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Wear from the bearing surface is still the most debated issue in THA
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by Per Kjaersgaard-Andersen, MD
Total hip arthroplasty has become one of the most successful orthopaedic procedures ever developed — in most cases effectively ridding patients of pain and disability. Patients are free to sleep without disturbance from aching groin pain, and they often enjoy a quick return to their daily activities, practically “forgetting” that they recently underwent a major surgical procedure.
The benefits of total hip arthroplasty (THA) have been observed in the early era of its implementation. Since then, orthopaedic surgeons have tried to overcome the side effects from having implanted an artificial joint in the hip.
In the 1960s the main issue was postoperative deep infection. This is still debated and dealt with today, but thanks to developments in clean air theaters, intravenous treatment with broad-spectrum antibiotics and careful patient selection, deep infection has been minimized to less than 0.5%, which, overall, is acceptable.
Changing focus
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In the early era of THA, nearly all implants were cemented. Surgeons observed patients coming back with loose implants and considered cementing to be the “bad boy.” Cement disease was discussed, and noncemented implants gained popularity as a possible solution to these problems in the 1970s. Hereby, new side effects were recognized, such as polyethylene wear, stress shielding and severe osteolysis. Debate then began on wear-related loosening and osteolysis.
Bearing surfaces became the subject of focus in the 1980s. Metal-on-metal, ceramic-on-ceramic and ceramic-on-polyethylene were all increasingly used as standard bearing surfaces, vs. the global standard — metal-on- polyethylene.
At this time, the Swedish Hip Arthroplasty Register began collecting data on all of the nation’s hips. By the 1990s, the register could provide details on the outcome of several combinations in fixation and bearings.
What we’ve learned
Continuing into the new millennium, orthopaedic surgeons have recognized the importance of improving the wear resistance of the most frequently used bearing surface in the socket — polyethylene. We have learned about crosslinking, free radicals and the influence of third bodies in “runaway-wear.”
Based on experiences in my daily practice and this brief history of THA — which probably can be seen from other aspects depending on where you are from — I feel strongly that the main issue of frequent debate during the last 40 years of THA is wear. National registers have provided us with excellent data supporting the notion that problems related to fixation of both cemented and noncemented implants have been “solved,” but wear and its negative side effects are still major issues.
Looking ahead
Therefore, EFORT has created a forum at our congresses to debate and present results on wear and its related topics. We call this “Tribology Day,” which started at the Vienna Congress in 2009, and will be repeated here in Madrid. We have decided to hold the event again in 2011 at the Copenhagen Congress. We hope that, by giving special attention to this serious problem, we may begin to see significant advances made toward its solution. We know, however, that currently no bearing surface is 100% perfect, never leading to a reason for revision.
So, what bearings will be the major players in the future? If the newest generation highly crosslinked polyethylene bearings show the same low or no wear at the longer term, without changes in mechanical quality, I’m convinced that this socket bearing surface will achieve optimal outcomes with any size or material femoral component. Ceramic-on-ceramic should also be considered, although more research is needed to determine the reason behind and consequences of squeaking before this low- or no-wear bearing should be used more frequently in the future. And finally, metal-on-metal has been here for generations — but only recently has it been troublesome due to metal debris creating aseptic lymphocyte-dominated vasculitis-associated lesions (ALVAL) and pseudotumors in a small percentage of patients. Clinical studies are needed to answer questions as to why this change has occurred and how it may be overcome as our patients ask for resurfacing and very large heads.