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<v ->The third plica is the inferior plica

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or ligamentum mucosum.

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If you look at this image,

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you can see it arises from two anterior alar synovial folds,

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it courses back posteriorly.

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So part of it is located anteriorly within Hoffa's fat pad,

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part of it is located intrasynovially.

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It passes up into the intercondylar notch

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just anterior to the anterior cruciate ligament.

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Diagrammatically maybe it would look like this.

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Now I first learned about this plica

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when I was doing standard arthrography of the knee.

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(man coughing)

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No MRI arthrography, no CT.

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(man coughing)

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What we, excuse me.

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What we would do, we would go ahead and inject the knee

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with the ionic contrast agent

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and then we would take some radiographs of that.

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And sometimes when there was a completely torn

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anterior cruciate ligament,

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we would mistake this plica

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for an intact anterior cruciate ligament.

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That was one of the mistakes that we would make.

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So when we talk about this particular plica and its anatomy,

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you can see the intrasynovial portion here,

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paralleling the anterior portion of the ACL,

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and then it curves up.

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And its attachment sites are somewhat variable.

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It can attach to the patella,

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typically pretty deep on the patella.

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And sometimes at the osseous

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or the chondro-osseous junction.

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It can attach to the patella tendon.

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It could attach to both.

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And occasionally it attaches

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to the anterior transverse meniscomeniscal ligament.

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So a lot of attachments.

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That is why some people believe

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that it can influence patellar tracking

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and may lead to altered patellar tracking.

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To show you what some cases of inferior plica syndrome,

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I would tell you that I have seen

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a few of these in cadavers.

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This is one of the nicest example that we saw

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in a cadaver,

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where you can see how thickened this structure is.

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That's not the ACL, all right?

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The ACL was back here, look how thick it is.

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And then you can see how it curves up and attaches to here.

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It looks like to the patella cartilage.

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Here, image is showing you what that looks like

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and you can see its attachment to the patella

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and you can see edema around that plica

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or ligamentum mucosum.

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Now in my view, this is another sign

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of altered patellar tracking.

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I know I've talked briefly about edema within the fat pads,

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but this particular location,

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Hoffa's fat pad edema about the ligamentum mucosum,

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I think is a reliable sign of altered patellar tracking.

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It's not specific, but it certainly is a sign.

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Here's another one.

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All right.

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You can see here not only that there is abnormal signal

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in Hoffa's fat pad about the ligamentum mucosum.

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Look at the patella and you can see reactive changes

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within the patella itself.

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And following an injury,

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and there are reports in the literature of injuries

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to the ligamentum mucosum-producing hemarthrosis,

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Clyde Helms, a well-known bone radiologist,

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for an article on this years ago.

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His cases were much more subtle.

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I don't think when you see edema that's subtle

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around the ligamentum mucosum,

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you can say that it's injured.

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Other things can do that as well.

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But when it's this prominent, as you're seeing here,

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and it looks like there is actually avulsion

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of a portion of the ligamentum mucosum from the patella,

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that's related to trauma.