Effect of Biologically Oriented Preparation Technique on the Stress Concentration of Endodontically Treated Upper Central Incisor Restored with Zirconia Crown: 3D-FEA.

The aim of this study was to evaluate the effect of biologically oriented preparation technique on the stress concentration of endodontically treated upper central incisors restored with zirconia crown (yttria-stabilized zirconia polycrystalline ceramic) through finite element analysis (FEA). Four models of maxillary central incisors containing enamel, dentin, periodontal ligament, cortical and medullary bone were created in CAD. Each model received a polymeric core-build up with nanofilled dental resin composite. The evaluated models were SM-preparation in shoulder 90°; CM-chamfer preparation; BOPT-biologically oriented preparation technique and BOPTB-BOPT preparation 1 mm below the cement-enamel junction. All models received zirconia crowns (5Y-TZP), fiberglass post and 1 mm ferrule. The models were imported into the analysis software with parameters for mechanical structural testing using the maximum principal stress and the tensile strength as the analysis criteria. Then, load of 150 N was applied at the cingulum with 45° slope to the long axis of the tooth, with the fixed base for each model. The type of marginal preparation affected the stresses concentration in endodontically treated teeth and in the zirconia crown margin. Considering the stress magnitude only, BOPT is a viable option for anterior monolithic zirconia crowns; however, with the highest stress magnitude at the restoration margin.

Evaluation of Tissue-Level Brain Injury Metrics Using Species-Specific Simulations.

Traumatic brain injury (TBI) is a significant public health burden, and the development of advanced countermeasures to mitigate and prevent these injuries during automotive, sports, and military impact events requires an understanding of the intracranial mechanisms related to TBI. In this study, the efficacy of tissue-level injury metrics for predicting TBI was evaluated using finite element reconstructions from a comprehensive, multi-species TBI database. The database consisted of human volunteer tests, laboratory-reconstructed head impacts from sports, in vivo non-human primate (NHP) tests, and in vivo pig tests. Eight tissue-level metrics related to brain tissue strain, axonal strain, and strain-rate were evaluated using survival analysis for predicting mild and severe TBI risk. The correlation between TBI risk and most of the assessed metrics were statistically significant, but when injury data was analyzed by species, the best metric was often inconclusive and limited by the small datasets. When the human and animal datasets were combined, the injury analysis was able to delineate maximum axonal strain as the best predictor of injury for all species and TBI severities, with maximum principal strain as a suitable alternative metric. The current study is the first to provide evidence to support the assumption that brain strain response between human, pig, and NHP result in similar injury outcomes through a multi-species analysis. This assumption is the biomechanical foundation for translating animal brain injury findings to humans. The findings in the study provide fundamental guidelines for developing injury criteria that would contribute towards the innovation of more effective safety countermeasures.

Three dimensional finite element analysis used to study the influence of the stress and strain of the operative and adjacent segments through different foraminnoplasty technique in the PELD: Study protocol clinical trial (SPIRIT Compliant).

INTRODUCTION: Percutaneous endoscopic lumbar disectomy (PELD) is one of the most popular minimally invasive techniques of spinal surgery in recent years. At present, there are 2 main surgical approaches in PELD: foraminal approach and interlaminar approach. What's more, foraminoplasty is a necessary step for both approaches. However, there are few biomechanical studies on the formation of different parts of the intervertebral foramen. The aim of this study is to explore the effects of different foraminoplasty methods on the biomechanics of the corresponding and adjacent segments of the lumbar through a 3-dimensional finite element model analysis. METHODS: We established a normal 3-dimensional finite element mode of L3 to L5, simulated lumbar percutaneous endoscopy by doing cylindrical excision of bone whose diameter was 7.5 mm on the L5 superior articular process and the L4 inferior articular process, respectively, so that we obtained 3 models: the first one was normal lumbar model, the second one was the L4 inferior articular process shaped model, and the third one was the L5 superior articular process shaped model. We compared the biomechanics of the intervertebral disc of L3/4 and L4/5 when they were in the states of forward flexion, backward extension, left and right flexion, and left and right rotation on specific loading condition. DISCUSSION: If the outcomes indicate the trial is feasible and there is evidence that one of the foraminoplasty technique may make few differences in biomechanics of corresponding lumbar intervertebral disc, we will proceed to a definitive trial to test the best way to foraminplasty, which could make biomechanical influence as little as possible. TRIAL REGISTRATION: Chinese Clinical Trial Registry, ChiCTR1900026973. Registered on September 27, 2019.

