Orthopaedic Crossfire® Tackles Hip Squeaking

This debate was held in December 2008 in an Orthopaedic Crossfire^® session at the 25^th Annual Current Concepts in Joint Replacement™ (CCJR) Winter meeting in Orlando, Florida. The CCJR meetings are organized by A. Seth Greenwald, D.Phil. (Oxon) and the Orthopaedic Crossfire^® debates serve to frame contemporary controversies and contribute information in a uniquely compelling format within the very popular CCJR meetings (www.CCJR.com).

Dr. MacDonald:  (A video starts which shows a mock physician’s office—Dr. Murphy’s office—where a patient calls with a ridiculously squeaky hip.) “I’m sorry, Mrs. Jones. I don’t hear anything, ” says the assistant. “Dr. Murphy? He’s in audiology getting fitted with some special earplugs.”

“There is no perfect bearing surface. Here is a 24-year-old woman who had recovered from acute lymphocytic lymphoma and had bilateral hip avascular necrosis. This is the ideal indication for ceramic-on-ceramic (and I did this surgery for her). The biggest challenge on the squeaking is not being sure of the incidence and not understanding the etiology…and if we don’t understand the etiology then it’s hard to solve. We have several series from well respected authors; one shows less than 1% incidence and up to 21%. What percentage do you quote your patients?”

“I took an informal survey at a closed Hip Society meeting…almost everyone indicated that they had seen squeaking in ceramic-on-ceramic. This isn’t a new bearing…why all of a sudden are we getting these increased incidents of squeaking? We have two well-documented FDA IDE [investigational device exemption] studies with no squeaking. One explanation is if the incidence of something is only 1 or 2% then you could miss that in an FDA trial or in a few hundred patients because it is underpowered. But it’s not like we had a plethora of case reports either in the 70s, 80s, or 90s about this problem.”

“There are a number of possible causes. There is rim impingement leading to microseparation, with subsequent edge loading and stripe wear. There are papers saying cup position matters and others saying it doesn’t matter. Maybe it is metal particulate debris getting into the bearing. Is it head size? And there is neck length…again, there are authors saying ‘yes’ and others saying ‘no.’ Or, is it the ceramic material? There’s alumina versus a delta material.”

“What has changed in the last 20 to 30 years? For one thing…design. There are two groups: metal backed and non-metal backed. The latter design has the ceramic acetabular liner and metal shell level, is used in several current designs, and has a successful clinical history. Another more contemporary design has a metal backing on the ceramic acetabular liner and can be designed such that there is a prominent metal rim above the metal shell. This design has not been used historically and is really focused to one device.”

“The level mount one really has very rare squeaking reports and the prominent one does have a high report of squeaking; all series with very high squeakers are in that one design—it’s that simple. Rodriguez recently published a series looking at this exact shell with two different stems; one stem had a less than 1% rate of squeaking with that design. Another stem had a 5-10% [rate] so it’s probably a combination of things such that a different stem allows amplification of the vibration (so you hear squeaking). The design is critical, the way we do it is important…but we should avoid minimizing the complications and we shouldn’t vilify an entire class of devices.”

Dr. Murphy:  “It is true that I don’t hear very well. It’s also true that I’ve always used flush mounted non-metal backed ceramic liners without an elevated rim for the past 11 years. So Steve has made half of the argument for me and I’d like to make the other half. Appropriately designed alumina ceramic-on-ceramic bearings have been used in our institution over 1, 100 times for more than a decade by nine surgeons, none of whom has ever had a patient with a squeak. Our experience is that the loud, clinically reproducible common squeaking is associated with one specific hip implant combination. This is an issue of metal material and design around the bearings—not an issue of the bearings themselves.”

“Overall, alumina ceramic-on-ceramic bearings have had superb outcomes in ten year studies. All of the reported problems seem to have happened after the FDA clearance when any femoral component was able to be used with them—before that they were restricted. The first report of common loud squeaking was made by the Lenox Hill group; this report was 36 years after the first alumina ceramic-on-ceramic hip, ten years after we started the FDA studies, but only three years after people were allowed to do more or less anything they wanted.”

Wagging a finger at his colleague, Dr. Murphy noted, “I’m disappointed with my friends from New York. They implied that the squeaking happened commonly with all ceramics even though they had only used one design…and they didn’t have the scientific justification to make that statement. Also, they never said what implants they were using; and they never mentioned that they had changed the design or the biomaterials. Lastly, they didn’t seek or heed the experience and knowledge of people that had much more experience and knowledge than they had.”

