Hip Basic Science (2): Metal on Metal, Polyethylene, Stainless steel and Cobalt Chromium



This on-demand medical teaching session will explore the history of hip surgery with a specific focus on metal-on-metal bearings. Learn from experts about the techniques of the pioneers and how challenges such as corrosion, carcinogenic properties and adverse reactions to metal debris have been addressed. Gain insider knowledge on the pseudotumor and MRI investigations relating to metal-on-metal hips. This unique session promises a comprehensive overview and understanding of this area of hip surgery.
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Learning objectives

Learning Objectives: 1. Identify the background of how metal-on-metal hip replacements arose in Norwich. 2. Describe the risk factors associated with metal-on-metal hip replacements and causes of failure in the devices. 3. Examine clinical findings that may arise in patients with a metal-on-metal hip replacement. 4. Demonstrate an understanding of the investigation techniques and imaging modalities used to diagnose metal-on-metal joint failure. 5. Explain the terminology and classifications used for metal-on-metal failure and adverse reactions.
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The following transcript was generated automatically from the content and has not been checked or corrected manually.

And to talk about what's happened here, how has it happened or what the follow up is following it, So I'm going to go through a few of those things, so a lot of these slides have been borrowed from people who've gone before me john Nolan gym, Wimmer, so acknowledgments to them and others as well, so um so first of all about Norfolk, you know Norfolk's an enchanting place you know lovely, feels home of Colman's mustard, alan partridge, Crazy delia and obviously people with six fingers yeah anyway, so just a bit of history about Norwich and metal on metal how it all started, so a lot of you registrars may not know that. Actually no, it was very prominent in the early history of hip surgery and actually development of hip replacements now tommy britain in 1935. This is the cathedral in Norwich in the middle, and he walked around the sort of city center and he saw these things at the side, and he saw these, what are called flying buttresses and he was inspired by that and he thought hmm I could use that in my hip fusions, so this is the britains arthrodesis, so once upon a time when people were 30 40 you know even 50 years old or, and even older. Rather than giving them a hip placement, people have hit fusions and they walked around on these for many, many years now. This is becoming increasingly common. Many of you will never seen a patient in clinic with an arthrodesis. I myself even as a revision hip surgeon have never done one of these myself okay, but this you can see the issue of femoral arthrodesis and this is quite an easy question for them to put up saying what do you see here, but that is a hip arthrodesis issue femoral arthrodesis. This is the britain arthrodesis anyway, so let's move on from there, so one of the great pioneers of surgery of hip surgery. Everyone remembers the name charlie, but actually as ken mckeon 19 forties, they sort of we're doing things alongside each other, not really collaboratively, but eventually they did pool their ideas, and there are bits that charlie borrowed, borrowed from a key and so, and so forth, and actually that bizarre photos when they were both going skiing and they both fell over, We're both worried they had hip fractures. Anyway, this is uh some winston churchill. This he actually was in Monte carlo the hotel deep very near opposite the casino, uh which I'm sure all of you know and he fell and broke his hip and was flown back to London and had this mckee pin and plate done okay, shame the screws and bicortical, but anyway, so as we move on, so mckeon 1940 which is 20 odd years before people credit anyone with the start of hip surgery. Uh He said that if you can replace the berries of a motorcar, you must be able to do it in human joints, and in the 19 fifties and sixties. Um These were his initial trials. These were fixed to the pelvis with screws alone and they're made entirely of cobalt chrome, so this is cobalt chrome on cobalt chrome and generally cobalt chrome is a good material to use of bearing surfaces. This is john watson farah, who's another famous name from Norwich and he came as kentucky's senior registrar, and so they came up with this hip together. This is called the maquis farah and that started going in the 19 sixties and I've actually seen a patient with one of these that was revised at 49 years following implantation okay and the number of these did marvelously well, but essentially these are cemented, cemented cup cemented stem radiolucent cement, and it's a metal on metal bearing. The cup is very trademark, looks like a sputnik, okay this was one of the most the first metal metal hips, and these are the survival curves for those metal metal hips and some papers show them doing extremely well out to 14 or 15 years okay remember these were done in the 19 sixties, so these kind of results were very good now. They did tend to fall off a cliff by about year 20 but still these results are pretty reasonable given this is the 19 sixties and this is follow up in the eighties, so as early as the 19 seventies before all of us were born okay. There was concern published in the lancer about the carcinogenic properties of where particles from prosthesis made from cobalt chromium alloy these and yet you wonder how it's come to pass that we have implanted tens of thousands of metal, metal hip places where there is a cobalt chrome and cobalt chrome articulation. Despite these concerns, and there is some evidence to show that there's an increased rate of hematopoietic cancers in these patient's, as well in the seventies and eighties designs progressed, but essentially continue with metal metal, and then there was the great hope, the ultimate TPS metal metal, which was a deep I implant, which was taken up by a few centers, Norwich being one of them. This was very similar to the extra design as a taper slip stem, which we knew which we knew was very successful. It was taper polished, cemented in, and there was a 28 millimeter metal head, so 28 m metal head, and it was a metal metal articulation. I'm colonists finished extremely well uh um so it it had tribe, ology wise and good clearance and also had mixed form lubrication. I'm sure, Miss spaces already talked to you about different forms of lubrication, but what you really want is a fluid film in arthroplasty where the articulating service don't actually touch each other that's pretty impossible to get. Um Some people say that once you get to a ceramic head above 36 millimeters in size, you can get that, but generally part of it is boundary part of it is fluid film, and initially the pilot study showed that all the patient's were extremely satisfied, more than 50% of them had no awareness that had a hip replacement, the plane sport, it all looked wonderful in 2002 by 2009, um which was