Reducing Contact Stress of the Surface by Modifying Different Hardness of Femoral Head and Cup in Hip Prosthesis (original) (raw)
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A finite element method comparison of wear in two metal-on-metal total hip prostheses
Proceedings of The Institution of Mechanical Engineers Part H-journal of Engineering in Medicine, 2006
The contact mechanics of two metal-on-metal (MOM) total hip prostheses was studied by means of the finite element method (FEM). The purpose of the work was to compare two total hip replacements (DuromTM and MetasulTM) with regard to the amount of wear debris released. Wear on the bearing surfaces was evaluated following Reye hypotheses from the pressure distribution, computed by means of three-dimensional FEM models; an approximate analytical model based on Hertz contact theory has also been developed and discussed. The results show that in the dry friction condition the DuromTM joint releases almost twice as much wear volume as produced by the MetasulTM joint. Therefore, while DuromTM implants can improve hip stability by increasing the prosthetic impingement-free range of motion (PIF-ROM), MetasulTM prostheses can be a valuable solution whenever wear represents a critical choice factor. could be attributed to the larger bearing diameter but also to the elasticity of the underlying bone
Journal of biomechanics, 2015
The contact mechanics of artificial metal-on-polyethylene hip joints are believed to affect the lubrication, wear and friction of the articulating surfaces and may lead to the joint loosening. Finite element analysis has been widely used for contact mechanics studies and good agreements have been achieved with current experimental data; however, most studies were carried out with idealist spherical geometries of the hip prostheses rather than the realistic worn surfaces, either for simplification reason or lacking of worn surface profile. In this study, the worn surfaces of the samples from various stages of hip simulator testing (0 to 5 million cycles) were reconstructed as solid models and were applied in the contact mechanics study. The simulator testing results suggested that the center of the head has various departure value from that of the cup and the value of the departure varies with progressively increased wear. This finding was adopted into the finite element study for be...
Predicting the wear of hard-on-hard hip joint prostheses
Wear, 2013
The wear of the bearing surfaces of hip joint prostheses is a key problem causing their primary failure. This paper introduces a wear prediction model with the aid of the finite element analysis. To mimic walking, the most common activity of a human body, a three-dimensional physiological loading gait cycle was considered. The wear at the bearing surface in gait cycles was calculated based on the contact stress variation from the finite element analysis and the sliding distance obtained from threedimensional hip gait motions. The geometry of the worn surface was updated considering the average routine activities of a patient. The model was applied to three hard-on-hard prostheses, i.e., PCD (polycrystalline diamond)-on-PCD, ceramic-on-ceramic and metal-on-metal couples. It was found that due to the gait motion, the intensity and location of the maximum contact stress in the bearing components change with the gait instances. With a given geometry and gait loading, the linear and volumetric wear on the cup surface increases with the number of gait cycles. With increasing the gait cycles, the surface wear can bring about scattered contact pressure distribution. Compared to the ceramic-on-ceramic and metal-on-metal couples, the PCD-on-PCD bearing has the lowest wear progression. It was also concluded that the computational wear model presented in this paper can reasonably predict the wear evolution in hard-on-hard hip implants.
Wear and friction characterization of materials for hip prosthesis
Wear, 2007
Many problems which lead to the loosening of a prosthesis are due to the wear of materials used for the substitution of the articulation. Wear reduces the lifetime of a prosthesis, induces the formation of potentially harmful debris and involves the risks of a new surgical operation. The goal of this study, carried out in the laboratory, is to quantify wear and friction of different materials used for the friction parts of hip prosthesis. Currently, the materials used are metallic alloys, ultra-high molecular weight polyethylene (UHMWPE) and ceramics. In this study, we carried out tribological tests with different couples (metallic alloys/UHMWPE, ceramics/UHMWPE and ceramics/ceramics) and we compared their behavior in terms of friction and wear scars morphology. The used ceramics are composed of alumina and zirconia which are produced by an original process. To carry out the tribological tests whose conditions are defined by international standards, a versatile tribometer has been developed. The results show a lower friction coefficient in the case of ceramics/ceramics couples than in the case of metallic alloys/UHMWPE couples. We also studied the wear surfaces by profilometry and electron microscopy. The wear of UHMWPE is very low when in contact with ceramics, low with Co-Cr alloy and high with stainless steel. Our ceramics/ceramics couples show no wear.
