This study investigated the effect of implant thickness and material on deformation and stress distribution within different components of cranial implant assemblies. Using the finite element method, two cranial implants, differing in size and shape, and thicknesses (1, 2, 3 and 4 mm, respectively), were simulated under three loading scenarios. The implant assembly model included the detailed geometries of the mini-plates and micro-screws and was simulated using a sub-modeling approach. Statistical assessments based on the Design of Experiment methodology and on multiple regression analysis revealed that peak stresses in the components are influenced primarily by implant thickness, while the effect of implant material is secondary. On the contrary, the implant deflection is influenced predominantly by implant material followed by implant thickness. The highest values of deformation under a 50 N load were observed in the thinnest (1 mm) Polymethyl Methacrylate implant (Small defect: 0.296 mm; Large defect: 0.390 mm). The thinnest Polymethyl Methacrylate and Polyether Ether Ketone implants also generated stresses in the implants that can potentially breach the materials' yield limit. In terms of stress distribution, the change of implant thickness had a more significant impact on the implant performance than the change of Young's modulus of the implant material. The results indicated that the stresses are concentrated in the locations of fixation; therefore, the detailed models of mini-plates and micro-screws implemented in the finite element simulation provided a better insight into the mechanical performance of the implant-skull system.

• Klíčová slova
• 3D printing, Cranioplasty, Finite element method, Mechanical properties, Skull implant,
• MeSH
• analýza metodou konečných prvků * MeSH
• experimentální implantáty * MeSH
• lebka * MeSH
• lidé MeSH
• mechanický stres * MeSH
• počítačová simulace * MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

BACKGROUND: The aim of this paper was to design a finite element model for a hinged PROSPON oncological knee endoprosthesis and to verify the model by comparison with ankle flexion angle using knee-bending experimental data obtained previously. METHOD: Visible Human Project CT scans were used to create a general lower extremity bones model and to compose a 3D CAD knee joint model to which muscles and ligaments were added. Into the assembly the designed finite element PROSPON prosthesis model was integrated and an analysis focused on the PEEK-OPTIMA hinge pin bushing stress state was carried out. To confirm the stress state analysis results, contact pressure was investigated. The analysis was performed in the knee-bending position within 15.4-69.4° hip joint flexion range. RESULTS: The results showed that the maximum stress achieved during the analysis (46.6 MPa) did not exceed the yield strength of the material (90 MPa); the condition of plastic stability was therefore met. The stress state analysis results were confirmed by the distribution of contact pressure during knee-bending. CONCLUSION: The applicability of our designed finite element model for the real implant behaviour prediction was proven on the basis of good correlation of the analytical and experimental ankle flexion angle data.

• Klíčová slova
• Endoprosthesis, Finite element method, Finite element model, Knee joint, Knee-bending, Oncological implant,
• MeSH
• algoritmy MeSH
• analýza metodou konečných prvků MeSH
• analýza selhání vybavení MeSH
• biologické modely * MeSH
• design s pomocí počítače MeSH
• kolenní kloub patofyziologie   MeSH
• kosterní svaly patofyziologie   MeSH
• lidé MeSH
• mechanický stres MeSH
• modul pružnosti MeSH
• nádory kostí patofyziologie   chirurgie   MeSH
• pevnost v tahu MeSH
• pevnost v tlaku MeSH
• počítačová simulace MeSH
• protetické vybavení metody   MeSH
• protézy - design MeSH
• protézy kolene * MeSH
• šlachy patofyziologie   MeSH
• software MeSH
• svalová kontrakce MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• validační studie MeSH

Biomechanical models based on the finite element method have already shown their potential in the simulation of the mechanical behaviour of cells. For instance, development of atherosclerosis is accelerated by damage of the endothelium, a monolayer of endothelial cells on the inner surface of arteries. Finite element models enable us to investigate mechanical factors not only at the level of the arterial wall but also at the level of individual cells. To achieve this, several finite element models of endothelial cells with different shapes are presented in this paper. Implementing the recently proposed bendotensegrity concept, these models consider the flexural behaviour of microtubules and incorporate also waviness of intermediate filaments. The suspended and adherent cell models are validated by comparison of their simulated force-deformation curves with experiments from the literature. The flat and dome cell models, mimicking natural cell shapes inside the endothelial layer, are then used to simulate their response in compression and shear which represent typical loads in a vascular wall. The models enable us to analyse the role of individual cytoskeletal components in the mechanical responses, as well as to quantify the nucleus deformation which is hypothesized to be the quantity decisive for mechanotransduction.

