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54-year-old man with a fall.

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He's got a PCL tear.

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The PCL is too small,

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and that's because the rest of the fibers

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are obscured by the edema and swelling within the PCL.

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If we scroll it,

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we can see some of those fibers right here that

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are blending in with the surrounding soft tissues

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and blood. We look inside the PCl,

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and there's high sign signal within

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the confines of the PCL.

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And on T1 there's gray signal within the confines

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of the PCL. But that's not all.

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Oh, there's more.

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This patient had a posteromedial corner injury.

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Now we're going to show you his

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posterolateral corner injury.

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So let's go there to the posterolateral corner

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where we ascertain the presence of a fracture and

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the attachment of the lateral meniscus

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to the popliteus region.

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And the inferior fascicle of the

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lateral meniscus is gone.

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That's why the meniscus looks like it's floating

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and blunted. What else is of interest to us?

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Well, the popliteus tendon.

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There's our papateous tendon,

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and our papateous tendon should have an attachment

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to the fibula called the papateofibular ligament.

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What's our papateofibular ligament doing?

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Well, let's draw over it.

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There's the popliteus tendon.

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And here is our papillateofibular ligament.

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It should go to here, not down here.

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It looks a little bit like a mermaid.

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There's the body of the mErmaid.

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There's the tail of the mErmaid.

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We've got the mermaid sign of pop fib ligament,

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or PFL tear,

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as a component of a posterolateral corner injury.

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What about the arcuate?

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The arcuate is this sort of irregular,

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wavy tissue right behind the Popliteus tendon.

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Popliteus tendon arcuate comes

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to a blunt end right there.

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That's the vertical limb of the arcuate.

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There's also an oblique limb that's a little

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bit deeper. So we actually see the arcuate,

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which you don't often get to do,

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and its blunt end.

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We see the popliteofibular ligament straggling

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down, caudal or inferior, on the image.

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Now let's go to the coronal projection.

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We've already established there are at least three

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components postrolaterally that are torn,

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the attachment of the meniscus,

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the arcuate, and the pop fib ligament.

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Let's take a look at the pop fib ligament.

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In the coronal projection,

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there's the popliteus tendon.

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It should come down and course anterior,

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inferior and medial. Kind of like this pop tendon.

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Then it should come down this way.

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It's some fibers off obliquely towards the fibula.

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Except that they're not very straight, are they?

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They're kind of irregular, drawing over them.

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Now let's take them away.

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That's the popliteofibular ligament.

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This is all injured tissue, bloody tissue.

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In fact, you can hardly even see it on the T1.

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weighted image. All you see there is blood.

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It's completely obscured by this material.

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And you see some fibrillated, crimped, irregular,

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ragged fibers right there.

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That is all part of the torn pop fib ligament,

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or PFL.

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What's right next to it?

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Right next to it is the arcuate.

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Better seen on the water weighted image.

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The arcuate vertical limb comes up.

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And it should be a straight structure.

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Not one that is wavy and corrugated like

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we see here. Why do we see it so well?

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Because it's bloody and thick.

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Normally, it'd be very hard to discern.

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So we've reaffirmed in the coronal projection.

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That the PFL is torn.

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At least a component of the arcuate is torn.

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A component of the meniscocapsular attachment is

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torn. There's a posterolateral corner fracture.

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You've seen the mermaid sign.

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All in conjunction with our PCL.

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Which puts our patient at risk.

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If these were the only two findings for PLRI.

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Posterolateral recurrent instability

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or rotatory instability syndrome.

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With all the findings of this case,

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the patient is certainly a surgical candidate.