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Good morning everyone. Well, it's morning for me. Anyway, I think it's maybe mid-afternoon for me. She's in Bahrain. Um, or early afternoon, maybe. Anyway, I just want to say hello to everyone. It's great to have you on a Saturday. Um Please do pop your questions in the chat for me. She'll get to them at the end of the event. At, at the end of her talk, she'll go through all the questions and answer them all as or as many as we can depending on how, how many you pop in there. Um, at the end of um, our session today, your feedback form will be in your inbox and then once completed, then your attendance certificate will be on your medal profile. Ok. So questions in the chat, we will get round to them. Please don't worry, we will get round to them and we'll answer them at the end. So I'm without any further ado I'm gonna hand you over to May who's joining us from Bahrain. Ok. Thank you ma thank you. Good morning, everybody. Good morning. Good afternoon. Good evening, depending on where exactly you are in the world. Thank you so much. For joining us today. And thank you to medal for this amazing opportunity. I'm very much up for sharing knowledge and uh disseminating knowledge throughout the world. This would help to upgrade and upscale our health care everywhere. And hopefully you'll learn something new today from my talk and I'm sure that I'll be learning lots of things from you from you all. And uh remember that um once you give knowledge, knowledge, always comes back in one form or another, I'll be talking about uh knee imaging today. So we'll, we'll be speaking about fundamentals of knee imaging. I think he is, the knee is probably the most commonly spoken about um uh joints around the body. So it, it's, it's probably a good idea to, to begin with it. So the objectives of this talk today is to learn about normal knee radiographic anatomy. And um uh I, I understand that the talk is mainly about MRI. But in order for us to understand MRI, we need to speak about plain radiographic anatomy. The second thing that's going, that we're going to be learning about is normal knee MRI anatomy. And with this, we'll be learning about examples of injuries. So I'll go, I'll go through structures one by one. And after describing each normal structure, I'll be talking about uh examples of injuries within this. So that's the information sinks in and you get to understand it's better and then I'll move to the next uh structure following that um without nontraumatic conditions on imaging, uh all pertinent to the knee. So, moving on to basic anatomy, the knee is the largest and most complex joint in the body. It is a synovial hind joint in all positions. The femur is in contact with the tibia and the area of contact is large. Therefore providing stability and in all positions, the patella is in contact with the femur through the anterior non weight bearing part of the femur, which is also called the trochlea. The bones do not interlock. So if you look at the knee, uh you you know the bones are overlying each other but they do not interlock. Uh So the stability is maintained by the different ligaments, tendons, the joint capsule and the menisci. So the first thing is uh the first topic is the plain radiographic anatomy of the knee. This is an A P projection of a knee in a skeletal immature or an adolescent uh patient. Um If you note here, this is the distal femur and this is the proximal tibia. We've got the growth plates here signifying or indicating that the patient has still not uh fused his growth plates. Um How do we know medial from lateral, on the A P projection? This is the fibula. So this is lateral and this is medial, this is the medial epicondyle and this is the medial femoral condyle. So the articular surface of the distal femur is called the condyle, whereas the area above it or proximal to it is called the epicondyle. So I've got medial epicondyle, medial condyle and similarly on the lateral projection, there's the lateral epicondyle and lateral condyle, those articulate with the medial and lateral tibial plateaus. And in the center, we've got the tibial spines. So the medial tibial spine, lateral tibial spine. This groove here is called the intercondylar notch because it is uh basically uh situated in between the medial and lateral condyles and overlying or overlapping the intercondylar notch. We could see an element shaped structure which is the patella is probably not well projected or not well visualized on an A P projection, but on lateral, it should be seen better. Uh Nevertheless, it's always important to, to assess for alignment here. And then as we said earlier, we've got the fibula uh naturally and the fibula has to overlap the tibia um on a on a proper A P projection moving on to the lateral projection. So, again, we've got the uh distal femur and we've got the patella, which is much better visualized than a lateral projection. This is the patella articular surface or the patella comes into contact with the trochlea. And the trochlea is actually this white line over here, which is basically uh the sulcus or the groove where the patella articulates or gets in contact with the medial and lateral uh femoral condyles overlie or overlap each other on a lateral projection. Uh this is the tibial articular surface and this is called the tibial tempos. So what do we normally look for on uh plain radiographs? And in addition to the normal, to identifying the normal structures, we need to ensure that they are all well aligned. Uh so that we can understand or we can appreciate whether any post traumatic or even congenital conditions have occurred. And the other thing is to look for um pathological findings like injuries, fractures, and uh soft tissue injuries, and even bony bony tumors, etcetera. In addition to uh bone on x-ray, we are able to appreciate a fat pads. So there are four different path, fat pads around the knee. Uh they're signified by uh indicated by those arrows. So the uh the the the the most superior one is called the pre femoral fat pad because it's in in front of the femur. So pre femoral, there's another one in the back of the femur. So retro femoral, so pre femoral, retro femoral and then around the patella. There are two of those, there's the suprapatellar fat pad which is above the patella and it has this triangular morphology or shape and the infrapatellar fat pad, which is also called hous fat pad, which is identified inferior to the patella and posterior to where the patella tendon is supposed to be. Um these are important to appreciate on x-rays, but they're also more important to appreciate on MRI. Once we touch touch base on that. Um We spoke about alignment on, on um plain radiographs and how to identify and look for all the different structures. So I'll show you a few ki few pieces of pathology so that you understand and appreciate the importance of alignment. Uh This is a normal x-ray and we could, we could see that the distal femur and the proximal tibia are well aligned, but there's a gap in between which is where the menisci and the ligaments uh happen to happen to live. And we can see the patella uh really well visualized here. Whereas in this case, we note that there is massive overlap of the distal femur with the proximal tibia. So this tells us that that there's something happening, something is wrong. And you can see that the patella is not where it's supposed to be. So if we look at the lateral projection of the same patient, we know that there has been a dislocation of the knee. So the entire tibia has moved uh anteriorly and is overlapping the distal femur in a way that is not not correct. So this means that this is considered an anterior dislocation. How do we determine whether it's an anterior or posterior dislocation within the um appendicular skeleton? We