Six months ago, at AAHKS [American Association of Hip and Knee Surgeons], using data from the New Zealand Registry—the same registry—Smith, et al. reported that patient specific differences—like comorbidities—were 2-6 times greater than the hazard ratio of infection decrease with ceramics. Every known risk factor is more likely to be present in the non-ceramic cohort.
Another major flaw in the data is coding accuracy, particularly of complications in registries. A large review article from the Journal of AAOS showed the complication coding is off by 20% (Patel, et al., 2016). Ten years ago, at the AAOS Annual Meeting, Froimson, et al., showed that coding of infections was off by about 40% at the Cleveland Clinic compared to what the surgeon’s thought was an infected case.
Until very recently, most trunnion cases were coded as infections. This could account for the apparent association with a higher infection rate. There’s no doubt that most of us believe strongly that there is less taper damage with a ceramic head. So, that’s a good reason. That’s why I use ceramic heads, just as you heard described. But not to lower the infection rate, just to lower the trunnionosis rate, which has been misdiagnosed as infection a high percentage of the time (Kurtz et al., CORR, 2013).
Many of the articles Thorsten showed you, every controlled trial where they did try to control for several confounding variables showed no difference infection, revision…only differences were in squeaking. In the large Cochrane reviews (BMJ, 2011), the results didn’t show any advantage for ceramic-ceramic compared with traditional metal- or ceramic-on-poly.
The Nordic Arthroplasty Register Association also showed no difference in revision rate except for a higher revision rate for fracture.
The other big issue is the confounding variables. Specialty procedures like ceramics tend to go to surgeons who have better patient mix and have lower infection rates. The failure to control for these confounding variables can lead to conclusions that are at odds with the literature and even the common sense.
In conclusion, I think registry data is invaluable. But it is very poor if it’s distinguishing small differences in well-performing devices. The vast majority are association and it leads to misuse.
Our great philosopher, Mark Twain, from Missouri up the river from St. Louis, said “There are three kinds of lies: lies, damned lies, and statistics.”
But my favorite quote from him is “Politicians and diapers must be changed often, and for the same reason.”
So, Thorsten, I was interested in the data you presented but to me it may be time to change that diaper.
Hi – Super important topic and discussion. I am currently completing my Masters in Epidemiology and appreciate a sensible discussion of exposure, outcome, cause and association. But my question today, is where did the syntax “peri-prosthetic infection” come from? Years ago we were discussing PJIs – prosthetic joint infection. Has the description changed officially to “peri-prosthetic”? If so, is this to signify an infection that reaches beyond the joint into the surrounding bone?
Thanks for your consideration,
Jo Elliott