson-Topper equation. Flexion produced the largest range of motion at the adjacent level. Axial rotation produced the largest von Mises stress in the spinal implants. Except for lateral bending, the von Mises stress predicted in the screws fused at the superior vertebra was larger than that in the screws fused at inferior vertebra. The method introduced in this study will be used to study different screw fixation methods in the future work.

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

2020 ◽  
Vol 43 (12) ◽  
pp. 803-810 ◽  
Author(s):  
Masud Rana ◽  
Sandipan Roy ◽  
Palash Biswas ◽  
Shishir Kumar Biswas ◽  
Jayanta Kumar Biswas
Keyword(s):  
Finite Element ◽  
Lumbar Spine ◽  
Range Of Motion ◽  
Pedicle Screw ◽  
Axial Rotation ◽  
Von Mises Stress ◽  
Lateral Bending ◽  
Intact Bone ◽  
Flexion Extension ◽  
Von Mises

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.

scholarly journals Effects of Revision Rod Position on Spinal Construct Stability in Lumbar Revision Surgery: A Finite Element Study

2022 ◽  
Vol 9 ◽  
Author(s):  
Quan-Chang Tan ◽  
Jin-Feng Huang ◽  
Hao Bai ◽  
Zi-Xuan Liu ◽  
Xin-Yi Huang ◽  
...  
Keyword(s):  
Finite Element ◽  
Revision Surgery ◽  
Spinal Instrumentation ◽  
Axial Rotation ◽  
Von Mises Stress ◽  
Fe Model ◽  
Interspinous Ligament ◽  
Moment Load ◽  
Von Mises ◽  
Changing Tendency

Revision surgery (RS) is a necessary surgical intervention in clinical practice to treat spinal instrumentation–related symptomatic complications. Three constructs with different configurations have been applied in RS. One distinguishing characteristic of these configurations is that the revision rods connecting previous segments and revision segments are placed alongside, outside, or inside the previous rods at the level of facetectomy. Whether the position of the revision rod could generate mechanical disparities in revision constructs is unknown. The objective of this study was to assess the influence of the revision rod position on the construct after RS. A validated spinal finite element (FE) model was developed to simulate RS after previous instrumented fusion using a modified dual-rod construct (DRCm), satellite-rod construct (SRC), and cortical bone trajectory construct (CBTC). Thereafter, maximum von Mises stress (VMS) on the annulus fibrosus and cages and the ligament force of the interspinous ligament, supraspinous ligament, and ligamentum flavum under a pure moment load and a follower load in six directions were applied to assess the influence of the revision rod position on the revision construct. An approximately identical overall reducing tendency of VMS was observed among the three constructs. The changing tendency of the maximum VMS on the cages placed at L4-L5 was nearly equal among the three constructs. However, the changing tendency of the maximum VMS on the cage placed at L2-L3 was notable, especially in the CBTC under right bending and left axial rotation. The overall changing tendency of the ligament force in the DRCm, SRC, and CBTC was also approximately equal, while the ligament force of the CBTC was found to be significantly greater than that of the DRCm and SRC at L1-L2. The results indicated that the stiffness associated with the CBTC might be lower than that associated with the DRCm and SRC in RS. The results of the present study indicated that the DRCm, SRC, and CBTC could provide sufficient stabilization in RS. The CBTC was a less rigid construct. Rather than the revision rod position, the method of constructing spinal instrumentation played a role in influencing the biomechanics of revision.

scholarly journals A Hybrid Uniplanar Pedicle Screw System with a New Intermediate Screw for Minimally Invasive Spinal Fixation: A Finite Element Analysis

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Jia Li ◽  
Li-Cheng Zhang ◽  
Jiantao Li ◽  
Hao Zhang ◽  
Jing-Xin Zhao ◽  
...  
Keyword(s):  
Finite Element ◽  
Minimally Invasive ◽  
Range Of Motion ◽  
Pedicle Screw ◽  
Axial Rotation ◽  
Von Mises Stress ◽  
Spinal Fixation ◽  
Lateral Bending ◽  
Maximum Displacement ◽  
Von Mises

