Part I: Decoding Hip Resurfacing with Professor Justin Cobb

In this episode of the AHF Podcast, host Joe Schwab delves into the controversial topic of hip resurfacing with special guest, Professor Justin Cobb, an orthopedic surgeon and chair of orthopedics at Imperial College London. They discuss the history, challenges, and advancements in hip resurfacing, including Professor Cobb's work on the H1 ceramic-on-ceramic hip resurfacing. The conversation covers the intricacies of hip function, long-term outcomes, and future directions in hip arthroplasty. Don't miss out on this insightful discussion!

Transcript

Joseph M. Schwab: 0:24

Hello everybody and welcome to the AHF podcast. I'm your host, Joe Schwab. Few topics in modern hip surgery seem to strike up as much controversy as hip resurfacing. Hip surgeons have been trying to solve this since, at least as far back as the 1920s, with both Marius Nygard Smith Peterson in the US and Ernest Haygrove in the uk, independently reporting on work they had been doing to restore function to arthritic hips, using things like glass and ivory. We've seen mold arthroplasty, cup arthroplasty, double cup arthroplasty, and more using. Materials from acrylic to Teflon to stainless steel and cobalt chrome. With the introduction of more modern metal on metal implants like the Birmingham hip resurfacing or the Conserve Plus, starting in the mid 1990s, hip resurfacing seemed to undergo not only a renaissance, but a considerable spike in popularity, thanks to the purported advantages of bone preservation, anatomic restoration of joint mechanics, and a very stable head to shell ratio. With renewed interest, however, came some renewed scrutiny and with a growing number of designs in the marketplace, it was clear that small design differences were associated with substantially different results. Some designs like the A SR we're seeing 10 year revision rates nearing 50% failures associated with the bearing surface. Materials seem to be a common theme though to be fair. Not all designs exhibited the same problems. So why do we come back to this concept year after year, decade after decade? That's the question for my guest today. Professor Justin Cobb is an orthopedic surgeon and chair of orthopedics at Imperial College London. Not to mention the fact he's been orthopedic surgeon to Queen Elizabeth II, as well as King Charles III. But most important to our discussion today is that he's been working to develop the H1 ceramic on ceramic hip resurfacing. And with that, he hopes to be the surgeon who finally cracks the code for a reliable, reproducible and durable hip resurfacing implant. Professor Cobb, welcome to the AHF podcast.

Justin Cobb: 2:38

You are very kind, delighted to.

Joseph M. Schwab: 2:41

So depending on who you talk to. Hip resurfacing is either potentially the pinnacle of all hip surgery, or it's an unmitigated disaster. Could you put hip resurfacing in a context that seems reasonable for the rest of us?

Justin Cobb: 3:00

Yeah. So. Um, I really got, um, convinced about, um, hip resurfacing when measuring function in our gait lab. And we looked at, I was, I got, it was very keen on resurfacing from, I guess around about 2000. It felt like a more conservative procedure and, but as you pointed out, many surgeons never really got on with it. And one of my friends who's a very good hip surgeon, thought it was the invention of the du and we really had parallel practices, same patient groups. I was resurfacing, he was replacing. And then the, and we, I got a, a grant paid for a, um, a, a instrumented treadmill so we could see how people walked, how they went faster and faster. And we weren't the, I think I can safely say nothing I've done has ever been the first in its field, but we showed what other people have shown, which is that healthy, normal people have got this fantastic continuously variable transmission gearbox in their brain. And when you put your foot on the gas and walk faster and faster, your stride length and your cadence smoothly increase until you start to run. And what we find with healthy adults is that's what happens in their thirties, forties, fifties, sixties, seventies, eighties even. That's what happens if you've got a stem in your femur that doesn't happen. Strolling is great on the catwalk. Nobody can tell. But if you wanna push, put your foot on the gas, the person with a hip replacement with a stem in their femur, and I'm, I don't think it's really, I'd love to say it's just because of the anterior posterior approach, it does seem to be the stem in the femur. I think, um, with a stem in your femur, once you start to stress the elasticity of the femur, um, it doesn't feel, people don't report pain. They just don't do it. So they don't push off so hard with the stem in their femur. But the resurfacings, huge posterior approach taking down gmax tendon, huge approach. A year later, they're walking very, very close to normal people in a way that no one's ever published a total hit that can do that. So that was, that was data. I was, and I, this was in the early two thousands and it was really exciting, the stuff. But as you pointed out, the metal or metal debacle. Um, meant that all of these patients, um, who were doing great, if you did it accurately, um, they were okay, but there was a growing feeling across the whole world that metal irons were bad. And so it was increasingly difficult to persuade people to have a, a procedure. And certainly in Britain there was an advisory. You had to have a metal land level test every year implying that you had a pros, a prosthesis that was about to explode. And so the metal work, it was, it was never going to be widely adopted around the world as, as you found out. But functionally, and the total hip industry has done a, I mean, as you know, in the anterior hip foundation, I'm a huge fan of the insult to the patient for anterior hip surgery is minimal. But in the end it's a hip replacement. And if you cut out someone's calcar, which is the strongest bit of the whole femur and you de power that calcar, you don't let the femoral head take all the force coming from your flexors and abductors. If you de power that, then you are, you are changing the biomechanics irreversibly. Whereas if you just resurface the hip, um, you can allow that femur to perform like a normal femur. And I think that's the difference.

