Metal-Metal Articulation: Maloney v. Schmalzried (Orthopedics This Week)
“Like taking candy from a baby,” says Bill Maloney. “There is very little/zero indication for metal-metal articulations.” “But the benefits of metal-metal are well known: high stability because of the large diameter, low wear potential, and they are unbreakable,” states Tom Schmalzried.
This week’s Orthopaedic Crossfire® debate is “Metal-Metal Articulation: Cease and Desist.” For the proposition was William J. Maloney III, M.D. from Stanford Hospital and Clinics in Stanford, California. Against the proposition was Thomas P. Schmalzried, M.D. of The Joint Replacement Institute in Los Angeles, California. Moderating was Thomas S. Thornhill, M.D. from Harvard Medical School.
Dr. Maloney: “This is like taking candy from a baby. In the early to mid ‘90s we had terrible problems with osteolysis, especially in young, active patients with conventional polyethylene with cementless devices. Then new bearings were introduced: highly crosslinked polyethylene, metal-on-metal and ceramic-on-ceramic. The hypothesis was that if you reduce the wear volume it would mean a reduction in the incidence of osteolysis and the incidence of aseptic loosening.”
“Ten years later: femoral component fixation is solved, and we’re seeing unique complications with metal-metal articulations. There is a spectrum of adverse tissue reactions that have been described as a foreign body reaction; there’s a toxicity reaction with cell necrosis, there’s potentially a hypersensitivity reaction, and then there’s ALVAL [aseptic lymphocytic vasculitis associated lesion].”
“In a paper from Oxford they showed this so-called pseudotumor formation with metal-metal resurfacings, and 1% of their patients developed symptomatic pseudotumors by five years…all females. The tumors were associated with extensive soft tissue necrosis, lower Oxford hip scores, and higher serum cobalt levels. One paper from Adolph Lombardi’s group showed 3% cup failure, 11 local adverse tissue reactions, and 27 loose cups. This is unique to the large metal-metal total hip replacement.”
“In one case from our institution there was a 65-year-old woman who presented with gross swelling of her right lower extremity. She has bilateral metal-metal total hip replacements. On the right the socket is abducted—not an optimal position—and the right was the affected side. On an MRI scan we could see the so-called pseudotumor tracking up the iliac wing, and the gross swelling of the leg.”
“Another case: an implant that’s supposedly had a good track record—metal-on-metal and a relatively small bearing surface. Several years ago looked at this in culture, and examined the difference between cobalt, chromium, titanium, and titanium aluminum. We did serial dilutions and exposed cells to these materials in culture; we found a fundamental difference between titanium and cobalt. Titanium was inflammatory and led to a typical inflammatory foreign body type reaction, with secretion of bone resorbing cytokines; at the same particle concentration cobalt killed the cells.”
“Remember that there’s a higher rate of cobalt ions. Cobalt is relatively soluble, whereas titanium and the other metals are relatively insoluble. When you look at revisions for metal-metal failures, the outcome is poor in general as compared to revision for femoral neck fracture resurfacing. And with revision for soft tissue reaction the outcome is poor. If you look at data from the Australian registry—28 mm heads or smaller—and adjusted for age and gender, you can see the worse outcomes at the five-year point were metal-metal. The best were metal-polyethylene. If you look at large heads, same outcome…worse for metal-metal and best for metal-highly crosslinked polyethylene.
“If you examine the English registry and examine implant survivorship in their hands, cemented total hip replacements do the best, followed by cementless and hybrid hip replacements; the worse were hip resurfacings and large head metal-metal total hip replacements. So in 2011 there is very little/zero indication for metal-metal articulations.”
Dr. Schmalzried: “The benefits of metal-metal are well known: high stability because of the large diameter, low wear potential, and they are unbreakable. The thin monoblock sockets allow for resurfacing with acetabular bone conservation. One of the risks is a higher loosening rate…and loosening is more of an issue than adverse local tissue reaction. Another is that there is position sensitivity. In addition, metal particles, ions, corrosion products, adverse local tissue reactions are a problem as well.”
“Hip dislocation is the number one reason for revision in the Medicare data set. A typical issue was having a 28 mm poly case that was dislocated…that is the kind of experience that drove the market in the direction of larger heads. And the largest head options were metal-metal, and the very largest options were monoblock sockets against very large heads.”
“You can end up with an exposed mass of metal in the front of the hip joint, and a large head-neck gap because of the drop off between the edge of the head and the neck. This has been associated with groin pain, psoas symptoms, but is it due to soft tissue inflammation or the stiffness of the cobalt chrome socket? There also seems to be an increased incidence of modular taper corrosion in association with large diameter metal-metal bearings.”
“The Australian data indicates that loosening is the problem, as opposed to adverse local tissue reaction. Don’t think that I’m not concerned about the latter, but loosening is associated with the larger heads and the monoblock sockets. In this registry the cause of revision is 0.5% metal sensitivity.”
“Monoblock sockets allow very large heads, but they can be more difficult to insert. Also, there’s no opportunity for adjuvant fixation such as screws, and they may not bone-ingrow.”