Development and Validation of Finite Element Analysis Model (FEM) of Craniovertebral Junction: Experimental Biomechanical Cadaveric Study.

STUDY DESIGN: Experimental Cadaveric Biomechanical Study. OBJECTIVE: To establish an experimental procedure in cadavers to estimate joint stiffness/stability at craniovertebral junction (CVJ) region with various implant systems and to develop/validate an indigenous cost effective 3D-FEM (three-dimensional finite element model) of CVJ region. SUMMARY OF BACKGROUND DATA: Finite element analysis (FEM) tools can provide estimates of internal stress and strain in response to external loading of various implant systems used in CVJ fixations. METHODS: Experimental setup for conducting biomechanical movements on CVJ region of cadaver was developed using cost effective innovative tools. A manually actuated seven- degrees of freedom parallel manipulator motion testing system (MA7DPM) was designed and developed to impart designed trajectories and to conduct various biomechanical motion studies at CVJ region for the present study. RESULTS: FEM model of CVJ region was developed and subsequently validated with CVJ morphometry data of 15 human subjects of Asian origin. Validated FEM was subjected to force motion studies at the CVJ region. The force-motion maps obtained from the FEM studies were subsequently validated against biomechanical experiment results from cadaveric experiment results obtained with three different implant fixations. CONCLUSIONS: A cost effective biomechanical tool (which did not require decapitation of cadaveric head) and a customised chair (to place cadaver in sitting position during conduct of biomechanical movements simulating real-life scenario) was indigenously designed and developed. Developed biomechanical tool (MA7DPM) for this study is likely to be useful for stress-testing analysis of various implant systems for individual patients undergoing surgery at CVJ region in near future. LEVEL OF EVIDENCE: 5.

Validation and Comparison of Monte Carlo and Finite Element Method in Forward Modeling for Near Infrared Optical Tomography.

Near infrared optical tomography (NIROT) is a non-invasive imaging technique to provide physiological information e.g. the oxygenation of tissue. For image reconstruction in clinical and preclinical scenarios, models to accurately describe light propagation are needed. This work aims to assess the accuracy and efficiency of different models, which paves the way for an optimal design of model-based image reconstruction algorithms in NIROT for realistic tissue geometries and heterogeneities. Two popular simulators were evaluated: the Monte Carlo (MC) method based MCX and the finite element method (FEM) based Toast++. We compared simulated results with experimental data measured on a homogeneous silicone phantom with well-calibrated parameters. The laser light was focused on the center of the phantom surface and images were captured by a CCD camera in both reflection and transmission modes. For transmittance measurements, the two models showed good agreement. Both achieve a cosine similarity of ~99%. In contrast, for reflectance measurements, FEM results deviated more from the measured values than MC, yielding similarity values of 86% and 94%, respectively. This study recommends the use of MC for NIROT in reflection mode and both MC and FEM yield excellent results for transmission mode.

Scanner influence on the mechanical response of QCT-based finite element analysis of long bones.

Patient-specific QCT-based finite element (QCTFE) analyses enable highly accurate quantification of bone strength. We evaluated CT scanner influence on QCTFE models of long bones. A femur, humerus, and proximal femur without the head were scanned with K2HPO4 phantoms by seven CT scanners (four models) using typical clinical protocols. QCTFE models were constructed. The geometrical dimensions, as well as the QCT-values expressed in Hounsfield unit (HU) distribution was compared. Principal strains at representative regions of interest (ROIs), and maximum principal strains (associated with fracture risk) were compared. Intraclass correlation coefficients (ICCs) were calculated to evaluate strain prediction reliability for different scanners. Repeatability was examined by scanning the femur twice and comparing resulting QCTFE models. Maximum difference in geometry was 2.3%. HU histograms before phantom calibration showed wide variation between QCT scans; however, bone density histogram variability was reduced after calibration and algorithmic manipulation. Relative standard deviation (RSD) in principal strains at ROIs was <10.7%. ICC estimates between scanners were >0.9. Fracture-associated strain had 6.7%, 8.1%, and 13.3% maximum RSD for the femur, humerus, and proximal femur, respectively. The difference in maximum strain location was <2 mm. The average difference with repeat scans was 2.7%. Quantification of strain differences showed mean RSD bounded by ∼6% in ROIs. Fracture-associated strains in "regular" bones showed a mean RSD bounded by ∼8%. Strains were obtained within a ±10% difference relative to the mean; thus, in a longitudinal study only changes larger than 20% in the principal strains may be significant. ICCs indicated high reliability of QCTFE models derived from different scanners.

