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Okay okay, cool, so I've been asked to speak about ceramics. I'm currently based at West Suffolk, doing hips, So this was a good learning experience for me um as with all the other materials, I'm going to cover composition, how they're manufactured very briefly, how they've developed over time and then properties and uses, but a lot of this has already been covered. So In terms of composition, a ceramic material is made up of metallic and non metallic elements um that are bonded together through kobelev bonds. Sorry this thing is stopping me from being besides. Um we can separate and classify ceramics into those that are bio in it and those that are bio active. So in terms of biona, we include materials including alumina oxen, e um we'll go on to talk about that in a bit and zirconia, bio active An example, B hydroxy appetite, I'm going to talk less about this, but hydroxy appetite is bio active coating, like we can see it in implants um as a coaching, and it's useful because um it's quite good for conduction of austrians and incorporating that material into um its surroundings, so this isn't working for me, hang on mm slides aren't about things that changing for you. It's more drum okay fine so manufacturing, I've split it up into four simple steps, so we start by mixing these ceramic powder with water. We then press it into a prefabricated cast um Then it goes through a process called centering, which is compacting into a solid mass and then applying heat and pressure, and this forms it into kind of one solid object without taking the temperature up to the point where the material go into liquefaction, and then we can then transform it, so we'll talk about transformational toughening in a bit, but we can add additional elements to improve the properties of the final ceramic that we use um. so in terms of development, um there's four generations um so the first generation ceramic ceramic was from the seventies, I think 70 for up to the late eighties, um predominantly made of aluminium and zirconia. Um These ceramics had long centering times, and this resulted in a very poorest material um the grain size of the original powder um and if you look at the cross section, micro cross section of the material, they had very large grain size, so more than five micrometers, and this resulted in crack propagation and fracture um. So to improve this the second generation, which was from the late eighties up to the mid nineties um They had the addition of centering aids so using micro oxidation basically they added calcium oxide and magnesium oxide um and this help to decrease the grain size and they found that there were less incidents of fracture um They develop this further from the nineties up to the mid two thousands um with the third generation, and they improved the manufacturing process through a number of different methods, so ISIS static pressing, laser etching, prove testing, and, and ultimately this created a much smaller brain size, so if the first generation was more than five, this was down to 1.51 point eight, and this massively reduced the rate of cracks um propagation and fracture um and the brand that we talk about is the biologics 40 and now we're up to the fourth generation, so forth generation ceramic, which is from the two thousands onwards um is made up of what we call an aluminum matrix composite. You might see it known as a m c um and that contains predominantly anime um zirconium, and strontium. Um As a result, we have better where properties, the grain uniformity is much higher and even smaller than the third generation, and as a result of the addition of these elements and the change in the proportions that they are found within this ceramic, um we've improved the property so the zirconia is increased the toughness of the material um and helps with shock absorption and therefore reducing crack propagation and I'll talk about that later strong anti in which leads to a platelet formation um and can deflect cracks and again, I'll show images later of this and then um chromium, which increases the hardness of the material um and the brands that we're using now is known as biologics. Day of Delta and you'll have seen that probably on the box is when you're in theater using ceramic implants and there's just a picture there of the micro structure of biologics delta with the elements that I mentioned above sorry I'm developing a bit of a cold um I just thought I briefly mentioned oxen e um um so this is a ceramics ized surface, so it's not a coating, it's classified under the bio, inert ceramics um and it's actually oxidizes zirconium alloy so um it'll be again a combination of those elements, but the surface is exposed to heat approximately 500 degrees um and so we develop a surface layer, approximately five micrometers thick um and that forms a biona bearing surface that we call locks any um and we see this used in a number of implants such as the very last hip or the genesis to knee replacement um and it's quite useful in patients with nickel energy um ceramics in general are quite low in terms of patient's reactivity, um but there are worse outcomes so if they're damaged or scratched when you're you know for instance, and hips. When you're doing your trial reduction, it can lead to catastrophic failure um crack propagation, fracture, and so on I thought I'd talk about properties um the six that I'm going to go over a lot of this has already been covered, um but I just thought I'd show this graph we've already seen it before, so it's a very brittle materials, so we know that there's a small plastic zone before failure, um So I just thought