 Welcome to noon conference hosted by MRI online noon conference connects the global radiology community through free live educational webinars that are accessible for all and is an opportunity to learn alongside top radiologists from around the world. We encourage you to ask questions and share ideas to help the community learning grow. You can access the recording of today's conference and previous noon conferences by creating a free MRI online account. Today we're honored to welcome Dr. Steven Pomeranz for a lecture entitled MRI of the Knee. Dr. Pomeranz is the CEO and medical director of ProScan Imaging, chair of Naples Florida Community Hospital Network and the founder of MRI online. He's authored numerous medical textbooks in MRI, including the MRI Total Body Atlas. He's also an avid conference lecturer and chairs the fellowship training program MR and advanced imaging. At the end of the lecture, please join him in a Q&A session where he will address questions you may have on today's topic. Please remember to use the Q&A feature to submit your questions so we can get to as many as we can before our time is up. With that, we're ready to begin today's lecture. Dr. Pomeranz, please take it from here. Dr. P, you just need to unmute and share your screen, please. Look, unusual. Okay. It's a big day. This is the beginning of Black Friday for MRI online. So, you can see there are some discounts out there for all of you. This is really beyond my area of expertise, but it's the busiest week of the year for MRI online and it's the most wonderful time of the year. It's a great time to sit by a fire and learn about MRI. I know that sounds kind of nerdy, but I am. Today, we're talking about MRI of the knee and I'm going to focus on really four major areas. Hyaline cartilage, I'm going to use the patella mostly as an example, the skeleton, ligaments, and menisci. And I'm going to come at this mostly from a biomechanical, biophysiological approach to injuries of the knee, so I'm not going to be talking much about things like gout and pseudo-gout. I might refer to them briefly, but this is really a discussion more about injuries and how the knee relates to those injuries. So let's start out with a pivot shift injury. This is our famed quarterback, Carson Palmer, who was injured by this evil Pittsburgh stealer who fell on his knee. You can see the foot is externally rotated, the tibia is internally rotated, the femur is externally rotated. That's hard to appreciate. There is an outside valgus force applied against the knee and most importantly, the toe is fixed on the turf. Had the toe been free, that injury probably wouldn't have been sustained. And we'll see some examples of the pivot shift injury in a moment, but we'll talk about various valgus, hyperextension, hyperflexion, rotational injuries, knee dislocation. We may or may not get to that today, a direct impact and the pivot shift injury. So let's begin with Highland Carlich, and I'm going to use the patella, and I'm also going to touch on the growth plate, since most people don't focus on it all that much as pediatric radiology is an island unto itself. I'd like to show you the normal growth plate, and this white striped area, which is a little thicker on the medial side, a little thinner on the lateral side consists of three zones, the zone of resting cartilage, proliferating cartilage, hypertrophying cartilage, and then stacked upon that is the laying down of bone, this thin black line delimited by the salmon color arrow, and that thin black line represents the zone of provisional calcification. So that's how the bone grows. The bone can also grow sideways from medial to lateral via the zones of Ranvier and the ring of Lacroix, a subject for another day in the pediatric knee discussion, but a common pitfall that may lead to the misdiagnosis of Assault or Harris-1 is the metaphyseal spongiosa, what I call shine, this shiny area right here, which is not edema. That represents the normal loops of vascularity that provides the ATP and the oxygen that allows the energy for laying down of bone, allows for the zone of provisional calcification. If you injure that via repetitive trauma, such as running and cutting on turf when you're a young person, and that goes unchecked, then the Benjamins stack up. What I mean by that is these three zones, the yellow zones will get thicker and thicker and thicker. They will not calcify, they will not ossify, and you will end up with a leg length discrepancy. Now, the patella, as promised, the patella has a medial facet, an apex, a lateral facet, a lateral tubercle, an odd patella facet that is not really covered by cartilage, and then the pre-patella plate, which consists of the continuity of the quadriceps tendon as it courses over the front of the patella. We'll have a medial para patella retinaculum, a lateral retinaculum, and we'll see later on, we'll have a medial patella firmal ligament. If the patient is under 18, the most common cause of pain in someone under 18, under age 18 in the knee is the patella. We're going to look at things like size, shape, the sets, the trochlea. We'll look for dysplasia, position, the plate status, the fat pads. Let's take a look at some examples of different patella shapes. I don't comment on these individually too often, but the two that do come out most frequently are the Weiberg shape and patella magna. Let's stick with the Weiberg shape for right now. In Weiberg shapes, you are actually comparing the length of the medial facet to the length of the lateral facet. The shorter this gets, the longer that gets, the greater the degree of dysplasia, the more likely the patient is to have some form of patellofermal subluxation, dislocation, or a maltracking syndrome. Another dysplasia that is carried out is the du jour classification of dysplasia. Let me see if my panel work here. There we go. If we have a trochlea groove like this, that's fine, that's peachy, but what if the groove is a little shallow, then we would have a du jour A. What if the groove is completely flat all the way across? We'd have a du jour B. What if we have a bump in the middle of the groove? That's a real problem. Then we'd have a du jour C. So those are a little bit more sophisticated, but they are very relevant to young people with knee pain. One of the few measurements, I don't measure a lot of things, but one of the few measurements I do make is the TT to TG ratio, and that is something you can Google and look up since we're time constrained. That is one of the few things I will include in a report, not routinely, but in young patients with patellofermal disease. Let's look at the arrangement of cartilage. We said we were going to use the patella as an example. These are T2 relaxation maps, so the colors reflect the T2 relaxivity. Color color means shorter relaxivity, and because of the proteoglycan and cartilage cell arrangement, this area is more dense, more hypo intense, shorter T2 relaxivity. Therefore the color is darker. The color lightens consistently and smoothly all the way across as we get more superficial, and this is known as the phenomenon of stratification. You can see how disorganized the stratification has become or lack thereof in this patient with a degenerated knee, and you're probably wondering, well, blue is not lighter than these other colors. Yellow is, but what is this blue area? The blue area is volume averaging of the zona splendens, which is a superficial very thin vesicular