Lewallen v. Hofmann: The Cemented All-Poly Tibia: An Affordable Care Act Solution
OTW Staff • Mon, December 12th, 2016
This week’s Orthopaedic Crossfire® debate was part of the 32nd Annual Current Concepts in Joint Replacement® (CCJR), Winter meeting, which took place in Orlando this past December. This week’s topic is The Cemented All-Poly Tibia: An Affordable Care Act Solution.” For the proposition is David G. Lewallen, M.D., Mayo Clinic, Rochester, Minnesota. Opposing is Aaron A. Hofmann, M.D., Hofmann Arthritis Institute, Salt Lake City, Utah. Moderating is Kelly G. Vince, M.D., F.R.C.S.(C), Whangarei Hospital, Whangarei, New Zealand.
Dr. Lewallen: I want to try to explain why an all-poly tibia is something that should be part of your armamentarium in caring for patients who require knee arthroplasty.
Looking back on a 30-year career, there are a lot of things that I was taught that I knew to be true during my training that some years later turned out to be completely false. Such as irrigation tubes were the standard for treatment of infected joints which are effective at producing pseudomonas infections.
I learned that cement disease was really the reason that we had failure of early arthroplasties and holes in the bone, later to find out maybe the polyethylene had something to do with that. We gave transfusions reflexively for everybody with a hemoglobin under 10. We now know that’s dangerous and unnecessary and expensive. And everybody got prolonged antibiotic therapy. I think in neurosurgery they were on them for several months after some of those procedures. So on and so forth.
We need to think critically about the things we think we know for sure. One of those is that metal-backed tibial trays are the gold standard for modern total knee. Really. It turns out one of the biggest challenges I’ve had in my career, and I think for you too, the last 10-15 years, has been particulate debris-generated osteolysis. We never saw this in earlier knee designs. This is a product of knee design change and it’s related to modular components, well-fixed devices with huge holes in the bone. It’s not that we never saw poly-wear and problems with the polyethylene and earlier implants. And these are all the different ways poly can get into trouble—surface deformation, pitting, embedded PMMA debris, scratching, burnishing, abrasion, delamination.
Widely adopted in the 1980s in order to allow ingrowth components with screws and other adjunctive fixation. And the argument was that it’s easier to balance the knee and it makes revisions easier later because you can swap out the poly. Do a so-called tire change. Turns out that’s a bad idea. The majority of time when you do this, especially in knees that have been in for a short period of time, the failure rate is extremely high and it’s because usually there’s some other problem in the knee that is not addressed by simple polyethylene exchange.
Locking mechanism instability is a fact of life. They all move at the beginning and they all move more as time goes by. And yes, some are much, much better than others and I use modular trays when I need them. I think some of the current designs are much improved. But you get undersurface abrasion, third-body wear from particulate metal debris and what that does is drive down the particle size. And small particles are the reason we see huge bone loss.
Backside wear and problems are not rare occurrences. They are well recognized. We tell our patients that knee surgery is a great operation and lasts a long time, but the trouble is we quote older literature with primarily factory-assembled, monoblock designs. If you look at modular implants, the failure rate is a bit higher.
We did a review of 14, 500 total knees that were done between 1988 and 2005. These are all comers. We had a mean of 9 years follow-up and looked at the performance of the tibial components—18 different implant designs. In all cases, in all cases, the all-polyethylene tibias performed better than metal-backed designs. Even after correction for age and gender. So in young, active males, better results.
I have a partner who does all-polys on everybody, including the young, active patients. Member of The Knee Society—he’s not crazy.
I think we understand the cause of osteolysis. I’m not telling you it’s just metal-backed components. It’s multi-factorial, but that factor is important in that problem. So why not embrace cross-linked poly? Well, the knee’s not a hip. We don’t have the data yet. We’re worried about the performance of this material. I think some of the products are probably pretty good and vitamin E may be even better. But the data is not there yet. And so, I think we have to see as time goes forward whether breakage, smaller particles and other issues will come up.
What about rotating platforms as an answer? Polish it. If you’re going to make it move, let it be designed for that. You get stress shielding with these rigid trays and it’s not proven that it’s going to reduce wear particulate debris as of yet. Some data is suggesting otherwise.
So what’s the bottom line? I think we’ve seen that all-poly outperforms modular trays and until we have data to convince us otherwise, I think at least in a certain percentage of your patients, it’s very reasonable to consider this very cost effective alternative as you start to focus more and more on the value of the operation that we perform.
Dr. Hofmann: Certainly total knee modularity gives us versatility. I’m not sure that anyone in this room is going to argue with that. I don’t know anybody that was convinced by Dr. Lewallen’s argument for the all-poly tibia. He’s a smart guy. There’s a lot of great things that come out of Minnesota, but it’s harder to get ideas into Minnesota than to get ideas out sometimes. And sometimes he’s never in doubt, but sometimes wrong.
