Gustke v. Schmalzried: Cementless TKA: As Older Patients Become Younger
OTW Staff • Tue, March 28th, 2017
This week’s Orthopaedic Crossfire® debate was part of the 17th Annual Current Concepts in Joint Replacement® (CCJR®), Spring meeting, which took place in Las Vegas this past May. This week’s topic is “Cementless TKA: As Older Patients Become Younger.” For the proposition is Kenneth A. Gustke, M.D., Florida Orthopaedic Institute, Tampa, Florida. Opposing is Thomas P. Schmalzried, M.D., Joint Replacement Institute, Los Angeles, California. Moderating is Joshua J. Jacobs, M.D., Rush University Medical Center, Chicago, Illinois.
Dr. Gustke: The common perception is that cementless total knee replacements are inferior. The literature is replete with older studies showing that cementless survivorship is inferior to cemented survivorship. One article from the Rush program, showed that 50% of metal-backed patellae were revised; 8% tibial components loosened by 11 years and many of them had osteolysis along the screws. So why are all these poor results reported in literature? I think it’s because they were poor implant designs with cobalt chrome porous interfaces, poor initial tibia component fixation (and they were) using metal-backed patellae as well as polyethylene that was gamma sterilized in air.
Obesity is also a major problem. In 2002 there were only 6% of patients with BMIs [body mass index] over 30. In 2009 it was 20%. And it’s estimated now at about 45-50% of the patients have a BMI greater than 30. Patients that are under the age of 64 have a four times higher likelihood of obesity than patients who are older than 75.
In one meta-analysis there was a 1.23 odds ratio for revision in patients (with) a BMI over 30 for aseptic loosening; and patients over 40 had an even worse survivorship.
Young patients and obese patients put increasing stress on the prosthesis-cement-bone interface. The cementless interface has repair potential and can strengthen with increased loading. Even an RSA study looking at cement versus cementless showed that non-cemented knees do migrate, but stabilize at three months, but cemented total knees continue to migrate.
Eliminating the metal-backed patella from the surgery dramatically improved the results to about 80% survivorship. Eliminating the tibial screws, eliminating the polyethylene wear debris track, improved it to the 90% range. And now with the use of highly cross-linked polyethylene in cementless knees, we’re up to equivalent or perhaps better than what we see with cement.
I think biological fixation is predictable. I’ve had only 1 revision for aseptic loosening or osteolysis in the last 760 cases that I’ve performed since 2002. I think it’s because of an excellent implant design in terms of its porous surface. I know a tibial component with 4 peripheral pegs obtains primary stability. You don’t have to use screws. This is not only my experience. It’s reported in the literature of other successful cementless series of over 95% success out at 18 and 20 years. Excellent clinical results have been reported for young as well as young and heavy patients in mid-term series.
I think cemented total knee replacement is ultimately doomed to failure. The question is just ‘When?’ and that’s because a cemented interface is going to fail biologically because macrophages migrate in from the periphery over time. They resorb the trabecular bone from the cement-bone interface and they form membranes. This was reported in a landmark paper over 20 years ago by Dr. Schmalzried.
In summary, biological fixation is now reliable due to improvements in implant design. I think cementless fixation is the preferred method for young, active and heavy patients because it’s a biological interface, better suited to deal with the increasing stresses, rather than using cement.
Dr. Schmalzried: This is a timeless debate. When you look at survivorship data, you’ve got to remember there are many causes for revision of total knees and younger patients are at greater risk. The real topic is improving fixation. Better cementless—I’ve got nothing against it, but, let’s look at (the) bigger picture. What about better surgery and what about better cementing? We start talking about new…is it new and improved, or is it new and unproven. Clearly, for this argument, the burden of proof is on cementless.
AOANJRR [Australian Orthopaedic Association National Joint Replacement Registry] data shows that survivorship over 14 years is better with cement. The curves separate prior to 2 years, so there are more early failures in the cementless group and the curve stays wide. We don’t see a change in the curve as Dr. Gustke would suggest.
Why do cemented knees fail? A lot of times it’s a failure of the cementor and not the cement. A report from Ormonde Mahoney showed that, in his hands, a varus misalignment is a problem. For each degree of varus, there was a 3.8 times risk of loosening of the tibia over 5 years.
Similar sort of thing, from Merrill Ritter’s cases; big number—more than 6,000—and he takes out infection to kind of make it a little bit cleaner. Greater than 2 degrees of varus is a risk factor. And obesity is a risk factor. If you miss in varus with an obese patient, you’re going to get a loose tibia.
How does this happen? We reported this back in 2001. Tibial debonding is associated with lysis. We found it in 2.9%, or 16 out of 557 knees. This posterior stabilized prosthesis had a titanium baseplate with a matte finish and failed via rotational loosening due to box-post impingement.