band that sits on the surface of the cartilage, kind of keeping it snug against the osteoconval surface. So that's a thing unto itself. Let's look at stratification in real life. This is an anatomic specimen. Here's a real MR, medial facet, odd facet, apex, lateral facet, lateral tubercle. Let's take the apex, for instance, and in the apex, the deeper portion is a little bit darker. The superficial portion is a little bit lighter, and we see the zona splendens, that hypo intense area that we referred to earlier, the outer shell that encases the cartilage. Let's turn our attention now to cartilage grading, which may be confusing for many of you. For some reason, as radiologists, we turned our attention to a pathologic grading system some 27 years ago, the outer bridge classification system, and we modified it for MRI. And our colleagues in the American College of Orthopedic Surgery modified it even further. So let me show you how we currently do it. Grade one is either a pure intrasubstance abnormality with no deformity or less than 25% loss of thickness of the hyaline cartilage. Grade two, 25 to 50% loss of thickness or an intracartilaginous signal with a raised surface or so-called blister. Grade three, full thickness tears, they can either be focal or they can be broad based. Because they are full thickness when they're broad based, they frequently take on the appearance of crab meat. Another word about these cartilage defects, when these cartilage defects are very squared off like this, they are usually acute cartilage defects, traumatic cartilage defects, whereas the degenerative ones are more broad, more going shaped, more saucerized. So that's something to keep in mind when you're looking at the femurotibular articulation. Then in the lower right hand corner we have the exposed osteocondroplate and medullary bone of class four, chondromalacia. Let's take one example. Here is a pathologic specimen showing the crab meat configuration of grade three chondromalacia and on your right the MRI demonstrating extensive fishering of the apex and medial facet in a crab meat-like configuration. Now we said, remember, the highland cartilage is darker deeper and becomes brighter more superficially, but at least in the femur and probably in the tibia, we're not so deep. We're kind of in the middle and it looks very different than the other cartilaginous areas, and that's because this patient has the entity known as CPPD, calcium pyrophosphate dihydrate deposition disease. And sometimes you'll see something very similar to this, but it'll be a little bit more superficial, kind of like here, or there'll be little dots that are more superficial rather than in the interstitium of the cartilage. And this is known as the icing sign associated with GAL. So superficial, hypointensity gout, interstitial, mid-cartilage, hypointensity, chondrocalcinosis, or CPPD deposition. Okay, let's take a breath, take a sip of tea and turn our attention to the skeleton. When I look at any joint in the body, the first thing I do, I don't drill into the case right away. I sit back and I look at the shape of the joint. I look for conformity. How does one part of the joint fit into the other? I look for deformities. I look for dysplages, and I differentiate deformities from dysplages in that some may be acquired, some may be congenital or developmental. I also look at the bone pattern of injury. This will tell me what I am looking for. For instance, a fracture of the proximal fibula, a board question, the arcuate sign, posterior lateral corner injury. The second fracture of the lateral tibia, LCL lateral capsular injury. Pivot shift, non-kissing contusions, ACL tear, anterolateral femoral fracture, the teller dislocation, contusion of the anterior tibia, PCL tear, anterior femoral condyle and tibial rim fracture, hyperextension or knee dislocation injury. Let's take a look at an example, non-kissing contusions. What's kissing? Kissing is when they abut each other. One here and one here. But we have one here and we have one back here. How did they end up touching one another? How did this end up touching the anterior aspect of the medial femoral condyle? Well, because when you translate, when the tibia comes forward, now the anterior femur is going to hammer the posterior aspect of the tibia using my fists as an example. This is pathognomonic of a pivot shift injury. And most of these people are going to have serious ACL injuries. One that I promised I would show you is the Botellar Dislocation Syndrome. I'm not going to show you a full, full-out knee dislocation, although I may have one later on. I take that back. But here's another example of non-kissing abnormalities. There's one micro-turbicular big-time fracture, anterolateral femur. But the other fracture is over here. How did they find each other? The patella slid over the side and the medial patelloferma ligament, which usually tears over here near the adductor tubercle about 80% of the time. This time it tore at its patella reflection. It completely tore off right there. The patella dislocation syndrome, inferred by the pattern of non-kissing bone injuries. Here's an example of kissing bone injuries. They're kissing because they're touching each other. They're on the medial side. So if you kiss on the medial side, you're going to distract the lateral side. If you kiss on the lateral side, then you're going to distract the medial side. So this is an example of lateral side kissing injuries that would result in an MCL injury. Let's look at an example on the lateral side. This is the lateral femoral condyle, the lateral tibia. There are fractures with each when you associated osteodema, meaning that there must be an injury on the lateral side. Now I'm not showing you the lateral collateral ligament injury, which was there because this shows the fractures a lot better. But you can even see that the iliotibial band itself, this is on the lateral side is attenuated and was affected. The LCL was torn in this patient. An example of kissing contusions as a manifestation of a varus insult. Varus insults are often more serious than valgus insults. Let's look at the arcuate side. This you have to know for your core exam. This is an avulsion injury that occurs in the proximal fibular styloid. It's an indication of varus hyper extension, a lateral or postural lateral corner injury, and maybe associated with injuries of the arcuate ligaments. The fibular collateral ligament, the biceps femoris, the fevello fibular ligament, and the popliteal fibular ligament. Let's have a look at the arcuate side. This one non-displaced from the fracture. There's edema and bleeding into the biceps femoris. And there is a ligament that should come out of here that is missing the arcuate ligament. That's not the purpose of me showing it. I simply wanted to show you the common-nuded appearance of this abnormality, the arcuate side. And by the way, in this case, the arcuate side, more indicative of a capsular or postural lateral corner injury or arcuate injury. In this case, the fibular collateral ligament was essentially intact. Here's another example of a pattern of bone injury. Once again, non-kissing femoral terminal sulcus, postural lateral tibia. As soon as you see that, even though you don't see the ACL, you now know that the ACL is injured. You now know that there's a pivot shift. So now you could just go down your checklist. ACL, check, it's torn. Is there a vertical, wrist-burg type tear