SEARCH · PubMed Health

Results for “Finite Element Analysis”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 505 records · Page 28Linked to original sources

PubMed2004

Three-dimensional finite element analysis of residual stress in arteries.

Calculation of residual stress in arteries, using the analytical approach has been quite valuable in our understanding of its critical role in vascular mechanics. Stresses are calculated at the central section of an infinitely long tube by imposing a constant axial stretch while deforming the artery from the stress-free state to its unloaded state. However, segments used to perform opening-angle measurements have finite lengths. Further, the stress-free artery configuration is assumed to be circular. Experiments show that they are slightly noncircular. The numerical approach to residual stress calculation can allow us to study both these issues. Using 3D cylindrical geometries and an isotropic material model, we investigated how segment length can affect residual stress calculations and identified the appropriate segment length for experiments. Further, we recorded and used the true noncircular stress-free state of an artery segment, computed the residual stress distribution, and compared it to that from a similar, but circular segment. Our findings suggest that segment length must be ten times the wall thickness for it to be "long" enough. We also found that the circularity assumption may be a reasonable approximation for typical arteries.

Animals↗

PubMed2005

Firmness evaluation of melon using its vibration characteristic and finite element analysis.

The "Huang gua" melons were measured for their physical properties including firmness and static elastic modulus. The vibrational characteristics of fruits and vegetables are governed by their elastic modulus (firmness), mass, and geometry. Therefore, it is possible to evaluate firmness of fruits and vegetables based on their vibrational characteristics. Analysis of the vibration responses of a fruit is suggested for measuring elastic properties (Firmness) non-destructively. The impulse response method is often used to measure firmness of fruits. The fruit was excited using three types of balls (wooden, steel and rubber) and the vibration is detected by an accelerometer. The Instron device was used to measure the static elastic modulus of the inner, middle and outer portions of melon flesh. Finite element (FE) technique was used to determine the optimum excitation location of the chosen measurement sensor and to analyze the mode shape fruits. Four types of mode shapes (torsional or flexural mode shape, first-type, second-type spherical mode and breathing mode shape) were found. Finite element simulation results agreed well with experimental results. Correlation between the firmness and resonant frequency (r2=0.91) and between the resonant frequency and stiffness factor (r2=0.74) existed. The optimum location and suitable direction for excitation and response measurement on the fruit were suggested.

Cucurbitaceae↗

PubMed2006

Finite element analysis of the spondylolysis in lumbar spine.

Spondylolysis is a fracture of the bone lamina in the pars interarticularis and has a high risk of developing spondylolisthesis, as well as traction on the spinal cord and nerve root, leading to spinal disorders or low back pain when the lumbar spine is subjected to high external forces. Previous studies mostly investigated the mechanical changes of the endplate in spondylolysis. However, little attention has been focused on the entire structural changes that occur in spondylolysis. Therefore, the purpose of this study was to evaluate the biomechanical changes in posterior ligaments, disc, endplate, and pars interarticularis between the intact lumbar spine and spondylolysis. A total of three finite element models, namely the intact L2-L4 lumbar spine, lumbar spine with unilateral pars defect and with bilateral pars defect were established using a software ANSYS 6.0. A loading of 10 N.m in flexion, extension, left torsion, right torsion, left lateral bending, and right lateral bending respectively were imposed on the superior surface of the L2 body. The bottom of the L4 vertebral body was completely constrained. The finite element models estimated that the lumbar spine with a unilateral pars defect was able to maintain spinal stability as the intact lumbar spine, but the contralateral pars experienced greater stress. For the lumbar spine with a bilateral pars defect, the rotation angle, the vertebral body displacement, the disc stress, and the endplate stress, was increased more when compared to the intact lumbar spine under extension or torsion.

Adult↗

PubMed2004

Evaluation of load transfer characteristics of five different implants in compact bone at different load levels by finite elements analysis.

