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Knee Case 3

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Case number three is not gonna be a case of a meniscal tear,

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it's not gonna be a meniscal tear, there may be a meniscal tear

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there, but that's not the reason why I'm showing you the case.

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In fact, there is actually a meniscal tear here, but that's not why

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I wanna show you the case. I wanna show you the case for

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a different reason. I wanna start with the sagittal T1 as I always

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do. I think it's very important to get into a habit

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of looking at things. So I'm starting laterally. I'm already noticing that

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there's a little bit of signal in the posterior and lateral tibia maybe

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the anterior lateral femur there, okay, maybe... Yeah,

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maybe some meniscal signal right here, but you wanna look at it on

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a proton density or a T2 weighted, okay, so

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there's something going on there. When I turn to the sagittal T2s.

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Okay, and then look at the marrow. Oh, wow, okay, so I'm already

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seeing marrow edema along the anterior lateral femoral condyle right here.

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Posterior lateral tibial plateau. Okay, so these are likely microtubule

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contusions that have occurred. If I go immediately, I'm also seeing Bone

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Marrow Edema along the posterior medial tibial plateau.

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So there are microtubule contusions, these are micro fracture in the bone.

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Okay, that's what this is. And The patella overall looks okay.

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So I wanna bring Ashley in here to ask question number

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four. Okay, so based on this, what soft tissue structure is injured in

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this patient that has bone marrow edema in both the anterior lateral femoral

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condyle and the Posterior tibial plateau? Is it the ACL, the PCL,

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the media collateral ligament, or the medial retinaculum, which soft tissue

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structure is injured based on the marrow edema findings that you're seeing

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here? Okay, so 89% of people got this correct, the ACL, the Anterior Cruciate

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Ligament, that's exactly right. Okay, good. So this is a pivot shift injury,

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this is a pivot shift injury when you get marrow edema along the

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anterior lateral femoral condyle as in this case, in the posterior lateral

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tibial plateau. That should ring alarms in your brain automatically, okay.

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This is a pivot injury. The ACL will be torn in 100%

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of cases. Okay. In every case that I've seen of this,

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the ACLs has always been at least partially torn if not completely torn,

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okay. This is a pivot shift injury, this happens in people like... Skiers

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or American football players, okay. When a valgus load is applied to

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a knee with a femur, either an internal rotation or the tibia in external

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rotation. Right? So if the valgus load is applied to a flex knee,

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where the femur is internally rotated or the tibia is externally rotated,

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you get this pivot shift injury mechanism where you get

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loading on the ACL and the ACL is pretty much torn. Okay. And

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you get these microtubule contusions in these areas. Now I'm gonna show

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you the ACL, just look at that. Look at this ACL it's thickened, there's

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fluid transecting, the mid substance of it. It's just...

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That's a complete rupture or a complete tear, you can't trace all the

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fibers because you have this fluid discontinuity right here in the middle

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of the tendon... Of the ligament, excuse me. So, this is a complete

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tear of the ACL. With a Pivot shift mechanism with bone marrow microtubule

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contusions along the anterior lateral femoral condyle, the Posterior lateral

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tibial plateau. In fact, the reason why I'm showing you this case,

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is that Bone Marrow Edema patterns in the knee are extremely,

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extremely important. Okay. The Bone Marrow Edema patterns predict the soft

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tissue structure that's injured. Okay, so if you get...

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This is one of five marrow edema patterns that's recognized

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as a classic pattern that predicts soft tissue, this is known as the pivot

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shift mechanism of injury. When you get, if you get marrow edema of the

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anterior lateral femoral Posterior lateral tibial plateau, the ACL is always

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injured. There's four other classic contusions patterns that... I'm actually

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gonna show one of them later on in this talk, but this is

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the pivot shift mechanism of injury. And I wanna show you another

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finding in this case, so this is the medial, and again,

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notice that the posterior horn is double the size of the interior.

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There is a little bit of signal here,

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it's not really going to the inferior or the superiority that... So maybe

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this slightly degenerative signal or equal degeneration within the meniscus

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without the sweet terry. But as we come laterally... Look at the anterior

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horn, the posterior horn, there is a little bit of signal here kinda going

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to superior and the inferior surface there. Okay, it looks a little abnormal,

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seen on two or three slices. If I go to the

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coronal stars to focus on that lateral meniscus there...

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Okay, so yeah, there's a signal here, this meniscus is torn,

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there's a tear that the periphery of this... Of the

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lateral meniscus, the posterior horn of the lateral meniscus. This is anteriorly

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with a meniscus is attaching with a transversal ligament along with a tibial

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root attachment, and then if we go posteriorly, it doesn't look that great.

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This may involve the root, this maybe a root ligament here as well

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on the posterior root about ligament. And you can see part of the...

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It's sort of a complex tear, there's some signal here and there's some

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signal there, so this lateral meniscus is not looking great, okay. So you

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can see the nice microtubule contusions here along the lateral femoral condyle.

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You wanna make sure there's no condyle defects. So this is the marrow,

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this hypo intense dark line is the cortex, and this great intermedia signal

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is the articular cartilage. So you wanna scrutinize this cartilage well,

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I like looking at it at the coronal's the best, especially the medial lateral

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femoral condyle, I think the coronals is the best. For patella department,

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I think the axial is better to look at the articular cartilage,

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you can see the cartilage better, but you wanna make sure that the

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signal is preserved and it's nice and great. You start to see a fluid

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signal, you know that there may be a defect in the cartilage can

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be partial thickness, or if it involves the entire thickness of the cartilage.

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It's a full thickness. Here, the cartilage actually looks relatively preserved.

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When you have intermedia signal within that cartilage, there's debate whether

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that's normal, that could be cartilage generation or early cartilage generation,

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but here the lateral compartment cartilage, I think looks, okay. Okay,

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you can actually also see the ACL, this is the ACL right here, look how

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it's amorphous, it's not well defined, there's fluid all around it,

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this is a torn ACL. The PCL on the other hand,

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which is a dark hypo intense structure is preserved. I can see it

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inserts extra articularly, about the proximal tibia, and If I trace it approximately,

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I can see it inserting right there on the medial intercondylar notch, that's

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a normal PCL, okay. Good, you can see here too look at this

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fibular collateral, create one, maybe create two sprains of that fibular

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collateral ligament approximately, okay. Other findings here as well.

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Come back to the sagittal. We can again, take a look at these

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here, there is probably a small joint effusion, this is more than just

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physiologic, there's likely a small super patellar joint effusion. The quadriceps

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tendon looks intact. The extensor magazine, the patellar tendon, I think

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probably looks okay, there is a little bit of pre patella soft tissue

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edema here, along the posterior joint capsule here. So those are all findings

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that you wanna kinda take a look at, when you're reviewing a case

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like this. Okay, so this is a pivot shift injury, they can be

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associated with meniscal tears... Meniscal... Both medially and laterally.

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In this case, we had a lateral meniscal tear, but the pivot shift

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is, 100% of the time is associated with an ACL tear,

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as we saw in this case. The Anterior Cruciate Ligament is torn. When

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you have... The moral of the story, and this... The teaching point here

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is that when you have marrow edema along the anterior lateral femoral condyle,

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posterior lateral tibial plateau as in this case, the ACL is totally torn,

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in those cases. Okay? Alright, good.

Report

Description

Faculty

Omer Awan, MD, MPH, CIIP

Associate Professor of Radiology

University of Maryland School of Medicine

Tags

Trauma

Musculoskeletal (MSK)

MSK

MRI

Knee

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