laterally? Check, it's torn. Is there a postural medial ramp lesion? Not shown, but yes, check, it's torn. Was there a varice or valgus component? Check, let's look at the MCL. Check, let's look at the LCL. So these contusions and bone injuries are signs. You go right down your mental checklist and you're good. Let's take a look at another sign. This one you also have to know from your core exam and that is the sagun fracture, the evulsion flake fracture. And normally, off the fibular collateral ligament, which looks horrific, here's the fibular collateral ligament seen and here's the stump right there. Now, from the fibular collateral ligament, this is just a mushy fibular collateral ligament, this thing that I'm putting my green dot over, now I'm going to take it away, that is a ligament. That goes right here. That's known as the lateral oblique ligament of the knee comes off the fibular collateral ligament. When you have that, you have a lateral or postural lateral corner injury. This patient has both. The fibular collateral ligament is torn. The postural lateral corner looks like just a mush pot. This is blood and retracted ligaments and capsule and even anteriorly in this poor unfortunate soul from this various internal rotation injury, the iliotibial band and anterolateral capsule is also ruptured. Let's look at another, gourd worthy, arcuate sign. Where is the proximal fibular styloid? Nowhere to be seen. It's out of the plane of section, but also nowhere to be seen is the biceps femoris attachment. The fibular collateral ligament, the vertical limb of the arc, which should come straight up here, you don't see it. The oblique limb of the arc, which is right there. You can see it as a stump. It is also missing. And this patient did not have a fevello fibular ligament. So that was irrelevant, but the fevello fibular ligament is inversely proportional in size to the vertical limb of the arcuate ligament. OK, ligaments. Let's take a drink. Let's start out with my favorite, the anterior cruciate ligament, which most of you see pivot shift injuries on television and NFL national football league contact sport. But you also see it in Aussie rules football and I know we have people from all over the world. I don't know what the incidence of ACL tears is in the sport of cricket, but I suspect it's pretty high in the sport of rugby. The ACL shares a common sheath with a posterior cruciate ligament. And that is why the posterior cruciate ligament is often incorrectly diagnosed as torn with the ACL when you're simply looking at its sheath, bathed in fluid and blood. If these two tear together, you better be worried about a knee dislocation. There are two main bundles, antromedial dominant, posterior lateral subdominant. They arise from the lateral femoral wall and insert in the intertibial spinous notch and to a lesser degree on the tibial spines. Approximately 13 millimeters in diameter is the ACL in children. It's about eight in women. It's about nine or 10 lies inside a sheath. Inside that sheath, there is no synovial. So this is an intraarticular, yet extra synovial structure. I use the sagittal to look at the mid ACL, the coronal to look at the tibial end and the axial to look at the femoral end. In other words, I use all three planes. Take it from our total body atlas in MRI is the anterior cruciate ligament. And we see its origin from the lateral wall of the femoral condyle as it comes down, it gets a little more spread out, a little more fan shape, a little more triangular in shape along with its sheath, which is also a little more triangular in shape right here. And it gets a little grayer as it fans out. And that's all OK. That's totally and perfectly appropriate. Now, sometimes when there is a complex injury with a hemarthrosis, anifracture, and varus or valgus, the ACL is concealed. It's hidden, it's bathed in fluid and blood. And you may have to resort to specialized ACL views, which you acquire like this off the sagittal projection, tangent to the anterior cruciate ligament. And there we have its origin from the inner lateral femoral condyle or wall inserting on the tibia and tibial spines. Now, sometimes the ACL may be at risk if there's displasia. Remember, we said at the very beginning, sit back, look at architecture, look at conformity, look for dysplasia, look for remodeling. Here we have dysplasia. The cross section or the length from medial to lateral of the femoral notch should be about two centimeters or greater in men. This one's one point five. So the ACL and the PCL, but mostly the ACL is getting squished. And you can see some signal in here, even though there has been no trauma. This is an anterior cruciate ligament that's at risk. And here's what it is at risk for. A ventral rupture right in the mid portion, which is where the sagittal view really shines mid ACL tears, the proximal tears are like the axiom for distal tears. I like the coronal. Here's the T two weighted image also showing you this huge gap. But buyer beware, what is the signal of ligament? Ask yourself, black, what's the signal of fibrous tissue? Black, what's the signal of hemicidrin? Black, so you can have a pseudo ligament that is filled with fibrous tissue and ciderosis and have it look like on a T two weighted image. The ACL is intact. And that's why you must have you must have a proton density, fat suppression sequence to look at chronic ACL tears. The PCL is curved, lacquer and thicker, about 18 millimeters in thickness. Rather than having two parallel bundles, the bundles are more braided. They cross over each other. And this creates a scenario whereby the PCL does not retract most of the time. Most of the time, the high grade tears are interstitial. It shares a very close base with the medial meniscus and tier two at the ligament of Humphrey, post-tier two at the menisco femoral ligament of Risper. It is a very broad, complex, femoral insertion. There are 13 insertion points as defined by the esteemed orthopedic surgeon, Frank Noyes, there's an anterolateral bundle and there's a postural medial bundle, the exact opposite of the ACL. The ACL is antromedial and postural ladle. So there are two PCL bundles. Here's your curve PCL. Yes, it's curved, it's blacker, it's thicker. It has a broad footprint on the femur and tier two at the menisco femoral ligament of Humphrey, post-tier two at the menisco femoral ligament of Risper. And the capsule with the oblique popliteal ligament sitting directly behind in the midline. Let's take a look at a PCL mechanism of injury falling on the tibial tubercle with the toe pointed right there, driving the tibia post-tiering. And this is what you get, a large functional full thickness tear, even though it doesn't retract, interstitial tear of the PCL. And a lot of times the tibia will sag post-tiering. In an ACL, you'll get antiretibial translation this way. In a PCL, you'll get it this way. We call that the sag sign on MRI of a PCL deficient knee. Is another example of a PCL. There's interstitial signal in this PCL. They look a little bit similar to each other. Here's the water weighted image. Here's a water weighted image, but this patient has had no trauma. And they have complex bursitis anteriorly. And it's a man. And he's about 40 or 50 years of age. He's got big bursitis. He's got complex bursitis. He's got a big tendon, sorry, a big ligament. He's also got a big tendon. The popliteus tendon is buried in all of this inflammatory tissue. And the ACL is buried in all of this