Same reoperation rates for the monobloc—4 infections; 4 aseptic revisions. And this type of implant is one-piece when implanted and you can remove the device if you need to change the polyethylene.
I, like Aaron, have started to use the all-polyethylene implants. I think it is a price performer. For some patients, the geometry is better. It does remove a little bit more bone. We unfortunately had a very bad track record with the AGC all polyethylene implant, so we were hesitant to do this. But we began to dabble in this again. We only do it in skinny folks.
Looking at our non-modular implants, the metal-backed AGC and the one-piece all-poly AGC…unfortunately we had catastrophic 10-year failure rates of over 30% (Faris, et al., JBJS, 2003). The majority of these were due to mechanical loosening and medial collapse, as Aaron showed. We’ve studied this extensively in our laboratory with varus malalignment and osseous remodeling under the medial plateau. I think you have to be careful with implant design, high BMI, and varus alignment of the limb (Small, Berend, et al., JOA, 2011).
We’ve studied it computationally and the metal backing underneath the tray distributes the load in the proximal tibia better and I think can eliminate this type of medial overload process (Tokunaga, Small, Berend, et al., J Biomech Eng, 2016).
If you look at surgical technique and BMI, I think those are far more important than modularity in the arthroplasty. Tibial component alignment is the first thing – we need to put them in straight. We found in our series of failed tibias, the average varus alignment of the implant was over 3 degrees. And then the same thing for overall limb alignment. With a one-piece implant, especially all-polyethylene, I think you have to avoid varus (Berend, et al., CORR, 2004).
When considering BMI, this is about 10 years’ worth of work, and it was the first time that we showed the linkage of varus malalignment and high BMI (Berend, et al., CORR, 2004). So, I think in high BMI people, whether you use modular or one-piece, it’s critical to get it in straight.
Finally, the long-term data from the Mayo Clinic…if you look at patient and implant factors, they concluded looking at their entire series, the most predictable long-term durability of an implant is a non-modular, metal-back implant, cemented, all-poly patellar component. And, of course, to Paul, retention of the PCL (Rand, et al., JBJS, 2003).
