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Back to Basics: Orthopaedics 101 Femur Fractures Mr Amresh Singh



This course will cover the features and management of hip, shaft and distal femur fractures. It will discuss the deforming forces that affect these fractures and the differences between high energy and low energy fractures. It will also provide an overview of the history of femoral nailing as a method of fixation. Medical professionals will benefit from the discussion of various techniques for reducing and managing these fractures, techniques for identifying associated fractures, and an understanding of the special considerations for each fracture type.
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Series of Orthopaedic lectures and interactive teaching sessions directed at tier 1 level. Delivered by a mix of consultants and registrars, this series of teaching aims to cover the basics of Orthopaedics, including spinal and paediatric cases. Excellent for those who are orthopaedically minded, those studying for the MRCS or have an upcoming Orthopaedic job!

4th session of the Back to Basics: Orthopaedics 101 series. We will discuss the fractures if the femur, including neck of femur fractures, shaft fractures and distal femur fractures. Moreover, we will cover how to treat them, and expected goals of management.

The first session will be given by Mr Amresh Singh,Consultant Revision hip surgeon at NNUH, followed by Mr Benjamin Davies, ST6 Trauma and Orthopaedics EoE.

This session will be recorded, it is interactive, by joining this session you are agreeing that your name, your voice and your image can be included in the recording.

Learning objectives

Learning objectives: 1. Identify sub troch fractures and their causes 2. Describe the different fracture types commonly seen in femoral shaft fractures 3. Understand the deforming forces at play with femoral shaft fractures 4. Analyze the best management strategies for femoral shaft and distal femur fractures 5. Identify possible associated injuries seen in high energy femoral fractures.
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Computer generated transcript

The following transcript was generated automatically from the content and has not been checked or corrected manually.

And I'm going to just carry on, in essence, going a bit lower. So we're going to move into sub troch fractures, which is strictly defined between the lesser trach counter and five centimeters further. And the reason it gets its own, very specific classification is basically, it's a relatively poor watershed area and has a relatively poor blood supply. And as a result, it's not always the greatest bit of your body to want to heal. So that's why it tends to be, you know, get its own little definition, but it accounts for 10 to 30% of all hip fractures most commonly, if it's high energy, it's in people who are young. Um So road traffic accidents, motorcyclists, in particular, low energy, the fall from a standing height. It's obviously an older population. It's also quite a favorite place for tumors to go so often, you know, they are pathological. So 35% of all sub fractures that are diagnosed tend to be pathological and tumor related. It is an area of bone because it's just under in, you know, in essence, it's the bit that transmits the force from the, the neck and the tantric region to the rest of the shaft, the medial side of the uh bone is under quite a lot of compressive force. And the lateral side means it's tensile force. Tensile, basically being the opposite of compression and tensile is being pulled apart. And because it's mostly cortical bone, uh and because of the water shed area in terms of the blood supply, uh it isn't uh the best for healing, as I've mentioned. Um Ben touched upon this already in terms of the deforming forces and you know, it isn't something you just see in a textbook, they do happen very much in, in that regard because of the pull of the abductors, er at which in essence flexes the hip and ab abducts it. So, so as flexes it, um the abductors flex the hip out abduct, the hip outwards and then you've got the abductors which basically pull the shaft in. So getting these reduced is quite interesting. And often we traditionally put a lot of these patients on traction and just to yank and hope that the yanking will allow these things to reduce. But obviously, in cases like this, the more you yank on them often, the more they tend to displace interestingly. So, um in terms of how we reduce these er and surgically manage them, it is quite tricky and sometimes it requires an open reduction or sometimes you have little tools so often, er although you won't see it very much now you definitely don't see auxiliary crutches. You remember the really old fashioned crutches where people would have them under their arm and walk on them. So they'd often used to in the old days, keep one in theater. And when they were doing fractures like this, they would put a crutch and just basically, er, raise the patient right up in the air, put the crutch under the leg and basically lower the patient on the operating table with the crutch under the leg and basically keep lowering them until the fracture reduced um in the lateral plane because in essence, the crutch is pushing up on the femur. So often a lot of these were because you were so low operating, you had to basically try and figure out ways of making your own life easier. Um You uh i it's described that you can use half pins where you basically put in um X fixed pins to use this joysticks, an open reduction. Uh that uh picture at the bottom, er, left is something called the FB bar, uh which is