Dr. Bert J. Thomas, orthopaedic surgeon and chief of Joint Replacement Service at UCLA Medical Center, recently phoned in from California to discuss hip replacement surgery.
UCLA is ranked in the top 1 percent of all hospitals in the country by U.S. News & World Report. Its physicians are some of the best in the country, and it was one of the first hospitals in the country to perform hip replacements. As a world-class research hospital, UCLA is committed to advancing the science and technology of joint replacement.
Dr. Thomas is an award-wining surgeon with 30 years of experience in joint replacement surgery and is head of UCLA’s joint replacement program. One of his specialties is revising failed joint replacements, and he has helped more than 1,000 patients who have come from all over the world to seek his expertise in this area. The joint replacement program at UCLA often tackles some of the most complex surgeries, and a good portion of its patients are referred from other hospitals.
In the interview, Dr. Thomas graciously shares his vast knowledge about hip replacements. He explained the history of hip implant devices, particularly the science behind metal-on-metal implants and complications that can occur with these devices.
He also provides a fascinating look into the future of joint replacement surgery.
Hip replacement surgery improves lives; of this there is no doubt. The procedure has come a long way in the last few decades, and new technology has made implants more durable and safer.
“I have had patients (who had) been in wheelchairs for years,” Dr. Thomas said. “When you do the hip replacement, it’s a miracle for them. The pain is gone, and within a relatively short amount of time, they are up walking. And soon after that, they are back to being regular members of society.”
Back when hip replacement surgery was a younger technology, in the ’60s and ’70s, hips were replaced to take care of pain. Because implants did not last that long, younger patients were not candidates for the surgery. The functionality of the hip was not as good, and these cemented implants had a life span of about 10 years.
Now, the current implants can last up to 30 years and are used in patients much younger than 65.
“We’ve raised the bar substantially,” Dr. Thomas said. “Number one, we’ve allowed the procedure to go into younger and younger patients. And two, these materials that we are using now are so strong that we pretty much don’t restrict the activities.”
However, as with any surgical procedure, complications can still occur. Depending on the implant design, the prostheses can fail early – requiring additional hip surgeries called revision surgeries.
When a patient undergoes hip replacement surgery, this is called primary surgery or “index” surgery. A number of complications after primary hip surgery may require additional hip surgeries, which are known as revision surgeries.
Dr. Thomas explains that these surgeries are often more complex than primary surgery and require surgeons who have extensive experience and vast implant knowledge.
An implant may need to be revised (replaced) immediately if the patient develops an infection or dislocates the joint. An implant also must be replaced if it wears out, breaks or fails.
Most hips simply wear out after many years because of use. But some implants have above-average failure rates.
Metal-on-metal implants were designed to be more durable, but some of these implants began to fail early.
One implant, the DePuy ASR, reportedly has a failure rate of nearly 40 percent within five years. This means that almost half of patients require revision surgery shortly after primary surgery. The DePuy ASR was recalled in 2010.
Many experts – plus the U.S. Food and Drug Administration (FDA) – postulate that the rubbing together of the metal parts releases metal debris or ions into the tissues and blood, which can cause early implant failure and pain.
“In a small percentage of cases, if a metal surface rubs against another metal surface, it will release tiny metal ions, Dr. Thomas said. “For most patients, the ions will go into the blood stream and be excreted by your kidney.”
If you are one of the unlucky people who has a reaction to these particles, however, the complications can range from discolored, inflamed tissues to severe pain, swelling and loosening of the implant. An adverse reaction to the metal particles is called metallosis, which is a type of metal poisoning.
So, what causes some implants to release more ions or fail sooner than others?
“It turns out, the devil is in the details,” Dr. Thomas said. These details include design elements such as the locking mechanism, size of the implant and type of metal used.
Dr. Thomas said patients need to watch out for symptoms such as pain, swelling and noise in the hip, as these are often indicators that a metal-on-metal hip may need to be checked.
