“Ceramic-ceramic bearings are exceptionally reliable in young, high demand patients, ” says Steve Murphy. “Cross-linked polyethylene is a better option, ” says Doug Padgett. “There is a lot of basic science behind it, we can measure its performance, and people tolerate it well.”
This week’s Orthopaedic Crossfire® debate is “COC Bearings in the Young Patient: A New Standard Emerging.” For the proposition is Stephen B. Murphy, M.D. from Tufts University in Boston; against the proposition is Douglas E. Padgett, M.D. from the Hospital for Special Surgery in New York. Moderating is Robert T. Trousdale, M.D. from Mayo Clinic.
Dr. Murphy: “Our experience is with high demand patients (307 hips) less than 50 years of age of whom 60% were male. Most of these were part of a prospective FDA/IDE [investigational device exemption] study. We had uncemented femoral and acetabular components, a flush-mounted liner, and an 18 degree taper with no metal backing or elevated metal rim. Of this group, 17% had at least one prior surgery; all had preservation of the posterior capsule and short rotators. Bearings were small: 28mm (29%), 32mm (69%), and 36mm (2%). ”
“In that group, out to 16.5 years, nine hips were revised. There were three fractures, two of which were high energy polytrauma, three osseo-integration failures, two modular neck fractures, and one was revised at an outside institution for unknown reasons. Fourteen year survivorship with revision for any reason, any component was 96%. If you exclude the two prosthetic neck fractures, the survivorship at 14 years is 97%. There were no dislocations, no revisions for infection, and no osteolysis.”
“There are no studies of cross-linked poly (XLPE) at 14 years; we do have some studies with high survivorship (100% at 10 years, but only 50 patients and 56% of the hips were excluded from the study).”
“Why would people elect not to use ceramic-ceramic bearings? Cost, fracture, squeaking, dislocation. The cost is similar to most ceramic on XLPE; the cost is less than many with ceramic on XLPE with newer porous coatings. And with cobalt chromium (CoCr) we have taper corrosion at a higher incidence with those bearings, so CoCr is used less and less in hips. So you’re really talking about cost of ceramic on poly versus ceramic-ceramic. In fact, if you use enhanced porous coating with those constructs they’re actually more expensive than ceramic-ceramic.”
“The fracture rate in this high demand group is infrequent and associated with life-threatening trauma. The incidence of poly fracture may actually be higher. And if you do have to repair a fractured ceramic liner head, generally it’s an uninflamed joint and it’s a relatively simple procedure.”
“As for squeaking, we all know that’s a design issue. If you use the correct designs such as flush mounted liners without elevated metal rims…or you use standard titanium components rather than beta titanium alloys then this isn’t a clinically significant problem. Dislocation: In this particular study of 262 hips there were no dislocations, so I think stability is a function of soft tissue technique and component placement.”
“Regarding XLPE, lipids and loading reduce the oxidative stability of these bearings. Also, they have decreased tensile strength and edge loading; all retrievals show some subsurface oxidation in all types of XLPE. Vitamin E poly may be a good solution, but it has less cross-linking and short follow up. So I think these are exceptionally reliable bearings in young, high demand patients.”
Dr. Padgett: “Let’s look at the 2000 national registry from Sweden. While we knew that each decade we were getting better in terms of reducing our revision rates, there was one group—those under the age of 55—where they concluded that younger, more active patients were at greater risk for problems related to hip arthroplasty. And those problems from the 80s into the new millennium included older generation polys, the effect of sterilization, and the effect of shelf life. This led to an orthopedic fork in the road: either make a better poly or forget about poly and go to the alternatives.”
“MoM [metal-on-metal] bearings appeared to have lower wear rates, low rates of osteolysis, larger heads for stability, and no risk of fracture. The disadvantages were theoretical tumor induction, possible metal ion release, probable metal debris, and inevitable adverse tissue reaction. We know from multiple reports that the revision of these pseudotumors have done poorly. ”
“Looking at ceramics, alumina-alumina has extremely low wear rates, is wettable, and is hard. Then there is Murphy’s Law. There are the clickers and the squeakers. The former may represent a little microseparation. And regardless of the etiology of the squeaking everyone finds it annoying. As for fractures, whereas they used to be about 1/1, 000 now it’s down to 1/25, 000 but it’s still not zero.”
“We reported our experience with mal-seating. We don’t know what the significance of the metal jackets are. This may be a problem. We know that impingement is a problem, and marginal chipping can occur with ceramics. Metal transfer as a result of the impingement clearly affects the surface roughness. These observations support our long-held hypothesis that hard-on-hard bearings are extremely sensitive to component position.”
“So this leaves us with XLPE. There is a lot of basic science behind it, we can measure its performance, people tolerate it well, and it reduces strain due to both adhesive and abrasive wear mechanisms. There is 10 year data from Massachusetts General Hospital on the Longevity/Durasul method showing no increase in head penetration since the beginning of the first year (the bedding in period).”
