We’ve published on delayed dislocation (Lash, et a, Bone Joint J, 2016). It is the first presentation of about 10 patients. They had perfect positioning of components and then all of a sudden, after about 5 years, they dislocate.
Why is this happening now? We’ve been doing metal-on-poly since the 1960s and this didn’t seem to be a problem until recently. Well, there’s been a change in the trunnion. They’re shorter and smaller. The surface has changed on the trunnion to accept ceramic heads. There is a trend for increasing head size. I think we’ll all acknowledge with smaller incisions we’re not preparing the trunnion quite as well as we used to. And how hard we hit it. We don’t all hit it consistently.
I agree it’s uncommon. And there is some literature indicating it may be stem dependent. So, depending on the stem you use, you may only see a few of these cases and you may see a lot of these cases.
The issue is I cannot predict which patient will get it. You can have an 85-year-old lady and she can end up with a pseudotumor even with a 28 or 32mm head.
So, what would I say is the state of the art? Well, this is what we want our bearing couple to do. We want low wear. Low corrosion potential. I want to have a head size—I like to get up to 36mm, if I can. You want it generalizable, easy to insert and easy to take out down the line. Versatile. A lot of intra-operative flexibility. Familiar to us. Biocompatible. Revisable. Relatively cheap and safe.
So, for me the ceramic-on-poly total hip fulfills all the requirements of a modern bearing and that’s why I use it in 100% of my cases.
Dr. Engh: I may be a couple of years more progressive than you give me. I’m going to oppose the concept that ceramic heads should be used in all patients.
First, the increased use of ceramic-on-polyethylene in my opinion is a reaction to what remains a poorly understood and rare problem. That problem is mechanically assisted crevice corrosion, which subsequently leads to an adverse local tissue reaction. And this has been coined trunnionosis.
Second, for me and I think for many of us, this is still about cost. Ceramic heads cost more. The question I ask is what concerns you more today? The cost of your hospital’s stay or that patient’s 90-day event? Or a long-term cost prediction of what remains a rare and poorly understood problem?
Getting right to the data. The Australian Joint Replacement Registry [AJRR] 2017 Annual Report. In 2016 53% of the bearings were ceramic-on-poly and the trend is increasing.
In that report, the factors that contributed to this growth included the decreased use of metal-on-metal bearings, but also concerns regarding trunnionosis and corrosion.
Looking at the same 2012 article that Don quoted (Cooper, JBJS, 2012), they had 10 cases. Eight out of the 10 cases were from a single vendor. And this represented 2% of their revisions.
Another article with 27 cases (Plummer, JOA, 2016). And although we believe that a titanium stem with a chrome cobalt bearing ball is more common, in this series 70% of the cases were a chrome cobalt-on-chrome cobalt junction. Again, 21 of the 27 were from the same manufacturer. It’s also interesting that most of us use 36mm heads and 20 of the 21 heads in this series were less than 36mm in size.
Again, another article in 2017 (Hussey, JOA, 2017), actually that same single manufacturer, but this happened to be a titanium stem with a chrome cobalt ball. Out of 1,325 cases 3.2% either had elevated metal levels or had been revised. So not all of these were revised. They were being followed.
I think Josh Jacobs knows as much about this topic as just about anybody, so in a symposium from AAHKS (Jacobs, JOA, 2016), “the incidence, etiology and pathogenesis of mechanically assisted crevice corrosion are not well understood”—still in 2016—and I would say still in 2018.
