 Okay, our next meniscal focus is what I call the lateral meniscus rule. Now, in order to illustrate what I mean by that, I have to go back to my rudimentary drawing skills and I'm interested in discussing the anterolateral meniscus rule, which means there's a post-orolateral meniscus rule. But that's not the subject today. It's the anterolateral rule. So we've got a very busy party going on anteriorly. We have, as previously mentioned in some of our discussions, the transverse meniscal ligament of Winslow, which by the way is not present in every individual, but in most it is. The degree to which the transverse meniscal ligament extends along the anterior horn of the lateral meniscus varies, but it has a much more complex attachment. It has a slightly interdigitated attachment along with tissue that is made of capsule and synovium. And in order to illustrate that, I have to make a much thinner line, and I'll do that right now. So you're going to have quite a bit of interdigitation between the fascicles of the ligament and the capsule and the synovium, which I have drawn in green. So if you're looking at a normal meniscus, and let's do that, let's redraw our meniscus in cross-section as if it's a sagittal view. So this is our sagittal view, and it's a little thinner this time because I didn't have time to thicken up the line. Let me try it with a thin line. So there's your anterolateral meniscus. And usually the anterolateral meniscus is not straight up and down. It's sloped. Sometimes it's even sloped this much. I'll take out my eraser. Oops, didn't want to do that. Here's my eraser. So it'll often look a little bit like this. Then you have the transverse meniscal ligament of Winslow, which is going to sit right here. It should be in blue. Let's make it blue. And then you're going to have areas of interdigitation, which I will draw in green. I'll make them a little thicker now so that they're more easily seen. You have these little areas of interdigitation. Sometimes you have one dominant one. Sometimes you have a lot of little ones. You will also have some interdigitation that comes down from the top, especially as you get close to the root attachment. So if you have capsulocenivitis or capsulitis, these green areas of interdigitation will become more conspicuous, a little thicker, and they'll swell. And if they're pretty deep, let's say this one was really deep, you could easily go down the drain and call it a cleavage tear. So what's a mother to do? You've got interdigitation. You've got the transverse menisco ligament of Winslow. And to make matters even worse, you also have the largest menisco synovial recess of the knee, the enterolateral recess, which comes out like this. So if you have an effusion, very common for the effusion to hang right there. So now another structure has been lobbed into this inflamed knee, maybe some chondromylation in the neighborhood. So here is an important lateral meniscus rule. If you are imaging in the sagittal projection and you are unsure whether you have a tear or whether you're looking at inflamed areas of synovial attachment and ligamentous interdigitation, almost never will the tear sit here at the root and not propagate to the body horn junction. So if after the second slice, that signal suddenly and abruptly goes away, it's either not a tear or it's not a tear worth dealing with. We're not talking about the root coming detached and the meniscus floating away and the meniscus twisting. Talk about it's in its normal position and you see either one or more signals close to the midline. Rule number two, the lateral meniscus is a most favored nation meniscus for meniscal pseudosists of meniscal origin. More common lateral than medial. More often painful lateral than medial. More often smaller lateral than medial. More often anterior lateral than medial. So this is a good spot to get a perimeniscal pseudosist of meniscal origin. What's not good is the tail. The tail is going under the meniscus. That's a meniscus synovial recess or if it's under pressure and there's no fluid in the joint, it could be a ganglion. Whereas a true meniscal pseudosist of meniscal origin comes right out of the dead center of the meniscus. So it'll look something like this. It'll bisect it. I'll do it in pink. So a true meniscus pseudosist comes right out, we'll overlay it right there. That is what a meniscal pseudosist of meniscal origin should do. The tail should go right down the middle. Now should it come out the other side? It would be nice if it did but they don't know. They can be true intrameniscal tears and just blow out the peripheral capsular surface. How do you know? Well because it goes in at least half the depth of the meniscus. It's a white line that communicates clearly with the thermometer bulb of the pseudosist and it's right in the center. How did it get there? Usually there's an area of weakening so that there is diffusion along the radial bundles of the meniscus all the way out from the inner third to the outer third even though you might not see the inner third component. How do you deal with these? Ones that are intrameniscal you may have to go from the outside, take it out and then sew. The ones that communicate, you go from the inside and sew them shut and you leave the outside pseudosist alone and it usually dries up on its own unless it's inordinately large. But the take home message, the anterolateral rules are, lots of interdigitation along the anterolateral deep horn and root, both ligamentous and synovial interdigitation. Unless it's on the third, fourth, fifth, sagittal slice it's not going to be a cleavage tear and fluid containing areas anterior to the lateral meniscus are not of meniscal origin unless they come right down the middle of the meniscus.