always go by the distal structure. So the the distal structure here is the tibia. So the tibia has been anteriorly dislocated in relation to the femur. So this is one important um thing to look for is the, the alignment of the structures. This is another a P projection of the knee. And if we go by the same basics that we've learned, if we look at all the different um anatomical structures, uh we can see the distal femur, the proximal tibia, the the fibula. But do you not anything abnormal? Um If you look closely, this is where the patella is supposed to be. I know the the position is correct. But if we look at the lateral prediction, the patella is totally com comminuted. So there is a comminuted fracture of the patella. Um And if we go back to where to the same x-ray that we look at initially, we could see that there is a lucent line traversing the or like horizontal lucent line traversing the body of the patella indicated that indicating that there is a fracture. So one, once more, we have to identify all the different structures, make sure that we're looking at them carefully and that everything is in position and is in one piece. Is this a fracture? So again, if we look at the patella, there's this lucent line reversing the superior lateral aspect of the patella. And so uh no, this is not. The answer is no, this is not a fracture. This is a normal variant which is called a bipartite patella. So in utero and when uh and like in smaller Children, the patella has got two ossification centers. Uh sometimes one of them may not, the smaller 1 may not uh fuse with the larger one. So it means it remains as a well defined uh round fragment classically or typically over on the um on top of the superolateral aspect of the patella. Uh So that's the location is very important because it's, it's um patho pneumonic. And the other thing is that it's uh demonstrates a thin sclerotic line. So it is a well corticated fragment, unlike the one that we've seen earlier where the fragments are ill defined because they have been acutely fractured. Um These are examples of different fractures that can occur around the knees. So one of the commonest ones are tibial plateau fractures. They can happen for several different reasons, axial loading, like falling far from height, uh motor vehicle accidents and many different causes. Uh These have been classified. So you, you can, you can appreciate here that there's fractures of both the medial and lateral tibial plateaus. And there is an element of displacement and even some fragments over here. And if, if you remember earlier, we spoke about the fat pads, the suprapatellar fat pad is not really clearly seen and we could notice that there is a soft tissue density over here. And uh of course, on x-rays, we always talk about densities whereas an MRI we talk about signal intensities. So there is a soft tissue density over here indicating an effusion. Um There's a specific classification for these types of fractures called the shots classification, excuse me. Um And these are the six different types. So this one is considered as a shot for type five because it involves both tibial plateaus and it's called a bund diar fracture. This is a Coronal reformat image of the same patient uh from a from CT scan that he had. The reason we we we obtain a CT is to identify the different fragments. The amount of displacement or depression. In order for the surgeon to be able to operate on this patient, this needs to go to, to the operative theater and get it fixed. This is another fracture with a type three tsur injury. Again, it only involves one femoral condyle and it's a depression type of fracture. So instead of the condyle appearing as really smooth and well corticated, you could see a huge depression over here and there's probably a fragment that is displaced within the joints whenever we've got a fracture like we saw earlier. Um there's always an effusion. So sometimes you get to see only fluid which is a soft tissue density and sometimes you get to see a fluid fat level. So we can see layering of two different densities, um which is also called lipo hemarthrosis. And um this usually indicates that there is some sort of an intraarticular fracture. So this the fracture could be a cult even on imaging, especially on plain radiographs, but there's always a fracture line um that has to be um looked for, looked for invest or investigated whenever you see a lipo hemarthrosis um moving on to patellar malalignment, which is also a very important uh topic. So the patella, like we said earlier has to articulate with the trochlear groove, which is somewhere around, which is this, this area over here. In both cases, the patella is high riding, but it's much more higher up on the left side, which tells us either that it's a congenital abnormality. But it's again, it's very, very high for that, which is also called patella alta. Um or that there is an abnormality within the patellar tendon because once the tendon gets ruptured, nothing holds the patella to the tibia and it ends up flying higher, higher up and uh articulating with the distal femur rather than the trochlea. So this is called patella alta in both cases. Whereas if the patella is low lying, it's called patella Baha. There are different ways of measuring the alignment of the patella. So we can use the NNS and baty ratio, which is the commonest one used. It's basically a line that traverses the patella um compared to, to a line that goes from the inferior pole of the patella to the uh superior aspect of the tibial toity. The mean is usually one but um anything between 0.8 to 1.2 is normal and there are different uh methods of measuring the patellar alignment, one of which is the modified uh ratio and then the black black burn peel ratio as well. This is the same patient that I showed you the uh the plain radiographs earlier. So yes, the patella is high riding. And if you note that there is um this is the patellar tendon on MRI and the the tendon is supposed to be uh dark all the way. Whereas here you can see that it's right, uh grayish and with some whitish areas. And this indicates a tear of the patella tendon. So this patient was there was a case of patella alta with patellar tendinosis and tear. This is another abnormality that is commonly encountered on plain radiographs. Um Again, if we go back to our basics, distal femur, proximal tibia fibula, patella is supposed to be centralized, overlying the intercondylar notch and aligned with the tibial spines. However, in this case, we know that the patella is lateralized, it's going on to the lateral side of the of the uh joint. In addition, in addition to that, there's a small bony fragment that is seen here. So lateralization of the patella and a small bony fragment usually indicates a transient patella dislocation. So this means that uh the patella has been dislocated to the lateral side of the knee, sometimes it returns back to its normal position and sometimes it stays there uh somehow lateralized. So again, there is a large effusion and this also indicates that there has been an acute traumatic insult to the knee. So what happened? Um the patella is held on top of the trochlea by many different ligaments. The most 12 of the most important ones are the patella retinacula. So this is the lateral patella retinaculum and this is the medial one. And obviously, in order for the patella to go all the way to the lateral aspect of the knee, the medial has to be torn or at least severely injured. So, what's happened in that case was that the tibial, sorry, the medial retinaculum has been torn. The patella went all the way down to the lateral aspect of the, the, the femur and it hit uh the uh or rubbed off on the top of the lateral um aspect of the trochlea resulting in a fractured fragment from the patella itself. So, if you look at this