“Ceramic bearings are stable and popular worldwide…Australia (26%), France (43%), ” states Bill Walter. Bill Maloney counters, “There is interest in CoC because it’s a very low wear bearing surface. But is that relevant today with the other, lower cost bearing options we have? Probably not.”
This week’s Orthopaedic Crossfire® debate is “Ceramic-on-Ceramic Hip Arthroplasty: A New Standard.” For the proposition is William L. Walter, M.D., F.R.A.C.S., Ph.D. from Sydney Hip and Knee Surgeons in Australia; against the proposition is William J. Maloney, III, M.D. from Stanford Hospital and Clinics in California. Moderating is Clive P. Duncan, M.D., F.R.C.S. (C) of the University of British Columbia.
Dr. Walter: “It’s not really a new standard as ceramic bearings have been around since the early 1970s. In many countries ceramic bearings have been the standard for a long time. In Australia 26% of our primary hip replacements are ceramic-on-ceramic (CoC); in France it’s 43%; the U.S. has one of the lowest uses of CoC in primary hip replacements (<15%). And the Australian registry shows us that use of this bearing has been stable for about 10 years.”
“In our own practice we’ve done over 4, 000 CoC hip surgeries. Looking at the first 300 cases we published, our 10-year data shows survival with any revision for failure was 98% at 11 years. There were no failures after four years, so with ceramics—compared to the old poly—we’ve eliminated late failures due to wear. We did see some periprosthetic fractures early, as well as some early loosening. Out of those 300 hips, 0.6% were squeaking, but none of those were revised. Looking at the 4, 000 CoC hip surgeries from 1998 – 2010 we had 55 retrieved with ceramic heads; they were retrieved for reasons unrelated to the bearing (only two for squeaking). And we analyzed the wear of these bearings, and published that in 2012.”
“In ceramic bearings you don’t get concentric wear, you get stripe wear or edge loading pattern. We’ve measured wear volumes and found no measurable concentric wear, but edge loading wear occurs in 84% of our retrievals. The median wear rate is 0.2mm3 per year. Stripes that slope down have bigger wear and those that slope up have less wear. The down sloping ones are due to anterosuperior edge loading, which is less common; posterior edge loading is more common and it produces lower wear.”
“We’ve also related the width of the wear stripe to the volume, and we’ve measured the acetabular component position for anteversion and inclination. We found that it’s a combination of high anteversion and high inclination that leads to anterosuperior edge loading, while low anteversion and low inclination leads to posterior edge loading.”
“We did a logarithmic scale showing the wear of metal-on-metal with edge loading, metal with concentric wear, the Biolox Forte and the Biolox Delta…the last one has very low wear. Our data on revisions for osteolysis showed that ceramics had only one revision for osteolysis. Paradoxically, it may not be the ceramic debris that causes the osteolysis here. Looking at the histology, with the ceramic bearings we see there is mild synovitis. Compare that to poly where you have pseudotumors, visible debris, synovitis…and metal-on-metal where you also have necrosis.”
“With ceramic the tissues around the hip are very benign. We do see some yellow grainy debris in the macrophages; in the case with osteolysis there is black debris in the hip. When we looked at it in more detail we saw that this was not alumina, but it was titanium. So paradoxically in ceramic the wear debris that causes osteolysis is the titanium from impingement or from the tapers.”
Dr. Maloney: “The title is, ‘A New Standard.’ The dictionary says that ‘standard’ is something established by authority, custom, or general consent. This is clearly untrue for CoC THA [total hip arthroplasty]. Is there any indication for CoC THA today?”
“There is interest in CoC because it’s a very low wear bearing surface. But is that relevant today with the other, lower cost bearing options we have? Probably not. When you examine the wear data on conventional poly with ceramic, it probably makes a significant difference…especially when you’re comparing ceramic on old polyethylene or metal on old polyethylene with modern CoC. But when you look at highly crosslinked polyethylene (HCLP) it almost doesn’t matter what bearing surface you use…it’s hard to generate wear that will lead to lysis.”
“We did a study looking at retrieved femoral heads in revision hip surgery. If you look at roughness of femoral heads up against conventional poly, as the femoral heads get rougher the wear volume increases, thus increasing the risk for osteolysis and loosening. However, when you take the same femoral heads at five million cycles against HCLP, it was less than 0.1 mg of wear.”
“The negatives of CoC? One of the biggest is value…and whether you live in China, Australia, or the U.S., we’re going to have to bring the cost of implants down. I was told that in China it costs more than $1, 000 extra to do a CoC THA. To justify that you must reduce the revision risk. The revision rate in the U.S. with different bearing surfaces, comparing metal-on-plastic with CoC it’s clear that with regard to revision rates there’s no difference between metal-on-plastic and CoC. That is despite the fact that both bearing surfaces are used at high and low volume hospitals and in young and old patients.”
