Medical Minute 4-22: New Knee - A Leg Up for Patience

By: Vanessa Welch Email
By: Vanessa Welch Email

A little kicking. A little wading. A little swimming.

Charles Thompson's workout routine used to be high-impact until a knee injury shut him down.

"Day in and day out, pain, pain, pain. I can't even explain the pain."

He used to play college football, but after graduation, the pain kicked in. A couple of years ago, it all went downhill.

"In the last three years, I stopped going into the weight room because of pain."

The problem with older knee replacements: the material. The top portion is made of cobalt chrome, which is sturdy but wears down the plastic lower portion.

"You get a scratch on the metal, but then that metal, as the knee moves, starts rubbing on the plastic. It essentially becomes sandpaper, rubbing the plastic away," said David Watson, M.D., Florida Orthopedic Institute in Tampa, FL.

Doctor David Watson has the solution called Verilast Technology. It's a metal alloy - oxinium - that has the feel of a ceramic and is supported by new FDA approved evidence.

This smoother surface means less scratching and less wear. it can last 30 years, while the old chrome cersion - just 15. And simulations show, after three decades the alloy has 81% less wear than three years of the chrome.

"There's a real benefit with wear characteristics without the downside of ceramic in the knee."

One month after surgery, Charles hit the weights again after three full years on the sideline.

"Now, that I'm able to do the swimming and go into the weight room. I'm very happy again," he said.

And while he may be sore tomorrow, the real benefit is a knee that'll last as long as he does.

For more information on other series produced by Ivanhoe Broadcast News contact John Cherry at (407) 691-1500,



WHAT YOU DON’T KNOW ABOUT YOUR KNEE: The knee is the largest joint in the body. Normal knee function is required to perform most everyday activities. The knee is made up of the lower end of the thighbone (femur), which rotates on the upper end of the shin bone (tibia), and the kneecap (patella), which slides in a groove on the end of the femur. Large ligaments attach to the femur and tibia to provide stability. The long thigh muscles give the knee strength.

DO YOU NEED A NEW KNEE? Most patients who undergo total knee replacement are age 60 to 80, but orthopedic surgeons evaluate patients individually. Recommendations for surgery are based on a patient's pain and disability, not age. Total knee replacements have been performed successfully at all ages, from the young teenager with juvenile arthritis to the elderly patient with degenerative arthritis.

NEW KNEES: THE SOLUTION: Based on in-vitro wear simulation testing, the LEGION Primary Knee System with VERILAST technology is expected to provide wear performance sufficient for 30 years of actual use under typical conditions. The results of in-vitro wear simulation testing have not been proven to quantitatively predict clinical wear performance. Also, a reduction in total polyethylene wear volume or wear rate alone may not result in an improved clinical outcome as wear particle size and morphology are also critical factors in the evaluation of the potential for wear mediated osteolysis and associated aseptic implant loosening.

NEW KNEES: THE TECHNOLOGY: Previously, new knees were made from a top portion of cobalt chrome, and a lower portion of plastic. While this combination is proven to function well, normal activities force the coarse surface of the cobalt to wear-down the plastic – which results in a shorter lifespan of the knee. New technology allows for a smoother metal alloy (Oxinium) to be used instead of cobalt chrome – which decreases basic wear-and-tear, and increases the lifespan of the knee.

SURGICAL COMPLICATIONS: The complication rate following total knee replacement is low. Serious complications, such as a knee joint infection, occur in fewer than two percent of patients. Major medical complications such as heart attack or stroke occur even less frequently. Chronic illnesses may increase the potential for complications. Although uncommon, when these complications occur, they can prolong or limit full recovery. Blood clots in the leg veins are the most common complication of knee replacement surgery. Your orthopedic surgeon will outline a prevention program, which may include periodic elevation of your legs, lower leg exercises to increase circulation, support stockings, and medication to thin your blood.

Smith & Nephew Verilast Technology
(866) 867-6040


David Watson, MD, from the Florida Orthopedic Institute in Tampa, FL, discusses knee replacements and the novel medical advances made in his field of study.

Can you explain the basic components of a knee replacement and the goals you have to restore people’s quality of life with it?

Dr. David Watson: Virtually every knee implant has four parts. The first is an ephemeral capon, which is a cap that goes on the distal femur. The second is a tibia tray; the third being a patellar button, and the fourth is a plastic interface that goes between the femur component and the tibia component. The goal of knee replacement surgery is to return a person back to their routine activities and to allow for a pain free functional range of motion. Traditionally, the patients that we were managing with knee arthritis were put through a program with non-operative management, which is still the standard of care, and when a patient got to a point where the quality of life was impaired by the arthritis – the pain and stiffness that goes along with it – they were indicated for a knee replacement. Due to limitations in the technology that we have, we were often having patients prolong having joint replacement to minimize the risk of component failure with excessive wear in accessing secondary surgery. Joint replacement, whether it is of the knee or hip, is pretty much like getting new tires on a car (that is what I tell my patients). Any tire has only a certain number of miles on it, and depending on how fast you ride that car those tires are going to run out sooner. And so the analogy is that our younger patients – the more active patients – tend to put more miles on their knees or hips and tend to wear them out sooner.