STATEMENT OF PROBLEM: The external contour of an implant and the magnitude of occlusal loading can have significant effects on the load transfer characteristics and may result in different bone failure rates for different implant systems. PURPOSE: The goal of this study was to investigate the effects of external geometry and occlusal load magnitude on bone failure modes for 5 commercially available dental implant systems. MATERIAL AND METHODS: Five different implant systems; Ankylos, Astra, Bicon, ITI, and Nobel Biocare, comparable in size, but different in thread profile and crest module shapes, were compared using the finite element method. Type II bone quality was approximated and complete osseous integration was assumed. Occlusal loads of varying magnitudes (0 to 2000 N) were applied on the abutments supporting single tooth restorations at 11.3 degrees from the vertical axis with a 1-mm offset. Total overloaded bone area, where tensile and compressive normal stresses fell outside of the recommended limits of 100 and 170 MPa, respectively, was investigated for different load levels. RESULTS: For moderate levels of occlusal loads up to 300 N, the compact bone was not overloaded by any of the implant systems. At the extreme end of the occlusal load range (1000 N or more) the overloading characteristics of implants may be dependent on geometric shape. CONCLUSION: In general, overloading occurs near the superior region of compact bone, in compression, and it is primarily caused by the normal and lateral components of the occlusal load. At the region of intersection of compact and trabecular bone, overloading occurs in tension due to the vertical component of the occlusal load. For excessive forces greater than 1000 N, the overloaded areas of the bone varied considerably among 5 different implants systems evaluated.

Alveolar Bone Loss↗

PubMed2005

A three-dimensional nonlinear finite element analysis of the mechanical behavior of tissue engineered intervertebral discs under complex loads.

The use of tissue-engineering method holds great promise for treating degenerative disc disease [Gan JC, Ducheyne P, Vresilovic E, Shapiro IM. J Biomed Mater Res 2000; 51(4): 596-604]. This concept typically implies that nucleus pulposus (NP) cells are seeded on a scaffold, while the NP tissue is regenerated. Such hybrid implant is inserted into the host intervertebral disc. Because the success of a tissue engineering approach depends on maintenance or restoration of the mechanical function of the intervertebral disc, it is useful to study the initial mechanical performance of the disc after implantation of the hybrid. A three-dimensional finite element model (FEM) of the L2-L3 disc-vertebrae unit has been analyzed. The model took into account the material nonlinearities and it imposed different and complex loading conditions. In this study, we validated the model by comparison of its predictions with several sets of experimental data; we determined the optimal Young's modulus as well as the failure strength for the tissue-engineered scaffold under different loading conditions; and we analyzed the effects of implanted scaffold on the mechanical behavior of the intervertebral disc. The results of this study suggest that a well-designed tissue-engineered scaffold preferably has a modulus in the range of 5-10 MPa and a compressive strength exceeding 1.67 MPa. Implanted scaffolds with such properties can then achieve the goal of restoring the disc height and distributing stress under different loading conditions.

Biomechanical Phenomena↗

PubMed2005

Finite element analysis of the implantation of a balloon-expandable stent in a stenosed artery.

Intracoronary stent implantation (ICSI) has been widely used in interventional procedures. It can induce an even greater increment in intervention effectiveness and in success rate than traditional percutaneous transluminal coronary angioplasty (PTCA). However, owing to the complexities in geometries, material properties and interactions seen in ICSI, analyses of the complete stenting system composed of balloon, stent, plaque and artery are limited. In order to investigate the biomechanical characteristics of ICSI, a three-dimensional model of the complete stenting system and self-defined constitutive models for the plaque and the balloon were developed, which made the simulation well close to the real situation. Finite element method (FEM) was used to simulate the stent implantation under the balloon inflation and deflation. The simulated results show that the distal end of stent, which tilts after expansion, may injure the artery wall. High stress concentrates in the contacting areas between the stent and the plaque. The recoil ratios of the balloon-stent model, the balloon-stent-plaque-artery model (representing ICSI) and the balloon-plaque-artery model (representing PTCA) are 3.1%, 12.3% and 22.9%, respectively. In conclusion, FEM can help illustrate and quantify some biomechanical characteristics of ICSI. And it would be helpful for the general understanding of ICSI.

Angioplasty, Balloon, Coronary↗

PubMed2006

Finite element analysis of the penetrations of shear and normal vibrations into the soft tissues in a fingertip.