Joseph M. Schwab: 6:57

So, so this is interesting'cause when I look online at discussions, for instance, every once in a while you'll see a, a post on LinkedIn where somebody puts up, um, an x-ray of an arthritic hip and says, should they get a total hip? Should they get a hip resurfacing? And the discussion always comes down to recovery with many surgeons feeling like the recovery is simply easier with a hip replacement than it is with a hip resurfacing. But it sounds like you're talking more long-term functional recovery with people going back to normal, as opposed to what happens in the short term. Is that right?

Justin Cobb: 7:33

Um, I was until, um, uh, a couple of years ago, I would've said what you said is absolutely right, that with an anterior approach, total hip, you are up and going very, very fast and with, with a resurfacing your, you are a bit slower off the, off, off. You're not, you, you probably are a slower. I don't think there's a significant, I think if anything resurfacing are a bit quicker.

Joseph M. Schwab: 8:01

Well, and that, that actually brings up the other part of the discussion that I usually see is when somebody talks about a resurfacing, it's almost placed as an anterior approach, and hip resurfacing are at odds with each other. They're competing products, so to speak. But I mean, really what you're talking about is doing the surgical approach of an anterior approach to put in a, a bone conserving, hip resurfacing implant. Is that correct?

Justin Cobb: 8:28

That's right.

Joseph M. Schwab: 8:29

Yeah. So how do you think we should approach that discussion with those surgeons, you know, online about, uh, anterior approach, sort of versus hip resurfacing?

Justin Cobb: 8:41

so you and I, as surgeons, we know we really can only sell the shoes in our shop. And if, if you can't do an operation, you brief against it pretty vigorously.

Joseph M. Schwab: 8:53

Yeah,

Justin Cobb: 8:54

If you are a key opinion leader for a total hip arthroplasty, you better not promote something that the company that is paying you big bucks doesn't even have in their arsenal. So I think the online chat is, some of it is, I mean, some of it is real truth if you like people talking from their own personal experience and some of it is industry based noise slash testosterone fueled egos

Joseph M. Schwab: 9:27

That brings me to the H1 specifically.'cause uh, you know, one of the, uh, one of the things that you've been working on is the development of this, uh, product. And can you, first of all, can you tell our listeners, um, a little bit about the product and a little bit maybe about the release schedule for it?'cause it's not available everywhere at this point, is that correct?

Justin Cobb: 9:50

It is not available anywhere at this point, unfortunately. I mean, so Derek McMinn, who's a, um, uh, obviously very senior and August, but nevertheless, dear friend, um, Derek, when he was developing the Birmingham in I think six years, went through five major changes, cementing, uncementing, uh, different designs. These days, so we, we started with H1 in earnest with Ceramtec in 2013

Joseph M. Schwab: 10:19

Yeah.

Justin Cobb: 10:20

and really working very hard to get it into people. We got our first patients of the summer of 2017, and we got a CE mark, um, September of last year, and we expect it will be released in, I, we hope, six different European countries, including Switzerland. Um, this autumn. So the, the, the program of, um, regulation is just brutal. It's absolutely brutal. And I'm very sorry. The, the FDA, when we last spoke to them, they'd all just had a letter of Elon Musk saying, what are you doing every day? And,

Joseph M. Schwab: 11:03

yeah.

Justin Cobb: 11:03

and we were speaking English and they were speaking American. And it was a very uncomfortable experience. I mean, I really, I've never had that experience before. Very uncomfortable.

