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Bone Cement for Orthopaedic Exams
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Bone Cement for Orthopaedic Exams
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Language: EN.
Segment:0 .
We'll take it from there. Welcome, everyone. Handover to Firas. OK, thank you, Arthur. So this, we will run it as Viva style question and answer session between me as the examiner. Fortunately, I'm lucky the one, the lucky one and Arthur will be the candidate and lucky candidate.
We have collected the most common question that could be asked about bone cement. About nine questions. It's very unlikely you will be asked anything out of this. So we kept it as try to stay as concise and brief as possible in our answer, and just to give you a framework to build your answer on. This is the topic now. I'm sorry, can you please tell me what is bones to make bone cement or polymer tile?
Metal correlate is a composite material, and it can be described based on its mechanical properties and biomechanical or chemical properties and mechanical properties includes. Where tensile strength, moderate shear strength and strongest in compression, it is brittle. It is not sensitive and a young modulus between cortical and cancellous bone.
It has got viscoelastic properties. Which makes it undergo crepe stress, relaxation and exhibit hysteresis. Thank you. So here clearly, there's no I just want to emphasize there's no clear definition anywhere about what is bone cement, and you'll have to make up a definition in your preparation.
You have to come up with the ready made answer that Assad has given very nicely. What is bone cement? This is the definition. It's very simple. Definition really doesn't sell much. So you can't just say it's a composite synthetic material that's used in trauma and Orthopedics and stop there. You have to add something to it to promote the examiner, to direct the examiner that what cement is and what you want to proceed.
So after the simple definition, which you could see there, bone cement is a composite synthetic material that's used in trauma and Orthopedics as simple as that. Its main component is PMA. So you're showing the examiners that, there are various components. You may be inviting them to ask you, what are the components of different components? So that's the main component.
It has this elastic properties. And also here is showing, you know, the bail you understand and you have a vision about the biomechanical properties of this biomaterial of this material. It functions as a Grout and filler, so you very quickly within three or four sentences, you should the examiners you know what to bone cement is functions, properties and components, main components.
And thus now you won't score any points yet. But this will drive the examiners now into moving into the next question. They know they are facing candidates who quickly within a few seconds give very good definition. Move on now to the next question. Thank you for the good definition. Now, can you tell me? What are the properties of bone cement, please, for the property, then never explained it has got the mechanical properties where it is poor tensile strength, moderate shear strength with strong and compression.
It is brittle. It is not sensitive. It has got young modulus between cortical and counsellor's bone. It undergo crepe stress, relaxation and exhibit hysteresis, which are basically elastic properties. Excellent excellent answer, that's told everything about the mechanics of cement. So again, the examiner can take the question into any direction, but somebody's trying to cover all possibilities.
So we've started the bio mechanical properties of bone cement. It's a elastic material. And here it could go to the elastic properties. So but please straightaway tell the examiner, you know what viscoelastic material is. It exhibits three characteristics we just relax relaxation and hysteresis. And his thesis and then the examiner might then want if they want to.
But I mean, this question is about cement, but they won't want to take you in that direction. Drawing curves and stuff like this. Other properties, it's the other mechanical properties, it has very high compressive strength, very poor tensile, and she sustained the stress strain curve. It's has low stiffness. So it has low modulus of elasticity and the first component of the curve and the second component, it's brittle, so it has does not deform much and it breaks straight away.
So viscoelastic elastic material, compressive strength, low tensile strength, brittle and low stiffness. These are the main biomechanical properties of cement. So we move on. Next question. Arthur, can you tell me what are the clinical indications to use cement? So like every Christian, we'll start big and cement can be used as a Grout or a space filler.
It can be used as for eradication of infection, and it can be. Used to fill wide in born, whether it's osteoporosis, whether it's benign malignancy or whether it's a crush fracture. OK, thank you. So, again, classification for every answer. We have a clear definition.
What what cement is? We have clear bullet points of the mechanical properties and the functions now. We have two main functions mentioned to the examiner straight away. It's used to aid fixation and as a void filler. And then you start talking more about it. I'm sure you can fill these lines. So how it's fixation?
Very important. Make it clear it's a Grout filler. It's not a glue, it's a graph. It fills the gap between the processes and the bone, and it provides mechanical interlocking when it hardens and it sets. That's how thick the AIDS fixation. Grout, not adhesive. So that's the first function, second function is it's a void filler, and that can have many, many indications.
It could be used for cystic bony lesions to strengthen the bony defect. It can't be treated as a void filler to treat osteoporotic vertebral or vertebral fractures. It can't be used if there are bone deficiencies in cases of revision hip replacements. How it work is basically transferring the load from the prosthesis to the bone and acts as stress distributor.
Another indication is it could be used for treat infection as a void filler. If there is an infected cavity in the bone or surrounding soft tissues cement beads, these are the main indications for usage of cement fixation and void filler to achieve various functions, as we outlined here. OK I thought we move on to the questions commonly asked questions.
What are the main ingredients of cement, please? So there are two main ingredients. Again, I'm starting big and going small. Liquid monomer and powdered polymer liquid monomer that has been supplied in a glass wall contains metal metal, acrylic monomer, inhibitor stabilizer called hydroquinone and an activator and dye metal. Be it already, so liquid has got monomer, inhibitor or stabilizer and activate.
The next big heading is powdered polymer that contains polymer granules of PMMA. Inhibitor initiator, benzoyl peroxide and a radio opaque material, zirconium oxide or barium sulfate. Thank you, Arthur. So, again, classification to start with, it's made of two things, as I said powder liquid.