In order to check for tissue damage or excess metal in the blood, X-rays are usually a good indicator, since metal particles will show up in the films. But doctors also use blood tests and fluid tests.
Even then, no two patients have the same reaction to the particles. This makes treatment difficult. In most cases, the implant must be removed and replaced with a non-metal-on-metal alternative, such as a hip with ceramic or plastic parts in addition to metal.
At UCLA, the research continues into advancing joint replacement technology.
Dr. Thomas shared one exciting development. UCLA currently holds the patent on a polyethylene plastic that is incredibly durable and resistant to wear, and in simulation tests, no wear was registered even after the equivalent of 20 years. This plastic would be used with ceramic parts, eliminating the problem of metal ions.
Hi! Welcome to Drugwatch Radio. This is your host, Michelle Llamas. Today you are going to be listening to a special Podcast featuring Dr. Bert Thomas, orthopedic surgeon at UCLA Medical Center and head of the Joint Replacement program at UCLA Medical Center. In this episode, Dr. Thomas talks about different types of hip implants and the complications from metal on metal implants. He joins us today via telephone. If you have any questions about anything you hear on this Podcast, you can feel free to email us at firstname.lastname@example.org, or tweet us @drugwatchradio.
Welcome to Drug Watch Radio, and today I'm very fortunate to have with us, Dr. Bert Thomas, from UCLA Medical Center, Santa Monica. He is the head of the Joint Replacement Program over there. UCLA has a really top notch program. They are listed on the honor role for orthopedic surgery. Several doctors in the program are ranked best doctors in America. They are also a research hospital with world class, cutting-edge technology and some of the best facilities in the world. So, we’re very fortunate to have Dr. Thomas with us. Thank you so much for being here with us, Dr. Thomas.
Good morning, Michelle.
Morning. We are talking this morning on the phone. He's very graciously agreed to be our guest today. We are talking about hip replacement surgery and some of the issues that people might suffer from them, and what are some of the issues people should look out for. Hip replacement surgery has been one of the most significant advances in modern medicine, some would argue. It's helped countless people regain mobility, quality of life, and by 2013, we've heard that there will be about 600,000 hip replacement surgeries. It’s definitely come a long way. Dr. Thomas, can you tell us a little bit about your program there at UCLA?
Well, basically the Orthopedic Disease Department handles all orthopedic problems with your muscles, and your joints, and your tendons, and your bones. Starting from pediatrics, the problems children have, all the way through old age. Spine problems, tumors, arthritis, sports injuries, we pretty much cover the whole gamut. We're very proud of our Joint Replacement Program. We were one of the first programs to be able to do hip replacements in the United States. We continue to lead with advancing the science and taking the best care of our patients that we can.
You have the ability to be attached to one of the really awesome research facilities, so like you said, advancing the science is probably something you are doing every day at UCLA?
That's part of our job
Awesome. We talked about how great and how helpful these surgeries can be for some people that have had some debilitating injuries, or just suffering from osteoarthritis pain or something like that, regaining their mobility. There are also some complications that could happen, just like any other surgery, and they could require second surgeries called revision surgeries. Could you tell us the differences between revision surgery and primary hip surgery?
Well, quite simply, a primary hip surgery is the first surgery you have on your hip. We sometimes call it the index surgery to differentiate it from any subsequent surgeries you may have. Things can go wrong early, or things can go wrong later. Early things most frequent among these could be if you developed an infection after your surgery or if your hip dislocated. These would require a subsequent surgery relatively soon. The other problem, even if your hip surgery went well and did well for many years, the implant may eventually wear out. In those cases, if a part wears out, you would need to go into a second surgery to replace the worn out or broken part. That would be called a revision surgery, because you are revising the first surgery by taking out the first implant and putting in a new one.
OK, I see, typically though, people can expect an implant to last a decent amount of time if they are functioning properly, and the design is good? If it fits in the patient properly, this is not something the patient should worry about right away?