“Registry data from Australia shows that the best performers are ceramic on poly and metal on poly. There is an increasing interest in the use of ceramic femoral heads in the U.S. because of possible taper corrosion. Until we figure that out I’m using ceramic heads in my younger patients.”
“We have ten-year data on HCLP from our center on patients under the age of 50; there are no revisions for osteolysis and one case of osteolysis that you cannot see on an X-ray. There is some CT scan data showing some small osteolytic lesions; people are saying, ‘That’s osteolysis caused by HCLP.’ Remember, osteolysis can be caused by fluid pressure, and we don’t have the same data on CoC. The good news is that large ceramic heads do better than small ceramic heads.”
“But it’s a more demanding procedure, and if you get it in wrong you’re going to have an increased risk of problems. As for breakage, you can’t predict who is going to break. The new Delta ceramic is much better; it’s a harder material and the fracture risk will continue to decrease. Part of the risk of fracture is that we surgeons don’t assemble it right.”
“The other issue is squeaking. Patients who squeak don’t like it. I will close by saying, ‘you can squeak by with CoC, but it’s not the new standard.’”
Dr. Walter: “Dr. Maloney showed lab studies of polyethylene, but what they don’t include is oxidation in vivo. There is work from Harvard showing that the HCLP we’ve been using for 10 years reoxidizes and returns to the higher wear state. We heard 5 – 10 years ago that HCLP was going to be ‘the answer, ’ but now there’s a strong scientific argument that this isn’t enough…that it needs to be laced with vitamin E to stop the free radical formation. Regarding revision rates, all of the data that was presented was less than 10 years; when you’re using a CoC bearing you’re thinking about 30 – 40 year survival of the hip. We’re looking to put a hip in our young patients that will last many decades…and we don’t have the data in terms of revisions, either from the registries or from small studies, about how the HCLP will be long term. But we do know that CoC bearings have lower wear, so we expect them to last longer (20/30/40 years).”
Dr. Maloney: “Retrieval data is being re-evaluated as it relates to what actually is oxidizing in that material. We certainly haven’t seen it clinically in terms of 10-year data from Sweden and 8 – 10 year data from the U.S. The clinical significance of that is questionable and probably not relevant. We always say, ‘We have a 30/40 year hip.’ I’ve been doing this for 25 years and I’ve never seen a good 30 or 40 year paper; we keep changing things. So the implants that Bill is putting in today aren’t the implants he put in 10 years ago. And if you’re paying for this operation in today’s world you going to look at a justification for increased cost. If you examine the 10 year revision data for bearing surfaces—metal-on-plastic, ceramic-on-plastic, or CoC—they are not different.”
Moderator Duncan: “Bill, what about the revisability of the failed ceramic.”
Dr. Walter: “We’ve had about 4, 000 CoC bearings and have had three liners break and no femoral head breaks.”
Moderator Duncan: “But the ones that have been referred into you perhaps because there was edge loading or something.”
Dr. Walter: “If you have a broken ceramic head you need to revise the stem because the head taper will be damaged and you can exchange the ceramic insert. If you have a ceramic breakage on the acetabular side then you need to revise the cup, and you can retain the stem and change the head.”
Moderator Duncan: “So you change the stem because the trunion has become damaged by the fractured head?”
Dr. Walter: “Correct.
Moderator Duncan: “You can’t use a titanium adaptor?”
Dr. Walter: “We’ve never revised a broken ceramic head because we’ve never seen one. Because of the soft metal head articulating against the fragments of ceramic it damages the taper much more severely than with corrosion or another form of failure. In that situation I would study the head, and if the patient had been walking on it with a broken head then it would be too much damage to the trunion.”
Moderator Duncan: “Bill, if you have a young active patient who requires a 28/32mm head are you going with that? Or is it when you’re faced with a 36mm head and your large patient favors that so as to reduce the risk of instability?”
Dr. Maloney: “I haven’t used a 28mm head in more than five years, so I would use a ceramic 32mm head in a young, active patient; in an older patient I’d use a cobalt chrome head. For 36mm I tend to use mostly ceramic…and that’s solely for the taper corrosion issue. In our own practice we’ve got about 1, 000 36mm heads in and I’ve not seen a case of taper corrosion. And assembling it wet through small incision surgery is a risk factor with cobalt chrome on titanium.”
Moderator Duncan: “Bill, what’s happened to vitamin E poly? We’re not hearing about this lately.”
Dr. Maloney: “We did a randomized clinical trial (RCT) and we just got the five-year results. As you might expect it’s looking good…the same as the Longevity or other HCLPs that we have RCT data on. It tends to bed in at about a year and after that it flattens out; at five years we’re measuring no wear from the one to five year standpoint.”
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