Joseph M. Schwab: 11:11

So, uh, let's talk a little bit about the, the H1 itself, because like you said, you partnered with Ceramtec and so the, the prosthesis itself, the bearing surface is the Biolox delta, right?

Justin Cobb: 11:24

the, the device is monolithic Biolox Delta, which I've been using actually. I used, I was very happy with Forte before Delta came along and, but Delta now we've got, I think there's 13 or 14 years of experience and, and tens of millions of people with Biolox Delta in their bodies. So it seems like it's quite a safe material. Um, and so we felt very comfortable, um, going to them. So they. The device, it's then coated in Medicoat. Medicoat was set up in just outside Zurich to coat, actually it was set up by, um, Haki, um, Gruner to, to coat the furlong ha coated, um, uh, hip back in the eighties. And his son Philip, runs the company now and they, they've been coating Titan Tanium for a very long time and coating directly onto green machined ceramic that is new, but it seems to be, um, it seems to be, you know, if you do the testing, you can rip it off, you can shear it off, and the forces needed to, to take it off are a bit greater. Well, there's equivalent order of magnitude to ripping off, uh, plasma per titanium from titanium or cobo creme. It's a very, very strong bond. Um. But adhe, the, if you, I don't wanna talk about adhesion science. It's very, very niche. It's way outside. Orthopedic surgeons pay grades,

Joseph M. Schwab: 12:59

But, um, suffice it to say you can, you're putting these in without the use of cement, correct?

Justin Cobb: 13:04

so both sides. So I had good experience with Cementless, um, metal and metal resurfacing, and Paul Beaule in, in Ottawa, who's a real giant in this world. He, he's got, again, very good experience with the Conserve plus Cementless. Um, Tom Gross with, uh, cementless Recap in South Carolina. Um, KDA met in, in Gent has had, I think he's done all three of those, um, cementless. And it seems to, it seems as though the Cementless feral component, it's a safe construct. And so we have the experiment of plasma spray titanium on ceramic on both sides. So a single experiment, whereas. We felt that going cemented. That would be an experiment too. No one had ever got a device cement onto ceramic. That would be a new one too.

Joseph M. Schwab: 13:54

Why ceramic as the bearing surface? I mean, you have, I presumably there are a number of different options you could have considered. Why did you choose ceramic?

Justin Cobb: 14:04

yeah, so obviously initially, honestly the first thing that came along was the contour. So in the old days, in fact in the current resurfacings and with total hips, two groin pain is a thing in hip arthroplasty and it's between sort of three and five times as common. Sorry, commoner in, in resurfacing arthroplasty. Um, and that's partly, it looks like it's mainly the acetabular rim. You know, it looks like if someone sort of growing pain, you probably didn't get that anterior rim inside the pelvis enough. Um, and we. Back in 2007, well done, actually one of my PhD students, um, and I, we looked at the contour and we realized it was quite a mathematical contour. And so we, we, we patented that in 2007 and I wanted to do it with metal on metal, but as we were doing, it was obvious metal, metal was going nowhere, and so a contour metal on metal was never gonna run. So we then looked the different materials. As I'm sure you know, the poly motion is in use in North America right now. There's an IDE going on in North America, which is a metal on highly cross think poly, um, but what we, in our preclinical testing, um, it, one of the things about the, the group of people who want really benefit from resurfacing are the young, very active men with cams, all of whom have quite shallow sockets. And the young, very active women who, some have got cams, but quite a lot haven't. They've just got a bit of dysplasia, quite a shallow socket and leaving. So you have to have the opportunity to leave some substantial amount of uncovered bone uncovered prosthesis laterally to give them the good articulation and that unsupported polyethylene, um, the preclinical testing, it just fails it. So we unsupported, metal backed, it doesn't fail it, but without, um. Metal backing. We couldn't get polyethylene to to, to succeed. So we had to go to hard on hard. And in Europe, I think in every country in Europe, ceramic and ceramic is a well established, um, bearing couple. It's only really in North America that doesn't, doesn't accept that as a regular thing. Um, in Europe, um, we've all got really good experiences, I think of, of, of c ceramic bearings. And so we went to that and, and in fact the un unsupported, um, rim, it's a really, you've gotta have the ability to have a cup that is unsupported in mild or even moderate dysplasia that is not gonna fail.

