scholarly journals Biomechanical Effects of a Cross Connector in Sacral Fractures – A Finite Element Analysis

2021 ◽  
Vol 9 ◽  
Author(s):  
Meike Gierig ◽  
Fangrui Liu ◽  
Lukas Weiser ◽  
Wolfgang Lehmann ◽  
Peter Wriggers ◽  
...  
Keyword(s):  
Finite Element ◽  
Operative Procedure ◽  
Element Model ◽  
Biomechanical Properties ◽  
Patient Specific ◽  
Fe Model ◽  
Principal Stresses ◽  
Element Analysis ◽  
Fracture Area ◽  
Maximum Stresses

Background: Spinopelvic fractures and approaches of operative stabilization have been a source of controversial discussion. Biomechanical data support the benefit of a spinopelvic stabilization and minimally invasive procedures help to reduce the dissatisfying complication rate. The role of a cross connector within spinopelvic devices remains inconclusive. We aimed to analyze the effect of a cross connector in a finite element model (FE model).Study Design: A FE model of the L1-L5 spine segment with pelvis and a spinopelvic stabilization was reconstructed from patient-specific CT images. The biomechanical relevance of a cross connector in a Denis zone I (AO: 61-B2) sacrum fracture was assessed in the FE model by applying bending and twisting forces with and without a cross connector. Biomechanical outcomes from the numerical model were investigated also considering uncertainties in material properties and levels of osseointegration.Results: The designed FE model showed comparable values in range-of-motion (ROM) and stresses with reference to the literature. The superiority of the spinopelvic stabilization (L5/Os ilium) ± cross connector compared to a non-operative procedure was confirmed in all analyzed loading conditions by reduced ROM and principal stresses in the disk L5/S1, vertebral body L5 and the fracture area. By considering the combination of all loading cases, the presence of a cross connector reduced the maximum stresses in the fracture area of around 10%. This difference has been statistically validated (p < 0.0001).Conclusion: The implementation of a spinopelvic stabilization (L5/Os ilium) in sacrum fractures sustained the fracture and led to enhanced biomechanical properties compared to a non-reductive procedure. While the additional cross connector did not alter the resulting ROM in L4/L5 or L5/sacrum, the reduction of the maximum stresses in the fracture area was significant.

Finite Element Analysis of the Distributed Vibration Absorbers for Structural Noise Control

2005 ◽  
Author(s):  
Ashwini Gautam ◽  
Chris Fuller ◽  
James Carneal
Keyword(s):  
Finite Element ◽  
Numerical Model ◽  
Base Plate ◽  
Element Model ◽  
Fe Model ◽  
Vibration Absorbers ◽  
Element Analysis ◽  
Poroelastic Media ◽  
Hexahedral Elements ◽  
Component Models

This work presents an extensive analysis of the properties of distributed vibration absorbers (DVAs) and their effectiveness in controlling the sound radiation from the base structure. The DVA acts as a distributed mass absorber consisting of a thin metal sheet covering a layer of acoustic foam (porous media) that behaves like a distributed spring-mass-damper system. To assess the effectiveness of these DVAs in controlling the vibration of the base structures (plate) a detailed finite elements model has been developed for the DVA and base plate structure. The foam was modeled as a poroelastic media using 8 node hexahedral elements. The structural (plate) domain was modeled using 16 degree of freedom plate elements. Each of the finite element models have been validated by comparing the numerical results with the available analytical and experimental results. These component models were combined to model the DVA. Preliminary experiments conducted on the DVAs have shown an excellent agreement between the results obtained from the numerical model of the DVA and from the experiments. The component models and the DVA model were then combined into a larger FE model comprised of a base plate with the DVA treatment on its surface. The results from the simulation of this numerical model have shown that there has been a significant reduction in the vibration levels of the base plate due to DVA treatment on it. It has been shown from this work that the inclusion of the DVAs on the base plate reduces their vibration response and therefore the radiated noise. Moreover, the detailed development of the finite element model for the foam has provided us with the capability to analyze the physics behind the behavior of the distributed vibration absorbers (DVAs) and to develop more optimized designs for the same.