pretty much towards the latter years of my registrar training. It became very clear that lots of these patient's around the country around the world. We're getting unexplained pain with relatively normal x rays, people getting more likely to get paraprosthetic fractures late dislocations and actually the rate of uh revision uh up and you know was huge, far far far worse results than the standard cemented hip and you can see at Norwich the number of revisions that were done. Now, you don't expect in a year to be implanting 100 and 58 in the case and revising 26 of them now. That's obviously not the same hips but their historic hips, but you can see the revision burden was huge, um So what was the problem why did they have a problem was it. The 28 millimeter metal metal articulation were the cups going in very steep, were all taught, put are cups in at 40 42 degrees, but some of them in those days were putting at 50 55 was it the carbon mix was galvanic corrosion, crevice corrosion, and essentially I'm it was felt that it was a combination of all this the way that the stems corroded the way that you had trillion osis all caused the problem here and on retrieval of these stems at the time, revision you could see that that polished um that polished stem showed these signs of corrosion. There's often black debris left inside the cement mantle and all around the hip these are some other stems which have also shown corrosion as well so how how would we investigate patient's who came back with a painful metal metal hip okay and how were these patient's investigated so x rays of course clinical examination and Iggy what do you think you're looking for in clinical examination. Um They're they're gait whether they have a trendelenburg um so why would they have a trendelenburg gate, so if there are doctors are involved, so it's where of tissue mass yeah absolutely and in terms of the blood test obviously ESR and crp, what are the blood tests will be doing. Mike we're looking at their cobalt and chromium levels okay and do you know those levels in particular. I know there's two different measures, one of them's parts per billion, yeah, but I'm afraid, I don't know the numbers off the top of my head after that. We always remember why we always remembered seven parts per billion for exam. They changed all the the markers and it's nana mel's per liter and there's a conversion chart but if you say seven parts of a billion, you won't be wrong and then people had people really had bone scans now, but they did they used to have them, ultrasound was initially done to look for um problems uh pseudotumor and so so but the gold standard became uh maRS scan, what does mars stand for. mike, metal artifact reduction sequencing very good and Iggy um tell me about the, his, do you know about the histology associated with with this or what happened to these patient's, what is what's our vow uh So from our understanding, it's uh so it stands for um I think it's I know it's called pseudotumor colloquially, um but it's not so it's an aseptic and it's lymphocyte driven so a l, um I'm not sure what v. A. Is but legion um yeah, okay, that's fine, so it's been called lots of things okay. When I was doing my exam, we were all about elavil, aseptic lymphocytic vasculitis and associated lesion's now to be honest with you pseudo tumor has gone out of fashion. Um We do say pseudotumor is for these large fluid collection that almost on m. R. Look like big big solid tumor or big fluid filled tumor's but when you're dictating letters saying there's signs of pseudo tumor. Obviously patient's have access to their records and I never use the word pseudo tumor anymore in my clinic because if a patient sees so tumor, they don't what pseudo means they think oh my god I've got cancer okay um our val, as well, no one could really remember what it stood for okay, so um so we will stop using that were a hip surgeons after all, so we use something called a Rmd okay, adverse reaction to metal debris because that's really easy, you're armed a. R. M. D. That encompasses everything okay. You had some necrosis, some lymphocytes, all kinds of other things now the mars, metal artifact reduction sequencing the mike was talking about, we've really pioneered in knowledge and the seminal paper and the Anderson Classification Anderson was just a registrar at the time, but he worked with professor and and Dhoni tom's, who now works in cambridge. They came up with the, with the actual classification system and for those of you interested those uh those actual references, but essentially mri s showed these large fluid filled collections around the hip, often which were loculated, filled with debris. Uh There was a lot of a dema in both the muscle and the bone marrow, and as things progressed, the situation get worse. This is a an actual t two M are showing a pro, prosthetic fracture and also showing a corona view showing the papers that it fracture. You could clearly see comparing one side to the other The significant muscle atrophy. All of these hips as they were bathed in a soup of metal, metal. These were the pseudo tumor is that Iggy was talking about and these were sort of uh you know they look like growths, but they're not they are just out patching fluids which have matured and have this big scar tissue. The amount you could debride at the revisions is quite frightening. Really at revision surgery, there was yellow gray fluid, gray green, thick and capsule uh and sometimes you went in and the bone was completely dead. The stems believe it or not weren't loose, it wasn't that type of thing as stems were corroded, okay, and this is what the aspirate looked like from a hip with metal metal. This is not infected. If you were in theater asked to do a aspiration of a hip and you drew this out, the majority of you would say it's clearly past okay and that's what it could look like of varying colors When you went into the hip. This is what you encountered okay. This is the top of the femur and you can see that that entire top of that femur is completely dead and the problem with the metal metal hips uh might have you got someone else who wants to listen. I know it's entertaining, so he's just learning it's all right. It's all right yeah give them time all right, uh but essentially you can imagine that these hips for some people who absolutely great, but for some people, they could leave you like this within 43 or four years and to be honest with you. Uh you start asking the question would you have one of these um anyway, let's keep going so this is what very prosthetic fracture you can see and what would happen is. I don't know how big those are coming up, but you could see. Top. Left hand corner is the initial TPS. It then dislocates because it starts to become unstable as a result of abducted dysfunction. It's revised by someone to a longer neck. Um It's then dislocates again, um is the has a cup provisions to improve its version, dislocates again and ends up with the captive line, so these patient's often had multiple surgery to resolve their acute dislocations okay, so some people started saying this is a problem with