OK, so the examiner that you've seen cement before, you've used it. It might look silly, but it's very important that classify it like that, it's two components powder and liquid, and then you start going into these individually, so the powder. The way to remember is powder. P4p powder is the contains. The polymer powder is Mason contains.
Then we start with acrylic polymer. The powder also contains the radio or pacifier, which can be barium, sulfate or zirconium. The powder contains the initiator of the polymerization like benzoyl peroxide. And you could add in here to the exam, that's the polymerization reduces exothermic reaction, raises the temperature up to 50 degrees. In addition, sometimes not always antibiotic can be added to the powder.
Most commonly aminoglycosides, and also there is a dye that's been added to color it to make it more visible. That dye could be chlorophyll in palico, cement or ethanol and ascorbic acid in CMW cement. So these are the components of the powder. These are most common. My advice is whatever you use and I'm in theaters just out of the box, take the action leaflet that tells you ingredients and read it.
So when you go for the exam, the components of the cement you use. And the second component is liquid, the liquid is colorless. It's packaged in ampoules normally, and it has the monomer. In addition to the monomer, it contains the accelerator and the inhibitor. So the powder has the initiator, the liquid has the accelerator for us, it is colorless.
It's packaged in ampoules and contains the metallic relate monomer. And also the accelerator, and so the powder stops the reaction with the initiator and then the liquid takes over with the accelerator and the inhibitor. OK and obviously, this has proper scientific names. But I think that will suffice if you say initiator, which is I know it is benzoyl peroxide and there is also accelerator inhibitor.
OK, guys, so these are main components of cement. You know, it is very useful for you secure. Part one also for the Viva, this could come. OK our candidate. Can you answer very well about the components of cement, can you now tell us, how does the chemical reaction occurs between this polymer. And the monomer and what's the clinical significance of that?
So the chemical reaction that occurs between the monomer and the polymer is called a polymerization process. The reaction itself is exothermic and it's highly energy inefficient. So 90% of the energy get absorbed through heat. In the polymerization process, the carbon to carbon double bonds are broken down, and a new carbon single bond is formed to give long chain polymers that are largely linear and relatively free of cross-linking.
The reason of this explanation is when it's linear and it's free of cross-linking, it has got a very poor tensile strength, which is one of the properties of the cement. And as you use tensile forces in the cement, it breaks because of no crosslinking and hence this explanation is, is there? And the question is there? Excellent.
Thank you. That's that's very good. And I have to admit, it's not easy concept to understand and you explained it very well. So in summary, there's this process. I mean, you'll be doing well to be, I think, in my opinion, to be asked this question. So the question is now started is, you know, after passing and now you're heading towards good marks.
Yeah, absolutely. So the process is called polymerization. The reaction is exothermic and therefore will produce heat. It's energy efficient reaction. And as the author said, the carbon carbon double bonds are broken into single bonds and forms long, linear polymers. And unfortunately, this polymers don't have crosslinking property.
And that's why cement is weak in shear and tensile and the shear and the shear and tensile forces because of the lack of cross-linking. Between the carbon chains, excellent. So I thought you said that one of the powder components, sometimes antibiotics is added. Can you add any antibiotic or is there specific prerequisites for antibiotics to be added to cement?
So there are a few very important prerequisites for the antibiotics. The most important one, it has to be heat stable as the polymerization process initiate a thermal energy. And if the antibiotics it is heat label, its effect will be canceled by heating, so it has to be heat stable. It has to be a microbial like it covers all varieties of gram positive gram negative bacteria.
It has to have a long, effective period where it can last longer within the tissue and it it does not create too much porosity within the mixture so that it doesn't decrease the biomechanical properties of the cement. So these are the four properties I'm aware of. Thank you. So again, just to recap, main four properties of antibiotics added to the main should be thermally stable.
It should have wide spectrum of action. It has a long Ellucian time of typically gentamicin six to eight weeks, and it should not compromise or have less effect on the mechanical stability of the cement. And you can't count any antibiotics because they could affect the mechanical properties, so these are the main 4 and also could be tested on both part one and part two of the exam.
Great So I thought, you know, you told us about the components, various components and properties of cement. So now what happens when you mix all these components in clinical practice? What are the stages of how does how do they say within the clinical practice? This is called a recurring process, as if you're making a yogurt.
There is a dough time, which is the time when you mix the powder to the monomer and you are mixing it. Then there is a sitting time until the surface temperature is half of the maximum. And then there is a working time on which you can actually put the cement in. This is a difference between the dough time and the setting time. And then there is a working time, which is the last time.
And I think I'm not aware of it. So this is one question I didn't know is you're doing OK so far. So again, that that's the phases of cement setting. There's some controversy about it, a little bit of controversy. And that doesn't matter. Just find a system that works for you. This is a system that I use that I prepared for my exam, and I think this is clinically more practical.
I don't think examiners would argue much with this. So there are many four stages or four phases. Phase first phase is the mixing phase is the first few seconds, about 30 to 50 seconds. Vacuum is used obviously in advanced semantic techniques now to reduce the force and therefore increase the tensile strength of cement.
So first stage is mixing stage two stages, the doughy phase and that start from the beginning of mixing. So that include the mixing time, OK, from the beginning of mixing until the cement becomes any sticky to the fingers. That's the clinical implication of it. And that varies, obviously between cement and cement. And that's during this phase is where mainly the viscosity of cement carries some clinical significance.
So between low to medium to high viscosity cement, it all depends on how it acts during the doughy. The third phase is the working phase, and this working phase also includes the mixing sorry working phase starts after the dose phase. And that's the phase when you actually putting your implant on whether it's a hip replacement, knee replacement, et cetera this working phase or the implantation phase.
