 Here's a patient with signal in the lateral meniscus. Let's go all the way to the root. Here's our root, which we said is usually kind of a sloped triangle or a truncated triangle. And what's this? It's a swollen area of tissue. Hard to define what it is on one cut. Let's keep going, shall we? A round area of tissue, the transverse meniscal ligament. Which looks a little strange, and now they start to come together, and we have some interdigitation and some attachments anteriorly. And now, they don't come together. Well, we said that was a transverse ligament, but wait a minute. That's the meniscus, that's a space, that's a ligament, that's an attachment. Let's keep going, shall we? It's still there, but it's not round. If it's a ligament, why isn't it round? Let's keep going. Still not round. Still not round. Still not round, and it's actually into the body of the meniscus now. Let's go back for a minute. What I convinced you was a transverse ligament was not. It's a fragment of meniscus that broke off. There was no transverse ligament. That's a piece of meniscus, that's a piece of meniscus. That's a piece, that's a piece. That's a piece, that's a piece. That's a piece, that is a piece. And so it goes all the way into the body with this obliquely oriented tear with a cleavage component that finalizes in the body, and you can see it coronally too. There it is. There is no transverse ligament going from meniscus to meniscus. There is the root attachment. There is your giant tear, and the fragment is in front of this particular slice. So a large, complex, oblique, slash, cleavage tear with a fragment of meniscus anteriorly whose true etiology is displayed in the fact that on every single sagittal slice, all the way from the root to the body persists, and that's how you make the diagnosis of an anterolateral tear with these complex anatomic characteristics. In the next five minutes, I want to just talk about the concept of extrusions. And I don't mean the kind in your back. I mean the kind in your knee. What you say the meniscus does displace in the knee. You're walking around all day long and you've got these hoop stresses that are pushing down on a structure that looks somewhat like this. It actually isn't a triangle. It has a nice little slope in it to accommodate the femur, which I've drawn here in yellow, and the femur drives down into the meniscus and pushes it. Unfortunately, when we're young and healthy and vibrant, in other words under age 60, the meniscus can tolerate it. Because the attachments are nice and tight and firm. But as we get a little bit older, or if we abuse the meniscus by running 10k every day, and we start driving the femur down onto that meniscus, the attachments may get looser and stretchier and more plastic, and the meniscus starts to displace out of a line between the edge of the femur. We'll draw that line between the edge of the femur and the edge of the tibia. So the meniscus starts to migrate beyond that line. And that may be the primary cause of DJD or osteoarthritis of the knee, or it may be a secondary phenomenon. Once osteoarthritis begins, and we get a little synovial hypertrophy and inflammation, the ligaments digest, the meniscus starts to get a little a little plastic and deformed, and it starts to move out, and then the arthritis gets worse, and it's a vicious cycle. We here at ProSchem refer to this as pseudo extrusion, or plastic deformation of the meniscal attachments due to arthritis. Now what's a true extrusion? A true extrusion for us means one of two things. The attachments have given way, in other words something's ruptured, allowing the meniscus to be displaced or extruded either out peripherally or in towards the middle of the knee. I also reserve it for one other situation, and that is when the meniscus does this. When the meniscus is squished out like toothpaste coming out of a tube, it's starting to get pushed out this way, and it starts to migrate down the peritibial or migrate up the parafemoral gutter. Just to be a little clearer, this would be the femur, this would be the tibia. So now the meniscus is starting to prolapse along the free edge of the tibia or the free edge of the femur. In that scenario also, I'll use the term extrusion of the meniscus or displacement slash extrusion of the meniscus in the parafemoral of the peritibial gutter. Let's take a quick look. Here's exactly just that. Here's our meniscus, and our meniscus is truncated. We'll get to that in a moment. You already know one cause of truncation is a buck and handle tear, but not the case here. This is the most common cause of truncation. The surgeon, the surgeon did it. They truncated the meniscus, they went and cut the inner portion of the meniscus, which actually has a lot to do with the meniscus extrusion or displacement along the para-tibial gutter. Here it is right there. Our meniscus is in trouble, and this patient is lying on their back. They're not even standing up. There's no hoop stress driving down, pushing the meniscus out. When the patient is standing, it's even more extruded. Why did this occur? Because the meniscus got chopped right here. Now when you drive the femur down into a structure that is now paper thin and irregular and has lost some of its depth, you know from physics that that produces a scenario that enhances the pushing effect of the meniscus to one side. Most of the forces are coming down and out, down and out, and down and out on both sides. So the mere fact that there's a trimming increases the likelihood, the physical likelihood that a meniscus experiences more downward force, more hoop stress, and greater likelihood of displacement, and therefore displacement into the parafemoral and para-tibial gutter rendering it useless. So menisectomies are not to be taken lightly. And we'll talk about later on what circumstances they are absolutely indicator. Thanks.