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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.