It is well accepted that the effects of mechanical vibration on the finger-hand-arm system are strongly frequency-dependent: low frequency vibration can transmit from hand to arm, while high frequency vibration is absorbed in the local tissue of fingers. This assertion has not been validated directly. The purpose of the present study is to analyze the frequency- and deformation-dependent dynamic strains in the soft tissues in a fingertip that is subjected to vibration normal or tangential to the contact surface. The dynamic responses of the fingertip were analyzed using a multi-layered two-dimensional finite element model. The major anatomical substructures, i.e., skin, subcutaneous tissue, bone, and nail, are included in the model. The fingertip was found to have a major resonance around 100-125 Hz and a second resonance around 250 Hz. The resonances of the fingertip are found to be independent of the direction of exposure (in normal or shear direction). The simulations further indicated that the dynamic strains induced by the vibration at low frequencies will penetrate deeper into the tissue (> 3 mm) while that at high frequencies will be concentrated in the superficial skin layer (< 0.8 mm). The model predictions are consistent with the published experimental observations.

Computer Simulation↗

PubMed2007

Three-dimensional finite-element analysis of maxillary protraction with and without rapid palatal expansion.

The aims of this study were to determine the reaction of the craniofacial bones on the protraction force transferred to the maxillary body, and whether or not the midpalatal suture had opened during skeletal Class III treatment. A computerized tomograph was obtained from a dry skull with a normal occlusion to construct a three-dimensional finite-element model (3D.FEM) of the craniofacial bones and the maxillary teeth to simulate actual bone reactions. A protraction force of 500 g was applied at the first premolar region, directed 20 degrees inferior to the occlusal plane. The displacement and the stress distribution of the craniofacial bones and sutures were then calculated using the ANSYS 5.3 program dividing the analysis into two simulations, based on whether or not the midpalatal suture was opened. The results showed that there was less compressive stress and greater tensile stress in the circumaxillary suture areas when the midpalatal suture was opened. The amount of displacement and deformation when the midpalatal suture was opened also demonstrated a decrease in upward-forward rotation of the maxilla and zygomatic arch and greater amounts of displacement in the frontal, vertical, and lateral directions compared with no opening of the midpalatal suture. Analysis of these results showed that maxillary protraction produce similar changes to normal downward and forward growth of the maxilla and was achieved with accompanying opening of the midpalatal suture.

Cephalometry↗

PubMed1999

Finite element analysis of a novel design approach to resisting total hip dislocation.

OBJECTIVE: A new design concept has been developed to reduce the propensity for dislocation in total hip patients. The ability of this design to increase the stability of the hip joint is studied. DESIGN: The new design involves a convex-curved acetabular lip, extending from the hemispherical articulating surface to the outer edge of the cup. The femoral component has a matching, reverse curve. BACKGROUND: Dislocation is a continuing problem in total hip arthroplasty, a complication experienced by 2-11% of patients with primary surgeries, and much higher percentage of patients in revision series. Confounding factors and sources of variability in the clinical domain make it difficult to identify specific parameter influences. METHODS: A three-dimensional nonlinear finite element model has been developed for the purpose of studying the dislocation event. We report the first use of this finite element model to analyze the potential for improving hip stability by a new total hip component design concept. RESULTS: The results show that this new design achieves 28% more resisting moment build-up during dislocation, and has a higher range of motion from impingement to onset of subluxation. The new curved lip design also develops 50% less polyethylene von Mises stress in the impingement zone. CONCLUSIONS: This design has excellent potential for increasing the inherent stability of the total hip joint. RELEVANCE: Recurrent dislocation is the second leading cause of total hip failure next to late loosening. This study shows the potential of a new total hip design to increase the stability of the artificial hip joint.

Arthroplasty, Replacement, Hip↗

PubMed2001

Modeling the interactions between a prosthetic socket, polyurethane liners and the residual limb in transtibial amputees using non-linear finite element analysis.

Continuing earlier studies into the relationship between the residual limb, liner and socket in transtibial amputees, we describe a geometrically accurate non-linear model simulating the donning of a liner and then a socket. The socket is rigid and rectified and the liner is a polyurethane geltype which is accurately described using non-linear (Mooney-Rivlin) material properties. The soft tissue of the residual limb is modelled as homogeneous, non-linear and hyperelastic and the bone structure within the residual limb is taken as rigid. The work gives an indication of how the stress induced by the process of donning the rigid socket is redistributed by the liner. Ultimately we hope to understand how the liner design might be modified to reduce discomfort. The ANSYS finite element code, version 5.6 is used.

Amputation Stumps↗

PubMed2006

Assessment of carbon fibre composite fracture fixation plate using finite element analysis.

