Well, when it comes to sports-related knee injury, all of you have an advantage over most radiologists because of your understanding of the functional anatomy of the knee as well as traumatic mechanisms. And therefore, you can take a biomechanical approach in the interpretation. So what do I mean by biomechanical approach? Let's look at this 32-year-old soccer player who had a contact injury. And so my question for you is, what was the direction of force? So here, these are axial images. There's clearly a joint effusion. And what we're looking for is a bone marrow abnormality contusion to give us an indication of traumatic mechanism. So there's a shear injury of articular cartilage here. And as I come down a little bit further, here's the bone marrow contusion. And where is it located? Well, it's anterior and it's medial. And so if it's an anteromedial impaction, then it's more likely that there's going to be a posterolateral distraction injury. And therefore, once you see this, you can take a very focused and directed look at the posterolateral corner and also the fibular collateral ligament. And because of the anterior location, then hyperextension injury is also a possibility. So we're going to be focusing in on ACL injury and posterior capsular injuries. Okay, so back to these axial images. So we're going to zero in on the ACL. So the PCL is here. Here's the anteromedial bundle. And then here is the posterolateral, which is very, very small and surrounded by this high signal edema or hemorrhage. So we have a partial tear, a difficult diagnosis unless you're looking for it in a very targeted way, a partial tear of the ACL. And here is the normal posterior capsule. And then a little bit more distal, here is this abnormal posterior capsule showing this high-grade tear. So now let's look at the collateral ligaments. At the same level as the tibial collateral ligament, we should expect to see the lateral collateral ligament, which is right here. So we're going to follow it down with a suspicion of a posterolateral corner injury. And notice right around here, it's becoming indistinct. Here completely invisible. And where we expect to see the ligament, there is this surrounding edema or hemorrhage. So that is the sentinel sign that goes along with this high-grade subtotal or LCL rupture. Here in the coronal images, the same patient, the impaction fracture that's anteromedial causing you to take this focused look at the posterolateral corner following the LCL down and then seeing this high-grade tear. So now the axial images. The axial images for me are a go-to imaging plane for confirming that the ligament is normal. If you see an abnormal ligament on the axials, then you go to the coronal and sagittal planes to characterize it. Here is the tibial collateral ligament. And it's very linear. And look how close it is to the bone. So it's not displaced at all. So normal tibial collateral ligament. And the anterior cruciate ligament quickly separates from its femoral attachment site into two bundles, anteromedial, posterolateral. And typically you can follow those all the way down to the tibial attachment site. And then here is the lateral collateral ligament. And we can follow that down where it merges with biceps femoris and then attaches to the fibula. So the axial images are excellent for looking at those ligaments. And if you see an abnormality, now you can turn to the sagittal images where here there's an example of an ACL rupture. There's discontinuity. The ACL is lax in the notch and lying more horizontal. And then here a ligament that's showing a partial tear but looks like it's still attached partially but very, very lax and stretched. Here is the pathognomonic bone marrow contusion pattern in the lateral osseous compartment that goes along with an ACL rupture. Here's the ACL tear in this patient amid substance rupture. Still some visible proximal and distal fibers. Now in the setting of an ACL rupture, because of the anterior tibial translocation, there can be in different locations a force transmitted through the capsule to the meniscus. So you look for a meniscal tear in predictable locations versus a meniscal capsular injury. Some of them can be very subtle. Here's a T1-weighted coronal image that shows the bone marrow contusion. It doesn't do such a good job with the soft tissues, so you have to turn to the T2-weighted coronal fat-suppressed image. Here's the ACL tear. And then here at the post-remedial corner, here's the medial meniscus. Some high signals separating the medial meniscus from this little nubbit of meniscus at the capsular attachment site. And then better seen in the sagittal plane, this peripheral vertical longitudinal tear of the medial meniscus at the post-remedial corner in association with the ACL. Meniscal tears then, Jonathan has gone over some of the criteria. It's pretty obvious if there's an irregular contour and truncation. Linear defects can pose some difficulties when you're not sure if they are simply extending to, but not definitely through, an articular surface. Here is a peripheral signal abnormality that I think is extending through the inferior surface, therefore meets my MRI criteria for tear. And is this an unstable tear? In other words, is it one that's likely to propagate over time with a potential for a displaced meniscal fragment? Well, it can be very, very difficult to know. This one's peripheral. It's in the red zone. It has the potential for healing. And again, if it's unstable, it's gonna propagate in various predictable ways and lead to displaced fragments. Well, this person didn't do especially well and comes back six months later. So this is the baseline study. Here's the six months later study. And we're beginning to see that this tear is extending in a flap configuration along the inferior surface, and then out here popping through the free margin in a parrot beak or flap type configuration. So that was an unstable tear. I think it's very helpful to consider the width of the meniscus and its height, because there may be no other indication that there is a meniscal tear with a displaced fragment, taking into account also the possibility of a previous partial meniscectomy. 