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PubMed1984

A contact-coupled finite element analysis of the natural adult hip.

A non-linear two-dimensional finite element model was used to study phenomena of stress redistribution in the natural adult hip resulting from parametric material property variations in the juxtarticular regions of the femoral head. Despite the geometrical simplifications employed, the intra-articular contact stresses (computed using the FEAP program) were found to be in reasonable qualitative agreement with previous in vitro data for the case of a normal hip. Generalized sclerotic changes in the subchondral plate, as reflected either in apparent modulus increases or in plate thickening, were found to have only minor effects on the computed contact stress distribution, although stress levels within the plate itself were markedly influenced. Localized subchondral plate sclerosis, by contrast, led to marked stress elevations in the cartilage immediately overlying the stiffened bone. Cartilage modulus increases caused increased load uptake for a given imposed deformation, but involved stress distribution increases which were very nearly linearly proportional to the increases in resultant load magnitude. Friction coefficient elevations had no noticeable effects on normal contact stress or upon overall load transmission, but involved complex, possibly slip-related, changes in intra-articular and cartilaginous shear stresses.

Cartilage, Articular↗
PubMed1988

Three-dimensional model of the human craniofacial skeleton: method and preliminary results using finite element analysis.

The purpose of this study was to develop a three-dimensional finite element model of the craniofacial skeleton using a dry human skull. The model consisted of 2918 nodes and 1776 solid elements, and was used to investigate the biomechanical effect of a distally directed orthopaedic force on the craniofacial complex. The force was applied at the level of the maxillary first molar. The results indicated that in response to the force system applied: the nasomaxillary complex displaces in a backward and downward direction and rotates in clockwise sense; the nasomaxillary complex, including the zygomatic bone, experiences high stress levels in comparison with those at the remaining bones; the stress distribution in the maxillary basal bone area is relatively uniform; and the stress distribution across the opposing surface of the bony margins of the sutures is non-uniform.

Biomechanical Phenomena↗
PubMed1990

Finite element analysis of cardiac defibrillation current distributions.

We have developed a two-dimensional finite element model of the canine heart and thorax to examine different aspects of the distribution of current through cardiac tissue during defibrillation. This model allows us to compare various electrode configurations for the implantable cardioverter/defibrillator. Since we do not yet know the electrical criteria to apply for predicting defibrillation thresholds, such as the minimum current density required for defibrillation or the critical mass if indeed such quantities are applicable, we measured defibrillation energy in dogs to determine the voltages to apply to the model for calculating current distributions. By analyzing isopotential contours, current lines, power distributions, current density histograms, and cumulative current distributions, we estimated the critical fraction and threshold current density for defibrillation, compared various electrode configurations, and assessed the sensitivity of the defibrillation threshold to electrode position, patch size, and tissue conductivity. We found that blood can shunt defibrillation current away from the myocardium, particularly in configurations using a two-electrode catheter, that myocardial tissue conductivity strongly affects the current distributions, and that epicardial patch size is more important that subcutaneous patch size. Our results are consistent with successful defibrillation requiring that 80 +/- 5% of the heart must be rendered inexcitable by a current density of 35 +/- 5 mA/cm2 or greater. This two-dimensional, isotropic model has allowed us to analyze some of the determinants of defibrillation, but more detailed interpretation of experimental data may require the extension of the model to three dimensions.

Animals↗
PubMed1984

Three-dimensional finite element analysis of a simplified compression plate fixation system.

A three-dimensional, linear finite element model was generated for an intact plexiglass tube with an attached six-hole stainless steel compression plate. We examined external forces representing axial, off-center axial, and four-point bending, along with superimposed plate and screw pretension. Strain gage experiments were conducted to test model validity and the finite element results were contrasted to a composite beam theory solution. Excellent correspondence was observed between finite element and strain gage data for the most significant strain components. Composite beam theory tended to overestimate the neutral axis shift which results from plate application. The model also demonstrated fracture site distraction due to plate pretension, and the tendency for outer screw failure for the combination of bending-closed with a preload in the plate and screws.

