Contact mechanics of modular metal-on-polyethylene total hip replacement under adverse edge loading conditions (original) (raw)
Related papers
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...
The Effect of Loading on the Contact Stress of UHMWPE Material for Artificial Hip Joint Bearing
2012
An artificial hip joint consists of several main components. The components are femoral stem, femoral head, acetabular liner and acetabular shell. As its function as a bearing, an acetabular liner is designed to reduce friction and receive the high stress. The liner is made from Ultra High Molecular Weight Polyethylene (UHMWPE) material. It is reported that the UHMWPE liner bearing is occasionally fails inside the patient's body. This paper reports the effect of loading on the liner and predicts the liner ability in receiving the load. A finite element simulation is employed in modeling the contact system. The maximum load received by the artificial hip joint during human activities is used as input in the artificial hip joint models. The result shows that the acetabular liner receives the high stress distribution and the highest stress is located on the center of the liner. The maximum stress on the acetabular liner does not exceed the yield criteria of the UHMWPE material. It is concluded that the UHMWPE material is relatively able to carry the various loading. However, the failure of the acetabular liner can be caused by the unexpected conditions when the patient stumbles or falls down.
Analysis of contact pressure in a 3D model of dual-mobility hip joint prosthesis under a gait cycle
Scientific Reports, 2023
Hip joint prostheses are used to replace hip joint function in the human body. The latest dual-mobility hip joint prosthesis has an additional component of an outer liner that acts as a cover for the liner component. Research on the contact pressure generated on the latest model of a dual-mobility hip joint prosthesis under a gait cycle has never been done before. The model is made of ultrahigh molecular weight polyethylene (UHMWPE) on the inner liner and 316L stainless steel (SS 316L) on the outer liner and acetabular cup. Simulation modeling using the finite element method is considered static loading with an implicit solver for studying the geometric parameter design of dual-mobility hip joint prostheses. In this study, simulation modeling was carried out by applying varying inclination angles of 30°, 40°, 45°, 50°, 60°, and 70° to the acetabular cup component. Three-dimensional loads were placed on femoral head reference points with variations of femoral head diameter used at 22 mm, 28 mm, and 32 mm. The results in the inner surface of the inner liner, the outer surface of the outer liner, and the inner surface of the acetabular cup showed that the variations in inclination angle do not have a major effect on the maximum contact pressure value on the liner component, where the acetabular cup with an inclination angle of 45° can reduce contact pressure more than the other studied inclination angle variations. In addition, it was found that the 22 mm diameter of the femoral head increases the contact pressure. The use of a larger diameter femoral head with an acetabular cup configuration at a 45° inclination can minimize the risk of implant failure due to wear. A dual-mobility hip prosthesis was introduced to reduce the risk of dislocation up to a 0.9% dislocation rate for 10 years of use 1 and increase the overall stability and range of motion 2,3. It was made to increase the range of motion when used on a daily basis 4. An extended range of motion can avoid impingement in the hip joint prosthesis. Two general interactions that occur in a conventional dual-mobility hip joint prosthesis model are the acetabular cup with the liner and the liner with the femoral head, causing wear at two different locations 5,6. Ultrahigh molecular weight polyethylene (UHMWPE) is a widely used material, especially as a bearing material for hip joint replacement surgery 7,8. The type of UHMWPE used in the medical field has a molecular weight ranging from 3.5 to 6 million g/mol and has a degree of crystallinity ranging from 50 to 55% 9. In addition, metals are widely used in the orthopedic field, both in temporary and permanent equipment. The use of metal in permanent orthopedic equipment (prosthesis) cannot be separated from the consideration of chemical reactions that can occur when metal debris interacts with body tissues, especially bones 10-12 .
