Lewallen v Hofmann: The Cemented All Poly Tibia: Regardless of Age & BMI

This week’s Orthopaedic Crossfire® debate was part of the 19th Annual Current Concepts in Joint Replacement® (CCJR®), Spring meeting, which took place in Las Vegas. This week’s topic is “The Cemented All Poly Tibia: Regardless of Age & BMI” For 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 William J. Maloney III, M.D. – Stanford Hospital & Clinics, Stanford, California.

Dr. Lewallen: My task is to explain why I suspect most people in the audience aren’t doing enough all poly tibias. I put it to you that the concept that the Gold Standard for modern knee replacement is modular metal backed tibial trays will soon be on a pile of discarded thoughts.

Why is that? The biggest challenge of revision knee in the past two decades has been polyethylene wear, osteolysis and bone loss. We thought we knew why this has happened. We thought it came from the top side wear of the tibial component. However, we never saw lysis around implants despite lots of poly wear on the top side before the 1990s.

What’s going on?

The tarnished Gold Standard is based on modular components with implants that are moving around. They’re all rotating platforms. They just weren’t made for that. They all move to some degree, and some move more than others.

Articles from our institution tell you that isolated poly liner exchange is a bad idea (Babis et al., JBJS-Am 2002 and JBJS-Am 2001). One of the main arguments for having this is so surgeons can have the flexibility of swapping the poly liner at a later time. There are rare instances in the patient with wear at 10 or 12 years with a great knee until then where that’s a good operation. All those liner swap-outs at 1, 2, 3, 5 years are generally a bad idea because they are not fixing the underlying problem that’s resulting in the revision.

The unintended consequences of modular implants are: locking mechanism instability; backside abrasion and third body wear. It’s the metal particles, not because they’re so much metal, but because they drive down the size of the particulate. And it’s particle size that is everything for the biologic response, the debris, the wear and the lysis.

There are articles about locking mechanism failure and backside wear. The literature is replete with reports of problems related to this technology and yet we stick with it.

One of the early reports (Rodriguez, JA, Clin Orthop 2001) really called attention to the difference between all poly and modular implants. Same design and clear survival differences between the all poly monoblock (96%) version and a metal-backed modular (75%) version at 7 years.

We did a review at our institution (Maradit-Kremers et al., JBJS-Am 2014)—10,000 patients; 14,500 primary knees; 9-years mean follow-up; 18 different implant designs. Modular metal-backed and all poly versions. I can tell you, all-poly tibias did better than the metal-backed modular versions, even after we corrected for age and gender. Younger patients still did better.

A meta-analysis (Voss, et al., JOA 2016): 28 articles, 95,000 knees, all-poly tibias had a lower revision rate and fewer adverse events than the modular versions. Across the world’s literature.

A knee is not a hip, Cross-linked poly is not going to do it for us. Maybe rotating platforms will help, but the jury is still out. Right now the data clearly shows that all-poly implants do better than modular metal-backed.

Dr. Hofmann: Backstage, Dr. Lewallen says he’s going to crush me, Show of hands. How many people are ready to do all-poly tibias in all their patients? Maybe I saw one, I don’t feel crushed.

I certainly use all-poly tibias. I think they’re fantastic. But anytime you say “always” or “never” that’s just a catch phrase, I don’t “always” do anything. Here’s the whole crux of my argument…total knee modularity equals versatility.

I don’t need to show any more slides. That really says it all.

Dr. Lewallen is a smart guy, I kind of think of him as the Dalai Lama. I think he’s just spent too much time up North. Poly doesn’t deform and come loose in the cold country, but for the rest of us I think it is more of a problem.

Certainly, Dr. Ranawat has said you can use all-poly tibias in elderly patients. And we’re looking at these in our 80-year-old plus patients. People who have good bone stock and weigh less than 180 pounds. I can’t remember the last time I had a patient that was less than 180 pounds, so that’s not really my patient.

The problem, I think, with all-poly tibias is that they’re just not stiff enough, so you have a bending moment that can cause loosening. Certainly not in everybody. If you have thick enough poly maybe that doesn’t happen. But it makes me nervous.

We have metal-backed tibias. There is so much more you can do with them for filling bone defects, solving quality of bone issues, convenience, insert exchange, the obese patient and when you change your mind at the end of the operation when things aren’t quite tight enough. You have the option to change the polyethylene.

At one point in time, a one-piece component was a great idea. It’s not exactly all-poly, but it has a porous coating on the backside. The problem that I had with this is the same as with an all-poly tibia. What happens when it gets worn?

