Verticality of transcervical hip fractures in young patients is usually connected with typically high-energy fractures which are known as Pauwels type III. Artificial femoral head replacement surgery ...is mostly not considered for treating femoral neck fractures in such patients. The commonly used devices for the fixation of vertical femoral neck fractures are multiple screws or a sliding hip screw with or without an antirotation screw. Size, location and length of the screws are the most effective parameters in terms of the structural performance of internal fixation implants, but the optimal configuration of the screws is necessary to be investigated to direct the clinical practice. The aim of this study is to compare the biomechanical stability of the standard inverted triangle configuration with the various newly proposed
x
-crossed screw configurations. FEA simulations carried out in this study demonstrated that using an
x
-crossed-right assembly in treating Pauwels type III femoral neck fractures satisfies the biomechanical stability in terms of maximum von Mises stresses and maximum femoral head displacement. However, in terms of maximum relative neck fracture displacement, the
x
-crossed-right assembly would not entirely suffice the desired biomechanical stability. Therefore, using an
x
-crossed screw assembly in treating femoral neck fractures would provide the needed biomechanical stability.
Graphical Abstract
•Y-shaped locking plate is a possible alternative to traditional two-plate method for extra-articular distal humerus fractures.•Novel locking plate exhibits higher stiffness values and biomechanical ...properties than reconstructive plates under cyclic and static tests.•All models show minimal displacement within the limits of biomechanical stability during fracture healing.•LCP and test models demonstrated fewer loosened screw-bone-implant contacts compared to models with reconstructive plates.
Adult distal humerus fractures are infrequent, yet they account for one-third of all humerus fractures. For the treatment of comminuted and osteoporotic fractures, locking plates are claimed to be biomechanically superior to alternative internal fixing techniques. Treatment remains difficult despite recent advancements and the use of locking plates due to frequent comminution, low bone quality, and limited healing ability in osteoporotic bone. An optimal design of the newly constructed plate and the control model were selected. The biomechanical characteristics of non-osteoporotic and osteoporotic synthetic bone were compared on six models. The biomechanical properties of the new plate were tested and compared on 54 osteoporotic synthetic humerus models. The control models were reconstructive and parallel LCPs. The tests were carried out under static and dynamic axial, lateral and bending loads. Fracture displacements were measured by optical measuring system Aramis. The test model is significantly stiffer for lateral load (p = 0.0007) and for bending load at the moment of model failure (p = 0.0002), while for axial load the LCP model showed greater stiffness (p = 0.0017). During lateral dynamic loading, all three LCP models broke and there was a significant difference compared to the test model (p = 0.0125). The LCP model is dynamically significantly more durable under axial load, while the largest displacements were recorded with the test model (p = 0.029). The displacements induced by all three loads are within the limits that fulfil the parameters of appropriate biomechanical stability. A novel locking plate for extra-articular distal humerus fractures may provide an alternative to the traditional two-plate.
The price of material is an important factor when selecting the additive polymer procedure. In selective laser sintering (SLS), the price can be reduced by the recycling of material, i.e., with ...different shares of original and recycled material, as well as by the orientation of the product during manufacturing. Numerous tests warn that orientation in the direction of z axis should be as low as possible to reduce the total price of the product. The product also has to satisfy the influence of atmospheric conditions to which it is exposed during its lifetime, i.e., UV radiation and humid environment. UV light, with sun being its most common source, and average humidity in different parts of the world can be approximately from 20% to 90%, depending on time, day and geographic location. In this work, the test specimens have been made of original, mixed and 100% recycled material and then exposed to the influences of UV radiation and water absorption. After having been exposed to atmospheric conditions for a longer time, the mechanical properties of the polyamide products made by selective laser sintering were tested. The results show that exposure to UV radiation reduces tensile elongation at all ratios of recycled material and orientation of 70–90% except in the z direction, while in flexural deformation it is the other way around. The effect of water was observed only between the 7th–14th day of absorption with a decrease in strength until the deformation did not change.