Differences in hemodynamic characteristics under high packing density between the porous media model and finite element analysis in computational fluid dynamics of intracranial aneurysm virtual treatment.

OBJECTIVE: This study aimed to compare the hemodynamic differences among no sac (NOS), porous media (POM) and finite element analysis (FEA) models to investigate the recurrence-related risks for coiled intracranial aneurysms (IAs). METHODS: The study enrolled 10 patients with 11 IAs who received simple coiling treatment and hemodynamic simulations were performed for all IAs using the above three models. Velocity, wall shear stress (WSS) and residual flow volume (RFV) were calculated and compared in order to assess the model differences for both aneurysm sac and parent vessel regions. RESULTS: For parent artery regions, all three models produced similar flow patterns and quantification analysis did not indicate differences in velocity and WSS (p>0.05). For aneurysm sac regions, the FEA model resulted in higher sac-maximized (0.18 m/s vs 0.06 m/s) and sac-averaged velocity (0.013 m/s vs 0.007 m/s), and higher sac-averaged (0.55 Pa vs 0.36 Pa, p=0.006) and sac-maximized WSS (12.1 Pa vs 6.6 Pa) than the POM model. The differences in RFV between the POM and FEA models under 11 different isovelocity thresholds (0.0001 m/s, 0.001 m/s, 0.002 m/s, 0.005 m/s, 0.01 m/s, 0.02 m/s, 0.05 m/s, 0.1 m/s, 0.2 m/s, 0.5 m/s, and 1 m/s) showed that the POM RFV was generally larger than those of the FEA model. CONCLUSIONS: Compared with the FEA model, the POM model provides a lower velocity and WSS and higher RFV for the aneurysm sac, which could lead to incorrect estimates of the recurrent risk of coiled IAs under high packing density.

Contribution of Lateral Decubitus Positioning and Cable Tensioning on Immediate Correction in Anterior Vertebral Body Growth Modulation.

STUDY DESIGN: Computational simulation of lateral decubitus and anterior vertebral body growth modulation (AVBGM). OBJECTIVES: To biomechanically evaluate lateral decubitus and cable tensioning contributions on intra- and postoperative correction. SUMMARY OF BACKGROUND DATA: AVBGM is a compression-based fusionless procedure to treat progressive pediatric scoliosis. During surgery, the patient is positioned in lateral decubitus, which reduces spinal curves. The deformity is further corrected with the application of compression by cable tensioning. Predicting postoperative correction following AVBGM installation remains difficult. METHODS: Twenty pediatric scoliotic patients instrumented with AVBGM were recruited. Three-dimensional (3D) reconstructions obtained from calibrated biplanar radiographs were used to generate a personalized finite element model. Intraoperative lateral decubitus position and installation of AVBGM were simulated to evaluate the intraoperative positioning and cable tensioning (100 / 150 / 200 N) relative contribution on intra- and postoperative correction. RESULTS: Average Cobb angles prior to surgery were 56° ± 10° (thoracic) and 38° ± 8° (lumbar). Simulated presenting growth plate's stresses were of 0.86 MPa (concave side) and 0.02 MPa (convex side). The simulated lateral decubitus reduced Cobb angles on average by 30% (thoracic) and 18% (lumbar). Cable tensioning supplementary contribution on intraoperative spinal correction was of 15%, 18%, and 24% (thoracic) for 100, 150, and 200 N, respectively. Simulated Cobb angles for the postoperative standing position were 39°, 37°, and 33° (thoracic) and 30°, 29°, and 28° (lumbar), respectively, whereas growth plate's stresses were of 0.54, 0.53, and 0.51 MPa (concave side) and 0.36, 0.53, and 0.68 MPa (convex side) for the three tensions. CONCLUSION: The majority of curve correction was achieved by lateral decubitus positioning. The main role of the cable was to apply supplemental periapical correction and secure the intraoperative positioning correction. Increases in cable tensioning furthermore rebalanced initially asymmetric compressive stresses. This study could help improve the design of AVBGM by understanding the contributions of the surgical procedure components to the overall correction achieved. LEVEL OF EVIDENCE: Level III.

Biomechanical Analysis of Lateral Lumbar Interbody Fusion Constructs with Various Fixation Options: Based on a Validated Finite Element Model.

