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PubMed2005

Three-dimensional finite element analysis of the foot during standing--a material sensitivity study.

Information on the internal stresses/strains in the human foot and the pressure distribution at the plantar support interface under loading is useful in enhancing knowledge on the biomechanics of the ankle-foot complex. While techniques for plantar pressure measurements are well established, direct measurement of the internal stresses/strains is difficult. A three-dimensional (3D) finite element model of the human foot and ankle was developed using the actual geometry of the foot skeleton and soft tissues, which were obtained from 3D reconstruction of MR images. Except the phalanges that were fused, the interaction among the metatarsals, cuneiforms, cuboid, navicular, talus, calcaneus, tibia and fibula were defined as contact surfaces, which allow relative articulating movement. The plantar fascia and 72 major ligaments were simulated using tension-only truss elements by connecting the corresponding attachment points on the bone surfaces. The bony and ligamentous structures were embedded in a volume of soft tissues. The encapsulated soft tissue was defined as hyperelastic, while the bony and ligamentous structures were assumed to be linearly elastic. The effects of soft tissue stiffening on the stress distribution of the plantar surface and bony structures during balanced standing were investigated. Increases of soft tissue stiffness from 2 and up to 5 times the normal values were used to approximate the pathologically stiffened tissue behaviour with increasing stages of diabetic neuropathy. The results showed that a five-fold increase in soft tissue stiffness led to about 35% and 33% increase in the peak plantar pressure at the forefoot and rearfoot regions, respectively. This corresponded to about 47% decrease in the total contact area between the plantar foot and the horizontal support surface. Peak bone stress was found at the third metatarsal in all calculated cases with a minimal increase of about 7% with soft tissue stiffening.

Adult↗
PubMed2001

[Biomechanical studies and finite element analysis of a bone-implant interface].

In the present study, the fixation system of a femoral medullary nail connection was investigated. In surgical treatment of fractured femurs, the fracture is bridged by a medullary nail that is fixed by interlocking screws in the bone. Bone failure around these screws is the most common complication associated with the treatment of fractures of osteoporotic bone. The present study analyses the stresses present in the region of the implant/bone system. Three-dimensional finite element models were generated, a nonlinear structure analysis performed, and the stresses at material interfaces investigated. The highest concentration of stresses is to be found in the middle of the interlocking screws and the holes drilled in the bone. This is in agreement with the results of experimental investigations.

Biomechanical Phenomena↗
PubMed2006

[Three dimensional finite element analysis of the upper incisor with different levels of periodontal support].

PURPOSE: To study the stress variation and distribution of the periodontium and the tooth initial displacement when the lingual fixate forces were applied to the depressed periodontal height. METHODS: Spiral CT (SCT) scanning technology, digital image transfer and transcription were used to obtain the initial 3-D data of the upper central incisor. The 3-D finite element models at six periodontal support heights were created by reducing the height of periodontal support tissues. RESULTS: With the loss of the alveolar height, the maximum equivalent stress and the principle stress of the upper central incisor periodontium increased. The maximum draw stress located on the lingual apex, while the maximum compressive stress located on the lingual crest of the ridge. The increment of periodontium stress was not proportional to the horizontal alveolar loss. CONCLUSIONS: With the horizontal alveolar loss, the rotation center moved toward the apex and the capacity of periodontal support decreased significantly. In orthodontic treatment, the force should be decreased in proportion to retain the physiological movement and to avoid further injury of the support tissues.

Alveolar Process↗
PubMed2002

A case study of hemispatial neglect using finite element analysis and positron emission tomography.

