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Joint replacement is one of the most successful procedures in medicine today. The long-term success of total joint replacement is determined by two dominant factors: fixation of the prostheses to the skeleton/bone and avoiding problems related to wear of the bearing surfaces.
During the past 40 years, major advances have been made in each of these areas. Long-term successful fixation of the prostheses is now predictably achieved in a very high percentage of patients. The loosening rates of both total hip and knee replacement have been shown to be about 1 percent or less per year. In other words, after 15 years, only about 10 percent of patients have developed problems that require revision (re-doing) the replacement. These are extraordinary results and one of the many reasons why joint replacement is so successful.
In total hip replacement, excellent long-term fixation can be obtained by using porous metal materials (which the bone grows into) or by the use of bone cement (a grouting material). Increasingly, biologic fixation (permanent bone ingrowth into the prosthesis) is the preferred technique by many surgeons.
In total knee replacement, the use of bone cement has an excellent long-term track record and remains the technique of choice for most surgeons. Nonetheless, cementless fixation with porous materials is also frequently successful. The choice of fixation for both total hip and total knee replacements is typically made by the surgeon, taking into account the scientific data on the topic, the patient’s bone quality and the surgeon’s own experience.
Because of the tremendous success in permanently fixing the prostheses to the bone, the most significant long-term problem to be solved today is the problem of joint wear. All moving mechanical parts, which “rub” against each other, will cause wear. In our automobiles, we replace our oil every 3,000 to 5,000 miles to get rid of the metal debris the engine creates from the moving parts. In the human, this is obviously not an option. Therefore, we have had to try to solve this problem by creating bearing surfaces that are extremely wear-resistant, that is, create very few wear particles.
This is a very exciting time as it relates to so-called “alternative bearing surfaces”. These bearing surfaces are designed to create very, very few wear particles and have the potential to dramatically improve the length of excellent service of total joint replacements. Laboratory data with wear simulators and short-term clinical results have increased our enthusiasm for these technologies.
Around the world, there are three major new technologies designed to dramatically reduce wear. These “alternative bearing surfaces” have generated a great deal of interest and research. At this point, it is unclear as to which technology will prove to be the best. Many surgeons are optimistic that all will prove to be great advances. It is important to point out that patients cannot tell the difference between any of these bearing surfaces. There is no difference in pain relief, walking ability or any other clinical aspect of the materials.
These new bearing surfaces are called “hard-on-hard surfaces” (metal-on-metal and ceramic-on-ceramic) and highly cross-linked polyethylene. In the laboratory and in short-term clinical experience, all have been shown to dramatically reduce wear. All reduce wear by approximately 90 percent or more. If these laboratory data and clinical results hold true over the long term, all will likely prove to be incredible advances in the longevity of total joint replacements.
There are some differences in the pros and cons of these bearing surfaces. At this point, St.Vincent Center for Joint Replacement surgeons are very familiar with the advantages and disadvantages of each and select the bearing surfaces based upon their interpretation of this information and their clinical experience.
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