Interactive Transcript
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The first case we're going to tackle
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is a 16-year-old with medial knee pain and instability
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following an American football injury.
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Of course,
0:10
there's European football and they are querying
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an ACL tear.
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So generally,
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when I approach a knee case,
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because the axial comes up first,
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it's usually the first thing I look at.
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I have a high volume of cases that I read during
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the day, so I try and be as expedient as possible.
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But if I had to say what the sequence is,
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that gives me the most information.
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as an experienced reader,
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it's the coronal water weighted image.
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So, I can usually tell everything that's
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happening off that image alone.
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But let's go in the order how I might go if I was
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less experienced and I would start out with
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the axial, I'd look at the patellar shape,
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I'd look at the trochlear shape,
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and then I would look at the
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Medial Patellofemoral Ligament
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and the lateral retinaculum.
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I'd look for chondromalacia,
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I'd look at the size of the effusion,
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that gives me an idea whether anything's wrong.
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And then after that,
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I scroll and I read to the history,
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and I always read to the history for every single
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case, whether it's a spine, a liver, or a knee.
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And in my head, I have this thought
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that no matter what,
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whatever the patient says is true.
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There are very few patients who will malinger.
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Maybe in a personal injury case
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and maybe in a workman's compensation case,
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but that's rare.
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So the patient has a symptom.
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There was always a reason for that symptom.
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So I do read normal MRIs,
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but I'm very uncomfortable when I do because
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I know that there is something
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there in most instances.
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So, I continually drill mentally into the case
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until I either find it or I've exhausted every option.
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So here, we have an effusion.
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And just looking at the axial,
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I can tell right away,
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because I'm reading to the history,
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that in the axial projection,
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I know that this is lateral,
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because the patellar almost always tilts laterally.
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So I can tell this is the lateral side,
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and that means that the anterior cruciate ligament
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is going to be on the lateral side.
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So here's my posterior cruciate ligament,
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somewhat round or oblong, fat and dark.
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The ACL, not so much.
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When I follow that ACL, it's fairly gray,
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and I have a great deal of difficulty finding
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it as a contiguous line from anteromedial
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to posterolateral.
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So, I already know that I have an anterior cruciate
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ligament injury of some kind and that
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it's likely to be high grade.
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And this is what they were looking for.
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I'm also looking at the collaterals.
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I can see the lateral collateral
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complex over here.
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I'm not going to articulate all the anatomic
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structures right now in this projection,
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but I can see everything,
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it's pretty dark.
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On this side,
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on the medial side, everything is not so dark,
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especially anteriorly,
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where the tibial collateral ligament lives,
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right here.
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And so, I'm suspicious of a medial
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collateral ligament injury,
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and I have yet to look at anything else.
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I already know that the posterior cruciate
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ligament because of its contour and its signal is intact.
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So without even looking at any other sequence,
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I now know that I have an anterior cruciate
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ligament injury, an MCL injury, an intact PCL,
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and an intact LCL.
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And so,
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I'm going into my next sequences with a lot of knowledge.
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Because there's been a somewhat violent injury.
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You know, it's a football injury.
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It's a contact sport. There's an ACL.
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There's an MCL.
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I am discreetly checking the neurovascular bundle.
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You know, if you miss an ACL,
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not horrible.
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If you miss a vascular injury,
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horrible.
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So, we're checking out the flow voids in the vessels
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in the back and the artery, which is deepest,
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and we're looking at the neurovascular bundle,
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although usually the neurovascular bundle is not
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injured, unless you have a varus insole.
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In other words,
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an injury to the lateral side of the knee.
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So that's good news.
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Let's turn our attention now
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to the water-weighted sequences.
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And this is really how I do it.
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I go right to the water-weighted sequences,
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because, again, for me, time is very important.
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And I know for you, most of you are,
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in private practice, time is very important.
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And even outside of practice,
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time is your most valuable asset.
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So, we're scrolling back and forth.
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We see that there are a series of bone injuries
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which tell you the mechanism of injury.
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First of all,
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there is a microtrabecular injury of
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the inferior patella.
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Right there.
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And what do I mean by microtubecular injury?
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Anything other than a macro fracture.
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Anything other than a visible fracture is a
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microtubecular injury.
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What's in that category?
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Low grade contusion, high grade contusion,
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microtubecular infraction,
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and microtubecular fracture.
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Those are the four stages before you actually have
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a macro fracture.
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So, what's a low-grade contusion?
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You only see it on a water-weighted image.
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What's a high grade contusion?
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You see it on a water-weighted image
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and a T1-weighted image.
