The CT-Based Patient Specific Hip Joint 3D-Modeling; Potential to Create a Virtual Alignment

Finite element study of the proximal femur with retained trochanteric gamma nail and after removal of nail

The purpose of the study presented here is to establish a finite element (FE) model to simulate the wear process of a polymer-to-polymer sliding system. Two polymer components which are named as slider and ground are operated on the slant-horizontal contact region reciprocally. A total of 3500 cycles was conducted. The sliding wear motion of the real product is simplified into a two-dimensional model for FE simulation. According to the requirement of the actual application, we are interested in one of effects of the wear performance - the horizontal driving force (HDF) which is applied on the slider component to generate the sliding motion [1]. Two commercial polymer materials have been considered in this paper: 33% glass reinforced, heat stabilised black nylon copolymer resin and BK15945% glass reinforced modified polyethylene terephthalate. For the solution of the wear simulation and prediction, the FE analysis software ANSYS and some mathematic wear equations have been used to build an analysis procedure for this polymer contact structure. First, the FE simulation model is applied to gain the contact surface pressure distribution. Then, the mathematical wear equations are used to calculate the wear depth along the wear sliding surface. Next, the contact surface shape with the wear depth datum is modified. Now, a new model with the upgraded geometry is carried out. Repeating the above four analysis steps, the whole wear process will be represented in the simulation model. In this paper, a series of simulations are performed for every 500 operating cycles for a total of 3500 cycles. The major task of ANSYS is to plot the stress and pressure distribution of the fields of contact and the HDF variation with the sliding motion. Both components have been map-meshed and the two-dimensional structure solid element which is designed as PLANE42 in ANSYS is used for the solid body of the model. The contact pair is described by the flexible surface-to-surface contact elements CONTAC172 and the flexible surface-to-surface target element TARGE169. Twenty load steps across the contact surface are setup for gathering the necessary datum (stress, surface pressure, reaction force, etc). To get a better convergence of the iterative solution, two treatments are also configured. First, the calculation algorithm the pure penalty is switched to the augmented Lagrange. Second, the contact stiffness parameter is adjusted to balance the precise result and the acceptable convergence. Furthermore, an approximate method is introduced to simplify the contact geometry of the upgraded model which is generated by applying the wear depth to the original model. Wear equations employed in this paper are proposed by Archard [2] and Yang [3]. The Archard's equation considers the wear in a steady-state and Yang's equation involves the running-in (transient) wear phase. Both of them based on metal materials and have been extended for the application of polymer materials by Ashraf [4]. A number of simulation results are obtained from a sequence of finite element analyses by progressively removing material and are compared with physical testing results. The simulation results of the horizontal force in an operation cycle of 3500, shows that the force increasing along the slant sliding surface and the position where the peak force occurred are very similar to the experiment. The plot of the von-Mises stress distribution from the FE simulation indicates the maximum stress appears at the top of the slant contact surface. Therefore the maximum wear depth should occur at this region. The variation of the peak horizontal force during the 3500 wear cycles demonstrate a dramatic reduction in peak force over the first 1500 cycles, followed by a gradual decrease in the rate of reduction. For subsequent cycles, the force has decreased continually but at a slower rate. It is found that the FE results have the similar trend with the experimental measured results which support the possibility of using the approximate FE simulation model to estimate the wear process in this particular structure. There are several ways to gain more accurate results. First, refine the model mesh and the load steps. Second, abandon the approximate method which is used to simplify the contact surface after wear. It makes the simulation condition more similar to the actual wear status than the approximate model. Third, apply FE simulation for more wear operation cycles. Due to the model simplifications and the input data of the material properties, this simulation model is only effective for this particular product. Further research will be carried out to extend it to more general the application.

This study presents the development of refined three dimensional (3D) finite element (FE) models with the ability to reliably simulate the mechanical behavior of full-scale bolted T-stub connections. FE models incorporated material nonlinearity, geometric nonlinear behavior, several contact interactions between faying surfaces, and prescribed displacements for generating initial bolt pretension. These FE models were used to compare experimental test results, which verify that advanced FE modeling methods make a notable contribution to reproducing the overall behavior of connections and components accurately, including the moment-rotation curves. In addition, the FE models provide some useful information which is difficult to obtain during physical testing, i.e., the distribution of stress and strain, friction forces between shear faying surfaces, and bolt reaction forces. The validated FE models are also used for additional parametric studies so as to comprehensively understand their response mechanisms. Moreover, the observation of FE analysis results supports the statement that connection models presented herein were designed to reach the yielding of connection components when the structural beam produces its full plastic moment at the plastic hinge.

