Moderator Trousdale: Michael, that was very good. You didn’t add that Linus Pauling said; ‘Don’t believe the older person unless it’s Chit Ranawat’. Let me see a show of hands from the audience—how many people in the audience are shooting for a neutral mechanical axis—so-called mechanical axis alignment? Okay, so a boatload. How many people are shooting for a kinematic alignment? So a few.
Michael’s got a good point, Chit, we’ve got 10-15% of our patients not satisfied with our total knees. You’ve been around the block a long time, what do you think the major factor is as to why they’re not satisfied? Is it alignment issues or is it other issues that Michael brought up?
Dr. Ranawat: It has nothing to do with alignment. Even if you align properly, about 8% of patients in my practice have some anterior knee symptoms. And that is due to substance-P nerve fibers, which are in the anterior part of the knee, mostly in the infra-patellar area in the soft tissue. It’s because those fibers are still there that you cannot eliminate anterior knee pain. And don’t associate that with alignment or any other particular problem.
Moderator Trousdale: Michael, you want to address that? So, you brought up a nice point Mike, that most of the studies, and a couple of randomized trials about kinematic alignment versus mechanical alignment…we’ll talk about those in a minute, but is alignment a factor? Is it soft tissue balancing? Is it rotation? Is it slope? Is it flexion of the femoral component? I mean there are loads of factors in our total knees. What do you think is the primary driver of dissatisfaction?
Dr. Dunbar: It’s all of these things and it’s probably also the glass ceiling associated with metal and plastic if at the end of the day we’re cutting the bone and sticking metal on it it’s non-physiologic so how satisfied could you be with that. But, it doesn’t mean you can’t start evolving it. I think the point is now that we have tools where you can start to identify that there is an individual variation.
The question now is; what would you choose to do about it?
It’s compelling when you see a boatload of patients for second opinion come in with perfect looking X-rays based on neutral mechanical and they all say the same thing…they say it in different words, but they say, “I don’t care what the surgeon says, that knee’s in there wrong.”
It gets a little wackier when you extrapolate because kinematic alignment is really about how you move. It’s really four-dimensional alignment. How you get up out of a chair. How you walk through time and space.
We don’t have the ability as a modern surgeon to impute that data now. There are too many variables as you’ve alluded too.
But I think the future…the surgeon of the future…will impute the biometrics for that patient, figure out what the flight plan is and then get robots to execute that plan. That’s how we’re going to get to that next level.
Moderator Trousdale: I agree with that. Chit, do you change your alignment based on whether the knee’s a varus knee preop or a valgus knee preop?
Dr. Ranawat: Most of the varus knees—no, but in the valgus knee I can leave 1 to 3 degrees extra valgus because to perfectly align to neutral / slight varus alignment in a valgus knee it requires too much soft tissue release posterolaterally and that kind of release can cause flexion instability sometimes.
Moderator Trousdale: Gentlemen, thank you very much. It was a great debate.
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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.