E3S Web of Conferences, 2021
A common problem with artificial hip replacements is increased wear of the material in contact. Materials that are in contact result in contact pressure caused by the patient's daily activities so that it triggers wear. This study adopts a finite element method (FEM) to predict wear of the artificial hip joint, by studying the behavior of a hip joint prosthesis that has clearance under a certain load. The aim of this study was to observe contact as a function of clearance and body weight. The modeling uses metal as femoral head and polycarbonate urethane (PCU) material as the acetabular cup. Contact modeling as a hard material in contact with a deformable material. Four variations of clearance (0.001, 0.005, 0.01, 0.016) and three variations of body weight (500N, 700N, and 1000N) were used in this study. The simulation results show that the lower the distance and weight, the lower the contact pressure.
A Comparative Study on Wear Behavior of Hip Prosthesis by Finite Element Simulation
Biomedical Engineering: Applications, Basis and Communications, 2002
A numerical approach was proposed to investigate the wear behavior occurred in the artificial hip joints in this paper. In the numerical simulations, the wear coefficients taken from pin-on-disk tests were introduced into the wear analysis model to assess the wear rates of polyethylene acetabular cups against metallic or ceramic femoral heads. For the established material combinations, different values of polyethylene wear rates were obtained respectively, which were not necessarily the realistic one as expected in vivo but could be confirmed after further discussion on the wear mechanism involved in wear tests. Current results indicated that the polyethylene/ceramic couples represented better wear performances than the polyethylene/metal couples. Furthermore, the ratio of wear rates for polyethylene cups against alumina and the metallic femoral heads was 0.5, which agreed well with that deduced from clinical studies or laboratory hip simulators. It is obvious that these comparable ...
Modelling of metal on metal hip prostheses
2015
Metal-on-metal (MOM) total hip replacement is an artificial hip joint has been used to replace damaged or diseased natural joints. MOM studies have demonstrated severe complications due to metal wear debris in tissues adjacent to the implants. Reducing the wear rate and operating with full film lubrication could reduce these problems; a better understanding of the lubrication mechanisms is also relevant to other hard bearing materials such as ceramics or new metal alloys. Ball-in-socket MOM contacts were analysed using the Abaqus Finite Element package to simulate dry contact between the acetabular cup and the femoral head. Different cup thicknesses of 4, 6, 8, and 10 mm were considered using a polyurethane foam block support system. Elastohydrodynamic lubrication (EHL) analyses were developed for the contacts using three different approaches to specify the contact. These were (i) A simple model based on the radii of relative curvature, (ii) An equivalent contact model developed so ...
Medical Engineering & Physics, 2014
The morphology of the contact bearing surfaces plays an important role in the contact mechanics and potential wear of metal-on-metal (MOM) hip prostheses. An ellipsoidal bearing surface was proposed for MOM hip implants and the corresponding contact mechanics were studied by using the finite element method (FEM) under both standard and micro-lateralization conditions. When under microlateralization, the maximum contact pressure decreased from 927.3 MPa to 203.0 MPa, with increased ellipticity ratio medial-laterally. And the contact region was found to shift from the rim of the cup to the inner region compared to the spherical design. Under standard conditions, an increasing trend of the maximum contact pressure for the acetabular component was predicted as the major radius of the ellipsoidal bearing surface was increased. Nevertheless, the maximum contact pressure reached an asymptotic value when the ellipticity ratio was increased to 1.04. Therefore it is critical to optimize the ellipticity ratio in order to reduce the contact pressure under micro-lateralization condition and yet not to cause a markedly increased contact pressure under normal condition. Additionally, the maximum contact pressure in the ellipsoidal bearing surface remained relatively constant with the increased micro-lateralization. It is concluded that an ellipsoidal bearing surface morphology may be a promising alternative by offering better contact mechanisms when micro-lateralization should occur and attributing to minimized wear.
Limitation of the Lubricating Ability of Total Hip Prostheses with Hard on Hard Sliding Material
Tribology Online, 2013
Recently, metal on metal hip prostheses have been revived following excellent clinical results. However, the risk of wear diseases has not been removed yet. Fluid film formation is necessary for long term reliability of a total hip prosthesis because solid contact of the prosthesis induces serious wear. However, the fluid film can be only formed under limited conditions together with an appropriate shape design. Radial clearance is also an important factor because the radius has an upper limit in the joint space. A radial clearance that is too small induces severe contact, whereas decreasing radial clearance enhances squeezed film formation. The most appropriate radial clearance currently remains unclear. We prepared some specimens with high accuracy of polishing, which were balls and cups of the Co-Cr-Mo alloy with a common radius of 16 mm and several radial clearances, 0.15-95.8 µm. Their lubricating ability was evaluated by a friction test using a pendulum machine. The frictional coefficient was a local minimum where the radial clearance was 20-30 µm. It was found that appropriate radial clearance of a total hip prosthesis with hard on hard material must exist within this range.