Whiteside v. Callaghan: The Cementless TKA: It’s About Time
OTW Staff • Mon, April 16th, 2018
This week’s Orthopaedic Crossfire® debate was part of the 33rd Annual Current Concepts in Joint Replacement® (CCJR®), Winter meeting, which took place in Orlando. This week’s topic is “The Cementless TKA: It’s About Time” For is Leo A. Whiteside, M.D., Missouri Bone & Joint Center, St. Louis, Missouri. Opposing is John J. Callaghan, M.D., University of Iowa, Iowa City, Iowa. Moderating is Robert T. Trousdale, M.D., Mayo Clinic, Rochester, Minnesota.
Dr. Whiteside: Seth. As a young man in wrestling I learned to thank God for my opponent and so thank you, Seth. John is professor at Iowa, president of the American Academy of Orthopaedic Surgeons (AAOS) and a very distinguished gentleman, but he’s wrong and it’s always much more fun to kick somebody’s butt if he’s really wrong and he’s really tough. So, thanks again Seth.
If cemented TKA works so well, why are we even talking?
A well-known study from Nelissen in the early ‘90s suggests that it does well forever. But if you look at the scores, not just survivorship, the results deteriorate down to the point that maybe 50% of them are good or excellent at 10 years after surgery.
Chit Ranawat has a nicely done study too that looked at weight and activity level and age and found that the tougher cases, the heavier ones, the ones that we’re doing now all the time, deteriorate beginning at 5 years and at 15 years, about 70% of them are doing pretty well.
I think there’s something wrong here and what’s wrong is the interface. Nielsen, looked at this with micro-analysis of the interface and he found that cemented implants, even though they’re stable to begin with, migrate and continue to migrate, whereas cementless implants when done well do not migrate.
Miller, et al. looked at this with cadaver specimens and found that when you get deep interdigitation of cement in the bone initially you find that this cement has been eroded and degraded. After 5 years in-vivo, it’s often 2mm thick and its adherence strength to the bone is about 0.2 megapascals.
If you don’t know much about megapascals, 0.2 megapascals is about what it takes to pick a scab off. We’re not talking about a lot of strength in that bone cement interface.
Now, John this may not occur to you, but things happen to the bone cement and the cement-metal interface. In fact, cement fails at the interface between the cement and the metal itself.
Also, cement bonding to the bone is weak. Stuck to metal, or stuck to bone, chunks of cement surrounded by fibrous tissue, don’t look comfortable to me. I think that’s why these are still hurting after a period of time.
Bartel, Burstein and Insall, nice paper that showed what you need is an effective stem, cement mantle that is deeply interdigitated in the bone and then peripheral contact. And even then the cement erodes.
With 9 to 11 years follow-up in 256 cementless knees, what we found was that one loosened and when we continued to follow these out past 18 years, we still found a survivorship rate greater than 99% and no deterioration in pain. Big difference.
What works? Current practice and techniques, better porous coating, stronger implants well-designed for fixation, a surgeon that will ensure a flat tibial cut surface, and then use a stem. Screw the tibial tray down, after you have driven it down as effectively as you possibly can.
The surgeon needs to know a few techniques and to perform these techniques.
Rigid fixation…it takes a little bit of work and then watch these interfaces mature.
Beware of new technology. Weak materials tend to break. Flexible materials do not work and if you try flexible and weak together, you’re going to lose.