“My team and I examined all of our revisions over five years; we had five revisions for squeaking. All had an elevated metal rim, impingement, and metallosis. This is consistent with Ian Clarke’s finding that was published several years ago. In a recent Mayo Clinic study they deliberately injured the bearings and caused squeaking. With lubrication a worn bearing doesn’t squeak and with lubrication but with metal staining a worn bearing does squeak. We also examined the influence of design and we found two groups, one with flush mounted liners and one with elevated metal rims. We subdivided the latter group into those with stems made of a conventional titanium alloy and those with stems made of a beta titanium alloy. Those with the beta titanium alloy and the elevated metal rim were by far statistically significantly problematic as far as squeaking.”

“We looked back at the Lenox Hill study and sure enough they used a recessed liner and a beta titanium alloy. Another recent study focused on neck length and found shorter necks to be associated with squeaking. What did they use? A recessed liner and a different stem with the same beta titanium alloy. A recent study by Dr. Restrepo of the Rothman Institute focused on cup position; they used more than one stem but they didn’t say how many of which. I checked with the authors and found that four retrievals had squeaking…and guess what…all had a recessed liner and a stem made of beta titanium alloy.”

“This has become like the fable of the blind men and the elephant. The one touching the tusk thinks it’s a spear…this is like the people who focus on cup or implant position. The blind man who touches the trunk thinks it’s a snake…that is like the group focused on neck length who never mentioned in their article that they were using a different biomaterial. The man who thought the elephant’s ear was a fan…like those focused on acoustics. Acoustics are the effect of squeaking—not the cause. And there was the blind man who felt the elephant’s tail and thought it was a rope…this is the group studying retrievals. They cannot determine what is going on if surgeons don’t tell them what the stems were that the retrievals were attached to. In fact, the big elephant is this beta titanium alloy. Occasional squeaking is multifactorial, but loud, frequent squeaking requiring revision is specifically associated with this biomaterial.”

Moderator Dr. Thornhill:  “Steve, we surgeons are trying not to be the blind man walking behind the elephant and stepping in something warm! Steve, what actually causes the squeaking? Is it a multiplicity of factors?”

Dr. MacDonald: “There is not just one factor. I think you need to have some type of metal debris at the level of the joint. If that is present you may get an increased rate of squeaking. All ceramic-on-ceramic has the potential to squeak.”

Moderator Dr. Thornhill: “Do you agree?”

Dr. Murphy: “You can get a squeak out of any hard bearing…it’s not very common and it’s multifactorial. Metal staining is certainly one of the causes. Conventional titanium stems hardly ever squeak with an elevated liner; we found that in order for a conventional titanium stem associated hip to get a squeak it had to be very malpositioned and have severe metallosis. We found that with a beta titanium you don’t need malpositioning and you only need a little bit of metallosis. When we investigate further I think we’ll find that it’s just small amounts of a particular adverse material that is causing the problem.”

Moderator Dr. Thornhill: “If it’s my hip then it doesn’t matter whether it’s ‘hardly ever!’ Have you had a squeak in a ceramic-on-ceramic bearing?”

Dr. Murphy: “I have had 0.5 incidents where patients say that their hip has squeaked. That could be once a year, it could have happened once and gone away, or it could be once a month…it doesn’t happen to anybody more than once a day. What I want people to understand is there is a difference between people who squeak with every step and having it happen occasionally—like people who complain that their kneecap clicks after a total knee. I don’t have any patients in my practice that have a relevant squeaking issue; these are not people who are having reoperations.”

Moderator Dr. Thornhill: “You could use a different stem so if we take out that combination are you OK with the very low incidence of squeaking?”

Dr. MacDonald: “Three publications have reported incidents of squeaking, all about half of one percent. It’s the same shell design and same elevated rim, but a different stem—so you haven’t eliminated the problem. I don’t consider that exceedingly rare; I think Steve has outlined the major driver but we need to study other things.”

Moderator Dr. Thornhill: “Steve, the beta titanium stem…is the problem that it actually increases titanium wear debris? Is it harmonics?”

Dr. Murphy: “There’s fact and there’s opinion. The fact is that this implant combination is associated with loud squeaking. My opinion is that the metal is getting into the joint, affecting the bearing, and creating the squeaking energy. The fact that the stem is also flexible and thin and amplifies the acoustics is a totally separate issue, which I also think is true.”

Moderator Dr. Thornhill: “So you think it’s the material properties rather than the stem design?”

Dr. Murphy: “I don’t think design of the stem and the shape has anything to do with it.”

Moderator Dr. Thornhill: “Will the delta ceramics make this problem go away?”

Dr. MacDonald: “There is not enough data to support or refute this.”

Moderator Dr. Thornhill: Ten second response?

Dr. Murphy: “Delta will be similar to alumina. If you contaminate the joint and cause a problem then you’ll have a problem; if you design things so that you don’t contaminate the joint then you won’t have a problem.”

Moderator Dr. Thornhill: “Thank you gentleman…nice debate.”

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