No, the parts should not wear out right away, certainly. When first surgeries were done in 1969-1970, back then, they were cementing in place, and they had plastic sockets. The general feeling was they would last about 10 years before having to be replaced. With our current technology, they shouldn’t wear out for at least two to three times longer. So they should last 20 to 30 years.
Oh, wow. So hip implants have come a long way then as far as durability and how long it is until the next revision surgery. Which is kind of good because, isn’t it true that now, more, younger patients are getting hip replacement surgeries? It’s no longer something you would expect people in your 70s or 80s, but we are talking about people in their 40s and 50s?
You’re exactly right, Michelle, historically this type of surgery was restricted to people 65 years and over because not only would the parts wear out or loosen, but the metal stems would actually break because [they weren’t] strong enough. That was a real problem in the early to the mid-70s. The stems were actually breaking if you put the hip replacement in someone who was active. Meaning someone who was trying to do heavy lifting or climbing. Things like that put an awful amount of stress on the hip. When you just walk across the room, your hip receives three times your body weight of pressure on it. For the stems, these are bending and twisting stresses that wouldn’t break immediately, but it would fatigue and eventually, if there were any defects in the metal, it would break right through. With current technology, the metal is much, much stronger. The metal is a so-called space age super alloy.
That’s good to know.
Previously they were cast, stainless-steel prostheses, which sounds strong but doesn’t hold up in the body.
Excellent, so what you are saying is that younger people who are getting these hip replacement surgeries do not necessarily have to stop doing some of the things they used to do prior to the surgery?
Actually, we’ve raised the bar substantially, again. Number one, we’ve allowed the operation to go into younger and younger patients. And two, these materials we are actually using now are so strong that we pretty much don’t restrict the activity.
Wow. That is a big deal.
Yes, so we have patients that are literally doing everything, participating in sports, running, and even extreme things like running marathons, competing in bicycle races, and playing tennis, playing volleyball.
Stuff that before, used to be a no-no.
Basically, the operation was originally designed to specifically relieve the pain because the pain was just awful. Even just sitting in a rocking chair and rocking would be uncomfortable.
Just like you said, though, the hip takes a lot of stress, so even simple movements would probably be a little bit of a problem.
Absolutely. Rolling over in bed wakes people up, who have bad arthritis. It literally puts people in wheelchairs. I’ve had patients who’ve been in wheelchairs literally for years, and when you do the hip replacements, it’s a miracle for them. Their pain is gone, and within a relatively short time, they are up and walking. Pretty soon after that, they are back as regular members of society, and at their jobs again.
Oh, yeah. I mean, quality of life is definitely one of the biggest things that this has helped people do. For sure.
We are going to take a quick break and we'll be back with more Drug Watch Radio.
Welcome back to Drugwatch Radio. I'm your host, Michelle Llamas. We were talking about the hip replacements and the materials and how they have been constructed and designed. One of the things that we have seen lately is that the FDA released a safety communication about the specific designs of implants, metal on metal implants to be precise. I believe these are the one's made up of cobalt and chromium where the two pieces, usually the hip and the ball, or the stem, and some other modular pieces might be touching each other, when people move, it's releasing these metal ions. Can you explain a little more about that, because it sounds pretty space aged to someone who probably doesn't know anything. I mean, what are these ions in it? How can they cause problems in patients?
OK, well, first of all, the original plastic liners were high-density polyethylene, and with every step you took - the metal head rubbing up against the plastic would generate polyethylene debris. Eventually, the plastic would actually wear through. In an attempt to solve that problem, surgeons and engineers looked for other materials. One of the other materials they looked at was metal. There were advantages to metal, it wouldn't wear and tear through, metal doesn't break.
Yeah, much stronger.