In the internal fixation of fractured bone by means of bone-plates fastened to the bone on its tensile surface, an on-going concern has been the excessive stress shielding of the bone by the excessively-stiff stainless-steel plate. The compressive stress shielding at the fracture-interface immediately after fracture-fixation delays callus formation and bone healing. Likewise, the tensile stress shielding in the layer of bone underneath the plate can cause osteoporosis and decrease in tensile strength of this layer. In this study a novel forearm internal fracture fixation plate made from short carbon fibre reinforced plastic (CFRP) was used in an attempt to address the problem. Accordingly, it has been possible to analyse the stress distribution in the composite plates using finite-element modelling. A three-dimensional, quarter-symmetric finite element model was generated for the plate system. The stress state in the underlying bone was examined for several loading conditions. Based on the analytical results the composite plate system is likely to reduce stress-shielding effects at the fracture site when subjected to bending and torsional loads. The design of the plate was further optimised by reducing the width around the innermost holes.

Bone Plates↗

PubMed2003

Kinematics, kinetics, and finite element analysis of commonplace maneuvers at risk for total hip dislocation.

Dislocation remains a disturbingly frequent complication of total hip arthroplasty (THA). Over the past several years, increasingly rigorous biomechanical approaches have been developed for studying dislocation, both experimentally and computationally. Realism of the input motion challenge data has lagged behind most other aspects of this body of work, and anterior dislocation maneuvers remain unstudied. To enhance realism of biomechanical studies of dislocation, motion data are here reported for ten THA-aged subjects, each repeatedly performing seven maneuvers known to be dislocation-prone. An optoelectronic motion tracking system and a recessed force plate captured the kinematics and ground reaction forces of these maneuvers. Using an established inverse dynamics model to estimate hip joint loading, 354 motion trials were evaluated using an existing finite element model of THA dislocation. Worst-case-scenario THA constructs were simulated (22 mm femoral head, acetabular cup orientations at the limit of the accepted safe zone), in order to deliberately induce impingement and dislocation. The results showed a high incidence of computationally predicted dislocation for all movements studied, but also that risk was very maneuver-dependent, with patients being six times more likely to dislocate from a low-sit-to-stand maneuver than from stooping. These new motion data hopefully will help facilitate systematic efforts to reduce the incidence of dislocation.

Activities of Daily Living↗

PubMed2004

Benefits of an anatomical reconstruction of the humeral head during shoulder arthroplasty: a finite element analysis.

OBJECTIVE: To study the influence of the shape of the prosthetic humeral head on shoulder biomechanics and then to evaluate the benefits of an anatomical reconstruction of the humeral head after shoulder arthroplasty. DESIGN: A 3D numerical model of a healthy shoulder was reconstructed. The model included the proximal humerus, the scapula and, for stability purposes, the subscapularis, infraspinatus and supraspinatus rotator cuff muscles. BACKGROUND: Shoulder prostheses used nowadays, called third generation, allow for a better adaptation of the implant to the anatomy of the proximal humerus than previously used implants. However, no biomechanical study has shown the benefits of this anatomical reconstruction of the humeral head. METHODS: The model was used to compare the biomechanics of a shoulder without implant with the biomechanics of the same shoulder after humeral hemiarthroplasty. Two humeral components were tested: a second-generation prosthesis and an implant with an anatomically reconstructed humeral head. RESULTS: The anatomical reconstruction of the humeral head restored the physiological motions and limited eccentric loading of the glenoid. Conversely, the second-generation implant produced contact forces in the superior extremity of the glenoid surface leading to bone stresses up to 8 times higher than for the intact shoulder. CONCLUSIONS: This analysis provided insights into the mechanical effects of different reconstructions of the humeral head and highlighted the advantages of anatomical reconstructions of the humeral head during shoulder arthroplasty.

Arthroplasty, Replacement↗

PubMed2003

Finite-element analysis of birefringence and dispersion properties in actual and idealized holey-fiber structures.

Using a full-vector finite-element method, we calculate birefringence and dispersion in index-guiding photonic crystal fibers, also called holey fibers. Through real-model simulations the polarization-dependent dispersion in actual fiber structures is numerically demonstrated, for the first time to our knowledge. Furthermore the transverse-electric-field vector distributions in the fabricated holey fibers are also clarified for the two linearly polarized fundamental modes.