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What's a microtubecular infraction?
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Little spidery lines that don't really involve the cortex.
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What's a microtrabecular fracture?
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Little spidery lines that do involve the cortex.
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And then a macro fracture,
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zigzag lines that go through the cortex.
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So now, as we scroll back and forth,
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we get an idea of what the mechanism of injury is.
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We have an anterior femoral terminal sulcus,
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microtubecular injury with slight depression and
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a non-kissing lesion in the back of the tibia.
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So what that means is, this is what happened.
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The femur went back on the tibia with the foot in
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external rotation and the tibia in internal rotation.
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And basically, the tibia subluxed
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relative to the femur.
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And this impartial knee flexion
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banged against that.
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That takes a lot of force to do that.
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So, when that happens...
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Look at my fists.
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The structures in the back will take a stretch.
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They'll also take a compression.
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So, this is a kid.
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It's a young kid.
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The structures are very pliable.
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So to injure these structures back here
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in a child, takes a lot of force.
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So now let's go to the back of the knee,
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and we're scrolling sagittally,
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and we're looking specifically at
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the posterolateral corner.
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And we're very interested in the
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popliteofibular ligament.
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Now remember, I said I didn't see
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a lateral side injury,
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but the posterolateral and
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posteromedial corners,
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you really have to look at the sagittal projection.
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So things look a little bit wavy and a little
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bit stretchy, but they're intact.
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Here is the arcuate ligament back here,
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this little thin structure posteriorly.
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Here's the popliteofibular ligament.
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It's a little bit wavy right there,
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but it's still present,
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still inserts on the fibular head.
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So, that's okay.
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What's not okay is there should be two attachments
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from the posterior meniscus.
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There should be attachment up high
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and an attachment down low,
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and it pretty much goes all the way across from
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lateral to medial, or from lateral to midline.
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Now, let's have a look.
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Let's scroll.
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There's one of the attachments.
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It's flopping in the breeze.
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The other attachment is not visible either.
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So, there is a meniscopopliteal fascicular
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detachment from that stretch.
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Some people might call this a
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meniscocapsular separation.
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I reserve that phrase for when the meniscus
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actually displaces more than a centimeter to a
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centimeter and a half, which hasn't happened here.
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So, I'm just going to call it a meniscal vesicular
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lateral detachment. Does that matter?
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It absolutely does matter,
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because the meniscus can start to do this.
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It can start to turn on itself,
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which is not great.
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Then, as we go a little bit deeper, we see this.
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Now, taking off from the lateral meniscus is a small
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ligament called the ligament of Wrisberg.
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I think we can see it right...
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Let's see.
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There.
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On the coronal.
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Now, that's a point of weakness.
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So at that takeoff,
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you can often get a little bit of a slit,
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and you should have that slit appear
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here normally.
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So, normally,
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the Wrisberg ligament would be separated
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from the meniscus by this little slit,
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and this would be the Wrisberg ligament.
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So let's go in tight into the midline,
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and here is your Wrisberg ligament.
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And look at that interface.
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Now, it's persisting.
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It's still persisting.
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It's persisting on too many slices.
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It's still persisting.
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So there is what we call a posterolateral
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pivot shift Wrisberg rip injury.
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Let's keep going, shall we?
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Let's go to...
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And there's the Wrisberg ligament,
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behind the posterior cruciate ligament.
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There's the Humphrey ligament in front
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of the posterior cruciate ligament.
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Now, let's go to the medial side.
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On the medial side, in children,
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I don't mind if there's signal in the outer third
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of the meniscus. I don't mind at all.
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But I don't want the signal to go like this.
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I don't want the signal to go up and down.
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I don't want the signal to hit the tibial surface.
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And it does.
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So, there's a very low-grade meniscal tear
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posteromedially, right there.
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And what would we do with that?
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Absolutely nothing.
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What would we do with the lateral meniscus?
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The lateral meniscus,
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we might have to tap down with sutures
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because of its hypermobility.
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So that'll be determined at surgery
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when they take the meniscus and see how
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hypermobile it is.
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They won't sew this meniscus.
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They will not repair that Wrisberg rip.
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Let's go back over to the medial side.
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Now with this huge stretch,
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with this massive stretch that's
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occurred in a child,
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where the tibia is translated anterior to the femur,
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the posteromedial capsule is under a stretch.
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What gave way on the lateral side?
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On the lateral side,
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the meniscal vesicular attachment is torn.
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But over here, the meniscocapsular reflection,
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with its multiple short ligaments
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that are hard to see, have been injured.
