Is there too much concern over squeaking hips? In a 2009 Current Concepts in Joint Replacement™ (CCJR) Orthopaedic Crossfire® debate entitled “The Squeaking Hip: Much Ado About Nothing, ” Robert T. Trousdale, M.D., from the Mayo Clinic argues that squeaking hips really are a comparatively minor trade-off for younger patients where longevity of the implant is a primary concern. Not so fast, counters Steven J. MacDonald, M.D., FRCS(C) from the University of Western Ontario. Squeaking hips could indicate malpositioning or other longer term problems. Who’s right? You be the judge. With Clive P. Duncan, MB, FRCS(C) of the University of British Columbia moderating, we present a lively debate regarding squeaking hips. Dr. Trousdale opens for the proposition.
Dr. Trousdale: “We’re going to talk about ceramic on ceramic bearing (Cr-Cr) surfaces. My conclusion? Cr-Cr is the best bearing couple for a select group of patients because it’s the best wear couple we have. The in vitro wear rates of cobalt chrome against conventional polyethylene, ceramic on conventional polyethylene, cobalt chrome on highly crosslinked polyethylene, metal on metal, ceramic on metal and ceramic on ceramic…Cr-Cr has the best in vitro wear rates. All bearings have risks; at a certain young age, the benefits of a superior wear couple probably outweigh the risks.”
“Consider a 12-year-old girl with bilateral severe avascular necrosis who underwent bilateral Cr-Cr hip replacement. Or an 18-year-old…bilateral, stage four avascular necrosis, huge lesions who received bilateral Cr-Cr hip replacement. The risks are real, but can be minimized.”
“Downsides: fracture risk, risk of runaway wear with malposition and edge loading, impingement risk that’s probably a higher penalty than metal or ceramic on polyethylene. Modular Cr-Cr junction problem, squeaking.”
“The fracture risk is decreased with modern technology; the ceramics now have smaller grain size and increased burst strength. There is better proof testing by manufacturers and the estimated risk presently is in the range of <1 in 2, 000 -10, 000, so relatively small. Runaway wear: really only seen in patients with severely malpositioned components. A very vertical cup can lead to edge loading, and that can lead to runaway wear. It can also occur with improper version of the acetabular component, with impingement of metal-ceramic or metal-metal.”
“Squeaking: usually not painful…occurs when walking or changing position. The prevalence varies according to series—0 to 20% of patients can squeak after a Cr-Cr hip replacement. I recently had my fellow look at all the Cr-Cr series he could find in the English literature; he found 123 squeaking Cr-Cr total hip arthroplasties—120 of those were of a certain acetabular design. The contributing factors are component malposition, poor offset, particulate debris, microfracture, metal transfer, stripe wear—all have been implicated in leading to squeaking.”
“We recently published our in vitro study using a model, an automated hip simulator, and under various conditions looked at squeaking. Under dry conditions we developed models for normal gait, normal loading, stripe wear, stripe wear and extreme load, edge wear and extreme load, metal transfer, microfracture—all squeak quickly and remain constant. If you add lubrication the squeaking disappears; once the lubrication wears off the squeaking returns. In lubricated conditions, the only situation where we found squeaking was with our material/metal transfer model. We took a titanium rod and transferred metal to the femoral head. This is consistent with much of the literature that squeaking is commonly seen with certain designs of Cr-Cr hips.”
“Think about this case as you hear Professor MacDonald criticize Cr-Cr. A 24-year-old female from Ontario with hip dysplasia with no to mild arthritis. She had an uncemented total hip replacement…apparently in Ontario they don’t mind operating on a normal joint space—the couple used was a Cr-Cr (which would be my choice for a 24 year old). And lastly, the surgeon: Steve MacDonald.”
Dr. MacDonald: “You’re right, Rob…in every 12-year-old girl I’m going to do a Cr-Cr. That being said there may be a little bit more that we can present. We’re all saying the same thing: there is no perfect bearing.”
“I think this talk should be entitled, ‘Ceramic-Ceramic: For the Young Active Patient who requires no bending, stair climbing, walking, or sexual activity.’ That list may be fine for orthopedic surgeons from Mayo Clinic, but for most of our patients that is a restrictive list. At our institution we use Cr-Cr; we’ve done 125 cases (young women of childbearing age).”
“The debate was to be about the issue of squeaking, but I’m not sure of the incidence nor of the etiology, and so how do you solve the issue? Very respected authors have an incidence of between less than 1% and all the way to 21%…so what do you quote your patients? For over 30 years there were very few reports of squeaking in the literature, two well documented FDA IDE [investigational device exemptions] clinical trials with no squeaking. Over the last four years we’ve seen an explosion in the reporting of squeaking in North America. Fair enough: if you have an incidence of 1-2% of something, you’re underpowered (in the context of) most IDE trials of 300-400, easy to miss that, but again, no case reports.”
