Finite Element Model Of Joint Research Articles

Evaluation of knee joint muscle forces and tissue stresses‐strains during gait in severe OA versus normal subjects

Osteoarthritis (OA) is the leading cause of pain and disability in the elderly with the knee being the most affected weight bearing joint. We used a musculoskeletal biomechanical model of the lower extremity including a detailed validated knee joint finite element model to compute lower extremity muscle forces and knee joint stresses-strains during the stance phase of gait. The model was driven by gait data on OA patients, and results were compared with those of the same model driven by data on normal controls. Additional analyses were performed with altered cartilage-menisci properties to evaluate the effects of deterioration during OA. In OA patients compared to normal subjects, muscle forces dropped at nearly all stance periods except mid-stance. Force in the anterior cruciate ligament remained overall the same. Total contact forces-stresses deceased by about 25%. Alterations in properties due to OA had negligible effects on muscle forces, but increased contact areas and cartilage strains and reduced contact pressures. Reductions in contact stresses and increases in tissue strains and transfer of load via menisci are partly due to the altered kinetics-kinematics of gait and partly due to deterioration in cartilage-menisci properties in OA patients.

Experimental Characterization and Finite Element Implementation of Soft Tissue Nonlinear Viscoelasticity

Finite element (FE) models of articular joint structures do not typically implement the fully nonlinear viscoelastic behavior of the soft connective tissue components. Instead, contemporary whole joint FE models usually represent the transient soft tissue behavior with significantly simplified formulations that are computationally tractable. The resultant fidelity of these models is greatly compromised with respect to predictions under temporally varying static and dynamic loading regimes. In addition, models based upon experimentally derived nonlinear viscoelastic coefficients that do not account for the transient behavior during the loading event(s) may further reduce the model's predictive accuracy. The current study provides the derivation and validation of a novel, phenomenological nonlinear viscoelastic formulation (based on the single integral nonlinear superposition formulation) that can be directly inputted into FE algorithms. This formulation and an accompanying experimental characterization technique, which incorporates relaxation manifested during the loading period of stress relaxation experiments, is compared to a previously published characterization method and validated against an independent analytical model. The results demonstrated that the static and dynamic FE approximations are in good agreement with the analytical solution. Additionally, the predictive accuracy of these approximations was observed to be highly dependent upon the experimental characterization technique. It is expected that implementation of the novel, computationally tractable nonlinear viscoelastic formulation and associated experimental characterization technique presented in the current study will greatly improve the predictive accuracy of the individual connective tissue components for whole joint FE simulations subjected to static and dynamic loading regimes.

COMPARATIVE STUDY ON STRENGTH OF KNEE JOINT USING VARIOUS MATERIAL MODELS

In this study, we adopt different material models to study the strength and stiffness of menisci of the knee joint using finite element method. The three-dimensional (3-D) knee joint finite element model is constructed based on the Magnetic Resonance (MR) images of a human knee joint, and the strength of menisci is analyzed under a specific vertical loading case. In this paper we categorize and implement three types of appropriate material properties, namely isotropic linearly elastic, transversely isotropic elastic and isotropic hyperelastic for menisci of the knee joint. Different strain energy models are also studied and compared under hyperelastic category. The comparative study demonstrates that the hyperelastic model with Ogden form is more appropriate in modeling menisci of the knee joint. By referring to the test data of different material properties from earlier studies by various researchers, we hope to provide a comparative study leading to appropriate menisci material models and properties for finite element analyses of knee joint structures.

Progressive damage and failure of mechanically fastened joints in CFRP laminates – Part I: Refined Finite Element modelling of single-fastener joints

This paper presents a refined Finite Element modelling for strength prediction, and especially bearing strength prediction, of mechanically fastened joints in CFRP laminates. Although the importance of delamination on the bearing strength of the joint is well established in the literature, only rarely has it been introduced into the models. In the present work, delamination onset and propagation are explicitly taken into account in the model by means of cohesive elements. The ply behaviour is described through a viscoelastic model combined with a progressive damage approach. A multi-model calculation strategy is developed to reduce the calculation costs. Prediction of the proposed model are compared to both bearing tests and open-hole tests results. For further validation, numerical predictions are also compared to filled-hole tensile tests and bearing/bypass interaction tests. Bearing, open-hole, and filled-hole tests are performed in this study. An original pin-bearing test configuration is proposed. Predicted strengths and experimental results turn out to be in good agreement. The obtained results are promising and demonstrate the capability of the proposed model to capture the material and stacking sequence effects on the joint behaviour and strength, as well as the influence of the geometrical dimensions of the joint.