the deploy implant. It never happened with Mickey families, but actually you could start to see that although I said the initial results are promising. They started to drop off a cliff, and there were other papers showing this as well, and they were very similar reasons for this, so back in the seventies, there were reports saying there were 10 failures with no infection, but lots of metallic debris in the soft tissues, and there were others saying look there are people with pain, dislocations, and fractures, and brown yellow fluid aspirate that were sterile this in the 19 seventies, yet the whole orthopedic industry steamed ahead promoting these implants. Um This is what the mickey pharaohs looked like and these were these are pictures from the seventies and eighties massive great pseudotumor risk arthur arthur arthrograms and this hot and the opening of that hip in the 19 eighties looks exactly the same as the ones. I showed you in the two thousands, all we always think oh that was the old days that was the seventies and eighties were much better than those guys. The new ones will be okay and the problem is as orthopedic surgeons, we don't tend to learn our lesson and if a rep comes along with a nice shiny bit of kit and says you can be the first one to use this mr, pollinger okay all of a sudden, we think yeah sounds good, yeah I I didn't mean you might but generally that's what we do so then it was oh we don't need a stem, we'll do surface replacements, less invasive to the femoral canal barely in operation. At all ok, it won't dislocate look at the size of that head, feels completely normal, better, scores great, and then we started implanting research things in their thousands. When I was training, resurfacing was a very common operation. We would see them every single week, and I did research things when I was in st, three okay as I went through my training, they came less and less common, but even all the way to the end of my training, some people were still doing them now. If you look around the region, the number of receptions that going in there are none in Norwich anymore, um and there may be a few in cambridge, but the numbers are tiny. Then someone had the bright idea that oh why don't we have a resurfacing socket, but actually give you a huge head with a stem because there are some patient's where you couldn't do a reserve seen and maybe we should do that for everyone. So deep, I came out with with the S are, which was an extra large metal metal head instead, and it was implanted in its thousands, luckily in Norwich, we didn't plant as many as some centers, Cardiff and planted hundreds. They've all come out, so then people said it doesn't happen with birmingham's and you still hear that to this day um Andy murray having a birmingham, so it doesn't happen with Burman's, birmingham's Great um but the West suffolk and Norwich cohort showed that there was a 3% revision rate at five years for metal osis and start issue necrosis. I remember patient that we had to revise at Norwich when I was a registrar who was 18 months down the line and he was 40 years old okay. The risk factors for people who would fail with metal metal hips were females, people of larger bill, smaller heads and if you put your cup in very open or vertical uh more than 55 degrees because of edge loading um and the Oxford Group felt that there was a 1% risk of pseudo tunes within five years, which is pretty frightening. This is what the birmingham's some birmingham's look like when you open up, so is that gonna be Andy murray Andy murray's hip in three years. We don't know okay, so the ASR was a copy of the birmingham, but it came with more variability in terms of cup sizes. You took away less acetabular bone, and they said that they've tweet some things to give you a reduced clearance of the head and the cup, which gives you better fluid for lubrication, lower wear, and it was all easy to use um and they felt that you can match it with a cry stem and it was fantastic. Unfortunately, um they failed disastrously okay. The large hailed head on a small try onion gave you significant rates of trichinosis, okay, don't worry about that. Um then in 2008, when people started whispering about problems with metal metal hips. The british Ship Society sent out a questionnaire and you know three out of 380 people, 50 surgeons had seen these problems okay, 40 of them and with the extra large metal metal hips and more female than male um So clearly, this is a problem and the problem with the s are as I said was edge loading. If you antivert it with a high cup angle, there's a lot more pressure going on a lot. More cobalt chrome will be shed into the surrounding area and then into the blood with subsequent problems and dead pelvises and things, and so essentially no women really get researching anymore. It's reserved for the elite Sports Mail and they have to have a larger head, okay, so can things get any worse than the failure. Um In 2008, there were there were there was a blood study published in the American journal showing that actually there were chromosomally abnormalities were significantly more common in the metal metal group translocation, an employee all seen in the metal metal group in people's d n a, in people's blood luke, sites uh This can't be a good thing okay, we don't know what the long term effects is is going to be. We know that Carson genesis takes a while to, to progress. Um Again, they looked at cancer risk after the Maquis Farah in 91 they felt that there was a lower risk well. The total cancer risk was not elevated because there was a low risk of kidney, bladder, and breast. For some reason, but there was a higher risk of blood borne cancers, and that's been a continual thing because these cobalt chrome levels increase in the blood okay. This visit, you're e, in 1996 found the rate of leukemia in patient's with metal metal hips was nearly four times higher than standard metal and polly hips. Now, it's felt that the difference wasn't statistically significant, but I'd be a bit worried okay, with four times greater and this is the time. This is an overall timeline of metal metal hips showing I mean it's it's quite busy but essentially all the way back to the seventies. There have been concerns about this and all the way going through. There have been multiple multiple repeated concerns about metal metal hips, but industry have driven forward change, which has been unchecked by the orthopedic um fraternity, and the most important thing going forward for for yourself as registrars is always do things that are evidence based. I think we are better than some of the people who've preceded us were, um but you have to question significant changes. Uh There have been numerous disasters in orthopedics changing the extra stem to a slightly more matte finish which have all been industry driven and luckily we have things like Odette. The NJ are now to monitor things a bit better so um again, what's the mhr, a uh medical healthcare regulatory agency yeah very good healthcare products or something yeah, but essentially they're a group that issued guidance 2006 and 2010, updated 2000 