Journal Article↗

PubMed1997

[Three dimensional finite element analysis of margin configurations and stresses of porcelain fused to metal crowns]

As to using the method of three dimensional finite element,this study has analyzed the stress distribution of the porcelain fused to metal crowns with three different labial margin configurations under the forces from diverse direction.The results showed that the chamber margins exhibited fewer tensile stresses than the shoulder or shoulder with a bevel margins.The labial margin exhibited more tensil stresses when the incisal edge of the crown was loaded with labial forces.so,we provide the mechanical basis for the conclusions as follows: (1)The labial chamber margin is preferable to shoulder or shoulder with a bevel margin. (2)The porcelain may fracture when the incisal edge of porcelain fused to metal crown is loaded with labial forces.

Journal Article↗

PubMed2005

Three-dimensional finite element analysis of the mandible and temporomandibular joint during vertical ramus elongation by distraction osteogenesis.

Distraction osteogenesis has been accepted as an alternative treatment modality for hypoplastic mandibles. Knowledge about the changes occurring in the temporomandibular joint region during mandibular distraction osteogenesis is, however, limited and controversial. Stress distribution in the temporomandibular joint region during unilateral vertical mandibular ramus distraction was studied using a finite element model. The finite element model was based on computed tomography scans and magnetic resonance imaging scans of a patient with unilateral hypoplasia of the right mandibular ramus caused by juvenile idiopathic arthritis. The character of stress distribution in the temporomandibular joint and mandible was analyzed quantitatively at different intervals of the vertical mandibular ramus elongation. During the distraction phase, the condyles, articular disks, and glenoid fossa regions were loaded with a differentiated stress pattern. The affected right condyle, disk, and fossa were submitted to increasing loads with increasing elongation compared with the contralateral temporomandibular joint. Loading on the unaffected left side shifted posteriorly and slightly laterally, because the left condyle was the center of rotation. The loading of the temporomandibular joint regions was low during the active distraction phase, although local areas were subjected to elevated peak stresses.

Arthritis, Juvenile↗

PubMed2002

Finite-element analysis of hepatic multiple probe radio-frequency ablation.

Radio-frequency (RF) ablation is an important means of treatment of nonresectable primary and metastatic liver tumors. RF ablation, unlike cryoablation (a method of tumor destruction that utilizes cold rather than heat), must be performed with a single probe placed serially. The ablation of any but the smallest tumor requires the use of multiple overlapping treatment zones. We evaluated the performance of a configuration incorporating two hooked probes (RITA model 30). The probes were lined up along the same axis in parallel 20 mm apart. Three different modes applied voltage to the probes. The first mode applied energy in monopolar mode (current flows from both probes to a dispersive electrode). The second mode applied the energy to the probes in bipolar mode (current flows from one probe to the other). The third method applied the energy sequentially in monopolar mode (in 2-s intervals switched between the probes). We used the finite-element method (FEM) and analyzed the electric potential profile and the temperature distribution at the end of simulation of a 12-min ablation. The alternating monopolar mode allowed precise independent control of the amount of energy deposited at each probe. The bipolar mode created the highest temperature in the area between the probes in the configuration we examined. The monopolar mode showed the worst performance since the two probes in close vicinity create a disadvantageous electric field configuration. We, thus, conclude that alternating monopolar RF ablation is superior to the other two methods.

Catheter Ablation↗

PubMed2000

Three-dimensional finite element analysis of skin suture. Part 1: spindle model and S-shaped modified model.

Suturing of postoperative wounds in skin unfortunately leads to extrusion of the skin, resulting in so-called "dog ear". We performed three-dimensional finite element method (FEM) analyses to investigate how suture methods affect the height of the extrusion. Three models were prepared: (1) conventional suture method Sp; (2) S-shaped modified suture model Si-1, in which one side of the curves is introverted; and (3) another S-shaped suture model Si-2, in which both sides of the curves are introverted. The results of FEM analysis agreed well with the figure and location of the extrusions in clinical suture surgery and the height of the extrusion was mimicked visually in three dimensions. The height of the extrusion peak of the S-shaped modified suture method Si-1 was decreased by 40% in comparison with the conventional suture method Sp.

Dermatologic Surgical Procedures↗