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I want to talk to you about a subject

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of biblical importance,

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and that is the prepatellar plate.

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Not too many people are excited about

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the prepatellar plate, but I am,

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which makes me a little bit nerdy.

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So, let's look at the patella

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in the sagittal projection.

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And then, let's take some tendon

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that's headed towards it.

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And that tendon is called a quadriceps tendon.

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Now, that tendon is actually composed

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of several layers of tissue.

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and that's why you're going to see within it some

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high signal intensity linear foci

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that look a little bit like this.

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Those are fat stripes and they occur because you

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have agglomerated or aggregated

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a group of structures that include

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the rectus femoris anteriorly,

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the vastus medialis and lateralis,

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in the middle,

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and the vastus intermedius is deep.

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So sometimes,

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that takes a little bit of fat with it

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as it fuses and comes towards the patella.

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Now, when it gets down to the patella,

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only the superficial layer comes down,

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which is the rectus layer,

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and this contributes to the pre patellar plate.

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Unfortunately,

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the prepatellar plate is a lot

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more complicated than that.

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A lot of you are familiar with the entity

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called prepatellar bursitis,

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but did you know that there are actually three

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different bursal layers in front of the patella

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in that little tiny space?

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That's crazy.

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Here's the skin,

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here's the prepatellar subcutaneous bursa.

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Here is the superficial transverse fascia layer.

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Then we've got another bursa,

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our middle bursa layer

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called the prepatellar subfascial bursa.

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Then we've got another layer

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of aponeurotic tissue,

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the intermediate oblique aponeurotic layer.

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And then we have another bursa,

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bursa number three,

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the prepatellar subaponeurotic bursa.

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And then, finally, we run into our longitudinal

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rectus fibers that are continuing over

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the top of the patella.

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So not one, not two,

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but three different bursa

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separated by aponeurotic layers.

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Now, structures may rub and tug against the patella

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and produce some bony proliferation.

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when it happens in the sagittal projection

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at the edges of the bone.

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Here's the patella,

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my weak attempt to drawing a sagittal patella,

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but when, let's say,

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the quadriceps is tugging on,

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it may make some spurs above,

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patellar tendon may make some spurs below.

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Let's pretend this is anterior here.

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Through continuous rubbing,

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sometimes the bone proliferates and makes

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these little wavy structures anteriorly.

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And this was described some time

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ago by the highly respected

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venerable and well known author,

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Ted Keats,

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who called this the tooth sign of the patella.

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And so the tooth sign on plane film,

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on plane radiography,

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described so beautifully in his variance book,

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is also visible on MRI,

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and it looks a little strange,

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so don't get put off by that.

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So now, let's look at our case.

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So, this 43-year-old man has knee swelling

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in the absence of injury.

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You're looking at a sagittal water-weighted image

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and a sagittal T1 weighted image,

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and you're struck by the high signal intensity

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anterior collection.

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And it has some blood products inside it,

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some high signal intensity,

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methemoglobin staining on the T1,

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fat-weighted image.

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So, immediately, you think trauma.

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But there's been no trauma,

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so that wouldn't really make a lot of sense.

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This is not an inconsequential thing you're seeing here.

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So, how can this happen?

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Well, by twisting,

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you know, perhaps it wasn't an injury.

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Perhaps it was a turn.

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You can shear off

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the fascia layers and produce what's known as

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fascial degloving, or Morel-Lavallée syndrome.

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Now, it's said thaat that's most common

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in the region of the hip and gluteal region,

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near the fascia lata.

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In our practice,

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we see more of them in the knee,

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but we do see quite a bit both

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in the hip and the knee.

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So, you can sit around and debate

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where it's more common.

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But the prepatellar space is a particularly common site,

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and you're probably wondering,

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well, which of those three bursa are involved?

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Well, that's pretty easy.

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You can pretty much count out the

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subcutaneous anterior bursa,

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because that one almost never distends.

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And if you look very carefully,

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and I blow this up for you,

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I'm going to do that right now.

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You can see there are actually two layers

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of fluid like signal here.

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This layer,

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which is a bit thicker,

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and the next layer behind it.

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Now, what's this linear structure?

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Another fascial layer.

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So, we have two layers that are distended.

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The prepatellar subfascial layer,

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not the subcutaneous layer,

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and the prepatellar subaponeurotic layer.

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And then this linear area right here

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is a little bit of stripping of the prepatellar plate.

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In other words,

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these are a few of the fibers separated

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from the rectus femoris tendon.

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So there's the rectus layer.

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There's a little bit of stripping

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of the rectus layer.

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There's the deep fascia layer that is degloved.

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There's the middle fascia layer that is degloved.

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And the subcutaneous fascia layer not seen,

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although there's superficial swelling.

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And the whole thing is associated

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with some hemorrhage.

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Let's look at it axially,

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because it goes over quite a bit to the side.

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And that can be a little bit confusing.

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Here's a little bit of separation of your rectus layer

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from your deeper rectus layer.

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So, you've got a little bit of rectus

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delamination of the plate.

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And then your deepest layer of bursa here,

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your middle layer here,

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and your superficial layer is not visible

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because it's not distended.

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This is Morel-Lavallée syndrome,

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or fascia degloving syndrome,

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with an injury to the prepatellar plate.