I'd show this picture so that if you had asked to draw a stress during curve for different materials in the exam, this is what ceramic would look like compared to the others. It's a very hard material, which means it's resistant to scratching, and it has a better scratch profile, so again we've already seen this image so as you know metal materials when they're scratched, result in ridges either side disparities and you get peaks and troughs, which can lead to advance where where a ceramic the scratch profile if your ostrich draw in the exam, um you don't get any disparities forming as a result and so the surface will be smooth and the scratch shouldn't be palpable. Um It's also a note we've already talked about this and I mentioned earlier transformation toughening, So this is well the way we can alter the composition of our material to improve the strength and activity. Um We've already gone over what these terms mean, so I won't go into that again, um but this is an example so transformational toughening um with the biologics delta. This has taken this image was taken from that website. Um it's ceramic tech that produced biologs, delta, and these are konia particles effectively act like airbags, so as a crackers propagating through the material. It reaches that particle of zirconia, which absorbs the energy and then stops the propagation of that crack, and then similarly um strong skin forms platelet like crystals, which deflect the energy of the crackers. It's attempting to propagate, so it meets the crystal. The energy is sent in different directions, and it stops the crack from propagating further um so again reducing rates of fracture um five, so it's very efficient so there's a low coefficient friction, which makes it an excellent bearing surface, and then finally it's also wet, toble, so wet ability is a fluids ability to be in contact with a solid um and we can measure this through the contact angle. I quite like the picture on the right of the droplet on the surgical drape there because I think that illustrates what ability in terms of contact angle quite nicely so with a ceramic um The picture on the left demonstrates the hydrogen bonds that formed between the ceramic surface and the fluid, um so it's able to maintain contact, and we've already talked a lot about lubrication, so a lot of the works done for me there. In terms of advantages, we've talked about it's low coefficient of friction um it's hard wetter but etcetera, and so when we're against bearing surfaces such as ultra high molecular weight polyethylene cross linked polyethylene, we find reduced rates of implant failure due to wear induced osteal isis, um So that's not the usual mechanism of failure um They degree the britney particles that are created are so small um that they don't initiate a macrophage response, however, as I've mentioned it's brittle so even with the fourth generation, you're more likely to fracture another complication being squeaking so that's a midrange movement that causes an audible sound that can be heard by the human ear when a patient is weight bearing, um and finally another disadvantage would be stripe worse so again, that's been mentioned before um and that was seen more commonly with 1st and 2nd generation ceramics um And it's just examples of that below. Um I quite like this um this table, because it just summarizes quite nicely um what the main disadvantages of different materials are, and I just thought I would highlight so ceramic on cross linked polyethylene um reduced mechanical properties, whereas ceramic on ceramic is the issues and breakage and squeaking. Um Obviously, a number of our colleagues have already kind of talked about metal and polyethylene and and metal on metal and then uses a bearing surfaces, so obviously we use it in a range of um implants and we commonly see ceramic on polyethylene and ceramic and ceramic and concept thank you video that was actually that was really good. Um Any questions for a video there, so I think that was quite comprehensive for the types of things that you would need to be able to talk about in the exam. Mike you look like you're in deep thought then uh just about whether the you talked about oxen, IEM knee and it doesn't have any nickel in it. It hasn't been actually any reports of people having reactions to nickel in any of the implants ever. I'm in my book. Next oh all right coming, it's a very good question there's not very many answers to it. They're pre, warning for the talk. Any other questions homework for any of you because the coney um um sorry oxy um comes up in my talk. Next, if any of you can find out what the central metal is of the head, let me know because I can't find it anywhere and they don't say on their website, so you have to cross this out of the recording bedroom. Um Yeah if you can find out let me know because I couldn't find out so although it is that surface layer is the oxidized ceramic, I don't know what the metal is in the middle, and I'm intrigued, so if anyone finds out let me know. Uh Thank you video that was really good uh moving swiftly on to metal hypersensitivity mr, finger perfect and oh um oh I didn't push is it still recording yes. It is uh lovely ok, so we're gonna talk a little bit about hypersensitivity, So what happens when you have a patient who has uh can't wear you can, can't wear cheap jewelry for example which is something you see quite commonly in clinic isn't it uh confessions, first though I do not have all of the answers for you on this topic, and there is no guideline formally available for it either, uh so some of this is experience and then others of parts of it is basically common, sensible, is