P005 Analysis of hydrodynamic lubrication in artificial hip joint replacements

The cyclic variation in both the load and speed experienced during walking was considered in an elastohydrodynamic lubrication (EHL) analysis for artificial hip joint replacements in this study. A general numerical procedure was developed to take both the entraining and squeeze-film actions into the solution of the Reynolds equation in the spherical ball-in-socket coordinate, simultaneously with the elasticity equation, using the Newton-Raphson method. The numerical procedure developed was then applied to an example of hip joint replacements employing an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup against either a metallic or ceramic femoral head under simplified cyclic load and speed conditions. The predicted minimum film thickness was found to stay remarkably constant, despite a large change in the angular velocity and the load. This was attributed to the combined effect of entraining and squeeze-film actions in generating, replenishing and maintaining the lubricating film in artificial hip joint replacements. Furthermore, it was pointed out that the average transient minimum film thickness predicted throughout one cycle was very close to that under quasi-static conditions based upon the average angular velocity and load.

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An axisymmetric contact model of ultra high molecular weight polyethylene cups against metallic femoral heads for artificial hip joint replacements

Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine ◽

10.1243/0954411991535158 ◽

1999 ◽

Vol 213 (4) ◽

pp. 317-327 ◽

Cited By ~ 34

Author(s):

Z M Jin ◽

S M Heng ◽

H W Ng ◽

D D Auger

Keyword(s):

Molecular Weight ◽

High Molecular Weight ◽

Hip Joint ◽

Contact Model ◽

Joint Replacements ◽

Artificial Hip Joint ◽

Artificial Hip ◽

Femoral Heads ◽

Hip Joint Replacements ◽

Ultra High Molecular Weight

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A general axisymmetric contact mechanics model for layered surfaces, with particular reference to artificial hip joint replacements

Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine ◽

10.1243/0954411001535453 ◽

2000 ◽

Vol 214 (5) ◽

pp. 425-435 ◽

Cited By ~ 8

Author(s):

Z M Jin

Keyword(s):

Contact Mechanics ◽

Hip Joint ◽

Joint Replacements ◽

Total Hip ◽

Mechanics Model ◽

Artificial Hip Joint ◽

Metal On Metal ◽

Artificial Hip ◽

Hip Joint Replacements ◽

Joint Prostheses

A general axisymmetric contact mechanics model for layered surfaces is considered in this study, with particular reference to artificial hip joint replacements. The indenting surface, which represents the femoral head, was modelled as an elastic solid with or without coating, while the other contacting surface, which represents the acetabular cup, was modelled as a two-layered solid. It is shown that this model is applicable to current total hip joint prostheses employing ultra-high molecular weight polyethylene (UHMWPE) acetabular cups against metallic, metallic with coating or ceramic femoral heads as well as metal-on-metal combinations. The effect of cement is also investigated for these prostheses using this model. The use of a metallic bearing surface bonded to a UHMWPE substrate for acetabular cups is particularly examined for metal-on-metal hip joint replacements. Both the contact radius and the contact pressure distribution are predicted for examples of these total hip joint replacements, under typical conditions. Application of contact mechanics to the design of artificial hip joint replacements employing various material combinations is discussed.

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Analysis of fluid film lubrication in artificial hip joint replacements with surfaces of high elastic modulus

Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine ◽

10.1243/0954411971534359 ◽

1997 ◽

Vol 211 (3) ◽

pp. 247-256 ◽

Cited By ~ 197

Author(s):

Z M Jin ◽

D Dowson ◽

J Fisher

Keyword(s):

Hip Joint ◽

Radial Clearance ◽

Joint Replacements ◽

Lubricating Film ◽

Artificial Hip Joint ◽

Artificial Hip ◽

Hip Joint Replacements ◽

Film Lubrication ◽

Fluid Film Lubrication ◽

Lubricating Film Thickness

Lubrication mechanisms and contact mechanics have been analysed for total hip joint replacements made from hard bearing surfaces such as metal-on-metal and ceramic-on-ceramic. A similar analysis for ultra-high molecular weight polyethylene (UHMWPE) against a hard bearing surface has also been carried out and used as a reference. The most important factor influencing the predicted lubricating film thickness has been found to be the radial clearance between the ball and the socket. Full fluid film lubrication may be achieved in these hard/hard bearings provided that the surface finish of the bearing surface and the radial clearance are chosen correctly and maintained. Furthermore, there is a close relation between the predicted contact half width and the predicted lubricating film thickness. Therefore, it is important to analyse the contact mechanics in artificial hip joint replacements. Practical considerations of manufacturing these bearing surfaces have also been discussed.

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A full numerical analysis of hydrodynamic lubrication in artificial hip joint replacements constructed from hard materials

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1243/0954406991522310 ◽

1999 ◽

Vol 213 (4) ◽

pp. 355-370 ◽

Cited By ~ 51

Author(s):

Z. M. Jin ◽

D Dowson

Keyword(s):

Film Thickness ◽

Hip Joint ◽

Hydrodynamic Lubrication ◽

Squeeze Film ◽

Radial Clearance ◽

Acetabular Cup ◽

Joint Replacements ◽

Lubricating Film ◽

Metal On Metal ◽

Hip Joint Replacements

A full numerical analysis of the hydrodynamic lubrication problem of artificial hip joint replacements with surfaces of high elastic modulus materials, such as metal-on-metal or ceramic-on-ceramic, under cyclic walking conditions is reported in this paper. The Reynolds equation in spherical coordinates has been solved for both entraining and combined entraining and squeeze film motions under a three-dimensional variation in both the load and the speed experienced in hip joints during walking. It has been shown that a finite lubricating film thickness can be developed during the walking cycle owing to the combined action of the squeeze film and entraining motions under some conditions. It has been found that the design parameters for plain spherical bearings, such as the femoral head radius and the radial clearance between the femoral head and the acetabular cup, have a large effect on the magnitude of the predicted lubricating film thickness. Some interest has been shown in recent years in the performance of metal-on-metal bearings in which a dimple has been machined at the pole of the acetabular cup. It is shown that a dimple on the acetabular cup can significantly increase the film thickness throughout the walking cycle, particularly for relatively large depths and if the location of the dimple coincides with the direction of the resultant force acting on the joints. It is concluded that there is a good possibility that a full continuous hydrodynamic lubricating film can be developed in ceramic-on-ceramic hip joint replacements, and perhaps for some well-finished metal-on-metal implants with a relatively small radial clearance. For some metal-on-metal configurations, the effect of elastic deformation of the bearing surfaces must be taken into account in the lubrication analysis, particularly for a relatively large radial clearance.

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