BACKGROUND: The authors present a patient who developed transient hemispatial neglect following surgical drainage of a large right frontotemporal arachnoid cyst. As symptoms evolved in parallel with brain shift over the subsequent months, the authors hypothesized that the disorder was associated with the appearance of mechanical stresses in the cerebral mantle. METHODS: To map tissue stress at the various stages of deformation, a finite element computer simulation was conducted on the basis of computed tomography scans of the patient. RESULTS: The authors' results demonstrate substantial shear and compressive stress concentrations in the parietal lobe, a region commonly associated with neglect, and where positron emission tomography confirmed hypoperfusion in this patient. Treatment with combined ventricular-peritoneal and cystoperitoneal shunts was accompanied by clinical recovery and improvement of right parietal lobe cerebral blood flow. CONCLUSIONS: The authors conclude that brain deformation was a contributing factor in the reversible neglect syndrome by compromising the normal flow of blood and/or the deactivation of subcortical circuits of the parietal lobe.

Aged↗
PubMed2005

Large deformation finite element analysis of micropipette aspiration to determine the mechanical properties of the chondrocyte.

Chondrocytes, the cells in articular cartilage, exhibit solid-like viscoelastic behavior in response to mechanical stress. In modeling the creep response of these cells during micropipette aspiration, previous studies have attributed the viscoelastic behavior of chondrocytes to either intrinsic viscoelasticity of the cytoplasm or to biphasic effects arising from fluid-solid interactions within the cell. However, the mechanisms responsible for the viscoelastic behavior of chondrocytes are not fully understood and may involve one or both of these phenomena. In this study, the micropipette aspiration experiment was modeled using a large strain finite element simulation that incorporated contact boundary conditions. The cell was modeled using finite strain incompressible and compressible elastic models, a two-mode compressible viscoelastic model, or a biphasic elastic or viscoelastic model. Comparison of the model to the experimentally measured response of chondrocytes to a step increase in aspiration pressure showed that a two-mode compressible viscoelastic formulation accurately captured the creep response of chondrocytes during micropipette aspiration. Similarly, a biphasic two-mode viscoelastic analysis could predict all aspects of the cell's creep response to a step aspiration. In contrast, a biphasic elastic formulation was not capable of predicting the complete creep response, suggesting that the creep response of the chondrocytes under micropipette aspiration is predominantly due to intrinsic viscoelastic phenomena and is not due to the biphasic behavior.

Animals↗
PubMed2003

Stress and strain distribution in the intact canine femur: finite element analysis.

Information regarding the stresses and strains in the canine femur during various activities is important for veterinary orthopaedic surgeons, engineers designing implants for dogs, and researchers of human orthopaedics who use dogs as models. Nevertheless, such information is currently unavailable. The objective of this study is to determine the stress and strain distribution in the canine femur during mid-stance, for two loading scenarios. Three-dimensional finite element models of the canine femur were created. Two loading cases were considered: the hip joint reaction force alone, and the hip joint reaction force with all muscle forces acting on the femur. Force directions and magnitudes were obtained from the literature. Analyses were performed with NASTRAN for Windows software. When all muscle forces were considered, stresses and strains were significantly reduced, peak compressive stresses were found to occur in the medial diaphysis, and peak tensile stresses occurred in the lateral diaphysis. While the canine femur seems to be loaded primarily in bending when only the hip joint reaction force is considered, the bending moment is significantly decreased when all muscle forces are considered as well. Further in vivo and in vitro experiments are needed to validate the results of the calculations described in this paper. It is expected that future studies will be carried out, in which the stress and strain distributions in femora with different types of implants and stems will be compared to those in the normal femur.

Animals↗
PubMed2004

Effect of a degraded core on the mechanical behaviour of tissue-engineered cartilage constructs: a poro-elastic finite element analysis.

The structure and functionality of tissue-engineered cartilage is determined by the tissue culture conditions and mechanical conditioning during growth. The quality of tissue-engineered cartilage can be evaluated using tests such as the confined compression test. Tissue-engineered cartilage constructs usually consist of an outer layer of cartilage and an inner core of either undeveloped cartilage or degrading scaffold material. A biphasic poro-elastic finite element model was used to demonstrate how such a core influences the reaction force-time curve obtained from a confined compression test. The finite element model predicted that higher volumes of degraded scaffold in the inner core would reduce the aggregate modulus calculated from the confined compression test and raised the estimate of tissue permeability. The predicted aggregate modulus reduced from 0.135 MPa, for a homogenous construct, to 0.068 MPa, for a construct that was only 70% cartilaginous. It was found that biphasic poro-elastic finite modelling should be used in preference to a one-dimensional model that assumed homogeneity in estimating the properties of tissue-engineered cartilage.