One of my patients back home has been waiting four years for me to give him that answer because he doesn’t want this thing chopped out. I can’t just take the poly out and put a new one in. And I think that’s an advantage of modular components.

Certainly, there has been a history of modular component problems, as Dr. Lewallen pointed out. We don’t need to go back into that. How some of the polyethylene was manufactured caused accelerated wear, delamination and backside wear (Engh et al., JBJS 2000).

But polys have improved. I’ve been in practice 37 years and I’m seeing patients that have had their poly in for 20 years. One of my patients—22 years later—I can take her worn poly out and just put another one in.

We have standard polys that would certainly delaminate and cause problems. Old radiated polys. The newer cross-linked polys, I think, have solved that problem at least for top side.

I don’t think you can even highly cross-link an all-poly tibia component because it’s too thick. And you can’t put a big, long stem in that’s polyethylene that’s cross-linked.

I try to do things that are very conservative, I do surface cementing and we’ve reported great results, 100% follow-up with 100% survival (Goldberg and Hofmann, JOA 2007). My perfect tibial component has metal-backing. You can use porous coating, non-porous coating, spacers, no spacers, short stems, long stems. Hopefully, an improved locking mechanism, And then cross-linked poly, or even vitamin E poly.

Modularity equals versatility. You can do all of these things—the ultracongruent option for patients that rupture their posterior cruciate ligament; if you have bone defects you can add spacers; and for fractures you can put in long stems and bypass the fractured part if you need to or treat fractures if they’re there.

Again, modularity equals versatility.

Moderator Maloney: David, you have 1 minute to rebut.

Dr. Lewallen: That was pretty convincing, Aaron, in case after case. But I didn’t see very many numbers. Not much data. We need data to support our arguments.

To be honest, I don’t do all-poly tibias in every patient. It’s a mix in my practice and there is a bias towards older patients. I do tend to use metal-backed implants for complicated cases where the advantages of modularity and stems are important. But I think there is a strong case to be made for all-poly components to have a major role in the reconstruction of knees, especially in patients over 65 and some of the low demand folks.

Dr. Hofmann: I agree with you. I use all-poly tibial components for the same reason you do. So, I certainly agree with your arguments and we certainly know that even with the highly cross-linked polyethylene, we’ve seen backside wear, we’ve seen some screw lysis, even though that wasn’t supposed to happen. The problem isn’t 100% solved. There’s no question about it. We’re making better locking mechanisms, but we haven’t solved it. So, there is a place for all-poly tibias. There, I’ve said it.

Moderator Maloney: So, there seems to be some agreement that there is a role for all-poly tibias. Let’s give the scenario that the 3 of us own our own hospital. We’re doing 2,000 total knees a year. We’re going to purchase our implants. The all-poly tibia is going to be probably in the neighborhood of $600 cheaper than the modular metal-backed tibia and we’re in a bundle. Where’s the cut-off going to be for that all-poly tibia?

Dr. Hofmann: Probably going to be the 75-year old patient. I’m not going to do it based on dollars.

Moderator Maloney: Is bone stock a concern?

Dr. Hofmann: No.

Moderator Maloney: David, where would you pick?

Dr. Lewallen: I think females over 65-the data would strongly support you and that would help your bundled situation greatly. And then I think in males, depending on activity level and size, very reasonable to start using it as people are a bit older, not quite as big. Maybe 70-75. Bone quality is less. Survivorship is less.

Moderator Maloney: What about versatility? Aaron makes a point that once we get options in the operating room, we hate to take them away. Every once in a while, I’ll do a trial reduction, it looks pretty good but when I put the baseplate in I find I want one size thicker. It happens.

Dr. Lewallen: I think you trial carefully and you get used to the fact that when there’s slop in the system, motion between the femoral trial and the bone, motion at the femur and the poly, motion between the poly and the baseplate trial, a little motion between…there’s a little more slack in the system, you want to play your hook, right? Play a little towards a little thicker. If you’re between a 10 and a 12, go to 12.

Moderator Maloney: We have some consensus here. There is a role for all-polyethylene tibial components and cemented total knee arthroplasty. Probably in the elderly patient. But data from the Mayo Clinic is pretty strong that if you use good surgical technique you could get pretty good results regardless of age and gender.

Gentlemen, thank you.

Please visit www.CCJR.com to register for the 2019 CCJR Winter Meeting, – December 11 – 14 in Orlando.