Browsing by Author "Henyš, Petr"
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- ItemCement augmentation of odontoid peg fractures: the effect of cement volume and distribution on construct stiffness(SPRINGER, 233 SPRING ST, NEW YORK, NY 10013 USA, 2020) Čapek, Lukáš; Řehoušek, Petr; Henyš, Petr; Bleibleh, Sabri; Jenner, Edward; Kulvajtová, Markéta; Skála‑Rosenbaum, JiříPurpose The cement augmentation of a conventional anterior screw fixation in type II odontoid process fractures for elderly patients significantly increased stiffness and load to failure under anterior-posterior load in comparison with non-augmented fixation. The amount and quality of bone cement are usually taken ad hoc in clinical practise. In this study, we wanted to clarify the role of bone cement amount and its quality to the stiffness of odontoid and vertebrae body junction. Methods Finite-element method was used to achieve different scenarios of cement augmentation. For all models, an initial stiffness was calculated. Model (1) the intact vertebrae were virtually potted into a polymethylmethacrylate base via the posterior vertebral arches. A V-shaped punch was used for loading the odontoid in an anterior-posterior direction. (2) The odontoid fracture type IIa (Anderson-D'Alonzo classification) was achieved by virtual transverse osteotomy. Anterior screw fixation was virtually performed by putting self-drilling titanium alloy 3.5 mm diameter anterior cannulated lag screw with a 12 mm thread into the inspected vertebrae. A V-shaped punch was used for loading the odontoid in an anterior-posterior direction. The vertebrae body was assumed to be non-cemented and cemented with different volume. Results The mean cement volume was lowest for body base filling with 0.47 +/- 0.03 ml. The standard body filling corresponds to 0.95 +/- 0.15 ml. The largest volume corresponds to 1.62 +/- 0.12 ml in the presence of cement leakage. The initial stiffness of the intact C2 vertebrae was taken as the reference value. The mean initial stiffness for non-porous cement (E = 3000 MPa) increased linearly (R2 = 0.98). The lowest stiffness (123.3 +/- 5.8 N/mm) was measured in the intact C2 vertebrae. However, the highest stiffness (165.2 +/- 5.2 N/mm) was measured when cement leakage out of the odontoid peg occurred. The mean initial stiffness of the base-only cemented group was 147.2 +/- 8.4 N/mm compared with 157.9 +/- 6.6 N/mm for the base and body cemented group. This difference was statistically significant (p < 0.0061). The mean initial stiffness for porous cement (E = 500 MPa) remains constant. Therefore, there is no difference between cemented and non-cemented junction. This difference was not statistically significant (p < 0.18). Conclusion The present study showed that the low porous cement was able to significantly influence the stiffness of the augmented odontoid screw fixation in vitro, although further in vivo clinical studies should be undertaken. Our results suggest that only a small amount of non-porous cement is needed to restore stiffness at least to its pre-fracture level and this can be achieved with the injection of 0.7-1.2 ml of cement.
- ItemComparison of current methods for implementing periodic boundary conditions in multi-scale homogenisation(Elsevier Ltd, 2019) Henyš, Petr; Čapek, Lukáš; Březina, JanCorrectly representing the micro-scale model boundaries is fundamental to the performance and accuracy of multi-scale homogenisation. Although enforcing periodic boundary conditions is known to lead to more effective property approximation in comparison with that achieved with kinematic/uniform force boundary conditions, implementing them imposes restrictions on the mesh generation process and makes the process of solving the underlying variational problem more complicated. This study reviews the current implementation methods, which employ meshless and finite element approaches to maintain field periodicity. Finally, we propose a new method based on Nitsche's weak formulation and compare it with other state-of-the-art techniques. The results of several benchmarks demonstrate that all tested methods are highly robust and accurate, with minor method-specific issues.
- ItemComputational modal analysis of a composite pelvic bone: convergence and validation studies(TAYLOR & FRANCIS LTD, 2-4 PARK SQUARE, MILTON PARK, ABINGDON OR14 4RN, OXON, ENGLAND, 2019) Henyš, Petr; Čapek, LukášThe purpose of the present study was to describe the structural density and geometry of the bone, as well as its sensitivity to the resolution of finite element discretisation. The study introduces a novel way to validate biomechanical model of the bone by experimental modal analysis. The structural density and geometry of the model was obtained from a composite bone. A detailed investigation of the weight dependence of the bone on the mesh resolution was performed to obtain the best match with the real weight of the tested bone. The computational model was compared with the experimental results obtained from the modal analysis. The overall changes of the modal properties and bone weight in the model caused by different mesh resolutions and order of approximation were below 10%, despite the bone was modelled with simple isotropic material properties. The experimental modal analysis shows a great potential to be a robust verification tool of computational biomechanical models because it provides boundary conditions-free results. The sensitivity analysis revealed that the linear approximation of the density field is not suitable for the modelling of the modal response of composite bone.