Purpose. A hybrid pedicle screw system for minimally invasive spinal fixation was developed based on the uniplanar pedicle screw construct and a new intermediate screw. Its biomechanical performance was evaluated using finite element (FE) analysis. Methods. A T12-L2 FE model was established to simulate the L1 vertebral compression fracture with Magerl classification A1.2. Six fixation models were developed to simulate the posterior pedicle screw fracture fixation, which were divided into two subgroups with different construct configurations: (1) six-monoaxial/uniplanar/polyaxial pedicle screw constructs and (2) four-monoaxial/uniplanar/polyaxial pedicle screw constructs with the new intermediate screw. After model validation, flexion, extension, lateral bending, and axial rotation with 7.5 Nm moments and preloading of 500 N vertical compression were applied to the FE models to compare the biomechanical performances of the six fixation models with maximum von Mises stress, range of motion, and maximum displacement of the vertebra. Results. Under four loading scenarios, the maximum von Mises stresses were found to be at the roots of the upper or lower pedicle screws. In the cases of flexion, lateral bending, and axial rotation, the maximum von Mises stress of the uniplanar screw construct lay in between the monoaxial and polyaxial screw constructs in each subgroup. Considering lateral bending, the uniplanar screw construct enabled to lower the maximum von Mises stress than monoaxial and polyaxial pedicle screw constructs in each subgroup. Two subgroups showed comparable results of the maximum von Mises stress on the endplates, range of motion of T12-L1, and maximum displacement of T12 between the corresponding constructs with the new intermediate screw or not. Conclusions. The observations shown in this study verified that the hybrid uniplanar pedicle screw system exhibited comparable biomechanical performance as compared with other posterior short-segment constructs. The potential advantage of this new fixation system may provide researchers and clinical practitioners an alternative for minimally invasive spinal fixation with vertebral augmentation.

Altered Load Transfer in the Pelvis in the Presence of Periprosthetic Osteolysis

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Jacob T. Munro ◽  
Justin W. Fernandez ◽  
James S. Millar ◽  
Cameron G. Walker ◽  
Donald W. Howie ◽  
...  
Keyword(s):  
Cortical Bone ◽  
Load Transfer ◽  
Von Mises Stress ◽  
Patient Specific ◽  
Fe Model ◽  
Stress Concentrations ◽  
Periprosthetic Osteolysis ◽  
Total Hip ◽  
Long Term Follow Up ◽  
Von Mises

Periprosthetic osteolysis in the retroacetabular region with cancellous bone loss is a recognized phenomenon in the long-term follow-up of total hip replacement. The effects on load transfer in the presence of defects are less well known. A validated, patient-specific, 3D finite element (FE) model of the pelvis was used to assess changes in load transfer associated with periprosthetic osteolysis adjacent to a cementless total hip arthroplasty (THA) component. The presence of a cancellous defect significantly increased (p < 0.05) von Mises stress in the cortical bone of the pelvis during walking and a fall onto the side. At loads consistent with single leg stance, this was still less than the predicted yield stress for cortical bone. During higher loads associated with a fall onto the side, highest stress concentrations occurred in the superior and inferior pubic rami and in the anterior column of the acetabulum with larger cancellous defects.

scholarly journals Study on the biomechanical responses of the loaded bone in macroscale and mesoscale by multiscale poroelastic FE analysis

2019 ◽  
Vol 18 (1) ◽  
Author(s):  
WeiLun Yu ◽  
XiaoGang Wu ◽  
HaiPeng Cen ◽  
Yuan Guo ◽  
ChaoXin Li ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Fluid Velocity ◽  
Fluid Pressure ◽  
Biological Information ◽  
Von Mises Stress ◽  
Fe Model ◽  
Heterogeneous Distribution ◽  
Material Parameters ◽  
Mesoscopic Models ◽  
Von Mises

Abstract Background Bone is a hierarchically structured composite material, and different hierarchical levels exhibit diverse material properties and functions. The stress and strain distribution and fluid flow in bone play an important role in the realization of mechanotransduction and bone remodeling. Methods To investigate the mechanotransduction and fluid behaviors in loaded bone, a multiscale method was developed. Based on poroelastic theory, we established the theoretical and FE model of a segment bone to provide basis for researching more complex bone model. The COMSOL Multiphysics software was used to establish different scales of bone models, and the properties of mechanical and fluid behaviors in each scale were investigated. Results FE results correlated very well with analytical in macroscopic scale, and the results for the mesoscopic models were about less than 2% different compared to that in the macro–mesoscale models, verifying the correctness of the modeling. In macro–mesoscale, results demonstrated that variations in fluid pressure (FP), fluid velocity (FV), von Mises stress (VMS), and maximum principal strain (MPS) in the position of endosteum, periosteum, osteon, and interstitial bone and these variations can be considerable (up to 10, 8, 4 and 3.5 times difference in maximum FP, FV, VMS, and MPS between the highest and the lowest regions, respectively). With the changing of Young’s modulus (E) in each osteon lamella, the strain and stress concentration occurred in different positions and given rise to microscale spatial variations in the fluid pressure field. The heterogeneous distribution of lacunar–canalicular permeability (klcp) in each osteon lamella had various influence on the FP and FV, but had little effect on VMS and MPS. Conclusion Based on the idealized model presented in this article, the presence of endosteum and periosteum has an important influence on the fluid flow in bone. With the hypothetical parameter values in osteon lamellae, the bone material parameters have effect on the propagation of stress and fluid flow in bone. The model can also incorporate alternative material parameters obtained from different individuals. The suggested method is expected to provide dependable biological information for better understanding the bone mechanotransduction and signal transduction.