“There is an extensive list of proposed causes for Cr-Cr squeaking; the thing that has changed over the past 20-30 years is the design. There are two generic designs: one where the ceramic insert basically flush mounts, and one that is encased in titanium with a prominent rim. The one with the flush mount, there are several current designs, where the one with the elevated titanium rim, there is one. The squeaking is rare in the flush mount and much more common in the elevated titanium rim. That being said, in North America this was the most common model used, so the ‘N’ is going to be greater and you’re going to see more reported in the literature.”
“But it may be more complicated. In a very interesting article, Rodriguez summarized six articles: all had the same shell, that same ceramic elevated rim, the same ceramic head…the only variable was the stem. Three series of the less than 1% incidence had one type of stem; another three series, an average of about 8-10% squeaking with a different type of stem. The thought was that the different stem allows increased amplification of vibration, secondary to different resonances, which may or may not be the case. Look at the article by Bill Walter, who looked at patient, surgical, implant factors, as well as acoustic and modal analysis, and noted that the natural frequency of titanium components lends itself to clinical squeaking.”
“In conclusion, are there any big surprises? No. We do need to avoid minimizing complications, and we need to avoid implicating a class of devices, whether it’s poly, metal, or ceramic, with one complication. We need to understand the drivers of it so we can fix it.”
Moderator Duncan: “Rob?
Dr. Trousdale: “We both feel the benefits of the wear couple outweigh the risks. It appears to be design related. One comment on the series that looked at different stems with different prevalence rates of squeaking. There may be a handful of factors there: they didn’t control for component position, so they were the same cups for different stems. Maybe one stem resonates different than the other; the stems are made of different metals, so maybe metal or material transfer from the junction of the head onto the stem transfers easier on one stem versus the other. I don’t know that, but certainly the common denominator in the English literature is a titanium rim backed acetabular component, which I have stopped using.”
Moderator Duncan: “Steve, a patient with a squeaking hip comes to you, which is an amusement at the cocktail parties she goes to. She asks, ‘What does the future hold? I’ve read this paper from the Mayo Clinic that says I’ve got a stripe on my hip and there is something wrong with the lubrication. Does that mean it’s going to fail? I’m going to get osteolysis?’ What does a squeaking hip mean if someone is prepared to live with it?”
Dr. MacDonald: “I think most people with a squeaking ceramic hip are willing to live with it. We don’t know the natural history of our current generation of ceramic on ceramics that squeak. We have older literature…I don’t think it is associated with any particular driver for osteolysis with that as a complication. But it depends on the etiology. For example, if you have a significant component malposition with impingement, a driver to perhaps having a metal-metal impingement with that stem on the back of the elevated titanium rim then that would be associated with lysis.”
Moderator Duncan: “Do you agree, Rob?”
Dr. Trousdale: “Yes. We don’t know the natural history, but we can tell patients that we don’t know what the future holds for sure, but there’s something mechanically wrong with a hip that is squeaking. If someone is young, in the face of severe malposition and we’ve got impingement, before runaway wear happens and multiple ceramic particles get in that bearing surface I would probably revise that patient.”
Moderator Duncan: “Neither of you stated why you’re uncomfortable using highly crosslinked polyethylene, for instance in the late teens, early twenties. What is in the literature to warn us that highly crosslinked polyethylene would be inappropriate in that group today? This is the 10th anniversary of that material and I’m not seeing any papers that are decrying the performance of crosslinked polyethylene. Rob?”
Dr. Trousdale: “I would favor ceramic-ceramic because the wear bearing surface is better in the lab than highly crosslinked polyethylene.”
Dr. MacDonald: “Great question. Say it’s a young woman we’re talking about…I tell her, ‘We have a new polyethylene, but it’s almost at ten years, with no significant reports of wear lysis. And we have a ceramic-ceramic bearing with lower wear and a theoretical longer longevity—because we really don’t know a 20 or 30 year track record with a poly. The one ‘con’ is a less than 1% incidence of squeaking and in that scenario—if a patient has an undue concern with ceramic, I go right to a metal-poly. We have ten-year data (with metal on highly crosslinked poly); we don’t have 20-year data, but our ten-year data looks a lot different than our previous generations of ten-year data in young patients.”
Moderator Duncan: “Closing comments…you’re opinion: ceramic on metal?”
Dr. Trousdale: “I’ve still got concerns with that bearing surface…the metal ion issues, the potential ALVAL [Aseptic Lymphocytic Vasculitis Associated Lesions] issues, and potential noise issues. It wears well in the lab, but the long term, mid term follow-up remains unknown.”
Dr. MacDonald: “Not approved in North America; used in about 40 countries worldwide. We only have very early data…two publications, both of which show equivalent clinical results…ion trends lower, so we don’t know.”
Moderator Duncan: “Interesting, but don’t hold your breath. Thank you both.”
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