Dr. Trousdale: The other point that wasn’t brought up is that all poly tibias are a little harder to do for a primary total knee. There are a few nuances of doing an all poly tibia. Once you cement the components, you can’t change them. I would argue that’s a relatively rare event, but it’s a little less versatile, so I couldn’t advocate that you jump in and do the monoblock tibias from the get-go. But once you have Aaron’s level in his career, even he could put in a monoblock tibia component.
Moderator Sculco: What about the weight restrictions? I can remember I did total condylars for years and in young active male patients—heavy—you would see, on occasion, bending of that polyethylene. Has that been an issue at all?
Dr. Trousdale: Dan Berry has a series on heavy set patients. All poly tibias. Survivorship is just fine. Our series looks like it’s pretty good. Having said that…if you look at the patient that’s really heavy set, that’s a patient I’ll probably put a metal-backed tibia with a short stem in. Concerned about? Sure, I go to a metal-backed tray. Having said that, there is good data for giving the heavy-set folks the all polys.
Moderator Sculco: What percent of tibias at Mayo currently are all poly? You’re doing them for primary knees, but is the whole knee group pretty much doing it?
Dr. Trousdale: No, most are modular total knees for sure. There’s a handful of surgeons that do it selectively. I’m probably the biggest user, but other surgeons are doing them okay in selective patients.
Moderator Sculco: The infection rate. Why do you think the infection rate is greater with metal-backed compared to the all polys? Is it debris?
Dr. Trousdale: It’s two reasons. One is patient selection. I think more complex, sicker patients, heavy-set diabetics, maybe; those patients getting the metal-backed. So it may be apples and oranges you’re comparing there. I also think these are designs that were done in the ‘80s and ‘90s and the sterilization method wasn’t that great. And the modularity issues with backside wear causing synovitis and increased infection. If you got a good locking mechanism, which I think we have now, that probably is going to fall off a cliff. That’s probably not going to be an issue.
Moderator Sculco: Aaron, let’s come to you. Cost is a real issue and you can put one of these all poly tibias in and it’s probably $1,000 less than a metal-backed. Rob is showing you outstanding results across the board with all poly tibias, so how can you justify metal-backed in the bulk of your patients?
Dr. Hofmann: A year ago I said I wouldn’t even listen to that argument, but having done 25 in a row in El Salvador last month, they are pretty easy to put in. This isn’t being recorded is it?
Moderator Sculco: You’re doing all polys in El Salvador?
Dr. Hofmann: Yes, in El Salvador, yes. We did a bunch when we were testing the water and they’re actually fun. They’re easy, they’re a little quicker. In that population, I think, in going back to cost, they can’t afford a $4,000-$5,000 total knee, so what are we going to provide to the rest of the world?
Dr. Trousdale: Aaron, is the Kubota tractor that you’ve got cheaper or better than your Dad’s tractor that’s sitting your backyard?
Dr. Hofmann: No, I think with appreciation, I think they are about the same. $5,000 versus $50,000.
Moderator Sculco: What do you think about Rob’s data about infection and failure with the metal-backed tibia? It’s a strong argument for doing all poly tibias.
Dr. Hofmann: Certainly when you get backside wear, you get particles, you get lysis, and there’s more things happening, more dead space, less vascularity, in those cases, that’s some really poor locking mechanisms that we’ve all seen over the years. I think they’re better, but that might explain a higher infection rate.
Moderator Sculco: I noticed also that the results in your older population weren’t as good. You think that a quality of the bone or…
Dr. Trousdale: Yeah, I think that the benefit of the backside wear issues is lost in the elderly patient. I’m different than most people in the very elderly osteopenic patients I’m using the metal-backed tibia and the 60-year-old patients, I’m using the all poly tibia.
Moderator Sculco: So how would you summarize then? I think there’s a real place for all poly tibias. I think we should be using more of them and I don’t know why we’re not. I think industry probably discourages us from using them because the margins are much greater with the metal-backed tibia than the all poly tibia. And I really think all those out there should rethink the use of it if you’re not using all poly tibias to a greater extent. Just as Aaron has. Aaron, comment?
Dr. Hofmann: I’m starting to use it…I think it’s great as a spacer, for example. I do an articulating spacer and I’ve just done a couple for that purpose. Before I would never think about doing that, but it does save the hospital a significant amount of money.
Moderator Sculco: Okay, so I think we have good arguments on both sides and certainly the all poly tibia is something to think about going forward. Aaron raises good questions about its versatility in the long-run and particularly in the revision situation. Thank our two debaters. I think they did a great job.
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Senior Editor: Jay D. Mabrey, M.D., whose 35 year career in orthopedics included residency at Duke University Medical Center, service in the United States Army Medical Corps, Fellowship at the Hospital for Special Surgery and a long, distinguished career at Baylor University Medical Center where, in addition to his overall leadership at that institution, developed the Joint Wellness Program that helped patients get up after surgery more quickly, developed the first virtual reality surgical simulator for knee arthroscopy and chaired the FDA Orthopaedic Device Panel, is Orthopedics This Week’s newest contributing writer and editor.