few years ago and essentially it was how you follow up these metal metal hips. Essentially, initially, it was felt that only the high risk patient for those who were symptomatic, needed following up then it was felt that every single ASR large head metal metal should be followed up, but maybe not reserve things now. They've come to the point where they said that absolutely everyone needs to be followed up lifelong, okay and they need to have blood tests on a yearly or two yearly basis. Once a birmingham gets to about 10 years, you can spread that out to sort of three years as long as they're asymptomatic and they need mars mri scans depending on their symptoms, but probably at least every 2 to 3 years and especially in those where the Oxford hip scores have dropped, um and we still see people who have had hips done 15 years ago. Now, you may ask look if they're okay at 13 or 14 years, are there people who suddenly take off and yes, there are we still see ultimate t. P s. That are doing okay is 8, 10 12, but 13 14 years, things start progressing, so this has been around for 50 years, okay, and it's been a problem or a potential problem for 50 years, but we haven't listened okay. The birmingham is still on the market and is going still going in in limited numbers and as long as the patient's are aware, there is no doubt that the birmingham hip placement can give you potential increased function over a standard hip placement. If you look at Andy murray winning tournaments doing reasonably well, I I don't know if he would get to that level with a standard hip replacement, okay, but the ASR was a disaster has been withdrawn. The problem is it's the local production of this metallic iron soup that kills the abductors, kills the pelvis, and this is do too well with the ultimate TPS, crevice corrosion, galvanic corrosion trillion osis, um so look in 2000, or this is going back to 2007, but it's hi, there were 10,000 metal or metals inserted every year that was out of about 50,040 50,000 hip places, so they were going in like smarties okay, and the problem is even three or 45% of those turned out to be a disaster. That's a huge revision burden, and there are some centers such as WAles and Norwich, where the majority of people's revision practice for a number of years was not extra tridents or standard hips. They were all these metal metal hips, so so look we've talked about the screaming screening, but essentially you have to screen everyone. Um you need to even mri, the asymptomatic, especially symptomatic six, and in terms of what happens in the long term about cancer, it's hard to know, so would I have one if you read that message quickly, you'll get my answer. Many of you got that disappointed. It took you that long to laugh is that yeah right acknowledgments too to gym and john and ben oliver, keith, Duck and son donal, who did a lot of this work and put some of those clinical photographs from them, but look the Norwich experience has been varied, um but what I as a knowledge surgeon of about 66 or seven years, I have noticed is really critically appraise the evidence okay and if someone came up to me with a new shiny implant, I would really really um just go back to the evidence. What's the evidence for this, some people say, look it stifles, innovation okay, and the metal metal should have been done in a controlled fashion in a small trial, 50 or 100 patient's follow them up for a number of years rather than rolling out in the 10 thousands, and that's the problem, I'm all for innovation when it's done in certain centers in small volumes in a controlled thing as part of a research setting, but the widespread application of untested technology is going to put your patient at risk okay um That's what I say all right any questions about metal metal. In general, I didn't really do a basic science talk. I just thought I want to get across the message that actually um there's a lot advertised about how great research things are how great the birmingham is and how everyone can be like Andy murray, um but you know, I'm not sure if this space is going to do them. When she comes to Norwich, she might put them in the thousands, but we'll see let's hope not any questions guys before. We let mr joel escape. Can I ask uh you're going to start from a practical perspective, so you do, presumably you do blood test, so say a patient I didn't hear that sorry, so, so for example, if say a patient gets referred by g. P. Uh 13 years down the line um never been followed up and then they say um they say they have a TPS ultima, um yeah and they've been doing fine, but what's the cut off in terms of if they're asymptomatic and never been, we've been needing any orthopedic input after 13 years, what would your treasure for symptomatic and to say if they come in. I would book them cobalt chrome uh then do a Oxford hip score, and I want to know what implant went in may well. If they've never had an MRI scan, yeah, then they definitely need a MARS, mRI scan okay even if they're asymptomatic because you can have people who are asymptomatic who have significant metal metal um disease, and they are indeed now, it may not be that you charge into them with a revision, but we have for people with raised cobalt chrome levels and bony involvement causing cal carl, isis significant osteolysis even before patient's are necessarily symptomatic. Um We have offered them revision because we know which way this is going to go and it's a question of do you wait, it's like I suppose it's like a mile a path, isn't it you're doing the operation to stop progression and if someone 60 and has had their ultimate TPS in for 10 years and they've never been followed up, have an mri, which looks horrendous and they have osteoporosis on their x rays, but they're still managing. I would still um and had see three disease with bony involvement and osteolysis. I would offer them revision personally because it's either have it done at 60 and take the risk of surgery then or wait another four or five years uh have a dead pelvis uh I'm being dramatic, but you have to have that discussion with your patient and obviously these are discussed in in a revision hip mdt da da da, that's what you have to trot out for your exam, but yeah that's what I'm saying blood level um is there a magic number that you then have to think about oh it's like 100 and 10 now, yeah it's it's all different now, it's different for cobalt and chromium ones one through five ones 1 20. I used to remember 7.4 billion. It's written on the reference ranges, um but it's not the case of oh once you get above 1 20. If it was, you know, 100 and 50 and the reference range is 1 20 the patient was a symptomatic with normal hicks scores and the MRI showed a tiny collection. I wouldn't jump to revise that one I would keep an eye on that patient, I would see them in a year. We repeat blood markers clinical examination and perhaps an MRI scan to look at it and you're looking for trends okay, someone never been followed up for the first two or three years. You might need to keep a closer eye on them, whereas if someone's having to yearly things and everything's