inflammatory tissue. No, this is gout. So when things don't match up, you've got to think a little bit obliquely to get to the right answer. And that patient had no trauma. And even though even if that patient had had trauma, I still would have been suspicious of the diagnosis of gout. Let's talk about the roots and root ligaments and fascicles. And let's start out with this lovely picture of the posterior lateral and medial meniscus. Look at the lateral meniscus. It fans out. We see these tiny little ligaments, one right there that is inserting on the base of the tibia. There it is again, looking rather beautiful, whereas this one is just chopped like you took an axe and just cut it off. There is no ligamentous attachment. And while the meniscus is not drifting immediately, it eventually will. And that can be the initiating factor for osteoarthritis, even in young individuals. Let's look at some of the other attachments. Let's go to the posterior lateral meniscus. Here we have attachments to the popliteus tendon. I have pointed out for you the popliteo-fibular ligament in the posterior lateral corner, but let's pay attention to the lateral meniscus and its superior and inferior fascicles, which pass through a hiatus in the popliteus tendon, but also attached to it, keeping it, keeping it anchored. And then as we go to the anterior lateral root, we start to see that things get a little feathery, a little speckly. And I don't mind if it does that as long as it doesn't go out into the meniscus body and more on that right now. So let's go to the most difficult of all the roots, the anterior lateral meniscus. It can be feathery, it can be striated, it can be plumped, and sometimes you can even sort out what the structures are. For instance, this triangular structure here is the transverse meniscus ligament of Winslow. This round gray structure here is synovium. This is the anterior meniscocapsular ligament. And that ligament has an intracubstance attachment, this gray line. And then we have the anterior lateral meniscus synovial recess, which is distended by fluid. Now, some of you who are first and second year residents or new to MRI are saying, how in the world am I ever going to differentiate this from a real tear? And the answer is very simple. You follow it out to the periphery. And if these signals persist more than, say, two slices, it's a very rudimentary way to do it, but it works, then you then you have a tear. If you have a conral disease, if you have oseous disease, if you have complexity, if you have change in shape, as you move from the midline to the periphery, you have a tear. Collaterals. Let's start out with the MCL, the easier of the two. We have three layers. They have all kinds of crazy names that you'll read about in the literature. But I'm going to make it simple for you. I'm going to give you three layers. Layer one, superficial layer, also known by the synonym cruise layer. Layer two, also known by the synonym middle layer. There are some other synonyms I won't confuse you with. But I refer to this as the middle layer or tibial collateral ligament layer. And then layer three, the capsular layer that includes the menisco femoral and menisco tibial ligament, also known as the coronary ligament. Now, between these, between these levels are areas of fat pad formation and bursa. So you can get a deep and superficial MCL bursitis. Let's see how we can get a valgus event. And here we go. Here comes the valgus event. Somebody's rolling up into this poor guy's knee right there. Now, this time the foot is not fixed on the ground. Otherwise, it would have been a much more severe injury. So that's a good thing. You can see the valgus pushing on the outside of the knee. And now let's look at what happened. The patient has an MCL injury. Let's go through the layers. Layer number one, the cruise layer right there. And it stops. It's torn. Layer number two, the tibial collateral ligament layer. It is rolled up in a ball. Now, the overwhelming majority of the time, we do not operate on PCL tears. And we do not operate on MCL tears unless the MCL specifically, the tibial collateral ligament is entrapped. Entrapped by what? Entrapped by the joint or entrapped by the pest and serine complex. If it's entrapped by the pest and serine complex and it is, there's the pest and serine, there's the tibial collateral ligament under it. And we call that a knee pseudo stener lesion. It also happens to be entrapped in the joint. The patient also has a detached menisco femoral ligament. They call it the menisco femoral ligament because it attaches to the femur, but this one does not. So this is a three layer tear that requires surgical intervention. Let's take a look at some menisco attachments, some unique ones. These are sagittal images at the level of the posterior and anterior horns. There's a little bit of signal anteriorly here as we have a synovial reflection between the meniscus, which is getting smaller and the transverse menisco ligament of Winslow and a little bit more synovial interdigitation here. Let's let's pay more attention to this one. In the back, the meniscus is attached by two pretty important structures. One is the Postier menisco tibial ligament, which you can just barely see right there. And the other one, which is more important or as important, is the Postier oblique ligament of the knee or POL. There are three components to this ligament, which we'll discuss in the more advanced knee lecture, which I hope to give you later on, perhaps early next year. And here is this little nubbin of hypo intensity where the POL attaches to and anchors the postural medial meniscus reflection. So there are postural medial menisco capsular attachments that we have to pay attention to. So you've seen an example of a a valgus injury. You've seen an example of a knee dislocation. You've seen an example of a pivot shift. How about a hyperextension injury? Let's have a look. Straight, direct hyperextension. These can be pretty nasty. If you stick your leg out under your desk, wherever you're sitting, you'll feel a little pressure on the back of your knee. So if it's a really violent, straight hyperextension, you can injure the back corners and the back capsule. But much of the time, the only thing you're going to see is a micro trabecular fracture in the anterior femoral rim and the anterior tibial rim and the recovery from this is very quick. A lot of times they will go out and play contact sport within a week or so. As long as it's very eccentric, very, very far forward and there's not a macro fracture, there's an example of one that occurred just like that. Except this time, the rim fractures, I'm not demonstrating them. There are also fractures in the back. And this patient has sustained a post-ear capsular injury. Let's go back for a minute and remember our POL attachment right there. Compare that to this one, which is seriously blunted. There it is. It looks like a little arrow from a bow and arrow. And it's separated from the meniscus, but we have more. We have blood in the capsule. The menisco tibial ligament is reduced to this smudgy structure right here. The capsule is wavy and the upper portion of the capsule known as the oblique popliteal ligament portion of the capsule is torn or ruptured with fluid leaking out. A post-eumedial capsular corner injury. And in this setting, you must turn your attention to the semi-membranosis. And it's five different attachment fascicles, which we won't review