We published some work where we introduced shear, compression and torsions forces into modern testing, to look at a more complex endeavor such as stair descent. Those were not looked at in the earlier designs. That’s why we have a lot more confidence in our future designs and we can actually look at the difference between two designs (Bhimji, et al., JOA, 2012). So modern testing has improved our confidence.
We can’t forget the technique. I think it’s really important to use the 4-Corner test—this I learned from Leo Whiteside—to make sure your tibia is cut flat. This is the critical point of making sure a press fit tibia works. So, you’ve got good designs now. Make sure that tibial cut is flat. And when you go to put your real implant in, it’s important that when you impact it that you allow your central pegs or your keel to maintain that stability. So, make sure the tibial implant and the tibial cut are co-planar as you go down. That maintains your mechanical integrity.
In summary, I believe cementless total knee replacement is the choice for the younger, more active patient. I do think patient selection is important. The principles of cementless fixation remain — adequate mechanical stability, maximum contact with viable host bone. Modern designs, I think, you can have a lot of confidence in the modern press fit designs. They’re very successful and surgical technique is critical.
Dr. Lee: Debating Mike is always a tall task. But ability is not reliability. Devices not only need to be viable; they also need to be durable, reliable, reproducible. Cemented fixation remains a gold standard even in the young, active patient.
I think desire for uncemented fixation is because we feel that biologic fixation is better than cement. Obviously, Mike already showed the biomechanical studies associated with that. The question you really need to ask yourself is, “Is cement really the weak link?” Or is cement breakdown the cause of failure and loosening over time (Sharkey, et al., JOA, 2014)?
If you look at the Australian National Registry, the risk of aseptic loosening or revision for aseptic loosening is about 2% at 15 years (AOANJRR Annual Report 2018). I think of young patients undergoing revision are not undergoing revision for loosening of implants because of cement breaking or failure. They are undergoing because of things like infection or instability.
Institutional series have shown that basically at 5, 10 and 15 years, large series of consecutive, cemented total knees arthroplasties have high survivorship and you don’t see this survivorship decreasing even at the 15-year mark (Vessely, et al., CORR, 2006).
In fact, if you do a good cemented total knee arthroplasty, and this happens to last over 8 years, there’s a greater chance of dying than the implant loosening. And even if you have the luck of having a good design, even in the very young patient, particularly with the IBI monoblock design, at 30 years very low rates of tibial loosening in this group of patients (Ritter, et al., JOA, 2016; Long, et al., JBJS-Am, 2014).
In my mind, cement is really not the root cause of aseptic loosening.
Cementless tibias, cementless total knee arthroplasties, you’ve seen are less forgiving, technically demanding, there are bone quality constraints, and they are costly. Which is not necessarily compatible with today’s environment.
Undoubtedly with older designs, cemented fixation was superior to cementless fixation (Duffy, et al., CORR, 1998). But even with contemporary comparative series, there was no difference in clinical outcomes but more aseptic loosening and more revisions in the cementless groups (Behery, et al., JOA, 2017).
