My second point is, this is really all about cost, clearly ceramic heads cost more and the question I’m going to ask you is, “What are you most concerned about today?” You have to deal with your hospital. Are you more concerned about the cost of the hospital stay, or are you more concerned about the long-term costs predicted from a model?
According to the American Joint Replacement Registry (AJRR), 53% of primary total hips are a ceramic on polyethylene bearing. Quote from the AJRR, “Factors that have contributed to this growth include, concerns regarding trunnionosis and corrosion.” This all really started in 2012. It didn’t really start then, we knew about corrosion. Corrosion has existed for a long time, but corrosion leading to an adverse local tissue reaction had been rarely described. In this first series (Cooper et al, JBJS-Am2012) there were 10 cases, it was 1.8% of their revisions.
The same center came back in 2016 with 27 cases (Plummer et al, J Arthroplasty2016). Interestingly 70% of their cases were a chrome cobalt head on a chrome cobalt taper, something that is relatively uncommon today—21 of the 27 were from a single manufacturer, and 20 of the 21 were femoral heads smaller than 36mm and most of us are tending towards the 36mm head currently.
In another study (Hussey et al, J Arthroplasty2017), a single manufacturer the data from a titanium stem with a cobalt ball was 3.2% of 1,300 cases either had an ongoing adverse local tissue reaction or had been revised.
So, a summary article from an AAHKS [American Association of Hip and Knee Surgeons] symposium from 2016 (Jacobs, J Arthroplasty) stated “As yet the incidence, etiology, and pathogenesis of MACC-associated with an adverse local tissue reaction are not well understood.” So, my question is, “Why are we reacting to a rare and poorly understood problem?”
My personal experience, I believe cost is a local issue, it’s not a long-term issue, it’s what you see in your own experience. In terms of parts per billion for cobalt, only out to 2 years, it was less than one part per billion and it didn’t change from pre-op to post-op.
This has been supported by another study that was published in 2013, interestingly after the previous study showing corrosion. They did not see cobalt levels greater than one part per billion out to 10 years in their metal on polyethylene bearings. My clinical experience with a metal ball on crosslinked poly includes a prospective randomized study now 16 years out. I’ve only had 3 revisions in these. These patients are doing very well: no infections, no loosening.
Pertinent to this talk no revisions for mechanically assisted crevice corrosion.
We have a long-term postmortem retrieval program at our center. I sent 56 of our postmortem retrievals up to Doug Padgett at HSS [Hospital for Special Surgery]. These have been in for 11 years: 43 were a cobalt chrome ball, on a cobalt chrome stem, 13 were ceramic balls, and a mix of 12, 14, 16 tapers. Both the ball and the head were graded for corrosion. The mean score in these 56 was 1.4 out of a possible 96. According to the table the HSS revisions, where you can see the corrosion scores are substantially higher.
As far as another view, for a long time we’ve been doing ball and liner exchanges for polyethylene wear. We have traditionally used a chrome cobalt stem and always replaced these balls, with a chrome cobalt ball. We took all these balls, graded them for corrosion, divided them into low grade corrosion, high grade corrosion, and saw no difference in the survivorship. Importantly, even when we put a new metal ball on a stem that had corrosion, there were no revisions for mechanically assisted crevice corrosion (Goyal et al, J Arthroplasty2014).