today, but we do see the semi-membranosis swollen, bent, but not broken. Now, when you insult the post-eumedial menisco capsular reflection, we've now learned that this has long term sequela. And we never paid much attention to this 10 years ago. But now we know when we lose these attachments and we start to flex and extend the knee, it's like a tire and it'll spit the meniscus out like you spit the gravel and snow out on your car when you're trying to get out of snow and ice. And this becomes much more problematic when you lose the menisco posterior tibial attachment and you partially tear or tear the semi-membranosis attachment. OK, take a sip. Now it's time for your ears to perk up and for your energy level to rise. I need you for this section because it's hard. This is the lateral collateral complex and the posterior lateral corner. Let's look from the back. So we're looking from the posterior aspect. There's the fibula, there's the medial tibia. And we have two bunny ears, a little bunny and a big bunny. The little bunny consists of the vertical arcuate limb and the oblique arcuate limb, also known as the lateral limb and the medial limb. There is an inverse relationship between the vertical limb and the fevello fibular ligament. Then we go to the big bunny ear. The big bunny ear is composed of the fibular collateral ligament and the bicep femoris, which don't really fuse. So this is not a completely accurate diagram, but they're right next to each other. So they receive the name conjoined tendon, misnamed. Because they're not really conjoined. And then our fibular collateral ligament origin is slightly above the popliteus tendon origin. And from our fibular collateral ligament is the posterior lateral oblique ligament of the knee, the so-called sagoon ligament, which you've already seen. And then one you have already seen normal is the popliteus fibular ligament. And we're going to return to the popliteus fibular ligament. I showed it to you in the sagoonal projection earlier. So now let's drill into the lateral side of the knee. Now, if you're squeamish, don't look because this is ugly. Yep, it looks like as an ankle is dislocating. He's a 300 pound Iowa former football player trying to make the professional football team, but really his knee is dislocating laterally. And it's a full knee dislocation. His ankle is just bending. He didn't have any serious ankle injury at all. Look at it one more time. That's pretty ugly to watch. And here is a normal diagram showing you the fibular collateral ligament. That's volume averaging. And here is what the patient looked like. He had ruptured the popliteus. He had ruptured the FCL. He had ruptured the biceps femoris. The capsillis torn fluid is leaking out and not shown. He ruptured his perineal nerve and was left with a permanent deformity and foot drop. I promised I would drill into a little further the pop fib ligament. Let's do that. I am not showing you on the MRI, the fibular collateral ligament, whose origin sits above the popliteus tendon. But here's the popliteus tendon and the popliteus hiatus where gout loves to occur. And it courses inferior, posterior and medial into the screen. Inferior, posterior and medial into the screen. And that structure, which is that structure, is not inserting on the fibular head and that is your pop fib ligament. Now, sometimes when it tears, it rolls up in a ball. Here's a normal one. Here's one that's rolled up in a ball. It looks like the mermaid's tail. And that's what's known as the mermaid's sign when you rupture the pop fib ligament. There's no linear structure going down there. Here it is right here going sideways. And what's all this hemorrhage and debris in the arcuate ligament? So a very serious posterior lateral corner injury. OK, take a breath or onto menisci. See how we're doing for time. We're doing great. Menisci are fibrocardilage like they're shock absorbers. They distribute axiolobe. They are stabilizers of the knee. Make no mistake about it. Many of your patients who come in say, my knee feels like it's going to give out and the ACL is fine, the PCL is fine. It's the meniscus that creates that sensation. The menisci circulate fluid. There are spongy radial areas in the menisci that allow that fluid to imbibe and course through it, creating intraminiscule signal, especially in the outer third of the menisca. Intraminiscule signal is also commonly seen in children as miniscule vascularity. And here is the vascularity with a reticulant stain and with a gross specimen showing you the redness of normal hypervascularity in the outer third of the meniscus where things do heal. So I don't like to see operations for tears in this location that are vertically oriented, they will typically heal on their own unless they're gapped or widened or they are very, very long, four or five, six centimeters long. What else causes signal in a meniscus? It can be contused. You could have meniscal degeneration. You can have intraminiscule tears, especially in discoid lateral meniscus. You can have meniscal cysts. You can even have bleeding into the meniscus that results in ossification of so-called meniscal ossicle. Let's talk about our one third double rule. What does that mean double rule? Well, the anterior meniscus, the body and the posterior horn are divided up a third, a third and a third. So if we sort of put a line on it and then we have to extrapolate in other projections, which you as radiologists are very good at doing, then this would be anterior third, middle third, posterior third, anterior horn, body, posterior horn, body horn junction, body horn junction. What's the other part of the double third? The other part of the double third is inner third, middle third, outer third, white, white zone, inner third, no healing, red, white zone, may or may not heal. And then the outer red, red healing zone, which you saw earlier. The meniscus, as you now know, is anchored in its periphery, not completely all the way around, but for the most part. And it's particularly anchored in the roots, which you'll see in a few moments. We have this outer third area, which is a potential healing zone, the zone of respect. We don't operate on vertical terrace here. There is normal signal in this area. And that signal in adults is related to diffusion of synovial fluid into the radial fibers of the meniscus in children, it's related to vascularity. The free edge of the meniscus is like the free wings of a manta ray. It is not attached to anything. So when you put fluid in the joint, like synovial fluid or an effusion, it will be a little bit wavy and may scrunch up on itself. And this is known as meniscal flounce. Let's look at the menisci from this excellent article by Thompson and radiographics from this year. We have the radial fibers, which allow fluid to come in and that radial fiber shape is very consistent. It's like a slingshot. Eventually it comes together. It can it can exit the papsillary because that's where the fluid comes in, but it should stop just shy of the middle third. If it keeps going past the middle third, then you have a problem. Then you have pathology. You also have vessels out here in children. There are circumferential fibers, which will ignore today. The meniscus is a stabilizer. It also is a shock absorber for the hoop stresses that come down when you perform athletic activity. When Michael Jordan dunked the basketball, he was measured at exerting 12 times his body weight on his menisci. So