It would actually bend rather than breaking. There was a history with metal against metal. In a small percentage of the cases, while the metal doesn't break and it won't wear through, but you're exactly right, if the metal rubs another metal surface, it will release tiny metal ions. For most patients the ions will go into your bloodstream and be excreted by your kidney. So for most people don't cause a problem. For some people, and we don't fully understand why, people's reaction to these ions do vary. Certainly someone who has problems with their kidneys, can't excrete the excess ions. We have never recommended metal on metal for people with kidney failure.
OK so that's important right there, the kidney factor.
Yes, the kidneys have to work. There is a possibility that the kidneys are working, you put in the hip implant, and then the kidney stops. Then there's the problem of the build-up of ions for your body to handle. There are other reactions, some people can wear jewelry, and other people can't. So people who can't wear jewelry get a reaction to metal touching their skin. We think something like that happens inside the body as well, it's called hypersensitivity reaction. That will generate pain and inflammation and that is another way that the metal can cause problems. The metal-on-metal seemed like such a good idea. Doesn't wear out, didn't break. A number of companies felt, “OK, well, we need to have this in our products.”
Yeah, so everyone started doing it.
All of a sudden, instead of one or two companies, we have a dozen companies making metal on metal, and it turns out there are many things that are very subtle, from an engineering standpoint, and it turns out that the devil is in the details.
What metallurgy you use
What tolerances you use
How you make your design
The locking mechanisms
Did you have any sharp edges showing anywhere? All these things can make a huge difference in the performance of the implant.
So there's a lot of details, lots of details.
Basically, there were a few designs that actually performed way, way worse than other designs.
Oh, yeah, when you say that, I already know which one now has been, really, sort of, [laughs], looked at and in need of –
Being looked at for bad function. Those designs basically had problems far higher that what was expected, and eventually – like I've said – any design is like someone's child, whoever's making it, doesn't want to acknowledge. Basically those designs have been removed from the market. Unfortunately, they have been put into a large number of patients, and those patients need to be followed.
So, now with your experience with that, have you had patients come to you there in the department and program, that have had to have revision surgery from some of these more problematic implants? Like I can think of one. That is DePuy ASR, for one, that of course it's not on the market anymore now, but some of the studies were saying up to 40 percent failure rate for these things. So, did you have patients come in with these things that you'd have to help them out with failed implants?
Well, UCLA is called a referral center, that means that if you have your index or primary surgery done at a community hospital, which is where the majority of these surgeries are done – at a community hospital – and the majority of them do well. 95 percent of them do well, but if you are of the five percent who has a failure in these community settings, the surgeon may not have enough experience with revision surgery. So, he will send it to a referral hospital. That's what we are, a referral center, or a so-called tertiary medical center. Actually, almost half of my practice is cases like that, referred for revision.
Oh, wow. So it's like you were saying, other surgeons may not have the experience that you all do there at UCLA. It's kind of the really complicated.
It's kind of our claim to fame, taking the complicated cases and making them turn out right. So, yes, we've revised some of the metal on metal implants that have failed. It's an interesting and somewhat confusing group of patients, because almost no two of them will present exactly the same. It could be anything from a very minimal reaction from the soft tissue, to huge collections of fluid and damage to the surrounding tendons, and muscles, and bones. We are not exactly sure as to why there is such a huge difference in the reaction because presumably it is the same process. That's one of the things we are studying and trying to sort out. I think part of it – what I was talking about earlier, which is different – patients have immune systems that respond differently to these sorts of stimuli. Some people react like how some people have hay fever when there's pollen in the air. They literally can't breathe. Their eyes water up, and their nose and lungs get congested. They just can't stand to be outside. Other people are like, “Oh, isn't this lovely?” [Laughs].
Oh, yeah. No, for sure, they don't need any Claritin or anything like that.
Some patients react really, really extremely to the metal ions.