BACKGROUND: Lateral lumbar interbody fusion using cage supplemented with fixation has been used widely in the treatment of lumbar disease. A combined fixation (CF) of lateral plate and spinous process plate may provide multiplanar stability similar to that of bilateral pedicle screws (BPS) and may reduce morbidity. The biomechanical influence of the CF on cage subsidence and facet joint stress has not been well described. The aim of this study was to compare biomechanics of various fixation options and to verify biomechanical effects of the CF. METHODS: The surgical finite element models with various fixation options were constructed based on computed tomography images. The lateral plate and posterior spinous process plate were applied (CF). The 6 motion modes were simulated. Range of motion (ROM), cage stress, endplate stress, and facet joint stress were compared. RESULTS: For the CF model, ROM, cage stress, and endplate stress were the minimum in almost all motion modes. Compared with BPS, the CF reduced ROM, cage stress, and endplate stress in all motion modes. The ROM was reduced by more than 10% in all motion modes except for flexion; cage stress and endplate stress were reduced more than 10% in all motion modes except for rotation-left. After interbody fusion, facet joint stress was reduced substantially compared with the intact conditions in all motion modes except for flexion. CONCLUSIONS: The combined plate fixation may offer an alternative to BPS fixation in lateral lumbar interbody fusion.

Prediction of fracture load and stiffness of the proximal femur by CT-based specimen specific finite element analysis: cadaveric validation study.

BACKGROUND: Finite element analysis (FEA) of the proximal femur has been previously validated with large mesh size, but these were insufficient to simulate the model with small implants in recent studies. This study aimed to validate the proximal femoral computed tomography (CT)-based specimen-specific FEA model with smaller mesh size using fresh frozen cadavers. METHODS: Twenty proximal femora from 10 cadavers (mean age, 87.1 years) were examined. CT was performed on all specimens with a calibration phantom. Nonlinear FEA prediction with stance configuration was performed using Mechanical Finder (mesh,1.5 mm tetrahedral elements; shell thickness, 0.2 mm; Poisson's coefficient, 0.3), in comparison with mechanical testing. Force was applied at a fixed vertical displacement rate, and the magnitude of the applied load and displacement were continuously recorded. The fracture load and stiffness were calculated from force-displacement curve, and the correlation between mechanical testing and FEA prediction was examined. RESULTS: A pilot study with one femur revealed that the equations proposed by Keller for vertebra were the most reproducible for calculating Young's modulus and the yield stress of elements of the proximal femur. There was a good linear correlation between fracture loads of mechanical testing and FEA prediction (R2 = 0.6187) and between the stiffness of mechanical testing and FEA prediction (R2 = 0.5499). There was a good linear correlation between fracture load and stiffness (R2 = 0.6345) in mechanical testing and an excellent correlation between these (R2 = 0.9240) in FEA prediction. CONCLUSIONS: CT-based specimen-specific FEA model of the proximal femur with small element size was validated using fresh frozen cadavers. The equations proposed by Keller for vertebra were found to be the most reproducible for the proximal femur in elderly people.

Contact stresses, pressure and area in a fixed-bearing total ankle replacement: a finite element analysis.

BACKGROUND: Mobile-bearing ankle implants with good clinical results continued to increase the popularity of total ankle arthroplasty to address endstage ankle osteoarthritis preserving joint movement. Alternative solutions used fixed-bearing designs, which increase stability and reduce the risk of bearing dislocation, but with a theoretical increase of contact stresses leading to a higher polyethylene wear. The purpose of this study was to investigate the contact stresses, pressure and area in the polyethylene component of a new total ankle replacement with a fixed-bearing design, using 3D finite element analysis. METHODS: A three-dimensional finite element model of the Zimmer Trabecular Metal Total Ankle was developed and assembled based on computed tomography images. Three different sizes of the polyethylene insert were modeled, and a finite element analysis was conducted to investigate the contact pressure, the von Mises stresses and the contact area of the polyethylene component during the stance phase of the gait cycle. RESULTS: The peak value of pressure was found in the anterior region of the articulating surface, where it reached 19.8 MPa at 40% of the gait cycle. The average contact pressure during the stance phase was 6.9 MPa. The maximum von Mises stress of 14.1 MPa was reached at 40% of the gait cycle in the anterior section. In the central section, the maximum von Mises stress of 10.8 MPa was reached at 37% of the gait cycle, whereas in the posterior section the maximum stress of 5.4 MPa was reached at the end of the stance phase. DISCUSSION: The new fixed-bearing total ankle replacement showed a safe mechanical behavior and many clinical advantages. However, advanced models to quantitatively estimate the wear are need. CONCLUSION: To the light of the clinical advantages, we conclude that the presented prosthesis is a good alternative to the other products present in the market.