image, we know that there are so many different ligaments holding the patella to its position. And um obviously, this ligament has failed for, for the patella to be on the lateral side. So um moving on to the MRI, uh MRI on MRI, we there are many different structures that we evaluate within the knee. The menisci are amongst the most common followed by the anterior and posterior cruciate ligaments, the medial and lateral collateral ligaments, the extensor mechanism, which is the patella, the quadriceps and patellar tendons. In addition to the fat pads and the muscles. So this is a mal projection. So on MRI, we, we know that MRI is um it's a threedimensional scan where we image patients in three different dimensions AX which is basically like slicing the, the patients from top to bottom and then sagittal which is uh cutting through the sides and coronal which is from anterior to posterior or from the front to the back of the knee. Uh an MRI like we said earlier, we speak about signal intensity. So we say hyperintense, if something was bright or white, uh hypo intense uh if we if something was on the darker side. So this is a me coronal projection of the knee. It's like as if it's an A P projection of an x-ray, the knee x-ray. So again, we've got the medial and lateral epicondyles. We've got the medial tibial plateau, medial spine, tibial spine, lateral tibial spine and lateral tibial plateau. And um we know that there are these triangular structures which are the menisci. The menisci are identified along the medial and lateral aspects of the knee. They're hypo intense or dark on all imaging sequences. They're wider within the periphery and they taper off into the center. Each meniscus has got a body. So this is the body of the meniscus and it's got anterior and posterior horns. The signal intensity of the menisci is the same. And, but the, the shape of the menisci is different on the medial and lateral aspect. So this is the medial meniscus which is uh larger than the lateral meniscus. And this is quite uh quite makes sense because most of our uh weight bearing or loading on the knee occurs along the medial side of the knee. So this means that the medial side has to be larger in order to accept this uh larger load, the horns of the medial meniscus. So there is an anterior and the posterior horn, the posterior horn is usually as uh twice as large as the anterior horn. And this is very important in the context of injury because um once uh once we talk about uh tears, we have to, to appreciate that the posterior horn is quite large and not the same size as the anterior horn on the medial side. And this helps us identify injury easier. Whereas along the lateral meniscus, the anterior and posterior horns are both equal in size. Um in order for the menisci to stay in position, there are so many different ligaments helping them uh to attach. So we got, so this is like an axial uh projection of the menisci as if we're looking at them from the top. So again, here, we appreciate that this is the medial meniscus. It's much larger and it has a c-shaped appearance or morphology which is seen over here. Um It's got an anterior horn, a body. And again, you can notice that the posterior horn has almost 1.5 to 2 times the thickness of the anterior horn. Um the lateral meniscus is o shaped, so it's more uniform, it's smaller in size. And again, there's an anterior horn, a body and a posterior horn. Each menisci are attached both anteriorly and posteriorly via meniscal root ligaments to the tibia. So you get to see those on both sides and both anterior horns are attached to each other through the transverse meniscal ligament. Uh the medial meniscus is also attached to the posterior joint capsule. So there's no gap in between the edge of the posterior horn and the joint capsule. This is very important for stability. But on the other hand, it's um it results in rigidity of the meniscocapsular junction. And this means that this area is much prone to injury. Whereas the lateral meniscus is loosely attached to the popliteal tendon via, via three sets of fascicle which helps the meniscus. The posterior horn of the lateral meniscus be more mobile. In addition to the ligaments described earlier, there are two other important ligaments which are called ligaments of humph free, which was anterior to the PCL or the ligament of sber, which is this black dot posterior to the PC L and they, they run from the posterior horn of the lateral meniscus to the medial tibial um sorry, medial femoral condyle. And their, their basic function is to pull the menisc. The la the lateral meniscus inwards do during flexion during, during knee flexion and this helps to prevent injury. So what do the menisci do? We all know that the menisci are basically shock absorbers. So their, their job around the knee is to uh disseminate or transmit the or take a lot, a large amount of the, the load of the osseous structures. So about 30 to 50% 30 to 70% of the load along the knee is being taken by the meniscus. And that, that is why when people end up with meniscal tears or uh degenerative knee. Um the the there's a, there's a higher load on the osseous structure or on the underlying bones. The other thing is it also provide stability to the knee. So it helps with it prevent, helps prevent excessive knee flexion and extension. It increases the surface area um and stability of the knee and believe it or not, it does help in nutrition. So the vascular supply to the knee is along the periphery and to the to the peripheral third of the menisci. Whereas there's no vascular supply to the internal parts of the knee. And how do does the nutrition reach the other structures, the internal structures uh by movement. So once the menisci moved, they sort of help disseminate the nutrition. I'll explain to you about meniscal tears before we move on to different structures. So there are different tears that may happen around the knee. Some of them are degenerative and some of them are traumatic uh by definition, in order to call anything uh a tear on MRI, we have to appreciate a signal abnormality, which is usually a hyperintensity or fluid signal intensity. So we said earlier that the menisci have to be a flow signal on all imaging sequences regardless of the sequence we perform. Whenever we see a fluid signal or um a hyperintense signal within the meniscus that is similar to the joint fluid. Uh We, we, we need to be concerned about the tear. In addition to the signal abnormality, the t the signal has to be seen in two slices and it has to reach an articular surface. So it has to extend either to the femoral or to the tibial articular surface or to the meniscal capsular junction. So this is called the two slice touch rule. So the tear has to be seen in, it has to be off a fluid signal. It has to be seen on two slices and it has to touch somewhere. Uh The other thing is an abnormal meniscal morphology. So we said earlier that the menisci are almost oti or triangular in shape, the peripheral part is um is straight, whereas the the central part is more tapered off like a sharp edge of the triangle. So if we lose this morphology, we we need to be concerned about the tear as well. So horizontal or oblique tears are one of the commonest tears that you would see either in a usually in a traumatic setting or like a wear and tear type of uh uh injury, but can also be seen with trauma. So what happens is that there's a tear that traverses the meniscus. I always um say it's as if you're cutting through layers of and not vertically but horizontally. So it's basically um like a horizontal signal that goes through and through and into the fibers of the menisci. And it appears here as an oblique or uh horizontal, oblique signal. Again, we know it's it is a fluid signal intensity. So similar, similar to the joint fluid, it touches an