basically er, something that you put around the patient's leg, you can get sterile versions of it and in essence, you yank on it and as you yank, it pushes one side while lifting the other, it goes around the thigh and then it rotates. So the idea is that it either does that or that um so that you can either try and manipulate the uh the fracture. My preferred method is actually pretty much to ignore the fracture not to reduce it, try and get an entry point in the correct plane and then basically, er pass down a reduction finger or a AAA reduction tool where you in essence, use the reduction tool in the proximal bit of bone as a joystick to then line it up and then push it in and once you've lined it up, you can then usually find the end bit of bone, try and reduce it that way. And that's how I tend to, to do a lot of these. Um I do have a relatively low threshold for opening them as well. I don't like long operations and if that just means making an extra cut and visualizing the bone, so you get a better idea of how to reduce it, then I'm, I'm not averse to that at all. Um, shaft fractures are typically high energy injuries. You don't see many shaft fractures in the um, er elderly, but it, it is possible, er, if I mean, often the, the majority, as Ben's mentioned, our neck of femurs and the majority of shaft fractures that you'll see will typically be high energy injuries in again, RT CS, er, or pedestrians, you know, versus cars and things like that. The one thing you have be wary of is that if you have a shaft fracture, there is somewhere between a, depending on the literature, you read a 6 to 8% or all the way up to a 10 to 15% risk of an ipsilateral neck of femur fracture that may not always be evident. Er, and you have to go looking for it in particular. The other thing is that because of uh higher injuries, femoral shaft fractures are a marker of a lot of energy going through your body. And often it can be associated with other life-threatening injuries in the low energy. As I say, you can get it in the elderly, you can get it on a fall from a standing height. And typically, if that happens, it's either because their foot is caught and they've twisted on their thigh bone which results in a spiral fracture or they've fallen on something and in essence, er have given themselves a direct blow in the middle of the femur. Um in terms of patterns, there are typical ones that are described, you'll see these described for the vast majority. But again, in terms of being able to describe them on radiographs, it is worth having an idea of what they are. So, a transverse fracture is just a fracture that's going straight across an oblique is an angled fracture. And a spiral is, as the name suggests, looks like a spiral. But when we look at x-rays, the way you tell the difference between an oblique and a spiral is an oblique fracture. If a transverse is like this, an oblique is about 30 degrees and anything more than 30 degrees is classified as a spiral fracture. Um You can also get segmental fractures, which is basically where you have a completely free floating bit of bone. So the radiograph here is that of a segmental fracture. Um and combi just means more than one piece. So that can apply to other, you know, you can get spiral fractures that are comminuted or you can get simple spiral fractures. And these are typically managed um with femoral nailing or an open reduction internal fixation. But the commonest way to manage these uh particularly uh at the moment is with the femoral nailing, distal femur fractures refers to the distal 15 centimeters of uh the femur um 7% of all femoral fractures uh and 31% if you exclude neck femurs, which obviously makes sense because the femur is divided into thirds pretty much. Um Again, as we've talked about in the past er earlier, it's a high energy or a low energy um bimodal distribution. Uh And again, these are often um fall onto a knee or a road traffic accidents where you get a direct blow, a dashboard injury. Uh and something then basically blows out your uh distal femur. Um in terms of the deforming forces here, what happens is you've got the gastros that tend to act and it wants to pull that fragment down the thigh muscles and the patella tendon basically contract and want to pull the other muscle up. Some of it depends on the fracture pattern. And whether, for example, if the gastro bony attachment has been pulled off as well. But otherwise, if they're often truly distal, then they are just as the, the image shows and you tend to get shortening and anterior displacement of the shaft through the pull of the quads and then the, the gastros pull the other bit down. So as you can, well imagine if you were to put a wedge underneath it to correct this, you'd want something underneath the distal fragment this time. Um So again, what we tend to do in theater is use, some people have a bucket. Um You can get designed wedges. Um You can get, just get bits of general packs or basically bits of towels or gowns that you roll up and anything that you can basically wedge under the leg. So you hang over it, bend the knee by bending the knee. You help to relax gastric anemias and you also help to push that fragment back up again. And as I've mentioned in the past, again, people might use femoral distractors or pins as joysticks, um percutaneous clamps or whatever you might want to try and do to get a close reduction. Um Invariably a lot of these if they're managed with nailing if again, because I have a relatively low threshold for uh messing around. I find that I, I if I've tried and for more than about 20 minutes or so. Can't get a good closed reduction or not enough that I'm