0:00

We're talking instability, both micro and macro.

0:03

Instability, unidirectional, multidirectional.

0:05

And we're focusing on the sagittal projection.

0:09

Um, I use the T2 spin echo with fat suppression,

0:14

either spur, spare, uh, special, and even at

0:17

low field STIR in my sagittal projection to

0:21

complement my coronal proton density image.

0:25

Now, the difference between these two is

0:27

this one is more heavily water-weighted.

0:30

And so it may pick up things that

0:32

the T2-weighted image may miss.

0:34

In other words, it's more sensitive, the PD fat suppression.

0:38

On the other hand, if you have an explosion of

0:40

blood and fluid and swelling, you may have so

0:44

much signal that the structures you're interested

0:47

in are just simply buried in a morass of signal.

0:51

And that's where the T2-weighted image comes in handy.

0:54

Because you'll have signal dropout of areas

0:57

that are not as swollen, and the tendons

1:01

may then come forth and show you their edges.

1:05

Or, the fibrocartilage may come

1:07

forth and show you its edges.

1:10

So this is a refining sequence in the acute setting.

1:14

It's also very good for dating or aging things.

1:17

So in other words, the proton density is so sensitive

1:20

with fat suppression for water signal, that even things

1:23

that are subacute to chronic are going to be bright.

1:27

And that includes both labrum

1:28

pathology and rotator cuff pathology.

1:31

But on the other hand, on a T2-aided image, not so.

1:35

Late subacute to chronic, those

1:37

abnormalities are going to be grey to dark.

1:40

So this helps you refine abnormalities in the acute setting.

1:45

But it also helps you date abnormalities

1:48

in the acute, subacute, or chronic setting.

1:51

Helping you decide how old they are.

1:54

Now let's talk the sagittal projection per se.

1:58

When you're looking at your sagittal

1:59

projection in an instability case, you want

2:01

to be looking for your Hill-Sachs lesion.

2:07

to determine the severity of the Hill-Sachs.

2:10

The coronal and the axial are better suited because

2:14

you get a better feel for size and also position.

2:18

Remember, in other vignettes, we've said closer to

2:21

the apex of the humeral head, closer to the top, or

2:24

more medial, the Hill-Sachs has a poorer prognosis.

2:28

And size does matter.

2:29

So you can see the Hill-Sachs here.

2:31

And this is a projection, naturally, we

2:33

would look at things like the rotator cuff.

2:35

And the biceps long head.

2:37

You can see it come off the superior

2:39

tubercle of the glenoid right there.

2:41

There's your biceps.

2:42

You'd follow it down and around.

2:43

We're not here to talk about that.

2:45

This would also be a good

2:46

projection to look at your scapula.

2:48

To look at your acromion and its slope.

2:50

Here's your acromion right there.

2:52

And its slope.

2:52

To look at your acromioclavicular ligament.

2:54

And even your AC joint.

2:56

This is all routine stuff, as well as looking

2:58

at your rotator cuff, your infraspinatus, your

3:01

supraspinatus, and your subscapularis right here,

3:04

with its four, five, or three different, uh, subunits.

3:10

So what else is relevant in the setting of instability?

3:14

Well, in micro-instability, the sagittal projection at the

3:18

glenoid rim level is good for picking out little cysts.

3:22

Sometimes you'll see them studding all the way around

3:25

the glenoid cup like this and then you know you've

3:27

got multidirectional micro-instability or potentially

3:31

a SLAP tear with circumferential labral detachment.

3:36

On the other hand, in the acute setting, if

3:38

you've had an acute dislocation, this affords

3:41

you the opportunity to look at the glenoid cup.

3:46

And the labrum is shaped like a pear.

3:49

I've got two cuts I'm toggling back and forth on.

3:57

And if you're really determined, and you want to make some

4:00

measurements, you can make a circle out of your glenoid.

4:04

I'll do it on this one too.

4:05

You can make a circle out of it.

4:11

And that was an okay circle.

4:12

You can see my drawing skills are just so-so.

4:16

And then you can look at the amount of glenoid bone

4:18

loss that you have and translate that into the

4:23

degree of instability for risk of future dislocation.

4:29

We're going to talk about that in subsequent

4:32

cases, but I want to give you just kind

4:33

of a general view of what's important.

4:35

And this cut where you see the coracoid and

4:38

the glenoid cup is a very important one.

4:41

So you make your circle, a best-fit circle.

4:44

Uh, my fit's pretty close.

4:45

We'll use it.

4:46

And then you put a point in the middle.

4:49

Which is typically where the bare area of the glenoid is.

4:52

And that's why the glenoid tends to

4:53

be a little lighter in the center.

4:56

And then you take a radius going one way.

4:58

Let's take our radius in red going backwards.

5:02

Assuming my point's in the center.

5:04

And then I'll take a radius

5:05

going the other way in the front.

5:07

Let's use something like purple.

5:12

And these should be equal.

5:14

So in other words, R1 should equal R2 over here.

5:21

So what happens if you have a

5:23

bony Bankart or bony glenoid loss?

5:28

So let's color that in with another color.

5:30

So let's say we've lost this portion of the glenoid.

5:35

So now our radius is only this big, or this long.

5:39

And our radius in the back is this long.

5:41

And when we get to the point where we've lost

5:44

half the radius in the front compared to the

5:46

back, we've got ourselves a huge problem.

5:50

So we're going to talk about what the percent

5:52

of loss using this radial measurement technique

5:55

means in terms of recurrent instability.

6:02

what's important in instability in the sagittal projection.

6:07

And it is this view, this glenoid cup view, with your best

6:12

fit circle, looking at the degree of glenoid bone loss.

6:16

Also, as shown earlier, looking at your Hill-Sachs

6:19

lesion, although better in the axial and coronal

6:22

projection, and then we'll talk a little bit more in

6:26

detail about on-track and off-track measurements for

6:30

engagement or lack of engagement in people with recurrent

6:34

dislocation and subsequent more advanced vignettes.

6:38

Remember, this is a T2 Vaspineco with fat suppression,

6:42

not as sensitive as the PD spur, and a little more

6:45

specific and useful for dating or aging an abnormality.

6:51

Let's move on, shall we?