artic touches actually both articular surfaces. So it does extend to the tibia and it goes all the way to the meniscal capsular junction. So this is an example of horizontal or an oblique term uh vertical, longitudinal tears. So instead of the horizontal tear going through and through the meniscus, this goes parallel to the long axis of the meniscus and it appears as a signal intensity that goes usually to both sides of uh the articular surfaces to the femoral and the tibial articular surfaces. These are usually post traumatic and they can become unstable. So for example, the tear extends throughout the long axis of the meniscus. And this part flips anteriorly, this is called a bucket handle tear. This is an unstable form of meniscal tears and may result in um knee locking, which requires surgical intervention. So again here, this is the posterior cruciate ligament. And this um low signal intensity structure seen immediately anterior to it within the central part of the knee and to the intercondylar notch, it's actually a displaced bucket handle tear arising from the medial meniscus. So we can see here that the lateral meniscus is clearly seen. Whereas the body of the medial meniscus is much, much smaller. In this case, the rest of the body has been displaced until the inter content a notch. And this is called the double PCL sign. So instead of actually just the um seeing one PCL, you get to see both. And this indicates a a bucket handle tear, radial tears are also very common. They occur along, they usually start at the free edge of the meniscus where the meniscus is the thinnest and they propagate into the rest of the meniscus. Um They may be seen as an area of blunting. So instead of seeing the meniscus sharply marginated towards the central part here, it's blunted. So we know that there has been, there is a missing fragment over this area and it may appear as a gap within the meniscal tissue. So we've got the posterior horn here and then there's this white gap and then the meniscus continues into the body. This is called a ghost meniscus because there's an area that we cannot visualize. And this also indicates a radial tear, uh radial tears can occur close to the root ligament of the meniscus and they're called root tears. If this happens on the medial side along the medial meniscus, this is considered a degenerative tear. Whereas if it happens along the lateral meniscus, it's usually a posttraumatic tear. There's a variant of radial tears which is a little bit hooked and like a parrot's beak. And it's called a parrots, beak, tear tears can be complex. So instead of having either a vertical, longitudinal or horizontal or radial tear, you can have more than one variant happening together. So for example, in, in this uh posterior horn of the lateral meniscus, there's an oblique tear that is pointing towards the uh the posterior aspect. And then there's another one that goes all the way to the meniscal um sorry to the femoral articular surface. And these by definition are complex or multidirectional tears. Uh There sometimes we, whenever we report the tear, we need to, to describe whether it is stable or unstable. So there is a criteria for instability. So by definition, any complex tear is considered an unstable tear because any of those fragments may move and get displaced and dislodged into the joint and result in um the symptoms. Uh The other, the other uh criteria is to have a tear greater than one centimeter, which is usually seen in more than two consecutive slices. So whenever you see a tear extending over more than two slices on a on a scan, then you should, you need to consider it being an unstable tear. And in addition to that, whenever you see a displaced meniscal fragment, this always indicates a um uh an unstable tear. So looking for displaced meniscal fragments is crucial because these need to be identified and uh uh conveyed to the or to the arthropod who's going to perform the arthroscopy in order for them to take them out or fix them. So for example, there is a displaced meniscal fragment over here and it's very easy to see because if you note that's here over the lateral side, the meniscus is clearly visualized, whereas the medial meniscus is not seen, it's actually seen in different bits and pieces. So it's important to identify that there are displaced fragments. Sometimes the meniscal fragments may get displaced into the joint and again, result in locking. But these need to also be identified and reported. Another entity is uh meniscocapsular separation. So if you recall, I've, I've said earlier that the posterior horn of the medial meniscus is adherent to the joint capsule, which is this area over here and this makes it more prone to injury. So in addition to tears happening like vertical, longitudinal tears, um this area can separate as as we can see here and it gets filled with fluid. And this is another, it's it's basically similar to meniscal tears. This also needs to be fixed at times. Um In addition to the the developing tears, sometimes we develop cysts which are large uh structures arising from the menisci. And you can see clear continuity to the anterior horn of the lateral meniscus. Whenever we see a cyst um and and intimately related to a meniscus, this is virtually pathognomonic of a meniscal tear. So even we sometimes get patients on ultrasound, uh investigated for like a a lump or a cystic structure. And whenever you're able to trace it to the to the to the knee joint, you should also request an MRI or at least trace the suspicion of a perennial cyst secondary to a meniscal tear. And the tears are usually um horizontal cleavage in this case, moving on to a cruciate and collateral ligament. So I'm sure everyone each and every one of you have has heard of the anterior cruciate ligament which is commonly injured upon athletes amongst athletes and other individuals. And I think with everybody being um like a fanatic of exercise over the past few years, we've been here, been seeing a lot of ACL injuries recently. So we've got two cruciate ligaments. We've got the anterior cruciate ligament and the posterior cruciate ligament. The anterior cruciate ligament is a uh a strong ligament that runs from the medial aspect of the lateral femoral condyle and inserts into the uh lateral aspect of the anterior of the tibial spine. It traverses the intercondylar node. So you see it through and through going from the distal femur into the proximal tibia. And it's actually made of two bundles and anteromedial and the posterolateral bundles. Uh So this is exactly where the AC L arises from the inner aspect of the lateral femoral condyle. It passes through the uh intercondylar notch. And you could you get to see here that there's one bundle over here and another one over there which gives us, gives it an inverted U shaped or a horse shoe uh appearance. And it, it acts as um a primary restraint to anterior tibial translation. So it prevents the tibia from going anteriorly as much as like uh abnormally an anteriorly. And because it has 22 different bundles, both bundles enter or sort of uh get squeezed uh towards each other in order for it to hold the tibia or prevent it from going anteriorly. And whenever we extend our knee or flex it, there's always an an amount of uh rotation happening. So the AC L is responsible for this um to uh to uh to, to restrain the, the excessive internal rotation and it also prevents, has a minor role in preventing valgus and various injuries. The posterior cruciate ligament is also made of two bundles just going back to the AC L. You can see you, you also get to see the two bundles on the sagittal projection. So this is the anteromedial bundle which is really dark and we've got the posterolateral bundle which is a little bit brighter and you can see that it's made of different fibers. So these are