0:00

Let s take on a case.

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This is a 25-year-old man

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who's been in a motor vehicle accident,

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and he reports lateral pain.

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Rule out ACL was the history.

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You know,

0:12

typical ACL presents often with a

0:16

pivot shift mechanism of injury.

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And that is where the tibia internally rotates.

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The femur externally rotates.

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There's often a valgus impact so that there's

0:28

an impact from the outside to the inside.

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So the medial side opens, but not always.

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And there's frequently a component of twist,

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and that creates a classic pattern of bone

0:39

injuries, which I am not going to show you here.

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So the reason for me illustrating this is because

0:45

of the bone pattern in this case,

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it's completely atypical. It's counterintuitive.

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As we scroll through the water weighted image,

0:56

the proton density fat suppression, spur or spare,

1:00

you should be totally thunderstruck by the volume

1:04

of edema that is in virtually every single bone.

1:08

The tibia, the fibula with a step off fracture,

1:11

the antralateral femur and the patella.

1:14

So this isn't the usual average bear.

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This isn't the classic pivot shift mechanism

1:20

of injury, although the ACL, as we'll see,

1:24

is very abnormal.

1:25

So what I try and do in all my orthopedic

1:29

cases is figure out what happened.

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If it's a sports injury case, obviously,

1:34

if it's a tumor, I'm not going to do that.

1:36

And then I try and match the imaging findings to

1:40

what the clinician needs to know, wants to know,

1:43

or if I'm surprising him or her.

1:45

What they have to know.

1:47

That's going in the conclusion.

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So, at first glance, there's been a major impact.

1:53

Okay. MVA. Not unexpected.

1:56

So where was the impact?

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Well, we have a fibular fracture.

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More of the edema is lateral than medial,

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although, admittedly,

2:03

there's a fracture right here

2:05

in the posteromedial corner.

2:07

But just judging by the soft tissues,

2:10

the impact came from the anterolateral side.

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My guess is he impacted something in the motor

2:16

vehicle that smashed the anterolateral aspect

2:19

of the knee and drove everything backwards,

2:22

probably the tibia more than the other structures,

2:25

and that's what's led to the ACL injury.

2:28

I also know that he has not had a major valgus

2:32

force because the MCl layer number two,

2:36

also known as the tibial collateral ligament,

2:39

normal. There's no swelling here.

2:41

So where was the force transferred?

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Well, if it's not there, I have to wonder,

2:45

in my mind, maybe it's posteromedial,

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because he had an anterior lateral force

2:52

that would be directed posteromedial.

2:55

And we have evidence to back it up.

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Right, we've got a fracture back here.

2:58

Right there.

2:59

So now the next thing that should

3:01

go through your head.

3:03

Yes, we're going to go back to the ACL.

3:05

No question.

3:06

What about the posteromedial corner?

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So at first glance,

3:11

the posteromedial corner right there is a little

3:13

bit swollen. There's the meniscus.

3:16

It looks normal at first glance.

3:19

And now let's turn to the sagittal projection

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and let's go to the posteromedial corner.

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There's our fracture.

3:26

There it is on the T1 slightly depressed.

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It's a macro fracture.

3:32

So what other type of corner

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abnormalities do we have?

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We have injured the meniscocapsular junction.

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That's one component of the corner.

3:41

Did we tear away the meniscus?

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In other words,

3:44

is the meniscus flipped or separated?

3:46

No, but there's bleeding in there.

3:49

The attachments are injured.

3:50

Did we tear the actual meniscus?

3:53

No, we didn't. That's another component, though,

3:57

of the posteromedial corner.

3:59

What about the semimembranosus?

4:01

Did we tear it off?

4:03

No. Did we injure it?

4:06

Yes. Look how swollen it is.

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And you all know from watching MRI online,

4:11

there are five expansions of the semimembranosus.

4:14

This is not the time to go through those five

4:16

expansions, but let's stay with the corner.

4:19

What's another aspect of the corner?

4:22

The popliteal oblique ligament. The pol,

4:27

that should be a thin,

4:29

crisp line right here merging with a thicker line.

4:32

And if I blow this up really big,

4:36

that is not a thin, crisp,

4:39

straight line right there,

4:41

which should merge with this band right here,

4:44

which is the capsule. So not unexpectedly,

4:47

the popliteal oblique ligament has taken a hit,

4:52

because right next to it is the capsule,

4:54

and they all kind of blend together.

4:56

We're not done yet. We've got the pol,

4:59

the postural oblique ligament of the knee.