“In the 2010 Australian National Joint Registry they had greater than 96% five-year survival of modular metal-metal constructs. Large is forgiving…for stability. But it is no more forgiving of position. There are growing numbers of studies showing that if you have a metal-metal bearing or any hard-hard for that matter, that has a lateral opening angle of greater than 50-55 degrees then you are likely to have a wear related problem. The same thing has been shown by at least one observer with version outliers—too much anteversion or too little anteversion.”
“The concept of the bearing coverage area relates to both the acetabular and femoral positions; it’s a fundamental parameter, and it’s position and component design. Also, component position recognition is a current issue.”
“Our own investigations have shown the common denominator to be the path mechanics of that joint. Low lateral opening angle or high combined anteversion leads to edge loading, edge wear and aberrant wear mechanism and an adverse local tissue reaction. Crosslinked polyethylene is now available in larger diameters; that’s going to lower the dislocation risk. The downsides: fracture risk because the liners are thinner, higher volumetric wear (will that matter over time), and there is the potential for in vivo oxidation.”
“Perhaps antioxidant polyethylene is the way to go—time will tell. We need longer term data on crosslinked polyethylene with equivalent head size and diameter. Delta-delta has been approved for 28 mm, but that’s not going to help us much with the range of motion and stability issue.”
“The majority of my metal-metal experience is with hip resurfacing. The patients I care for are unaccepting of disability and they want no restrictions. The requirements include substrate strength, range of motion and stability, low wear and revisability. There are learning issues, but Treacy’s experience (2010) shows 98% 10-year survival for males and 96% 10-year aseptic survival for all comers. In the 2010 Australian registry they had greater than 96% survival in males younger than 65 with osteoarthritis, and greater than 96% survival when you have a large patient.”
“In my opinion the benefits still outweigh the risks in appropriate patients.”
Moderator Thornhill: “Thirty second rebuttal, Bill?”
Dr. Maloney: “I focus on the adverse tissue reactions because once you get one you may not recover. Tom has said that not only do we have problems with adverse tissue reactions, we have a very high failure rate as it relates to socket fixation…and it’s technically more difficult to put in. As it relates to activity level, Tom, your own data suggests that it’s a patient selection issue with resurfacing…that you have patients who have come in who are of that mindset who are not candidates for resurfacing and had total hip replacements and have had high activity levels. So it’s not accurate to attribute the activity level to the implant.”
Dr. Schmalzried: “I agree. I think we’ve come to a point where we are very risk averse, but my experience has been overwhelmingly favorable with regard to metal-metal resurfacing.”
Moderator Thornhill: “Tom, should we do metal-metal in a non-resurfacing situation?”
Dr. Schmalzried: “In a total hip, probably not.”
Moderator Thornhill: “Bill, what’s the best way to diagnose this?”
Dr. Maloney: “Ultrasound or CT, depending on your institution. I think hip aspiration plays a valuable role; if you examine the fluid, with an adverse tissue reaction it usually has a very low white cell count…and if there is an infection it will have a high white cell count.”
Moderator Thornhill: “How about measuring serum cobalt chromium levels?”
Dr. Maloney: “We’re doing this on all patients who come in with a painful metal-metal; what these measurements mean is yet to be determined. I think there’s an association with higher metal ion levels and adverse tissue reaction, but it’s not a one-to-one correlation.”
Moderator Thornhill: “Who do you measure levels in, Tom?”
Dr. Schmalzried: “On anybody that wants to be checked, and anybody who’s not perfect. You take someone who’s having some symptoms or a component position issue, the likelihood that patient will have elevated ions is increased. And if there’s a concern, then do an imaging study. The workup is cookbook.”
Moderator Thornhill: “Let’s say you have a patient who is asymptomatic, but wants the levels done…and they’re elevated.”
Dr. Schmalzried: “I would get a MARS MRI scan. I am looking to see if there is a local tissue reaction.”
Moderator Thornhill: “Bill, same thing?”
Dr. Maloney: “Yes.”
Moderator Thornhill: “Are we dealing with a local toxicity or type 4 hypersensitivity, or are they both in different clinical situations?”
Dr. Schmalzried: “There is a spectrum of soft tissue reactions. In some cases it looks like a foreign body reaction; with the ions I think there’s a toxicity and the lymphocytic infiltrate may be related to some type of hypersensitivity reaction.”
Moderator Thornhill: “Tom, what is a large head? Above 36?”
Dr. Schmalzried: “Thirty-six has been the cutoff point that registries have used. But that mixes modular systems with monoblock systems and that muddies the waters.”
Moderator Thornhill: “Bill, the court of public opinion…how should we, as academic leaders of orthopedics, respond to that?”
Dr. Maloney: “It’s hard to respond because they have the pulpit. Tom?”
Dr. Schmalzried: “There are societal forces that are driving perception. If you have a patient with a cobalt chrome total knee replacement and you measure their cobalt and chromium ions, you’re going to have 2-3 parts per billion in that patient. It’s not just an issue of metal-metal bearings, so the issue of exposure (dose, cause, and effect) becomes very important.”
Moderator Thornhill: “I think we have a consensus that we wouldn’t advocate using metal-metal in a total hip, but limit it to those people who require resurfacing. Thank you.”