 It's a 41-year-old woman. Right lateral knee pain for one week. Injury while playing soccer. So I'm going to call up just three different projections. Any three, any three planes. This is how I'll assess a case like this. Complex case. You noticed earlier when I was hunting for meniscal pathology, I went right up with the proton density, fat suppression, spur, spare, special, low field stir. That's my hunter sequence. But now I have to look at anatomy and morphology. I don't necessarily have to look at a small triangle and drill into that triangle. I've got to look more broadly, so I'm going three projections right off the bat. Any three. So I've got the axial. I've got a sagittal PD fat suppression. And I put up a coronal, I believe. This is another coronal PD fat suppression. So let's scroll the axial first, because that's probably what we would do if we were alone. Take a quick look at the axial. We know something very bad has happened here. There's a big effusion. There's an object here, hard to define what it is. The patient does have a reasonable-looking trochlea. Trochlea depths over three, lateral femoral ridge to medial ridge, probably about five to two. The reason I bring that up is patellar dislocation. It would always be a consideration in a big swole in knee like this. It's a violent injury. The retinaculum is a bit laminated looking and stretched out, so it's not normal. The patellar femoral mechanism isn't normal. The fluid has driven the patellar over, but that isn't the primary problem. Let's keep looking. There's something going on over here. Now, I choose not to define it, because I am reading 100 MRIs a day or 50 MRIs a day. I'm going to define it on the more user-friendly sequence, but you could if you had to define it. It's in the posterior lateral knee. It's lateral and in the posterior lateral corner. Problem. How about our anterior cruciate ligament? There's our anterior cruciate ligament. Questionable at its proximal end. Here is our posterior cruciate ligament, very swollen. Let's keep going. Let's go to the more relevant sequence now, the sagittal PD fat suppression. So even though there's some motion mismapping and wraparound, aliasing artifact, also known as the 55-degree artifact, we're having a hard time finding our anterior cruciate ligament. It is not acceptable to say in your report, don't see the anterior cruciate ligament. Might as well just put a big sign on your head that says, kick me. You can always see the anterior cruciate ligament. If it is absolutely true that the image quality is so bad that you can't see the anterior cruciate ligament, patient needs to come back. That almost never happens at any field if you know how to look for the anterior cruciate ligament in all three projections. Proximal end axial, mid-substantial sagittal, and distal end coronal. There's the distal end, but I'm having a hard time finding the proximal end. Now, that's not the way I'm going to finish the report. But at this juncture, I am deeply concerned about its status. Never mind that the patient has completely blown the entire lateral stabilizers of the knee. Actually, be mindful that they blew all the stabilizers laterally, which means the patient has had a varus insult. So in a varus insult, you might get compressive forces here. Don't see them. Maybe a little bit, a little bit of a compressive force. Why do I bring that up? If you take the knee and you put the knee in straight varus, sorry, in straight varus like this, what's going to happen? They should clunk together the medial femal condyle and the tibia. So if they don't do that, then there's another possibility. Is this one easier to? This one's laterally blown, sure. So if you do this, yeah, we've got everything here. If you do this, they should hit each other. But if they don't hit each other, then this might have happened. That might have distracted and dislocated. Otherwise, why didn't they impact each other? So you've got to be worried about a knee dislocation. Once you hear that, say, OK, first thing I better do, check the neurovascular bundle. I better check the popliteal artery and the perineal nerve. And you would do that by going to the axial projection, finding the tibial nerve. There's the tibial nerve. And then following the perineal nerve from it. Here's the perineal nerve right here. Let's follow it back. There's the perineal nerve. Here it is. And now you follow it around. Let's see if we can follow it into this mess. Here it is. And it made it through the mess. It's amazing. It made it through. There's the nerve. I'm keeping the arrow right on it. Critical. OK, let's go back to our sagittal. Am I confident enough to say this ACL is blown? You bet I am. I got it in three projections. I certainly have it in two projections. Proximal and looking pretty bad. That and that are not connected. Those fibers and those fibers are not connected. It's actually easier in the coronal. How about our PCL? One cut, pretty good. Where does the PCL tear? That's one of our questions. Mid. Yes, it can evulse the tibial fragment. Yes, it does get surgery if it evulses the tibial fragment. No, it doesn't get surgery if it is a mid-substance tear. And most of them are high-grade, interstitial, functional, full-thickness, mid-substance, tears. As we go off to the side, we're right in the middle of the PCL, right there. As we go off to the side, it's definitely not normal. Look at it coronally. Look how swollen it is right here. So there, let's blow it up. It's almost like a split tear that you would get in an extensor carpial narrus. So it's got an interstitial tear. Now, this one's close to the femoral end. Let's follow it. It's still there. It's getting a little better. It's gone. So it's a mid to mostly femoral end tears. Now, in my experience, femoral end PCLs, bad sign. Femoral end PCLs have a higher likelihood of being associated with a complex instability or any dislocation. So now I've got an ACL rupture, a PCL interstitial tear. The LCL is obliterated. We're going to go through that in a minute. And I don't have a meniscus tear. How does that happen? Only one way, knee distracts, knee dislocation. Very complex, very interesting, very unfortunate. Look how good the menisci look. Amazing. How about the menisco-capsular attachments? Remember our young girl that was missing the fascicle? Missing both fascicles? One was a dysplasia. Here are some fascicles. Look pretty good. Present, maybe a little swollen, but present. All the way across. How about our medial side? It's a little swelling