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We're talking PCL in a 54-year-old man

0:03

who's had an unknown mechanism of injury

0:05

but now has knee swelling.

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Let's scroll the axial T2 where

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most people might start,

0:12

and you should be struck by this fluid

0:16

fluid level or blood fluid level,

0:18

which suggests a serious injury

0:20

and most likely a fracture.

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Now, on T2 imaging the signal intensity,

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while very bright for heavily fluid laden

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areas such as blood and fluid or water,

0:34

doesn't do as good a job when you look

0:36

inside ligaments and tendons,

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because acute blood is black.

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Tendons are black, ligaments are black.

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So, in the acute setting,

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unless you've got a lot of fluid and generalized

0:46

swelling, if there's a lot of blood present,

0:48

you could get fooled into thinking

0:50

your structures are intact.

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That's also true chronically on a T2 On a T2

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weighted image, the tendon is going to be black.

0:58

Fibrous tissue is black. Hemocytrin is black.

1:01

You could potentially miss a chronic posterior

1:03

cruciate and even anterior cruciate ligament tear.

1:07

So, buyer beware.

1:08

Combine your T2 with your heavily water weighted,

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fat suppressed pd spur or stir imaging.

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So,

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let's look at our pcl on the sagittal water

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weighted image. And it just looks too thin.

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So, is that atrophy,

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or are we losing a lot of the bulk of the PCL as

1:29

it blends in with the surrounding swollen tissues?

1:33

And the answer comes into the coronal projection.

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You've got to do what intel does.

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Intel inside. You got to look inside the PCL.

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Let's scroll it.

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And inside the PCL is a well defined area of

1:46

hyperintensity right in the center of the archery

1:50

target. You're not volume averaging the fluid,

1:54

the sheath, the swelling,

1:56

and the blood around the pcl,

1:58

you are actually seeing damaged tissue inside

2:01

the PCL. So that's how you do it.

2:04

That's how you affirm the diagnosis of a PCL tear.

2:08

This patient also has a huge Humphrey ligament

2:12

and does not have a ligament of Wrisberg,

2:14

which is a variation and has a very large

2:17

footprint of insertion of the Humphrey and the

2:20

PCL on the femur. But there's so much more.

2:24

We're going to talk about the corners,

2:27

because a corner injury with a PCL injury is a

2:31

much different animal than an isolated PCL injury.

2:36

Now most of you are noticing that the ACL is

2:39

attached to some bone that is no

2:41

longer attached to the tibia.

2:43

So we have an ACL deficient knee

2:46

and a PCL deficient knee,

2:49

and we haven't even gotten to the corners yet,

2:52

but we will.

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Let's have a look at what happens to the knee when

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you lose the PCL and either one of the corners.

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Let's start out with the medial

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corner in the back.

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The medial corner consists of the semimembranosus,

3:06

the posterior oblique ligament of the knee,

3:07

the pol, the OPL, the oblique popliteal ligament,

3:11

the meniscus,

3:12

and the meniscal capsuler attachments.

3:14

If I say it enough times,

3:15

you're going to remember it when you lose those

3:18

structures and you externally rotate the knee.

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Now the tibia will jut forward on

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the medial side excessively.

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You can see it from a side view as well.

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So this is Amri,

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PCL plus posteromedial corner.

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What about PLRI?

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Posterolateral rotatory instability,

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also sometimes called posterolateral recurrent

3:44

instability. Rotatory type when it's missed,

3:47

also in external rotation. But this time,

3:50

instead of the medial tibia jutting forward,

3:53

the posterior instead of the anteromedial

3:56

tibia jutting forward,

3:57

the posterolateral tibia goes backwards.

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So look at it from the back and then

4:03

look at it from the front.

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In external rotation,

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the tibia is dropping back on the lateral side.

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To make matters worse,

4:11

you often lose this ligament right here,

4:14

the fibular collateral ligament, as part of PlRi.

4:17

So you also have val varus instability.

4:20

So the joint opens in a varus pattern,

4:24

so the tibia goes back and the joint opens with

4:28

a combined fibular collateral ligament tear.

4:30

Posterolateral corner injury and a PCL.

4:33

This is a very serious type of injury

4:35

that often requires reconstruction.