the most sensible or at least harmful thing to do for that patient, so just to put it into perspective. The incidence of sensitivity to these metals in the general population, most commonly, nickel is the most sensitive metal that people will have an allergy to so about 13% of the population and then much lower 2% of the population being sensitive to cold boat and 1% to chromium. So if you actually extrapolate that out to the number of hips and knees that have been done in the n. J. R. As around 364,000 patients in the n. J. Are in theory that potentially have hips or knees with the nickel allergy, 56 thousands that are allergic to chromium and 28,000 that are allergic oh sorry to cobalt and 28,000 that potentially are allergic to chromium, so it's quite a large number of patient, but we don't really seem to have that much experience in how to manage it, So these kind of patient's you might encounter pre op because they say they can't wear cheap jewelry uh It might be that they already know that they're allergic to nickel because they've been tested and it might be that the patient just raises it with you as a question or a query as to what the implant is made of because they've had reactions in the past. Most often, I wouldn't say that it's us as surgeons who pick it up in clinics. I don't think we're particularly asking about it, but more likely uh certainly as a register of the times that I've been involved in it is when a pre assessment nurses email to say that they've asked about allergies and somebody's raised it and probably most of the time you encounter it in your practice. You're actually blissfully unaware of it and so your patient's but POSTOP you might get for example a patient coming back after a knee replacement who has an ongoing painful stiff knee with some swelling and actually with all of the investigations done, you still find no reason for why that knee is painful and actually we should stop and think about whether or not there might be a sensitivity, that's involved patient being unsatisfied with an outcome. Again, it might be that the patient had a suspicion that they were had as nickel allergy beforehand or a cheap metal in in sensitivity and we've gone ahead and use the implants and they're unsatisfied afterwards. When they find out, it's metal multifactorial reasons for these things sometimes POSTOP, I guess you might come across this patient when it's a second opinion, so somebody who's got a painful joint. All of the investigations been unremarkable and they're sent for a second opinion to consider a revision, but no surgical source and so again I wanna point important point to think about in the back of your head if you're giving a second opinion, uh so I'm gonna put this question out to you because I think sometimes we forget that actually sensitivity reactions can come up as a basic science question, so what type of sensitivity reaction is this or immune reaction is this. If you have an allergy to nickel. This is going back to med school days yes. He said that Gideon oh how many other things yeah perfect, So you have your four types of reactions and this is your delayed t cell mediated response okay. Um You should briefly be able to talk through each of those because all of them in some ways can be made relevant to orthopedics, talking about anaphylaxis to the antibiotics and induction things like that good, so as we've already heard today, they're pretty common orthopedic materials that we use, so what are the symptoms was this patient going to come to clinic and potentially complain of after they've had a joint replacement well. They're pretty uh bland symptoms in the sense that there could be anything else so two thirds of them will come in with pain, 20% or one in five of them might have soft tissue swelling around the joint. A third might have erythema around the area of the surgical site, about 20% go on to develop asthma and 20% my iv may even go on to show some evidence of loosening on their x rays due to the soft tissue changes. In a similar way, I suppose to metal on metal hips and our vows you can with these patient's who have got quite florid, hypersensitivity reactions develop a lot of soft tissue production around it and again um this reaction can go on to cause loosening of the implants and ultimately all of these things might look like infection. So the biggest thing in these patient's is to make sure you've excluded infection. If they're POSTOP so, if we take the example of a 55 year old who's two years following a primary hip, they've had rheumatoid and they well, they have rheumatoid and they've never been happy with this hip. It's stiff and painful what are the kind of things that go through your head. N. E. S. T. Three scores want to start off, weren't you still send him great, Thank you, wait a minute around uh yeah go ahead. Mike yeah, uh maybe go through the process that mr joel, went through for the metal or metals to try and find out what type of hip replacement it is and then examine, check some bloods and consider whether you want some further imaging uh is there a problem to do with it. Uh You want blood for infection, but the problem might be with their underlying rheumatological problems. Uh Yes, the blood for infection, cRP, and ESR check it's not some weird metal on metal, but you might want to check that the implants are compatible with each other, yeah that they had the right uh try onion for the stem oh, pardon me, um and then go on and get some further imaging like an mri, yeah, yeah, absolutely so anything in the history. When you're speaking to this patient that you particularly, might be interested in whether it's just their