O steolysis is due to particulate wear debris and is responsible for the long-term failure of total hip replacements. It has stimulated the development of alternative joint surfaces such as metal-on-metal or ceramic-on-ceramic implants.Since 1988 the second-generation metal-on-metal implant Metasul has been used in over 60 000 hips. Analysis of 118 retrieved specimens of the head or cup showed rates of wear of approximately 25 µm for the whole articulation per year in the first year, decreasing to about 5 µm per year after the third. Metal surfaces have a 'self-polishing' capacity. Scratches are worn out by further joint movement. Volumetric wear was decreased some 60-fold compared with that of metal-on-polyethylene implants, suggesting that second-generation metal-on-metal prostheses may considerably reduce osteolysis. [Br] 1998;80-B:46-50. Received 20 April 1998; Accepted after revision 8 July 1998 Osteolysis is due to particulate wear debris 1,2 and is mainly responsible for the long-term failure of total hip replacement (THR). The Charnley THR has been shown to give satisfactory clinical results with a survival rate of 85% at 20 years. When radiological evidence of loosening was added to that seen at revision operations, 22% of the acetabular and 7% of the femoral components were considered to be unstable. Polyethylene wear was shown to be significantly related to acetabular loosening and resorption of the femoral neck in nearly two-thirds of cemented THRs in patients younger than 20 years at the time of operation. 4 About half a million polyethylene wear particles are produced at each step due mainly to abrasive wear. 5,6 Contact of particle-laden articular fluid with the surrounding bone could be a key factor in the development of osteolysis. Joint fluid under pressure invades soft tissues and bone and expands the effective joint pace. J Bone Joint Surg7 As a result, activated macrophages may be found in cysts around the prostheses. 8It is not only the concentration of accumulated polyethylene particles which affects the amount of osteolysis, but also their capacity for phagocytosis.9,10 Particles with a critical size of between 0.5 and 10 µm are needed to induce the secretion of interleukin-6 by macrophages in vitro. It is still unclear as to whether polyethylene or cement debris induces more osteolysis. Severe lysis around a stable uncemented press-fit titanium shell is a clear indication of polyethylene wear.11 Polymethylmethacrylate (PMMA) cement alone is less harmful if it does not contain radiopaque additives. In vitro, monocytes and macrophages responding to particles of bone cement are capable of differentiation into osteoclastic cells. Their capacity for bone resorption is activated only when radiopaque additives are introduced with the cement particles, with a doubling of the rate for Ba 2 SO 4 compared with ZrO 2 . 12Osteolysis therefore has a multifactorial pattern and the biological activity of all possible wear particles has to be considered when introducing new implants. 13There have bee...
As wear is inevitable with artificial joint replacement, it has to be minimized to avoid possible aseptic loosening following osteolysis due to particle-initiated foreign body reaction. Co-Cr-Mo-C alloys have a long history with only minimum wear when articulating with themselves. This investigation shows that the choice of the alloy has an effect on the wear rate of this articulation couple. Tribological studies in a screening device, a pendulum apparatus and a hip joint simulator showed a marked influence of the environment as well as the diameter of the implants with metal-on-metal articulation. A wear-resistant combination with low friction characteristics has been developed by using a wrought Co-Cr-Mo-C alloy and reducing the implant diameter to 28 mm. Clinical wear rates are comparable with laboratory data and demonstrate the potential of the metal-on-metal articulation to solve the problem of wear-induced osteolysis of hip joint endoprostheses.
Osteolysis is due to particulate wear debris and is responsible for the long-term failure of total hip replacements. It has stimulated the development of alternative joint surfaces such as metal-on-metal or ceramic-on-ceramic implants. Since 1988 the second-generation metal-on-metal implant Metasul has been used in over 60 000 hips. Analysis of 118 retrieved specimens of the head or cup showed rates of wear of approximately 25 microm for the whole articulation per year in the first year, decreasing to about 5 microm per year after the third. Metal surfaces have a 'self-polishing' capacity. Scratches are worn out by further joint movement. Volumetric wear was decreased some 60-fold compared with that of metal-on-polyethylene implants, suggesting that second-generation metal-on-metal prostheses may considerably reduce osteolysis.
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