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Here is a nine-year-old girl

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with nonspecific knee pain.

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As we look at this, I don't

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see a lot of abnormalities.

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But one thing, as we look at these radiographs,

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we have to really pay attention to is not just

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the femur and the tibia, but also the patella.

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And you have to try to look through

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the distal femur into the patella.

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And when I look at the patella, I can

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see a faint outline right over here.

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Okay?

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And so I lose it at the inferior

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border, but I can sort of imagine

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that this is what it looks like.

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Now, within that circular area,

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there is a subtle lucency.

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Can you find it?

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Let me point it out to you

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with the freehand tool.

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It's right here.

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I know it's very hard to see,

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but that's where it would be.

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Let me go ahead and delete it.

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That's where that lucency is.

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Let's look at some other projections.

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Let's look at the oblique view.

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In oblique view, I don't see that very much,

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but what I do see is another area of sort of

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funny lucency over here at the medial aspect.

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Again, I'm gonna try to outline that for

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you, and this is less well-defined,

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but I'm gonna do the best job I can.

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Looks sort of, looks something like this,

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like that, and that's what I'm talking about.

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So let's delete that.

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Okay, so I think you see that area.

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One other area I'm going to show

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you on the other oblique.

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So again, I see a little haziness

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over here, a little lucency, but here

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is that thing on the patella around

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a lucency in the patella over here.

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None of these things are in

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and of itself abnormal, okay?

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But every so often, you know, you may have

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an inexperienced person looking at this.

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And an MRI will be obtained for

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these quote-unquote lesions.

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And I just want to show

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you what these are on MRI.

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So let's look at some MR images of this patient.

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I'm going to bring up the sagittal image.

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This is the fat-suppressed

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fluid-sensitive sequence.

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And let's first pay attention to

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the patella, quote-unquote, lesion.

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Here is the patella, and here is what we

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are seeing, that lucency on the radiograph.

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I'm going to blow this up a little

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bit, like that, and I'm going to show

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you exactly what I'm talking about.

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Here is our patella.

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Well defined.

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The margin between here and here is obscured.

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But what we do have is what looks

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sort of like a mushroom cloud.

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Here's the stalk of the mushroom and

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here's the little undulations of the cloud.

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And this is a very characteristic MR appearance

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of what's called a dorsal defect of the patella.

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It's a normal finding.

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Again, a little controversial.

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Because let's go back to our

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exam here on the plain films.

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If you look at this lesion, the

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cartilage here is actually quite thick.

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Okay, there may be a little

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indentation, but it's quite thick.

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Uh, there's a little bit, perhaps a

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little edema, but it's not very much.

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Let's see what this area looks

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like on the axial projection.

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On the axial projection, we see it right here.

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There are some areas of edema, some

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areas of high signal, if you will.

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I'm going to zoom that up just a little bit.

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So this is a very characteristic appearance

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of a dorsal defect of the patella.

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Some people say this is asymptomatic and

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other people say it can cause symptoms.

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I personally think it does cause symptoms.

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If it didn't, why would there be edema?

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Oftentimes there's tugging here at the

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retinacula or the medial patellofemoral

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ligament and the lateral retinaculum.

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So when that happens, when these things

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tug, okay, it can cause some pressure

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across this area that's not quite intact.

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So I think you can have some knee pain

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with this, but this is what the dorsal

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defect of the patella looks like.

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If you see it on plain films, comment

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on it, but it doesn't necessarily

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require an MRI for evaluation.

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Okay, because there's nothing

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that's going to happen about this.

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There's nothing they're going to do about this.

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Remember that subtle lucency

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we saw at the back here?

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This right here, this ends up being,

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if we look on the sagittal images,

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this thing here, okay?

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So this is where you have muscular attachments.

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It's the medial side, it's going to

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be the medial head of the gastroc.

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So this is a little tug lesion, okay?

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The muscles that attach here are

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pulling on it as the person is active.

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That also is a benign finding.

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You don't want to call this pathological and get

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biopsied because this area will demonstrate high

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mitotic rates and it can be confused with a tumor.

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But this is a very, very common

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location of a cortical desmoid.

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So don't call this abnormal.

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Even though it looks like this.

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Let's show you what that looks

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like on the axial projection.

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Coming back here, you can see it.

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Let me pan up a little bit so

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you can center and zoom up.

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That's what this looks like.

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This is not an abnormal finding.

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This is a little tug area from

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the medial head of the gastrocnemius.

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Gastrocnemius.

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Let me zoom out so you can see.

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Coming back up, totally normal finding.

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I'll bet you this person has the

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same thing on the other knee.

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Okay, finally, did you notice as I

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was going through the sagittal images?

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Let me zoom out a little bit.

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Did you notice that this person also has this.

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And what was that from our previous vignette?

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That was our FOPE.

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Very good age range, right?

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So we've got a central area of a

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little bar between the physis going

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from the epiphysis to the metaphysis

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and causing a little bit of edema.

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So this is the focal periphyseal edema, a

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completely normal finding in this patient.