absolutely fine, then you can spread out 2 to 3 years um Yeah that's what say the mhr A have actually got a flow chart haven't they, I think for if you want to look up the finer details of how you should be following them up, but I don't think you need to be able to, I don't, i, I looked at that do that, but I thought you don't, I don't even know that myself I just do what I think is best um they have it in terms of what stem, it is what size head, it is whether you do one year, two year, three year, when you need bloods, but I think you get a feel for a patient. If someone's never been followed up just do everything okay. If someone's come back two years ago and has had a maRS mRI scan, which is completely normal, um which is has a fluid collection. Then you're just gonna repeat it okay, uh but yeah miss facing kate's right in that there is a there is a flow diagram, but I don't think you need to know that through exam at all essentially exam, you need to know, there's a checkered past to this. You need to test their abductors, look at their symptoms, but be aware that people who even asymptomatic kind of significant changes in their maRS, mRI scan and can have sky, high blood markers as well. It's all putting all three of them together clinical blood tests and memory and then you come to the decision well and just last question if if if it's that okay um we've revised it say, for example, see three decided you're PFR um loads of dead bone um does it then create an environment where it just perpetuates itself even though you've done the p. F. R. And they're still cobalt chrome levels in the soft tissues that yeah, so so there are some people who continue to have had this reaction to metal debris despite you taking away the metal metal articulation um and actually one of the guidance is states that post operatively you should look at metal metal iron levels a year down the line we don't tend to do that. We're quite bad. Most revision hip surgeons think that their revision hip surgeries queued it cured everything and they you know they come in and save the day, but the truth is um I'll be honest with you. I haven't checked their blood levels at one year, but if people then come back at a year and they're symptomatic, I would I would say let's have a look at what those blood levels are doing and some people their blood levels take a long time to come down and they can can continue. Thank you right. Any other questions, do you tell these people to what's their weight down what once they've had it done, yeah if it's a risk factor for getting these problems. If Andy murray gets looked began to get problems, so look uh increased weight is a problem, no matter what hip you have okay, so anyone who's larger than average and you're doing a hip place of them. You need to tell them that they're implants, survival may be impaired by their body habitus, so it's no different to a metal metal um that's standard across the board okay doris who weighs six stone and you know walks around her house and occasionally lets the dog out, is going to wear the hip hip hop a lot less than mr joel, if he ever has it, uh but that goes without saying okay all right what's the next talk okay. Um Panels is going to talk about polyethylene do, I need to take my slides off you, just stop yeah, so if you go down to the box that yeah, perfect okay, I got it thanks him. I'll see you monday, thanks a lot guys. All right are you starting monday yeah, I'm not doing that customer, told you yeah you text me, thanks okay all right get to spend Valentine's day with me now. No I thought my wife got jealous, yeah we're still recording ok panas is going to talk to us about polyethylene and then I think which we did it I did it in uh panels on polyethylene and then warren's going to talk to us about stainless steel and cobalt chrome. Thank spano's, can you see this line uh I was thinking it might be useful actually to start with uh some questions that are taken from fr cs level virus uh. So if you can put over perfect love it, go for it. Yeah just just tell me which one they're now put out as we go. If you start first, basically I was thinking if we see what everybody understands and hopefully I can address those four questions through the talk because I'm trying to present what we need to know for the example, so all questions uh first question we'll start yeah first question just to see the general sort of knowledge on and just to let everyone read it and reply mhm, that is good how has that been got to receive two responses. Actually 13 responses come on guys good, so I can tell you the answer is just to make progress with this, but the answer is not the first one, so surprising we'll talk through that can you put the second question up please, and this is a negatively phrase question which I would struggle with in the fcs, they don't do that anymore, so don't worry about it, you won't struggle with it, so you're not uh yeah, so they might be still using some of the old questions in the UK, but the um the advice we get given when we write questions for the uk is that we're no longer allowed to do it, We're not allowed any double next these topics come up in that obviously maybe uh and then the question uh so there's a bit of a spread on this one. Obviously for the answers, So we'll talk through these methods, and I understand we do need to know the basics for these. When it comes to us during the bible's okay okay, so I'm gonna start with talk and hopefully we can address those questions and explain what they mean. Uh So the competition of polyethylene is a c two h four. There's basically a long chain polymer of multiple ethel immune it's and it's joined back available. It's, I thought it was important to understand the history of it to to understand the generation of polyethylene, so it started in the sixties when charlie put it in the first hit at the time. It was called by some papers as a high density polyethylene, but other papers call it an ultra high molecular weight polyethylene, and I will talk about that. Essentially, it's used as a bearing surface uh arthroplasty both in the upper and lower, uh so it started in the sixties and historically it's been associated with uh where nasty alliances and also delamination duty oxidation. These modes of failure different in the hip and the knee, and I will explain them in a moment in the nineties. The first generation of highly crossing uh polyethylene came about and the way you make highly cross linked polyethylene is by irradiating it with uh stabilizing it with gamma radiation. Currently in the last decade, we're using the second generation, we're basically they're using synthetic vitamin E analog to reduce the oxidation uh and counteract some of the problems with b. The ASIA are found in many papers that there's no definition of manufacturing processes, so I'm sure every manufacturer uses a different process, so it's quite difficult to actually specifically say what polyethylene is. There are five stages that we need to know for the exam. Uh These are polymer ization, shaping, sterilization, heating, and packaging. Uh We'll start with the first