Locking plates nowadays represent an important treatment in bone trauma and bone healing due to its strong biomechanical properties. The purpose of this study was to both computationally and ...experimentally validate a novel screw locking system by comparing it to another locking system from state-of-the-art and to apply it in an environment of a fractured mandible. FEA was used to test both systems prior to experimental tests. The systems were locked in the plate holes at 0°, 10°, 15°, and 20°. Cyclic bending tests and push-out tests were performed in order to determine the stiffness and push-out forces of both locking systems. Finally, newly designed locking system was implemented in mandibular angle fracture. Control locking system was biomechanically superior in push-out test, but with no greater significance. In contrast, the new locking system showed greater stiffness by 17.3% at the deflection angle of 20° in cyclic tests, with lower values for other deflection angles. Similar values were displayed in fractured mandible angle environment. Greater stiffness of the new locking system in cyclic loading tests, together with polyaxiallity of the new locking screw, could lead to easier application and improved biomechanical stability of the mandible angle fractures.
Graphical abstract
Good clinical outcomes for locking plates as an external fixator to treat tibial fractures have been reported. However, external locking plate fixation is still generally rarely performed. This study ...aimed to compare the stability of an external locking plate fixator with that of a conventional external fixator for extraarticular proximal tibial fractures using finite element analysis.
Three models were constructed: (1) external locking plate fixation of proximal tibial fracture with lateral proximal tibial locking plate and 5-mm screws (ELP), (2) conventional external fixation of proximal tibial fracture with an 11-mm rod and 5-mm Schanz screws (EF-11), and (3) conventional external fixation of a proximal tibial fracture with a 7-mm rod and 5-mm Schanz screws (EF-7). The stress distribution, displacement at the fracture gap, and stiffness of the three finite element models at 30-, 40-, 50-, and 60-mm plate-rod offsets from the lateral surface of the lateral condyle of the tibia were determined.
The conventional external fixator showed higher stiffness than the external locking plate fixator. In all models, the stiffness decreased as the distance of the plate-rod from the bone surface increased. The maximum stiffness was 121.06 N/mm in the EF-11 model with 30-mm tibia-rod offset. In the EF-7 model group, the maximum stiffness was 40.00 N/mm in the model with 30-mm tibia-rod offset. In the ELP model group, the maximum stiffness was 35.79 N/mm in the model with 30-mm tibia-plate offset.
Finite element analysis indicated that external locking plate fixation is more flexible than conventional external fixation and can influence secondary bone healing. External locking plate fixation requires the placement of the plate as close as possible to the skin, which allows for a low-profile design because the increased distance from the plate to the bone can be too flexible for bone healing. Further experimental mechanical model tests are necessary to validate these finite element models, and further biological analysis is necessary to evaluate the effect of external locking plate fixation on fracture healing.
The effect of annual rings’ orientation on bending strength was examined on subfossil elm wood. Elm is extremely rarely found as subfossil wood, and during the last 50–60 years it has almost ...disappeared from natural forest stands of south-eastern Europe, due to the Elm Dutch disease. The samples were cut from approximately 670 years old subfossil elm trunk retrieved from the bed of the river Sava in the area between the villages Grebnice and Domaljevac in north Bosnia. The wood was identified to the genus level based on optical microscopy analysis of three wood sections—transverse, tangential and radial. Bending strength was determined by the three-point bending test. The load was applied to the longitudinal–tangential surface (LT) and to the longitudinal–radial surface (LR). The bending strength values of subfossil elm do not differ from the values of recent elm, despite the 700-year resting in anoxic river conditions. Bending strength in LT direction was slightly higher than bending strength in LR direction. The coefficient of variation and the standard deviation of the arithmetical mean were higher for LT direction. It was found that the measured bending strength for both directions follows Weibull distribution. Coefficient of determination of Weibull functions was close to 1 for both directions. The Weibull shape parameter was higher for LR direction.
