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This is a 49-year-old female with knee pain.

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Sensation of catching,

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and she has had prior arthroscopy.

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Let's begin with a series of sagittal images.

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On the far left is the proton density fat

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suppression, the water sensitive sequence,

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the T2 in the middle,

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and the fat weighted morphologic sequence

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on the right. Let's scroll.

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If so,

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she did not have a specific episode of trauma.

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I will give you the penetrating trochlear groove

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erosion and the one in the patella.

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They probably clang against each

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other with a knee inflection.

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But the purpose of showing you these three

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sagittals is to demonstrate the abhorrent

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appearance of the anterior cruciate ligament.

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It is lying down. The axis is abnormal.

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It is headed towards the posterior cruciate

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ligament, which is right there.

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And you can't really see any normal

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tissue on the T1. weighted image.

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So what tissue we're seeing

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here is severely diseased.

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The proximal tissue is basically pulverized.

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There's no proximal acl.

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So this is an acl tear in the absence of a known

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traumatic event. So how did this happen,

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by the way?

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Some of you may be focusing on this small little

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cystic area here. That's an intraoceus ganglion.

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It's a distractor. Ignore it.

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What's it from? Friction.

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What's the friction from? Dysplasia.

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What's the dysplasia?

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Well,

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let's take a look in the sagittal projection.

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Let's draw a line along Blumenstadt's

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line right there.

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And then let's take a line right down the

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barrel of the center of the tibia.

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So the tibial axis.

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And we're assuming the knee is pretty straight,

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if we look at this angle,

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this angle should be about 138 degrees.

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As this angle closes,

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more stresses are placed upon the native anterior

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cruciate ligament. So in other words,

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as Blumenstadt's line becomes more horizontal,

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the stresses in the knee notch become greater.

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There are other stressors on the anterior

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cruciate ligament. In the knee notch,

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sometimes you have dysplastic bony ridges.

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This patient has one, actually.

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Sometimes you'll have spurs that encroach on the

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acl, secondary notch dysplasia or notch stenosis.

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And then you can look at the axial.

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Let's do that. Let me close my window,

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my drawing window for a minute here.

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Let's take a look at the axial.

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And as we come up a little bit,

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look at this ridge right here that's pressing

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against the front of the notch,

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and then look at the notch.

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It's kind of narrow, then broad,

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then narrow again in the back.

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And we're going to have a separate

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vignette to look at measurements,

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which I often don't do because they take a lot

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of time, and I find them of limited utility.

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But we'll show you some ways to measure the

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anteroposte dimension and the transverse dimension

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and some ratios of these dimensions relative

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to the condyles. At a separate sitting,

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let's take a look at the notch in the coronal

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projection for a moment in this patient with an

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utterly pulverized torn anterior. Christian,

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let's bring down a gradient echo in

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the middle and a T1 on the right.

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Look at how the notch has a very wide patulus,

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globular appearance. Up high, it's rather tall,

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and then as it comes down,

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there's a pretty sharp taper.

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So that in itself is a form of dysplasia.

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Has a very weird shape to it.

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It's almost like a perfect oval, if you will.

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And in the coronal projection,

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you again identify the squiggly, wiggly, diseased,

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pulverized fibers of the anterior crucial

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ligament on the gradient echo image.

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Now, I could say pay no attention to the meniscus,

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but that would probably be a little too dismissive

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since there is a giant, complex,

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chronic cleavage tear of the medial meniscus,

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generating a massive perimeniscal pseudocyst of

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meniscal origin. These tend to be bigger.

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They tend to go more posterior.

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They tend to be more painless on the medial

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side than the lateral side.

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Lateral side,

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they like to be a little more anterior.

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They're smaller, they're more painful.

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No, that is not a perimenoiscal lateral cyst,

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as some of you might have thought.

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Those are vessels.

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So a little pitfall or trick there.

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Let's look at our meniscus and our acl

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on the T1 There's our missing acl.

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There's a fiber of it right there.

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And here is our large medial meniscus tear with

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our proteinaceous perimeniscal pseudocyst,

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a meniscal origin.

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Why is it a pseudocyst not lined by epithelium,

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not lined by synovium?

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It is lined by fibrous tissue.

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Diagnosis,

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dysplasia of the knee notch resulting in

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spontaneous rupture of the acl due to

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repetitive friction and microtrauma.

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With a myriad of other findings,

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including a large medial meniscus tear and a

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perimeniscal pseudosystem. Meniscal origin.

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Let's look at another one, shall we?