There's really no way of telling beforehand, right? Like, some patients could be completely healthy, fit, they don't show any risk factors for having a reaction. But, yet, after the fact –
Well, if someone knows that they are allergic to metal, like I said, the people who cannot wear jewelry, we'll sometimes have our immunologist take a look at them. The funny thing is, at least traditionally, their tests were that they take various metals and tape them onto your skin. If you get a red mark underneath the metal sample, each metal you're having a reaction to –
You see, I am one of those people who can't wear the jewelry.
You would've been someone that we would say, gee, we should consider using a material other than metal to –
Yeah, like ceramic or plastic, I think, right? The other choices? All right, well we were talking about the other complications, we're going to take a quick break here and then we're going be back with more Drugwatch Radio and we're going talk about metallosis next.
Time for a break.
Welcome back to Drugwatch Radio. If you are just joining us, we are speaking with Dr. Bert Thomas of the Joint Replacement Program at UCLA Medical Hospital in Santa Monica. I'm your host, Michelle Llamas.
One of the strangest complications that we’ve heard about, and we’ve seen in some literature is metallosis, which is essentially a metal poisoning. Can you explain a little bit about it for some people who might not know what we’re talking about when they hear metallosis mentioned?
The first cases of metallosis that we saw were actually in the 1980s. We had metal backed, polyethylene liners in the socket of the hip. The idea was having the metal backing support the polyethylene and stop the plastic from deforming. Because the polyethylene wasn’t quite the standard that we use today, it would sometimes wear through. The metal head rubbed up against the metal back socket and generated a huge amount of metal debris. In fact, the metal backing on the socket was Titanium which was a strong metal, but soft in comparison to a cobalt chrome, usually the heads were a cobalt chrome. So, if a cobalt head rubs directly against a Titanium backing, it rubs right through the titanium. If you go into the case, you’ll see the cobalt chrome head is still shiny and new. The Titanium shell will have run a hole right through it and the whole joint will have turned black.
And the black is the tissue reaction, right?
Well, I think the metal is just looking black. There is a tissue reaction, and once again it varies from patient to patient. In the 1980’s we didn’t understand all these issues, we just saw the metal had turned black, and black just didn’t look good.
Yeah, you're like, “That is not a healthy color.” Then the joint fluid contained bits of the metal as well?
Exactly, and in fact, that was one of the ways you could diagnose with regular X-rays. Because, if you have a fluid sac around the hip, that has metal debris that shows up on an X-ray. Metal, in fact, is the only thing that shows up on an x-ray. That’s why when you shoot and X-ray the only thing that shows up is your bones. The reason your bones show up is because they have metal in them.
If someone had an X-ray with this showing up, then it was definitely a problem. You’d be like, oh, ok, I think we probably need to go take a look at this.
Absolutely. And once again, you had a hint if you looked at the x-ray and you saw little white dots in the fluid, you knew when you opened it up, it was going to be black and full of metal debris.
Now obviously this causes a lot of pain, and I think – is joint failure possible from it? If someone has severe metallosis?
With the traditional metallosis you couldn’t get that unless the plastic was worn completely through. If you had modular plastic liners, that would occasionally dislodge from the metal backing. If the locking mechanism wasn’t strong enough, and then the metal head would be allowed to directly rub against the titanium shell.
And when that happens this is a revision surgery situation, right? It’s when you have to go in and replace the parts?
Yes, there is no way to correct that without a surgery.
You mentioned the problems with the older implants, now the newer ones. Obviously they’ve changed some of the designs, they’ve made changes, they’ve improved them, but the metal on metal things is still kind of an issue.
Is this just because when you’ve got metal you’re gonna have some ions released, or, you know, is there a, I think we mentioned a design…?
Any design, in any material, if two surfaces rub against each other then there’s going to be friction and the release of debris. Some small amounts of material will be released with friction. In this case, if you have any metal on metal articulation, metal ions will be released. Depending on the design and metallurgy, and things like the contact area, which is determined by the actual fit of the components together, it can vary on an order of millions. The number of particles released can be increased tenfold easily by just a small change of the design.