So it's from the end of the day, we phase to the. Did that? Yeah, so it starts from the end of the day of the doing phase, and it's normally about six to 7 to eight minutes of cement you use, so you need to know that each phase for the type of cement you use and the many factors that affect the duration of these phases. The last phase is the hardening. It does start from the end of the workweek working phase and could last up to 24 hours.
It's very important and it is one of the principles of Exeter stem, how it subsides into its position in the bone so it could take 24 hours and even more to reach its ultimate strength. I have this diagram I've taken from your Biden's notes. I hope you guys can see. And it is very good reminder of the various phases of cement setting.
It will be there for you to see, but I think this is clinically most practical one that I could find. So again, four phases of cement setting. OK and just to remind you, that's. The only constant time is the mixing time that's controlled by you, scrub nurse. But the rest of them there are affected by many external factors.
Mainly the temperature. Maybe the instrument used to pressurize and stuff, so increase temperature and increased mixing and handling. Of the cement. And will reduce the working time, so if you have a high temperature, if you have. If you have. Nurses who.
And mix by hand a lot that will reduce your working time, and you need to be aware of that, obviously intraoperatively humidity will in contrast, lengthen the down time and and also you need to be aware of that. So these are the extra factors that could affect your cement setting. OK, so I thought, is cement completely safe or any serious complications and serious complications for cement, starting with bone cement implants syndrome, which is the most serious complication, it's rare, but it can cause hypertension for fat embolism, and it can make patients really unwell.
Secondary to the other complications of the cement can include thermal necrosis, either of the bone or the soft tissue around it. Chemical chemical necrosis of the bone tired body where cement mental defects and cement reaction to patients who are allergic to it. They are rare but significant complications and cause problems. Thank you.
I think generally when you proposing treatment and they start to ask you about complications, that means you, you should be doing quite well. So there are various issues that can happen with. The most serious complication is what's so-called bone cement implantation syndrome. And there is no specific definition of this. Syndrome in the literature, because it's poorly understood. However, it's what we know, it's a rare it's a rare but life threatening condition if the kids around the time of implantation of the bone, cement symptoms and signs are hypoxia, hypertension, cardiac arrhythmia and can eventually lead to cardiac arrest.
The exact cause is debatable. And please don't come. The most commonly the most common cause is. Fat embolism causes fat embolism and is thought to be due to increased intermediary pressure. Other possible causes are air embolism.
A exothermic reaction or toxic hypersensitivity or anaphylaxis to the monomer. Now, the next question is then I could ask you. And it is higher order thinking question is, how do you prevent this syndrome? And the way you approach it is again classified. So what anesthetist can do and what the surgeon and the surgical team can do, what the minister can do is this test gives fluid to maintain normal volume and instead gives high concentration of oxygen.
And these are all these steps could be taken by the anaesthetist, by the surgeon. To reduce the risk of fat embolism. And both lavage and brushing of the medial epicondyle of the femur to remove any fat debris that could be pressurized into the bloodstream to reduce the risk of air embolism. It's recommended now to mix in vacuum.
To put the ventilation tube inside the femur. To let any excessive air comes out and to use the retrograde segmentation. Mason and that's also the advanced cementing technique, so retrograde cementing with a gun. And these measurements will all reduce the risk of air embolism. And now we're talking about it.
Just remember also, there is another factor related to hydrogen peroxide usage and the concentration of hydrogen peroxide. Hydrogen peroxide is used for other hemostatic agents to reduce. A bone bleeding and that will allow better Interdigital of cement into the bone. The risk is that it can produce air embolism. And mhra, the MHRA guidance that should be diluted.
OK, we'll move on now again, another high volume question. Other do you know of any radiographic grading system of cementing? So yes, there is Harris modification of Barack's grading system. It is graded from A to D. A is complete whiteout. B is nearly complete with some cortical defect. C is when there is 50 to 99% radial nuisances, or less than 50% radial nuisances, and D is gross deficiency in cement.
For example, there is no cement distal to tip or there is any part of the implant, which is touching the bone. It can be avoided during the errors as the second generation increases from grade 1 generation to fourth generation. So one generation first generation was hand mixing finger packing. Second generation was made.
Plug can all preparation cement gun. Third generation was vacuum mixing, cement pressurization and proximal centralization distal centralization. Fourth generation is all of the above, with distal and proximal prostheses centralization, and that gives even similar mental all around the prosthesis, which is bad at creating a thank you. I thought I have nothing to add to that.
This is the classification, but I can address in front of you. As the author said, it segmentation generation generation also about could be a little bit confusing sometimes, but it's good to be aware of, and it's mainly used for the femur anyway. It's not generic. Um, so it's also a good topic to know, but this is Barack, and Harris is the graphic grading system implementing techniques ABCD from white out.
No distinguishable border between the bone and cement the effects of less than 50% Then he is defects. More than 40% of regulation C and D is either 100% regulation C around the stem or absence of cement distal to the tip of the prosthesis bring in. Now you've done so well, I thought now I'm going to I'm intrigued to know what cement you use and why.
OK, well, so now this is really I'm burning my wings here. It's really high order question. And the only thing I know is bellicose are G. It is widely used. It's been it has various studies available, both in humans and experimental. And it's the old cement I can use. I can think of.
But I'm not. I don't know this question that, well, I'm sorry. That's OK. That's OK. You passed already. But like any other material used in your practice, will you see says trauma implant suturing anything you should have for the exam? Evidence based backup of why you use it.
So answers like that's what I'm normally used, that's the only one I have in my hospital, that's what my boss used. These are all wrong answers have you should have your own thinking and background reasoning because when you become a consultant, you have to use your own implant and materials and justify it. So the cement I use is bellicose.
