A Study of The Effect of Model Geometry and Body Mass Index on The Elastohydrodynamic Lubrication Performance of Metal-on-Metal Hip Joints (original) (raw)
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Journal of Medical Device Technology
This study aims to provide benefits on the manufacturing side in considering design parameters for optimization of total hip arthroplasty based on body mass index (BMI) categories. The femoral and cup geometries in Total Hip Arthoplasty (THA) are modeled in a simple ball-on-plane form to analyze the pressure and thickness of the lubricant film in the elastohydrodynamic lubrication of artificial hip joints with vertical loads and parameters based on body mass index using the finite element method. The factor of being overweight is one of the causes of increasing the maximum load during activities. This study applies a maximum load based on BMI which is divided into two categories, namely normal and high BMI to obtain the distribution of contact pressure and fluid pressure on the bearing surfaces that are in contact with each other so that the thickness of the lubricating film formed can be determined. Validation of contact pressure and film thickness was carried out. The femoral head...
Medical Engineering & Physics, 2009
An elastohydrodynamic lubrication (EHL) simulation of a metal-on-metal (MOM) total hip implant was presented, considering both steady state and transient physiological loading and motion gait cycle in all three directions. The governing equations were solved numerically by the multi-grid method and fast Fourier transform in spherical coordinates, and full numerical solutions were presented included the pressure and film thickness distribution. Despite small variations in the magnitude of 3D resultant load, the horizontal anterior-posterior (AP) and medial-lateral (ML) load components were found to translate the contact area substantially in the corresponding direction and consequently to result in significant squeeze-film actions. For a cup positioned anatomically at 45 • , the variation of the resultant load was shown unlikely to cause the edge contact. The contact area was found within the cup dimensions of 70-130 • and 90-150 • in the AP and ML direction respectively even under the largest translations. Under walking conditions, the horizontal load components had a significant impact on the lubrication film due to the squeeze-film effect. The time-dependent film thickness was increased by the horizontal translation and decreased during the reverse of this translation caused by the multi-direction of the AP load during walking. The minimum film thickness of 12-20 nm was found at 0.4 s and around the location at (95, 125) • . During the whole walking cycle both the average and centre film thickness were found obviously increased to a range of 40-65 nm, compared with the range of 25-55 nm under one load (vertical) and one motion (flexion-extension) condition, which suggested the lubrication in the current MOM hip implant was improved under 3D physiological loading and motion. This study suggested the lubrication performance especially the film thickness distribution should vary greatly under different operating conditions and the time and location that potential wear may occur was very sensitive to specific loading and motion conditions. This may provide some explanation to the large variations in wear from hip simulators and clinical studies, and also stress the importance of using more realistic loading and motion conditions in the tribological study of MOM hip prostheses.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2009
Long-term successful function of artificial hip joint replacements strongly depends on the design parameters of the bearing such as the diameters of femoral head and acetabular cup and the corresponding radial clearance, which determine the lubrication regime experienced in the prostheses. Generally, there are two types of numerical models for elastohydrodynamic lubrication (EHL) analysis of the bearing in the hip joint replacements: ball-in-socket model and effective ball-on-plane model. As the real hip joint is in ball-in-socket configuration, the ball-insocket lubrication model should be the reasonable approximation to the real bearing. The ball-insocket model solves a lubrication problem in spherical coordinates, which means all of governing equations, including Reynolds equation, film thickness and load balance equation, should be written in the spherical coordinate forms. In addition, the calculation of the elastic deformation of the bearing surfaces in artificial joints is not a trial problem. Complex spherical geometries in the joint bearing often require employing the finite-element method to determine/extract the displacement influence coefficients at first, and then the deformation is evaluated through using an equivalent discrete spherical convolution model. Fortunately, the fast Fourier transformbased approach is recently developed to speed up the deformation calculation. In comparison with the ball-in-socket model, the effective ball-on-plane model is simple and easy to conduct EHL analysis. The main characteristic of the effective ball-on-plane model is that the elastic deformation was evaluated under an assumption of semi-infinite solid and certainly without the consideration of the curvature effect associated with the ball-in-socket configuration. In the present study, some typical cases of EHL analysis for hip joint replacements were conducted to systematically demonstrate the capability of these two models. It was found that both models were able to provide quite close results in most situations, and the difference may only take place when the head is positioned near the edge of the cup bearing surface. artificial hip joint replacements could have served long time, but still some of them failed due to the loosening of prosthetic components, particularly in metal-on-polyethylene hip joint replacements, resulting from the adverse biological reaction caused by wear and wear particles. As the demands of younger and more active patients, very long wear lives and much improved durability are expected.