hip that's been stiff and painful or any other joints, mhm, so they're well controlled, Otherwise, so the joint, other joints are fine. It's just this this hip postop hip that's the problem, any history of trauma or other any other allergies, so they mentioned that they do get a reaction to wearing cheap jewelry, so they get kind of a reddish rash around their neck, if they wear a cheap necklace okay, so I guess we're going down the line of what you're talking about, so have they got loosening secondary to their nickel yes, so it might be that the implants become loose. Um You'd be pretty worried seeing a hip that's loose at two years, wouldn't you what in particular about the rheumatoid might be interesting in this point, so if you think someone's got hypersensitive activity to a metal what kind of things might you do to try and confirm that you do practice testing. Yeah do you think a patient with rheumatoid behaves in a similar way uh. Huh, when they have patch testing, imagine it's all over the place uh so it could be um but rheumatoid patient exactly so if you're on an immune modulator, it might affect whether your patch testing works or not. So that's why I put this one in all right, so the key things here are the history you want to know as mike said is this the only joint that's a problem because actually is this just generalized uncontrolled rheumatoid uh what are they on for their rheumatoid, so are they, what are the effects on your next steps for testing okay, so are they on an immunomodulator, are there any symptoms of any infection around the time of the primary surgery or recently because your differential is going to include infection and then were they ever happy with it and then it's become a problem or have they just never been happy with it from the start okay and really in this situation, the the horse has bolted, hasn't it as you've already put an implant in that there, potentially having a hypersensitivity reaction to um and so what are the things in the examination that you're going to look for mm. The main things are going to be the ones that we've mentioned already, so is there any erythema, are there any skin changes that could be signs of eczema or signs from scratching. For example, is there any warmth in the area, are there any systemic signs of or local signs of any infection, so it's as much as looking for uh to rule out this hypersensitivity as well as your differential of infection. You will get your x rays because we know that one in five might have some loosening of the implants, and as mike said, you're going to get some blood stun, mainly looking at inflammatory markers because you're going to want to exclude infection and in this situation mike if I know she's got rheumatoid, but if her bloods came back as showing a raised CRP and ESR would you aspirated it uh let's see if she's systemically unwell, mhm, um you can look at the trend of her bloods, so she would have had some bloods postop. She'd have an idea whether let's say that her crp any s are generally sitting around the 20 thirties, but at the moment her crp is sitting at 60 so I think aspirations reasonable yeah I think so too because at the end of the day this patient is on is rheumatoid and on immune modulation isn't it uh so their chances of infection are higher than somebody who isn't and you need to whenever there's a painful joint that's been replaced. Consider infection don't you so uh to hammer home the point, rule out infection in the first instance and quite rightly I would go ahead and get an mRI scan to look for any uh you know collection or any signs of infection on there or untoward um you could see, for example florid sign of ITIS and that would be difficult in this patient to tell whether that's rheumatoid or hypersensitivity, uh but it would at least give you more information and then if you need to obviously consider your aspiration main thing exclude infection okay. Uh So if we take this patient, she's a 60 year old. She's had end stage arthritis and is listed for a hip replacement. Uh She's on the waiting list and she says to the nurses in uh pre assessment. Uh I've got this rash on my neck. When I wear, I wear this necklace um does it make any difference to me going ahead with my surgery, so what are the types of things that you're going to ask her. Uh you can nominate someone uh early because I can't see who who's still sounding do you want to nominate someone mike anybody there, so I'm guessing you want to do some formal testing before you proceed with a hip replacement right, so what testing options do you have. I think from my point of view, I would involve the immunology Service to get a definitive diagnosis prior to the listening to patient, are you going to a specific tests that a well that's a really good point actually panel, so there are testing available, but how how valid are they is a very good point that. Hopefully, I will also mention a little bit later on um So for this, one obviously things in the history that we want to determine what is it that she's allergic to um so what material is this that she's wearing that she's reacting to what effect it has how long it lasts for, and whether she's already had some formal testing and then has she had any other joint replacement, So why might we be interested in that if she's had her other hip tum and she's happy with it, would you be perhaps less worried or more worried about doing the next joint. It would be reassuring if there's been a yeah probably a month at least yeah, exactly so give it some time. But if she's if she's been quite happy with the chances are that she only has a superficial contact dermatitis perfect good, uh