satisfied with, then I will open it and just make a hole at the side of the leg because often if nothing else, it's just easier to put the bone back when you can physically feel it. Uh And then you can either reduce it and then put a nail up if that's your choice or indeed to fix with the plate and screws. Uh if that's your choice as well. Um I touched upon this, the neck shaft, er, fractures. It is something just to be very careful of because when you, particularly if you get a, in an interview, er, you just get shown a femoral shaft fracture in someone uh who's had a road traffic accident, almost invariably, almost invariably. Um the scenario will perhaps potentially lead on to a uh an ipsilateral neck fracture as well. And then there's, you know, begs the question of how you might treat it and which ones you treat first and, and things like that, but it's just something to be aware of um other associated injuries, as I've mentioned because they're high energy are patella fractures, acetabular fractures or, or pelvic fractures. So most of the, well, most of our femoral fractures are managed with nailing. Um There were plates that were designed, um they don't really work well in the femur, the femur works, you know, tends to be best managed when you have something going down the shaft of it. And so I'm going to talk to you about the history of, of nailing. And perhaps would you believe it was first found or first described in the 16th century in Mexico where Aztecs were placing wooden rods in the long bones of bony nonunion um in the 19th century. Uh they, well, ber in 18 86 described a paper um using ivory pegs. So in essence, what you do is is you've got the fracture, you move it out the way you pull the bone ends out, stick a peg in one hole, stick it down the other hole and the peg acts like a little nail just to help prevent displacement of your fracture in 9 18 90. Though, I'm not entirely sure how they would have done it. There's also the description of locked ivory nails, er where you've clearly got a hole at each end, but I don't know how they managed to find the hole to put a bit of ivory through or whether they just put a solid bit of ivory down the rod and then drill two holes in the bone and then shoved ivory pegs um through it as well. Uh in the 20th century, um Holand in the USA described using autogenous bone as intramedullary implant. So you basically get a span of cortex, cut it out and you pass the bone down each end of the fracture. So again, you pull out both ends of the fracture site, stick it down one end, stick it in the other end and then you've got your own bone rather than ivory, in essence, spanning across your fracture site. This was in 1917, in World War One Haygroves who probably saved the lives of countless people. Um, described, er, using again a more, quite a bit like a traditional nail but, er, not a short rod, a much longer rod. So what he described is basically making a hole bringing out the fracture end and you get your nail and you basically hammer it through the proximal end until it comes out at the top, realigning the fracture and then hammering it er, back down again. But obviously, these were uh reamed uh nothing, you know, they were just literally rods that you put down again to hopefully prevent displacement. So again, this was World War One, um Smith Peterson in the 19 thirties, although it was called the Smith Peterson Nail. It was probably, er, earlier to, er, er, you know, a kin to a DH s in essence, er, and he described it for intracapsular fractures, but it was at that point called the Smith Peterson nail, which is why I've, I've mentioned it, Gerhard Kucher. Um this chap was born in 1900. He is considered the, the father of um nailing basically. And he originally described er, a V shaped stainless steel antegrade nail in World War two, he was banished to the finish front where he collaborated with local surgeons. And in the 19 forties generated something called the cloverleaf nail, which is the, the picture that you can see down at the bottom. If you perhaps squint your eyes, you can imagine it looks like, er, the three leafed clovers. And the idea was that the elastic recoil provided grip so it would expand once you put it down the bone and it came after some, you know, considerable European interest because what was happening is that you had all these American prisoners of war who were being returned to America, um, with bits of metal inside them. And you can find this article in 1945 by the US Time magazine, which was named the Amazing Thigh Bone, which basically talked about metal rods that were implanted in soldiers that would have invariably saved their lives. But at that point was, um, you know, quite a remarkable thing. I'm very hopeful that this video might work. Um, and it's a, it's on youtube but it's a video of Gerhard Kucher doing a nail. So you can see what, er, what it was like, perhaps for him and bear in mind we have image intensifiers back in his day. You got an x-ray, I mean, a real x-ray and then someone had to go down and develop it and then run back up to see what it was. So it's, you couldn't get lots and lots of films, you just have to maybe get one or two and this is, I mean, how DH ss used to be done where you might get at most one or two x-rays in theater. Um er So again, you can see his image intensifier as well. Nag long or dash lift up. We there K A let me of click to the patient's skin that must hurt. If you keep watching, he will continue to make every attempt to insert the drape inside the patient as well. But um again, so that's his nail that's going down. There you go x-ray to confirm. And I believe that is what is used to