This paper presents a surface contact static stress of a spur gear system combined with dynamic characteristic using transient Finite Element Method (FEM). Traditionally, the static stress analysis is done separately with dynamic properties due to limitation of complex equation and avoiding of error occurred. However, in this paper, static stress information is combined with the dynamic mechanism due to the time consuming during the design and analysis stage. A transient FEM analysis is carried out to formulate and solve large systems of algebraic equations in order to obtain a relationship between the contact parameter and the kinematics function. The methodology of the research is started with static stress analysis on tooth surface contact of a pair of the spur gear. Finite element modeling is run by choosing a certain static condition. The loading conditions are applied suitable with the gear mechanism. Degree of freedom controlled is based on the transmission system. The process is repeated until diagnosing work is satisfied. The result of the surface contact stress is visualized at each condition. Modeling of spur gear system is continued by combining stress analysis with dynamic characteristic via transient finite element method. Analysis of gear mechanism is obtained by investigate the stress distribution on real time application. Time range is set at the beginning of the analysis. Duration of the analysis is depended on a time frame chosen. By the transient FEM analysis, the stress occur at each step of the work cycle is performed. Results of the kinematics functions are derived and qualitative kinematics variations due to contact changes in time-step domain is identified. The simulation results from static and transient FEM are compared due to the validating procedure. The finite element results are in good agreement compared with the theory calculation.

Finite element (FE) models are very efficient tools to study internal stresses in human structures that induce severe pressure sores. Unfortunately, methods currently used to generate FE models are not suitable for clinical application involving wheelchair users. A clinical-oriented method, based on calibrated-biplanar radiographs, was therefore developed to generate a subject-specific FE model of the buttocks in a non-weighted sitting position. The model was then used to analyze the stress distribution within the buttocks and compare two wheelchair seat cushions designs. Additional radiographs and pressure measurements in a weighted sitting position were acquired to validate the FE model experimentally. Results from the FE model were in good agreement with experimental data and related literature. An internal peak pressure of 45.3 kPa was observed while seated on a flat foam cushion, corresponding to an interface pressure of 23.6 kPa. Both pressures occurred underneath the ischial tuberosities. When compared to the flat foam cushion, the contoured foam cushion reduced internal and interface peak pressures by 18% and 33%, respectively. The method developed in this study has a great potential for clinical use. The FE model, by predicting realistic stress distributions, allows for the selection of a convenient wheelchair seat cushion.

Pre-operative planning help the surgeon in taking the proper clinical decision. The ultimate goal of this work is to develop numerical models that allow the surgeon to estimate the primary stability during the pre-operative planning session. The present study was aimed to validate finite-element (FE) models accounting for patient and prosthetic size and position as planned by the surgeon. For this purpose, the FE model of a cadaveric femur was generated starting from the CT scan and the anatomical position of a cementless stem derived by a skilled surgeon using a pre-operative CT-based planning simulation software. In-vitro experimental measurements were used as benchmark problem to validate the bone–implant relative micromotions predicted by the patient-specific FE model. A maximum torque in internal rotation of 11.4 Nm was applied to the proximal part of the hip stem. The error on the maximum predicted micromotion was 12% of the peak micromotion measured experimentally. The average error over the entire range of applied torques was only 7% of peak measurement. Hence, the present study confirms that it is possible to accurately predict the level of primary stability achieved for cementless stems using numerical models that account for patient specificity and surgical variability.

Non-linear 3D finite element analysis of precast reinforced concrete Beam-Column joint under monotonic static load