Biomechanical Phenomena↗
PubMed2000

Monitoring water content in deforming intervertebral disc tissue by finite element analysis of MRI data.

Mechanical loading, occurring during normal daily life, causes fluid to be expelled from intervertebral discs. Excessive fluid loss during heavy loading might make the disc more vulnerable to damage. In this study, fluid loss was investigated in vitro through monitoring the loss of MRI signal intensity in four bovine coccygeal intervertebral discs, compressed at 2000 N during 1.5 hr. The MRI signals were analyzed with the aid of finite element models to account for the deformation of the tissue. A gradual signal loss over time was found during loading, the most pronounced loss occurring in the central disc region. Initial patterns of signal distribution were quite variable between specimens but repeatable within specimens.

Animals↗
PubMed2006

Finite-element analysis of geometrical factors in micro-indentation of pollen tubes.

Micro-indentation is a new experimental approach to assess physical cellular properties. Here we attempt to quantify the contribution of geometrical parameters to a cylindrical plant cell's resistance to lateral deformation. This information is important to correctly interpret data obtained from experiments using the device, such as the local cellular stiffness in pollen tubes. We built a simple finite-element model of the micro-indentation interacting partners - micro-indenter, cell (pollen tube), and underlying substratum, that allowed us to manipulate geometric variables, such as geometry of the cell, cell radius, thickness of the cell wall and radius of the indenting stylus. Performing indentation experiments on this theoretical model demonstrates that all four parameters influence stiffness measurement and can therefore not be neglected in the interpretation of micro-indentation data.

Elasticity↗
PubMed2000

[Three dimensional Finite Element Analysis of the Effects of Posts and Cores with Different Angles]

OBJECTIVE:The test is an analogue of the conditions that cast post and core can be made with different angles to get the core incline lingually or facially in clinic, so that the arrangement of the anterior teeth may be improved.METHODS:Analyse the stress distribution and concentration in the dentin of posts and cores with different angles by Ansys three dimensional finite element stress analysis method.RESULTS:The stress in root was positively related to the angles between the load and the axis of the tooth, the stress distributoin in dentin was related to the direction of the core but not related to the angles. The closer the distance from the load to cemento enamel junction,the greater the effect of the load on the stress in dentin.CONCLUSION:When the cast post and core with angle was used to rectify the facially malpositional maxillary anterior teeth, the core should not be inclined lingually excessively. It is important to assure the thickness of the facial and lingual canal wall during tooth preparing and to adjust the occlusion so that the root fracture can be avoided.

Journal Article↗
PubMed2005

Three-dimensional finite element analysis of stress in the periodontium.

The aim of this study is to calculate the stress produced in the periodontium at different bone levels under occlusal load. Four finite element models of maxillary incisors were designed consisting of the tooth, pulp, periodontal ligament and alveolar bone at various levels of bone height (25%, 50% and 75%). An occlusal load of 24 kg at an angle of 50 degrees to the long axis of the tooth was applied on the palatal surface, at the level of the middle third of the crown. All the models were assumed to be isotropic, linear and elastic and the analysis was performed on a Pentium IV computer using the NISA II Display III software. The results showed that maximum stress in the tooth was seen at the cervical region and to a greater extent at the apex for all the models. In periodontal ligament, maximum stress was seen at the alveolar crest in models with normal alveolar bone height and with reducing alveolar bone height maximum stress was at the apex. There was no significant stress distribution in alveolar bone, while no stress was seen on the pulp. The results of the study demonstrated a significant increase in stress concentration at the apex with loss of alveolar bone height.

