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Results for “Finite Element Analysis”

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PubMed2001

Finite element analysis of the mechanical behavior of a scapula implanted with a glenoid prosthesis.

OBJECTIVE: The objective of the present study was to analyze the mechanical effect of some of the surgical variables encountered during shoulder arthroplasty using the finite element method. The effect of one eccentric load case, cement thickness and conformity has been investigated. DESIGN: A 3D finite element model of a healthy cadaveric scapula implanted with an anatomically shaped glenoid has been developed from computed tomography (CT) images. BACKGROUND: Glenoid component fixation can present the most difficult problem in total shoulder arthroplasty, loosening of this component remains one of the main complications. METHODS: The 3D finite element model was first validated by comparison with experimental measurements and by fitting of the mechanical properties of the cortical bone. Then the articular pressure location, the surface contact geometry and the cement thickness have been analyzed to observe their effect on stresses and displacements at the interfaces and within the scapular bone. RESULTS: The antero-posterior bending of the scapula was a notable feature and this was accentuated when an eccentric load was applied. The gleno-humeral contact area had a major role on the stress level in the supporting structures though but not on the global displacements. Varying the cement mantle modified stresses according to the load case and it essentially changed the latero-medial displacement of the cement relatively to the bone. CONCLUSIONS: This analysis provided an insight into the mechanical effects of an implanted scapula according to different parameters related to implantation technique. RELEVANCE: Results emphasized the role of some of the parameters a clinician may face. They demonstrated the importance of the humeral head centering in the horizontal plane. Conformity decreasing may involve drastic increase of stresses within structures and a thick cement mantle is not necessarily advantageous relatively to the stresses at the cement/bone interface.

Arthroplasty↗

PubMed2006

[Finite element analysis (FEA) for the structure capacity of proximal femur during falling--(I) FEA model and the failure criteria for the bone].

Femur fracture from falls is considered one of the most serious types of the elderly. FEA has proved to be an extremely useful tool in the structure analysis of the proximal femur. In this paper, a FEA model of proximal femur is introduced, and Hoffman failure criteria are built based on the experimental strength data for both cortical bone and trabecular bone of the femur from some references. The FEA model and the failure criteria are verified using other researcher's experimental results. The predicted trabecular failure load was only 0.5% lower than the experimental data and cortical failure load was 4.2% higher than the experimental result. This result shows that our FEA model, combined with the Hoffman criterion for both cortical bone and trabecular bone, can effectively predict the structural capacity of the femur during falling.

Biomechanical Phenomena↗

PubMed2005

A three-dimensional finite element analysis of the combined behavior of ligaments and menisci in the healthy human knee joint.

We present here a three-dimensional FE model of the healthy human knee that included the main structures of the joint: bones, all the relevant ligaments and patellar tendon, menisci and articular cartilages. Bones were considered to be rigid, articular cartilage and menisci linearly elastic, isotropic and homogeneous and ligaments hyperelastic and transversely isotropic. Initial strains on the ligaments and patellar tendon were also considered. This model was validated using experimental and numerical results obtained by other authors. Our main goal was to analyze the combined role of menisci and ligaments in load transmission and stability of the human knee. The results obtained reproduce the complex, nonuniform stress and strain fields that occur in the biological soft tissues involved and the kinematics of the human knee joint under a physiological external load.

Finite Element Analysis↗

PubMed1998

[Finite element analysis of human tibia in vitro].

This investigation was aimed at the fatigue fracture of tibia that often occurs in soldiers, as well as in dancers and athletes. The data of ground reaction force(GRF) of soldiers were measured using a force platform in three common gaits: marching, parading and running. The stress distribution in tibia under these GRFs were analyzed with a FE model. The results showed that the smallest GRF(744.8N) is in quick marching, the next (1156.4N) in parading and the largest (1391.6N) in running. The stress distribution under GRF was mot uniform in the tibia. The maximum stresses occurred at a site 1/3 tibia length below the knee where tibia fracture is often seen clinically. The maximum stresses were 110 MPa and 115 MPa in parading and running respectively. This means that the tibial tractures in soldiers are mostly associated with stress, i.e. the greater the stress is, the higher the incidence of stress fracture comes about.

Adult↗

PubMedDate not supplied

Mandibular implant-retained overdenture: finite element analysis of two anchorage systems.

Transmission of masticatory load in mandibular implant-retained overdentures was evaluated using a three-dimensional finite element model. The reaction forces on the distal edentulous mucosa and the stress on the perimplant bone were compared in overdentures retained either by two ball attachments or by two clips on a bar connecting two implants. In the finite element model, a 35 N load on the first mandibular molar induced a greater reaction force on the distal edentulous ridge mucosa of the nonworking side when the overdenture was anchored by ball attachments than with the clips/bar attachment. Stress on peri-implant bone was greater with the clips/bar attachment than with the ball attachment.

Alveolar Process↗

PubMed2001

[The influences of the stress distribution on the condylar cartilage surface by Herbst appliance under various bite reconstruction--a three dimensional finite element analysis].

OBJECTIVE: The distribution of stress on the surface of condylar cartilage was investigated. METHODS: Three-dimensional model of the 'Temporomandibular joint mandible Herbst appliance system' was set up by SUPER SAP software (version 9.3). On this model, various bite reconstruction was simulated according to specified advanced displacement and vertical bite opening. The distribution of maximum and minimum principal stress on the surface of condylar cartilage were computerized and analyzed. RESULTS: When Herbst appliance drove the mandible forward, the anterior condyle surface was compressed while the posterior surface was drawn. The trend of stress on the same point on the condyle surface was consistent in various reconstruction conditions, but the trend of stress on various point were different in same reconstruction conditions. CONCLUSION: All five groups of bite reconstruction (3-7 mm advancement, 4-2 mm vertical bite opening of the mandible) designed by this study can be selected in clinic according to the patient's capability of adaptation, the extent of malocclusion and the potential and direction of growth.

Cartilage, Articular↗

PubMed2002

Finite element analysis of slow drug release through deformed coating film: effects of morphology and average thickness of coating film.

This paper, a continuation of our previous work, is a presentation of the effect of the morphology and the average thickness of the deformed coating films on the slow diffusional release characteristics analyzed numerically under the constraints of the constant volume of the drug matrices and the coating films, if the films have the same average thickness. Increasing the average thickness of the coating films slows down the fractional release and the average release rate of the drug and smoothen the initial burst of the drug, as well as increase the initial lag time. The effect due to deformation of the coating films on these diffusional release characteristics are found to be less significant with the increasing average thickness of the coating films. Interestingly initial lag times are found to be the same for the coated particles having the same smallest thickness but different average thickness of coating films. The effect due to the change in the average thickness of the coating films on the characteristics of the slow controlled-release is discussed to shed light on the design of a better controlled-release device.

Algorithms↗

PubMed2005

Influence of tooth preparation design on the stress distribution in maxillary central incisors restored by means of alumina porcelain veneers: a 3D-finite element analysis.

AIM: The present study aimed at providing 3D-FEA engineering tools for the understanding of the influence of tooth preparation design on the stress distribution and localization of critical sites in maxillary central incisors restored by means of alumina porcelain veneers under functional loading. METHODS: A 3D-FEM model of a maxillary central incisor is presented. An arbitrary chewing static force of 10 N was applied with an angulation of 60 and 125 degrees to the tooth longitudinal axis at the palatal surface of the crown. The model was considered to be restored by means of alumina porcelain veneers with different tooth preparation designs. The differences in occlusal load transfer ability of the two restorative systems are discussed. RESULTS: The maximum Von Mises equivalent stress values were observed in the window restorative system for both 125 and 60 degrees load angulations. When the chamfer with palatal overlap preparation was simulated, the stress distributed uniformly in the cement layer, whereas in the window preparation the stress mainly occurred in the incisal area of the cement layer. SIGNIFICANCE: When restoring a tooth by means of porcelain veneers, the chamfer with palatal overlap preparation better restores the natural stress distribution under load than the window technique.

Aluminum Oxide↗

PubMed2001

[The influences upon the passive tensile of the masticatory muscles and ligaments by Herbst appliance under various bite reconstruction--a three dimensional finite element analysis].