Running-in of two fresh and unworn surfaces in contact is a transient phase where friction and wear vary considerably in time. During running-in the surface properties of the components are adjusted. If the initial surface roughness of the rubbing surfaces is correctly chosen, the running-in changes into the steady-state phase. At this stage, the rubbing surfaces are in general smoother and their wear rate is low and constant. On the other hand, an inappropriate choice of roughness may lead to a rapid deterioration of the rubbing surfaces. The micro-geometry of the surface is an important factor in determining the life of mechanical components. During the running-in phase, the highest asperities are “flattened”, thereby increasing the number of asperities in contact and, as a result, increasing the load-carrying capacity of the surface. Fundamental studies that attempt to consider the details of running-in phenomena are relatively rare. This research is conducted with the aim of exploring the running-in phase for the rolling, sliding and rolling-sliding contact. Finite element simulations are conducted to calculate the stress distributions for the three types of contact motions during the running-in phase. The evolution of the contact pressure for a certain rolling or sliding distance is studied to unravel the running-in phase. During running-in of rolling contacts, the change in the surface topography results in the transformation from a rough surface to a smoother surface: the flattening of the high asperities induces a reduction in surface roughness. This flattening of asperities is due to plastic deformation and causes a higher equivalent residual stress at the surface. The transition of the running-in phase to the steady-state phase of a rolling contact is governed by the transition of plastic to elastic deformation on roughness level. In sliding contacts, the proposed finite element (FE) model combined with the Archard wear equation successfully predicts the contact pressure evolution and change in the topography on a macroscopic point of view. The change in the topography in a sliding contact is mainly caused by wear. A new FE model, with respect to the artificial and real surface roughness, is discussed. It is found that the proposed model is a useful tool to study the running-in of a surface on roughness level. The changes on macroscopic and on microscopic level of the surface are also discussed in the running-in of rolling-sliding contacts considering two aspects: wear and plastic deformation. The geometrical change of the contacting surface due to wear is predicted using the present FEM model, combined with the Archard wear equation, and has been compared with results from the literature. Calculations are performed to predict the wear of an artificial rough hemisphere in rolling-sliding contact with a smooth cylinder. The model also predicts the change of real rough surfaces which were in good agreement with the experimental results. The change of a rough surface, represented by an arithmetic average surface roughness, Ra, is predicted for lubricated rolling-sliding contacts using the load-sharing concept. The results obtained are in good agreement with experimental results. A FEM based model has been developed to study the running-in of rolling, sliding and rolling-sliding contacts on macroscopic level as well as on roughness level. However, the transition between the running-in phase and the steady-state phase for sliding and rolling-sliding contacts cannot be determined by considering only one single parameter; likewise for the rolling contact situation. Wear is an ongoing process.

Introduction: Partial fibulectomy has been suggested for patients who encounter with severe varus/valgus or ununited fractures of the tibia. This study develops a finite element (FE) model of partial fibulectomy to study stress distribution in the tibiofemoral joint. Materials and Methods: A 3D magnetic resonance imaging (MRI)-based of tibiofemoral joint and FE model was developed for study from a man volunteer with the normal left knee. Components consisted of the exact geometry of femur, tibia, fibula, meniscus, and articular cartilages. Firstly, geometries were constructed in Mimics and then exported to Rapid Forming XOR2 and finally, the Computer-aided design (CAD) model was analyzed in ABAQUS 6.10. Mechanical properties of the model for soft tissues were considered to be linear elastic, isotropic and homogenous and for bony parts were considered to be rigid. Results: Model predictions were compared with normal one and used to derive stress distribution under physiological loading for standing in quasi- static condition. The results showed load transferring toward lateral condyle due to partial fibulectomy. The variation of stress distribution would increase the risk of osteoarthritis. Conclusion: Our results have been predicted that partial fibulectomy could be an unknown risk factor for osteoarthritis and the model could be used for extended similar studies.

Prophylactic augmentation implants in the proximal femur for hip fracture prevention: An in silico investigation of simulated sideways fall impacts

Background. Robotic-assisted thoracic surgery (RATS) is now standard for lung cancer treatment, offering advantages over traditional methods. However, RATS’s minimally invasive approach poses challenges like limited visibility and tactile feedback, affecting surgeons’ navigation through com-plex anatomy. To enhance preoperative familiarization with patient-specific anatomy, we devel-oped a virtual reality (VR) surgical navigation system. Using head-mounted displays (HMDs), this system provides a comprehensive, interactive view of the patient’s anatomy pre-surgery, aiming to improve preoperative simulation and intraoperative navigation. Methods. We integrated 3D data from preoperative CT scans into Perspectus VR Education software, displayed via HMDs for in-teractive 3D reconstruction of pulmonary structures. This detailed visualization aids in tailored preoperative resection simulations. During RATS, surgeons access these 3D images through Tile-ProTM multi-display for real-time guidance. Results. The VR system enabled precise visualization of pulmonary structures and lesion relations, enhancing surgical safety and accuracy. The HMDs offered true 3D interaction with patient data, facilitating surgical planning. Conclusions. VR sim-ulation with HMDs, akin to a robotic 3D viewer, offers a novel approach to developing robotic surgical skills. Integrated with routine imaging, it improves preoperative planning, safety, and accuracy of anatomical resections. This technology particularly aids in lesion identification in RATS, optimizing surgical outcomes.