• MeSH
• analýza metodou konečných prvků MeSH
• buněčný převod mechanických signálů * MeSH
• endoteliální buňky metabolismus   MeSH
• lidé MeSH
• mikrotubuly MeSH
• modely kardiovaskulární * MeSH
• počítačová simulace * MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

Patient-specific approach is gaining a wide popularity in computational simulations of biomechanical systems. Simulations (most often based on the finite element method) are to date routinely created using data from imaging devices such as computed tomography which makes the models seemingly very complex and sophisticated. However, using a computed tomography in finite element calculations does not necessarily enhance the quality or even credibility of the models as these depend on the quality of the input images. Low-resolution (medical-)CT datasets do not always offer detailed representation of trabecular bone in FE models and thus might lead to incorrect calculation of mechanical response to external loading. The effect of image resolution on mechanical simulations of bone-implant interaction has not been thoroughly studied yet. In this study, the effect of image resolution on the modeling procedure and resulting mechanical strains in bone was analyzed on the example of cranial implant. For this purpose, several finite element models of bone interacting with fixation-screws were generated using seven computed tomography datasets of a bone specimen but with different image resolutions (ranging from micro-CT resolution of 25 μm to medical-CT resolution of 1250 μm). The comparative analysis revealed that FE models created from images of low resolution (obtained from medical computed tomography) can produce biased results. There are two main reasons: 1. Medical computed tomography images do not allow generating models with complex trabecular architecture which leads to substituting of the intertrabecular pores with a fictitious mass; 2. Image gray value distribution can be distorted resulting in incorrect mechanical properties of the bone and thus in unrealistic or even completely fictitious mechanical strains. The biased results of calculated mechanical strains can lead to incorrect conclusion, especially when bone-implant interaction is investigated. The image resolution was observed not to significantly affect stresses in the fixation screw itself; however, selection of bone material representation might result in significantly different stresses in the screw.

• Klíčová slova
• Bone tissue, Computational modeling, Computed tomography, Finite element method, Image resolution, Mechanical strain,
• MeSH
• analýza metodou konečných prvků MeSH
• biomechanika MeSH
• kosti a kostní tkáň * MeSH
• kostní šrouby * MeSH
• lidé MeSH
• mechanický stres MeSH
• rentgenová mikrotomografie MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The present study utilises the extended finite element method (XFEM) to model fibre-reinforced composites, with a focus on crack initiation and propagation. Silicon nitride-based ceramics were selected as a model material; they represent a broad class of short fibre ceramics and have received a lot of attention in recent decades. Some peculiarities when using the XFEM, including its selected modifications, are discussed in response to applied external stresses, mainly in the viscoelastic range. Promising approaches are recommended, which lead to a more accurate description of these materials under operating conditions, focusing on the correct calculation of the macroscopic stress ahead of the propagating crack front. The authors draw on years of experience with the material and investigate the possible improvements and modifications to the XFEM.

• Klíčová slova
• computational modelling, crack initiation and development, extended finite element method (XFEM), fibre composites,
• Publikační typ
• časopisecké články MeSH