The aim of this work is to estimate the parameters of elastoplastic and damage laws for nodular graphite cast iron from a cyclic uniaxial test on a dog-bone sample. The paper focuses on the ...identification of material parameters coupling finite element models and full-field measurements. The gap between the measured and simulated data is used to estimate the quality of the proposed constitutive postulates.
Last, a cyclic uniaxial experiment is carried out in a lab tomograph to reveal the damage micromechanism. Digital volume correlation is used to measure displacement fields in the bulk of the sample. The correlation residuals are used to detect the damage mechanism occurring in the heterogeneous microstructure of the material.
•Identification of three different nonlinear models coupling full-field measurements and load data.•Coupled identification of elastoplastic and damage model.•Analysis of damage mechanism via computed tomography and DVC.
To compare the finite element models of two different composite radius fracture patterns, reduced and stabilised with four different fixed-angle dorsal plates during axial, dorsal and volar loading ...conditions.
Eight different plastic models representing four AO/ASIF type 23-A3 distal radius fractures and four AO/ASIF 23-C2 distal radius fractures were obtained and fixed each with 1 of 4 methods: a standard dorsal non-anatomical fixed angle T-plate (3.5mm Dorsal T-plate, Synthes), anatomical fixed-angle double plates (2.4mm LCP Dorsal Distal Radius, Synthes), anatomical fixed angle T-plate (2.4mm Acu-Loc Dorsal Plate, Acumed) or anatomical variable-angle dorsal T-plate (3.5mm, Dorsal Plate, Zrinski). Composite radius with plate and screws were scanned with a 3D optical scanner and later processed in Abaqus Software to generate the finite element model. All models were axially loaded at 3 points (centrally, volarly and dorsally) with 50 N forces to avoid the appearance of plastic deformations of the models. Total displacements at the end of the bone and the stresses in the bones and plates were determined and compared.
Maximal von Mises stress in bone for 3-part fracture models was very similar to that in 2-part fracture models. The biggest difference between models and the largest displacements were seen during volar loading. The stresses in all models were the highest above the fracture gap. The best performance in all parameters tested was with the Zrinski plate and the most modest results were with the Synthes T-plate.
There was no significant difference between 2-part (AO/ASIF type 23-A3) and 3-part (AO/ASIF 23-C2) fracture models. Maximal stresses in the plates appeared above the fracture gap; therefore, it is worth considering the development of plates without screw holes above the gap.
In this paper the nonlinear behavior of nodular graphite cast iron is investigated under in-plane biaxial loading regimes. Multiaxial experiments enable a wide variety of loading paths to be ...investigated. In the presented study two loading histories are proposed, namely, equibiaxial and “snail” loading paths corresponding to proportional and nonproportional regimes. The center gauge zone of the testing cruciform specimen is observed. Mean strain fluctuations are measured and presented in order to determine the material response for the prescribed biaxial loading paths. For the equibiaxial and snail loading histories finite element model updating will couple 2D-DIC measurements with 3D-FE analyses to calibrate material parameters describing elasticity, isotropic or kinematic hardening.
•Multiaxial tests on cast iron.•Identification of isotropic or kinematic hardening laws.•Snail loading history very discriminating.
Numerical analysis is carried out for a frictionless receding contact problem of a perfect-fit pin and bushing in a uniaxially loaded plate. The problem is analysed using the finite element method ...under the assumption of plane strain and linear elasticity. The problem is investigated for the influence of external load and for different geometries. The obtained contact pressures show uncharacteristic behaviour, where higher peak values occur on contact surfaces with larger contact angles. This seemingly contradicts not only the physics of receding contact problems, but also the physical laws of contact problems in general. It is shown that the reason for this unusual behaviour is, in fact, in the physical reduction of the contact area as the radius of curvature decreases. This class of problems shows to be linearly dependent on the intensity of load as regards the contact stresses, and load has no influence on the contact angles.
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