25 years old, here's a ACL rupture. And here in the medial compartment is the medial meniscus, normal or abnormal. Well, it's pretty black. It's pretty smooth in contour, not perfectly smooth. There's a little bit of truncation. For me, the main thing is that it's decreased in size. So a piece is missing. And as we head more towards the intercondylar notch, here's one displaced fragment from the anterior horn, the other displaced fragment from the posterior horn, and then this double PCL sign that Jonathan mentioned. Coronal plane, same person. The displaced meniscal fragment, so the stable peripheral fragment, very small in size, so decreased height and width, and then the unstable displaced fragment under the PCL. So classic bucket handle tear. This person also has a truncation involving the posterior horn of the medial meniscus, some intrameniscal signal as well. This means I gotta take a much closer look in locations where it's most common to see displaced meniscal fragment. And that can be in the intercondylar notch, but also it can be in the inferior recess of the medial gutter. So here is this truncated medial meniscus. Here's the tibial collateral ligament. And underlying it, here's an extra low signal focus with adjacent sentinel edema involving the medial tibial rim. So this edema, for me, is very, very important. So the meniscal flap then, it's an unstable tear, it can lead to propagation, and therefore displaced meniscal fragments. Oftentimes there are two displaced fragments. One is in the posterior aspect of the intercondylar notch, and the other is in one of the gutters of the medial gutter, one of the recesses of the medial gutter. T1-weighted coronal, fat-suppressed T2-weighted coronal, large effusion, lots of periarticular edema. Here the medial meniscus looks pretty good. And then what happens? All right, so we're starting to see some edema involving the medial tibial rim. That's the first tip-off that there is going to be an adjacent displaced meniscal fragment. We're starting to see it right here, and then it gets bigger, and then bigger. Also here in the intercondylar notch, there's another displaced fragment. So posterior horn, and then this is abnormal. So this was a longitudinal tear complex involving the middle and posterior thirds of the medial meniscus, resulting in two partially detached displaced fragments. One here in the notch, and the other in the inferior recess. And you can apply these principles, oh, and then here is that tibial collateral ligament and the displaced fragment partially underlying the tibial collateral ligament. So the same principles can be applied in other locations. So medial meniscus, truncation, think displaced fragment. Here the displaced fragment is in the superior recess of the medial gutter, underlying the tibial collateral ligament, causing adjacent sentinel bone marrow edema. Tibial collateral ligament, we come up a little bit, and then here is that displaced fragment adjacent edema. So although the most common site of meniscal tear is medial, in the setting of an ACL, look for lateral meniscal tears. And it's because of this structure mentioned by Jonathan earlier, the meniscal femoral ligament. So in the setting of ACL tear and translocation of the tibia, tension is transmitted through the meniscal femoral ligament to the posterior horn of the lateral meniscus, resulting in transverse tear or a longitudinal tear, sometimes even a root ligament avulsion. So pathognomonic contusion pattern for ACL rupture, pretty obvious, posterior horn lateral meniscal tear. But my point here is this meniscal femoral ligament and the fact that the tear is located right at the ligament attachment site. Sagittal plane, here is the Risberg, and we're going to follow it down to the attachment site of the meniscus, and that's where the tear is located. Coincidence, no. In this case, there's an ACL rupture, and there is a peripheral vertical longitudinal tear of medial meniscus, but don't stop there, you need to take a look at the lateral meniscus as well. So we come to the notch, PCL looks good, here's the ACL rupture. Here is Humphrey, and we follow that down to the posterior horn. And really on the next slice, it should be attached, but the space gets wider, and then we continue to see this tear, this peripheral vertical longitudinal tear involving the posterior horn of lateral meniscus at the meniscal femoral ligament attachment site. So combination injury, medial lateral unhappy triads, medial ACL, MCL in one of the menisci. So what about this medial meniscus, sorry, tibial collateral ligament, normal or abnormal? Well it looks like it's continuous, but look how separated from the tibia it is with the underlying high signal, and it's very, very lax. So this may be all you see in the setting of a distal MCL rupture, and the location of that rupture may not actually be