The reason I use it, it has a high viscosity, so therefore it has short with time. I don't have to wait long time for that. And it has a very good working time. That's the time I need the cement, the implantation time. It has a green, distinct, distinguishable green color, so it's easy to identify if any leaks into the surrounding tissues are relatively easier to find in case, you can see it. It has these four gentamicin antibiotics.
It's very good antibiotics together to cement it as a consistent antibiotic. Release the. Radio pacifier added to it is zirconium, so it could be seen on x-rays. And it is sterilized using ethylene oxide, and this method of sterilization will preserve the mechanical integrity and mechanical properties of the cement.
In addition, as anything to do with implantation of joint replacement, anything like this? MJR, please. These figures are a little bit old, but the inji are a data support, the use of calicoes as the best segment with reduction of revision when used for both drugs and hip replacement and totally replacement, but has a major backup. I'm also aware that pellicle contains traces of peanut oil and therefore has to be could be contraindicated or couldn't be used with caution in people who have peanut allergy.
But whatever cement you use, whatever implants you use, always have an answer to it, and I feel when they ask you this one, that means doing really, really well. And if you ask this question, well, you will be scoring very hard. And I think these are all nine questions we prepared the answer myself.
We don't know that anyone being asked anything about cement out of these main points, to be honest, I think this covers what you need to know. You will pass. I think if you know this information about cement and again, classify. Keep it simple. Scientific and. Just keep talking.
Answer the question to the examiner and don't give them a chance to ask you any awkward questions. As I've said to him that the void is a cavity filler, so it fills a cavity, a defect in the bone and Grout is an interface between the bone and the implant, so it fixes the implant. Yeah, I think that's very good. OK, I can I just clarify that question about how the question I brought up about the hydrogen peroxide for us first before I do that, other demonstrated to everyone very nicely do not answer that last question with I use this and then stop and for us very well demonstrated why you should not do it.
Go to the basic science of what you're using and what you want to talk about. The ideal prosthesis. Talk about the ideal cement. Talk about the ideal anything. You don't have to name a company or a particular product. You just need to talk about what it is you want from the product they want to do and the science behind what you're using now to go back to that hydrogen peroxide.
Just to make you aware the MHRA recommendation for hydrogen peroxide is that it's all prescription for our capacity and that it's at your discretion if you use it. The issue associated with it is that there has been a registered death associated with high dose of hydrogen peroxide use. Its use is multifactorial, correct for us. It is for hemostasis and it is for.
But it's also used as an antiseptic mechanical antiseptic. It kills bacteria by mechanical means. It's also used as a divider of tissue bulk, so it is off work. And as I said, I published a guidance and there is a British society letter sent out in the 2006 2015 reference to that guidance. I'll send it. I'll send it on the telegram group.
Thank you. I think just I found it. I agree what you said, exactly, Sean. And just to add, it's the concentration there is British society and image sharing guidelines about it. But I think the normally in clinical practice, I think the bottle comes in concentration. I think of 6% and the MHRA guidelines, it should be 1.5% So don't let the nurse pour that straightaway into the galley pot, they have to dilute it for you to get the concentration of 1.5% this, you will be breaching the MHRA guidelines, and that's obviously a serious thing.
If you talk about hydrogen peroxide, please mention it has to have 1.5% concentration. So someone asked someone else about hani hani. Albert DC is asking that the pharmacist examiner ask me what happens when the patient with cemented starts weight bearing. So I think the answer to that, I think he's probably trying to point you towards two types of cement prostheses shape closed and force closed to shape.
Closed design is a complex cantilever design, and it rely on friction shear forces between the femoral stem and the surface. And it is. It makes bone and cement one so you can just read bear on it and there is no substance. The force close design, which is the new generation, which we use now, which is the triple taper Exeter Polish stem, it relies on controlled substance or femoral stem component to cause radial compression of the cement so it compress the cement radially and in return it causes, which is resisted by the hoop stress generated within the femoral cortex.
The stem is known to subside in air filled centralism, which leads to low shear stresses and high compressive stresses. So using the cement mechanical properties show on discussing this elastic material of cement and the reason why you use cement in and the reason why your prosthesis is a triple j. Bas status design, you've described it perfectly well. This is OK.
So this is an interesting question. I'll answer to this one straight off. How can you remove cement after if you accidentally drop the stem on the ground? First thing you. Is get lots of cold saline and throw it into the prosthesis and pull as much cement out as you can and then hope that you've managed to take as much as you can saving, saving, taking out as much cement and then you're going to revision prosthesis type techniques.
But one technique you can consider if you've taken not all, but some amount is cement in cement technique. So you need to use a smaller prosthesis, smaller stem, not smaller head, smaller stem. And you can then wait for the original cement you put into cement and then use a smaller prosthesis. The problem with doing that, then, is you've got a massive cement mantle, and that can cause the kinematics of your across the hip replacement to change and higher risk of cement fracture and a loosening of your prosthesis.
The other option is switch to revision mode. And what's the difference between segments of different viscosity? So I know that I know this question because I use cement of different viscosity. So a high viscosity cement is required as a Grout, which is between implant and bone. A low viscosity cement is required as a space filler because sometimes when you're doing osteoporotic fracture, vertebral classes and all the rest you're squeezing cement through small tubes and a high viscosity cement will not flow through those small tubes.
It needs a low viscosity cement. Again, if you're doing a cement to cement revision like Sean described and you have used a high viscosity cement initially, you don't want to use another high viscosity cement straight on. That will fill the whole gap. So you want something that allows you time to fill the gap, and it can go into small areas of defect, which is not, which cannot be filled with a high risk capacity, so low viscosity can be used.
