Metal-backed tibias definitely equal versatility for bone defects, for convenience, for poly exchange, the obese patient. It protects the bone better. Tibial insert-tray modularity was introduced in the 1980s. Isolated exchange can be done. And as you get older, I realize almost every week I’m doing a poly exchange on a patient of mine that’s anywhere from 20 to 30 years out—and they do wear out. They’re poly and I don’t have to revise everything on these elderly patients.
Isolated exchange did not have a good track record, but that’s because the polyethylene was radiated in air and that is a problem. We certainly have better poly. We have better locking mechanisms. So, using crosslinked poly is important. I think that might be the answer long-term rather than throwing out the baby with the bath water.
Not all locking mechanisms are the same. I like to use either a more robust, or even one with a screw. I took one out at 25 years and the screw held. You could still read the words on the backside of the polyethylene, indicating that the poly is not moving and that locking mechanism is working.
Modularity equals versatility. I’d like to stick with that most of the time.
An 85-year-old patient I had 22 years later, fell off the sidewalk and ruptured her PCL [posterior cruciate ligament]. We simply exchanged to an ultracongruent insert…that was a simple operation, 20-minute operation for that patient where it would have been a major operation if we had to revise everything. So, I like ultra-congruent inserts in those cases of PCL deficiency. You can add spacers to metal-backed tibias. You can add stems in the case of hardware removal or old tibial fractures. You can use the same tibial components for revision.
I like new stuff. I like my old 1952 tractor…that’s the first tractor my father ever bought…but I like my Kubota that has a front-end loader and a backhoe and has all bells and all the whistles. I also like my wife’s Mercedes. I like this 1957 Chevy that I saw in Cuba, but I prefer the new over the old. Let’s make orthopedics stay great by sticking with the modular tibia.
Dr. Berend: I think if you used one-piece implants, you wouldn’t have to change the polys every week. I think there is a lot of agreement as to how we approach arthroplasty, but I would also say that you don’t need modularity in every case. Use it when you need it. If you want to eliminate poly wear, I think there is excellent long-term evidence of how to do that.
I agree modularity is clearly the Gold Standard. I would pose the question, ‘do the advantages of modularity outweigh long-term concerns over poly wear?’ We learned a lot from the uncemented phase of things—as to how polymer wears in a knee arthroplasty. The important question is: ‘What role do age and BMI {body mass index} play in selection of the implant?’
We’ve learned a lot about ways to potentially reduce polyethylene wear in knee arthroplasty. Improving the locking mechanism has certainly brought that forward. Perhaps we change the femoral material. We introduce more mobility with a mobile-bearing type device. We change crosslinking or add things to the poly. I think a non-modular implant with long-term data such as the AGC and IB1. Different compression molding techniques have really been the hallmark of reducing the poly wear in knee arthroplasty.