one polymerize ation forms powder, Essentially the historic method is to do addition polymer Ization and that was used for high density polyethylene, but it resulted in uh ritalin implants with poor resistance fatigue. Currently, we're using conversation polymerization, and that is the gold standard for that step of the process. In terms of shaping, there is machining and that is around about exclusion or a seat compression molding, I think we just need to know the very basics here so for ambar exclusion, what they used to do and they still do that for not claim complications is basically put the put the powder in a barrel, uh drive a rod through the barrel and then create a cylinder, and then they would take the cylinder block of polyethylene and cut it into the uh bearings that we use that was acceptable to failure and the reason for that is you couldn't guarantee the quality of the polyethylene throughout the big block that you had, so the best method is data compression molding, which was the correct answer for the question as well where you basically take the pounder put it in a mold and you create the influence right away. The next step is sterilization and again historically and for nuclear complications, this was this was being done in the oxygen rich environments, uh which was creating free radicals and that increases the degradation of the surface or it was being done in the enclave, but when you hit up polyethylene, uh you weaken the structure of the polyethylene, so the gold standard again now is to use gamma radiation and do this in an inert environment and that basically improves the work characteristics, but the downside is that it creates free radicals when you use gamma radiation. That's when you create highly cross linked polyethylene, which is the current right here in the manufacturing process is basically a balance between making something that is strong and durable, uh but while minimizing the free radicals, but whatever you do despite the best intentions, there's always gonna be some free radicals, so what are you doing Step four is heating now previously, heat heat heating was done to the point of melting, but that causes weakness in the polyethylene, so what they're doing now is called A kneeling were basically the cycle the material through cycles of radiation and heating it before the melting point polyethylene melts at about 100 and 35 degrees, so with that kneeling, every manufacturer is different, but they heat it up to about 80 to 100 degrees, and they do three cycles of that followed by radiation and kneeling radiation and so on and that is the best balance of maintaining the structural properties of the prolia 30. The final step is packaging, and the reason that is important is because no matter what you do even with the best technology, there's gonna be some free radicals and they react with their so packaging. It is being packaged and then in uh environment, but with time, oxygen can enter the packaging and react with free radicals, and that can lead to degradation of the polyethylene so polyethylene as a material is doctor down, that means it has a large zone of plastic information, as we discussed in the morning, it has a young modules that is similar to bone, and it has low surface hardness and what I wanted to serve here is with uh usually it's combined with steel or a ceramic when steel scratches, it creates those peaks or asperity zor, as we explained earlier, whereas one ceramic scratches, it creates a dip and the actual surface is smooth. So from a theoretical lab point of view, that explains party why ceramic has better polyethylene work now, I use pictures a lot to learn, but I thought it might be best to summarize the key points of hostile license in this slide uh For you guys to take a picture of you watch as well because I think all the questions can can come out and the answer from this slide essentially the key points are the polyethylene particles will be produced no matter what you do you will produce about a billion particles every year, according to some papers, even with the best polyethylene uh structures, and when they enter the joint space, they initiate the osteo license, which is micro face driven, so the macrophages will engulf the particles and they will express interleukin one, prostate gland in the m tnf a one. They will also, these factors will stimulate osteoblasts. The other way that osteoblast are stimulated is because sorry let me do that again, so macrophages will express these uh side of parents and they will stimulate the osteoblasts and it will also produce i 06, so these become two separate pathways of activating the osteo class, so the osteo classes are directed by the Republican six and also by the osteoblast directly, and the end result is that the macrophages directly observable, hope that was clean, so what can we do to reduce uh polyethylene wear, so the first thing is implant alignment and soft tissue balancing, and that's particularly during the knee. The reason for that is if you have high stress over one small contact surface of the polyethylene, it will lead to fatigue, so you want to space out the stress and have an even balance. You want to make sure you don't move any debris such a cement to prevent a description of the body athlete and then when it comes to infants election, we have to be aware of the two modes of failure that are different the commons modes of failure and hips and needs so with hips, It's usually osteal is, is secondary to abrasion, so the process starts with micro abrasions of the polyethylene causing his dialysis and that is why highly cross linked polyethylene is used in hips because it has better resistance abrasion. As I said earlier highly crosslink polyethylene is more susceptible to fatigue and therefore, currently it's not recommended for using need systems, although there are some companies that make it so it needs what you'd like to do is have uh polyethylene that is has better resistance to cyclical loading as opposed to self this abrasion, but ideally you want to have both, so it means you don't want to have a minimum fitness, which is eight millimeters supported, but the important thing to say here is when a manufacturer pose eight millimeters that means when you're looking at the front of the polyethylene, you're measuring eight millimeters, but the actual thinnest point can sometimes be four or five millimeters, so ideally you want to be aiming for 10 millimeters or more on the label um And then in the knee the main mechanism of failures by delamination and what that means is there is subsurface cracking and fatigue of the polyethylene, which can lead to catastrophic failure and ultra high molecular weight polyethylene, it's more resistant to that, so again in the hips, it's the surface of polyethylene that is the weak point and you will use the highly cross linked, whereas it needs its subsurface cracking, and we use the ultra high molecular weight and that is the end of talk. Thank you, thanks panels that um covers polyethylene very well actually um not uncommon for questions about production of materials to be brought up in the