الفهرس 
Tribological Properties Of Different Bearing MaterialsOnly 14 pages are availabe for public view
 |  | from | 126 |  |  |
| | | from | 126 | | |
Abstract
Despite the undisputed role of total hip arthroplasty (THA) in restoring function and mobility to patients with end-stage hip osteoarthritis, the longevity of the artificial joints is limited In other words, with longer follow-up, some deterioration is evident.
As yet, the most notable factor limiting the longevity of hip arthroplasty, particularly in young, active individuals, is wear of the bearing surface and the ensuing aseptic loosening.
The release of wear particles, mostly from the articulating bearing surfaces, activates a complex inflammatory pathway that leads to loosening of the prosthesis and osteolysis.
The role of the bearing surface has become even more important
as patients undergoing arthroplasty seek high-perfor- mance prostheses to meet their expectations.
Since joint arthroplasty was first introduced surgeons and engineers have made adjustments to try to increase its longevity and improve outcomes. One extremely important development is the introduction of a new generation of bearing surfaces. Improvements in design, advancements in manufacturing, and introduction of alternative bearing surfaces have positively affected THA outcomes over recent decades. Introduction of bearing surfaces with better wear characteristics led to a decline in the release of biologically active wear debris and tremendously reduced wear-related failures. Furthermore,
availability of better bearing surfaces with increased resistance to wear has allowed orthopedic surgeons to use larger femoral heads, which in turn has led to a substantial decline in the incidence of instability after hip arthroplasty.
The conventional low-friction metal-on-polyethylene (MOP) bearing surface, which has served the patients so well, is
increasingly being replaced by the newer generations of bearing surfaces. However, these modern bearing surfaces are not without their own problems.
A main concern in the developing implants for total hip replacement (THR) is the interaction between the implant’s bearing surfaces as they contact during motion. Abrasive and adhesive wear mechanisms can lead to formation of wear debris. The accumulation of debris can activate macrophages to stimulate the production of antibodies, which attack the debris, the implant, and the surrounding bone. This process can cause osteolysis, aseptic loosening, and failure of the implant.
A new alternative, which has gained interest in recent years, is
that of soft bearing materials aimed at reducing wear by maintaining a fluid film between the articulating surfaces, reproducing the tribological function of the natural joint. The theoretical and actual wear properties of soft orthopedic bearings have been explored since the 1980s.
These studies demonstrated clear advantages towards this type of bearing compared to hard bearings in terms of reduced friction and wear. Only recently, however, have cushion bearing implants been produced and their performance characterized in laboratory and animal studies.
Newer generations of HXPE, MOM, ceramic, and metal-onceramic bearing surfaces are being developed. In addition, coating bearing surfaces with materials such as amorphous diamond may contribute to further reduction of wear and ion release. New bearings, with a ceramic femoral head on a metal acetabular insert, have wear characteristics similar to those of COC bearing surfaces and potentially reduced risk for component fracture.