“So based on the lack of apparent wear at 10 years and the absence of identifiable lysis…based on the ability to use larger heads and the rare catastrophic events, it is apparent that XLPE is indicated in young patients.”
Moderator Trousdale: “Steve?”
Dr. Murphy: “Squeaking is totally design related, and every case that Doug showed where there is mal-seating, metal transfer, squeaking, etc…that is all elevated metal liners and is a different issue. Regular flush mounted liners don’t have a significant problem with squeaking and I’ve never revised anyone for that reason.”
Moderator Trousdale: “Doug, what about the 20-year-old that needs a THR [total hip replacement]?
Dr. Padgett: “You might consider a ceramic-ceramic bearing. The harder bearings are more sensitive to position; I would use enabling technology to make sure it’s right down the pike.”
Moderator Trousdale: “Steve, would you use ceramic on that kid?”
Dr. Murphy: “Sure.”
Moderator Trousdale: “And for a 50-year-old?”
Dr. Padgett: “Ceramic on poly.”
Moderator Trousdale: “Justify why you would use ceramic on poly versus metal on poly. Ten year survivorship data seems to be the same.”
Dr. Padgett: “I think something’s happened in the last ten years as far as the trunion/taper design.”
Moderator Trousdale: “Steve, when do you stop using ceramic on ceramic?”
Dr. Murphy: “Anyone who is old enough so that there’s no possibility that ceramic on poly would wear out. Depending on their medical history it would be somewhere between 65 and 75.”
Moderator Trousdale: “Steve, a lot of the data you gave was on alumina-on-alumina so can you discuss the differences of alumina, etc.?”
Dr. Murphy: “Delta-Delta and alumina-alumina wear are almost identical. Delta is stabilized to reduce the possibility of crack propagation, so it’s about twice as strong. Because of that the designs have changed so that they’re stressed more…so the fracture rate is no lower because they’re designed close to the edge. If you use the exact same design then the fracture rate would go down.”
Moderator Trousdale: “So the head fracture seems to be lower, but the socket Delta fractures are pretty similar to the alumina?”
Dr. Murphy: “They are very similar. That’s a design issue. Doug mentioned the Mass General study at 10 years where they had virtually no wear. Even though that was a perfect polyethylene they don’t use it anymore. Why is that?”
Moderator Trousdale: “So Doug there are some downsides to the Delta. It’s got almost 20% zirconia. Should we be concerned about that?”
Dr. Padgett: “We have about 40 retrieved Deltas at this point—the longest is at 5.5 years. We looked at phase transformation in terms of maybe the roughness changes, and the good news is that there seems to be little of that phase transformation. So at this point I’m cautiously optimistic.”
Moderator Trousdale: “Steve, if we’re using a ceramic-ceramic should we use alumina-alumina or Delta-Delta where there’s no 10 year data?”
Dr. Murphy: “If you design the Delta-titanium junction to be as strong as the one for alumina then it would be a great bearing. If it’s the same bearing distribution (28-32-36) then that’s all you need.”
Moderator Trousdale: “Doug, Steve mentioned that fracture was relatively easy to handle. Some people would argue that. How do you handle a patient who is young, with a ceramic-ceramic bearing whose head has exploded?”
Dr. Padgett: “Tough question. The problem is that these are small shards of glass, and if you wind up going back to a metal or ceramic-poly bearing then the wear rates could be exceedingly high. The key for me is a meticulous debridement. As for the bearing option at that point, if you’ve already exploded one ceramic-ceramic then do a complete synovectomy. Then probably consideration of either the ceramic or metal on poly.”
Moderator Trousdale: “Steve, would you go back to ceramic-ceramic in a fracture?”
Dr. Murphy: “If it’s a head fracture—like a fall from a height on concrete—and there’s polytrauma, but the hip is pristine and the liner is fine, then I’d change to a Delta with a titanium sleeve…quick case, quick recovery. I’d go Delta against alumina.”
Moderator Trousdale: “There have been rumors about ceramic creating a suction effect for stability.”
Dr. Padgett: “We did about 800 ceramic-ceramic hips, and of all the subgroups our dislocation rate in the ceramic-ceramic group is the lowest. This was four surgeons. I don’t know why…same approach as we’ve always done. There may be something to that.”
Moderator Trousdale: “If ceramic-ceramic is so good why aren’t all the hip surgeons doing it for most of their patients?”
Dr. Murphy: “There’s a myth that it’s more expensive, but when compared to a lot of the stuff people are using now it’s less expensive. It is more technique sensitive, so it’s more forgiving for a lower volume surgeon.”
Moderator Trousdale: “Thank you.”
Please visit www.CCJR.com to register for the 2014 CCJR Spring Meeting, May 18 – 21 in Las Vegas, Nevada.