Hyperelastic properties of human meniscal attachments

Meniscal attachments are ligamentous tissues anchoring the menisci to the underlying subchondral bone. Currently little is known about the behavior of meniscal attachments, with only a few studies quantitatively documenting their properties. The objective of this study was to quantify and compare the tensile mechanical properties of human meniscal attachments in the transverse direction, curve fit experimental Cauchy stress–stretch data to evaluate the hyperelastic behavior, and couple these results with previously obtained longitudinal data to generate a more complete constitutive model. Meniscal attachment specimens were tested using a uniaxial tension test with the collagen fibers oriented perpendicular to the loading axis. Tests were run until failure and load-optical displacement data was recorded for each test. The medial posterior attachment was shown to have a significantly greater elastic modulus (6.42±0.78 MPa) and ultimate stress (1.73±0.32 MPa) when compared to the other three attachments. The Mooney–Rivlin material model was selected as the best fit for the transverse data and used in conjunction with the longitudinal data. A novel computational approach to determining the transition point between the toe and linear regions is presented for the hyperelastic stress–stretch curves. Results from piece-wise non-linear longitudinal curve fitting correlate well with previous linear elastic and SEM findings. These data can be used to advance the design of meniscal replacements and improve knee joint finite element models.

Prediction of hot spot stress distribution for tubular K-joints under basic loadings

In the fatigue life assessment of tubular joints subjected to cyclic loading, the hot spot stress at the weld toe is critical for determining the number of cycles that the tubular joints can sustain before fatigue failure. Although there are many reported parametric equations of the stress concentration factor (SCF) for predicting tubular joints subjected to basic loadings, i.e. axial loading (AX), in-plane bending loading (IPB) and out-of-plane bending loading (OPB), it is not accurate for estimating the hot spot stress value of a tubular joint subjected to complex loading only from a superposed stress result from a combination of two or three basic loadings because the peak stresses at the weld toe for a tubular joint subjected to different basic loadings are not located at a fixed position. To calculate an accurate peak stress value along the weld toe for a tubular joint subjected to complex loading, it is necessary to know accurate stress distributions of the tubular joint under three basic loadings. Then the stress distribution of the tubular joint subjected to combined loading can be obtained from a superposition of stress distributions of two or three basic loadings. Then the peak stress is easily located from such a stress distribution. The stress distributions of uni-planar tubular K -joints under three basic loadings are analyzed using a finite element method in this study, and the influence of geometrical parameters on the stress distributions is also investigated. Based on the numerical results of 287 K -joint finite element models, a set of parametric equations for calculating the stress distribution of a K -joint under AX, IPB and OPB respectively are presented using a curve fitting technique. The accuracy of the proposed parametric equations is evaluated by comparing the predicted stress distribution results with the analyzed finite element results, and it is found that the parametric equations are reliable and accurate for calculating the stress distributions along the weld toe for K -joints under basic loadings.

Patient-specific knee joint finite element model validation with high-accuracy kinematics from biplane dynamic Roentgen stereogrammetric analysis

Little is known about in vivo menisci loads and displacements in the knee during strenuous activities. A new method that combines high-speed kinematics measured with biplane dynamic Roentgen stereogrammetric analysis (DRSA) and a subject-specific finite element (FE) model for studying in vivo meniscal behavior is presented here. Further model calibration in a very controlled uniaxial low and high-rate compression loading condition is presented by comparing the model behavior against the measured high-accuracy menisci DRSA kinematics and direct tibio-femoral pressure measurement from a K-scan sensor. It is apparent that certain model aspects such as removing of the pressure sensor from the model can result in relatively large errors (14%) in contact parameters that are not reflected in the change of the measured meniscal kinematics. Changing mesh size to 1 mm by 1 mm elements increased the magnitude of all but one of the contact variables by up to 45%. This local validation using accurate localized patient-specific geometry and meniscal kinematics was needed to enhance model fidelity at the level of contact between menisci and cartilage.