Joseph M. Schwab: 16:52

So do you think the reason, um, the, the, is the primary reason that the cups were sort of exposed anteriorly or groin pain was occurring anteriorly more common in resurfacings because of the material, because of the shape of the device or because of the size of acetabular prosthesis relative to a more conventional total hip or a combination of those

Justin Cobb: 17:16

Combination. Combination. So, um, I wanted, I'll send you a last picture showing the, um, uh, of an acetabular component of a metal, metal one and our contour. And the fact is, if you haven't got a cutout for the oop pubic recess anteriorly, where the S comes and the ichi, it's much more gradual recess posteriorly. If you haven't got those cutouts, you've gotta put the socket a long way further in to avoid, avoid, um, conflict. And we can, we can leave the center much more where it wants to be with the contours. Um, so, so I think it really makes a substantial difference to the surgeon trying to get the socket in the right place because it doesn't have to overhang except to give you back your, your where whale scar was. You've now got a lovely big, um, peninsula there, but you haven't got overhang for sos um, anteriorly.

Joseph M. Schwab: 18:19

Interesting. So you, you briefly mentioned indications and, and let's, let's talk about this because, um, indications over time for hip resurfacing kind of shrank substantially, uh, from everybody can get it to, you know, maybe males with a larger bone size and their, you know, who are very active in their, you know, fifties to sixties, forties to sixties. It's different depending on the literature you look at. But certainly over the last 20 years, the relative indications for a traditional hip resurfacing contracted. From your perspective and with the development of the H1, does it address some of the reasons for those, uh, changes in indications and what are your

Justin Cobb: 19:04

so so the, it, it wasn't so much the indication, I think it was the, as the truth of the matter, the problem was edge loading of the wear scar in a metal or metal bearing. That was the problem. That was the only problem. And to get a, and I've got several very, um, prominent female athletes and dancers and so on who are 10 and 15 years after every resurfacing, doing just great. But you had to get the socket orientated, right? You didn't get it right. They got, um, um, high Medline levels and Tom Gross has published on this, and he is a real master of this. Um. So the indication in women is very strong. If there isn't a contraindication, the contraindication of a, um, a uniform thickness metal bearing couple means you've just got this very small surface area on the smaller sizes. With ceramic, ceramic, the rules are completely different with literally, I think I don't, with millions of ceramic and ceramic bearings with decades in humans, the case report of edge loading of runaway wear has yet to be published. And because we all love bad news, you know, we all love bad news. If there was bad news, the ceramic and ceramic haters would be putting up pictures of edge loading of runaway wear on every talk they gave. But it seems to be a, a, a a more, a much, much more benign tribal environment. Um, so the worry about edge loading of runaway wear doesn't seem to be there. And so for women. Um, resurfacing is a great option for women. It really is. It's fantastic. And unlike the sporting, um, we, uh, athletic man, women live forever. Okay? They're never gonna die. And, and to cut large bits out of them, um, unnecessarily, it seems like a big mistake. So, so our indications are adequate bone mass. And the one thing that gives me the heebie-jeebies is bisphosphonates someone who's had bisphosphonates preoperatively. I think that's a. I, I don't that, that's a difficult, I, I think it's just too scary for us right now. Um, but if someone's got a, if they're a healthy adult, that means that we know Wolf's law carries on working in your nineties and hundreds. You know, if you are active, you keep your bones active. So, so, um, in our trial we had 70 as the upper age limit. Um, and I, I had one, um, built muscular Californian man who literally sent money trying to Bri he was 72 trying to bribe his way onto the study. Um, and so since the trial, I mean, people in their seventies, as you know, there are lots of really good people in their seventies. And to say to them, no, you've gotta have your femoral head and neck cut out and someone bang a big bit of metal into their fma, well, you know, you don't have to have that, I don't think.

Joseph M. Schwab: 22:16

I suppose how, how about things like, um, certain types of pediatric hip deformity. So you said adequate bone stock, is that just dealing with osteoporosis or things like perthes, advanced Perthes and,

Justin Cobb: 22:29

So the planning, I mean the, the we've done a really difficult per is is really difficult. It's really hard. Um, of course it is. And so there's some things that are just too difficult and you can't do very much with people's. Um, you know, you can't do what you can do with an estro with resurfacing, of course you can't. But I have, um, done corrective osteotomies and resurfacing, um, simultaneously with fractures of the proximal femur. I think that's something you can do, um, and just resurface the feral head. Um, but I think in bad path, I mean, and bad av n too, of course you can't use it for those things.