Biomechanical Phenomena↗
PubMed1990

[Finite element analysis on physiological mobility of individual teeth].

The initial movement of the tooth was investigated by the finite element method. The mechanical properties of the periodontal membrane were estimated from the results of the simulation. The analysis was made by using an 8 point isoparametric finite element method. The upper central incisor with an axial directional load was simulated. The concept of the apparent elastic modulus was introduced to the stress-strain relation of the soft tissue, that is, soft tissue such as the periodontal membrane and the gingiva was considered to have stress dependent elastic moduli. At the first stage of the simulation, the stress and strain distributions in the paradentium were calculated by the conventional method. From the next stage, the apparent elastic moduli for the soft tissue were introduced to the calculation, that is, the elastic moduli for the soft tissue were computed from the calculated equivalent stresses of the previous stage. The calculations were repeated until the displacement values converged. The initial displacement of the tooth was not proportional to the applied load but showed a non-linear relationship. The relationship between load and displacement was approxiated by the n-th power equation. These results were in agreement with the clinical experimental results. The periodontal membrane is built up of different elastic moduli. The elastic moduli were low at the alveolar edge and the root apex. The equivalent stresses of the periodontal membrane were marked low in the alveolar edge and the root apex. In conclusion, the concept of the apparent elastic modulus is useful to investigate the initial movement of the tooth and estimate the mechanical properties of the periodontal membrane.

Computer Simulation↗
PubMed2006

Finite element analysis of impact and shaking inflicted to a child.

This study compares a vigorous shaking and an inflicted impact, defined as the terminal portion of a vigorous shaking, using a finite element model of a 6-month-old child head. Whereas the calculated values in terms of shearing stress and brain pressure remain different and corroborate the previous studies based on angular and linear velocity and acceleration, the calculated relative brain and skull motions that can be considered at the origin of a subdural haematoma show similar results for the two simulated events. Finite element methods appear as an emerging tool in the study of the biomechanics of head injuries in children.

Biomechanical Phenomena↗
PubMed2002

Finite element analysis of a glass fibre reinforced composite endodontic post.

In this work the mechanical response to external applied loads of a new glass fibre reinforced endodontic post is simulated by finite element (FE) analysis of a bidimensional model. The new post has a cylindrical shape with a smooth conical end in order to adequately fit the root cavity, and to avoid edges that could act as undesired stress concentrators. Mechanical data obtained by three-point bending tests on some prototypes fabricated in the laboratory are presented and used in the FE model. Under various loading conditions, the resulting stress component fields are hence compared with those obtained in the case of two commercial endodontic posts (i.e. a cast metal post and a carbon fibre post) and with the response of a natural tooth. The gold cast post-and-core produces the greatest stress concentration at the post-dentin interface. On the other hand, fibre-reinforced composite posts do present quite high stresses in the cervical region due to their flexibility and also to the presence of a less stiff core material. The glass fibre composite shows the lowest peak stresses inside the root because its stiffness is much similar to dentin. Except for the force concentration at the cervical margin, the glass fibre composite post induces a stress field quite similar to that of the natural tooth.

Acrylic Resins↗
PubMed2004

[Finite element analysis of changes in femoral stresses after elite total hip arthroplasty].

OBJECTIVE: To determine the variation in femoral stress after insertion of Elite cemented femoral prosthesis. METHODS: Three-dimentional finite element models of the normal human femur and Elite femoral prosthesis were developed through CT scan. With the application of hip joint loading, quantitatively measure stress changes of an intact femur with corresponding femur inserted with Elite implants were measured. RESULTS: Compared with intact femur, insertion of Elite implants into the femoral canal decreased the proximal femoral stresses level, especially in calcar femoral, femur wall and tuberositas. However, the stress in the prosthesis distal end. CONCLUSION: Insertion of Elite implants induced significant stress shielding in the proximal femur, especially at calcar femoral, femur wall and tuberositas. However, stress concentrates in the prosthesis distal end.