clearly separate even on MRI. Whereas if you look at the PCL, it's also made of two bundles, but it's very dark and uh because the fibers are really well knitted together and they're, they're, they're really tight. The PC L um is stronger than the AC L and it is less prone to injury. So, uh moving on to ACL injury, the ACL um is very commonly injured, I'm sure that um everybody has, has a relative or, or a friend that had or even a, had personally injured their ACL. Um So there are different signs that we get to see on imaging. The commonest sign is or most the primary sign of ACL injury is obviously discontinuity of the ligament. So if we look at the ACL over here, this is the posterior cruciate ligament, but the anterior cruciate ligament can be followed along the um distal part of it or, but until like more proximally, you're not able to see the ligament. So this indicates a, a complete or a full thickness tear of the AC L. This is another case of a cl disruption. I I know that you can see the fibers through and through but the fibers are not normal. Um There are lot, lots of small areas of interruption and even the femoral attachment is not seen. So this is in another complete tear of the ACL. In this case, the ACL is not seen altogether So none, none of the fibers are visualized. And this happens with chronic um a chronic complete ACL tear where the, where the entire fibers are absorbed. And this is called a ghost. Um A CL because obviously, we're, we're fond of ghosts in MS K. Um but it's also called the TY sign. There are secondary signs of an ACL injury that can be seen either on plain radiographs or on MRI the first. And one of the commonest ones is called the deep sulcus sign. So we we've seen earlier that the anterior part of the femoral condyles which articulates with the patella is called the trochlea. So the trochlea is the non weight bearing part of the femur and it accounts for one third of the femoral art like the surface area. The posterior two thirds are the weight bearing parts which articulate with the tibia and the junction between the anterior and posterior parts is called the sulcus terminalis, which is this groove over here. Typically, this groove has to be less than three millimeters in size. So if it gets uh deeper than three millimeters, is called the deep sulcus sign, which is an indication of an ACL injury. The other one is a seon fracture which is an avulsion of the lateral capsular ligament. So there's like a small fracture at the tip of the lateral tibial plateau. If we put these in this information on uh plain radiographs, sorry, an MRI, this is how it looks like on MRI. So you get to see edema at the sulcus terminalis and edema along the posterior aspect of the lateral tibial plateau. So what's happened was that um because the ACL has failed, the uh the tibia has gone and, and we've said earlier that the ACL is responsible for preventing excessive anterior translation of the tibia. So because this AC L has got disrupted, this part of the tibia has hit the, that hit the distal femur and there's a small bump over here with a lot of edema, which is this white or bone bruise, which is this white area. And similarly, this happened along the tibia. So this is called a pivot shift type of injury. The second fracture is also visualized on uh MRI where you get to see that this is where the lateral capsular ligament attaches. And this is the small bony fragments, which is seen here again, this is pathognomonic and the secondary sign of AC L injuries. There are other signs that are uh described only on MRI and not seen on plain radiographs. One of them is buckling of the PC L. So the posterior or the distal sorry, the distant limb of the PC L appears as concave over here. So this is uh considered as buckling. This is a secondary sign of AC L injury, uh disruption of the PCL line. So if we draw a line along the distal limb of the PC L it should in intersect with the distal femur about five centimeters at um at the distal femur. Whereas because of the anterior translation, this does not happen. So this is called the PCL line. Uh anterior tibial translation. Again, we said the ACL is responsible for keeping the tibia in place. So once the ACL goes, the tibia is anteriorly translated. And there this wera line along the tibial plateau and the femoral condyles and and the posterior corner of the tibia, this should not be more than seven millimeters. Whereas here, it's obviously much more than that. So this means that there is an anterior tibial translation going ahead with, this is cover uncovering of the lateral meniscus. So the posterior horn of the lateral meniscus is supposed to be sitting on top of the tib tibial plateau. Whereas here it is uh sort of uh uncovered. Um And this is again another um indication for AC L injury. Um Additionally, we've spoken about fat pads earlier. So this is the infrapatellar or ho fat pad. And then we appreciate a sheer type of injury going through and through the pat the hos fat pad, which is a secondary sign of ACL tear. So speaking about fat pads on, on MRI, uh we've seen them earlier on um plain radiography. So an MRI on TT one weighted images where everything fat is bright, we can see them as bright areas of uh uh or hyperintense areas and on the uh fluid sensitive or fat suppression sequences, these appear as dark. So there's the pre femoral suprapatellar, infrapatellar and retro femoral fat pads. And again, here we've got the patella, the quadriceps and patella tendons. Another very minor sign of AC L injury is buckling of the patellar tendon AC L injuries is also associated with meniscal tears. One of the commonest ones are vertical, longitudinal tears that we've seen earlier where there is a tear uh perpendicular to the long axis of or or parallel to the long axis of the meniscus and extends to both the femoral and tibial articular surfaces. And it's also associated with injuries to the medial and lateral collateral ligaments which we'll see in later on. Um the ACL may not necessarily be completely torn. Sometimes it could be sprained or partially torn and partial tears are a little bit more tricky than uh complete tears. For the reason that they, we're, we're unable to identify uh the disruption of the, the ligament fibers. What we see here is a wavy or irregular ligament and uh the signal intensity is not like what we're used to seeing in, in uh in a healthy or normal ACL. So there are some clues we look for. Like I said, it's this wa view or regular appearance of the ligament loss of the normal uh dark signal at the anteromedial aspect and the fibrillary appearance of the posterolateral aspect. And another sign is that the A healthy or normal A cl has to always be parallel to the roof of the intercondylar notch. So if we draw a line um at the roof of the intercondylar notch, which is called the blumen sate line, this has to be parallel to the AC L. Whereas in this case, there's obviously no alignment. So this again is another in um indication or point to look for whenever we're, we're suspecting an AC L injury or a partial tear, just like anything else in the body. The AC L can degenerate so it can expand and get filled with fluid, which is called either an intrasubstance ganglion cyst formation or mucoid degeneration of the AC L. And it does reme resemble a celery stock um which is uh why, why it's called the ace the Salary stock sign moving on to the posterior cruciate ligament. Like we said, the PCL is twice as stronger as the AC L. So it's half as prone to injury. Um Injuries can occur anywhere in the ligament itself. So the ligament has an anterior limb, a posterior limb and the curve in between is called the genu. In this case, the genu and the proximal part of the posterior limb, sorry, the inferior limb is not, not well visualized, which means that there has been a tear on