Gehrke v Barrack: Ceramics Decrease the Incidence of Peri-Prosthetic Joint Infection

If you go to the bigger countries like the UK, the same—not significant—but still a lower infection rate in favor of ceramic-on-poly.

And if you put many registries together, 10 registries with more than 1.1 million patients, an almost statistically significant difference between them is reported. In New Zealand you find the same.

But what is reason? The reason could be that the material does not allow the formation of biofilm on its surface (Peters, Dtsch Ärztebl, 1988).

So, what is important if we develop a peri-prosthetic infection? Type of biomaterial can influence bacterial adhesion, like roughness, pH, molecular composition, ionic strength. And we also know from the literature that certain surface treatments have been described to promote osteoblast adhesion or to inhibit bacterial adhesion.

It’s proven and it’s published that adverse local tissue reaction creates an environment for bacteria growth. There is published data supporting this theory where they cultured S. epidermidis and S. aureus on different surfaces and concluded that biofilm formation is much lower on ceramic surfaces than on metal surfaces (Rimondini, ISTA, 2015).

In summary, registries suggest, not very significantly, that ceramics are associated with lower risk of infection in total hip replacement. The first in-vitro and ex-vivo results show lower bacterial biofilm adhesion on ceramic bearing surfaces.

Dr. Barrack: The thing is…we really don’t disagree because your concluding slide said that ceramics are associated with a lower incidence of infection. And they are associated with it. But, especially with registry data, associations are easy to show; causation is not so easy.

Ceramics don’t cause a lower infection rate, they’re just associated with a lower infection rate. I’ll show you the danger of not understanding the differences.

In the Midwest, on the farms every morning the rooster crows and the sun comes up, so they are associated. But most of us don’t think that the rooster controls the sun coming up.

So, to say that they decrease PJI is inaccurate because it implies causation. There is no causation, just an association.

So, what is the data? Looking at big registry sets it’s easy to find associations. It’s like quoting the Bible—you can find any association you’re looking for, but the associations are weak. When you’re up to 100,000 and your hazard ratio is only 1.2-1.5, it really is sort of meaningless.

In fact, these small differences are easy to explain by differences in the patient population.