Do you need modularity? Sure we do. We need modularity in revision cases. We need modularity in complex primary cases in those patients that have a big deformity. The obese patients. And those patients that have marked ligament problems. You should use modularity. But in the routine total knee, the all poly tibia seems to be a very durable, reliable operation.
So well designed monoblock all poly tibial components are now entering their fifth or sixth decade of use. To date they’ve provided very durable fixation and I continue to use a monoblock, all poly tibia for the majority of my knee patients. And it’s my belief that the benefits of modularity for routine total knee replacement do not outweigh the negatives in the majority of our patients.
Dr. Hofmann: I don’t know if anybody was watching PBS last week, but they had the making of the movie “Frozen” that was actually shot in Rochester, Minnesota. So, things are a little slower there, hard to catch up with what’s going on with the rest of the orthopedic world. All poly tibias, no, modularity yes, versatility yes. That’s what we need.
So, I always have to listen to Dr. Ranawat because I know he’s like probably the smartest guy in the room and I know that he’s written a lot about all poly tibias, so I’m using some all poly tibias. I’ll have to admit that at the beginning here.
We started using metal-backed tibias in the first place to protect the underlying bone.
What about the monoblocks with a metal-back? They’re supposed to be quite good. And they are, at least in the short term, but you know a patient is going to come in with medial wear. Now we’re going to have to cut that thing out instead of just doing a poly change, which would be a 10- to 15-minute operation. That turns into a big deal. Certainly metal-backed tibias are great for bone defects; for poor quality bone. I just think it’s more convenient and it’s easy for insert exchange, which is happening more and more for old guys like me.
My patients are coming back at 20-25 years that have worn out their poly. Certainly modularity was introduced in the ‘80s for those very same reasons. Isolated polyethylene exchange isn’t very popular. Certainly not the right answer early on for a patient that’s having a problem, but long-term patients that have poor poly, especially that was irradiated and is breaking down, it’s easy to change that.
Not all locking mechanisms are the same. Three percent of my patients long-term lost their posterior cruciate and had to have their polyethylene exchanged. One patient, 22 years later, still had the markings on the back of the polyethylene insert so there’s no backside wear, but the top was pretty beat up. And just changing that from a congruent to an ultra-congruent was actually a pretty easy solution, 15-minute operation on a lady that’s 85 years old.
We need modularity if we have bone defects; we can add spacers. If we have old tibial fractures, we can add stems, or longer stems. So, you have the choice of old or new. The first tractor my dad ever bought was in 1952. I loved driving it. I loved driving it in parades, but I leave it parked most of the time and I drive my new Kubota that has a backhoe, it’s got a front-end loader; it’s all wheel drive, so I’d rather drive that tractor most of the time than my Dad’s 1952 Allis-Chalmers. I took a picture of a 1957 Chevy in Cuba last year, and it’s great to look at these old cars, just like it’s good to look at these old knee designs. But my wife would rather drive her 400 Mercedes and I’d rather drive my 550 Mercedes convertible. I like looking at these old things and I wouldn’t mind driving them once in a while, but not every day.
Moderator Sculco: Rob, let’s start with you. Aaron raises a couple of good questions here about all polys. One, how do you speak to the versatility and the modularity of revision?
Dr. Trousdale: I think that’s a valid point. There is a small percentage of our patients that would benefit from isolated poly exchange. And Aaron pointed out very nicely that the patient that fails late rather than early would, but I would argue that’s relatively rare. Most patients’ total knees will last them forever, if they’re over the age of 50 or 60, I think. Secondly, Aaron, we’ve got these things called a saw in Rochester, so if you need to revise an all poly tibia you take a saw to the interface at the cement and burr—it takes about 37 seconds or so. (laughter)
Dr. Hofmann: Can you use a wood chipper? (more laughter) We do that in Fargo.
