 54-year-old man reported a few days ago that he had a twisting injury, and now he can't bear weight, limited range of motion and swelling. We're interested in the corners. And let's look at the axial projection first, which many of you might ignore with regard to postural medial or postural lateral corner pathology. So let's get you oriented. This would be the medial side. You can see the middle layer of the MCL standing out quite nicely. Right, it is the POL, postural oblique ligament of the knee, and that transitions into the OPL, which goes across the knee over to the opposite side. Now, let's go to the joint line on the opposite side on the lateral side, and things don't look quite right along the posterior bony margin on the lateral side. They look irregular, and if you're experienced, you would assume there's a fracture present. You'll be able to corroborate that on the series of coronals I'm going to show you in a minute. Not on the medial side. There's something sitting posteriorly on both sides, medial and lateral. Those are either bone fragments or areas of coagulated blood. They happen to be bone fragments. And let's look at the coronal T1 for a minute, because that's where you're going to get your best depiction of the fractures. There is a depressed fracture in the femoral terminal sulcus, and there are paired postural medial and postural lateral fractures. This patient has had a component of a pivot shift, but remember he reported a twist. So if he had a straight valgus injury, you'd see rupture of the MCL. If he had a straight varus injury, you'd see rupture of the LCL, or fibular collateral ligament. And we're able to identify that structure, both in the coronal projection and in the sagittal projection. It is right here. That is the fibular collateral ligament. That's the popliteus. That's the FCL, the next layer out. And then the next layer out is the long and short head of the biceps femoris, 1, 2, 3. So here in the coronal projection, we have popliteus, fibular collateral ligament, and then biceps femoris, 1, 2, 3. Because this patient has had a twist as opposed to a varus or valgus, we have to be worried about the corners. And we are. That's why we're showing the case. But that also explains why you have a fibular head comminuted fracture. So that tells you a little bit more about the mechanism of injury, and your concern about the corners should be heightened. Let's briefly take a look at the postural medial corner, which has a little bit of swelling associated with it. The middle layer of the MCL, fibular collateral ligament, normal. The superficial layer, normal. The menisco femoral ligament, normal. The menisco tibial ligament, there it is right here. It's right there. It's visible. It's present and accounted for. How about the lateral side? I think we do ourselves justice by bringing down our sagittal projection. So let's make that the highlight now, and let's blow it up a little bit. And let's go to the less affected corner first, the postural medial corner. You can see a small fracture. There's some cortical disruption, a little bit of depression, and the semi-membranosis is still inserting. And I'll stop right there. There is a little swelling at the menisco capsular junction. That's part of the corner. It's a little more swelling as we move off towards the lateral side. Now there's a lot more swelling, but still I want to focus my and concentrate my efforts and discussion on the lateral side. So let's keep going. There is our posterior cruciate ligament. Let's work our way to the lateral side, and there is our demolished, pulverized anterior cruciate ligament, which goes along with our pivot shift injury. Could we see it in the axial projection? You bet we could. We got a lot of information off the axial. We could tell we had paired fractures in the back, which should lead us to the conclusion there's been a serious shift of femur relative to tibia, and the ACL, which should be a linear straight structure right here, is just a big, gray blob. It almost looks like a PCL, it's so round. So it is totally fibrillated, totally pulverized, and the patient has had a pretty violent pivot shift with rotation. So now let's work our way over to the lateral side, PCL is intact, and the capsule, the posterior capsule, which also has fused to it, the OPL is torn superiorly. Right there. That should attach to that. All you see is an area of fuzzy gray signal intensity. Let's keep going over to lateral side. There's a little more capsule, certainly swollen, and let's get into our posterior lateral meniscus. Our posterior lateral meniscus has an upper attachment and a lower attachment, which forms its hiatus. These attachments go from superficial to deep, so here we are superficial. There's a lower attachment. There's a nice triangle here. Here's an upper attachment. Here's another fascicle of the attachment. Let's keep looking. So the attachments are still present until we get in deep, and right there the meniscus appears to float. So in deep towards the midline, the inferior attachment of the lateral meniscus has come undone from the fractured posterior lateral tibia. That by itself is usually not problematic. Those will usually heal, although occasionally you'll see isolated tears up here of the upper fascicle that allows the meniscus to twist or twirl, but we've got much bigger fish to fry in this case. Let's now look at our popliteo-fibular ligament. Our popliteus tendon, which perhaps we see best coronally, there it is in the hiatus. Let's follow it down. There's its arcuate course, as it plunges info, anterior, and medial. It's intact. So we can clear the popliteus, but not the pop-fib ligament. There's the popliteus tendon. There is the pop-fib ligament, and it is swollen, ill-defined, and demonstrates the mermaid sign. Here's our mermaid right here. I'm going to draw over our mermaid. There's the body of the mermaid, and there is the mermaid's tail. And now I'm going to take it away so you can see it. And now I'm going to blow it up so you can see it even better. So we have a popliteo-fibular ligament rupture, certainly a high-grade tear. Now what's behind here? What's behind the popliteus tendon? The arcuate. It is a glorious mess. This would be the arcuate space right here. Here it looks a little more linear or straight, but then on the very next cut, as we get out more peripherally, it turns into a bag of blood and stressed out, torn, coiled, arcuate complex. Let's see if we can identify any of the arcuate in the coronal projection. Here is a blunted vertical limb, the lateral limb of the arcuate, and then there should be an oblique limb that comes right from here and courses over this way. And now look at that course. It's filled in with blood. So we have an arcuate tear. We have a poplite ligament tear. We have an ACL transaction. We have multiple micro- and macro-tribecular bone injuries, including real life, honest of goodness fractures, including the lateral femur and the fibular head, and relative sparing, mild injury of the post-romedial corner, sparing of the PCL, and I would weave those key points into my conclusion. The rest of the findings, including the soft tissue swelling, et cetera, the more minor findings go in the body. The only other pertinent negative I probably would put in my conclusion is the status of the menisci, which were spared.