he was blessed with excellent tissues and that he never had a meniscal problem. Some people are just blessed. So now let's go back to the root ligaments and fascicles because this has become a critical jumping off point for radiologists in the MSK world and especially when you're assessing people for OA or the potential for OA early on in life. Here we have our more C-shaped lateral meniscus, our more banana shaped middle meniscus, and these yellow areas are roots anterior root, posterior root, anterior root, posterior root, many of which you've already seen, but we'll revisit them in a moment. We also have attachments to the periphery. We have the menisco femoral ligaments and the menisco tibular coronary ligament. And these come around and in the back, this is known as the ramp area because you get ramp injuries of the menisco capsular reflection when you have a pivot shift. We also have peripheral attachment back here laterally. And we have to deal with the popliteus tendon and the menisco femoral ligament of Risberg, all of which we will do. And on the accompanying MR diagram, we see the anterior and posterior roots, lateral and medial. Let's turn our attention now to these roots in the sagittal projection. Let's start up with these two higher images, A and B. Let's ignore the menisco femoral ligament of Risberg for now. And we'll focus on our ACL and PCL and their relationship to the roots. The anterior meniscus root, not as striated as its posterior cousin. This one's a little more striated, but don't be bothered by those vertical striations. Look at the close relationship. The posterior root has with the PCL base and the tibial PCL fossa. Now let's go to C and D. Again, let's ignore the menisco femoral ligament of Risberg. Here's our anterolateral meniscus root, the yellow arrow. What's that? The ACL. Look at the relationship between the anterolateral root and the ACL. It's intimate. And then look at the relationship between the posterior lateral root and now the menisco femoral ligament of Risberg. It's also intimate. Let's have another look back to a slide you saw earlier. The pop fib ligament, but we're more interested in the attachments of the lateral meniscus that perforate and also attached to the popliteus tenon, one superior, one inferior. And they have pretty good breath to them from side to side. And then we also mentioned earlier that there is some stippling and linearity that's allowed in the anterolateral meniscus root and this this image you've already seen. Let's turn our attention now to the LePron classification for meniscal root tears. I'm not here to try and impress you with a bunch of classifications, nor do I want you to memorize them. I just want you to know that this is now a focus of musculoskeletal radiologists around the world to save the whales, save the knees, save the menisca. These are important injuries. And frequently it's a woman who feels a pop and the radiologist overlooks this one small tear in the back of the knee and the meniscus root that is either a partial radial tear or a full depth radial tear. These are the two most common. Let's ignore the rest of the grading system, which you can Google and learn on your own. You're in diagrams of all five. Again, I don't want you to learn all five right now. I just want you to pay attention to one and two, the two most common, a partial radial tear and a full depth radial tear. Inner third, middle third, outer third. For some of you that are learning and especially those of you in other countries that don't do a lot of MSK MRI, a radial tear is this. It's a subtype of vertical tear. It comes from the inside like the spokes of a wheel. On the other hand, another kind of vertical tear is the longitudinal circumferential vertical tear. And is there one more there is? There's one that occurs in the middle third of the meniscus. That'll then get wider and wider and wider. And that becomes a bucket handle tear. So there are actually three kinds of vertical tears. The bucket, the circumferential longitudinal tear and the radial type tear. And the roots were interested in the radial type tear. You saw this slide earlier, chop, chop. We chopped off the attachment of the meniscus to the tibia. Now, here's another little pearl. We had that La Prod classification and it talked about different kinds of tears and evulsions. But what it didn't talk about was the ligaments. This is not a meniscus tear. This is a ligament tear. The meniscus is absolutely perfect. It is the attachment that's gone. So sometimes it's very important, especially from a therapeutic aspect to differentiate what is a pure ligament tear, what's a pure meniscal tear and what's both. And then we also have the normal attachments that you've already seen on the lateral side. So this is a particularly informative and instructive case. So here's a patient that's had a pivot shift injury. The tibia translates anteriorly and puts a puts a pretty big stress force on the menisco capsule reflection. So you bleed into the capsule, you get this vertical ill defined signal. The posterior menisco tibia ligament is no more. We don't see it at all. And this is referred to as a ramp one type injury. We refer to these ramp injuries in the setting of pivot shift injuries. What are some other kinds of ramp injuries? Well, the one is when you tear the capsule and you bleed into the capsule and you get this funny looking serrated reflection between the capsule and the meniscus, a two partial tear upper surface, three partial tear lower surface, four all the way up and down, five, two tears right next to each other, so called double tear. So an example of a four would be this, an example of a five would be this pretty simple, but taking a little bit to memorize, but who memorizes better than you doctors? You're the best memorizers on the planet. When NFL football players tell me how great they are at sports, I say, well, that's fantastic. But you know what, my guys, my docs, my colleagues have some of the greatest minds in the world and they can memorize entire textbooks in a month or two. How's that for athletic capability? And it's true. So here's a sagittal projection demonstrating a full depth ramp for Abner Mallet, just like that right there had there been another one next to it. It would have been a ramp five. And we do have to pay pretty close attention to these because they can result in detachments and they can result in osteoarthritis if left completely unchecked when they are higher grade. The lower grade ones will heal on their own. So here is an example of a higher grade one that did not heal on its own. It's a menisco capsular separation. When do I use the term separation when I have menisco migration? About 30 years ago, one of our esteemed MSK colleagues reported that an eight millimeter distance was required to diagnose menisco capsular separation between here and the edge of the tibia. That turned out not to be true. But when you have a centimeter and a half, two centimeters and blood in this space and the meniscus is clearly forward and you have displacement, you have a menisco capsular separation and this requires an operation. So what contributes to making a meniscal tear unstable? Because most meniscal tears should really be left alone. Cleavage tears, leave them alone. Vertical tears in the red, red zone with it with a pivot shift, leave it alone. When do you start getting nervous about tears? When they're really long over four centimeters, when