The real issue is corrosion. I had the recent experience with a couple of patients, titanium stem, metal head, highly crosslinked poly bearing — their cobalt levels were 10, chrome was 1. We saw, when we got into the operating room, that the whole abductor mechanism was necrotic. This is a problem I do not have a good solution for. There is the corrosion on the inside of the cobalt chrome femoral head. There it is after a little debridement; the whole abductor mechanism is gone. No good answer for that problem.
Another of my patients, also titanium stem, cobalt chrome femoral head against highly crosslinked polyethylene and when we got in to open up the hip joint, going through the facia we saw that sort of dirty dishwasher appearing fluid and the abductor mechanism is completely necrotic after 8 years of use of this cobalt chrome on highly crosslinked poly bearing.
This is a problem I’ve not seen with ceramic on a titanium taper and the common thread appears to be cobalt chrome. As you see that dirty sort of dishwasher fluid, the abductor mechanism is to your right, the foot is to the left, and the whole abductor mechanism is dead. We can get rid of the cobalt chrome, but I can’t solve the abductor muscle problem.
Some basic science data from the group in London, Ontario (Tan et al, J Arthropolasty2016) looking at tribocorrosion between ceramic zirconium and cobalt chrome femoral heads. The combined score was greater with cobalt chrome versus ceramic. So, you certainly get corrosion with ceramic, but the corrosion byproducts are ceramic and titanium versus the toxic cobalt chrome.
There are a lot of unknowns with cobalt chrome heads. We don’t know the rate of clinically significant corrosion, we don’t know the factors that lead to corrosion, but we do know that cobalt chrome is the common thread.
Cytotoxicity, I also give the advantage to ceramics. Serum metals are increased, cardiac cobalt levels appear to be increased, and we know cobalt is cytotoxic.
And lastly—cost: I give a slight advantage to the cost to ceramic. Many centers are getting their ceramic heads at the same price as their cobalt chrome heads, but even if they’re a little more expensive there is a cost to working up the painful total hip replacement. If we make some assumptions, 12% of our patients have a little bit of pain, 12% of those get a work up, and 1% get a revision. Ceramics can be much more cost effective even if it’s a few more dollars at the front end. In the long-term, ceramics are going to be a little bit cheaper.
I think ceramic wins. In the elderly, they get stainless steel on highly crosslinked poly. Majority of my patients get ceramics on highly crosslinked poly, and then in the ultra-young, I’m still using ceramic on ceramic.
Dr. Engh: So, I’m going to oppose the concept that ceramic heads should be used in all patients. Rob and I are very much alike here, I have a selection process, and I’m probably about 50/50 ceramic heads and metal heads. So here in this debate, the increased use of ceramics on polyethylene is, in my opinion, a reaction to what is a poorly understood and rare problem. That problem is mechanically assisted, crevice corrosion (MACC). Not just corrosion but corrosion that leads to an adverse local tissue reaction (ALTR) called trunnionosis.
