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Knee Replacements on Shaky Scientific Ground


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knee replacements

Knee replacement image courtesy of iStockphoto/33karen33

As the U.S. population ages and continues packing on the pounds, knee replacement surgeries are becoming increasingly common. More than 650,000 total knee replacements were performed in 2008 (according to the latest data available).

And as materials and surgical technologies improve, the promise of newer and better implants is making the procedure even more appealing to the millions of people who suffer from arthritis of the knee. Many of these implants have yet to prove their mettle when it comes to long-term efficacy and safety, however, according to a new report published online Monday in The Lancet.

“In the past 40 years, the number of implants available on the market has substantially proliferated, often with little or no evidence of effectiveness or cost-effectiveness,” noted the authors of the report, led by Andrew Carr, of the University of Oxford’s Department of Orthopedics, Rheumatology and Musculoskeletal Sciences. He and his co-authors reported that there simply isn’t enough data to be sure implants—especially new designs—provide the most pain relief and hold up well to wear and tear.

Unlike new medications, knee replacements and other implants often get far less scrutiny from regulatory agencies, such as the U.S. Food and Drug Administration. A 2011 report from the Institute of Medicine found that medical devices have long lacked adequate safety and efficacy testing. Information on the safety or success of knee replacement implants, in particular, comes primarily from small studies done by individual surgeons who might be the inventor or co-owner of the technology. That connection can lead to bias and conflict of interest in reporting results. “Without high-quality, unbiased and reliable information, surgeons can not make informed decisions,” Carr said in a prepared statement.

If artificial knee implants aren’t working well, doctors and patients should know, Carr noted. So should the public: In 2008 alone, full-knee replacement procedures cost the U.S. health system more than $10.4 billion.

With so much money—and so many knees—at stake, “widespread surveillance of existing implants is urgently needed alongside the carefully monitored introduction of new implant designs,” the researchers wrote in the Lancet paper.

Close scrutiny is all the more important because the demand for knee replacements is expected to increase. Most total knee replacements are recommended for people with osteoarthritis who have severe pain that is hampering their daily lives, although specific criteria for candidates for the procedure are lacking. The main two causes for such pain are age and obesity—both of which are on the rise in the U.S. and across the globe.

Successful surgery can vastly improve a person’s mobility and quality of life. “The outcome of modern knee replacement is very good and continues to improve,” the researchers wrote. And by many counts, some 80 percent of total knee replacements leave patients relatively pain free and without serious problems.

But complications such as infection, implant wear or malfunction are not uncommon. Carr and his co-authors argue that doctors and patients need to be more familiar with the risks and benefits of the procedure—and the vast array of implant options. They noted that implants should be tested, like drugs, in large randomized controlled studies and that countries should continue to create long-term registries for the implants so that their track records can be tracked.

In the meantime, the researchers caution that even though doctors and patients often expect that the latest technologies will automatically be better, that is not always the case. Sometimes the tried-and-true device might indeed be the best choice. And because any surgical procedure carries risks, the goal for individuals as well as societies should be to develop ways to avoid the need for knee replacements in the first place.

Katherine Harmon Courage About the Author: Katherine Harmon Courage is a freelance writer and contributing editor for Scientific American. Her book Octopus! The Most Mysterious Creature In the Sea is out now from Penguin/Current. Follow on Twitter @KHCourage.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. BillR 8:49 am 03/6/2012

    I am curious… How you do large randomized controlled studies of these devices without actually implanting the devices into people. And how do you implant the devices into people until the studies are completed.

    I suspect that since they are mechanical devices, the mechanics need to be tested in some sort of experimental setup to test the wear and tear expected in a real joint over time. They would also need to be tested for the ability properly fuse with the bone and for the ability to align it correctly for pain free long term operation.

    Then there would be the quality control procedures and tests during manufacture and the training of surgeons to properly install them.

    Sounds like a lengthy process that would increase the cost of the devices as well.

    Link to this
  2. 2. MadScientist72 8:52 am 03/6/2012

    According to the wikipedia page on him “Professor Carr’s research interests are primarily focused on developing and evaluating surgical technologies including joint replacement, arthroscopy and tissue engineering.” So, of course Dr. Carr is going to say that these procedures need more study & evaluation… studying & evaluating surgical procedures is what he does for a living. Dr. Carr calling a procedure adequately studied would be about as likely as H&R Block supporting simplifying the tax code.

    Link to this
  3. 3. MadScientist72 9:00 am 03/6/2012

    @ BillR “how do you implant the devices into people until the studies are completed” – You get them to sign waivers acknowledging that this is an experimental procedure, that they are aware of the risks involved & that they won’t sue you if things go wrong. the bigger question is how do you keep the patients & monitors from knowing who’s in the experimnetal group & who’s in the control group. It’d be pretty obvious if the controls haven’t had surgery, but you can’t exactly go cutting patients’ knees open & do nothing once you’re in there. Not only would it be unethical, it’d totally disrupt the accuracy of your data.