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This is too swollen.
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There is normally a meniscal posterior tibial ligament.
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Here it is very stretched out.
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That should attach over here.
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So, this is known as a posteromedial ramp lesion.
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Now, another thing that's happening.
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The child is not even standing up.
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Look at what's happening to the meniscus.
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It is prolapsing posteriorly.
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It's a little puffed out right there.
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That's called a brake-stop mechanism injury
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because the posteromedial stabilizers
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at the meniscocapsular reflection are injured.
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Now, a ramp lesion.
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A ramp lesion is a stretch-type injury
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that occurs at the meniscocapsular reflection.
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And we only use this term posteromedially.
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We don't use it anywhere else.
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What are the five types of ramp lesions?
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Well, the first type is this type
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where you've injured
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this posterior meniscal tibial ligament.
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The capsule is swollen and there's nothing else
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vertically orient it.
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That would be a Ramp 1.
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Then you have ramps 2 and 3
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where you might have a vertical partial depth tear
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from the top or from the bottom.
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What's a 4?
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A 4 would be when you have a line in the
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meniscus going all the way from top to bottom.
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What's a 5?
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A 5 would be where you have a double tear
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along with all this going on in the back.
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So now we've got an ACL tear,
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a Wrisberg rip injury,
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a lateral menisco fascicular detachment,
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injury to the brake stop mechanism with a ramp 1 lesion.
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A tiny little, but mostly intra-substance tear
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of the meniscus, we're not going to touch.
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Let's go to the cruciate.
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Let's zoom out.
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And right there in the middle,
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the anterior cruciate ligament stump.
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The distal posterior cruciate ligament stump.
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And there is a giant hole in the middle.
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You can drive a large Toyota through that hole.
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Posterior crucial ligament, as we suspected.
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Fine.
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All right,
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let's go to the coronals and
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look at the collaterals.
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Popliteal origin, tendon origin, normal.
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Fibular collateral ligament, intact.
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Scant swelling, but intact.
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The biceps femoris and conjoined insertion
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on the fibular head, intact.
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The medial collateral ligament, as we suspected,
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torn anterior and proximal.
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There's also a meniscofemoral ligament.
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It's intact right there.
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There's also a meniscotibial ligament.
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It's intact right there.
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When you get anteriorly,
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this is known as the meniscopatellar ligament.
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This should go towards the patella and it should
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arc off towards the superomedial aspect of
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the knee as it does.
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This is normal.
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That's normal. That's not a detachment.
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All right,
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let's look at the T1-weighted image for giggles,
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because we're not going to get
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a lot more out of it.
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Now, I know in Aus, you guys do a lot of proton-density
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imaging instead of T1 imaging.
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I'm against that.
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And you do it because it helps your visualization
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of meniscal tears. But you don't need that.
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If you combine the T1 and the proton-density
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fat suppression, you don't need that.
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And a proton density will obscure the
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bone findings, including fractures,
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including osteomyelitis.
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So, I'd much rather have a true T1.
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You can also see our very low grade
14:29
meniscal injury right there.
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You can see our swelling and the slight
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corrugation of the posterior meniscotibial ligament.
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How are the growth plates?
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They're open. They're fine.
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That's important because it's a child.
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To fix this ACL,
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you want to avoid drilling through
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open growth plates.
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We have an effusion with a dilute hemarthrosis
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with a little methemoglobin staining.
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There is your fracture.
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There is your fracture,
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microtrabecular fracture with cortical involvement
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in the posterior tibia.
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You're not going to see that on an x-ray.
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Then, you've got your ramp lesion on your medial side,
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and you're pretty much done.
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There is a T2.
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It doesn't add much except showing you,
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once again, the hole, the size,
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the sheer absolute rupture of the mid portion
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of the anterior cruciate ligament.
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Now, there's one other finding here that's
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a little bit confusing.
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Some of the fibers of the anterior cruciate
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ligament have folded down on themselves,
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creating the impression of a mass right there.
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So, that might be a little confusing.
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You want to go back and make sure, see,
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there's the ACL twisted down on itself.
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You want to make absolutely sure you
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don't have a bucket handle tear.
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You look for meniscus truncated and separated
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from itself into two pieces.
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The patient does not have that.
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That would completely change the management of
15:58
this case and how long you wait for surgery.
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They will let this knee cool off.
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They will try and repair the ACL while
16:05
avoiding the growth plate.
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They will leave the medial meniscus alone.
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They will test the lateral meniscus at surgery
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to see if it needs to be tacked down.
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They will leave the MCL alone.
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