expand the nail that puts the bend on it, that our nails come with, but he has to pre he has to bend his Z good and that will be them getting their x-rays. So um I, I hope that was er interesting. I, I, as I say, I do like stuff like this. It's quite fascinating. But so in the 19 fifties, er kno went on to develop flexible rema er that we now all use and this allowed for larger nails, more contact with the bone and interlocking screws. So again, as say, pretty much just developed the whole procedure in the 19 sixties, you have the foundation of the A O. Now, I'm sure you all know about A O classifications and things like that. Now, we always used to think A O was always orthopedics. It's not, it starts with a, a bit GES for osteo synthe FRN. So the German for the association of the study of internal fixation, um and they went very much along the lines of absolute stability, absolute reduction, compression, plating of everything. And at that point for that decade, nails went on a bit of a hiatus. Um but Ke Zel in that time did develop the Ke me nail. Um But I think what was found was that because they used to strip all the soft tissues to get the bones exactly in the perfect position. Um They damaged so much soft tissues that bones would invariably not heal. And 19 seventies onwards, there was a resurgence of um nailing with the increased use of reaming and the use of non Slatter nails and they moved on to titanium and we'll see why. So in terms of the generation of nailing, uh the first generation nails were piriform uh fossa entry. So entry to the top of the uh hip um with proximal and distal locking screws that were aimed to span the femur but nothing into the femoral neck. The second generation allowed fixation into the femoral head, but again, remain at the entry site being the pyriform fossa. Now, the reason that's relevant and the reason why it's changed is um the blood supply, as we know from the pictures that Ben showed us um sit around the base of the capsule. And at the pyriform fossa, the medial and circumflex, femoral have an anastomosis. So, if you make big holes, there, there is a chance that you will damage that anastomosis and lead to subsequent uh avascular necrosis. Um which is why the third generation of nails, the more sort of modern nails that we tend to use, which are er trochanteric entry that fix into the femoral head distally lock but span the entire femur. So that's the picture on the furthest left and even more recent than that um is the lateral entry nail which is very lateral, but it has much more of a bend on it and is typically used in things like er Children. So the petty nail is a lateral entry nail. Simply because if they've got a phy cyst there, you don't want to damage it, the biomechanics of nailing it because this metal rod is in essence going to either be load bearing in your femur. So completely take your weight or load sharing, it needs to be strong. So the reason why you want to put the thickest nail in the biggest nail in is it confers additional strength? So, as you increase the wall thickness, you increase the torsional rigidity by a factor of four. So that's basically um its ability to withstand being er torted twisted or if you increase the nail diameter, you resist the bending stiffness by a factor of four, which again just means that small incremental increases in that diameter lead to much better resistance to the nail, in essence, bending and breaking. And the reason most nails are now titanium rather than steel is because titanium is considered to be 1.5 times or just over 1.5 times stronger, the cross sectional shape of it. So kna described that clover leaf now and the idea was that the open slot would expand to try and fit the canal. But that hopefully the open slot would decrease rigidity, which makes for bones a more, you know, in theory would make it a more favorable environment for it in which to heal the use of interlocking bolts that you put at the bottom basically allows some resistance to axial loading and rotational stability as well. And the only other thing that I'm sure that perhaps those of you who've been to theater and seen it is sometimes one of the things we're always worried about is when we put in nails, we always worry about going out the front of the femur or reaming out of the front of the femur. And that's simply because the radius of curvature is different. So the radius of curvature of an average femur is 100 and 20 centimeters versus that of a nail is 100 and 50 or to 300 centimeters. The way it works out is if you see the curve of that femur, if you imagine I was drawing a circle and I followed on from the femur and just kept following that sort of gentle curve. It would eventually obviously come back upon itself. The radius of that circle would be 1 100 and 20 centimeters. Now, if you can imagine that that nail often has a much lesser curve on it. And so when you draw that circle, it's a much gentler curve draws a much bigger circle. And that's why you get a, a radius of uh anywhere from 100 and 50 to 300. But in essence, we're trying to put something not that bent down, something that is very bent, which is why it doesn't always fit in every patient nicely. The question of reaming versus not reaming. Um so some nails are designed to be reamed, some nails we'd put down reamed on purpose. But the idea behind reaming in particular is that in essence, you're always aiming for the biggest nail that you can get down. In theory, you also help increase the rate of union and increase the periosteal blood supply. So what happens when you first ream in the canal is that you damage the er endosteal blood supply and it gets worse. But