m. C. U. Uh personally didn't get anything along the material lines in my basic science, but it obviously lends itself to it quite nicely. Are there any questions that anybody wants to ask panels. No fabulous panels, send me a note if you want um Warren is going to talk to us. Next, If Warren is there, just a second lovely warren is going to cover stainless steel and coal, but crow and then Vicky is going to cover titanium and then we'll have coffee or tea where they fancy yes, thanks for uh So can everyone see the slides yeah great awesome. I'm one of one of the trainees in west of the hospital. I'm just gonna be speaking about metal alloys in orthopedics, primarily looking at stainless steel and cobalt chrome, uh so just some definitions to start with so an alloy is essentially a combination of metallic and non metallic elements, and the ultimate goals when it comes to allowing is to improve the strength, dactyl itty, elastic, elasticity of corrosion resistance, and by compatibility of the material in oughta be ticks, we use three main materials uh these are stainless steel uh cobalt, chrome, and titanium, so the focus is certainly going to look at the manufacturing process as well as each individual materials properties and usage in orthopedics, so when we look at the manufacturing process in a generic way for all of the metallic materials uh they could be split into several stages. Uh This begins with casting, where the liquid metal is essentially poured into a mold uh This is then um stretched by rolling or extending it in a process called routing, Then we go onto a protocol forging, which is essentially manufacturing process to optimize material property, is using pressure and it can either be classified as cold, warm or hot working, and it's all relative to the re crystallization temperature of the relevant material in cold working. The method is forging to a new shape by building it at room temperature, and during this there's an application of a stress level that's below the ultimate tensile strength so there are there will be changes to the properties of the metallic material, but it doesn't break it and from what I understand of it, this essentially shifts the materials stress strain curve to the left there by making it more brittle in hot working uh The material is heated above the personalization temperature, which is usually about 60% of the melting point, and it allows larger defamation to be made without over hardening or fracturing the metal and also as a result, makes it more dark tile and malleable. Um then we move on to shaping it into the required shape and uh then the annoying processes essentially mixing all different elements, whether the metallica nonmetallic and then the product is quenched, where it's immersed in cold water or oil to essentially cool it down and in the final stages, pass ovation, which is something mr shock. Carney touched on earlier and during which there's a layer oxidation, oxidation that's formed and that sits on the outside of the metal essentially makes a resistance to where, and it's very important when it comes to corrosion, so beginning with stainless steel, it's one of the most widely used material when it comes to the orthopedic implants. Um It has a very high modular of elasticity, which makes it very good for brigid construction and that's why we often use it for fracture fixation and stabilization. Historically speaking, um some of the earlier in traumatically nails were made out of stainless steel and most of them were treated. Most of the patient's were treated successfully with these, but they started noticed that some of the patients went into a traffic nonunion, and this was due to the significant stiffness of the steel implants, and this uh this goes back to talking about stress shielding, which was covered earlier this morning from the 19 seventies onwards, steer saying the seal was used more for rigid construction. Also, we're talking about screws and plates and we also began to use highly polished steel when it comes to arthroplasty procedures. Furthermore, what makes stainless feel very good is that it is quite doctor, so you know in theater, you can often uh bend plates, for example to the show if you needed to fit the anatomical structures that your facebook looking at the composition, the most commonly formed stainless steel that we use is 3 16 L um so the three represents 3% of molybdenum 16 is to 16% of nickel and L is to correspond to the low carbon concept, so carbon is what gives a lot of the strength to the material, but it also risks increased risk of corrosion. As a result, you want to try and keep it as low as possible. Majority of stainless steel is iron um and is followed by chromium, which uh owned a chromium oxide layer on the on the surface of the method and helps uh against corrosion and there's also a small amount of nickel uh as mentioned earlier at 16% and also uh manganese and selenium. When it comes to properties of steel, it's very cheap, very strong, and it's tough, it's relatively ductal and has good fatigue resistance. It is however, susceptible to crevice and stress corrosion. It does have a poor way of resistance, and like I mentioned earlier, it does have a very high young, modular, so stress shielding or bone due to superior stiffness as a result of the construct and yeah in orthopedics, we primarily use it for fracture fixations or screws and plates, as well as highly polished family extents like the exeter really force it moving onto cobalt chrome. It's commonly used in bearing surface in metal on polyethylene bearing applications, uh going back into the jailhouse talk. It's also primary seen on metal, metal, hips, and some of the cerclage wise that we use in fractures are also made a more doctor version of the cobalt chrome alloy, the composition of cobalt chrome it's primarily cobalt to make almost two third of the material and is followed by chromium, which again helps with the corrosion resistance, and there are small amounts of carbon and nickel looking at the biological activity um bulk cobalt chrome is biologically inactive. It does contain a small amount of nickel, which can lead to metal hypersensitivity reaction, and a lot of surgeons tend to avoid this material in patients with severe nickel allergy. Um With regards metal, metal, cobalt chrome particles can generate a lymphocyte mediated response and can lead to widespread bony destruction and also the unabsorbed metal debris can lead to super tumors, but it's also important to remember that metal debris induced osteal ISIS, and tunis is not limited to metal metal settings. It can also occur at junctions of the hip stem and hip head and result in funny in osis, and this is because of the relative motion at the junction, creates a similar wear particles that generate the micro particles which result of these osteal issers or pseudo tumors. Uh Cobalt chrome Again, it's very strong, has excellent wear properties, it's very good against resistance, has a very good long term buy, compatibility, and it has a very low notch sensitivity uh From what I understand of that is that if there is a a small