this area. And in this case, the entire distal limb is not seen and is filled with a cystic structure which indicates that there has been a chronic complete tear of the PC M. Uh sometimes the PC L gets severely sprained. So here we're able to see the entire ligament but the ligament is abnormal in morphology. And sometimes the PC L does not get injured at its substance, but it does get avulsed from the tibia. And this is more common amongst Children and adults tends where the ligaments are stronger than the bones. So instead of the injury affecting the ligament, you can see a bony fragment arising from the attachment of the uh PC L into the tibia. The pattern of injury that happened with the PC L is usually a hyperextension or dashboard type of injury. So this results in kissing types of contusions where you see contusions along the distal femur and the proximal tibia at the same area. So this indicates or this means that there has been a hyperextension um injury where the tibia has rubbed into the anterior part of the femur, moving on to the medial collateral ligament, which is the most important medial supporting structure. The ligament arises from the medial femoral condyle and inserts into the medial aspect of the tibial diaphysis about seven centimeters, distal to the knee joint. It's made of different layers with the, there's the MC L proper, which goes from the distal femur to the tibia. As we said, there's a deep MC L uh component which are small ligaments arising from the meniscus and going proximally into the femur. So the menisc femoral ligament and distally into the tibia. So, meniscotibial ligament show these really thin lines um at holding the menisci, the medial meniscus into the distal femur and proximal tibia. And in between those two layers, there is a bursa, a potential space which is called the uh deep MCL bursa superficial to the MCL proper. There's another bursa called the superficial MCL bursa. And these are potential spaces that only get filled during inflammation or traumatic conditions. Additionally, the pes and, and tendons which are three tendons uh arising from the poster poster medi aspect of the distal thigh enter to one or overlap with the MCL and therefore, providing a third layer of stability at the median uh aspect of the knee, there are three different levels of injury to the MC L. So the first one is uh is considered as a sprain and it's called a medial sorry, an MC L sprain or a grade one injury, you could see that the ligament is completely visualized but appears abnormal. Um and especially like there's this fluid signal intensity and superficial bursa on top of it. So this is considered as grade one injury. There could be a partial thickness tear of the ligament. So part of the ligament is visualized here which is also abnormal, but the rest of it is not. So this is a grade two or a partial thickness tear of, of the ligament. Whereas in this case, the entire proximal attachment is not visualized and is replaced by thick, irregular soft tissue. So this is a grade three or a complete tear. The lateral collateral ligaments are four different structures uh from anterior to posterior. It's the iliotibial band and the popliteus tendon which arises. So the Popliteus muscle is probably the only muscle in the body which has the, the muscle distally and the tendon proximally. So the muscle is around in, in this area overlying the dorsal aspect of the tibia where the tendon attaches to the femur. And then we've got the fibular collateral ligament and the biceps femoris tendon and identifying those tender structures and making sure that they're all normal is very important in stability. So many different things can happen to those ligaments similar to the medial collateral where you can get a sprain or a tear of the ligaments. Um This is a tree from my country, Bahrain. It's, it's called the tree of life. So it's just a break and just relax your eyes for a bit. Um It's found in the middle of the desert and it's been there for at least 400 years and it, it has no known water supplies. So a lot of people consider it as a miracle and they come to, to see it. And I think it just tells you how strong and resilient creatures on this earth are and like whenever there's a will, there's always a way we should all be all be strong and resilient like this tree, but also be flexible like its leaves and um and just uh try to accommodate whatever difficulties we face in life. So we've covered the traumatic conditions around the the knee. I think we're running out of time, but I'll, I'll go through nontraumatic conditions because not everything that happens around the knee is, is about trauma. I'll talk about infective, inflammatory and tumorous conditions as well. Uh This is a case as one of my colleagues um has encountered, this patient is um is a young boy, four years old with congenital sensitivity to pain and he did develop a fracture at his um at his grand his growth plate. And you can see that there's a lot of new bone formation. So again, distal femur, proximal tibia fibula, um the growth plate is abnormal, it looks like it's widened and there is this uh line visualized over here and there is a lot of uh bone formation. So he did have a fracture but a few um um I think a few weeks later, he did, his condition did worsen. And in addition to the fracture, you can see that there's a lot of soft tissue swelling around the knee. So he did have an MRI scan. This is a T one weighted image. And how did we know that? Because the fat is really bright and uh this is a tt two fat suppressed image. So the reason we do fat suppression is to um have all the fat dark in order for anything fluid or inflammatory to, to um show up. So, t one is always our friend, although a lot of people do not like it, but it's really very important to look at T one. So this is the patient's right neck and you can see that the, this is the normal uh signal of a healthy um tibia. It's very bright, it's it's no normally bright. Whereas here you get to see some really dark areas identified. So this indicates that there is a pathological condition going on either an infection or a tumor. So, if we go to the um fluid sensitive sequences, we know that there is a fluid track or sinus tracking along the fracture line and extending through this area um distally. And in addition to that, there is a lot of uh surrounding soft tissue abnormality. This is a sagittal image of the same patient. And um we could see the same signal intensity here. And this is a post contrast scan indicating um solid enhancement of the soft tissues, but no enhancement of this area, which is an intra um osseous abscess or uh a collection within the fracture site. So this is a case of osteomyelitis on top of a fracture. Uh This is another case with soft tissue infection. So this is an uh an adult uh patient which came with diffuse swelling of his uh of his lower limb. And you can see the contralateral side being normal with normal fat suppression and normal thickness of the subcutaneous fat. Whereas here we appreciate diffuse abnormality and edema of the subcutaneous fat. And obviously, there is a huge discrepancy in the diameter of the soft tissues. Uh post, post contrast, there's um there are areas of enhancement and non enhancement of the subcutaneous tissues. So this is cellulitis. This is another patient who who had AC T scan. This was a really, really sick patient and, and admitted to the hospital, I honestly forgot what was wrong with him. But uh obviously, you could see that there are multiple specs of air within the soft tissues and muscles of the patient. And this is necrotizing fasciitis, which is a serious and life-threatening condition if not uh treated. So, whenever we see subcutaneous air uh in a sick patient, we should consider uh necrotizing fasciitis, which is a surgical