THE BIOMECHANICAL EFFECTS OF CEMENT AUGMENTATION AND PARTIAL VERTEBRAL HEIGHT RESTORATION ON THE LOAD TRANSFER CHANGE OF ADJACENT VERTEBRAE IN VERTEBROPLASTY

2015 ◽  
Vol 15 (03) ◽  
pp. 1550025 ◽  
Author(s):  
CHIEN-YU LIN ◽  
WENG-PIN CHEN ◽  
PO-LIANG LAI ◽  
SHIH-YOUENG CHUANG ◽  
DA-TONG JU ◽  
...  
Keyword(s):  
Load Transfer ◽  
Cement Augmentation ◽  
Erector Spinae ◽  
Von Mises Stress ◽  
Fe Model ◽  
Vertebral Height ◽  
Adjacent Disc ◽  
Before And After ◽  
Von Mises ◽  
Von Mises Stresses

Vertebroplasty is commonly used to treat vertebral wedge fractures (VWFs). However, differing degrees of vertebral height restoration (VHR) have been reported after vertebroplasty, and little is known about how grades (steepness) of VWF deformities affect loadings on the fractured and adjacent unfractured vertebrae. Therefore, the goal of this study was to create a non-linear finite element (FE) model of the T10–L2 thoracolumbar segments. With this model, we aimed to evaluate the biomechanical outcomes of three different collapse models (25%, 50%, and 75%) at the T12 vertebra before and after cement augmentation (CA) and with and without VHR. In these VWF simulations, the forces of the erector spinae, the intradiscal pressure, and the maximum von Mises stresses in the endplates and vertebral bodies increased as vertebral deformation increased. Performing CA alone, without restoring vertebral height for the fractured vertebra, did not change the stiffness of multiple spinal segments or the pressures on the adjacent disc, but it did decrease stresses on the endplates and the vertebral bone. A 10% restoration of vertebral height after CA reduced the maximum von Mises stress in the endplates and bone structures more than when CA did not restore vertebral height (no VHR). These results suggest that achieving partial VHR during vertebroplasty may help prevent postvertebroplasty fractures in the fractured and adjacent vertebrae.

scholarly journals A Novel Rat Model of Orthodontic Tooth Movement Using Temporary Skeletal Anchorage Devices: 3D Finite Element Analysis andIn VivoValidation

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Neelambar Kaipatur ◽  
Yuchin Wu ◽  
Samer Adeeb ◽  
Thomas Stevenson ◽  
Paul Major ◽  
...  
Keyword(s):  
Finite Element ◽  
Alveolar Bone ◽  
Tooth Movement ◽  
Orthodontic Tooth Movement ◽  
Von Mises Stress ◽  
Fe Model ◽  
Sprague Dawley ◽  
Element Analysis ◽  
Von Mises ◽  
The Right

The aim of this animal study was to develop a model of orthodontic tooth movement using a microimplant as a TSAD in rodents. A finite element model of the TSAD in alveolar bone was built usingμCT images of rat maxilla to determine the von Mises stresses and displacement in the alveolar bone surrounding the TSAD. Forin vivovalidation of the FE model, Sprague-Dawley rats (n=25) were used and a Stryker 1.2 × 3 mm microimplant was inserted in the right maxilla and used to protract the right first permanent molar using a NiTi closed coil spring. Tooth movement measurements were taken at baseline, 4 and 8 weeks. At 8 weeks, animals were euthanized and tissues were analyzed by histology and EPMA. FE modeling showed maximum von Mises stress of 45 Mpa near the apex of TSAD but the average von Mises stress was under 25 Mpa. Appreciable tooth movement of 0.62 ± 0.04 mm at 4 weeks and 1.99 ± 0.14 mm at 8 weeks was obtained. Histological and EPMA results demonstrated no active bone remodeling around the TSAD at 8 weeks depicting good secondary stability. This study provided evidence that protracted tooth movement is achieved in small animals using TSADs.

scholarly journals AP1000 Shield Building Dynamic Response for Different Water Levels of PCCWST Subjected to Seismic Loading considering FSI

