“Femoral neck modularity lacks proof of superiority, increases the risk of corrosion and fracture, and makes everyone’s life miserable, ” argues Mike Dunbar. “Let’s not overreact, ” cautions Fares Haddad. “We need to learn from modular implant failures and then move forward and still be able to use modularity for patients in the future.”
This week’s Orthopaedic Crossfire® debate was part of the 31st Annual CCJR – Winter meeting, which took place in Orlando this past December. This week’s topic is “Femoral Neck Modularity in Primary THA: No Role at All.” For the proposition is Michael J. Dunbar, M.D., F.R.C.S.(C), Ph.D. of Dalhousie University in Halifax, Nova Scotia. Fares S. Haddad, M.B., F.R.C.S. from University College Hospital in the UK is in opposition. Moderating is Thomas S. Thornhill, M.D. of Harvard Medical School.
Dr. Dunbar: “The proposed advantages to modularity are reduced impingement and subsequent reduced dislocation. And associated with both of those are better balancing of leg length and offset with improved subsequent function.”
“Regarding impingement, it can be an issue with ceramic liners. You don’t want to load under compression at the edge of a ceramic liner—or tension, I should say. It may cause a fracture. My rebuttal to that is: don’t use ceramic liners. I can’t find anything in the literature saying that they outperform conventional polyethylene—at least in the registries. In terms of impingement related to acetabular/femoral component functioning, this is a technical error. To that I would say, ‘Get your components right and don’t rely on modularity to bail you out.’”
“But let’s say that the modularity allows you to better balance the hip and reduce impingement. Then we would expect to see fewer dislocations. However, data from the 2014 Australian joint replacement registry found that there are more revisions for dislocations in the modular group than in the fixed group. This is partly a function of getting the leg length and offset right. And it’s somewhat a function of whether you’re using a cemented or uncemented stem because with the latter your broach will often follow the anatomy of the femur, and it will bite up in a position you may not like, and you’re forced to use some modularity to get you out of this situation.”
“I think this is a strong argument to use a cemented stem. With this, you have the ability the change the potting distance. I can adjust the leg length by where I put the cement mantle. And by changing the version in terms of ante- or retro-version, I can reduce impingement…and I can do that all with the broach envelope and the cement mantle.”
“There are three major areas of disadvantages to modularity. The first is that we’re introducing a new mechanical interface and subsequently introducing new problems…corrosion and fracture. The second is that the ten-year outcomes are actually worse than fixed neck stems. The third is that they have poor value.”
“Regarding corrosion, there are two recent papers regarding the Rejuvenate and ABG voluntary recall. One is from Bill Walter, Sr.’s group in Australia where they showed that a couple of years after insertion the calcar experienced resorption, and they measured cobalt chromium ions and noticed that cobalt was elevated in these patients. When they retrieved the necks they saw lots of corrosion.”
“In a paper from 2014 (Meftah et al.) on the Rejuvenate the researchers looked at survivorship by cobalt chromium levels and cobalt seemed to be the culprit. The other issue is fracture associated with this new mechanical interface. A paper from 2010 (Grupp et al.) looked at a series of 5, 000 modular necks with a fracture rate of 2.4%. So is it acceptable to say to your patients, ‘One in forty of you are going to break your component in a few years, but I’m going to carry on with this technology.’”
“We reported on our experience with 452 modular necks implanted; we now have close to 30 that have fractures. These are very difficult revisions because the neck is broken…you’ve got nothing to grab onto so you can extract the component. You’re almost always forced to do an extensile osteotomy and go to a big revision component.”
“That creates the horns of a dilemma in two ways. First, you have patients with modular necks who now have elevated cobalt ion levels with pain. They don’t know if they should revise just the neck…will that increase the fracture risk? What material should be used? What will this do to my ion levels? Or, should I have a complete revision with all the risks? Should I have a Mars MRI or an ultrasound? What is the significance of these levels of cobalt? The second horn of a dilemma is because I’ve got this modular neck—potentially a ticking time bomb. Should I revise it or not?”