included on the MR image, it could be cut off. So this is a rupture of a distal MCL, bone marrow contusion, head back more posterior, this is the ACL rupture, same person, here's the peripheral tear involving the medial meniscus. So MCL, MCL, medial meniscus. Tibial collateral ligament here, it looks like it's intact, maybe it's a little bit fuzzy contour and thickened. Same patient, three years earlier. So this is pretty amazing. So three years earlier there's what appears to be a subtotal tear, a rupture of the MCL, and here it is a side by side comparison. It looks normal, three years earlier it was very, very torn. So this is an incompetent MCL that is remodeled. It's scarred, it's remodeled, but it's not normal tissue. And then here on the axial images, what appears to be a normal MCL, but here clearly there's a high grade tear. So as good a job as MRI does in the acute setting, in the chronic setting it can be very, very confusing. This is, that principle can be applied to the ATFL in the knee and the UCL in the elbow. It can also be applied to the ACL. So here is a person who has what most radiologists would call an ACL rupture. And now three years down the road, an ACL that looks nearly normal. It's a little bit lax. And then comparing side by side, a rupture versus what appears to be intact, but is in fact an incompetent ligament. And that person underwent an ACL reconstruction. Side by side baseline three years later, looks intact, but it was completely ruptured. So the lateral unhappy triad, to wrap things up, is going to be ACL plus minus PCL in the posterolateral corner. So conveniently, this 15 year old had a knee MRI when the knee was pretty much normal, but then really did have a substantial injury with a varus flexion internal rotation mechanism. So we have a side by side comparison. 15 years old, normal, 17 years old, the injury, here's a bone marrow contusion, lateral femoral condyle, pathognomonic for an ACL rupture. Here's the ACL at the not normal time point and the absence of the ACL down the road. Notice that the PCL is also abnormal. So it's thickened, there's some edema, and then here there's a partial tear involving one of the bundles. Bone marrow contusion pattern, posterior aspect, lateral tibial plateau. And then the popliteus tendon looks like it's intact. Here's the LCL with some adjacent edema or hemorrhage. And then here's quite a bit of edema and hemorrhage at the posterolateral corner in comparison to the absence two years earlier. So the sagittal images, normal ACL and then ruptured ACL. And we're going to move our way over to the lateral compartment, typical pathognomonic bone marrow contusions. And then what I'm pointing out here is all this edema and hemorrhage at the posterolateral corner. And it's going to be best to characterize that on the axial images. So here we are. First of all, the tibial collateral ligament is a little bit separated, but the ligament is otherwise intact. And then in the intercondylar notch, here's the normal ACL and then the absent ACL, the PCL which is swollen, and then this posteromedial bundle showing this partial tear. Okay, so ACL rupture, partial PCL. And here's the lateral collateral ligament. And this is the normal ligament. And it's a little bit thicker than it is. It's more attenuated at the time of injury but not ruptured and surrounded by some edema or hemorrhage. And we're going to come down to the popliteal fibular ligament. So you identify the fibular head and then come up to the apex. And if you're lucky here in the normal situation, you can see that popliteal fibular ligament and its disruption two years later. So a posterolateral corner injury in combination with an ACL rupture, partial PCL, and a partial LCL. And this is the last case I have. And this calls back to the very first case where there was an anteromedial impaction injury. So here are kissing contusions involving the medial femoral condyle and the medial tibial plateau indicating that there must be a distraction injury at the posterolateral corner. So we're going to continue posteriorly into the intercondylar notch. And there is no ACL visible and there's no PCL visible as well. So both cruciate ligaments look abnormal. This is the condylar fossa where the popliteus tendon should be attached. And there is no popliteus tendon. And then here is the fibular collateral ligament showing this laxity and discontinuity. So that's ruptured as well. So it's a three ligament injury at this point plus the loss of a dynamic stabilizer, the popliteus tendon. On the axial images, patellofemoral alignment looks good. There's a joint effusion. The tibial collateral ligament looks great in the intercondylar notch. Here is some displaced ACL fibers and absence of the PCL. So we come up to the MCL attachment site where we should see an LCL, but it's missing. So another sign of LCL rupture. And then in the popliteus fossa, no popliteus tendon. We come down a little bit further. Here is the retracted popliteus tendon. And then a little bit distal, the LCL also pulls itself together. And then the biceps femoris in this case is normal. And you can follow it down to the fibular attachment site. So that's the pathophysiological approach or biomechanical approach that I know all of you guys can take because of your understanding of functional anatomy, recognition of patterns of injury. So have fun with knee MRI using this biomechanical approach. Thank you.

knee MRI scans

sports-related knee injuries

biomechanical approach

ligament tears

meniscal tears