Alveolar Process↗
PubMed2004

Physical signals and solute transport in cartilage under dynamic unconfined compression: finite element analysis.

A specialized model for charged hydrated soft tissue containing uncharged solutes (such as glucose and uncharged growth factor) was presented based on the more general, mechanoelectrochemical mixture theory (Gu et al., J. Biomech. Eng. 120:169-180, 1998: Lai et al., J. Biomech. Eng. 113:245-258, 1991). This model was applied to analyze the mechanical, chemical and electrical signals within the cartilage sample under dynamic unconfined compression (5% dynamic strain) using a finite element method. The effects of the permeable loading platen, loading frequency, and fixed charged density on the physical signals and the transport of fluid, ions, and uncharged solutes were investigated. Numerical analyses show that a permeable platen will increase the rate of dynamic fluxes of fluid, ion, and uncharged solute in the region near the permeable platen, but not the fluid pressure and electrical potential in the central region of the tissue at 0.1 Hz. The increase in fixed charge density (FCD) will decrease the dynamic fluxes of fluid, ion, and uncharged solute, but increase the fluid pressure and electrical potential within the tissue. For both permeable and impermeable loading platen cases, the electrical current density within the tissue is close to zero (approximately 10 microA/m2) except at the small region near a corner of the sample. On the radial edge of the sample, the dynamic solute flux for the large neutral solute is different from that for small neutral solute (glucose). This study is important for understanding mechanobiology of cartilage and for designing a bioreactor to be used in cartilage tissue engineering.

Biological Transport, Active↗
PubMed2002

The three-dimensional finite element analysis of fixed bridge restoration supported by the combination of teeth and osseointegrated implants.

This study investigated the designs of osseointegrated prostheses in cases of free-end partial edentulism using comparative stress interpreted with the three-dimensional finite element method. Three free-end fixed osseointegrated prostheses models with various connection designs (i.e., rigidly connected to an abutment tooth and an implant, rigidly connected to an implant and two abutment teeth, and rigidly connected to an implant and three abutment teeth) were studied. The stress values of the three models loaded with vertical, buccolingual, and linguobuccal directions at 30 degrees angled to vertical axis forces were analyzed. When the fixed partial denture was connected to the three natural abutment teeth and an implant, the lowest levels of stress in the bone were noted.

Alveolar Process↗
PubMed2002

Initial stress produced in the periodontal membrane by orthodontic loads in the presence of varying loss of alveolar bone: a three-dimensional finite element analysis.

The aim of this study was to investigate the stress components (S1 and S3) that appear in the periodontal membrane (PDM), when subjected to transverse and vertical loads equal to 1 N. A further aim was to quantify the alteration in stress that occurs as alveolar bone is reduced in height by 1, 2.5, 5, 6.5, and 8 mm, respectively. Six three-dimensional (3D) finite element models (FEM) of a human maxillary central incisor were designed. The models were of the same configuration except for the alveolar bone height. Special attention was paid to changes of the stress components produced at the cervical, apical, and sub-apical levels. In the absence of alveolar bone loss, a tipping force of 1 N produced stresses, which reached 0.072 N/mm2 at the cervical margin, up to 0.0395 N/mm2 at the apex and up to 0.026 N/mm2 sub-apically. In the presence of 8 mm of alveolar bone loss, the findings were -0.288, 0.472, and 0.722 N/mm2, respectively. Without bone loss, an intruding force of the same magnitude produced stresses of -0.0043, -0.0263, and 0.115 N/mm2, respectively, for the same areas and sampling points. In the presence of 8 mm of alveolar bone loss the findings were -0.019, -0.043, and 0.185 N/mm2 for intrusive movement. The results showed that alveolar bone loss caused increased stress production under the same load compared with healthy bone support (without alveolar bone resorption). Tipping movements resulted in an increased level of stress at the cervical margin of the PDM in all sampling points and at all stages of alveolar bone loss. These increased stress components were found to be at the sub-apical and apical levels for intrusive movement.

