Přemysl Janíček

Reliability of the Ceramic Head of the Total Hip Joint Endoprosthesis Using Weibull’s Weakest-link Theory

The paper deals with calculation of the parameters of ceramic material from a set of destruction tests of ceramic heads of total hip joint endoprosthesis. The standard way of calculation of the material parameters consists in carrying out a set of 3 or 4 point bending tests of specimens cut out from parts of the ceramic material to be analysed. In case of ceramic heads, it is not possible to cut out specimens of required dimensions because the heads are too small (if the cut out specimens were smaller than the normalised ones, the material parameters derived from them would exhibit higher strength values than those which the given ceramic material really has). On that score, a special testing jig was made, in which 40 heads were destructed. From the measured values of circumferential strains of the head’s external spherical surface under destruction, the state of stress in the head under destruction was established using the final elements method (FEM). From the values obtained, the sought for parameters of the ceramic material were calculated using Weibull’s weakest-link theory

Stress And Reliability Analyses Of Damaged Ceramic Femoral Heads

Today, the problem of reliability of the hip joint ceramic heads becomes important, since world-wide the destruction of the ceramic head has generally been stated in a non-negligible number of patients. Therefore stress and reliability analyses of the ceramic heads were made using experimental and computational modelling aimed at finding the causes of the head destruction. The deformation and stresses are obtained by computational methods (finite elements) under testing conditions, in accordance with 1S0 7206-5. Head reliability is based on the Weibull weakest link theory. The head’s stress and reliability are significantly influenced by manufacturing inaccuracies of the cone contact areas, The considered manufacturing inaccuracies are modelled as axisymmetric or 3D. The effects of manufacturing inaccuracies on the head’s hoop stress and the head’s contact pressure along the contact taper are analysed in detail, because the maximum tensile stress acts in this region, Finally, the effect of the mentioned manufacturing inaccuracies on the head’s failure probability during the loading is shown. The results obtained are used in clinical practice and in the technological processes of stem and ceramic head manufacturing.

Stress-Deformation Analysis of an Elbow Articulation with Radial Head Replacement

this contribution speaks about the progress of forming a geometric elbow model, generating the FEM network in the created volumes; stress-deformation analysis of the Final Element Model (contact task) and suggests possible geometric models of partial alloplasty of the radius’s proximal part.

Calculation of the Bio-ceramic Material Parameters

The paper deals with calculation of the parameters of bio-ceramic material from a set of destruction tests of whole ceramic heads of total hip joint endoprosthesis. This approach is suitable in the case if it not possible to cut out the specimens from the ceramic heads, because the heads are too small. From the measured values of circumferential strains of the head’s external spherical surface under destruction, the state of stress in the head under destruction was established using the FEM. From the values obtained, the sought for parameters of the ceramic material were calculated using Weibull’s weakest-link theory.

Strain — Stress Analysis of Artificial Hip Joint, Influence of Bearing Material on Contact Pressure

Hip resurfacing surgery has been proposed as an alternative to THR for younger more active patients. The metal-on-metal hip resurfacing procedure involves fitting the femoral head with a metal surface and lining the acetabulum with a metal cup to form a pair of metal bearings. Short-term clinical results persuade us to deal with FE analyses because it is important for development of the surface replacement prosthesis. The objective of this contribution is to perform finiteelement analyses of computational model of the total surface replacement with different materials of bearing couples (acetabular cup/femoral head) and physiological hip joint. All results will be compared one another and then confronted with results of the physiological hip joint. The three-dimensional computational model consists of these components: sacral, pelvic and femoral bone, muscles, artificial socket, and surface hip replacement. The geometrical models of bones are generated by means of computed tomography (CT) images. The geometry of the surface replacement was proposed. The FE model of bone reflects two types of the bone tissues (trabecular and cortical bone) and muscles that are important when standing on one leg. The model was loaded by force, corresponding to load during slow walking and by standing on one leg.

Computational Modelling of the Shape Deviations of the Sphere Surfaces of Ceramic Heads of Hip Joint Replacement

The problem of the damage of the bioimplants is very important today. In the endoprosthesis surgery there is a large percentage of implant defects, which cause the failure of the whole prosthesis. One kind of the total hip replacement functionality loss is acetabular cup pull-off from pelvis bone. This paper is aimed at manufacture perturbations (shape deviations) analysis as one of the possible reasons to this kind of failure. Dimension and of geometry manufacturing perturbations (roundness) were analyzed in detail. It was found, that these perturbations affect considered values of contact pressure and frictional moment. Contact pressure and frictional moment are quantities affecting replacement success and durability.

Computational Modeling of the Probability of Destructions in Total Joint Endoprosthesis Ceramic Heads using Weibull's Theory

Computational Modeling of the Probability of Destructions in Total Joint Endoprosthesis Ceramic Heads using Weibulls Theory This report deals with the issue of finding causes of ceramic heads destructions in total joint endoprostheses. It has been identified that the head fractures were caused by improper mutual geometry tolerances in the taper joint between the ceramic head and the metal stem. This fact was revealed by the results of deformation-stress analyses of heads with various geometric imperfections in the taper contact with the stem using FEM. The issue was further elaborated in the sense of determination of probability of head destruction by existing shape macro-deviations of the taper contact surface of the head and stem, such as varying taper ratio and ovality, taking into consideration micro-roughness from splinter machining of the surfaces of the internal taper of head and the external taper of stem. To estimate the probability of head destruction, we used weakest link Weibulls theory.