0:00

Let's introduce the concept of on-track and off-track

0:03

very simply using a simulated CT anatomic set of images.

0:10

Uh, this is going to be anterior where your defect is, and

0:14

this is going to be posterior just to get you oriented.

0:18

And this concept was introduced in

0:20

arthroscopy, The Journal, in 2014 by D.Giacomo.

0:23

0:25

So we've got a Hill-Sachs lesion that's much smaller

0:28

than our glenoid width from anterior to posterior.

0:33

So this would be an on-track morphology.

0:36

Whereas simply on the right, the Hill-Sachs

0:39

anteroposterior length is greater than the blue

0:42

anteroposterior glenoid length because we have a defect.

0:47

Now, how do you quantify the Hill-Sachs lesion?

0:52

Let's pretend that we were in the

0:54

position where this lesion was over here.

0:56

So we're going to make it, let's make it black

0:59

because I think it's a little easier to see.

1:01

Let's say this was our lesion and it went from a bony

1:04

ridge right here to, let's say, the medial insertion of

1:09

the rotator cuff, which we'll pretend, oh, we better pick a

1:12

better color, something a little more unusual like purple.

1:15

Let's say our cuff ends are over here, and that would make

1:19

this measurement with the calipers look something like this.

1:25

We make that measurement, and

1:26

let's say it's, uh, 18 millimeters.

1:30

So that would give us one measurement.

1:33

Then we've got to deal with the glenoid.

1:36

That is a more difficult measurement.

1:38

Issue to tackle.

1:40

So let's take this on-fuss picture of the glenoid cup.

1:47

Yes, it's a little bit lighter right here,

1:49

because that's where the bare area is.

1:51

There's also a little notch there, the notch of Ozaki.

1:54

It looks like a pair, but we're going

1:56

to use the best-fit circle technique.

2:01

And we're looking for percent of glenoid bone loss.

2:06

So I'm going to make my circle in white,

2:08

because that's the color that's up.

2:09

And I did pretty well.

2:13

Now there are a few ways to calculate

2:16

the amount of glenoid bone loss.

2:19

You could say, okay, let's say

2:23

we've lost this amount of glenoid.

2:26

It's 20 percent all the way from front to back.

2:30

That would be one crude way of measuring it.

2:33

And individuals actually use

2:36

that number as a prognostic tool.

2:39

But if you want to get a little bit

2:41

fancier, let me get my eraser out.

2:45

What you might do, and I'm going to have to

2:47

make my drawing a little bit thinner, so bear

2:50

with me, this is a complex issue to tackle.

2:53

And I think pink is a lovely color.

2:56

So I'm gonna take a spot right in the center here

3:00

in pink, and then I'm going to have a radius going

3:04

posterior, and I'm gonna have a radius going anterior.

3:07

And I'm gonna make my anterior radius maybe a double color.

3:13

Put a little light green on it.

3:15

And those are equal, right?

3:17

Radius in front is equal to the radii in back.

3:21

Now, what if we had a scenario

3:28

where we have lost anterior glenoid tissue?

3:34

Now we've got a scenario where

3:38

the two radii are not equal.

3:41

The pink radius in the back is longer, we'll

3:44

give it a new color, than the new radii in

3:47

the front in orange, so this one's shorter.

3:53

So what we might say is, okay, the pink

3:58

radius minus the orange radius, over the

4:01

pink radius gives us a percent radius loss.

4:08

Now here is another way to measure

4:12

the degree of glenoid bone loss.

4:15

Probably the more conventional way.

4:18

The way I just gave you is a little bit faster.

4:20

It gives you just a quick and dirty. Not so dirty, actually.

4:24

A quick and elegant way to measure the amount of glenoid

4:29

radial bone loss using what I call the radial technique.

4:35

So, now let me get my eraser back out.

4:38

I know this is a little complicated, but bear with me.

4:43

I've lost a little bit of my cup.

4:45

I better, I better get that cup back.

4:47

Otherwise, I'm gonna spill my wine.

4:50

Let's make it a little thicker.

4:51

There, here comes my cup.

4:54

So now we look at the diameter.

4:57

So let's say the diameter is X.

5:02

Call that X.

5:05

There's your X.

5:07

And now, we've got glenoid bone loss.

5:10

So we're gonna use the best fit technique,

5:12

whether there's glenoid bone loss or not.

5:14

So let's say, there's glenoid bone loss over

5:16

here, but I've extrapolated my brown line, my X,

5:24

all the way to where I think the circle would be.

5:27

Using a best fit circle technique.

5:30

Now I go back and I say, Hmm, the diameter

5:34

with this glenoid bone loss is not as great.

5:38

I'll pick another color like orange.

5:41

And now the diameter only goes to here.

5:45

So now I take 83% of D, big D, which is this X.

5:54

We'll call it big D.

5:55

Let's change it to big D.

6:00

Big D, which is the whole diameter, minus little d.

6:07

Let's see if we can get another color for little d.

6:09

Aquamarine blue.

6:11

So 0.

6:11

83% of big D minus little d is going to give you

6:17

an idea of the width loss of the glenoid.

6:23

You can then take that information

6:25

and extrapolate it to a table.

6:28

And that table will tell you how much area you have lost,

6:33

based on these measurements.

6:35

And that is called the Nofsinger table.

6:38

We're going to talk about the

6:39

Nofsinger table in a few moments.

6:42

But when you, when you have areas that are 50% to 60%

6:46

using the Nofsinger table, that's extrapolated

6:50

from these measurements, there's a darn good chance

6:54

that you are going to have engagement and a situation

6:58

where there is recurrent repetitive dislocation.

7:03

Now, engagement is usually seen when the Hill

7:08

Sachs lesion is a lot bigger than the glenoid.

7:13

Non-engagement, you may have it when the Hill

7:16

Sachs lesion is a lot less than the glenoid.

7:18

But when the glenoid loss is large, then

7:21

those rules don't necessarily apply.

7:24

It just depends on where the Hill Sachs lesion is,

7:28

how much glenoid bone loss you have, and how much

7:32

capsular interruption and destruction you have.

7:36

And we'll turn to those concepts in a subsequent vignette.