emergency, but not all areas bad or abnormal. If the patient had a recent surgical intervention, like this patient who had a total knee replacement, we're expected to see intraarticular and subcutaneous s air for up to 10 days POSTOP. So this is not considered as an abnormal uh pathological condition, moving on to inflammatory conditions. This is another young boy who presented with uh uh right knee swelling. So you could see sorry, left knee swelling. So we can see that the left knee is swollen, we're unable to see the normal uh location of the patella and the surrounding soft tissues. He did have an x-ray which showed the few soft swelling surrounding the knee, um osteopenia. So the bone density is reduced and a large effusion. So, radiographs are important in the context of uh of inflammatory arthritis. And the early the early findings are soft tissue swelling, joint effusion and osteopenia. Again, osteopenia is nonspecific but it it needs to be considered or looked into. Uh later findings on pain, radiography are bone erosions, joint, space, narrowing and growth disturbances. And whenever growth disturbance happens, unfortunately, this is irreversible. So this is why it's really important to detect inflammatory arthritis earlier and to be able to treat the patient. This is an MRI case of uh inflammatory arthritis. So you get to see that there is an effusion which is this white area around the knee. And these really low signal intensity or tiny black dots which are, which are r by these uh secondary to inflammation. These areas. Uh Upon contrast administration appear, the synovial enhancement is thick and irregular. So this um so this is how a normal synovium is supposed to look like post contrast really thin and linear. Whereas here it appears nodular which tells us that there is a synovial process going on. In addition to that, there is this depression over here and uh which is an erosion. So, marginal erosions with right body sino Vitis and osteitis or inflammation of the bone. So this is a case of inflammatory arthritis, most likely rheumatoid. This is how rice bodies look like on uh on MRI. This is another case of um this is a case we rarely encounter, but there are so many different and interesting findings in this patient. Obviously, the growth plates are still open. So this means that they, this is a child and we still cannot see the normal morphology of um the the the the distal femur appears abnormal. In in addition to that, we see those wide horizontal lines seen along the the distal femoral and proximal tibial uh with the diaphysis and these are called growth arrest and recovery lines. So the reason for these lines to uh to happen is that whenever a patient undergoes or encounters a uh an episode of severe illness, the entire growth within our body stops. So th this is, it's exactly like the lines we see around in trees. So almost similar uh whenever the growth stops, these lines form and then when growth continues, it just keeps on going and again, it stops whenever the patient gets really sick again. So whenever we see these lines, we know that this patient has undergone some areas of severe stress. In addition to that, we see these sheet like areas of calcification within the soft tissues and the muscles on both sides. These are also we also seen in the patient's hand and these are almost pat mnemonic of uh um a medical condition. Again, this is an MRI scan of the patient and we get to see edema and areas of low signal intensity within the muscle. So there there's sheet like deposition of calcification within muscles and soft tissues. And this is in keeping with scleroderma or systemic sclerosis moving on to tumors. Um This is another patient whose uh skeletal immature may be about around 16 or seven, maybe 15 years of age. If we note here there, this is the distal femoral. So, diaphysis metaphysis, epiphysis within the distal femoral diaphysis. There is an, there's an abnormality. So the bone appears distracted and the pattern of destruction is ill defined. So you can't really delineate. Where did it start and where did it end? It's not very clear. In addition to that, um we know it's periosteal new bone formation and the periosteum appears straight over here and then it goes and gets elevated or lifted. So this is called the Codman triangle. And whenever you see a Codman triangle of periosteal abnormality, you should always think of a sinister or an aggressive bony lesion. And the reason for the Codman triangle to happen is that there is a lot of cellularity or soft tissue formation deep to the periosteum that keeps on pushing any periosteal uh bone that is being formed. And if we look at the lateral projection, there is this soft tissue density over here and even along the posterior part of the knee, which is displacing the normal knee structures. So aggressive bony lesion with periosteal bone formation and soft tissue signal. The number one thing that comes into our mind is an osteosarcoma. This patient did have an MRI scan. And again, as we said earlier, once the MRI, the T one is really dark, you should always think of something sinister, either a severe infection or an o a malignant or an uh uh pathological condition. So, this is um again, disruption and disruption of the medullary cavity with the soft tissue signal. And this is where the Codman triangle was. Um all of this was a soft tissue mass that demonstrated enhancement with enhancement of the intramedullary cavity and some areas of necrosis. So, this was an osteosarcoma. This is another osteosarcoma and they, they typically occur along along the distal femur and the posterior parts of the knee. You could see that there is massive uh uh uh bone formation which appears irregular and uh there is an associated soft tissue component. So this was an uh another osteosarcoma that was seen, not all bony tumors are malignant. Some of them are benign but still need to be uh monitored and watched. So again, this is an excessive uh deformity happening around the knee. You get to see these um bony uh out projections that arise from around the knee joint but project away from it. So there's those projecting towards the to the femur and these projecting away from the knee as well. And the key here is to identify Cort mell dis uh continuity. So the whatever bony uh projections we see are continuous with the cortex, which is the black line and also the medullary cavity, which is the white area. So Cortico medullary continuity and multiple um osseous a projections pointing away from the joint is pathognomonic for diaphyseal ais or multiple hereditary exostosis. These are benign bony projections. But there is a criteria for um uh there's a 1% chance of each and every one of them to um for malignant transformation. And there is a criteria for that. This is another patient who has this destructive lesion along the anterior aspect of the uh knee involving the tibial uh tuberosity. Um it appears well defined although we do not see a sclerotic margin and there's no clear soft tissue component on x-ray, but a CT scan was performed and we note expansion of this area with which is completely made of um low density. And you can see here that there is thinning of the the preexisting cortex. The patient also did have an MRI scan performed. And if you note here there are different, there are layers of uh fluid. So there is this white fluid and then there are some areas of dark fluid appreciated. So this is called a fluid fluid level. And um whenever we see this, we we, we have to be um we have to think of a condition called an aneurysmal bone cyst, which is um basically dilatation of uh blood channels within abnormal dilatation of blood channels within uh an osseous structure. Um aneurysmal bone cysts can either be primary meaning that they exist on their own with no underlying conditions and