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3/31/2016 – Every patient that has bone-on-bone arthritis in the hip or knee has thought of this question when considering whether or not to have surgery. All mechanical parts have a working life, but trying to answer this question for parts that are implanted into people is difficult because each person is different, and may put different demands on their artificial joints. Nevertheless, it is important to give patients an idea of what they can expect out of their surgery. The question becomes harder to answer as significant improvements are made in artificial joint design, but these advances also hold the promise of providing better longer lasting implants.
The biggest scientific advancement in total hip and knee replacement has been in the polyethylene or “plastic” liners. The majority of hip and knee replacements implanted in the United States consist of a metal and plastic articulation or bearing surface. This is the part of the joint replacement that actually moves. One of the most common sources of failure is the metal or “hard” surface wearing away the plastic or “soft” surface. A recent article on the long term results of new plastic liners in hip replacement found that at 13 years after surgery in relatively young, high demand patients (age 45-65), 100% of the hip replacements done with new plastic had survived. Furthermore, none of those hips had any indication of plastic wear visible on x-rays.
The newer plastic technology was adopted later in total knee replacement, and long term data are not as clear. Mechanical simulator testing, however, has shown no wear in knee replacement plastic liners after one million cycles. A recent study found that when including all risk factors for failure of knee replacement including those that are unforeseen such as infection, 95% of artificial knees lasted at least 10 years.
As doctors we must give our patients a thorough explanation of risks, benefits, and alternatives to joint replacement surgery. That being said, delaying an effective and durable treatment that has been shown to improve quality of life because of a fear of implant failure may not be necessary for a large number of patients.