Towards an in-plane methodology to track breast lesions using mammograms and patient-specific finite-element simulations.

In breast cancer screening or diagnosis, it is usual to combine different images in order to locate a lesion as accurately as possible. These images are generated using a single or several imaging techniques. As x-ray-based mammography is widely used, a breast lesion is located in the same plane of the image (mammogram), but tracking it across mammograms corresponding to different views is a challenging task for medical physicians. Accordingly, simulation tools and methodologies that use patient-specific numerical models can facilitate the task of fusing information from different images. Additionally, these tools need to be as straightforward as possible to facilitate their translation to the clinical area. This paper presents a patient-specific, finite-element-based and semi-automated simulation methodology to track breast lesions across mammograms. A realistic three-dimensional computer model of a patient's breast was generated from magnetic resonance imaging to simulate mammographic compressions in cranio-caudal (CC, head-to-toe) and medio-lateral oblique (MLO, shoulder-to-opposite hip) directions. For each compression being simulated, a virtual mammogram was obtained and posteriorly superimposed to the corresponding real mammogram, by sharing the nipple as a common feature. Two-dimensional rigid-body transformations were applied, and the error distance measured between the centroids of the tumors previously located on each image was 3.84 mm and 2.41 mm for CC and MLO compression, respectively. Considering that the scope of this work is to conceive a methodology translatable to clinical practice, the results indicate that it could be helpful in supporting the tracking of breast lesions.

Impact Response Comparison Between Parametric Human Models and Postmortem Human Subjects with a Wide Range of Obesity Levels.

OBJECTIVE: Field data analyses have shown that obesity significantly increases the occupant injury risks in motor vehicle crashes, but the injury assessment tools for people with obesity are largely lacking. The objectives of this study were to use a mesh morphing method to rapidly generate parametric finite element models with a wide range of obesity levels and to evaluate their biofidelity against impact tests using postmortem human subjects (PMHS). METHODS: Frontal crash tests using three PMHS seated in a vehicle rear seat compartment with body mass index (BMI) from 24 to 40 kg/m2 were selected. To develop the human models matching the PMHS geometry, statistical models of external body shape, rib cage, pelvis, and femur were applied to predict the target geometry using age, sex, stature, and BMI. A mesh morphing method based on radial basis functions was used to rapidly morph a baseline human model into the target geometry. The model-predicted body excursions and injury measures were compared to the PMHS tests. RESULTS: Comparisons of occupant kinematics and injury measures between the tests and simulations showed reasonable correlations across the wide range of BMI levels. CONCLUSIONS: The parametric human models have the capability to account for the obesity effects on the occupant impact responses and injury risks.

Biomechanical evaluation of a novel dualplate fixation method for proximal humeral fractures without medial support.

BACKGROUND: Comminuted fractures of the proximal humerus are generally treated with the locking plate system, and clinical results are satisfactory. However, unstable support of the medial column results in varus malunion and screw perforation. We designed a novel medial anatomical locking plate (MLP) to directly support the medial column. Theoretically, the combined application of locking plate and MLP (LPMP) would directly provide strong dual-column stability. We hypothesized that the LPMP could provide greater construct stability than the locking plate alone (LP), locking plate combined with a fibular graft (LPSG), and locking plate combined with a distal radius plate (LPDP). METHODS: LP, LPMP, LPSG, and LPDP implants were instrumented into the finite element model of a proximal humeral fracture. Axial, shear, and rotational loads were applied to the models under normal and osteoporotic bone conditions. The whole simulation was repeated five times for each fixator. To assess the biomechanical characteristics, the construct stiffness, fracture micromotion, stress distribution, and neck-shaft angle (NSA) were compared. RESULTS: The LPMP group showed significantly greater integral and regional construct stiffness, and endured less von Mises stresses, than the other three fixation methods. The stresses on the lateral locking plate were dispersed by the MLP. The LPMP group showed the least change in NSA. CONCLUSIONS: From the finite element viewpoint, the LPMP method provided both lateral and medial direct support. The LPMP system was effective in treating proximal humeral fracture with an unstable medial column.

