ABSTRACT
Objective To study the contact performance of hip joint replacements with different material combinations typically used in clinic. Methods The finite element model of spherical conformal contact of hip joint replacements was developed to analyze the different contact mechanics performance of hip joint replacements with different material combinations by simulation test under a vertical constant load within one normal walking gait. The corresponding wear prediction was also evaluated. Results The contact mechanics performances of hip joint replacements with the material combination of metal-on-metal (MOM), metal-on-ceramic (MOC), ceramic-on-ceramic (COC), metal-on-polyethylene (MOP) and ceramic-on-polythene (COP) were analyzed. The results obtained from the simulations showed that contact stress was decreased in the order of COC＞MOC＞MOM＞COP＞MOP, while contact area was decreased in the order of MOP＞COP＞MOM＞MOC＞COC. Conclusions Hip joint replacement with the material combination of high elastic modulus and low Poisson’s ratio has smaller deformation, but could induce larger local stress, while flexible material polythene of low elastic modulus and high Poisson’s ratio might have smaller concentrated contact stress, but cause larger deformation and edge contact phenomenon on the acetabulum cup of hip joint replacements. In addition, hip joint replacements with MOC and MOM material combination may have lower contact bearing performance, which provides references for material choices of typical artificial hip joints in clinic.
ABSTRACT
Objective To investigate the edge contact behavior of conformal spherical hip joint replacements under the given dynamic contact displacement condition. Methods Based on the developed spherical-grid-data model, the contact behavior and corresponding edge contact behavior of a typical metal-on-metal hip joint replacement was simulated under the increasing displacement between the acetabular cup and femoral head. Results It was found from the obtained results that the vertical and horizontal component of the support force due to contact pressure increased with the dynamic contact displacement increasing. The vertical component of support force for the edge contact showed a slower variation tendency than that for the non edge contact, while the corresponding horizontal component of support force increased more significantly with the dynamic displacement. In addition, the corresponding contact pressure distributions and the contact areas of hip joint replacements for edge contact and non-edge contact were different. Conclusions The significant edge contact behavior of hip joint replacements with bigger cup inclination angle occurrs with the increasing displacement of femoral head to the acetabular cup, which will cause the sliding between contact surfaces and additional wear since the horizontal support force increases. This provides a reference for the wear assessment and manufacturing of hip joint replacements.
ABSTRACT
Objective Due to the limitation of manufacturing techniques, possible design optimization selecting and influence of its wearing in clinical application, the bearing surface of hip joint replacements is presented as non-spherical geometry, and the finite element method can be used to study the contact mechanics behavior in such kind of non-spherical hip joint replacement. MethodsThe reconstructing of non-spherical articular surface based on spherical-grid-data model (SGDM) was developed to investigate the effect of contact mechanics of an ellipsoidal head against a spherical cup in a typical metal-on-metal hip joint replacement. Results The maximum contact pressure of the non-spherical bearing was decreased effectively, and meanwhile the contact area was increased when curvature radius of the ellipsoidal head around the centre of the contact zone was increased, while the effects of the cup inclination angle on the maximum contact pressure and contact area of the non spherical bearing under the same load showed relatively small, but the contact pressure distributions were different. Conclusions A well-controlled non-sphericity can improve the magnitude and distribution of contact pressures on metal-on-metal hip joint replacements. In addition, the developed model and evaluation method in this paper can be used for simulation of dynamic contact and wear prediction of non-spherical hip joint replacements.
ABSTRACT
Objective To develop a wear prediction model for hard-on-hard hip joint replacement under the condition of complex dynamic loading and time-dependent motion, and to apply it to the study on wear prediction of the typical metal-on-metal hip joint replacement in the complicated three-dimensional (3D) physiological motion condition. Methods The finite element model for contact mechanics was established and the fixed-tracked method was adopted to make the dynamic wear reappear on the bearing surface of artificial hip joint with 3D Euler transformation, and the data communication about the corresponding contact and wear for simulation was also made. Results The wear prediction test showed that the spherical bearing geometry of the artificial hip joint gradually became the non-spherical form due to the wear with time; meanwhile, the corresponding contact area was increased, the distribution of the contact pressure tended to be flattened, and the maximum contact pressure was decreased. Conclusions The wear prediction model developed here for metal-on-metal hip joint replacements with bilateral bearing surfaces under the condition of complex dynamic loading and motion could be used to carry out simulation test for the wear prediction of metal-on-metal artificial joint, which provides a new method to understand the wear mechanism of hip joint replacement.
ABSTRACT
Objective To study the contact mechanics of metal-on-metal hip joint replacements under different walking conditions, particularly for the edge contact behavior between the cup and the head of the bearing due to large range movement. Methods The finite element model of a typical hip joint replacement with conformal spherical bearing was established to simulate the edge contact of hip joint replacement under the given cup inclination angles and vertical loads. Results The maximum contact pressure decreased slightly and the contact area increased when the cup inclination angles increased within the range of 0°~60°. When the cup inclination angles were more than 80°, the corresponding contact area moved to the cup edge, the maximum contact pressure and distribution range increased, but the position of the maximum contact pressure moved from the initial contact point to the new point with 6°~9° in the direction of the increasing cup inclination angle to balance the corresponding contact pressure distribution and the loaded human weight. Conclusions Different edge contact behavior of hip joint replacements tends to occur due to the bigger cup inclination angle. Therefore, much attention should be paid to the problem of edge contact for both the clinical surgery and the manufacturing of hip joint replacements.