BACKGROUND AND OBJECTIVE: Total knee arthroplasty (TKA) with modern all-polyethylene tibial (APT) components has shown high long-term survival rates and comparable results to those with metal-backed tibial components. Nevertheless, APT components are primarily recommended for older and low-demand patients. There are no evidence-based biomechanical guidelines for orthopaedic surgeons to determine the appropriate lower age limit for implantation of APT components. A biomechanical analysis was assumed to be suitable to evaluate the clinical results in patients under 70 years. The scope of this study was to determine biomechanically the appropriate lower age limit for implantation of APT components. METHODS: To generate data of the highest possible quality, the geometry of the computational models was created based on computed tomography (CT) images of a representative patient. The cortical bone tissue model distinguishes the change in mechanical properties described in three parts from the tibial cut. The cancellous bone material model has a heterogeneous distribution of mechanical properties. The values used to determine the material properties of the tissues were obtained from measurements of a CT dataset comprising 45 patients. RESULTS: Computational modeling showed that in the majority of the periprosthetic volume, the von Mises strain equivalent ranges from 200 to 2700 με; these strain values induce bone modeling and remodeling. The highest measured deformation value was 2910 με. There was no significant difference in the induced mechanical response between bone models of the 60-year and 70-year age groups, and there was <3% difference from the 65-year age group. CONCLUSIONS: Considering in silico limitations, we suggest that APT components could be conveniently used on a bone with mechanical properties of the examined age categories. Under defined loading conditions, implantation of TKA with APT components is expected to induce modeling and remodeling of the periprosthetic tibia. Following clinical validation, the results of our study could modify the indication criteria of the procedure, and lead to more frequent implantation of all-polyethylene TKA in younger patients.

• Klíčová slova
• All-polyethylene tibial component, Bone mechanics, Finite element model, Orthopaedic biomechanics, Total knee arthroplasty, von Mises strain,
• MeSH
• analýza metodou konečných prvků MeSH
• biomechanika MeSH
• kovy MeSH
• lidé MeSH
• mechanický stres MeSH
• polyethylen MeSH
• protézy - design MeSH
• protézy kolene * MeSH
• tibie diagnostické zobrazování   chirurgie   MeSH
• totální endoprotéza kolene * metody   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• kovy MeSH
• polyethylen MeSH

BACKGROUND: Total knee arthroplasty (TKA) with all-polyethylene tibial (APT) components has shown comparable survivorship and clinical outcomes to that with metal-backed tibial (MBT). Although MBT is more frequently implanted, APT equivalents are considered a low-cost variant for elderly patients. A biomechanical analysis was assumed to be suitable to compare the response of the periprosthetic tibia after implantation of TKA NexGen APT and MBT equivalent. METHODS: A standardised load model was used representing the highest load achieved during level walking. The geometry and material models were created using computed tomography data. In the analysis, a material model was created that represents a patient with osteopenia. RESULTS: The equivalent strain distribution in the models of cancellous bone with an APT component showed values above 1000 με in the area below the medial tibial section, with MBT component were primarily localised in the stem tip area. For APT variants, the microstrain values in more than 80% of the volume were in the range from 300 to 1500 με, MBT only in less than 64% of the volume. CONCLUSION: The effect of APT implantation on the periprosthetic tibia was shown as equal or even superior to that of MBT despite maximum strain values occurring in different locations. On the basis of the strain distribution, the state of the bone tissue was analysed to determine whether bone tissue remodelling or remodelling would occur. Following clinical validation, outcomes could eventually modify the implant selection criteria and lead to more frequent implantation of APT components.

• Klíčová slova
• All-polyethylene tibial component, Computational modeling, FEA, Finite element method, Knee replacement, Metal-backed tibial component, TKR, Total knee arthroplasty,
• MeSH
• analýza metodou konečných prvků MeSH
• kovy MeSH
• lidé MeSH
• polyethylen MeSH
• protézy - design MeSH
• protézy kolene * MeSH
• senioři MeSH
• tibie diagnostické zobrazování   chirurgie   MeSH
• totální endoprotéza kolene * MeSH
• Check Tag
• lidé MeSH
• senioři MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• kovy MeSH
• polyethylen MeSH

BACKGROUND: The spatially varying mechanical properties in finite element models of bone are most often derived from bone density data obtained via quantitative computed tomography. The key step is to accurately and efficiently map the density given in voxels to the finite element mesh. METHODS: The density projection is first formulated in least-squares terms and then discretized using a continuous and discontinuous variant of the finite element method. Both discretization variants are compared with the nodal and element approaches known from the literature. FINDINGS: In terms of accuracy in the L2 norm, energy distance and efficiency, the discontinuous zero-order variant appears to be the most advantageous. The proposed variant sufficiently preserves the spectrum of density at the edges, while keeping computational cost low. INTERPRETATION: The continuous finite element method is analogous to the nodal formulation in the literature, while the discontinuous finite element method is analogous to the element formulation. The two variants differ in terms of implementation, computational cost and ability to preserve the density spectrum. These differences cannot be described and measured by known indirect methods from the literature.