OBJECTIVE: This study aimed to provide some biomechanical references for the clinical use and improvement of Herbst appliance. METHODS: The three-dimensional model of the 'Temporomandibular joint mandible Herbst appliance system' was set up by SUPER SAP software (version 9.3). On this model, the passive tensile in the masticatory muscles and ligaments were analyzed under various bit reconstruction designed according to specified advanced displacement and vertical bite opening. RESULTS: When Herbst appliance drove the mandible forward, there was not any tensile in the medial, lateral pterygoid and the collateral ligament, while the temporalis, the deep paret of masseter, the stylomandibular ligament, and the sphenomandibular ligament were passively drawn. Under various bite reconstruction, the passive tensile in the medial temporalis, the posterior temporalis, the stylomandibular ligament and the sphenomandibular ligament increased with the amount of the advancement of the mandible; The passive tensile in the posterior temporalis and the deep part of masseter increased with the amount of vertical bite opening of the mandible. CONCLUSION: The StL, SpL, PT and AT played an important role in functional reconstruction of mandible by Herbst. All five group of bite reconstruction (3-7 mm advancement, 4-2 mm vertical bite opening of the mandible) designed by this study can be selected in clinic according to the patient's capability of adaptation, the extent of malocclusion and the potential and direction of growth.

Finite Element Analysis↗

PubMed2004

Finite element analysis of moment-rotation relationships for human cervical spine.

A comprehensive, geometrically accurate, nonlinear C0-C7 FE model of head and cervical spine based on the actual geometry of a human cadaver specimen was developed. The motions of each cervical vertebral level under pure moment loading of 1.0 Nm applied incrementally on the skull to simulate the movements of the head and cervical spine under flexion, tension, axial rotation and lateral bending with the inferior surface of the C7 vertebral body fully constrained were analysed. The predicted range of motion (ROM) for each motion segment were computed and compared with published experimental data. The model predicted the nonlinear moment-rotation relationship of human cervical spine. Under the same loading magnitude, the model predicted the largest rotation in extension, followed by flexion and axial rotation, and least ROM in lateral bending. The upper cervical spines are more flexible than the lower cervical levels. The motions of the two uppermost motion segments account for half (or even higher) of the whole cervical spine motion under rotational loadings. The differences in the ROMs among the lower cervical spines (C3-C7) were relatively small. The FE predicted segmental motions effectively reflect the behavior of human cervical spine and were in agreement with the experimental data. The C0-C7 FE model offers potentials for biomedical and injury studies.

Biomechanical Phenomena↗

PubMed2001

Finite element analysis of a tandem screw configuration in sagittal split osteotomy using biodegradable osteosynthesis screws.

The goal of the present study was to determine the mechanical stability of selected osteosynthesis screws in a paired linear configuration in cases of bilateral sagittal split osteotomy of the mandible. A mandible model was created that consisted of 22,846 elements and 4,879 nodes. The following screws were tested in the tandem screw configuration: the poly-L-lactic acid (PLLA) in accordance with Harada and Enomoto, the Isosorb screw (Aesculap, Germany), the BioSorbFX screw (Bionix Implants, Finland), and the Lactosorb screw (WL. Lorenz, USA). The mechanical parameters of the materials studied were adopted from the literature or were based on manufacturer information. With the precondition that the materials each be stressed to the ultimate tensile strength, the following chewing forces could be neutralized: 100 N by 2.0-mm titanium mini-screws, 117.5 N by PLLA screws in accordance with Harada and Enomoto, 90.0 N by Isosorb screws, 89.0 N by BioSorbFX screws, and 35.0 N by Lactosorb screws. Here the peri-implant bone was stressed within limiting values with the titanium miniscrew, and the PLLA screw according to Harada and Enomoto, but not the osteosynthesis material itself. The finite element method (FEM) appears suitable for simulating complex mechanical stress situations in the maxillofacial area. As a result, significant time and materials (animal tests) can be saved when developing new or modified materials

Absorbable Implants↗

PubMed2006

Biomechanical evaluation of intra-articular and extra-articular procedures in anterior cruciate ligament reconstruction: a finite element analysis.

BACKGROUND: Intra-articular techniques (single and double bundles) are the most widely used procedures for the anterior cruciate ligament reconstruction. Lemaire introduced in 1967 the extra-articular techniques, and combined intra-articular and extra-articular reconstruction, to better restore the stability of the knee. However, the effectiveness of these procedures (intra-articular, extra-articular combined or not with intra-articular) seems to be controversial. METHODS: In the present study, we developed numerical models of a knee joint to evaluate the effects of these different procedures on the kinematics and biomechanics of the knee during an internal rotation test. Six cases were simulated: intact anterior cruciate ligament, intra-articular reconstructed anterior cruciate ligament (single and double bundles), extra-articular reconstructed anterior cruciate ligament alone, and combination of extra- and intra-articular reconstructions. The loading condition was an internal tibial torque of 2 N m at 0 degrees, 15 degrees, 30 degrees and 45 degrees of knee flexion. Internal rotation of the tibia and forces within the grafts and the ligaments were calculated. FINDINGS: This study showed that both single and double bundles intra-articular reconstructions restore similar internal rotation control and biomechanics of the soft structures as the intact anterior cruciate ligament situation. On the other hand, our results indicate that extra-articular reconstruction reduces appreciably the internal rotation and modifies the charges distribution in the soft structures when compared to the intact anterior cruciate ligament. INTERPRETATION: The extra-articular procedure alters the kinematics of the knee, which might overconstraint the ligaments and the femorotibial joints, leading to the failure of the anterior cruciate ligament reconstruction.