Finite Element Mesh Generator Applying Constraints’ Propagation and Isoparametric Mapping

1991 ◽  
Author(s):  
J. Rodriguez ◽  
M. Him
Keyword(s):  
Finite Element ◽  
Mesh Generation ◽  
Element Model ◽  
Finite Element Mesh ◽  
Fe Model ◽  
Element Analysis ◽  
Element Mesh ◽  
Mesh Generator ◽  
Generation Algorithm ◽  
Essential Input

Abstract This paper presents a finite element mesh generation algorithm (PREPAT) designed to automatically discretize two-dimensional domains. The mesh generation algorithm is a mapping scheme which creates a uniform isoparametric FE model based on a pre-partitioned domain of the component. The proposed algorithm provides a faster and more accurate tool in the pre-processing phase of a Finite Element Analysis (FEA). A primary goal of the developed mesh generator is to create a finite element model requiring only essential input from the analyst. As a result, the generator code utilizes only a sketch, based on geometric primitives, and information relating to loading/boundary conditions. These conditions represents the constraints that are propagated throughout the model and the available finite elements are uniformly mapped in the resulting sub-domains. Relative advantages and limitations of the mesh generator are discussed. Examples are presented to illustrate the accuracy, efficiency and applicability of PREPAT.

Patient-Specific 3D Finite-Element Analysis of Miniscrew Implants During Orthodontic Treatment

2009 ◽  
Author(s):  
Hussein H. Ammar ◽  
Victor H. Mucino ◽  
Peter Ngan ◽  
Richard J. Crout ◽  
Osama M. Mukdadi
Keyword(s):  
Finite Element ◽  
Orthodontic Treatment ◽  
3D Model ◽  
Patient Specific ◽  
Stress Concentrations ◽  
Element Analysis ◽  
Miniscrew Implants ◽  
Operative Planning ◽  
Miniscrew Implant ◽  
Maximum Stresses

Miniscrew implants have seen increasing clinical use as orthodontic anchorage devices with demonstrated stability. The focus of this study is to develop and simulate operative factors, such as load magnitudes and anchor locations to achieve desired motions in a patient-specific 3D model undergoing orthodontic treatment with miniscrew implant anchorage. A CT scan of a patient skull was imported into Mimics software (Materialise, 12.1). Segmentation operations were performed on the images to isolate the mandible, filter out noise, then reconstruct a smooth 3D model. A model of the left canine was reconstructed with the PDL modeled as a thin solid layer. A miniscrew was modeled with dimensions based on a clinical implant (BMK OAS-T1207) then inserted into the posterior mandible. All components were volumetrically meshed and optimized in Mimics software. Elements comprising the mandible bone and teeth were assigned a material based on their gray value ranges in HU from the original scan, and meshes were exported into ANSYS software. All materials were defined as linear and isotropic. A nonlinear PDL was also defined for comparison. For transverse forces applied on the miniscrew, maximum stresses increased linearly with loading and appeared at the neck or first thread and in the cortical bone. A distal tipping force was applied on the canine, and maximum stresses appeared in the tooth at the crown and apex and in the bone at the compression surface. Under maximum loading, stresses in bone were sufficient for resorption. The nonlinear PDL exhibited lower stresses and deflections than the linear model due to increasing stiffness. Numerous stress concentrations were seen in all models. Results of this study demonstrate the potential of patient-specific 3D reconstruction from CT scans and finite-element simulation as a versatile and effective pre-operative planning tool for orthodontists.

An assessment of the Sachs method for measuring residual stresses in cold worked fastener holes

1998 ◽  
Vol 33 (4) ◽  
pp. 263-274 ◽  
Author(s):  
D J Smith ◽  
C G C Poussard ◽  
M J Pavier
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Cold Working ◽  
Element Model ◽  
Fe Model ◽  
Working Process ◽  
Element Analysis ◽  
Near Surface ◽  
Cold Worked ◽  
Good Agreement

Measurements of residual stresses in 6 mm thick aluminium alloy 2024 plates containing 4 per cent cold worked fastener are made using the Sachs method. The measurements are made on discs extracted from the plates. The measured tangential residual stress distribution adjacent to the hole edge are found to be affected by the disc diameter. The measured residual stresses are also in good agreement with averaged through-thickness predictions of residual stresses from an axisymmetric finite element (FE) model of the cold working process. A finite element analysis is also conducted to simulate disc extraction and then the Sachs method. The measured FE residual stresses from the Sachs simulation are found to be in good agreement with the averaged through-thickness predicted residual stresses. The Sachs simulation was not able to reproduce the detailed near-surface residual stresses found from the finite element model of the cold working process.