the resurgent recovery of it basically allows a better blood supply. In the end, you also help, basically release a bit of osteo conductive elements because you are generating bits of bone that end up lining the entire shaft and decreases hardware failure because obviously, if you've got a bigger implant, it's more rigid and stronger. It's less likely to fail. The downsides are though that every time you put something down that canal, you elevate the pressure. And as a result, you elevate the pulmonary artery pressure, you're more at risk of getting fat embolism and obviously damage to the endosteal blood supply, which if it doesn't come, excuse me, it doesn't come back is a problem. Um There are lots of studies that have shown that reaming helps to increase the time to union. So as I say, very rarely now, would we not consider er reaming a femur? So the main indications for antegrade nailing, which is going from the top to the bottom is as you've seen in the pictures uh basically for the shaft, subtrochanteric regions or the shaft and the neck. Although that is a perhaps a, a different debate, but there are contraindications. As I said, you know, not everyone is designed to have a femoral nail put down them and particularly if you get very significant bow femurs or pats or anything, you know, that just won't look right. Obviously, it's a contraindication to nailing and then you have to somewhat think outside of the box when it comes to um how you're gonna treat it. I mean, the only other things to consider again in poly traumatized patients or unstable patients is the surgical hip, the instrumenting, the canal, the risk of fat embolism and you have to think about whether doing the nailing at that particular time is the right thing to do or whether actually the patient needs to be resuscitated to be settled and then come back and do it. You can get patients with very, very narrow, narrow canal diameters. If they have a super thick cortex and a really teeny tiny canal, then again, the question becomes, can you physically get the smallest implant that you have down in terms of set up? Again? I'm sure if you've come to theater, you've hopefully seen that most people will set up as the A O images have shown where you have an image intensifier, how we'd often set them up for DH SS. The only other reason I've included the picture down at the bottom is some people will do a lateral free hand nail. It's just another technique that doesn't use traction. And again, you know, different trauma surgeons have different er preferences as to how you may choose to set it up. Um The piriform entry as I touched upon when I mentioned, its disadvantage is hopefully, as you can see in that picture, particularly in that bottom left, you can see the blood vessels, er, where they come into the anastomosis. And if you can imagine point B on that top er left, um that is basically where you're going to be drilling a hole. And in essence, that's just the risk of damaging the blood supply. And in counter bar studies, they showed that the medial femoral circum effect artery was damaged in all cases of Perier Ry. And it's just the risk of whether the rest of the blood supply is enough or whether you're uh you're going to be, you know, unlucky and get a VN. The only other thing to consider is you can cause um proximal fractures as well through your entry point at that point, trochanteric entry as the name suggests goes through the very tip of the GT. And the idea is that you avoid the piriform fossa. Er er in theory, er and again, use a guide wire on all to start er making your whole lateral entry points goes a point even further. And as I said, it's considered for the pet nail mostly because it's easy. You don't need to damage the muscles. So you don't split the gluteus medias. So, but again, why risk damaging their ab uh abductors? And again, if you have open growth plates, you would get to avoid those as well. Avascular necrosis following nailing is it's not something we really keep a massive eye on, but it is a definite possibility. I think the reason we worry about it a lot less now in fairness is because of the fact that most of our entry points are now lateral sorry are either lateral entry or RIC entry. But piriform entry nails, you can see the shadows of the nails that have been subsequently removed, but you can see the AVM that's there as well. Um Again, particularly if you were doing it in younger people and adolescents, you have to keep an eye on it because you have an incidence of 3 to 4% in the older population. Now, again, it's not something we would routinely follow up. Um But, and I think that's simply because we've changed our entry points, a retrograde nail, uh in essence, as the name suggests, goes the opposite way. So from the knee uh to the top of the hip, uh where again, the idea is that you are hopefully maintaining in axis fixations. What I mean by that is the bits of bone are all in line. Um Sometimes people use plates to fix these, but because of the pre the shape of the plates, because they're basically pre-made uh based upon an average of what the average human skeleton looks like. Sometimes it can either move, push or pull the distal end of bone in the incorrect position. And so, rather than getting a perfectly reduced femur, you get a femur that looks a bit like an L because one bit of bone has been translated often medially the distal bit. Um in terms of nailing, its indications are for fractures that are lower down. And the reason being that if you imagine if you were going from the top, you wouldn't get much hold just with your couple of bolts down at the bottom. And the, and the worry is that, um, er, you