Again, these are very these are plenty of minutia, and I don't expect these things to be answered, but there is a double taper.
Segment:0 .
We'll take it from there. Welcome, everyone. Handover to Firas. OK, thank you, Arthur. So this, we will run it as Viva style question and answer session between me as the examiner. Fortunately, I'm lucky the one, the lucky one and Arthur will be the candidate and lucky candidate.
We have collected the most common question that could be asked about bone cement. About nine questions. It's very unlikely you will be asked anything out of this. So we kept it as try to stay as concise and brief as possible in our answer, and just to give you a framework to build your answer on. This is the topic now. I'm sorry, can you please tell me what is bones to make bone cement or polymer tile?
Metal correlate is a composite material, and it can be described based on its mechanical properties and biomechanical or chemical properties and mechanical properties includes. Where tensile strength, moderate shear strength and strongest in compression, it is brittle. It is not sensitive and a young modulus between cortical and cancellous bone.
It has got viscoelastic properties. Which makes it undergo crepe stress, relaxation and exhibit hysteresis. Thank you. So here clearly, there's no I just want to emphasize there's no clear definition anywhere about what is bone cement, and you'll have to make up a definition in your preparation.
You have to come up with the ready made answer that Assad has given very nicely. What is bone cement? This is the definition. It's very simple. Definition really doesn't sell much. So you can't just say it's a composite synthetic material that's used in trauma and Orthopedics and stop there. You have to add something to it to promote the examiner, to direct the examiner that what cement is and what you want to proceed.
So after the simple definition, which you could see there, bone cement is a composite synthetic material that's used in trauma and Orthopedics as simple as that. Its main component is PMA. So you're showing the examiners that, there are various components. You may be inviting them to ask you, what are the components of different components? So that's the main component.
It has this elastic properties. And also here is showing, you know, the bail you understand and you have a vision about the biomechanical properties of this biomaterial of this material. It functions as a Grout and filler, so you very quickly within three or four sentences, you should the examiners you know what to bone cement is functions, properties and components, main components.
And thus now you won't score any points yet. But this will drive the examiners now into moving into the next question. They know they are facing candidates who quickly within a few seconds give very good definition. Move on now to the next question. Thank you for the good definition. Now, can you tell me? What are the properties of bone cement, please, for the property, then never explained it has got the mechanical properties where it is poor tensile strength, moderate shear strength with strong and compression.
It is brittle. It is not sensitive. It has got young modulus between cortical and counsellor's bone. It undergo crepe stress, relaxation and exhibit hysteresis, which are basically elastic properties. Excellent excellent answer, that's told everything about the mechanics of cement. So again, the examiner can take the question into any direction, but somebody's trying to cover all possibilities.
So we've started the bio mechanical properties of bone cement. It's a elastic material. And here it could go to the elastic properties. So but please straightaway tell the examiner, you know what viscoelastic material is. It exhibits three characteristics we just relax relaxation and hysteresis. And his thesis and then the examiner might then want if they want to.
But I mean, this question is about cement, but they won't want to take you in that direction. Drawing curves and stuff like this. Other properties, it's the other mechanical properties, it has very high compressive strength, very poor tensile, and she sustained the stress strain curve. It's has low stiffness. So it has low modulus of elasticity and the first component of the curve and the second component, it's brittle, so it has does not deform much and it breaks straight away.
So viscoelastic elastic material, compressive strength, low tensile strength, brittle and low stiffness. These are the main biomechanical properties of cement. So we move on. Next question. Arthur, can you tell me what are the clinical indications to use cement? So like every Christian, we'll start big and cement can be used as a Grout or a space filler.
It can be used as for eradication of infection, and it can be. Used to fill wide in born, whether it's osteoporosis, whether it's benign malignancy or whether it's a crush fracture. OK, thank you. So, again, classification for every answer. We have a clear definition.
What what cement is? We have clear bullet points of the mechanical properties and the functions now. We have two main functions mentioned to the examiner straight away. It's used to aid fixation and as a void filler. And then you start talking more about it. I'm sure you can fill these lines. So how it's fixation?
Very important. Make it clear it's a Grout filler. It's not a glue, it's a graph. It fills the gap between the processes and the bone, and it provides mechanical interlocking when it hardens and it sets. That's how thick the AIDS fixation. Grout, not adhesive. So that's the first function, second function is it's a void filler, and that can have many, many indications.
It could be used for cystic bony lesions to strengthen the bony defect. It can't be treated as a void filler to treat osteoporotic vertebral or vertebral fractures. It can't be used if there are bone deficiencies in cases of revision hip replacements. How it work is basically transferring the load from the prosthesis to the bone and acts as stress distributor.
Another indication is it could be used for treat infection as a void filler. If there is an infected cavity in the bone or surrounding soft tissues cement beads, these are the main indications for usage of cement fixation and void filler to achieve various functions, as we outlined here. OK I thought we move on to the questions commonly asked questions.
What are the main ingredients of cement, please? So there are two main ingredients. Again, I'm starting big and going small. Liquid monomer and powdered polymer liquid monomer that has been supplied in a glass wall contains metal metal, acrylic monomer, inhibitor stabilizer called hydroquinone and an activator and dye metal. Be it already, so liquid has got monomer, inhibitor or stabilizer and activate.
The next big heading is powdered polymer that contains polymer granules of PMMA. Inhibitor initiator, benzoyl peroxide and a radio opaque material, zirconium oxide or barium sulfate. Thank you, Arthur. So, again, classification to start with, it's made of two things, as I said powder liquid.
OK, so the examiner that you've seen cement before, you've used it. It might look silly, but it's very important that classify it like that, it's two components powder and liquid, and then you start going into these individually, so the powder. The way to remember is powder. P4p powder is the contains. The polymer powder is Mason contains.