there's gapping or separation, folding, displacement or detachment, full depth, you know, superior to inferior. When it involves the inner third, the middle third and the outer third. When there's migration as in menisco capsular separation or the knee is locking from your meniscal pathology. And you can correlate the exam with the MR findings. There's an axial T2. What's that? This triangular shaped structure. It's a meniscus that has been spit out. There's been a root rupture, a trizonal radial root rupture, and that's allowed the meniscus to migrate out into the periphery, into the tibial gutter, creating this little comma right here, the so-called meniscal commisine of a lateral meniscus tear with an extrusion. And the ACL, by the way, is truncated right there. It's also torn as another example of an unstable tear. It should have looked like this in the axial projection. Now it looks like that is completely ripped off. It's peripheral re-attachments, which you now have learned about at nauseam. Let's look at some other tears. There is a vertical tear. It's full depth. It's in the red, red zone. Would I operate on this tear if it's not gapped? Absolutely not. There's another tear, a horizontal cleavage tear. Let's say this is in a 70 year old. Would I operate on this tear? Absolutely not. What would make me operate on it? If it started to split apart, if there's a big, big cyst inside it. If it folded over on itself within maybe. But cleavage tears, you really can't do much with your sewing machine to show them back together. So here are some of our tears. We said vertical tears, there are three kinds. There is the radial, there's the longitudinal, and then there is the bucket handle tear. The longitudinal is in the outer third, the bucket handle is in the middle third, and it widens. We've also got the curved flap tear. When you have a little flap tear in the entrolateral body or in junction, we call that a parrot beak tear. Sometimes flap tears will fold over on themselves. And I think that's enough on shape. Now the meniscus, when you image it in the coronal projection, should not make a tongue all the way on to the tibial tubercle for more than one cut. So if you see that tongue sitting on the tibial spine for more than one cut, and this was, you should be worried about discoid meniscus. What else should prompt you to be worried about it? If the femoral condyle is not as distal as the opposite femoral condyle, or if you have a giant, large, fibular head, so-called fibular dysplasia. So any kind of femoral dysplasia, any kind of tibial dysplasia, any kind of fibular dysplasia should make you conjure up the diagnosis of discoid, lateral meniscus, or variant thereof. Any signal that occurs outside of the outer third in a discoid meniscus is a tear. What do you do about it? Nothing until it ruptures. This patient had locking. Our hand was forced. This was coming apart back together, coming apart back together. We know that from the physical exam. There was audible clunking. The meniscus looked pretty good from the outside. At first glance, it was convex upward. When we took it out and put it on the table, we had to do a total menisectomy. It kind of fell apart into two pieces. Meniscal flounce. We have spoken about the anchoring of the menisci peripherally. And we said that the inner tip is free. Sometimes when synovium accumulates, it'll push the tip up. It may even blunt the tip. So the tip will look something like this. The temple get a little crinkly and it looks a little bit truncated. And you may make the false diagnosis of a radial tear. This is a particularly common mistake. Another important type of tear that's associated with pivot shift injuries is the Risburg rip type tear. Here is the menisco femur ligament of Risburg, which arises from the posterior lateral horn, not the root, the horn. In a pivot shift, you may propagate this weak area laterally. And when that happens, you have what's known as the Risburg rip. When you image it sagittally, it will look something like this. You'll see this curvilinear interface between Risburg and meniscus. Now, you're allowed to see that on one cut, but you're not allowed to see it on two, three, four, five different cuts. And it'll continue to get smaller and smaller and smaller or bigger and bigger and bigger, depending upon what direction you're going in. Let's ignore these other Risburg type of injuries which are described beautifully in the Thompson article from Radiographics, the complete radial tear and the meniscus on a string sign. We have a radial tear that spares the menisco femur ligament of Risburg. It displaces and now you have the meniscus on a Risburg string. As an example of a Risburg tear, I don't mind that the menisco femur ligament of Risburg is separated by a cleavage plane from the lateral meniscus root. Now, I mind. I don't like the looks of this. It's too thick. It's getting bigger. It's getting more conspicuous. It should be getting less conspicuous as I go from the root to the body. And here we are again, more conspicuous. Risburg, meniscus, tear. Risburg, meniscus, tear. And now it changes direction because we're not looking at the tear anymore. We're looking at the popliteus reflection. Another type of tear is the vertical outer third tear. Yeah, they can be a little bit oblique. I don't mind. I leave those alone. They are frequently associated with pivot shift injuries. This one is, how do we know? They're multirominal sulcus injury. Postural lateral tibial injury. The ACL is injured or torn. It was torn. There's another one, an oblique tear, also known as a flap tear. They can be pretty big. And sometimes they're so big, they allow the upper border or the upper surface to flop over on itself. And that's exactly what's happened here. It's flopping over on itself. And sometimes it can flop over on itself as a fragment that is caught in the back of the knee and very hard to retrieve clinically with the arthroscope. So mapping that out for the clinician is incredibly important. The radial tear, it's one of the three types of vertical tears. It's like the spokes of a wheel. They're small. What's important? Depth. Is it in the inner third, middle third or outer third? In other words, is it in all three thirds? You do not get an isolated radial tear in the outer third. That does not happen. Do not use that descriptor. But the ones that are worse are the ones that go through all three thirds. The ones that are worse are the ones that have a fair amount of gapping at their base, 8, 10, 12, 16 millimeters of gapping. So that's how you decide whether you're going to intervene upon a radial tear in concert with clicking and locking. It used to be said that every radial tear needs to be fixed. I think the orthopedic community has migrated away from that particular statement. In the sagittal projection, when you perform anterior to posterior sagittal projection, sorry, when you perform the anterior to posterior sagittal projection, it'll look something like this. You'll volume average the free edge of the radial tear. And here you've done just that. You volume average the free edge of the meniscus. Now, very similar looking to the radial tear, but smaller. And having a predilection for the enterolateral body horn junction is this little nubbin of a tear, the parrot beak tear. It's a lot like a flap tear, but much smaller. I stated it likes the enterolateral body horn junction. And it has this sort of curvilator look. There is