Computer assisted evaluation of plate osteosynthesis of diaphyseal femur fracture considering interfragmentary movement: a finite element study.

A semi-automated workflow for evaluation of diaphyseal fracture treatment of the femur has been developed and implemented. The aim was to investigate the influence of locking compression plating with diverse fracture-specific screw configurations on interfragmentary movements (IFMs) with the use of finite element (FE) analysis. Computed tomography (CT) data of a 22-year-old non-osteoporotic female were used for patient specific modeling of the inhomogeneous material properties of bone. Hounsfield units (HU) were exported and assigned to elements of a FE mesh and converted to mechanical properties such as the Young's modulus followed by a linear FE analysis performed in a semi-automated fashion. IFM on the near and far cortex was evaluated. A positive correlation between bridging length and IFM was observed. Optimal healing conditions with IFMs between 0.5 mm and 1 mm were found in a constellation with a medium bridging length of 80 mm with three unoccupied screw holes around the fracture gap. Usage of monocortical screws instead of bicortical ones had negligible influence on the evaluated parameters when modeling non-osteoporotic bone. Minimal user input, automation of the procedure and an efficient computation time ensured quick delivery of results which will be essential in a future clinical application.

Análisis de la variación del comportamiento mecánico de la extremidad proximal del fémur mediante el método XFEM (eXtended Finite Element Method) / Analysis of mechanical behavior variation in the proximal femur using X-FEM (Extended Finite Element Method)

Introducción: El fémur humano ha sido ampliamente estudiado desde hace muchos años de manera experimental con análisis in vitro, y ahora, gracias a los avances de la informática, también se puede analizar de manera numérica. Algunos autores han demostrado la capacidad del método de los elementos finitos para predecir el comportamiento mecánico de este hueso, pero todavía son muchas las posibilidades recurriendo a la sinergia entre el método de los elementos finitos y ensayos experimentales. En este trabajo, por ejemplo, se estudia cómo afectan distintas simulaciones de osteoporosis a las cargas de fractura del fémur. El objetivo de este estudio es predecir la fractura de cadera, tanto la carga a la que se produce ésta como la propagación de la fisura sobre el hueso. Aplicando el método de los elementos finitos al campo de la biomecánica se puede realizar una simulación que muestre el comportamiento del hueso bajo diferentes condiciones de carga. Material y métodos: A partir de imágenes DICOM de tomografía computarizada de la extremidad proximal del fémur derecha de un varón se ha obtenido la geometría del hueso. Mediante un programa informático se han generado las propiedades mecánicas dependientes de la densidad mineral ósea de cada vóxel, y posteriormente se ha utilizado un código de elementos finitos para aplicar diferentes configuraciones de carga y estudiar los valores de fractura del hueso. El modelo numérico ha sido validado a través de un artículo de la literatura científica. Resultados: La carga de fractura en configuración de caída lateral es aproximadamente la mitad que la carga en el caso de la posición normal, lo cual concuerda con diferentes estudios experimentales presentes en la literatura científica. Además se han estudiado diferentes condiciones de carga en situaciones cotidianas, en las que se ha observado que la carga de fractura es mínima en la posición monopodal. También se han simulado condiciones de osteoporosis en las que se ha comprobado cómo desciende la carga de fractura al disminuir las propiedades mecánicas óseas. Conclusiones: Mediante el método de los elementos finitos en conjunto con una imagen médica DICOM es posible el estudio de la biomecánica de la cadera y obtener una estimación del fallo del hueso. Además se pueden aplicar diferentes configuraciones de carga y variar las propiedades mecánicas del hueso para simular el comportamiento mecánico de éste bajo condiciones osteoporóticas (AU)

Introduction: For years, the human femur has been extensively studied experimentally with in vitro analysis. Nowadays, with computer advances, it can also be analyzed numerically. Some authors report the usefulness of finite method in predicting the mechanical behavior of this bone. There are many possibilities using the synergy between the method finite element and experimental trials. In this paper, for example, we study how they affect different osteoporotic simulations involving femur fracture loads. The aim of this study is to predict hip fracture, both the load to which this occurs as the propagation of the crack in the bone. By applying the finite element method to the field of bio-mechanics, simulation can be carried out to show the behavior under different bone load conditions. Material and methods: Using DICOM images, CT scan of the proximal end of the right femur of a male has been obtained bone geometry. By a computer program they have been generated dependent mechanical properties of the BMD each voxel, and then used a finite code to apply different load configurations and study values bone fracture elements. The numerical model has been validated in the literature. Results: Load breaking in lateral fall configuration is approximately half the load in the case of the normal position, which agrees with different experimental studies published. In addition, we have studied various load conditions in everyday situations, where it was observed that the load fracture is minimal in mono-podal position. Osteoporotic conditions have also been simulated which confirmed that the load fracture has been reduced by decreasing mechanical properties. Conclusions: By using the finite element method in conjunction with DICOM medical imaging, it is possible to study the biomechanics of the hip and obtain an estimate of bone failure. In addition, different load configurations can be applied and vary the mechanical properties of bone to simulate the mechanical behavior of low osteoporotic conditions (AU)