Anterior Cruciate Ligament↗

PubMed1999

Finite Element Analysis of Simulations of Cancellous Bone Resorption.

A stochastic simulation of the resorption of cancellous bone has been developed and integrated with a finite element model to predict the resultant change in structural properties of bone as bone density decreases. The resorption represents the net imbalance of osteoclast and osteoblast activity that occurs in osteoporosis. A simple lattice structure of trabecular bone is considered, with an examination of the lattice geometry and discretization indicating that just five trabeculae need to be modelled. The results from the analysis show how the mechanical properties of the cancellous bone degrade with osteoporosis and demonstrate how the method can be used to predict the relationships between stiffness and density or porosity.

Journal Article↗

PubMed2006

A finite element analysis of ferrule design on restoration resistance and distribution of stress within a root.

AIM: To analyse the effect of ferrule height upon the mechanical resistance and stress distribution within a root to explain variations in the pattern of root fracture. METHODOLOGY: An extracted, intact, caries free, maxillary right central incisor was scanned by laser and then reconstructed on a computer to produce a model of the tooth and associated periodontal ligament. A simulated post/core/crown restoration was constructed on conventional tooth preparations with various ferrules. The crown was loaded with a simulated 500 N force and the simulated displacement of components and the tensile and compressive stress within the tooth structure were recorded. RESULTS: Without a ferrule preparation, the simulated crown tilted to the labial and rotated distally. With increasing ferrule height the displacement and rotation of the crown reduced in conventional and crown-lengthening models with maximum reduction occurring when the ferrule height reached 1.5 mm. In ferrule models, higher levels of tensile stress developed in internal (by a factor of 8) and mid-root palatal (by a factor of 90) dentine at the cervical margin of the preparation. With an increase in ferrule height, the area of tensile stress within the palatal mid-dentine expanded towards the cervical margin. Similar patterns and stress values were recorded for the crown-lengthening models. CONCLUSION: The study confirms that a ferrule increases the mechanical resistance of a post/core/crown restoration. However a ferrule creates a larger area of palatal dentine under tensile stress that may be a favourable condition for a crack to develop. Crown-lengthening did not alter the levels or pattern of stress within compared with conventional ferrule preparations.

Computer Simulation↗

PubMed2002

Finite element analysis of underwater capacitor micromachined ultrasonic transducers.

A simple electro-mechanical equivalent circuit model is used to predict the behavior of capacitive micromachined ultrasonic transducers (cMUT). Most often, cMUTs are made in silicon and glass plates that are in the 0.5 mm to 1 mm range in thickness. The equivalent circuit model of the cMUT lacks important features such as coupling to the substrate and the ability to predict cross-talk between elements of an array of transducers. To overcome these deficiencies, a flnite element model of the cMUT is constructed using the commercial code ANSYS. Calculation results of the complex load impedance seen by single capacitor cells are presented, then followed by a calculation of the plane wave real load impedance seen by a parallel combination of many cells that are used to make a transducer. Cross-talk between 1-D array elements is found to be due to two main sources: coupling through a Stoneley wave propagating at the transducer-water interface and coupling through Lamb waves propagating in the substrate. To reduce the cross-talk level, the effect of structural variations of the substrate are investigated, which includes a change of its thickness and etched trenches or polymer walls between array elements.

Artifacts↗

PubMed2006

Finite element analysis of the strain distribution in the humeral head tubercles during abduction: comparison of young and osteoporotic bone.