the snout of the parrot pointing in the opposite direction as the diagram, but so what? It gives you the it gives you the right idea. It's a slightly curved tear. It's an inner third tear. It has this little snout like curved characteristic. And finally, the bucket handle tear. It's a vertical central third tear that then does origami. It widens and creates a huge space. So when you perform your coronal projection, let's say you start over here and then here and then here and then here. You have meniscus, a giant hole and then meniscus. Now, if you get all the way out front, it'll come back together again. But sometimes that bucket will rupture all the way through the front. And then you have a free fragment. And sometimes it'll rupture all the way out the back to then you have a real free fragment where the whole thing floats all the way into the knee. It has to be retrieved. But here is how you infer a bucket handle tear. When you look at the medium meniscus, you say, ah, too small. Why is meniscus too small in a young person? Bucket handle tear number one on your list. Number two, radial tear number three, trimmed. Number four, menisco capsular inflammation from synovitis due to rheumatoid arthritis. Those would be some of the more common causes of a small, blunted meniscus. And of course, trimming. This one is a virgin knee never been trimmed. We see the double PCL sign of a bucket handle tear. We'll see how we get there in a moment. We have fragment, we have a hole, we have fragment. We have fragment, we have a hole and we have fragment. We have fragment, a hole and fragment and the same thing here. Now, word of caution. Couple pitfalls, first pitfall. The lateral meniscus is very C shaped. And for those patients that have a very tight, tight C, when you do your coronal, sometimes you will see meniscus, then a hole right there and then a meniscus. That is just the normal curvature. And you tell that from a real tear, it's only present on one cut. It doesn't persist slice after slice after slice. Second pitfall, the PCL has a very complex attachment. Its footprint is divided into 13 zones. One of those zones consists of the distal attachment as part of the Humphrey ligament mechanism. And there it is right there. Look at how close in proximity it is to the inner tip of the bucket. You can appreciate how some untrained observers might confuse that and that with a bucket handle fragment. So two pitfalls of the bucket handle tear. And I'm going to skip over this example of an convulsed displaced bucket and stop right there. I think we've looked mostly at non-experimental data and given you as much information as we possibly can to start your journey in MRI of the knee. And don't forget, this is Black Friday. So if you like what you hear on MRI online, don't forget to pay us a visit. Happy holiday to all. Questions? Chat. I see a few in the Q&A feature for you. All right. Any tips for distinguishing tears with calcinosis in the meniscus? Great question. Yes. Unfortunately, when you think of condro-calcinosis, you think of calcium. So are you going to see calcium against a background of a Black meniscus? You're not. But when you see this razor thin, very consistent cleavage type signal, and then you have inflammation that kind of bays around it, that's disproportionate to the characteristics of the tear, you should then think about condro-calcinosis, go right to the cartilage, inspect the cartilage and look for that interstitial middle layer hypointensity. And if you're not sure, ask for bilateral knee radiographs. How do I differentiate non-kissing and kissing contusions from edema? Well, one way is the history. You know, if a patient has had a traumatic event, then then you're going to call them contusions. Now, edema is a generalized term. Contusions are edema. You can get edema from, you can get edema from a tumor. You can get edema from trauma. You can get edema from infection. So edema is a more generalized term. A contusion is something whose term you use when you have no linearity. You have a history of trauma and you can discern a mechanism of injury. Thank you for the compliment. I appreciate that from Dr. Mohr's. Dr. Siddiqui, can you show the anatomy of muscles on the back side of the knee? Not sure how to do that. I'll tell you what, if you send us your email, Dr. Siddiqui, we will, I will send you some anatomic examples of the muscularity on the back side of the knee and some snapshots from our Atlas Total Body Atlas and MRI, and that should help you. It's pretty hard to do that in this forum. How do you how do you measure the TTG ratio? Well, here's how you do it. Let's see if my pointer will work. So you have the trochlear groove. You got that. And then you start scrolling down and you put a little dot here and you leave your dot there on your on your MR and you start scrolling down to your tibium. And when you get to your tibia, you get to your tibial tubercle. Let's say your tubercle is over here, not over here. Let's erase that. So now you've kept your little dot right there as you scroll down. And now you measure this distance right here. You measure that distance. Let's say that distance is 1.5. That's an abnormal TTG relationship. So so that is how you do it. You look at the the deepest part of the trochlear groove in the tibial tubercle and you see how malaligned they are medial to lateral one to the other. What is the benefit of axial thin slices in the meniscus? It's got moderate benefit. You know, in some cases, when you have decent sized tears, it doesn't add a heck of a lot. But when you have to map out the anatomy of a tear for a clinician, when they're deciding, do I have displacement? Do I have gapping? Do I have folding? Where do I go to find the fragment? Axial thin slices can be helpful. They're also incredibly enticing when you're in academic medicine and you want to show and teach the architecture of a tear. I think that's that's probably as big a benefit as it is clinically. How do you tell hypoxic ACL degeneration? I'm not sure that I can answer that question. Hypoxic ACL degeneration. But I will say this, when you see a swollen ACL without trauma, there aren't that many things that can do it. Here are the things that you should think about, not stenosis with impingement. Femro tibial shift from osteoarthritis with impingement from tibial spines, inflammatory synovial processes, tears of the ACL sheath. Remember, though, there's been no trauma. So those tears would have had to occur at some time in the distant past. And then finally, crystalline deposition disease, namely gout. So those are the things that should really cross your mind and be on your checklist for a diffusely swollen gray ACL. Let's see, I think that concludes our list of questions. With that, I will wish you all a great Thanksgiving and a happy holiday. Appreciate MRI online having me. Thank you, Dr. Pomerance, for your amazing lectures today and for everyone else for participating in this new conference. Those are some awesome questions. You can access the recording of today's conference and all our previous new conferences by creating a free MRI online account and be sure to join us next week on Thursday, November 30th at 12 p.m. Eastern for a case review live entitled Anatomy and Pathophysiology of the Four Foot with Dr. Jonathan Samet. You can register for this free lecture at MRI online.com. Follow us on social media for updates on future new conferences. Thanks again. Have a great day.