may, you know, you wouldn't have enough bone in which your nail would sit in the distal portion. So you might lose your fixation. Um, in terms of other indications though, even for femoral fractures where you could go either way, some people choose to go retrograde because if you've got a very fat patient who has got a lot of tissue over their buttock, actually, it's much easier to find the entry point to the knee. It is for the top of the hip. So it can be an indication in that regard itself. Some people will do it for um ipsilateral femoral neck fractures. So what you do with that is you treat the femoral neck fracture. However, you might, whether it be a DH S or cannulated screws or a Targo plate and then you run ad a uh then you run your retrograde nail up to treat your femoral fracture so that you're treating each fracture as, as best as it as you could if you have an ipsilateral thumb patella fracture and you're gonna be there anyway. Well, you may as well, you know, just do it through the fracture site from the patella cos you need to be there to fix the patella anyway. And the other indication is if you have an ipsilateral tibia cos again, you're gonna be there anyway, nailing that tibia. So why not just, you know, use the same incision to, to get both entry points. Um, contraindications are sub trop fractures because again, obviously, if you imagine it's now the opposite way around. If you're sending a nail up from the knee up to the top, you'll only have a tiny bit of nail within the proximal fragment. It's just not the right way to do it if you have a very limited knee motion because you've got to be able to bend the knee to be able to do a, a retrograde nail. So, if they've got a very stiff knee, it's a problem if they've got a, a patella bar. So that radiograph there shows a patella that's quite low down. So it's, it's just gonna be in the way you're gonna be fighting it the whole time, er, open feces. And the other indication that I haven't put on there is that if you've got a knee replacement with, er, a, um, a, a basically a very tight groove and you sometimes physically can't get a nail through the, the U, through the condyles of the knee replacement. Um, for those who might have ever done a, a knee replacement, the entry point is exactly the same as to where you put your starter drill. Er, where again you just go at the top of bloom and starts line, er, on the lateral and down the middle of the femur, er, on the A P. Er, and the idea is that you can either drop the knee or have it as most of us would do just over a bar. And then that allows you to not only get your fracture reduction but also find your entry point as well. Uh In terms of the technique, we always want to go above the area of the lesser trochanter, as I've mentioned to you that a sub troch area doesn't have the best blood supply. And if you can imagine if you're tending the nail, which is really rigid within the cortex. But in that slightly weak area of bone, if they have a fall, they're likely to break it. But if you send the nail up above the lesser trach, so that it sits in the medulla in the, in the um can sell us bone, you get better load sharing around that point. So if they were to fall, you're less likely to, to get um uh you're less likely to get another fracture at that point. However, proximal locking is front to back. And so you just have to be a bit careful as to where you uh make a hole because if you can imagine you're gonna be operating not too far away from the femoral artery and nerve and vein. Uh and it's just to be mindful of making sure you know exactly where you are before you send drills down. Um Complications of locking I is uh well, apart from the fact that you're making a little hole and guddle your way down to the bone and it's a long way down at that point in the thigh. You can damage the blood vessels so you can get profunda femoris damage, which can be catastrophic bleeding. Um You can get extra bone formations as well. You can get a decrease in the blood flow to the distal femur and the cruciate ligaments, but that's quite rare I'd suspect. Uh And you can get metal within the Synovium depending on how much uh drilling or how rough you've had to be to get the nail up because if you can leave debris uh within the knee itself, ok. Thank you very much. So, hopefully that was, I know that was a bit of a, a whip through um femur and nailing. Um But if there's any questions, I'm happy to take them, uh or if there's anything you want me to discuss further. Uh Thank you very much, Mister Singh. Um with the thing about the, the a the bow of the femur, I mean, I would understand if we add to the, you know, the very first generation nails that had to be straight due to some mechanical property. But why don't the nails therefore match that femur, femoral curve? It seems like it's almost there but not trying hard enough. So, but it's all based upon implant companies where it, a lot of it is just if you look at thousands and thousands and thousands of adults and you take their, and men, men and women and then you take all their averages. That's what they've come up with. That's what it basically boils down to. It's like, you know, when you get a Precontoured, proximal tibia plate or a wrist plate, we all use the angles that they come with because you just go, well, the implant companies have done their research, but ultimately, it'll depend on perhaps whatever population that they studied and what they feel is the average. But that is literally the example of the average but not everyone is average or most people aren't. So it's allowing them to get the nail down as many people as physically possible. Ok.