This week’s Orthopaedic Crossfire® debate was part of the 16th Annual Current Concepts in Joint Replacement® (CCJR) – Spring meeting, which took place in Las Vegas this past May. This week’s topic is “The All Poly Tibia in Younger Patients: An Affordable Care Act Alternative.” For the proposition is David G. Lewallen, M.D., Mayo Clinic, Rochester, Minnesota. Leo A. Whiteside, M.D., Missouri Bone & Joint Center, St. Louis, Missouri, opposing. Moderating is Aaron G. Rosenberg, M.D., Rush University Medical Center, Chicago, Illinois.
Dr. Lewallen: I’m going to talk about all poly tibias and why you may wish to consider this option, at least for some of your patients. I would put that you need to question things that you take for granted. These are things I thought I knew for sure during my career that I subsequently learned were complete BS. Suction irrigations were standard of care for infected joints. They produce pseudomonas infections. I learned that bone loss around failed joints was the fault of the cement and that would be solved by going cementless. We found out otherwise. Transfusions for anybody with a hemoglobin under 10, so on and so forth. The list goes on.
I think that one of those ideas is the concept of modular metal backed trays are required for total knee arthroplasty. This is the gold standard and somehow the highest quality implant that we can achieve. The biggest challenge I see as a revision surgeon is related to particulate debris from polyethylene and cement. This is an interaction of the implant and the patient is a man-made plague and it’s exploded with modular trays.
We’re familiar with this problem and the question is whether cross-linked poly is going to solve the wrong thing. Tibial articular surface wear may not be the critical issue. We think that top-side wear can be well tolerated in total joints. We never saw in early designs the explosive lysis that we’ve seen with modular implants and backside wear where the metal debris and poly participate in driving down particle size with this third body wear particle activity.
I think that would point to metal backed components as a tarnished gold standard. That insert exchange—the main reason that people say they can’t live without this—is a bad idea. Simple isolated poly exchange usually does not solve the underlying problem that caused failure in that knee. Locking mechanism instability is a real phenomenon. We’ve seen multiple designs from multiple manufacturers, monotonously showing backside surface wear, radial abrasions, and the metal debris is important because of what it does to the poly in driving down particle size and producing bone lesions.
Dr. Ranawat’s single series showed that all his polys did much better than a metal backed single design in his hands. I don’t think they were malrotated or malpositioned.
In another series we saw an incidence of radiolucency in balloon osteolysis which was seventeen times higher with modular components than monoblock designs. In another study done at our institution where we looked at over 10, 000 patients with 14, 000 knees, mean 9 year follow-up and 18 different implant designs we found that, in every case, all poly tibias did better than the metal backed designs. Even when corrected for age and gender.
Now the differences aren’t huge. You may make the argument that the improvement or better result in the all poly group is not clinically relevant. I’ll give you that. But it’s certainly not worse. You’re giving them an excellent implant that can perform very well.
So the bottom line, I think, the past compression molded poly and monoblock designs outperform the present modular metal backed designs and I encourage you to at least consider all poly designs. It’s cost effective and an excellent solution for at least a subset of your patients.
Dr. Whiteside: Well David, I wish I could agree with you but then we’d both be really wrong. I’ll tell you that cement has not worked in the knee even with all poly tibias since 1972 when we started and you were about 10 years old. And it never will work and I’ll show you why. For example, Neilsen’s study. Cemented total knee arthroplasty is looking great at 10 years for the probability of loosening (or the lack thereof). But your chances of having a good or excellent result drop to 60% or 50% rather than 95%. That’s because the pain starts to increase after about 2 years and progressively worsens. Ranawat, who is a very big proponent of cemented all poly tibias, has reported that something happens after 10 years in his knees. Further, his heavy patients start to deteriorate at 6 years.
Li found that only 82% of his patients at 10 years were radiographically intact. Lonner reported 12.5% loosening with a cemented metal backed tibial component. What is going on here? What’s going on is loosening.
Neilsen found that his cemented tibias worsened and continued to migrate up to 5 years and past. And his well-done cementless ones stabilized and stayed stable over the years. Tom Schmalzried has kind of helped us understand how this works. There’s an attack at the interface when you have cement in the cancellous bone. This is not the whole issue, but there is an attack at this interface that gradually loosens that implant, and why is it? Mark Miller has done some very interesting studies. He took cemented total hips in patients who died with them intact with an excellent looking interface and cut them into sections, pulled them apart and looked at them. For one thing he found that the bone was missing from where it had previously been, and pull-off strength resistance was 0.2 megaPascals. That’s about like picking off a scab. I’m telling you, these things are loose and, not only that, it gets worse.