so allergy testing can be done by patch testing, which is the gold standard allergy testing now most read it on day seven uh In terms of, I'm going to show you how it's done, but when they're read their red on day seven and if you read them any earlier than that, about 12% of allergies are actually missed, so um this can be a problem with metal testing because they generally become positive later than early on, so for example, somebody that is allergic to um peanuts. When they have a patch test done, they probably react quite quickly, but the metal sensitivities generally tend to be much later in that seven day window you can have um particularly elderly patient's, they're more likely to have positive results later um and so to bear that in mind that age may have some form of effect on it, particularly when we're thinking about arthroplasty most of the time, our patient's are going to be in that category of patient's and just say beware of those that are on biologics because they may not have the same immune response and so if they're immunotherapy has changed, they may then have more hypersensitivity reactions than if they are when they're on them okay, so it's done by either drawing out or having a drawing um that people a piece of paper that they draw out and label effectively a solution containing the allergen is put onto the skin and just a pinprick through that into the skin to introduce it to the kind of sub dermal layers and it might be that I remember going as a medical student to watch patch testing and being done so actually for some of the fruits, for example, they'll just put a bit of fruit on the back and then poke a needle through that into the skin to introduce some of it but for metro testing, I think they have a solution that they put on and then basically you put a plaster a clear film over them and weight you're seven days and then you're back, for example, might look something like this if you've had a reaction to lots of them, so you have that central welt where the needle has gone in and surrounding erythema. Um These ones are quite easy to say that they're positive aren't they but actually if you kind of get down here into that 10 and 10 that looks pretty negative, but then actually there is a little bit of changes around here is that positive is that negative it's quite difficult and it is to some degree subjective in how they're red because um unless it's very obvious you might say something is negative that's still positive. So these are some examples have been given if you have a blister, it's quite obvious that that is positive this is it just their natural skin color, For example, so there is a risk of false negatives, but there is also a slight risk of false positives if people are overreading, so you have to ever think about what it is that you are going to do in your practice because I think this actually lends itself to quite a nice conversation in the LCF if, in your exam, if it was to come up as a station, um There are no guidelines, but there is quite a lot of evidence talking about the effectiveness of patch testing. There are some other tests that you serum, um but they're quite expensive um and whether or not there any more reliable is still yet to be determined. So uh realistically, you can have hypersensitivity, but we don't know if a certain that causes adverse outcomes in hip replacements, you can have patch testing results unclear so you could be positive and it's missed you could be negative and actually still have hypersensitivity and even if you have a positive patch test that doesn't mean that that hypersensitivity is causing your knee replacement to be painful okay, uh so just to bear that in mind, just because it's positive, it doesn't mean that that person should necessarily undergo a revision, so there are a few things that we can do um to try and minimize them are risks as best as possible and realistically, it does come down to share their decision making on what risk the patient is willing to accept and these decisions should be documented in their clinic letters and in their notes, and I think for me if there's a patient with hypersensitivity. I document what I'm using on the consent form as well, so the first thing I would do is make. I would have offered my patient patch testing for commonly used materials so um nickel, cobalt, and chromium. If they test positive, I would do my best to avoid using those metals sometimes you can't completely avoid it and so you need to minimize content, but then that is a question whether or not that patient's happy to accept that risk and then to gain informed consent specifically to the use of those metals. If you're going to go ahead and use them okay. Um I've put the picture of the skin clips there because it's occasionally forgotten in metal allergy patient's and these are used and I think actually this is the main culprit sometimes for the localized reaction to metals. Um So this is best avoided, then we can think about the harder things that we can change so what kind of stem are we going to use what cup are we going to use um and what bearing surfaces are we going to use to try and minimize the metal exposure to that patient. What's going on here. So um we obviously if you have POSTOP patient coming to us with pain, we're going to exclude the other causes of pain, so around the hip that's going to be infection, that's going to be so s, impingement, for example whether you've got an uncovered cup, the component positioning that might be causing pain, whether you've got an uncemented cup that is not integrated and is loose, or if you've got a uh a septic loosening that's becoming painful. For example, you