Alveolar Bone Loss↗
PubMed2003

Finite element analysis of cervical spinal instability under physiologic loading.

The definition of cervical spinal instability has been a subject of considerable debate and has not been clearly established. Stability of the motion segment is provided by ligaments, facet joints, and disc, which restrict range of movement. Moreover, permanent damage to one of the stabilizing structures alters the roles of the other two. Although many studies have been conducted to investigate cervical injuries, to date there are only limited finite element investigations reported in the literature on the biomechanical response of the cervical spine in these respects. A comprehensive, geometric, nonlinear finite element model of the lower cervical spine has been successfully developed and validated under compression, anterior-posterior shear, and sagittal moments. Injury studies were done by varying each spinal component independently from the validated model. Seven analyses were conducted for each injury simulation (model without ligaments, model without facets, model without facets and ligaments, and model without disc nucleus). Results indicate that the role of the ligaments in resisting anterior and posterior shear and flexion and axial rotation moments is important. Under other physiologic loading (anterior-posterior shear, flexion-extension, lateral bending, and axial rotation), the disc nucleus is responsible for the initial stiffness of the cervical spine. The results also highlight the importance of facets in resisting compression at higher loads, anterior shear, extension, lateral bending, and torsion. The results provide new insight through injury simulation into the role of the various spinal components in providing cervical spinal stability. These findings seem to correlate well with experimental results as well as with common clinical experience.

Cervical Vertebrae↗
PubMed1999

Finite element analysis of vertebral body mechanics with a nonlinear microstructural model for the trabecular core.

In this study, a finite element model of a vertebral body was used to study the load-bearing role of the two components (shell and core) under compression. The model of the vertebral body has the characteristic kidney shape transverse cross section with concave lateral surfaces and flat superior and inferior surfaces. A nonlinear unit cell based foam model was used for the trabecular core, where nonlinearity was introduced as coupled elastoplastic beam behavior of individual trabeculae. The advantage of the foam model is that architecture and material properties are separated, thus facilitating studies of the effects of architecture on the apparent behavior. Age-related changes in the trabecular architecture were considered in order to address the effects of osteoporosis on the load-sharing behavior. Stiffness changes with age (architecture and porosity changes) for the trabecular bone model were shown to follow trends in published experimental results. Elastic analyses showed that the relative contribution of the shell to the load-bearing ability of the vertebra decreases with increasing age and lateral wall curvature. Elasto-plastic (non-linear) analyses showed that failure regions were concentrated in the upper posterior region of the vertebra in both the shell and core components. The ultimate load of the vertebral body model varied from 2800 N to 5600 N, depending on age (architecture and porosity of the trabecular core) and shell thickness. The model predictions lie within the range of experimental results. The results provide an understanding of the relative role of the core and shell in vertebral body mechanics and shed light on the yield and post-yield behavior of the vertebral body.

Aged↗
PubMed2005

Three-dimensional finite element analysis of unicompartmental knee arthroplasty--the influence of tibial component inclination.

Aseptic loosening and failure of a tibial component are recognized problems in unicompartmental knee arthroplasty (UKA). Excessive stress on the supporting cancellous bone is thought to contribute to the loosening and failure. Of factors that could influence supporting cancellous bone stresses, we focused on the inclination of a unicompartmental tibial component by analyzing the effect of coronal plane and sagittal plane inclination. Detailed geometrically accurate, three-dimensional finite element models were constructed from computed tomography (CT) data of a typical adult male proximal tibia. The material properties for the models were obtained directly from the CT data to simulate the inhomogeneous distribution of cancellous bone properties. Placing the component in slight valgus inclination in the coronal plane reduced the cancellous bone stresses. Posterior inclination in the sagittal plane caused a moderate increase in the stresses. Our results suggest that slight valgus inclination of a UKA tibial component may be preferable to varus or square inclination in the coronal plane. An excessive posterior slope of a tibial component should be avoided.

Arthroplasty, Replacement, Knee↗