of the menisco-capsular reflection. So low-grade ramp injury, right? It's a little swollen. It's actually not affected. The fat looks pretty pristine. Nope, not present. So that's another bad sign. In other words, it wasn't a classic pivot shift. Probably hyperextension, varus dislocation. Because if it was a pivot shift, you'd have ramp lesions at postural lateral injuries. So now we know the mechanism of injury. Hyper extension, varus, dislocation. So now let's go back to the lateral side. We're not expecting to see anything medially. Just for giggles, let's check it out. Maybe a little strain or interstitial injury of the vastus medialis, oblicus, and superficial MCL approximately. There's the superficial cruse, which merges with the anterior fibers of the MPFL. The mid fibers will intersect with the tibial collateral ligament at the adductor tubercle up here. Major stabilizer of the patella. Let's go to the lateral side. I think it's time to one-up the coronal. All right, let's focus on this coronal. We have a fibular collateral ligament, which takes off above the popliteus hiatus. And one thing I would like you to get in the habit of doing, very challenging, is I'd like you to get in the habit of tracing cortex. Because one of the most commonly missed abnormalities in MRI, pure cortical evulsion fractures. Very little marrow edema, but soft tissue edema. So you've got to look for the absence of the cortical line. I have a nice cortical line here, but I don't have a nice cortical line here because that is a piece of cortical tissue that is pulled off with the popliteus reflection in the popliteus hiatus. That's a very bad sign. The fibular collateral ligament. It's torn, let's follow it down. It goes nowhere, it flops out to the side. The biceps femoris, which together form the misnamed conjoined tendon, is off the fibular head. The fibular head, not fractured. The arcuate, which comes off here and forms an inverted Y. So the arcuate would be located right here. It should be vertical and then arc-shaped. Let's take that away. We should be able to see something there, we don't. And even though there's not a macro fracture, look at the tip of the fibula. There is a very subtle arcuate sign present, right there. And there, and there. So this patient does have an arcuate injury, although most of the injury is in the true lateral collateral ligament. We're not done yet. What else stabilizes the lateral side? There's a ligament that comes off the fibular collateral. And here's the fibular collateral. It's up higher, but I'm gonna just draw it in here. Fibular collateral comes down onto the fibula laterally. The arcuate comes off more medially. So the arcuate would be over here if I went a little further posterior. And then there's a ligament that comes off here that goes right in here. It's called the oblique ligament. It has various names. The sagun ligament is another name given to it. And that is off. Now sometimes you'll see a little flake fracture with it, a so-called sagun fracture. I don't think this one's too easy to spot, but I do have some examples for you in other cases that are easier to see. Unfortunately, when you see the popliteus ruptured, that's the end of the train. That usually means something really awful has happened upstream. That usually means the FCL is gone. There's a pretty good chance the popliteo-fibular ligament and arcuate are gone. So the popliteus is an end injury, a very serious injury, a high-grade injury of the LCL as soon as you see it. Let's go to the saginal and evaluate the posterior-olateral corner. Now typically people that dislocate with hyperextension, they often don't have corner injuries if they have a varus insult. If it's a straight varus without a twist, the corner will get spared. So this one looks more like a varus as opposed to a twist. If it's a twist with it, if it's a varus twist, then the corner will go and it could twist forward, it could twist back. So what are we interested in? We already know the arcuate is torn. We're looking for the popliteo-fibular ligament. We said that the popliteus tendon is the end game of the lateral complex. So if that's torn, pretty bad stuff has happened. Fibular collateral gone, arcuate gone. Popliteo-fibular ligament, not the sagun ligament. That's the oblique ligament coming off the FCL. A ligament coming off the popliteus tendon to insert on the fibular head, which should be right there, that's gone. Let's blow it up. That's what all this swelling is about. So there was a twist. There was a varus hyperextension injury with a twist. Spared the postural medial corner, killed the postural lateral corner. There should be an insertion from here to here. You can see on the T1, even though it's a little dark, I'll brighten it up for you in a minute. It should be something that goes right there. And it should be a little thinner than that. I've got a thick line there. It should come off the popliteus tendon from here and insert on the fibular tip. Let's brighten up the T1 so you can see how swollen it is. You should see it on your own too. That's just all blood. Now look at those beautiful fascicles. So something still survived, right? And there's your postural medial capsule reflection. That survived. So in summary, what's the conclusion gonna look like in this case? Conclusion. Hyper extension, you can see. I like to start my conclusions with the mechanism of injury. Hyper extension, varus twist, possibly with knee dislocation, period. ACL transsection, mid-deproximal. PCL interstitial tear, least moderate grade, period. Menisci spared, period. Lateral complex ruptured, including, A, fibular collateral ligament, B, popliteus rupture with evulsion fracture, C, lateral capsular rupture. D, pop fib ligament rupture. E, arcuate sign with arcuate tear. I know that was a nasty little case. Just a couple things to help you. Here's your arcuate. That's the vertical portion of the arcuate. That is the medial portion. The medial is more arc-shaped. You're looking from the back. Typically, this limb is inverse in size to the fevella fibular ligament. So if the patient has a fevella, they usually don't have one of these. The best way to see this is with sagittal imaging and very thin coronal imaging following the apex of the fibular head. The arcuate medial to the biceps femoris and FCL, whose footprint is out laterally. From the fibular collateral ligament is this ligament, the pop fib ligament, which in our patient was ruptured. And here's another look at it in color. All right, let's move on.