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Wk 4, Case 5 - Review

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Our first case is a 15-year-old male with lateral

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left knee pain after a hyperextension injury

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while playing football, American football,

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two weeks ago.

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So this is a two-week-old injury.

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And the case is a little bit challenging in

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that there are findings in obtuse places.

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So, let me start out with my approach to imaging

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extremities, which I've shared with you before.

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I take a biophysiologic approach to these cases.

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So, if I can latch on to a soft

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tissue or a skeletal finding,

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I use that to figure out the mechanism of injury.

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I also try and figure out whether the abnormality

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that I'm looking at is acute, subacute, chronic,

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or remote,

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and then, I will go on to rate its severity

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and comment with some selective words on

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its overall impact in management.

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So, I usually start out almost every

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case by looking at the axial,

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because that's what comes up first.

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And on a T2-weighted image, there is a

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collection that is not simple fluid.

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How do I know that this is a T2 weighted image?

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It's a heavily water weighted image,

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and water should be white.

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This collection is not white.

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It's gray, and that's because the signal

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is down-averaged from the blood that has

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accumulated in the joint.

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What are some other causes of down-averaging

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of fluid signal, which should be white?

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Well, something heavily proteinaceous could down average,

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but usually that's somewhat heterogeneous.

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You'll see internal signals within.

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So, I do not see a fluid level or a fat fluid level yet,

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but I'm going to be on the lookout for that.

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One of the more common causes for this in

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a 15-year-old is patellar dislocation.

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So that's immediately where my mind would go,

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and I would look at the Medial Patellofemoral Ligament,

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which is right here.

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And the Medial Patellofemoral Ligament comes off

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the femur here at the level of the adductor tubercle,

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and that is intact.

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So, so far, no signs of that.

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A medial patellar fracture. No signs of that.

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A lateral patellar fracture is a sign of patellar

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dislocation, but the fracture is over here,

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not over here. So what are we looking at here?

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We're looking at a saucerized abnormality

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that's broad, that's devoid of edema,

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that does not communicate or

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contact with this fluid.

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So, this abnormality here is absolutely positively

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unrelated to the effusion or hemarthrosis.

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So, this is what makes the case a little difficult.

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This can suck you in and throw you off.

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This is the anterolateral form

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of osteochondritis dissecans,

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which is usually seen in individuals that have

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an element of patellofemoral dysplasia.

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With rest, these usually go away

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in juveniles in 14, 15-year-old boys,

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by the time the growth plate completely closes.

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So these are treated 98% of the time, conservatively.

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So, let's keep going then.

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T2-weighted imaging is not particularly

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sensitive for the skeleton.

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It's good for ligaments.

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It's pretty good for cartilage.

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So, let's go to something more water-weighted.

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Let's go to our sagittal water weighted proton

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density fat suppression image.

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Now, you know it's fat-suppressed

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because the fat is dark.

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When you look at the echo time,

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I like to have my echo times around 40.

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This one's a little short, but that's okay.

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We're not going to spend much

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time on protocol right now.

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And this is where you would see the patellar

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dislocation fracture. Does not have that.

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You go to the other side,

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and you do have

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an impaction injury of the femoral condyle.

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Now, how do I know that's an impaction injury?

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Well, I know because it has this sort of starburst,

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ill defined pattern to it.

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You almost don't see any fracture lines.

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Let's go to the T1-weighted image.

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It looks like it bursts on the scene.

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You've got these speckled areas of white signal,

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and then it even crosses the

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growth plate right here.

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I wouldn't ascribe the term Salter-Harris to it

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because that's a plain film grading system.

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There's no line going through it.

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So, I wouldn't try and use

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a Salter-Harris grading system here.

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But this star burst effect where you have these

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little speckled areas of fat signal intensity,

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very typical of somebody that's taken

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a direct blow to the knee.

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This is also not a good place where you would

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get a typical varus or valgus type.

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This is the type of fracture you'd see in patellar dislocation,

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but on the other side of the knee,

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on the lateral side.

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So this person took a blow to the medial side of

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the knee and has what I call an impaction

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fracture that involves the growth plate.

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I would not use Salter-Harris

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grading in this instance.

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I would say that the patient has a hemarthrosis.

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Again, I'm looking for a blood fluid

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level or a fat fluid level,

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and I do see a blood fluid level right there.

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If you look very carefully,

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I'll take out the lettering so it shows

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up a little better right here.

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There's the layering right there.

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You go over to the T1-weighted image,

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and it's a little bit bright.

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So, that is a little bit of fat that's floating

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superficially right there.

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So we do have a fat fluid level,

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the cellular components of the blood layer, dependently.

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So we've got this osteochondral defect,

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which is consistent with the anterolateral form of

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osteochondritis dissecans.

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How do we know that?

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It's very broad, it's very well defined.

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It's a juvenile. So that fits.

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And we're going to come back to that

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diagnosis a little bit later.

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We've taken a blow to the anteromedial knee.

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So what does that mean? If we've taken a blow

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to the anteromedial knee?

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In my mind, biophysiologically, bioanatomically,

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I want to check the posterolateral corner.

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Because if you hit somebody here,

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you'll put stress over here.

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So let's check that posterolateral corner,

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which looks a little bit swollen right here.

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Let's go right to it in the sagittal projection.

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And here it is.

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Here's the posterolateral corner.

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And that corner consists of

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the meniscopopliteal fascicles.

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There's an upper one and a lower one.

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They go across.

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So when you get to the inside of the meniscus,

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it looks a little bit attenuated right there.