going to offer patch testing postoperatively, if there are any concerns over hypersensitivity or you've got to the point where you can't find any causes for that pain, and you have concerns that you want to exclude it and if you're considering revising, I personally would put this through an m. D. T. Approach, especially if I have no specific other um surgical source for their pain, because it's very difficult to give a good outcome to that patient without knowing that there's something to target for certain and we know that you might have a positive patch test and that might be a false positive um and to make sure you document that share decision making the use of the m. D. T. Or even a second opinion. If you want and I think if you're going to go ahead and revise you need to be able to reduce the allergen as best possible and I think that that's a really detailed conversation to have with a patient so that they understand they're taking on the risks of a revision surgery and what that involves blood transfusion infection, um dislocation for the potential of just reducing that allergen saying one component, so where are the allergens actually coming from well. Two thirds of the stems that we put in our cemented and these are stainless steel exeter's um and so the nickel content there is around the 15% mark. Are cups are generally either uh polyethylene cemented cups or usually a titanium cups are less likely to be the source of the problem, but if you are putting in a cemented cup and it has a metal orientation on it recently, I did one for hypersensitivity um I don't get to take the metal off or not put it on, so that you at least are reducing it further um And we touched on this earlier, we're talking about metal heads and trunnion. Is you can have cobalt chrome striker heads, and you can also have stainless steel heads so bearing in mind what type of metal you're using and reducing the exposure there depending on what the person is allergic to, so your cobalt chrome heads had about 1% of nickel uh so just to bear that in mind, if you can use, if you use that, you will reduce their nickel exposure, then if you're using stainless steel, but you could argue further why not just use a ceramic and reduce it even further. Um Other sources that we can minimize, I've mentioned already, don't use skin clips because they will have a contact reaction potentially to those. If you're using an unscented stem that you're already using a stem that's titanium which has got a pretty low profile for hypersensitivity reactions and your cobalt chrome over um over things like um stainless steel, which has got the higher nickel levels in, is also better, um but again we've talked about stress shielding there, so you're less likely to see a cobalt chrome and cemented stem available anymore. In terms of your bearing surface, is considering your head, uh you could use cobalt chrome with it's 1% nickel content or you could use a ceramic or even oxen, e, um uh which we've already had a little bout bit about from video okay, and from a cup point of you using a cemented polly is pretty safe or it's got very little metal in. If you remove the orientation wire. If you're using an unscented cup, you've already minimized it, especially can anyway by using titanium, but some people can be allergic to titanium, so being very specific about your patch testing is important. Um In your pre up chats, you obviously want to make sure that the patient understands that patch testing isn't 100% accurate and that they could have false positives or false negatives, so they could base their decision on having a revision on something that isn't entirely, isn't 100% accurate. If you're deviating from your normal practice, are you you're going to use a difference, implant or different bearing surface uh. I think it's probably important just to mention that to them that you are making a compromise on your normal practice um to accommodate for that for that allergy, and that you are minimizing, not completely excluding the use of the metals, and I think really important point to make to them is that actually they may still have unexplained pain. It's very difficult in a revision setting for this um fiber sensitivity to say that you will have completely excluded the the allergen, so this is an oxen IEM head. Um I'll skip through this because videos covered this beautiful already, so it's not a surface coating, it's a ceramic sized metal alloy. I have no idea what the metal is in the middle because I couldn't find out, but it has no measurable nickel, and what I find fascinating is is that this is only five microns deep in that that surface layer, so um you wouldn't think that that would last very long, but it clearly does it has less um where than cobalt chrome, it is less brittle than a normal ceramic, and it has got additional local advantage, where it's less inflammatory uh than other surfaces, so uh ex vivo, they have shown that there's less cytokines produced. This is just the surface layer differences, so if there is meant to be some advantages to using um oxen IEM over standard ceramic heads. Uh In these patient's purely based on this difference in the expression locally, but I think from a hip point of view probably just as easily use a standard ceramic head, but in knee replacements, I think oxen e um has got obviously slightly more advantages to it uh so that's a whistle stop tour of hypersensitivity and what I've picked up on it over the more recent years and you will at some point come across them, but any questions that anyone wants to ask about that. I have one question um so off the record, let's say the safest option would be in a