• Klíčová slova
• Biomechanics, Bone fracture, Bone stiffness, Computational modeling,
• MeSH
• analýza metodou konečných prvků MeSH
• kosti a kostní tkáň * diagnostické zobrazování   MeSH
• kostní denzita MeSH
• lidé MeSH
• počítačová rentgenová tomografie * metody   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Dental implant failure is mainly the consequence of bone loss at peri-implant area. It usually begins in crestal bone. Due to this gradual loss, implants cannot withstand functional force without bone overload, which promotes complementary loss. As a result, implant lifetime is significantly decreased. To estimate implant success prognosis, taking into account 0.2 mm annual bone loss for successful implantation, ultimate occlusal forces for the range of commercial cylindrical implants were determined and changes of the force value for each implant due to gradual bone loss were studied. For this purpose, finite element method was applied and von Mises stresses in implant-bone interface under 118.2 N functional occlusal load were calculated. Geometrical models of mandible segment, which corresponded to Type II bone (Lekholm & Zarb classification), were generated from computed tomography images. The models were analyzed both for completely and partially osseointegrated implants (bone loss simulation). The ultimate value of occlusal load, which generated 100 MPa von Mises stresses in the critical point of adjacent bone, was calculated for each implant. To estimate longevity of implants, ultimate occlusal loads were correlated with an experimentally measured 275 N occlusal load (Mericske-Stern & Zarb). These findings generally provide prediction of dental implants success.

• Klíčová slova
• bone loss, implant dentistry, osseointegration, finite element,
• MeSH
• analýza metodou konečných prvků * MeSH
• analýza zatížení zubů MeSH
• časové faktory MeSH
• lidé MeSH
• mandibula patologie   MeSH
• mechanický stres MeSH
• osteointegrace MeSH
• síla skusu MeSH
• zatížení muskuloskeletálního systému MeSH
• zobrazování trojrozměrné MeSH
• zubní implantáty * MeSH
• zubní protéza - design MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• zubní implantáty * MeSH

PURPOSE OF THE STUDY In this study, our aim is to examine the effect of proximal fibular osteotomy on knee and ankle kinematics with finite element analysis method. MATERIAL AND METHODS One 62-year-old, female volunteer's radiologic images were used for creating lower limb model. Osteotomized model (OM) which was created according to definition of PFO and non-osteotomized model (NOM) were created. To obtain a stress distribution comparison between the two models, 350 N of axial force was applied to the femoral heads of the models. RESULTS After PFO, the average contact pressure decreased 26.1% at the medial tibial cartilage and increased 42.4% at the lateral tibial cartilage. The Von Mises stresses decreased 57.1% at the femoral cartilage and decreased 79.1% at tibial cartilage. The stress on the tibial cartilage increased 44.6%, and stress on the talar cartilage increased 7.1% at the ankle joint. CONCLUSIONS FEA revealed that main loading at the knee joint shifted from medial tibial cartilage to the lateral tibial cartilage after PFO. Additionally, the stresses on each cartilage were redistributed across a wider and more peripheral area. FEA also demonstrated that the Von Mises stresses of the tibial and talar cartilages of the ankle joint increased after PFO. Key words: knee pain, osteoarthritis, osteotomy, finite element analysis, axial loadings.

• MeSH
• analýza metodou konečných prvků MeSH
• biomechanika MeSH
• hlezenní kloub * diagnostické zobrazování   chirurgie   MeSH
• kolenní kloub * diagnostické zobrazování   chirurgie   MeSH
• lidé MeSH
• mechanický stres MeSH
• osteotomie MeSH
• tibie diagnostické zobrazování   chirurgie   MeSH
• Check Tag
• lidé MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH