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Metal-on-Metal Musings


Debate about the future of metal-on-metal implants was among the hot-button issues keeping this year’s installment of the AAOS annual meeting buzzing.


Group Editor


Managing Editor

As the American Academy of Orthopaedic Surgeons (AAOS) kicked off its annual meeting this year San Diego, Calif., much of the “buzz” during the event was about metal-on-metal implants and the most recent machinations surrounding the technology. The implants have been widely used for years to replace joints damaged by the ravages of time, trauma and arthritis.


The U.S. Food and Drug Administration (FDA) recently launched a webpage detailing some of the issues surrounding metal-on-metal implants, and agency officials said they are taking a close look at all-metal hips, which have faced sales pressure amid concerns about metal particles wearing off and causing medical problems. Some patient advocacy groups have laid blame at the FDA’s feet, accusing the agency’s review process of being too lax.


As a consequence of the sliding action of joint replacement devices, wear particles form in the joint space. Implant, design and materials selection can limit the concentration and size of the particles that develop during the expected life cycle of the implant, but essentially it is unavoidable. It is the presence of the wear particles, at certain concentrations and specific size ranges, that largely contributes to osteolysis (bone cell death) through various cell responses in the body. The formation of wear debris undoubtedly has created considerable concern about the long-term viability of the implants.


For this reason, the FDA requires manufacturers to show the wear particle size, shape distribution and concentration development during biomechanical testing. They must demonstrate that the particles produced are outside of the bioactive size range and also are of low concentration.


The agency said it’s “actively working in several areas to further assess the safety and effectiveness” of the devices.


The agency also made detailed recommendations to surgeons, such as avoiding all-metal implants in patients with certain problems such as suppressed immune systems or known metal sensitivity. People react to metal particles differently, and it’s not currently possible to predict who will have a reaction, what it will entail or when it could happen, according to the FDA. The agency recommended patients with all-metal hips talk to their surgeon immediately if they develop new or significantly worsening problems such as pain, swelling, numbness and walking issues.


In August last year, Johnson & Johnson’s (J&J) DePuy orthopedic division issued a voluntary recall of its ASR metal-on-metal implant after new data from a joint registry in the United Kingdom indicated an unusually high rate of repeat procedures. Zimmer Holdings Inc. suffered a blow in mid-2008 when it suspended U.S. sales of a metal hip cup called Durom amid reports of issues such as cup loosening, which the company pegged to surgeons needing retraining. Biomet Inc., which is privately held, also manufactures a metal-on-metal hip.


All-metal hips most often are constructed of cobalt-chromium alloy.


Stryker Corp. doesn’t make all-metal hips. Zimmer still does, though company officials have said it is not a big business for them. Stryker and Zimmer both have reported upticks in their non-metal hip business as a result.


AAOS issued a statement thanking the FDA for its “thorough and well-considered look” at concerns surrounding the implants.


“The FDA is a partner in patient safety and education. We believe that a significant majority of metal-on-metal hip replacement implants have successfully relieved pain and improved function without any problems for the patients who have received them but there have been some concerning exceptions,” John J. Callaghan, the academy’s past president, said in a release. “We are working together to investigate and report these concerns and will continue to communicate with our 36,000 members, the medical community and the public.” In Callaghan’s disclosure, he reported receiving royalties from DePuy.


According to data from the Nationwide Implant Sample database, in a one-year period from 2005-2006, approximately 39,200 metal-on-metal hip replacements were performed.


AAOS has helped to establish the American Joint Replacement Registry (AJRR). The AJRR will track data on outcomes and devices, just as joint registries in other countries do. This national database will serve as an early alert system for continued or new device problems.
The data collection process has just begun and will allow orthopedic surgeons to track the success and failures of any implant used nationwide, according to academy officials.


Data from a recent study performed by DePuy indicated that as many as 12 percent of patients who received ASR implants through a replacement or resurfacing required corrective surgery in fewer than five years after their initial surgery due to a failure of the component device. This is much sooner than the average follow-up procedure, which occurs roughly 15 to 20 years after implantation. The problem with more frequent revisionary surgery is that every surgery has risks, and every additional surgery involving the hip joint exponentially increases the chances of serious complications such as blood clots, bone loss, nerve damage or infection. Of course, there also is the associated pain, rehabilitation time and expense.


In early 2010, DePuy reported that it would phase out these implants because not enough of the devices were selling to justify the costs of manufacture. Consumer watchdog groups and medical professionals, however, feel that DePuy’s announcement was motivated by its own misgivings about the problems with the device.


The most common complication associated with these particular ASR implants is something called metal hypersensitivity. Surface sensitivity to metals is relatively common. An estimated 10 to 15 percent of the population has some form of allergic reaction to metal, from hives, redness and itching to eczema in the affected area.