“There are a slew of case reports showing that these things are breaking. The ten year (plus) outcome data from the Australian registry shows that the modular necks have an adverse outcome with respect to survivorship. And when you look at the reasons for revision you see that it’s primarily because of aseptic loosening.”
“Retroverting the stem is not benign. Putting a different slant or bias on a modular neck can lead to deleterious outcomes because of stress. So if you think about it, if I have a slightly anteverted stem and I load it, I’ve got a force lever arm…but if I retrovert my stem the lever arm increases significantly. So it’s not a free lunch to put a retroverted neck on it.”
“And what do we have for our investment? An increased revision rate and an increased risk of corrosion and fracture. There is no role at all for femoral neck modularity in primary total hip arthroplasty.”
Mr. Haddad: “I have a clear conscience…I have not used primary modular neck stems. But it is important that we understand modularity overall.”
“We have made mistakes, one of the biggest being the uncontrolled adoption of primary modular stems. But we also need to be concerned about overreaction…because when we innovate and get it wrong we need to recognize that and do something about it and retain the ability to innovate.”
“Our patients have increasingly high standards. Modularity—when you get it right—allows us to match the patient’s anatomy with what we ultimately do. There are a variety of types of modularity; some types have a good track record. I think that in revisions, modularity has been a life saver.”
“There is an issue with primary modular necks. Recent data from a large Australian observational study shows higher failure rates. When you see this kind of data it is not gospel…this is population level work. If you drill down you will find that the recalled products—which accounted for less than 1% of all the stems—were 20% of the revisions. So what you’re ‘picking up’ is some bad stems, perhaps some bad surgeons, and not necessarily a group problem.”
“Certain studies show that modular stems with a good track record will deliver what you want. They may not be the answer right now (because of our fears), but drill down into the data and you will find some successes. So beware of throwing the baby out with the bathwater.”
“What we need to do is reevaluate and continue to innovate. To do that we must take the opportunity to understand the taper. We do have frictional interlock, and that has been modified in such a way that we’re getting corrosion and secondary problems. In the settings where we’re not getting corrosion we ARE getting weakness and overload and failures. Mike has also alluded to retroversion, but those Oxford studies involved cemented stems.”
“We have created novel materials in our labs. By changing the coating on modular stems and modular tapers you can significantly reduce corrosion, yet retain the strength.”
“If we get the design right and simplify the technique then it can be useful for some patients—and we’ll certainly continue to use it in revisions.”
Moderator Thornhill: “Fares, you folded like a $3 suitcase. However, you used a brilliant debating technique. You took the strongest argument that you have—in this case it was modularity—and if you pound on THAT then you win the debate. Congratulations…BUT…Are we going to go back and have femoral neck modularity? If so, what’s going to be the innovation that will make it occur?”
Mr. Haddad: “First of all, we will retain modularity elsewhere. We’ll find similar problems elsewhere with modularity, but not as severe. But as of now, modularity of the femoral neck is a problem because of the designs and the way it has been used. As we understand the taper better, as we get the mechanics, the coating, the length, the application better, it’s something that we must not lose sight of. The key thing is that when this all happened, we lost sight of the science that was done 20-30 years ago on the taper, so we got this slightly wrong. But with new materials and new coatings I think going forward there will still be the potential to do this.”
Moderator Thornhill: “Michael, same question.”
Dr. Dunbar: “I don’t use them. As for overreacting, you do tend to do that when you see the carnage. We’re actually sending some patients to counseling for post traumatic stress disorder because of this.”
Moderator Thornhill: “Fares, do you think that modularity of necks may be a surrogate for bad technique?”
Mr. Haddad: “Registries are a surrogate for a number of things, one of which is the adoption of technology before it’s been fully tested. If we get everyone doing the procedure right then there will still be a role for getting the biomechanics right for that patient, which you can’t do for every patient with a cemented stem.”
Moderator Thornhill: “Thank you, gentlemen.”
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