A three-dimensional finite element model from computed tomography data: A semi-automated method

2001 ◽  
Vol 215 (2) ◽  
pp. 203-212 ◽  
Author(s):  
P M Cattaneo ◽  
M Dalstra ◽  
L H Frich
Keyword(s):  
Computed Tomography ◽  
Finite Element ◽  
Three Dimensional ◽  
Patient Specific ◽  
Fe Model ◽  
Element Analysis ◽  
Automated Method ◽  
Bone Properties ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

Three-dimensional finite element analysis is one of the best ways to assess stress and strain distributions in complex bone structures. However, accuracy in the results may be achieved only when accurate input information is given. A semi-automated method to generate a finite element (FE) model using data retrieved from computed tomography (CT) was developed. Due to its complex and irregular shape, the glenoid part of a left embalmed scapula bone was chosen as working material. CT data were retrieved using a standard clinical CT scanner (Siemens Somatom Plus 2, Siemens AG, Germany). This was done to produce a method that could later be utilized to generate a patient-specific FE model. Different methods of converting Hounsfield unit (HU) values to apparent densities and subsequently to Young's moduli were tested. All the models obtained were loaded using three-dimensional loading conditions taken from literature, corresponding to an arm abduction of 90°. Additional models with different amounts of elements were generated to verify convergence. Direct comparison between the models showed that the best method to convert HU values directly to apparent densities was to use different equations for cancellous and cortical bone. In this study, a reliable method of determining both geometrical data and bone properties from patient CT scans for the semi-automated generation of an FE model is presented.

scholarly journals Interfacial crack arrest in sandwich beams subjected to fatigue loading using a novel crack arresting device – Numerical modelling

2017 ◽  
Vol 21 (2) ◽  
pp. 422-438 ◽  
Author(s):  
G Martakos ◽  
JH Andreasen ◽  
C Berggreen ◽  
OT Thomsen
Keyword(s):  
Finite Element ◽  
Sandwich Beam ◽  
Interfacial Crack ◽  
Fatigue Loading ◽  
Element Model ◽  
Crack Arrest ◽  
Design Tool ◽  
Fe Model ◽  
Sandwich Beams ◽  
Element Analysis

A novel crack arresting device is implemented in foam-cored composite sandwich beams and tested using the Sandwich Tear Test (STT) configuration. A finite element model of the setup is developed, and the predictions are correlated with observations and results from a recently conducted experimental fatigue test study. Based on a linear elastic fracture mechanics approach, the developed FE model is utilised to simulate crack propagation and arrest in foam-cored sandwich beam specimens subjected to fatigue loading conditions. The effect of the crack arresters on the fatigue life is analysed, and the predictive results are subsequently compared with the observations from the previously conducted fatigue tests. The FE model predicts the energy release rate and the mode mixity based on the derived crack surface displacements, utilising algorithms for the prediction of accelerated fatigue crack growth as well as the strain field evolution in the vicinity of the crack tip on the surface of the sandwich specimens. It is further shown that the developed finite element analysis methodology can be used to gain a deeper insight onto the physics and behavioural characteristics of the novel peel stopper concept, as well as a design tool that can be used for the implementation of crack arresting devises in engineering applications of sandwich components and structures.

NONLINEAR FINITE ELEMENT ANALYSIS OF FRP STRENGTHENED RC BEAMS

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
Prabin Pathak ◽  
Y. X. Zhang
Keyword(s):  
Finite Element ◽  
Plastic Material ◽  
Experimental Studies ◽  
Material Model ◽  
Element Model ◽  
Steel Reinforcement ◽  
Elastic Model ◽  
Fe Model ◽  
Rc Beams ◽  
Element Analysis

A simple, accurate and efficient finite element model is developed in ANSYS for numerical modelling of the nonlinear structural behavior of FRP strengthened RC beams under static loading in this paper. Geometric nonlinearity and material non-linear properties of concrete and steel rebar are accounted for this model. Concrete and steel reinforcement are modelled using Solid 65 element and Link 180 element, and FRP and adhesive are modelled using Shell 181element and Solid 45 element. Concrete is modelled using Nitereka and Neal’s model for compression, and isotropic and linear elastic model before cracking with strength gradually reducing to zero after cracking for tension. For steel reinforcement, the elastic perfectly plastic material model is used. FRPs are assumed to be linearly elastic until rupture and epoxy is assumed to be linearly elastic. The new FE model is validated by comparing the computed results with those obtained from experimental studies.