Development of a finite element model of the shoulder: application during a side impact

The shoulder is the most complex joint on the human body. Once shoulder injury occurs it can induce strong instability and a long rehabilitation period. Many studies in both fields of automotive safety and orthopaedic surgery have highlighted the fragility and the frequent injuries of the shoulder. To complete the understanding of shoulder biomechanics through usual experimental approaches, Finite Element simulation appears to be a valuable tool to investigate mechanical behaviour and failure processes involved in trauma situation (daily living, accident road, etc.). Hence, an advanced Finite Element model of the shoulder joint is under design and validation. This model aims to investigate the shoulder virtual trauma or instability problem. In this study we chose to focus on bone structure injuries especially with the clavicle fracture in side-impact situation.

A Three-Dimensional Dynamic Finite Element Model of the Prosthetic Knee Joint: Simulation of Joint Laxity and Kinematics

For testing purposes of prostheses at a preclinical stage, it is very valuable to have a generic modelling tool, which can be used to optimize implant features and to avoid poor designs being launched on to the market. The modelling tool should be fast, efficient, and multi-purpose in nature; a finite element model is well suited to the purpose. The question posed in this study was whether it was possible to develop a mathematically fast and stable dynamic finite element model of a knee joint after total knee arthroplasty that would predict data comparable with published data in terms of (a) laxities and ligament behaviour, and (b) joint kinematics. The soft tissue structures were modelled using a relatively simple, but very stable, composite model consisting of a band reinforced with fibres. Ligament recruitment and balancing was tested with laxity simulations. The tibial and patellar kinematics were simulated during flexion-extension. An implicit mathematical formulation was used. Joint kinematics, joint laxities, and ligament recruitment patterns were predicted realistically. The kinematics were very reproducible and stable during consecutive flexion-extension cycles. Hence, the model is suitable for the evaluation of prosthesis design, prosthesis alignment, ligament behaviour, and surgical parameters with respect to the biomechanical behaviour of the knee.

人工関節置換に対応した三次元CADシステムの研究(J03 CAD/CAE,J03 次世代のCAD/CAE)

In this study, a three-dimensional CAD system for biomechanical simulations was developed. Some human interfaces and the graphical routines were utilized effectively to emulate the medical operations and to enhance intuitive ones. A pair of the knee joint finite element model was used to evaluate the performance of this system. The replacement of the artifial joint and the control of the insertion direction of the prothesis were possible easily compared with the traditional CAD systems.

333 Automation Tools for Finite Element Analysis of Adhesively Bonded Joints

This article presents two new automation creation tools that obtain stresses and strains (Shear and peel) in adhesively bonded joints. For a given adhesively bonded joint Finite Element model, in which the adhesive is characterised using springs, these automation tools read the corresponding input and output files, use the spring forces and deformations to obtain the adhesive stresses and strains, sort the stresses and strains in descending order, and generate plot files for 3D visualisation of the stress and strain fields. Grids (nodes) and elements can be numbered in any order that is convenient for the user. Using the automation tools, trade-off studies, which are needed for design of adhesively bonded joints, can be performed very quickly.

Modeling and evaluation criterion for thermocompression flip-chip bonding

A single joint finite element model (FEM) using a newly developed configuration independent evaluation criterion has been created, and experimentally verified, to provide more accurate predictions of bond formation based on the joint design and assembly process parameters. This model is based on the joint interface mechanics resulting from joint bump compression. Previous studies used a deformation criterion that depended on a specific joint configuration to evaluate the effectiveness of the expected bond. This limited the applicability of the model results to the joint design for which the deformation criterion had been experimentally determined. The technique reported in this research, uses finite element models to compute detailed distributions of stresses/strains at the interface of a joint when it is plastically deformed under compression. The evaluation criterion is defined to be the change in the differential area at the bonding interface, and is shown mathematically as follows: /spl Delta/A=/spl epsi//sub xx/+/spl epsi//sub yy//spl ges/(/spl epsi//sub xx/+/spl epsi//sub yy/)/sub crit/. Models using this criterion allow for the comparison of the effects of various joint design and manufacturing process parameters on the bond joint mechanics, and the resulting probable bond joint quality. A determination of the minimum deformation required for joint formation can be obtained for any design within specified limits.