Arthroplasty, Replacement, Hip↗
PubMed2006

Three-dimensional finite element analysis of the pediatric lumbar spine. Part I: pathomechanism of apophyseal bony ring fracture.

The purpose of this study was to (1) develop a three-dimensional, nonlinear pediatric lumbar spine finite element model (FEM), and (2) identify the mechanical reasons for the posterior apophyseal bony ring fracture in the pediatric patients. The pediatric spine FE model was created from an experimentally validated three-dimensional adult lumbar spine FEM. The size of the FEM was reduced to 96% taking into account of the ratio of the sitting height of an average 14-years-old children to that of an adult. The pediatric spine was created with anatomically specific features like the growth plate and the apophyseal bony ring. For the stress analyses, a 10-N m moment was applied in all the six directions of motion for the lumbar spine. A preload of 351 N was applied which corresponds to the mean body weight of the 14-years-old group. The stresses at the apophyseal bony ring, growth plate and endplate were calculated. The results indicate that the structures surrounding the growth plate including apophyseal bony ring and osseous endplate were highly stressed, as compared to other structures. Furthermore, posterior structures in extension were in compression whereas in flexion they were in tension, with magnitude of stresses higher in extension than in flexion. Over time, the higher compression stresses along with tension stresses in flexion may contribute to the apophyseal ring fracture (fatigue phenomena).

Adult↗
PubMed2003

Finite element analysis of knee injury risks in car-to-pedestrian impacts.

In vehicle-pedestrian collisions, lower extremities of pedestrians are frequently injured by vehicle front structures. In this study, a finite element (FE) model of THUMS (total human model for safety) was modified in order to assess injuries to a pedestrian lower extremity. Dynamic impact responses of the knee joint of the FE model were validated on the basis of data from the literature. Since in real-world accidents, the vehicle bumper can impact the lower extremities in various situations, the relations between lower extremity injury risk and impact conditions, such as between impact location, angle, and impactor stiffness, were analyzed. The FE simulation demonstrated that the motion of the lower extremity may be classified into a contact effect of the impactor and an inertia effect from a thigh or leg. In the contact phase, the stress of the bone is high in the area contacted by the impactor, which can cause fracture. Thus, in this phase the impactor stiffness affects the fracture risk of bone. In the inertia phase, the behavior of the lower extremity depends on the impact locations and angles, and the knee ligament forces become high according to the lower extremity behavior. The force of the collateral ligament is high compared with other knee ligaments, due to knee valgus motions in vehicle-pedestrian collisions.

Accidents, Traffic↗
PubMed2007

Stent expansion in curved vessel and their interactions: a finite element analysis.

Coronary restenosis after angioplasty has been reduced by stenting procedure, but in-stent restenosis (ISR) has not been eliminated yet, especially in tortuous vessels. In this paper, we proposed a finite element method (FEM) to study the expansion of a stent in a curved vessel (the CV model) and their interactions. A model of the same stent in a straight vessel (the SV model) was also studied and mechanical parameters of both models were researched and compared, including final lumen area, tissue prolapse between stent struts and stress distribution. Results show that in the CV model, the vessel was straightened by stenting and a hinge effect can be observed at extremes of the stent. The maximum tissue prolapse of the CV model was more severe (0.079 mm) than the SV model (0.048 mm); and the minimum lumen area of the CV was decreased (6.10 mm(2)), compared to that of the SV model (6.28 mm(2)). Tissue stresses of the highest level were concentrated in the inner curvature of the CV model. The simulations offered some explanations for the clinical results of ISR in curved vessels and gave design suggestions of the stent and balloon for tortuous vessels. This FEM provides a tool to study mechanisms of stents in curved vessels and can improve new stent designs especially for tortuous vessels.

Biomechanical Phenomena↗
PubMed2003

A nonlinear finite element analysis of the periodontal ligament under orthodontic tooth loading.