In Mark Miller’s study in the knee, where he looked at knees for patients who’d died within a year of the implant, he found a bunch of bone interdigitated with cement. The cement heats up like hell in the bone as it polymerizes. It’s all dead. And after a couple of years, 3 years in this study, all that bone is removed. It’s no longer interdigitated and you go a little bit longer and the interdigitation is now with fibrous tissue and it’s worthless. It does not help you. Cement doesn’t stick to metal and it doesn’t stick to polyethylene and it does not stick to bone. There are a lot of studies now showing cement loosening from the metal. Dr. Lewallen found that cement didn’t stick to metal…I wonder if he thinks it sticks to the polyethylene. Well, let me tell you…it doesn’t. And other people are finding that this bond between cement and anything is tenuous at best.
Does bone ingrowth offer advantages? Well, early reports didn’t look good. Poor fixation. Flat gamma irradiated poly. And poorly designed modular components. And that’s what Dave was talking about—the old days. That’s the way it used to be. Certainly not like that anymore. But reliable technology has been around since 1980. Bartel and Burstein showed that you have to have a metal back with a metal stem to fix these tibial polyethylenes and anything else is not going to work well. You also have to have a well-fixed upper surface of the tibia and modularity available in the stem to be sure that it gets tightly fixed to bone.
Does it work clinically, long-term? In my personal experience—up to 18 years–the pain does not progressively worsen as in a cemented knee. I reported no loosening in younger patients. And no loosening in rheumatoids. Aaron Hofmann has reported the same sort of thing. Steve Harwin is reporting that now. Merrill Ritter’s group is reporting that now.
So let me just summarize quickly. Cement doesn’t work in the knee. It doesn’t work. It works a little bit for inactive patients who are not going to stress as much. Because you’re going to get a fibrous tissue interface pretty soon and it’ll hold up in a very light-weight patient. Don’t try it in an active, heavy patient.
Dr. Lewallen: I feel like the guy who brought a knife to a gunfight. I thought we were talking about all poly tibias and metal backing rather than cement versus cementless. But I do understand that if you’re going to do cementless there might be the perception that you have to use modular metal-backed designs. Although, that isn’t entirely true. I’m actually a fan of cementless fixation, as Leo knows, in some of my patients. But I use a non-modular monoblock implant with a trabecular metal surface and we’ve published very good results with that device. I do think that this issue of modularity is a real one. I’ll give you the fact that it is different between designs for sure. Some designs have much less trouble than others, no question. But they all move at the beginning and all move more as time goes by between the poly and the metal backed tray and that’s not a good thing. I think in some designs it can be catastrophic.
Moderator Rosenberg: So the locking mechanism in modular designs or locking mechanisms period when there’s modularity are susceptible to the same type of influences that you despise when you have bone cement. That is they’re non-biologic and fatigue.
Dr. Whiteside: You’re not exactly a nonpartisan moderator, but I’ll give you that. Let me respond to that. Matter of fact, you can design a locking mechanism that is captured peripherally and also sealed such that the polyethylene debris does not get out from under the polyethylene component. Sealed in there with just a sealing rim and it gets tighter as time passes. This is a matter of a very simple engineering design. Sealed bearings are very common in almost every industry except for medical and I’m not sure why they’re allowed to still put in these polyethylene components that are not sealed into the tray. Doesn’t make any sense to me. So that’s what I use. I use a poly that’s snapped in, that’s pressed in peripherally all the way around but has a sealing rim so that the debris that’s generated underneath doesn’t get out. It’s also locked tight, as tightly as you can lock them in the factory. It’s just a matter of simple, basic engineering.
Moderator Rosenberg: Leo, final thoughts on the future of cementless fixation in the knee. Do you think we’re going to see any newer ingrowth type surfaces or any biological additions to ingrowth that will make this more commonly accepted?
Dr. Whiteside: I think we’re going to improve that technology. We’re going to be able to put porous coatings on the surface of these metal components without weakening them. Without heating them up so much. In fact, that’s what I’m doing now. I’m using an advanced plasma spray technology to give a more porous surface and we’ll improve our overall instrumentation.
What we have to look out for is improvements in marketing. If somebody tells me ‘I’m going to press fit this tibial component in 8 seconds.’ I’m going to find another implant to do. You want the guy to stand there and get it really good and just right and finally say, ‘Yeah, that’s perfect.’ And if somebody comes forward and says, ‘I got this component. We’re going to put this whole thing in in 5 minutes.’ I don’t call that advancement in technology. That’s advancement in marketing.
Moderator Rosenberg: Failure of craftsmanship. Well, gentleman, thank you very much for your participation.
Please visit www.CCJR.com to register for the 2015 CCJR Winter Meeting, December 9 – 12 in Orlando.