Mechanobiological adaptation of subchondral bone as a function of joint incongruity and loading

Computed tomography (CT) has been employed to determine non-invasively the distribution of subchondral bone density in joints and to evaluate their dominant loading pattern. The objective of this study was to investigate the relationship between subchondral bone adaptation, joint incongruity and loading, in order to determine to what extent the loading conditions and/or geometric configuration can be inferred from the distribution of subchondral density. Finite element models of joints with various degrees of incongruity were designed and a current remodeling theory implemented using the node-based approach. Appropriate combinations of joint incongruity and loading yielded subchondral bone density patterns consistent with experimental findings, specifically a bicentric distribution in the humero-ulnar joint and a monocentric distribution in the humero-radial joint. However, other combinations of incongruity and loading produced similar subchondral density patterns. Both the geometric joint configuration and the loading conditions influence the distribution of subchondral density in such a way that one of these factors must be known a priori to estimate the other. Since subchondral density can be assessed by CT and joint geometry by magnetic resonance imaging, the dominant loading pattern of joints may be potentially derived in the living using these non-invasive imaging methods.

A Cosserat continuum model for layered materials

Modelling the behaviour of materials consisting of a large number of layers is often required in geomechanical applications. In this study, an equivalent continuum model suitable for describing the mechanical response of such layered materials is considered. The model is based on the Cosserat continuum theory and incorporates the moment (couple) stresses in its formulation. The layers are assumed to have equal thickness and equal mechanical properties with elastic behaviour. In contrast to the earlier Cosserat models, the possibility of layer interface (joint) plastic-slip as well as tensile-opening during loading is considered. The importance of moment stress in describing the behaviour of such materials is discussed and highlighted through an example. It is shown through numerous examples that when there is a possibility of inter-layer slip and subsequent layer bending, equivalent continuum models based on the conventional anisotropy theory may not represent a true response of the layered materials. The relationship between the large-scale (Cosserat) description of the layered material and the fine-scale (micro) description of the stress-strain state of an individual layer is determined. The model is incorporated into the finite element (FE) code AFENA and several examples of load-deflection problems in layered materials are analysed. The Cosserat model is verified against the explicit joint FE model. Comparison between the two models shows a remarkable agreement suggesting that the Cosserat model is capable of providing an accurate prediction of the load-deflection behaviour of layered materials.

Free vibrations of coupled walls by transfer matrices and finite element modelling of joints

A transfer matrix analysis of coupled shear walls is combined with finite element models for joint flexibility. Every joint is considered as a single rectangular element with a displacement model that is consistent with the kinematic constraints imposed by the adjacent beams. The derivation of the element stiffness is based on plane stress elasticity. The overall problem can be solved for the static and free vibrational response of coupled shear walls on flexible foundations. Assessment of its performance and comparison with simpler models for joint deformation is accomplished through the determination of natural frequencies and modes of vibration for a range of previously tested or analysed specimens. Having established the accuracy of the proposed high-order finite element joint model, the effect of joint flexibility on higher frequencies and modes of vibration is then assessed.

A three-dimensional nonlinear finite element model of lumbar intervertebral joint in torsion.

Torsion as a cause of failure in the lumbar intervertebral joint was studied using a three-dimensional nonlinear finite element model. The role of facets and ligaments as well as the stress distributions in the posterior elements, the disk, the ligaments, and the vertebral body were examined. For physiological range of torsion, the facets carried 10 to 40 percent of the torque. The fiber stresses in the disk were the highest at the lateral margin of the outer layer of the annulus. Therefore, torsion itself is unlikely to cause posterior or posterolateral disk prolapse.