Then we start with acrylic polymer. The powder also contains the radio or pacifier, which can be barium, sulfate or zirconium. The powder contains the initiator of the polymerization like benzoyl peroxide. And you could add in here to the exam, that's the polymerization reduces exothermic reaction, raises the temperature up to 50 degrees. In addition, sometimes not always antibiotic can be added to the powder.
Most commonly aminoglycosides, and also there is a dye that's been added to color it to make it more visible. That dye could be chlorophyll in palico, cement or ethanol and ascorbic acid in CMW cement. So these are the components of the powder. These are most common. My advice is whatever you use and I'm in theaters just out of the box, take the action leaflet that tells you ingredients and read it.
So when you go for the exam, the components of the cement you use. And the second component is liquid, the liquid is colorless. It's packaged in ampoules normally, and it has the monomer. In addition to the monomer, it contains the accelerator and the inhibitor. So the powder has the initiator, the liquid has the accelerator for us, it is colorless.
It's packaged in ampoules and contains the metallic relate monomer. And also the accelerator, and so the powder stops the reaction with the initiator and then the liquid takes over with the accelerator and the inhibitor. OK and obviously, this has proper scientific names. But I think that will suffice if you say initiator, which is I know it is benzoyl peroxide and there is also accelerator inhibitor.
OK, guys, so these are main components of cement. You know, it is very useful for you secure. Part one also for the Viva, this could come. OK our candidate. Can you answer very well about the components of cement, can you now tell us, how does the chemical reaction occurs between this polymer. And the monomer and what's the clinical significance of that?
So the chemical reaction that occurs between the monomer and the polymer is called a polymerization process. The reaction itself is exothermic and it's highly energy inefficient. So 90% of the energy get absorbed through heat. In the polymerization process, the carbon to carbon double bonds are broken down, and a new carbon single bond is formed to give long chain polymers that are largely linear and relatively free of cross-linking.
The reason of this explanation is when it's linear and it's free of cross-linking, it has got a very poor tensile strength, which is one of the properties of the cement. And as you use tensile forces in the cement, it breaks because of no crosslinking and hence this explanation is, is there? And the question is there? Excellent.
Thank you. That's that's very good. And I have to admit, it's not easy concept to understand and you explained it very well. So in summary, there's this process. I mean, you'll be doing well to be, I think, in my opinion, to be asked this question. So the question is now started is, you know, after passing and now you're heading towards good marks.
Yeah, absolutely. So the process is called polymerization. The reaction is exothermic and therefore will produce heat. It's energy efficient reaction. And as the author said, the carbon carbon double bonds are broken into single bonds and forms long, linear polymers. And unfortunately, this polymers don't have crosslinking property.
And that's why cement is weak in shear and tensile and the shear and the shear and tensile forces because of the lack of cross-linking. Between the carbon chains, excellent. So I thought you said that one of the powder components, sometimes antibiotics is added. Can you add any antibiotic or is there specific prerequisites for antibiotics to be added to cement?
So there are a few very important prerequisites for the antibiotics. The most important one, it has to be heat stable as the polymerization process initiate a thermal energy. And if the antibiotics it is heat label, its effect will be canceled by heating, so it has to be heat stable. It has to be a microbial like it covers all varieties of gram positive gram negative bacteria.
It has to have a long, effective period where it can last longer within the tissue and it it does not create too much porosity within the mixture so that it doesn't decrease the biomechanical properties of the cement. So these are the four properties I'm aware of. Thank you. So again, just to recap, main four properties of antibiotics added to the main should be thermally stable.
It should have wide spectrum of action. It has a long Ellucian time of typically gentamicin six to eight weeks, and it should not compromise or have less effect on the mechanical stability of the cement. And you can't count any antibiotics because they could affect the mechanical properties, so these are the main 4 and also could be tested on both part one and part two of the exam.
Great So I thought, you know, you told us about the components, various components and properties of cement. So now what happens when you mix all these components in clinical practice? What are the stages of how does how do they say within the clinical practice? This is called a recurring process, as if you're making a yogurt.
There is a dough time, which is the time when you mix the powder to the monomer and you are mixing it. Then there is a sitting time until the surface temperature is half of the maximum. And then there is a working time on which you can actually put the cement in. This is a difference between the dough time and the setting time. And then there is a working time, which is the last time.
And I think I'm not aware of it. So this is one question I didn't know is you're doing OK so far. So again, that that's the phases of cement setting. There's some controversy about it, a little bit of controversy. And that doesn't matter. Just find a system that works for you. This is a system that I use that I prepared for my exam, and I think this is clinically more practical.
I don't think examiners would argue much with this. So there are many four stages or four phases. Phase first phase is the mixing phase is the first few seconds, about 30 to 50 seconds. Vacuum is used obviously in advanced semantic techniques now to reduce the force and therefore increase the tensile strength of cement.
So first stage is mixing stage two stages, the doughy phase and that start from the beginning of mixing. So that include the mixing time, OK, from the beginning of mixing until the cement becomes any sticky to the fingers. That's the clinical implication of it. And that varies, obviously between cement and cement. And that's during this phase is where mainly the viscosity of cement carries some clinical significance.
So between low to medium to high viscosity cement, it all depends on how it acts during the doughy. The third phase is the working phase, and this working phase also includes the mixing sorry working phase starts after the dose phase. And that's the phase when you actually putting your implant on whether it's a hip replacement, knee replacement, et cetera this working phase or the implantation phase.