The Patient-Specific Brace Design and Biomechanical Analysis of Adolescent Idiopathic Scoliosis

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Wen-Zhong Nie ◽  
Ming Ye ◽  
Zu-De Liu ◽  
Cheng-Tao Wang
Keyword(s):  
Finite Element ◽  
Measurement System ◽  
Element Model ◽  
Biomechanical Study ◽  
Biomechanical Analysis ◽  
Patient Specific ◽  
Sacral Slope ◽  
Element Analysis ◽  
Biomechanical Behavior ◽  
Idiopathic Adolescent Scoliosis

Brace application has been reported to be an effective approach in treating mild to moderate idiopathic adolescent scoliosis. However, little attention is focused on the biomechanical study of patient-specific brace treatment. The purpose of this study was to propose a design method of personalized brace and to analyze its biomechanical behavior and to compare the brace forces with the I-Scan measurement system. Based on a three-dimensional patient-specific finite element model of the spine, rib cage, pelvis, and abdomen, a parametric patient-specific model of a thoracolumbosacral orthosis was built. The interaction between the torso and the brace was modeled by surface-to-surface contact interface. Three standard strap tensions (20 N, 40 N, and 60 N) were loaded on the back of the brace to simulate the strap tension. The I-Scan distribution pressure measurement system was used to measure the different region pressures, and the equivalent forces in these regions were calculated. The spinal curve changes and the forces acted on the brace generated by the strap tension were evaluated and compared with the measurement. The reduction in the coronal curvature was about 60% for a strap tension of 60 N. The sacral slope and the lordosis were partially reduced in this case, but the kyphosis had no obvious change. The brace slightly modified the axial rotation at the apex of the scoliotic curve. The forces generated in finite element analysis were approximately in good agreement with the measurement. The design and biomechanical analysis methods of patient-specific brace should be useful in the design of more effective braces.

Simulation of the Transverse Fractures of the Sacrum Using a Finite Element Model of Lumbar Spine-Pelvis Segment

2008 ◽  
Author(s):  
A. Ivanov ◽  
A. Kiapour ◽  
N. Ebraheim ◽  
V. K. Goel
Keyword(s):  
Finite Element ◽  
Lumbar Spine ◽  
Finite Element Model ◽  
Treatment Options ◽  
Element Model ◽  
Severe Trauma ◽  
Fe Model ◽  
Element Analysis ◽  
Modern Computer ◽  
Transverse Fractures

The sacrum fractures are very severe trauma which frequently accompanied with lumbar spine fractures. The surgical procedures often require primary stabilization of both lumbar spine and sacrum. To understand the rationale of the instrumentation numerous cadaveric studies were conducted to elucidate the anatomy of fractures and treatment options [1,2,3]. The modern computer technology allowed simulating the fractures and repairing using the Finite Element Analysis, also [4,5]. The last method has a raw of advantages versus cadaveric method such as higher reliability, accuracy, and safety. Finite element investigations of the pelvic fractures allowed comparing the influence of implants on pelvis stability. However, the extensive search of the literature failed to find a finite element model which includes the pelvis and lumbar spine together. Current study is the first step to accomplish this goal. An experimentally validated model of ligamentous lumbar spine was combined with the FE model of pelvis [7], and simulation of the sacrum fractures was conducted.

Computationally Efficient, Explicit Finite Element Model for Evaluation of Patellofemoral Mechanics

2007 ◽  
Author(s):  
Mark A. Baldwin ◽  
Paul J. Rullkoetter
Keyword(s):  
Finite Element ◽  
Contact Mechanics ◽  
Probabilistic Approach ◽  
Element Model ◽  
Relevant Information ◽  
Composite Fiber ◽  
Computational Time ◽  
Patient Specific ◽  
Fe Model ◽  
Explicit Finite Element

Patient-specific finite element (FE) models can provide clinically relevant information about contact mechanics and kinematics that may be difficult or infeasible to obtain otherwise, and have potential to guide pre-operative planning. However, substantial uncertainty in model variables exists in patient-specific modeling, and suggests a probabilistic approach. Although efficient probabilistic methodology has been recently developed, multiple analyses are still required, and computational time for a fully deformable FE model throughout a flexion cycle has typically made this impractical. Therefore, the goal of the present study was to develop an explicit FE model of the patellofemoral joint with deformable cartilage and deformable, wrapping extensor tendons, and to compare kinematic and contact mechanics results with a model modified for computational efficiency. The efficient model incorporated rigid femoral and patellar cartilage representation with an optimized contact pressure–surface overclosure relationship, and composite-fiber tendons.

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