What are some of the factors that go into wear?

Dr. David Watson: Well, there are a number of factors that go into wear, some of which are surgeon factors, patient factors and furthermore product factors. The surgeon factors are the position that the implants are put in, the patient factors are how active they are, and the implant factors are the specific wear characteristics of the implant; and those are really a product of how smooth the implants are (rubbing together), as well as the wear characteristic of the plastic portion. The basic limitation in knee replacements has been the interface between the ephemeral components rubbing on the plastic insert.

Will the second, third or even fourth knee replacement for that matter be as efficient as the first?

Dr. David Watson: There’s no doubt that the best knee replacement you have – for most people – is the first knee replacement. If you can optimize that first knee replacement and optimize the longevity (or how long it is going to last) then you are far better off.

What is the difference between the original metal-based ephemeral components used for knee replacement surgeries, and the novel one used today?

Dr. David Watson: The traditional knee replacement ephemeral component was cobalt chrome, which is a good metal. It has a certain surface roughness on it and a certain toughness, which is its ability to resist scratching and other issues that can come from rubbing on plastic. For years it has worked pretty good, but had some limitations. The newer material that we are discussing is again a metal-based ephemeral component – a little bit of a different metal that undergoes a treating process that allows the surface that actually rubs on the plastic to behave like a ceramic zirconium oxide, and that has much better wear characteristics and surface smoothness than those traditional cobalt chrome components.

The scratches that you see on the knee replacements, are those associated with wearing?

Dr. David Watson: Yes. Those scratches that you are seeing are related to wearing; so you get a scratch on the metal, but that metal (as the knee moves) starts rubbing on that plastic and essentially becomes sandpaper as it incessantly rubs that plastic away, and more than likely hasting the demise of that knee replacement. So fewer scratches means better wear characteristics and better longevity of the implant.

How much longer will these new-fangled components last in comparison to the original cobalt chrome components?

Dr. David Watson: I am very cautious telling people exactly how long an implant is going to last. I think that what we have is very good laboratory data on this suggesting that the wear characteristics are much better – certainly in the lab where this has been suggested in the last upwards of thirty years, which is wonderful – does not necessarily take into account all of the potential factors, but it is reassuring, particularly for our younger patients looking to get a knee replacement.

Is there a specific age group that would be better candidates for this kind of surgery?

Dr. David Watson: There is no exact age of when a person should or shouldn’t have a joint replacement surgery. A lot of factors go into it – patient expectations, patient activity level and the quality of life. For me . . . quality of life is the big issue. Anytime that you are making a decision of surgery, you are balancing the risks of surgery where the eventual wearing out of the implant and needing further surgery is one of them; compared to the benefits, which is return to pain free function. There is no doubt that when we are treating younger patients with arthritis, that sort of late potential for wearing out is a big factor that we talk about because secondary surgery has high risks and not always as good as an outcome. With better technology, it is always reassuring to be offering younger patients – who are going to be more active on their joint replacement – a replacement sooner knowing that it is probably going to last longer than it would with the normal implants.

Can you briefly explain what makes this new technology better and more efficient than its predecessor?

Dr. David Watson: For most prosthesis, whether it is knee or hip, the factor that really affects the longevity are the parts that rub together. In traditional materials for knee replacements, you have cobalt chrome rubbing on plastic. Fairly good, but the cobalt chrome has a rougher surface and is far less scratch resistant than the newer product that we are talking about. With the oxinium – it is a zirconium alloy that is heat treated, and the outer portion of this transitions into an oxide, which is a ceramic. Ceramics have far better wear characteristics on polyethylene with the plastic insert. The downside to ceramics historically (especially in the knee) is their brittleness; the risk of fracture. With the treatment process on this metal, that risk of fracture is no longer there. There is a real benefit to wear characteristics without the downside of the ceramic in the knee.

Are you seeing younger patients with arthritis?

Dr. David Watson: There is no doubt about it. We are.

Do you know why that is?

Dr. David Watson: We’re not sure why we are seeing so many younger patients, but it probably has to do with our patient’s expectations. People are having arthritis pains, but they do not want to decrease their activity levels the way that they used to or were sort of asked to. So patients are starting to treat their arthritis earlier, and also reaching that tipping point where their quality of life is affected by arthritis sooner than patients before them, thus they search for pain relief through surgery.

Is there a difference between the original material and the new one, specifically for the patients?

Dr. David Watson: I don’t think that there is a huge difference. There is a certain piece of mind when coming to the decision of having an implant that has been known to show much greater longevity.

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