The stressed state of the periodontal ligament (PDL) is understood to play a critical role in the tooth movement initiated by orthodontic treatment. Finite element simulations have been used to describe PDL stresses for orthodontic loading; however, these models have predominantly assumed linear mechanical properties for the PDL. The present study sought to determine the importance of using nonlinear mechanical properties and nonuniform geometric data in computer predictions of periodontal ligament stresses and tooth movements. A 2-dimensional plane-strain finite element model of a mandibular premolar was constructed based on anatomic data of transverse sections of tooth, PDL, and bone from a 24-year-old cadaveric man. A second model was constructed of the same tooth but with a PDL of uniform thickness. Each of these was prescribed linear or nonlinear elastic mechanical properties, as obtained in our own experiments. Predictions of the maximum and minimum principal stresses and von Mises stresses in the PDL were determined for extrusive and tipping forces. The results indicated that biofidelic finite element models predicted substantially different stresses in the PDL for extrusive loading than did the uniform thickness model, suggesting that incorporation of the hourglass shape of the PDL is warranted. In addition, incorporation of nonlinear mechanical properties for the PDL resulted in dramatic increases in the stresses at the apex and cervical margin as compared with the linear models.

Adult↗
PubMed1995

In vivo assessment of nonlinear myocardial deformation using finite element analysis and three-dimensional echocardiographic reconstruction.

In vitro data have shown that the myocardium exhibits nonlinear passive stress-strain relationship and a non-linear pressure-volume relationship. A finite element (FE) analysis and optimization algorithm was used on three-dimensional reconstructed left ventricular (LV) geometry using echocardiographic images, along with hemodynamic measurements, in seven closed-chest dogs to show a nonlinear stress-strain relationship in vivo. Our analysis included the computation of Poisson's ratio from the measured volumetric strain of the myocardium and a simulated pericardial pressure load ("equivalent pericardial pressure") applied to the epicardial surface of the reconstructed LV. LV geometry was reconstructed in three or four incremental time steps in diastasis and the myocardium was assumed to be homogeneous, isotropic, and linearly elastic during these short intervals in this initial study. Simultaneous LV chamber pressure and equivalent pericardial pressure were incorporated into the algorithm to predict actual LV expansion. Computations were performed iteratively at each interval to compute the optimized elastic modulus. By performing the FE analysis and optimization at each interval (a step-wise linear analysis approach), a linear relationship between the myocardial elastic modulus and LV chamber pressure was derived (r = .87 to .98). Such a linear relationship is equivalent to an exponential myocardial stress-strain relationship in vivo. Detailed measurement of nonhomogeneous regional deformation are becoming possible with the advent of sophisticated imaging techniques. The methodology described in this study, with appropriate modifications in the FE analysis and optimization algorithms, can be applied to assess the complex three-dimensional pressure-deformation characteristics in vivo.

Algorithms↗
PubMed1996

Automated finite element analysis of excised human femora based on precision -QCT.

The creation of 3-D finite element (FE) models of bone and implant-bone systems is a labor-intensive task due to the need to model different cases and variations, to perform patch tests and to account for the nonhomogeneous material properties with an acceptable amount of work. In this study, we developed an interface between a precision QCT and a FE system and applied it to a specimen bone. With the new method, the time necessary for model generation was reduced substantially. Furthermore, the elastic properties for each element were automatically derived from the corresponding CT-values. In order to demonstrate the importance of taking into account inhomogeneity, a comparison between the nonhomogeneous model and a homogeneous, "averaged" model was performed.

Biomechanical Phenomena↗
PubMed2002

Finite element analysis of the stresses around endosseous implants in various reconstructed mandibular models.