    Link to this
  4. 4. drafter 11:37 am 03/6/2012

    Heres a simple study.
    How many have already been re-replaced. If they know how many are first time implants then they should already know the number of complications surguries to correct any problems.
    With some 650,000, per the article, implants already in place that should be a large enough study group already in place.

    Link to this
  5. 5. bigbopper 12:58 pm 03/6/2012

    @mad: Actually you can do “sham surgery” on the control group where you just make an incision and then close it again. This is not necessarily unethical. Very few such studies have been done, but there have been a few. One was done to evaluate the efficacy of arthroscopic knee surgery for knee pain which showed that going in and “cleaning out” the knee (removing foreign bodies, trimming and shaving torn cartilage, etc) was no more effective than sham surgery in relieving knee pain. (Moseley JB, O’Malley K, Petersen NJ, et al. A controlled trial of arthroscopic surgery for osteoarthritis of the knee. N Engl J Med 2002;347:81-88). There was also a negative trial of vertebroplasty for osteoporotic vertebral fractures which used a control group undergoing sham surgery (Kallmes DF, Comstock BA, Heagerty PJ, et al. A randomized trial of vertebroplasty for osteoporotic spinal fractures. N Engl J Med 2009;361:569-579).

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  6. 6. GeorgeCait 1:47 pm 03/6/2012

    The heading for this article on Facebook: “Knee Replacements Aren’t as Good as They Should Be.” However, this article isn’t saying that knee replacements are unreliable! The issue being discussed is the quality and amount of evidence in support of their utility.

    They are not studied as stringently as medications because the effects of a knee replacement are rarely systemic (unless there is an infection). The effects of a knee replacement are local: an alteration of joint function at the knee and the trauma of surgery.

    I feel that the article misrepresents the risks of knee replacement and doesn’t say much, overall. Talk to anyone that has had their knee replaced and most likely, they will be very happy they did.

    Link to this
  7. 7. crypto68 2:08 pm 03/6/2012

    I had a total knee replacement in Aug 2010 and have been very pleased. After two Arthroscopic surgeries, injections, and a brace the pain and mobility was terible. The doctor that did the replacement provides antibiotics to prevent infection and has been very accessable for questions and assistance. There is sometimes moderate pain, but nothing like prior to the replacement. I am notified of scheduled update visits for the purpose of tracking quality and status of the implant.

    Link to this
  8. 8. degoodwin 8:07 pm 03/6/2012

    While I was working as a student for the company called Halifax Biomedical, I offered to oversee the writing of a Scientific American article about knee replacement technologies and the innovation of RSA technology. HBI, as the company is also known, uses Stereo Roentgen Xray analysis coupled with their own innovation. They create beds with two planes implanted with very small tantalum beads. These two planes create a reference frame. Two Xray machines snap timed frames that are stored, and sent to Hospital Storage, and offsite storage where HBI’s analysts are able to use software to analyze movements with near micrometer precision.

    One more element, so to speak, is required. HBI’s engineers have designed insertion tools that allow the Orthopaedic Surgeons to insert the tantalum beads in the new joint, and in the bone below the joint. These beads then, when analyzed, show up in relation to the planes defined by the bed. The software used by the analysts uses machine learning methods to perform the initial steps in the analysis. In one information session held by Chad Munro, the president of the company, Chad claimed that the field of joint repair had virtually no precision data available; HBI and its technology is beginning to address this issue.

    Just this year HBI has begun to make the transition from with Clinical Studies, to working with organization in Clinical Practice.

    If you are interested, contact me and I will put you in touch with HBI.

    Link to this
  9. 9. MadScientist72 8:54 am 03/7/2012

    @bigbopper – Arthroscopic surgery is a completely different animal from joint replacement surgery, with a much shorter healing time. In order to perform “sham surgery” that would accurately mimic the healing time of actual knee replacement, you’d have to do significant damage inside & that would certainly be unethical. Plus, you’d never be able to tell how much of their later pain was naturally occurring & how much was a result of what you did, which would ruin their value as control subjects.

    Link to this
  10. 10. Grumpyoleman 6:52 pm 03/7/2012

    The article blames overweight for the recent rash of knee replacements. A TV news spot blamed it on the popularity of running and hiking among the B-boomers in the 70s and 80s.

    Link to this
  11. 11. AKpeanut 2:45 pm 03/10/2012

    I had a knee replacement in 1981. The style I have is no longer available… which is really too bad! It has it’s assorted issues, but it works fine still. I have been told it is the oldest one still in a person. The reason I have been told it still works is that I have kept up muscle mass and activity.

    The need to keep up my leg, to keep the artificial knee supported, is a really compelling reason to keep my weight down and stay fit.

    It is very difficult to evaluate the performance of artificial knees installed in people who have ruined their first knee with overweight and weakness. Perhaps the answer is to encourage people to lose weight and get strong instead of replacing so many knees, so young, in people who did not care about their original equipment to keep THAT up. Education and physical conditioning might be a better investment in a lot of these people, and equally effective. The artificial ones are not the advertised equal of the original equipment. They involve surgical risks, nerve damage, muscle damage and loss, reduce the blood flow to that extremity, expose you to infection, get cold, do not move as the original ones… God does really good work, and it is worth keeping.

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