In a Mayo Clinic study, tibial debonding was the most frequent cause of revision - 1.9% of their cases - and what they did to speed up the curing of the cement, was they would warm the Simplex powder so that it would go off more quickly. Eight surgeons used this prosthesis and contributed cases to the study. There is one surgeon where he never had this complication and another surgeon where it happened in 4.5% of his cases. That’s quite a broad range and anytime I see something like that, it doesn’t suggest that the common denominator is the prosthesis, it suggests surgeon variability.
There have been a couple of reports of tibial debonding with high viscosity bone cement. Dry cement and debonding. So we did a little study, 48 tibial components were tested on an Instron machine and we used 3 different cementing times—early, so the cement is wet when you put it on the prosthesis, a medium viscosity and late where it’s doughy or dry. Late cementing reduced the interface strength of Simplex by 47% and Palacos by 63%, because Palacos is more doughy to begin with, it’s going to have a more dry effect. Early cementing increased the interface strength of Simplex by 48% and Palacos by 139%. Fat contamination really screws up the interface.
I think cement still rules. You’ve got a lower revision rate. Lower cost. And, you can add antibiotics to it. So to minimize loosening: avoid varus, especially in the obese and avoid dry cement. The burden of proof is on cementless and we need multicenter trials with concurrent controls and risk stratification to really see if there is better cementless. And by the way, I want to believe.
Moderator Jacobs: I’ll start by asking Tom, Ken laid down the gauntlet quoting your own study that says that cement is doomed. Do you believe based on what you know about failures of cemented femoral components—is that the case? Is this doomed over time to a macrophagic reaction that’s going to eventually loosen?
Dr. Schmalzried: The quote is from a paper that was actually for the mechanism of loosening of acetabular components, and so I don’t know that the analogy is that strong, because the joint fluid pressures in the hip are way higher than they are in the knee. To me the problem we’ve got in knees is not that it starts at the cement-bone interface…the problem in knees that I see is that it starts at the metal-cement interface. So that’s where I think we need to focus our improvements.
Moderator Jacobs: Any response Ken?
Dr. Gustke: Well, I think Tom’s correct in that we need to improve the interface between the implant and the cement, but still that’s only one side of the interface and I’m still concerned about the live interface that’s going to change over time in response to stresses. Even though the implant itself may not debond from the cement, you’re still going to have an issue with the cement itself loosening from the surrounding bone.
Moderator Jacobs: Ken, a question for you. You’re espousing the use of cementless techniques in high BMI individuals based on mechanical factors. I’m certainly aware of some of the early studies showing the relationship between micromotion of cementless devices and the amount of bony ingrowth. If there’s greater than, say, 150 microns that’s likely going to get less bone ingrowth. So why wouldn’t that be the case for these very high BMI individuals? And have you stratified the data enough to know that cementless fixation will be better results than cement?
Dr. Gustke: No, I don’t have the data that I could actually prove that. The patients who are obese tend to have much better bone quality. We all know that implants migrate, and cementless migrate, too. The key is that you don’t want to put that component in so much mal-alignment that the stresses are on a shear rather than under compression. Because the RSA study shows that if it’s under appropriate compression, under appropriate alignment, it actually stops migrating over time because of the fact that it has biological attachment.
Moderator Jacobs: Any response Tom?
Dr. Schmalzried: I’ve got nothing against that. I hate waiting for cement to cure. I would love to be able to put in a cementless implant and have confidence that it was going to do as well as I can do right now with cement. I want it to be true. You’re going to say we’re going to give up on cement and we’re going to go cementless. And I’ll say I’m not sure I’m ready to do that because I think we can do better with cement if we understand why cement doesn’t work. I don’t think it’s the biologic side. I think all the work I’ve done says that the primary problem we’ve got right now is not getting alignment right, and not getting the cement stuck to the metal.
Moderator Jacobs: Tom, I think you did well in bringing up the role of technical factors in the performance of the cemented arthroplasty. Can you tell us a little more detail?
Dr. Schmalzried: The first one is penetration. You really don’t want more than 3-4mm of penetration because the cement…the more mass of cement that you have, the higher the temperature goes up and the more likely you are to cause bone necrosis. Really only 3-4mm penetration is all you need.
The next one is antibiotics. I use antibiotics in high risk cases. A high risk case would be immunosuppression or morbid obesity.
And the last one is the back of the implant. Others have done these tests looking at how the roughness matters. Rougher surfaces are going to bond to the cement better, so I think if you’ve got a smooth or a matte finish, I don’t think that’s desirable. I think a heavy grit blast is probably more desirable because the cement will adhere better to that.
Moderator Jacobs: I’ll ask Ken the same questions. What are those technical factors that are associated with success of cementless implants and I’d also like you to answer when during a case, if ever, will you abandon cementless implants because things aren’t right?
Dr. Gustke: I have a very sophisticated test—put my thumb on the tibia and if I get an imprint on the bone, then it’s not good enough for cementless.
There are multiple studies in the literature that show that cementless implants have a lower infection rate. You have to be more meticulous when you do your surgery.
Moderator Jacobs: Thanks very much. I’d like to thank the debators.
Please visit www.CCJR.com to register for the 2017 CCJR Spring Meeting, – May 21 - 24 in Las Vegas.