AIM: The aim of this work was to design an accurate 3D digital model of the humerus and rotator cuff muscles. This model was then used to study strain distribution in humeral tubercles according to bone density. MATERIALS AND METHODS: The geometry of bone and muscle structures was reproduced using SURFDRIVER software, based on anatomical sections, CT scans and MRI images from the Visible Human Project image library. The contours were transferred to PATRAN software to rebuild volumes and mesh them. Calculations of strains and their distribution were performed using NASTRAN software. All the elements were considered to be isotropes. RESULTS: The study of the distribution of stress magnitude according to the type of bone modeled, shows that some stresses in cortical bone are greater than those in cancellous bone and are also greater in old bone, implying more deformation in old bone at constant force. This study also shows that stresses do not penetrate deeply into cancellous tissue. CONCLUSION: Observing the simulation results led understanding of the pathology of certain fractures of the proximal end of the humerus. This study also helped explain why certain types of osteosynthesis fail due to tubercles reconstruction failures.

Bone Density↗

PubMed1999

Poroelastic finite element analysis of a bone specimen under cyclic loading.

It had been suggested that the fluid embodied in bone lacunar-canalicular porosity may play an important role in bone remodelling [Weinbaum et al., 1994. Journal of Biomechanics 27, 339-360]. In this paper a finite element model of a poroelastic prismatic solid of rectangular cross-section is considered to simulate bone behaviour, precisely as in the previous work by Zhang and Cowin [Zhang and Cowin, 1994. Journal of Mechanical Physics of Solids 42, 1575-1599]. This solid is subject to combined cyclic axial and bending loads at its end. The objectives of the study are: (1) to verify the accuracy of the simplifying hypotheses underlying the analytical solutions established by the above authors; (2) to provide further insight into the behaviour of that solid; (3) to test the advantages in generality and versatility and the computing costs of general-purpose finite element codes in poroelastic analysis. The study is parametric with respect to the fluid leakage coefficient, to the ratio of the bending moment and axial load, and to the ratio of the characteristic relaxation time of the pore pressure over the excitation period. Results show that, for all the cases considered, the pore pressure distribution along the section height of the poroelastic beam exhibits a very good matching with previous analytical results. Stresses transversal with respect to the beam axis (assumed as constant or zero in previous analytical solutions) are evaluated. The analysis pointed out that: (1) the effects due to end-loads with zero resultants practically extinguish within a distance from the beam end almost equal to a typical length of the cross-section; (2) cross-sections remain plane above that distance; (3) the transversal total stresses are three orders of magnitude lower than axial stress.

Adaptation, Physiological↗

PubMed2003

Finite element analysis of the cervico-trochanteric stemless femoral prosthesis.

OBJECTIVE: To investigate the biomechanical performance of a newly designed cervico-trochanteric stemless prosthesis by comparing the stress distribution with that of the traditional stem-type porous-coated anatomic prosthesis. DESIGN: Three-dimensional finite element models were created for the intact femur, cervico-trochanteric implanted femur and porous-coated anatomic implanted femur. The stress distributions on the femur and the implant were compared. The effects of using two or three screws fixation for the cervico-trochanteric implanted femur were also investigated. BACKGROUND: Local bone loss after implantation of traditional stem-type prostheses remains an unsolved problem during the long-term application of total hip replacement. The stress shielding effect and osteolysis were thought to be the two main factors that result in local bone loss after prosthesis implantation. In order to eliminate the mechanical and the biological causes of bone loss after total hip arthroplasty, a newly designed stemless femoral prosthesis was investigated. METHODS: Three-dimensional finite element models were created for the intact, cervico-trochanteric (with two or three fixation screws), and porous-coated anatomic implanted femora with the geometry of a standardized composite femur. Analysis was performed for a loading condition simulating the single-legged stance. The von Mises stress distributions of each model were analyzed and compared. RESULTS: The results can be summarized as follows: (1) Von Mises stress in the proximal, medial femur for the cervico-trochanteric implanted model was higher than that of the intact model and the porous-coated anatomic implanted model; (2) stress-shielding effect of the cervico-trochanteric models (with two or three fixation screws) were eliminated as compared with the porous-coated anatomic model; (3) no obvious difference in von Mises stress distribution for the cervico-trochanteric implanted model with two or three fixation screws. CONCLUSIONS: The cervico-trochanteric femoral prosthesis may reduce the stress-shielding effect of the proximal femur and achieve a more physiological stress distribution on the proximal femur than that of the porous-coated anatomic prosthesis. RELEVANCE: The new concept of cervico-trochanteric stemless prosthesis has proven to possess several advantages based on the current results, and may be an alternative for traditional stem-type prostheses in future clinical applications.

Biomechanical Phenomena↗