Clearly, the metal sensitivity experienced by hip replacement patients cannot be treated by an analgesic cream or a topical antihistamine. The problem occurs when metal-on-metal devices either are installed incorrectly or they fail altogether—causing the metal surfaces to scrape together with more friction than normal, releasing microscopic particles of metallic debris into nearby tissue.


A buildup of this metal can cause inflammation, pain in the groin region, bone loss, systemic immunological responses and tissue death. These serious complications often require the revisionary surgery referenced above to correct tissue problems or even swap out the faulty joint for a new one. That is why medical professionals have recommended—in a recent edition of The Journal of Arthroplasty—that physicians only use these particular ASR devices once they have carefully considered the possible benefits and risks to the patient.


The Physician’s Perspective


Maybe it was some sort of sixth sense or perhaps it was just coincidence, but Joshua J. Jacobs, M.D., has never been a big fan of metal-on-metal implants.


“I have been doing research in this area for many years, and I simply thought there were alternatives that would be better [than metal],” Jacobs said during an expert roundtable discussion with journalists during the AAOS conference. “The degree of research and development on polyethylene was more intense historically at the time of my decision than for other bearing surfaces. That’s why I chose polyethylene.”


While Jacobs’ revelation of his choice of implant material did little to add to the controversy surrounding metal-on-metal artificial joints, it nevertheless provided a good forum for discussion of the issue and a unique perspective from an orthopedic surgeon who also is an adjunct professor of materials science and engineering. Jacobs currently is the second vice president of AAOS.


Despite recent concerns and recalls, however, most metal-on-metal implants work well and seldom cause problems for patients, Jacobs said. He noted that only a small percentage of metal implants fail; still, even a small percentage can produce large failure rate figures when the number of total joint replacement procedures performed annually in the United States is taken into consideration. “There are about 350,000 total joint [replacements] done each year. Even if the failure rate is, say, 1 percent … 1 percent of 350,000 is still a lot of people,” he told reporters.


Though metal implant failures can be caused by many factors, Jacobs believes one of the main reasons for the inadequacy (and high revision rates among certain patient populations) is shortcomings within the technology.


“There are pros and cons of any choice,” he said. “The Holy Grail in hip reconstruction surgery is the 25- to 30-year hip—the kind of hip you can put in that will last the rest of your life. That is the goal. That is what many of our patients demand, but we are not there yet with the technology. That’s what we are seeking. But in order to get there, we have to be able innovate.”


Good News for Total Knee Replacements


If you had a knee replacement 20 years ago, chances are you’re getting around just fine, according to the results of a new study released at this year’s meeting.


Most patients who undergo total knee replacement (TKR) are age 60 to 80. More than 90 percent of these individuals experience a dramatic reduction in knee pain and a significant improvement in the ability to perform common activities. However, questions have been raised about the decline in physical function over the long term despite the absence of implant-related problems.


About 581,000 knee replacements are done annually in the United States, according to AAOS, often after the knee is severely damaged by arthritis or injury.


New research unveiled during the annual meeting evaluated patient functionality 20 years after knee replacement.


“It is a common concern for older adults to wonder how they will function several years after the knee replacement and if revision will be necessary,” said John B. Meding, M.D., study author and attending orthopedic surgeon at the Center for Hip and Knee Surgery in Mooresville, Ind.


Although aging may cause a gradual decline in physical activity, a remarkable functional capacity and activity level continues 20 years of more after TKR, the study authors concluded.


Between 1975 and 1989, 1,757 primary cruciate (the ligament behind the knee)-retaining TKRs were preformed at the Center for Hip and Knee Surgery. The study examined 128 patients who were living at the 20-year follow-up point. The average age at operation in the group of 171 TKRs was 63.8 years. Eighty-two percent of these patients had osteoarthritis and 73 percent were female. The average follow-up was 21.1 years and the average age at follow-up was 82.3 years.


The study found:


• Ninety-five patients could walk at least five blocks;


• Nearly half, 48 percent, of patients reported unlimited walking;


• All but two patients could negotiate up and down stairs without a banister;


• Only three patients were considered housebound; and


• There were no implant failures after 20 years.


“These findings definitely add to the conversation with patients considering surgery. If a patient actually lives that long, a well-functioning TKR may help allow them to maintain a remarkable functional capacity and activity level not just for five or 10 years but for 20 years and beyond,” said Meding. “This research refutes any perception that the importance of a well-functioning TKR diminishes over time because of an overall declining functional status.
Elderly people are using their surgically replaced knees for fairly active lifestyles many years after surgery.”


Patients considering knee replacement should talk to their orthopedic surgeons about the implant’s life expectancy, researchers urged.


Dr. Meding and his co-authors received no compensation for their study.




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