- ItemDiagnostic Tool for Initial Fixation of Acetabular Implant(Technická Univerzita v Liberci, 2015) Henyš, PetrInitial fixation of cementless components of Total Hip arthroplasty (THA) plays a crucial role for long term survival of implant and the overall success of the surgical procedure. Every year a million of THA is performed and objective intra operative assessment of initial fixation has not been available for clinical use yet. Currently, surgeons have to rely on their clinical experience, however they have a sophisticated screening method, but not suitable for intra operative assessment of initial fixation. They can use RSA, EBRA or the radiographic analysis for checking the healing process of implant, evaluating implant migration or bone resorption and osteolysis around the bone implant interface. These methods are suitable for follow - up studies, but do not assist the surgeon during implantation process. Vibrational analysis has been recognized as a promising tool in biomechanics to identify mechanical properties of bone structure, to assess the primary and secondary stability of dental implants and to evaluate fracture healing of bone. In literature some studies dealing with intra operative initial fixation assessment during THA can be found. Most of them are focused on femoral stem fixation, although acetabular component (AC) fails with the same rate as femoral stem or even frequently. The main objective of proposed work is to investigate the ability of vibrational methods reflect the initial fixation of acetabular implant in some measurable quantity. The bone - implant interface is recognized as one of the potential candidates that would explain the changes in dynamic response of bone - implant system undergoes an ambient excitation. The bone - implant interface is investigated trough numerical modeling. In the experimental part of thesis, different pres fitting forces are compared with the dynamic response of bone - implant system. From numerical analysis it follows that there is a different level of relation between shared contact area and modal parameters of system. Experimental part shows also the relation between evaluation of fixation of implant and its response parameters.
- ItemDiagnostic Tool for Initial Fixation of Acetabular Implant(Technická Univerzita v Liberci, ) Henyš, Petr
- ItemMulti-scale Smoothed Finite Element(2019) Henyš, PetrSimulations in material engineering must consider complex physical phenomena that have a non-linear character and interact with multiple time and space scales. In spite of the intensive development of computational technologies, spatial and temporal simulations penetrating signi cantly di erent scales, starting with the electron structure and visible at the end, can still be realized only very limited. This work is devoted to multi-scale homogenization starting from mathematical formulation and ends up with the construction of a model derived from real data. The rst part introduces a new implementation of periodic boundary conditions in the sense of the Nitsche's method and subsequently tested on complex material structures. The second part introduces the gradient smoothing technique and its use to improve the convergence properties of the nite element method and the accuracy of the estimation of the e ective material properties. The third part is devoted to the e ective reconstruction of brous textile structures from tomographic data including the estimation of morphological parameters.
- ItemNávrh a realizace přístroje měřícího primární stabilitu meziobratloých plotének(Technická Univerzita v Liberci, 2011) Henyš, Petr; Čapek, LukášThe aim of this dissertation is to design an experimental device that will be able to identify the primary stability of the intervertebral disc replacement and evaluate it. The first section summarizes the information on the anatomy of the spine and the loss of its function. At the end of this section are presented diagnostic methods used in medicine. The next chapter is devoted to the physical principle of the measuring device and its construction. The design section is divided into three parts (design of exciter, its amplifier and control program written in NI Labview). The last part deals with the measurement and evaluation of experimental data in vitro. Various measurements were performed under conditions which were similar to real conditions. Finally, the results are summarized and discussed.
- ItemZařízení pro vrtání skla ultrazvukemHenyš, Petr
- ItemZařízení pro vrtání skla ultrazvukem(Technická Univerzita v Liberci, 2008) Henyš, Petr; Horák, MarcelThis baccalaureate work deals with using ultrasonic in drilling process of glass products. This work describes a construction design of device that is able to shape glass by way of ultrasonic wave. First part of work is theoretic and deals with physical base of ultrasonic and use in industry. Second part is about a new design of ultrasonic drilling machine. This part is focused to the solving fundamental device elements. Third part describes laboratory measuring. Experimental results were verified and used for optimization power elements of designed machine. Optimal drilling conditions are analyzed and effectivity of drilling process is considered.