So it's from the end of the day, we phase to the. Did that? Yeah, so it starts from the end of the day of the doing phase, and it's normally about six to 7 to eight minutes of cement you use, so you need to know that each phase for the type of cement you use and the many factors that affect the duration of these phases. The last phase is the hardening. It does start from the end of the workweek working phase and could last up to 24 hours.
It's very important and it is one of the principles of Exeter stem, how it subsides into its position in the bone so it could take 24 hours and even more to reach its ultimate strength. I have this diagram I've taken from your Biden's notes. I hope you guys can see. And it is very good reminder of the various phases of cement setting.
It will be there for you to see, but I think this is clinically most practical one that I could find. So again, four phases of cement setting. OK and just to remind you, that's. The only constant time is the mixing time that's controlled by you, scrub nurse. But the rest of them there are affected by many external factors.
Mainly the temperature. Maybe the instrument used to pressurize and stuff, so increase temperature and increased mixing and handling. Of the cement. And will reduce the working time, so if you have a high temperature, if you have. If you have. Nurses who.
And mix by hand a lot that will reduce your working time, and you need to be aware of that, obviously intraoperatively humidity will in contrast, lengthen the down time and and also you need to be aware of that. So these are the extra factors that could affect your cement setting. OK, so I thought, is cement completely safe or any serious complications and serious complications for cement, starting with bone cement implants syndrome, which is the most serious complication, it's rare, but it can cause hypertension for fat embolism, and it can make patients really unwell.
Secondary to the other complications of the cement can include thermal necrosis, either of the bone or the soft tissue around it. Chemical chemical necrosis of the bone tired body where cement mental defects and cement reaction to patients who are allergic to it. They are rare but significant complications and cause problems. Thank you.
I think generally when you proposing treatment and they start to ask you about complications, that means you, you should be doing quite well. So there are various issues that can happen with. The most serious complication is what's so-called bone cement implantation syndrome. And there is no specific definition of this. Syndrome in the literature, because it's poorly understood. However, it's what we know, it's a rare it's a rare but life threatening condition if the kids around the time of implantation of the bone, cement symptoms and signs are hypoxia, hypertension, cardiac arrhythmia and can eventually lead to cardiac arrest.
The exact cause is debatable. And please don't come. The most commonly the most common cause is. Fat embolism causes fat embolism and is thought to be due to increased intermediary pressure. Other possible causes are air embolism.
A exothermic reaction or toxic hypersensitivity or anaphylaxis to the monomer. Now, the next question is then I could ask you. And it is higher order thinking question is, how do you prevent this syndrome? And the way you approach it is again classified. So what anesthetist can do and what the surgeon and the surgical team can do, what the minister can do is this test gives fluid to maintain normal volume and instead gives high concentration of oxygen.
And these are all these steps could be taken by the anaesthetist, by the surgeon. To reduce the risk of fat embolism. And both lavage and brushing of the medial epicondyle of the femur to remove any fat debris that could be pressurized into the bloodstream to reduce the risk of air embolism. It's recommended now to mix in vacuum.
To put the ventilation tube inside the femur. To let any excessive air comes out and to use the retrograde segmentation. Mason and that's also the advanced cementing technique, so retrograde cementing with a gun. And these measurements will all reduce the risk of air embolism. And now we're talking about it.
Just remember also, there is another factor related to hydrogen peroxide usage and the concentration of hydrogen peroxide. Hydrogen peroxide is used for other hemostatic agents to reduce. A bone bleeding and that will allow better Interdigital of cement into the bone. The risk is that it can produce air embolism. And mhra, the MHRA guidance that should be diluted.
OK, we'll move on now again, another high volume question. Other do you know of any radiographic grading system of cementing? So yes, there is Harris modification of Barack's grading system. It is graded from A to D. A is complete whiteout. B is nearly complete with some cortical defect. C is when there is 50 to 99% radial nuisances, or less than 50% radial nuisances, and D is gross deficiency in cement.
For example, there is no cement distal to tip or there is any part of the implant, which is touching the bone. It can be avoided during the errors as the second generation increases from grade 1 generation to fourth generation. So one generation first generation was hand mixing finger packing. Second generation was made.
Plug can all preparation cement gun. Third generation was vacuum mixing, cement pressurization and proximal centralization distal centralization. Fourth generation is all of the above, with distal and proximal prostheses centralization, and that gives even similar mental all around the prosthesis, which is bad at creating a thank you. I thought I have nothing to add to that.
This is the classification, but I can address in front of you. As the author said, it segmentation generation generation also about could be a little bit confusing sometimes, but it's good to be aware of, and it's mainly used for the femur anyway. It's not generic. Um, so it's also a good topic to know, but this is Barack, and Harris is the graphic grading system implementing techniques ABCD from white out.
No distinguishable border between the bone and cement the effects of less than 50% Then he is defects. More than 40% of regulation C and D is either 100% regulation C around the stem or absence of cement distal to the tip of the prosthesis bring in. Now you've done so well, I thought now I'm going to I'm intrigued to know what cement you use and why.
OK, well, so now this is really I'm burning my wings here. It's really high order question. And the only thing I know is bellicose are G. It is widely used. It's been it has various studies available, both in humans and experimental. And it's the old cement I can use. I can think of.
But I'm not. I don't know this question that, well, I'm sorry. That's OK. That's OK. You passed already. But like any other material used in your practice, will you see says trauma implant suturing anything you should have for the exam? Evidence based backup of why you use it.
So answers like that's what I'm normally used, that's the only one I have in my hospital, that's what my boss used. These are all wrong answers have you should have your own thinking and background reasoning because when you become a consultant, you have to use your own implant and materials and justify it. So the cement I use is bellicose.