Joseph M. Schwab: 23:12

So do you look at version of the femur? Um, for instance, before you're, when you're planning for a, a hip resurfacing, would you correct a femoral version? Or obviously you're not gonna do that through the prosthesis, um, but or do you just prefer to put them where they anatomically came from?

Justin Cobb: 23:29

So it's a great question, and in, in really bad DDH with huge, um, femoral inversion in my old days of metal on metal, um, I, on a couple of occasions did a rotational osteotomy of the femur the same time as, um, during the resurfacing. I haven't seen, you know, it's a, it's a real question, but I just haven't seen that for a while. Um, and I, but I think the rules are the same in all arthroplasty. You've got to give somebody a biomechanically sound, um, reconstruction, which may require corrective osteotomy,

Joseph M. Schwab: 24:09

I think, um, the, the kinematic alignment total knee folks are challenging our conventional wisdom as to what, uh, biomechanical soundness is. And, uh, I, I, I find that interesting as well from a total hip

Justin Cobb: 24:21

for the, from the femur, you know, the, I I hope we're gonna publish quite soon, some more work on, on the, the elasticity of the femur and, um, and the, the, the impact of e femoral stem on that, on the biomechanical properties of the femur. Um, and if you've, if you can save the compression trabecula from the car, car going up onto the femoral head, if you can save those, then your hip flexes are just driving straight up them. If you cut them off, they've gotta go down into the. Um, shaft to bond onto the metalwork and then go back up. It's just, it's a tortuous route for the forces to be delivered.

Joseph M. Schwab: 25:07

you've mentioned briefly your detractors, uh, well, you said sort of jokingly, you know, if, if detractors were finding these problems, of course they'd be bringing'em up online. I. I'm certain you must have run into some detractors in during this development period for some reason or another. What are they saying and has their message changed over time or has it gotten louder or quieter? What would you say?

Justin Cobb: 25:31

um, I think I got, I've gotta be, um, gotta be polite. It's DA data. You know, there are big hip groups that publish huge amounts of stuff that have never published any outcome data. Not not revision rates, but actually outcome. And if you look at the Swedish registry, and the Swedes have, have done a pretty, a very good job of looking at how their patient's doing, not just revision rate, but everything else in their registry. Um, the, uh, cemented stem isn't that great, you know, functionally in terms of outcome studies. They're not that great and cement less stems seem to be better, but not as good as resurfacings in functional terms. Now, of course, there's selection bias and all that. Of course there is, but no one's ever done the other way around. No one's ever shown, um, that the, the resurfacings do really badly, um, functionally. Um, and so to say, I insist on cutting out your femoral head and, and fossilizing the inside of your proximal femur. So the big arguments in Britain, honestly, it's about cemented stems. Can you believe that? Um, it's amazing. They really are devoted to that.

Joseph M. Schwab: 27:00

Is there, um, do you have any thoughts or plans on, um, uh, turning the H1 into, uh, sort of a smart implant or something that has some built in sensors so you can understand, um, maybe a little bit more in depth what the interface with the bone is like, what the load transfers are like, or any other, um, uh, any other changes to the

Justin Cobb: 27:24

So, I mean, it's a really interesting, it's a really interesting question. I, I feel the, um, because you are just putting a coating on the, on that femoral head, um. It behaves, it behaves very like a normal femur. It really does. Um, and I think it's a, I think the, I mean the thought of going through ethics and the, all the development pathway to get the strain gauges into something in the femoral head, I'm not up for that yet. I think when we've got, you know, we've only got seven and a half year results so

Joseph M. Schwab: 28:01

Yeah.

Justin Cobb: 28:01

and

Joseph M. Schwab: 28:01

Yeah.

Justin Cobb: 28:02

nobody thinks that's long term. I think if we absolutely know what the 10 and 15 year results are like, then I wouldn't feel bad about asking someone to do that. But for the moment, I think we, we, I wouldn't ask someone to have that done.

Joseph M. Schwab: 28:19

Thank you for joining me for this episode of the AHF Podcast. Be sure to join me next week for part two of my conversation with Professor Justin Cobb. Please take a moment to like and subscribe. You'd be helping us find more people just like you to share this content with. And as a subscriber, you can always drop an idea for a topic or any feedback you like in the comments below. You can find the AHF podcast on Apple Podcasts, Spotify, or in any of your favorite podcast apps, as well as in video form on YouTube slash at anterior hip foundation, all one word. New episodes of the AHF Podcast come out on Fridays. I'm your host, Joe Schwab, reminding you to keep those hips happy and healthy.