scratch your defect on the metal, if for example titanium, it has a high much sensitivity, So if there's a scratch of defect, it will fail, but easily, whereas cobalt chrome is much more resistant to this, but the drawbacks of this is of course it's that it's very expensive and it has a very high uh young module is making it tremendous tremendously stiff and again leads to issues such as sheer stress yielding yeah, that's gonna talk, sorry, it's much shorter than your palaces lovely. Thank you warren any questions for warren around his reading okay. Um You said something about 3168, so why do we not use it or any kind of other stainless steel, I mean that's that's the most commonly available one and the combination of the, of the different elements is the most biological in ertz kind of version you have that's the 316 hour isn't it yeah, so Iggy why wouldn't you use 3168 high carbon uh I don't know actually I was just wondering currently probably any answer, I've been trying to look for it to the high carbon is, uh your risk of corrosion, so you want to try to uh yeah so that's the main thing hmm, and it's 16% nickel isn't it weird. We don't really consent, trauma patient's for nickel allergies, but we consent for elective patient's okay statement or question. Uh. Yeah no it's true, it's true uh One question do we know roughly the incidents of train you know sis, um in patient's, are they going in elective hip replacement uh not off the top of my head. I don't have ms, spacey, not only numbers um number wise off the top of my head. No it's going to depend on what it is that you're using um so it depends on what stem material you're using and then what type of bearing your head is going to be and then also the effect of your head size okay and do we know if there is any greater incidents in combination of cobalt chrome heads with stainless steel or titanium, for example, so what might be the potential problem of using a cobalt chrome head on a titanium stem mm. Anyone anyone risk of corrosion because you're using two different metals. Yeah what kind of corrosion is that SAM galvanic, yeah what is galvanic corrosion uh well why have I chosen the difficulty a catheter, and you know they, there's an electrochemical reaction between the two, which creates where particles yes, a transfer of 11 material to the other. Um The problem is with the biggest electrochemical differences, so um you can minimize that by using those that are closer electro, clinically to others, but the worst one is stainless uh gonna get stainless still on titanium is the worst so the problem with those bearing surface is um is um incompatibility due to galvanic corrosion, so you'll often see if a paraprosthetic fractures being plated. You'll see titanium cables as well as um stainless steel cables available yeah so it's about not causing a mismatch in your metal, So if you're using a titanium un cemented stem, you might want to use a ceramic head and that takes that problem with galvanic corrosion out of the equation, stainless uh chrome, adam, cobalt, chrome, and stainless steel are not drastically dissimilar to one another, so you can get away with it in those situations, but it's still you're still mixing principles, so in an exam, ideally you want to use an exit to taper polish stem, which is stainless still with a stainless steel head. If you're using a metal metal on polly bearing surface, yeah, but ideally to, to avoid the risk for trainee nurses, we we should use ceramic head right, you should use your same or your same metal okay, you're using a big head, so you're putting a 36 metal head on you're better or you'll have less tanyon osis. If you use the 36 ceramic head okay, fabulous, thank you is vicky there, vicky, poor, vicky, is post night, so thank you for agreeing, Vicky sorry I can't hear too well can you hear me very well, can now let me he's going to talk to us on titanium, thanks dot, so it's like I'm going to talk about titanium, I was going to do that iggy, but I don't know how to put sound into presentation and I'm not mr, king, so titania is apparently the fourth waste abundant metal and it makes that 0.60% of the s crust, but it's rarely found in its pure form and typically exists in minerals and it's very costly because of the process that was, is required to isolate it out of those minerals. say the manufacturing process of titanium is apparently called the Kroll process and it's named after a a man called william Kroll who invented it back in 1940 it's got several steps similar to the ones warren. We talk was talking about earlier, essentially extraction, purification, creation of an alloy forming and shaping, and in a bit more detail it kind of looks like this so essentially um they get the titanium your and they convert into what they call a sponge and they do this by conducting an electoral charge through the ore and that's done in the chlorinate er, and this produces titanium tetrachloride and the oxygen is removed from this um causing it to form a liquid titanium tetrachloride, and then they use fractional distillation to purify the liquid and they add either magnesium or sodium to create a metallic titanium sponge. This sponge is then essentially crushed and pressed and then it's melted in an electrode vacuum arc furnace that really really extremely high temperatures, and then each batch which they call an inga is allowed to harden and solidify in the fairness and then it can be made into the things that we use it for so properties of titanium. Its advantages are that it has got a low modulates of elasticity, which is very similar to cortical bone, so it makes it very bio compatible, especially in orthopedics. Um It also forms an adherent oxide coating through self preservation, which makes it resistant to corrosion, which is better than some of the other metals. We've talked about but some of the disadvantages of titanium, it has quite poor resistance to wear um and it generates more metal dha, break than cobble chrome and what do we use it for well. We use it for quite a lot of stuff in orthopedics and these are just some of the examples of how we use titanium and that's it lovely. Thank you, Vikki short and sweet, but it got the point across um any questions for vicky, why are we not going to use a titanium uh femoral head warren, so talked about why we're trying, we've said we've got titanium stem, how we're going to prevent chronic nurses well. Why not just use a titanium from your head. Um I think it probably has a higher risk of lead, isn't it so high risk of where, yeah, so it's likely to feel much, uh so what are the properties that it has that makes it likely to have a highway. Is it the low youngest model, this nope that makes it less stiff, so it has quite high notch sensitivity, yeah that key point for tighter good all right guys, let's have a tea break and then videos very kindly going to speak to us about ceramic and then I'll do a bit on what to do if a patient has hypersensitivities, metals, and then we'll just close up the day with some mcq type questions and some five cases so should we have 20 minutes come back at 10 to 3 thanks guys.