can, can also be secondary meaning that they can exist or coexist on top of other uh bony lesions. So, it's very important to make sure that they're isolated and not associated with other um conditions. So once when, when a patient had a contrast uh scan, we note that there is enhancement only of the periphery of the cyst, which indicates that this is a primary aneurysm, bone cyst. These are usually curettaged and packed. Um One of the other common conditions that can happen around the knee is uh 10 synovial giant cell tumors or um which was previously known as pigmented nodular synovitis, which is basically abnormal deposition of hemos or abnormal hemorrhage into either into a joint or into a um tendinous structure. And this results in areas lobulated areas of low signal intensity on all imaging sequences, but most pronounced on the gradient sequences where these appear really, really dark because of their paramagnetic um um properties. And on the post contrast scan, the area does not enhance except for the for the um there's a variable pattern of enhancement, but it could be heterogenous with non enhancement of some of the areas. So this is a 10 of synovial joint cell tumor or PNS. Um Just two more final slides. Uh This is very common in, in my country where we've got, we've got a higher rate of sickle cell disease. So we know that there is a geographic area. It probably looks like a map of a country. It's um that's why it's called geographic area of alternating sclerosis, which is the white areas and lucency, which is the dark areas. It appears as again, it has a variable appearance on um MRI depending on the stage of it. And, but it also appears as geographic well aligned within the medullary cavity um of the distal femur here and this is an intramedullary infarct. Um It it occurs for different, for different reasons. There's a whole differential diagnosis for this. But in, in Bahrain, it's very common among people with sickle cell disease. Um One final case. Um so these are multiple intraarticular bodies uh which appear hyper sclerotic or dense. And this is a condition called synovial chondromatosis. It may be either primary in which it just happens for no reason and uh the patient develops multiple bodies of similar or uniform size into the joint which can either be resected but do have a, a chance of recurrence or the patient will end up with a sino omy removing the entire sino VM in order for the for them to salvage or save the knee because these results in erosions and limitation and movement or maybe, um the condition may also be secondary to trauma. Um, in particular. Um Well, once the, the cartilage or bony structures are injured or also post are secondary to osteoarthritis. Um So in summary, we learned about the normal radiographic and MRI anatomy of the knee. We've identified common traumatic injuries on both brain radiography and on MRI, we've recognized nontraumatic conditions that may occur and I would sincerely thank you. I like to thank you for your uh patience and your um and for attending today, I know it's a weekend in many different countries. So I'm glad that you've all made it and I hope that you've learned something new. Thank you. Thank you. That was brilliant. So, questions, let's go for this. Shall we? Brilliant? So we have now, just so everyone knows I'm not medical, so I may mispronounce some of these words. Ok. So we have a question here. What's the, what's the significance of inal? Yes. So basically the ter issue is important, er why? Because we've said that there are lots of conditions that can happen um because of the patellar malalignment. So whenever the patella is not in place, usually because of congenital reasons, this affects um how we move, uh how, how our knee basically functions. So the patella ends up instead of rubbing with the normal uh trochlear cartilage, it rubs either with the one of the fat pads or with the femur, this can result in a lot of pain around this area and also in premature osteoarthritis. So, once we identify that the patella is malaligned, either on plain radiography, which is typically done in uh 30 degrees flexion, lateral projection or an MRI. Uh we can alert the surgeon and depending on the amount of malalignment, either physiotherapy strengthening of the quads or um sometimes uh repositioning surgeries or realignment surgeries are performed. Perfect. Um Someone else has put cellulitis. I think this was uh basically um to answer one of the slides. Perfect. Perfect. Um We'll chat about uh your slides and the video. Um Does anyone else have any other questions? Now's your time to get them in? I have to give them a chance to type. That's all. I don't know how quick they are at doing this, but a lot of them know that I can't help when it comes to these medical things. I'm like, I just toast. I know you've done an amazing job and you basically replied to all my emails and you were very prompt. So thank you. I appreciate that as well. We try. There's a lot of thank you. As you can see, there's lots and lots of thank yous. This teaching is really invaluable and we love that we get to, to host this. So any other questions I'm gonna give you one more minute to type in your question. Um And then we will. Oh, do you have any recommendations for MS K radiology resources? Um Of course, an MS K radiology. Doctor Resnick is, is our Doctor Donald Resnick is the most famous author. Um His books are always very invaluable. Um There are so many books honestly and references. There's a book called Fundamentals of, I think Musculoskeletal MRI. Um some of them may be outdated, but to me, basic knowledge never gets uh outdated. There is always something that you can learn. And um there are a lot of online resources like only like if you go to the is ss the International Skiffle Society, they've got their own journal. There's the American Journal of Radiology, a lot of them are actually free. And um when I was in my residency, we used to carry books all around the place. But nowadays, everything is available online. So I'm sure that there are many different references that I'm not aware of. Funny. You should mention the first person that you mentioned. We actually have um a chap called Dennis Becky. Um He actually has ran events for Donald, you said. And actually Dennis has an event. I'm going to pop it in the chat. Dennis has an event on tomorrow actually for the UK, it's midday and I've just popped in the chat. A link to that. Dennis is a senior lecturer and a senior MS K speciality radiologist that was a mouthful for this. So there you go. One website called DRO R ad source. It also belongs to Doctor Resnick in his group and they actually, they, they discuss lots of different cases, important cases and in detail, I think it doesn't. Um, exactly. And it's one word without space. Um, I'm not sure they still, um, like they, they, they're not up to date, they have stopped posting for a while but whatever is available on, on their website is amazing. Perfect because it is quite often where can you find the good information and not the same question? Yeah. Yeah. Yeah. So that's great. Do we have any other questions at all? I don't think we do. So we're gonna say goodbye to the delegates and we're gonna stay on this call ma just for a couple more minutes. Alright. So everyone staying in here, it's a long hour and I know it is on a weekend. So I appreciate all of your attending. Brilliant. Thank you very much. Everyone, your feedback form will be in your inbox, please fill it out and then I can pass this that on to May, hopefully she might commit to another teaching session with us. Um It's always, I've always got my fingers crossed and um I will see the delegates at some point in the future at one of our next er medical education events. Ok? And for everyone have a great weekend and hopefully see you soon.