Contact mechanics of metal-on-metal hip implants employing a metallic cup with a UHMWPE backing
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 2003
The contact mechanics in metal-on-metal hip implants employing a cobalt chromium acetabular cup with an ultra-high molecular weight polyethylene ( UHMWPE ) backing were analysed in the present study using the nite element method. A general modelling methodology was developed to examine the e ects of the interfacial boundary conditions between the UHMWPE backing and a titanium shell for cementless xation, the coe cient of friction and the loading angle on the predicted contact pressure distribution at the articulating surfaces. It was found that the contact mechanics at the bearing surfaces were signi cantly a ected by the UHMWPE backing. Consequently, a relatively constant pressure distribution was predicted within the contact conjunction, and the maximum contact pressure occurred towards the edge of the contact. On the other hand, the interfacial boundary condition between the UHMWPE backing and the titanium shell, the coe cient of friction and the loading angle were found to have a negligible e ect on the contact mechanics at the bearing surfaces. Overall, the magnitude of the contact pressure was signi cantly reduced, compared with a similar cup without the UHMWPE backing. The importance of the UHMWPE backing on the tribological performance of metal-on-metal hip implants is discussed.
2021
Latterly, the polycarbonare urethane (PCU) has suggested a viable substitude to conventional bearings. The aim of this study is to determine the von Mises stress and contact pressure as a function of different of acetabular cup thickness. The analysis of this study was conducted by the finite element method. Six variation of acetabular liner thickness (5mm, 10mm, 15mm, 20mm, 30mm, and 40mm) were used in this simulation. The contact pressure was determined to predict the wear performance of PCU acetabular liner. The result shown that the thicker of the acetabular liner, the smaller the contact pressure and the smaller the contact radius. Thus predictable that the thinner the PCU acetabular liner, the higher
Edge loading in metal-on-metal hips: low clearance is a new risk factor
Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine, 2012
The revision rate of large head metal-on-metal and resurfacing hips are significantly higher than conventional total hip replacements. The revision of these components has been linked to high wear caused by edge loading; which occurs when the head-cup contact patch extends over the cup rim. There are two current explanations for this; first, there is loss of entrainment of synovial fluid resulting in breakdown of the lubricating film and second, edge loading results in a large local increase in contact pressure and consequent film thickness reduction at the cup rim, which causes an increase in wear. This paper develops a method to calculate the distance between the joint reaction force vector and the cup rim--the contact patch centre to rim (CPCR) distance. However, the critical distance for the risk of edge loading is the distance from the contact patch edge to rim (CPER) distance. An analysis of explanted hip components, divided into edge worn and non-edge-worn components showed t...
IOP Conference Series: Materials Science and Engineering, 2017
Contact area and stress distribution of the polyethylene liner (PE liner) have a major influence on the wear process. The main factor that affects the contact area and stress on the PE liner is thickness. The International Standards Organization (ISO) recommends a minimum PE liner thickness of 6 mm. However, the thickness of PE liner in a bipolar hip prosthesis has a limited range of motion compared to the unipolar one due to the addition of the outer liner component. Therefore, the study of the effect of PE liner thickness on the contact area and stress distribution in the bipolar model is interesting. Theaim of this research is to investigate the effect of the PE liner thickness to the contact area and stress distribution on the surface of contact between head and PE liner and the contact between outer liner and cup in the bipolar model. This research was carried out by finite element analysis. The results showed that the highest contact stress on the liner occurred at the lowest liner thickness. The maximum contact radius on the liner surface took place at the highest liner thickness. The bipolar model with the liner thickness of 4.5 mm in this research provided the lowest contact stress.
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.
Finite element study on the predicted equivalent stresses in the artificial hip joint
Journal of Biomedical Science and Engineering, 2012
The subsurface fatigue that occurs in the Ultra-High Molecular Weight Polyethylene (UHMWPE) hip joint cup has been identified to be correlated with the contact stress at that cup. This cup stress is known to be affected by the implant design, dimensions and materials. In this study, a 3D finite element modeling has been used to investigate the effects on the cup contact stress when using low stiffness Titanium alloy (Ti) as a femur head. Also, the effects on the cup contact stress due to using different sizes of femur heads, and the presence of metal backing shell with different thicknesses are studied. The finite element results show that the use of low stiffness Ti alloy femur head results in a significant decrease in the cup contact stress compared with Stainless Steel (SS) and Cobalt Chromium (Co Cr Mo) femur heads. The presence of metal backing shell up to 1 mm thickness results in a remarkable decrease in the cup contact stresses especially for small femur heads. Finally, the use of larger femur heads, up to 32 mm diameter, results in significant decrease in the overall predicted hip joint contact. The present results indicate that any changes in design and geometrical parameters of the hip joint have significant consequences in the long term behaviour of the artificial hip joint and should be taken into consideration.