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Daogang Lu ◽  
Yu Liu ◽  
Xiaojia Zeng
Keyword(s):  
Storage Tank ◽  
Seismic Analysis ◽  
Cooling System ◽  
Water Storage ◽  
Seismic Loading ◽  
Water Levels ◽  
Von Mises Stress ◽  
Fe Model ◽  
Water Storage Tank ◽  
Von Mises

Huge water storage tank on the top of many buildings may affect the safety of the structure caused by fluid-structure interaction (FSI) under the earthquake. AP1000 passive containment cooling system water storage tank (PCCWST) placed at the top of shield building is a key component to ensure the safety of nuclear facilities. Under seismic loading, water will impact the wall of PCCWST, which may pose a threat to the integrity of the shield building. In the present study, an FE model of AP1000 shield building is built for the modal and transient seismic analysis considering the FSI. Six different water levels in PCCWST were discussed by comparing the modal frequency, seismic acceleration response, and von Mises stress distribution. The results show the maximum von Mises stress emerges at the joint of shield building roof and water around the air inlet. However, the maximum von Mises stress is below the yield strength of reinforced concrete. The results may provide a reference for design of the AP1000 and CAP1400 in the future.

scholarly journals ANALYSIS ON THE EFFECT OF HALF ANGLE ON THE DISPLACEMENT OF PEDICLE SCREW DURING AXIAL PULL-OUT TEST IN CANCELLOUS BONE USING 2D AXISYMMETRIC FE MODEL

2021 ◽  
Vol 57 (2) ◽  
pp. 153-158
Author(s):  
Harikrishna Makaram ◽  
◽  
Ramakrishnan Swaminathan ◽  
Keyword(s):  
Pedicle Screw ◽  
High Stress ◽  
Pedicle Screws ◽  
Stress Transfer ◽  
Von Mises Stress ◽  
Fe Model ◽  
Distal Half ◽  
Proximal Half ◽  
Pull Out ◽  
Half Angle

Pedicle screw fixations are commonly used in the treatment of spinal pathologies. For effective treatment, stable anchorage between the screw and bone is necessary. In this study, the influence of proximal and distal half angle of the screw, on the displacement of fixation and stress transfer are simulated using a 2D axisymmetric finite element model. A parametric study was performed by varying the proximal half-angle between 0° and 60° in steps of 10° and the distal half angles are considered as 30° and 40°. The material properties and boundary conditions are applied based on previous studies. Frictional contact is considered between the bone and screw. Results show that, displacement of fixation is observed to be minimum at a proximal half angle of 0° and maximum at an angle of 60°. High stress concentration is observed in first few threads with highest maximum von Mises stress at an angle of 60°. High stress transfer was obtained for proximal half-angles of 40° and 50°. It is observed that, this method might aid to develop better pedicle screws for treatment of Scoliosis.

Simulation of Brain Response to Noncontact Impacts Using Coupled Eulerian–Lagrangian Method

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Miao Na ◽  
Timothy J. Beavers ◽  
Abhijit Chandra ◽  
Sarah A. Bentil
Keyword(s):  
Brain Tissue ◽  
Mechanical Response ◽  
Brain Regions ◽  
Von Mises Stress ◽  
Fe Model ◽  
Brain Response ◽  
Fe Method ◽  
Angular Velocities ◽  
Von Mises ◽  
The Brain

Abstract Finite element (FE) method has been widely used for gaining insights into the mechanical response of brain tissue during impacts. In this study, a coupled Eulerian−Lagrangian (CEL) formulation is implemented in impact simulations of a head system to overcome the mesh distortion difficulties due to large deformation in the cerebrospinal fluid (CSF) region and provide a biofidelic model of the interaction between the brain and skull. The head system used in our FE model is constructed from the transverse section of the human brain, with CSF modeled by Eulerian elements. Spring connectors are applied to represent the pia-arachnoid connection between the brain and skull. Validations of the CEL formulation and the FE model are performed using the experimental results. The dynamic response of brain tissue under noncontact impacts and the brain regions susceptible to injury are evaluated based on the intracranial pressure (ICP), maximum principal strain (MPS), and von Mises stress. While tracking the critical MPS location on the brain, higher likelihood of contrecoup injury than coup injury is found when sudden brain−skull motion takes place. The accumulation effect of CSF in the ventricle system, under large relative brain−skull motion, is also identified. The FE results show that adding relative angular velocities, to the translational impact model, not only causes a diffuse high strain area, but also cause the temporal lobes to be susceptible to cerebral contusions since the protecting CSF is prone to be squeezed away at the temporal sites due to the head rotations.

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