Biomechanical effect of different femoral neck blade position on the fixation of intertrochanteric fracture: a finite element analysis.

Medial migration or cutout of the neck helical blade has commonly occurred in the treatment of trochanteric fracture of the femur. The position of the helical blade within the femoral head is one of the influencing factors that cause the blade to perforate the intact joint surface; however, the ideal placement of the helical blade is not currently known. A finite element model of a femur/nail construct was utilized to analyze five possible blade positions in the femoral head. Normal strain at the fracture surface, the minimum principal strain in the cancellous bone, and the von Mises stress in the implant itself were calculated and compared between different blade positions. The results showed that a large area of normal compressive strain at the fracture surface was observed in the inferior and posterior blade positions. The volume of cancellous bone strained to yielding in the femoral head and neck was lower for the inferior and posterior positions, whereas it was the highest for the superior position. The inferior and posterior positions had lower von Mises stress in the implant itself. The inferior and posterior positions may be the ideal position for the intramedullary nail with a helical neck blade.

Biomechanical analysis of a temporomandibular joint condylar prosthesis during various clenching tasks.

The objective of this study was to evaluate the effect of clenching tasks on the stress and stability of a temporomandibular joint (TMJ) condylar prosthesis, as well as on the stress and strain in the whole mandible and bone surrounding three screws. Three-dimensional finite element models of the mandible and a TMJ condylar prosthesis using three screws were established. Six static clenching tasks were simulated in this study: incisal clench (INC), intercuspal position (ICP), right unilateral molar clench (RMOL), left unilateral molar clench (LMOL), right group function (RGF), and left group function (LGF). Based on the simulation of the six clenching tasks, none of the inserted screws or the TMJ condylar prosthesis were broken. In addition, the stability of the TMJ condylar prosthesis was sufficiently high for bone ongrowth. For the whole mandibular bone, the maximum von Mises stress and von Mises strain observed in the cortical bone and cancellous bone were yielded by the ICP and RMOL, respectively. For the bone surrounding the inserted screws, the maximum von Mises stress and von Mises strain in both the cortical bone and cancellous bone were yielded by the LMOL. Clenching tasks had significant effects on the stress distribution of the TMJ condylar prosthesis, as well as on the stress and strain distribution of the whole mandible and the bone surrounding the inserted screws.

Consideraciones en la definición del modelo específico al paciente de la tibia / Considerations about the definition of a patient specific model of the tibia

INTRODUCCIÓN: los análisis por elementos finitos se usan para entender y predecir los procesos biológicos. En la biomecánica ortopédica, los modelos específicos al paciente se generan a partir de Tomografía Computarizada y empleados en la toma de decisiones médicas. Algunos procesos correctivos ortopédicos pueden simularse a través, de los análisis por elementos finitos. Para obtener modelos biomecánicos confiables, es muy recomendable reducir los errores en la definición del modelo en la etapa de pre-procesamiento del análisis por elementos finitos. OBJETIVO: analizar la influencia de la densidad del mallado y las propiedades mecánicas durante la definición del modelo específico al paciente en los resultados del análisis por elementos finitos. MÉTODOS: se empleó el Método de Elementos Finitos en la simulación de la tibia a compresión. La geometría de la tibia del paciente se generó a partir de Tomografía Computarizada. Se emplearon mallas con tamaño de elementos no uniforme y uniforme. Al modelo se le aplicaron propiedades mecánicas homogéneas y no homogéneas. RESULTADOS: los elementos de bajo orden convergen a la solución, las tensiones para las mallas con estos elementos son inferiores a las correspondientes las mallas con elementos de tamaño uniforme y de alto orden. Por otra parte, las propiedades mecánicas no homogéneas reducen la diferencia en el cálculo de las tensiones. CONCLUSIONES: para obtener modelos específicos al paciente confiables se recomienda, generar la geometría del hueso con superficies suavisadas, controlar la calidad de la malla superficial, usar propiedades mecánicas no homogéneas, y utilizar la malla generada directo en Abaqus con elementos de bajo orden y tamaño no uniforme.

