Tibial debonding is a suggested cause for revision. That’s debonding between the metallic tibial baseplate and the cement. It is associated with lysis. We first reported this in 2001 (Mikulak, et al., JBJS-Am), with a titanium matte-finish baseplate and rotational loosening in this Posterior Stabilized design with box-post impingement.
But other people observed this with other knees. From the Mayo Clinic…it was the most frequent cause for revision in their report, representing 1.9% of 1,300 knees (Arsoy, et al, CORR 2013). They warmed the Simplex cement in order to speed the curing.
Their failures, like everybody else’s, were associated with a more varus mechanical axis. What’s interesting to me is that there were 8 surgeons that contributed cases. One surgeon never had this type of loosening in his hands and another surgeon had it happen 4.5%.
If that doesn’t scream for some technical variability, I don’t know what does. But they blamed the implant.
Tibial debonding has also been associated with high viscosity cement in 2 other reports. Hazelwood, et al. (Knee) in 2015 and Kopinski, et al. (J Arthroplasty) in 2016. There’s something going on with how you use the cement.
So, we did a study. We used 48 of the same size cemented total knee components. Cobalt chrome with a heavy grit-blast undersurface. We cemented these into an acrylic mold, and we compared Simplex and Palacos with 3 different cementing times. We looked at the results when you put it on early, so it’s kind of wet cement. We looked at it per the manufacturer’s instructions, which is more of a medium viscosity. And we looked at it late when it was kind of dry and doughy. And we looked at cementing the plateau only versus the plateau and keel. We tried to control temperature and humidity and we did a push-out test on an MTS.
We also did a little fat contamination to simulate something getting into the interface when you are putting the keel down into the bone and maybe some residual fluid, blood, water, fat, whatever gets into the interface.
The highlights of the study are:
Late cementing reduced the interface strength of Simplex by 47% and Palacos, the doughier one to begin with, by 63%.
Early cementing increased interface strength of Simplex by 48% and Palacos by 139%. Fat contamination of the metal-cement interface reduced the interface strength to practically 0% with Simplex and -91% with Palacos. Cement pre-coating of the metal, prior to fat contamination, the bond strengths were -65% with Simplex and -1.6% for Palacos.
So, there IS variability in that initial cement-metal bond strength in the lab when we’ve got as controlled conditions as we can. Dry cement gives a weaker bond. Palacos is more sensitive to cementing time because it doughs up sooner. Contamination of the interface creates a weaker bond – which you’re not going to see as you’re seating the component in that keel region because you’re blinded by the baseplate.
My recommendations…thoroughly dry the bone. Beware of dry cement. Put wet cement directly on the implant to get the best metal-cement bond that you can.
You can blame the implant and change of technology, or you can get better.
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