PURPOSE: To calculate the location and intensity of the maximum stresses occurring around implants in the reconstructed mandible. MATERIAL AND METHODS: Human preserved mandibles and fibulae were used to design 3-D mandibular models on a Desktop Computer. Various 3-D simulation models representing mandibles were made. Implants (fixtures) and superstructures were then embedded in each model and occlusal pressure was applied to the cantilever portion of the superstructure. Von Mises stress, the maximum and minimum principal stress on each model were calculated using finite element structural analysis software. Finally, evaluation of the stresses around each fixture hole was performed. RESULTS: It appeared that for each fixture hole, the direction and the magnitude of the stresses were influenced by complex factors such as the thickness of the cortical bone where the fixtures were embedded, the degree of vertical displacement under load, and the relationship between adjacent fixtures. CONCLUSION: Location and intensity of the stresses occurring around fixtures differs significantly between various types of mandibular reconstruction. Published by Elsevier Science Ltd.

Bite Force↗
PubMed2005

Effects of the posterior cruciate ligament reconstruction on the biomechanics of the knee joint: a finite element analysis.

BACKGROUND: Previous experimental studies have been conducted to evaluate the biomechanical effects of posterior cruciate ligament reconstruction; but no consensus has been reached on the preferred method of reconstruction. METHODS: The 3D finite element mesh of a knee joint was reconstructed from computed tomography and magnetic resonance images. The ligaments were considered as hyperelastic materials. The tibiofemoral and patellofemoral joints were modeled with large sliding contact elements. The 3D model was used to simulate knee flexion from 0 degrees to 90 degrees in four cases: a knee with a "native" posterior cruciate ligament, a resected posterior cruciate ligament, a reconstructed single graft posterior cruciate ligament, and a reconstructed double graft posterior cruciate ligament. FINDINGS: A resected posterior cruciate ligament induced high compressive forces in the medial tibiofemoral and patellofemoral compartments. The pressures generated in the tibiofemoral and patellofemoral compartments were nearly the same for the two reconstruction techniques (single graft and double graft). The single graft resulted in lower tensile stresses inside the graft than for the double graft. INTERPRETATION: Firstly, a resected posterior cruciate ligament should be replaced to avoid excessive compressive forces, which are a source of cartilage degeneration. Secondly, the two types of posterior cruciate ligament reconstruction techniques partially restored the biomechanics of the knee in flexion, e.g. contact pressures were restored for pure flexion of the knee. The reconstruction techniques therefore partially restore the biomechanics of the knee in flexion. A double graft reconstruction is subjected to the highest tensile stresses.

Compressive Strength↗
PubMed2005

Comparative evaluation of implant designs: influence of diameter, length, and taper on strains in the alveolar crest. A three-dimensional finite-element analysis.

OBJECTIVES: Our aim was to analyze and compare systematically the relative and interactive effects of implant diameter, length, and taper on calculated crestal bone strains. MATERIAL AND METHODS: Three-dimensional finite-element models were created of a 20-mm premolar section of the mandible with a single endosseous implant embedded in high- or low-density cancellous bone. Oblique (200-N vertical and 40-N horizontal) occlusal loading was applied. Cortical and cancellous bone were modeled as transversely isotropic and linearly elastic. Perfect bonding was assumed at all interfaces. A two-level factorial statistical design was used to determine the main and interactive effects of four implant design variables on maximum shear strains in the crestal alveolar bone: diameter, length of tapered segment, length of untapered segment, and taper. Implant diameter ranged from 3.5 to 6 mm, total implant length from 5.75 to 23.5 mm, and taper from 0 to 14 degrees , resulting in 16 implant designs. RESULTS: Increasing implant diameter resulted in as much as a 3.5-fold reduction in crestal strain, increasing length caused as much as a 1.65-fold reduction, whereas taper increased crestal strain, especially in narrow and short implants, where it increased 1.65-fold. Diameter, length, and taper have to be considered together because of their interactive effects on crestal bone strain. CONCLUSION: If the objective is to minimize peri-implant strain in the crestal alveolar bone, a wide and relatively long, untapered implant appears to be the most favorable choice. Narrow, short implants with taper in the crestal region should be avoided, especially in low-density bone.

Alveolar Process↗