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And right there,

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you've truncated, you're missing somewhat

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this lower fascicle.

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There it comes back again.

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So there's a question as to whether the

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meniscocapsular attachments are torn.

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But more importantly,

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there is a meniscopopliteal ligament right there.

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And you can see it makes a little curve.

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It's a little stretched out,

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still present on the next cut.

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It has a little partial tear in it.

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So there's a low grade injury to the menisco...

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sorry, the popliteofibular ligament.

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And then behind that,

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these little shards right here.

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I'll draw over one.

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I'll draw over this one and this one.

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And they should be connected to each other.

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They should be connected like that.

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Now, I'll take it away.

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That is the arcuit right there.

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So the arcuit ligament is torn.

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There's a paplateofibular ligament strain.

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So, there's a posterolateral corner injury.

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And that's pretty much the case.

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So your conclusion would read something like,

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"Extensive impaction fracture of the medial femoral

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condyle, resulting in a posterolateral corner injury

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with partial tear of the popliteofibular ligament

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and arcuit."

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Next paragraph,

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"Incidentally noted is osteochondritis dissecans of the

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anterolateral femoral condyle.

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And by the way,

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that is the second most common location

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in a juvenile in the knee

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for osteochondritis dissecans,

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the most common and the most important,

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or the most common is the lateral aspect of the

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medial femoral condyle.

Report

Patient History
14-year-old with anterior knee pain and swelling after a football injury.

Findings
Menisci:

Medial Meniscus: Intact.

Lateral Meniscus: Intact.

Ligaments:

Anterior Cruciate Ligament: Intact.

Posterior Cruciate Ligament: Intact.

Medial Collateral Ligament: Slightly thickened, contused proximal tibial collateral ligament associated with subtle periligamentous edema/contusion.

Lateral Collateral Ligament: Thickened proximal fibular collateral ligament associated with periligamentous edema, consistent with low-grade sprain.

Posterolateral Corner Structures: Diffuse swelling of the arcuate ligament, associated with periligamentous edema, consistent with low-grade sprain. Diffuse moderate edema surrounding the popliteus myotendinous unit without macro tear or fiber waviness, consistent with a low grade (grade 1) myotendinous strain. Popliteofibular ligament intact but mildly swollen. Popliteal fascicles intact.

Posteromedial Corner Structures: Intact.

Extensor Mechanism:

Patellar Tendon: Intact.

Distal Quadriceps Tendon: Intact.

Medial Patellofemoral Ligament: Diffusely stretched, likely due to large knee joint effusion/arthrosis, but intact.

Medial and Lateral Patellar Retinacula: Diffusely stretched bilaterally is due to large hemarthrosis.

Hoffa Fat Pad: Mildly thickened infrapatellar plica. Otherwise unremarkable.

Articulations:

Patellofemoral Compartment: Low-grade trochlear dysplasia with trochlear sulcus insufficiency (Dejour A). Slightly lateralized patella could be attributed to the large hemarthrosis versus patellofemoral ligament injury. Borderline TT-TG distance measuring 1.5 cm. Incidental chronic, lateral, peripherally sclerotic, trochlear osteochondritis dissecans, measuring 2.4 x 1.2 cm diameter and 0.6 cm in depth. Overlying cartilage intact but demonstrates low-grade chondromalacia. No hyperintense fluid cleft to suggest potentially unstable fragment. No displaced fragment.

Medial Compartment: Normal.

Lateral Compartment: Normal.

General:

Bones: Diffuse direct medullary(enchondral) bone impaction fracture involving the medial aspect of the medial femoral epicondyle with associated high-grade confluent osteoedema/contusion extending through the medial femoral condyle epiphysis and metaphysis. No cortical depression.

Further subcortical contusion with osteoedema is noted at the posterolateral aspect of the medial femoral condyle.

Low-grade osteoedema consistent with contusion involving the inferior posterior margin of the lateral tibial epiphysis supporting a varus mechanism of injury.

Incidental note is made of mild lateral femoral condylar dysplasia, in addition to trochlear dysplasia.

Effusion: Large suprapatellar effusion/hemarthrosis with reactive capsular synovitis.

Baker’s Cyst: None.

Loose Bodies: None.

Soft tissue and Neurovascular: Unremarkable.

Conclusion
Evidence for recent varus mechanism of injury with medial impaction and the following findings:

1.Extensive direct impaction fracture of the medial femoral epicondyle with osteoedema extending to involve the medial femoral epiphysis and metaphysis.
2.Low-grade posterolateral corner sprain involving the arcuate ligament, popliteus myotendinous unit, popliteofibular ligament and proximal fibular collateral ligament. No high-grade injury, disruption or evidence for posterolateral instability.
3.Large knee joint effusion/hemarthrosis.
4.Incidental unrelated chronic anterolateral trochlear osteochondritis dissecans on a background of trochlear and lateral femoral condyle dysplasia. No evidence for unstable or displaced fragment.

Case Discussion

Faculty

Omer Awan, MD, MPH, CIIP

Associate Professor of Radiology

University of Maryland School of Medicine

Stephen J Pomeranz, MD

Chief Medical Officer, ProScan Imaging. Founder, MRI Online

ProScan Imaging

Jenny T Bencardino, MD

Vice-Chair, Academic Affairs Department of Radiology

Montefiore Radiology

Edward Smitaman, MD

Clinical Associate Professor

University of California San Diego

Tags

Musculoskeletal (MSK)

MRI

Knee

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