INTRODUCTION: finite element analysis is used to understand and predict biological processes. In orthopedic biomechanics patient specific models are generated by computed tomography and used for medical decision making. Some corrective orthopedic processes may be simulated by means of finite element analysis. In order to obtain reliable biomechanical models it is highly advisable to reduce the number of errors in the definition of the model during pre-processing of the finite element analysis. OBJECTIVE: analyze the influence of mesh density and mechanical properties on the results obtained by finite element analysis during the stage of definition of the patient specific model. METHODS: the finite element method was used to simulate tibial compression. The geometry of the patient's tibia was generated by computed tomography. Meshes were used with non-uniform and uniform element sizes. Homogeneous and non-homogeneous mechanical properties were applied to the model. RESULTS: low-order elements converge to the solution. Tensions for meshes with these elements are lower than those for meshes with uniform size and high-order elements. On the other hand, non-homogeneous mechanical properties reduce the difference in the estimation of tensions. CONCLUSIONS: to obtain reliable patient specific models it is recommended to generate the bone geometry with softened surfaces, control the quality of the surface mesh, use non-homogeneous mechanical properties, and use the mesh generated directly on Abaqus with low-order elements and non-uniform size.

Consideraciones en la definición del modelo específico al paciente de la tibia / Considerations about the definition of a patient specific model of the tibia

Introducción: los análisis por elementos finitos se usan para entender y predecir los procesos biológicos. En la biomecánica ortopédica, los modelos específicos al paciente se generan a partir de Tomografía Computarizada y empleados en la toma de decisiones médicas. Algunos procesos correctivos ortopédicos pueden simularse a través, de los análisis por elementos finitos. Para obtener modelos biomecánicos confiables, es muy recomendable reducir los errores en la definición del modelo en la etapa de pre-procesamiento del análisis por elementos finitos.Objetivo: analizar la influencia de la densidad del mallado y las propiedades mecánicas durante la definición del modelo específico al paciente en los resultados del análisis por elementos finitos. Métodos: se empleó el Método de Elementos Finitos en la simulación de la tibia a compresión. La geometría de la tibia del paciente se generó a partir de Tomografía Computarizada. Se emplearon mallas con tamaño de elementos no uniforme y uniforme. Al modelo se le aplicaron propiedades mecánicas homogéneas y no homogéneas. Resultados: los elementos de bajo orden convergen a la solución, las tensiones para las mallas con estos elementos son inferiores a las correspondientes las mallas con elementos de tamaño uniforme y de alto orden. Por otra parte, las propiedades mecánicas no homogéneas reducen la diferencia en el cálculo de las tensiones. Conclusiones: para obtener modelos específicos al paciente confiables se recomienda, generar la geometría del hueso con superficies suavisadas, controlar la calidad de la malla superficial, usar propiedades mecánicas no homogéneas, y utilizar la malla generada directo en Abaqus con elementos de bajo orden y tamaño no uniforme(AU)

Introduction: finite element analysis is used to understand and predict biological processes. In orthopedic biomechanics patient specific models are generated by computed tomography and used for medical decision making. Some corrective orthopedic processes may be simulated by means of finite element analysis. In order to obtain reliable biomechanical models it is highly advisable to reduce the number of errors in the definition of the model during pre-processing of the finite element analysis. Objective: analyze the influence of mesh density and mechanical properties on the results obtained by finite element analysis during the stage of definition of the patient specific model. Methods: the finite element method was used to simulate tibial compression. The geometry of the patients tibia was generated by computed tomography. Meshes were used with non-uniform and uniform element sizes. Homogeneous and non-homogeneous mechanical properties were applied to the model. Results: low-order elements converge to the solution. Tensions for meshes with these elements are lower than those for meshes with uniform size and high-order elements. On the other hand, non-homogeneous mechanical properties reduce the difference in the estimation of tensions. Conclusions: to obtain reliable patient specific models it is recommended to generate the bone geometry with softened surfaces, control the quality of the surface mesh, use non-homogeneous mechanical properties, and use the mesh generated directly on Abaqus with low-order elements and non-uniform size(AU)