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.