5:02

It has a corner attachment to the

5:04

posturo superior ligament.

5:06

That linear structure should go to that apex.

5:09

It's off.

5:11

Wow, that's pretty subtle.

5:14

That's why we have MRI online.

5:16

Now let's go to the coronal projection

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as we did before,

5:21

and all we really saw was a little

5:23

bit of swelling here.

5:24

I like to follow the tibial collateral ligament

5:27

back and see if that turns into the posterior

5:31

oblique ligament, which it does.

5:32

And in the coronal projection,

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it actually looks pretty good.

5:35

So the coronal projection is a little bit of a

5:38

fooler. The pol is a rather complex structure.

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Another way to see the pol is in the sagittal.

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So let's go to the sagittal with all our

5:47

fractures. Here's a fibular fracture,

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here's a tibial fracture, here's ephemeral injury.

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And as we're scrolling back and forth,

5:55

you're probably noticing that the

5:57

tibia is lurched forward.

5:58

There's passive anterior tibial translation,

6:01

which means the acl is deficient.

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It's not going to be there in a young person.

6:06

It's transected, and it is right there.

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And I'm going to show it to you very clearly on

6:12

the T2 weighted image and explain

6:14

how you use the T2 in a moment.

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But let's stick with the pol for a minute.

6:18

Let's go to the medial side.

6:19

So, straight up and down.

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We already said the tibial collateral ligament,

6:24

normal. There it is, straight up and down.

6:26

I should make it bigger on your behalf.

6:29

Straight up and down, intact.

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But right behind it,

6:33

you'll remember from MRI online making kind of a

6:37

horizontal v. We're going to see it right here.

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Now, it's going to be in this location.

6:42

As I scroll,

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it's going to be shaped like,

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this

6:49

is one of the critical components of the pol.

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There's a capsuler component up high.

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We don't worry too much about that.

6:56

It's also called a superior arm.

6:58

And then there's a component in the back

7:00

here that comes off the same location.

7:02

That's called the central arm.

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So this is the distal superficial arm.

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Central arm, capsuler arm. Now,

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let's scroll and see what we got right there.

7:12

There it is. Tibial collateral pol.

7:16

Swollen.

7:18

Definitely swollen. Let's go a little deeper.

7:21

Now we're out of it.

7:21

It's a very thin structure,

7:23

so we only see it on one sagittal projection.

7:26

At the very least,

7:28

the central and superficial arm of

7:31

the pol are sprained or swollen.

7:34

Now let's get to something a little easier.

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Let's go to the T2 where on your fourth

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pint of vodka, bourbon, scotch,

7:45

or the drink of your choice.

7:46

This is a no brainer.

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Now, what does the T2 really do for you?

7:53

Well,

7:54

sometimes it's a helper and sometimes

7:56

it hurts you. When does it help you?

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When you have a morass of blood and

8:02

fluid burying the structures,

8:06

especially on the PD spur.

8:08

Then you go to the T2 and all those signals die

8:12

down and the dark signal of the ligaments

8:16

stand out and you can see the two ends.

8:19

So in the acute setting, the T2 is queen or king,

8:25

there's a gap.

8:26

You could drive your volkswagen through that gap.

8:29

There's the proximal end, there's the distal end.

8:32

It's a no doubter.

8:33

Let's look at its appearance on the PD.

8:36

Yeah, it's a no doubter here, too.

8:39

But you might say, oh,

8:40

maybe that's a fiber intact.

8:42

No, it's not.

8:43

It's just a piece of a fiber just waving

8:46

in the breeze. There's a huge gap here.

8:48

This is a full thickness,

8:50

proximal to mid portion acl rupture.

8:55

And the T2 does it justice.

8:57

When does the T2 hurt you?

8:59

When the acl tears are chronic.

9:01

Because what's the signal of a ligament?

9:03

And we got a ligament.

9:04

It's black.

9:06

What's the signal of hemocytrine?

9:10

Oh,

9:10

we'll make a slightly different yellow color

9:12

like that. What's the signal of hemocytrin?

9:15

Black. What's the signal of blood?

9:18

Black. What's the signal of fibrous tissue?

9:20

Black.

9:21

So if you have fibrous healing or a fibrous union,

9:25

even if it's not stable,

9:27

of the ACl to the notch of the knee or to the PCl,

9:31

it's going to look like one contiguous structure

9:34

and you're going to get old.

9:35

That happens a lot, especially in kids.

9:38

This is a traumatic ACl rupture with a

9:43

posteromedial corner injury and innumerable bone

9:46

injuries, including some fractures. Let's move on.