I designed an all-poly tibia 20 years ago and I used it for a while. Dr. Ranawat has used them with great results. He quotes, “elderly, with good bone stock, less than 180 pounds.” Don’t have many of those in Utah which is the ice cream capital of the world.
Metal-backed tibias give us so much more versatility for bone defects, and to solve poor quality of bone and convenience, and insert exchange, and in the obese patient you can put thicker poly in those patients.
So I know Dr. Lewallen loves this implant too—the monoblock—it solves a lot of the problems. There’s no backside wear. But what do you do with a 66-year-old patient who’s 12 years out with poly wear and scared to death to have this monoblock tibia revised because we’re going to have to tear it out. If he had a modular part, we wouldn’t have to do that. We’d simply change the poly. But now this is going to be a much more extensive operation.
So modularity was introduced in the 1980s. You can do isolated exchanges for the right reason. You can retain the metal and maintain the bone stock. Certainly there’s been a lot of bad poly out there…and delaminated and broke and sterilized with gamma radiation that causes polyethylene to be a problem.
What do you with a patient with worn out poly? I can simply do a poly exchange.
My father’s first tractor…1952…is fun to drive, but it’s not that versatile really. I really like my new Kubota that’s got a front-end loader and a back hoe. There’s just so many more things that you can do with that.
Dr. Lewallen wants to drive this 1952 Chevrolet that I just saw in Cuba. He’d still like to drive that old car. But I prefer my Mercedes convertible that has 400 horsepower and all-wheel drive. It’s like that’s where we’re going and we don’t want to go backwards. Let’s throw out the old and stick with the new.
Moderator Vince: Aaron, just clarify when you would use the all-poly. There might be cost pressures that would force you. So who’s your candidate for all-poly?
Dr. Hofmann: I don’t have one. Actually, an infected case that I’m putting a spacer in, I think, would be a great candidate, there’s pus everywhere and I’m only going to keep it in there six weeks. I think that’s a perfect case for the all-poly tibia.
Moderator Vince: So Dave, Aaron hasn’t actually addressed the problems you pointed out of osteolysis and backside wear. Is they still the problems or have better poly and locking mechanism interfaces changed things?
Dr. Lewallen: I don’t think we know. I truly hope that current modern designs are much improved, but I think that remains to be shown. I’m not trying to say that you should use all-polys in every single patient. I don’t do that in my own practice. I do 50% revision in infection work. Every time I do a revision I use modular designs and I appreciate all of the features that Aaron has pointed out. They are critically important.
But for routine primary surgeries, especially in this era where we’re being forced to confront the need to pay attention to the value of the procedure, which means the cost over the benefit…combined with the benefit…we have to pay attention to what these implants cost.
All-poly is a very, very cost-effective alternative for surgeons who are increasingly being profiled economically or based on the economics of their practice. If you want to drive down your average, it’s a really very effective way to decrease the overall expense. But there are advantages to the modular implants for sure. They can be easier to revise in many cases, and of course, you’ll get more practice.
Moderator Vince: Dave, so of the 50% of your practice that are primaries, what percentage are you using all-polyethylene tibia components?
Dr. Lewallen: About 50-60% of my patients get an all-poly. I also do use a non-modular metal-based tray that Aaron showed, ingrowth for young, active patients. My hope is that will be a more durable way of providing fixation over the long term. That remains to be shown. We have data up to about 10 years to suggest it’s quite good. And then I continue to use modular trays in difficult patients - those with deformity when we need stems, correction of difficult problems, and when I’m concerned about the ligaments. If I’m worried about the potential for stretch and laxity over time in some of the deformity correction work, it is nice to be able to go back and put in a more constrained insert at a later time—not because of wear, but because of ligamentous laxity.
Moderator Vince: How do you identify the patient who’s a good candidate for an all-poly cemented tibial component in a primary?
Dr. Lewallen: So the typical patient who would get that in my hands is a patient who’s 70-75 years old, reasonable weight, average activity, varus knee 5 degrees, the typical kind of bread-and-butter total knee that we see all the time.
Moderator Vince: David, just simply says, “We don’t know” when it comes to the question as to whether there has been progress with design, materials, locking mechanism. Aaron, what do you think? Were in fact those cases of osteolysis…would those be old Chevys?
Dr. Hofmann: They might be old Chevys but it’s not a solved problem. You still see some osteolysis even with highly cross-linked poly. So the articular surface is good, the locking mechanism is not as good as it used to be when it was first put in. So those things start moving a little bit as Dr. Lewallen pointed out. We haven’t solved that completely.
I’ll make one comment about all-poly. So if you have all your modular stuff, now you’re going to add even more inventory to your hospital. The inventory becomes crazy. So, if you have congruent, ultra congruent, PS, CCK, I mean; where does it end?
Moderator Vince: Gentlemen, thank you for taking a stance on these positions.
Please visit www.CCJR.com to register for the 2017 CCJR Spring Meeting, – –May 21 – 24, 2017 in Las Vegas.