The reason I use it, it has a high viscosity, so therefore it has short with time. I don't have to wait long time for that. And it has a very good working time. That's the time I need the cement, the implantation time. It has a green, distinct, distinguishable green color, so it's easy to identify if any leaks into the surrounding tissues are relatively easier to find in case, you can see it. It has these four gentamicin antibiotics.
It's very good antibiotics together to cement it as a consistent antibiotic. Release the. Radio pacifier added to it is zirconium, so it could be seen on x-rays. And it is sterilized using ethylene oxide, and this method of sterilization will preserve the mechanical integrity and mechanical properties of the cement.
In addition, as anything to do with implantation of joint replacement, anything like this? MJR, please. These figures are a little bit old, but the inji are a data support, the use of calicoes as the best segment with reduction of revision when used for both drugs and hip replacement and totally replacement, but has a major backup. I'm also aware that pellicle contains traces of peanut oil and therefore has to be could be contraindicated or couldn't be used with caution in people who have peanut allergy.
But whatever cement you use, whatever implants you use, always have an answer to it, and I feel when they ask you this one, that means doing really, really well. And if you ask this question, well, you will be scoring very hard. And I think these are all nine questions we prepared the answer myself.
We don't know that anyone being asked anything about cement out of these main points, to be honest, I think this covers what you need to know. You will pass. I think if you know this information about cement and again, classify. Keep it simple. Scientific and. Just keep talking.
Answer the question to the examiner and don't give them a chance to ask you any awkward questions. As I've said to him that the void is a cavity filler, so it fills a cavity, a defect in the bone and Grout is an interface between the bone and the implant, so it fixes the implant. Yeah, I think that's very good. OK, I can I just clarify that question about how the question I brought up about the hydrogen peroxide for us first before I do that, other demonstrated to everyone very nicely do not answer that last question with I use this and then stop and for us very well demonstrated why you should not do it.
Go to the basic science of what you're using and what you want to talk about. The ideal prosthesis. Talk about the ideal cement. Talk about the ideal anything. You don't have to name a company or a particular product. You just need to talk about what it is you want from the product they want to do and the science behind what you're using now to go back to that hydrogen peroxide.
Just to make you aware the MHRA recommendation for hydrogen peroxide is that it's all prescription for our capacity and that it's at your discretion if you use it. The issue associated with it is that there has been a registered death associated with high dose of hydrogen peroxide use. Its use is multifactorial, correct for us. It is for hemostasis and it is for.
But it's also used as an antiseptic mechanical antiseptic. It kills bacteria by mechanical means. It's also used as a divider of tissue bulk, so it is off work. And as I said, I published a guidance and there is a British society letter sent out in the 2006 2015 reference to that guidance. I'll send it. I'll send it on the telegram group.
Thank you. I think just I found it. I agree what you said, exactly, Sean. And just to add, it's the concentration there is British society and image sharing guidelines about it. But I think the normally in clinical practice, I think the bottle comes in concentration. I think of 6% and the MHRA guidelines, it should be 1.5% So don't let the nurse pour that straightaway into the galley pot, they have to dilute it for you to get the concentration of 1.5% this, you will be breaching the MHRA guidelines, and that's obviously a serious thing.
If you talk about hydrogen peroxide, please mention it has to have 1.5% concentration. So someone asked someone else about hani hani. Albert DC is asking that the pharmacist examiner ask me what happens when the patient with cemented starts weight bearing. So I think the answer to that, I think he's probably trying to point you towards two types of cement prostheses shape closed and force closed to shape.
Closed design is a complex cantilever design, and it rely on friction shear forces between the femoral stem and the surface. And it is. It makes bone and cement one so you can just read bear on it and there is no substance. The force close design, which is the new generation, which we use now, which is the triple taper Exeter Polish stem, it relies on controlled substance or femoral stem component to cause radial compression of the cement so it compress the cement radially and in return it causes, which is resisted by the hoop stress generated within the femoral cortex.
The stem is known to subside in air filled centralism, which leads to low shear stresses and high compressive stresses. So using the cement mechanical properties show on discussing this elastic material of cement and the reason why you use cement in and the reason why your prosthesis is a triple j. Bas status design, you've described it perfectly well. This is OK.
So this is an interesting question. I'll answer to this one straight off. How can you remove cement after if you accidentally drop the stem on the ground? First thing you. Is get lots of cold saline and throw it into the prosthesis and pull as much cement out as you can and then hope that you've managed to take as much as you can saving, saving, taking out as much cement and then you're going to revision prosthesis type techniques.
But one technique you can consider if you've taken not all, but some amount is cement in cement technique. So you need to use a smaller prosthesis, smaller stem, not smaller head, smaller stem. And you can then wait for the original cement you put into cement and then use a smaller prosthesis. The problem with doing that, then, is you've got a massive cement mantle, and that can cause the kinematics of your across the hip replacement to change and higher risk of cement fracture and a loosening of your prosthesis.
The other option is switch to revision mode. And what's the difference between segments of different viscosity? So I know that I know this question because I use cement of different viscosity. So a high viscosity cement is required as a Grout, which is between implant and bone. A low viscosity cement is required as a space filler because sometimes when you're doing osteoporotic fracture, vertebral classes and all the rest you're squeezing cement through small tubes and a high viscosity cement will not flow through those small tubes.
It needs a low viscosity cement. Again, if you're doing a cement to cement revision like Sean described and you have used a high viscosity cement initially, you don't want to use another high viscosity cement straight on. That will fill the whole gap. So you want something that allows you time to fill the gap, and it can go into small areas of defect, which is not, which cannot be filled with a high risk capacity, so low viscosity can be used.
Again, these are very these are plenty of minutia, and I don't expect these things to be answered, but there is a double taper.
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