Effect of gap outside contact area on lubrication of metal-on-Metal total hip replacement
Computer Methods in Biomechanics and Biomedical Engineering, 2020
Ball-in-socket metal on metal (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 that its dry contact area and maximum pressure replicated the values obtained from the FE analysis, and (iii) A modified version of (ii) that also ensured equivalence of the gap shape outside the contact area. Published in vivo information for the hip joint contact forces over the walking cycle was used to specify the operating conditions for the EHL analysis. The analysis method was found to be effective for all points of the walking cycle for cases where the cup thickness exceeded 5 mm and modelling approach (ii) was identified as satisfactory. For a cup thickness of 4 mm, membrane action began to emerge in the FE analyses so that such contacts behaved in a different way.
Procedia Engineering, 2013
The common problem of artificial hip joint replacement is the excessive generation of wear due to contacted bearing coupled. Computational simulation is becoming popular to predict wear generation. However, wear factor computed from experimental data was found to be varied due to the improvement of conformity leading to increase of lubrication performance especially for metal-on-metal hip joint replacement. The objective of this study was to develop the predicted wear factor based on the lubrication performance. The predicted linear wear taken from computational wear simulation was validated with theoretical wear model to predict the lubrication performance after 1 million cycles. Wear factors from experimental data were calculated and then plotted in the running-in and steady state. It shows that wear factor was a function of lambda ratio which was correlated with femoral head size and diametral clearance.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2008
Lubrication modelling is of great importance in the design of artificial hip joints, especially for the demand of long life expectancy of those joints employing a metal-on-metal bearing. Through lubrication analysis, the dimensions of the head/cup and the clearance between them can be reasonably determined, and thus, if fluid film lubrication can be generated in artificial hip joint replacements, the wear and related failure can be reduced. In the majority of published numerical studies of the lubrication of hip joints, the synovial fluid for the natural joint and bovine serum used for in vitro simulator testing of joint replacements have always been treated as isoviscous, incompressible Newtonian fluids because the viscosity of these lubricants is almost unchanged at high shear rate. However, all these biological lubricants generally exhibit non-Newtonian characteristics of shear thinning, particularly under relatively low shear rates, and display a second Newtonian plateau at high shear rates.
The Analysis of Dimple Geometry on Artificial Hip Joint to the Performance of Lubrication
Journal of Physics: Conference Series, 2019
This research analyzed the effect of applied surface texturing on bearing component of the artificial hip joint due to lubrication performance. The main contribution of the paper was explaining the significant role of adding dimples in artificial hip joint surface bearing who can probably decrease friction interaction on the acetabular liner and femoral head that impact on improving wear resistance. This is achieved by analyzing the geometric variation (shape and diameter) of the dimple to the performance of lubricating metal-on-metal artificial hip joint bearings under normal walking conditions. The research method focused on numerical analysis using the Fluid-Structure Interaction (FSI) simulation method which reviewed the solid and fluid structure. From the simulation results, it can be seen that the variation of ellipse dimple with a diameter of 80 μm has the best lubrication performance, which is indicated by the largest hydrodynamic fluid pressure of 0.915 Pa, the smallest solid pressure is 0.433 Pa, and the largest lubricant thickness is 22.672 μm.
Lubrication effect of metal-on-metal in hip joint replacement
2014
The consumption of hard-on-hard material is one of alternative methods to replace the soft-on-soft or soft-on-hard material which has long been used in hip joint replacement. The famous the type of hard-on-hard material in hip joint replacement is metal-on-metal. It is the best method which is selected by surgeon to replace the original hip joint. However, the metal-on-metal hip implants can be producing the smallest wear particle as a result of attrition of contact surface between femoral head and acetabulum cup. Therefore, the lubricant must be located between the surface of femoral head and acetabulum cup to reduce wear particle. Hence, an analysis is carried out to examine the effect of lubrication on metal-on-metal hip joint replacement upon the occurrence of contact surface between femoral head and acetabulum cup. It includes two types of analysis namely dry and lubrication contact analysis. Based on analysis in dry contact, the maximum contact pressure occurs at the surface o...