This article aims to investigate the contact characteristics of mortise and tenon (M&T) joints in the traditional timber structures. In particular, the normal embedded compressive contact between contact surfaces of M&T joint was investigated. Based on basic contact theory and contact characteristics between mortise and tenon, a normal elasto-plastic contact model, which can reflect the real normal contact behavior of M&T joints in traditional wooden structures, was proposed. Coulomb friction contact was utilized to describe the tangential slipping characteristics of the contact surfaces. Micro-morphology scanning tests of wood samples with different roughness were carried out to determine the parameters involved in the normal contact model. The normal contact model subroutine of M&T joint was compiled by FORTRAN language, implemented into ABAQUS through user-defined interface (UINTER). Then the proposed model was verified by shear tests of wood contact surfaces considering different normal pressures. Finally, a finite element model (FEM) of straight tenon joint subjected to cyclic reversed loading, based on the proposed normal elasto-plastic contact model, was developed, and a FEM considering normal “hard contact” between the contact surfaces, was also performed. The simulation results were validated by the experimental results. Results showed that the user-defined normal elasto-plastic contact FEM was more in line with the actual force state and mechanical behavior of M&T joints, which can more accurately predict the failure modes and simulate the hysteretic behavior of M&T joints, compared to the FEM considering normal “hard contact” of the contact surfaces.

In this paper, a simple and practical finite element (FE) model coupled to a quasi-brittle damage law to describe the initiation and progressive propagation of multiple cracks based on element deletion is developed to predict the complete force-displacement curve and the fracture pattern of a human proximal femur under quasi-static load. The motivation of this work was to propose a FE model for possible clinical use with a good compromise between complexity and capability of the simulation. The model considers a limited number of parameters that can predict proximal femur fracture in more adequate physical terms than criteria-based fracture models. Based on experimental results, different damage laws for cortical and trabecular bone are proposed to describe inelastic damage accumulation under excessive load. When the damage parameter reaches its critical value inside an element of the mesh, its stiffness matrix is set to zero, leading to the redistribution of the stress state in the vicinity of the damaged zone (crack initiation). Once a crack is initiated, the propagation direction is simulated by the propagation of the broken elements of the mesh. To illustrate the potential of the proposed approach, the left femur of a male (age 61) previously investigated by Keyak and Falkinstein (Model B: male, age 61) was simulated till complete fracture under one-legged stance quasi-static load. The proposed finite element model leads to more physical results concerning the shape of the force-displacement curve (yielding and fracturing) and the profile of the fractured edge.

IntroductionGeometrical designs of nickel-titanium (NiTi) rotary instruments have a considerable influence on their mechanical performance, and thereby have the tendency to fracture.AimTo evaluate the effect of cross-sectional geometry, pitch, taper, and off-center cross-section on the stress distribution in NiTi instruments under bending and torsion conditions using finite element analysis (FEA).Materials and methodsEleven theoretical three-dimensional finite element (FE) models of rotary instruments were constructed and divided according to the geometric design tested into; group 1 (cross-section geometry): four FE models with four different cross-section designs (triangle, convex triangular, parallelogram, and rectangle). Group 2 (pitch): three FE models with different pitches (5, 10, and 15 threads). Group 3 (taper): two FEA models with two different tapers (0.04 and 0.06). Group 4 (centering): two FEA models (off-centered and centered cross section). The behavior of the instrument under bending and torsional conditions was analyzed mathematically in SolidWorks software package.ResultsThe pattern of stress distribution was varied by altering cross-sectional geometry, pitch, taper, and off-center cross section.ConclusionNo single geometrical design could be beneficial for all stress conditions. To decrease the stress accumulation during bending of rotary files in curved root canals, the rotary NiTi instruments should be designed with rectangle cross-section configuration, low pitch, reduced taper, and with centered cross section. This design improved the flexibility of rotary NiTi instruments. However, to improve the torsional resistance during root canal preparation of narrow canals, the file should be designed with parallelogram cross-sectional configuration, low pitch, increased taper, and eccentric cross-section design.

A finite element (FE) model has been developed based upon the recently measured micro-scale morphological, chemical and mechanical properties of dentin-adhesive (d-a) interfaces using confocal Raman microspectroscopy and scanning acoustic microscopy (SAM). The results computed from this FE model indicated that the stress distributions and concentrations are affected by the micro-scale elastic properties of various phases composing the d-a interface. However, these computations were performed assuming isotropic material properties for the d-a interface. The d-a interface components, such as the peritubular and intertubular dentin, the partially demineralized dentin and the so-called "hybrid layer" adhesive-collagen composite, are probably anisotropic. In this paper, the FE model is extended to account for the probable anisotropic properties of these d-a interface phases. A parametric study is performed to study the effect of anisotropy on the micromechanical stress distributions in the hybrid layer and the peritubular dentin phases of the d-a interface. It is found that the anisotropy of the phases affects the region and extent of stress concentration as well as the location of the maximum stress concentrations. Thus, the anisotropy of the phases could effect the probable location of failure initiation, whether in the peritubular region or in the hybrid layer.