We were talking about the design, the size, and the articulation surface…some of the newer ones are supposed to be more stable. I think they were mentioning that dislocation was a big deal, so they decided to design ones that were a little bigger, because they saw the surface – there would be less chance of dislocation with a larger surface. Do you see there would be more chance of debris from a larger surface like that, larger design?
You know I think I read that on an online site, but oddly enough, I believe this is incorrect. That was one of the things that was so enticing about metal on metal, a larger head will actually combat dislocation, and makes it more stable. That’s the good thing. You don’t want to have a dislocation when you just had a brand new hip replacement. The other thing, with a bigger head in plastic, wear of plastic was higher, smaller heads were better in plastic articulation. If you went metal on metal, the wear was actually less.
That was non-intuitive, but the engineers figured out why that was. It turns out, that the joint fluid with a bigger head will get more fluid to stick to it, and that actually creates a fluid boundary. The fluid boundary is better in bigger heads than in smaller heads.
I see, so the less complications come from when there is optimal fluid lubricating the joint?
Well, no, it’s less wear, and less dislocation. It’s a different algorithm if you have metal against plastic, then if you have metal against metal. From the surgeons’ point of view, wow, sounds like a win-win. I have less dislocations and less wear, so why not use the biggest head I can.
We may have gotten a little carried away with that, but you can see how attractive, but it’s not true that you get increased wear with a bigger head.
Oh, OK, but I mean what about the metal ions, because I think the ions can be released even without significant wear?
Well, no, with metal on metal heads didn’t wear out, and they didn’t break, they did get ion levels. If you have a good fluid layer you’ll get less ions. These are the things we are still trying to figure out. Why do some people get large bumps in their ion levels and others don’t? Why do some people not get any reaction to larger ion reactions, where others do? You get into the part of it due to the engineering problem, was it the problem with the fluid layer that led to increased erosion of the metal, and increased ion creation? And… what about these people that are really having problems and their ion levels aren’t that high, are they just especially sensitive? It’s some interplay that at least currently seems complex, but once we have it all figured out, people will say, oh yeah, that was obvious.
You mentioned testing earlier for metallosis or, you know, a high level of metal in the blood? You said X-rays are a good way to do this?
We would always start with an x-ray. Basically, you start with the history, you ask what are you noticing about your hip? Sometimes they give you a big hint when they say, My hip was squeaking.
Oh, OK, so a noisy hip is not a good thing?
Noisy hip, it certainly worries us. Some of the engineers think noise isn’t a big worry, but nonetheless, it worries the patient, and it worries me. In my mind, we shouldn’t be able to hear hips.
Well, yeah, it’s embarrassing, in my mind, but yeah, continue?
On the patient’s history, are they feeling some grinding? Are they hearing any grinding? Do they feel pain? Those are the key indicators and the most important things right off the bat. That’s the things they can just tell you. The thing that the patient will notice is, they’ll notice swelling in their hip, and they know it doesn’t feel right. Pain and swelling are the number one clinical indications. So, once we have those, we would definitely recommend the first test to be an X-ray.
What do you see now in the future of joint replacement? We’ve talked about how far these designs have come from the 1970’s. Just a matter of a few decades. Where so you think joint replacement is going go?
Oh, yeah, yeah. For me maybe you could find a lot. Go on.
We can get the primordial mesenchymal stromal cells and put that into a special mixture we have come up with, and the daughter cells will actually become cartilage. We actually can do osteo-chondrocyte transplants, grafting these biologic solutions are certainly something we are looking toward as the future so we do not have to put artificial material in the body at all. In the way distant future we are looking into preventing arthritis once we understand what is causing the arthritis.
And that's always good for sure, when you can get something that's actually tissue, natural to the body.
One of the things you’d like to know is what alternative is there to the metal on metal causing the ions. We think this is an excellent alternative. You do not have the concern of the ions, and for 20 to 30 years, you do not have the concern of wear, either.
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