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Let's tackle posterior micro and macro instability

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syndromes with a conceptual diagram that shows the

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anterior and posterior labral ligamentous complex.

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Now, there are some differences, although this diagram

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may not demonstrate them as optimally as I would like.

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So let's look at one of those major differences, and

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I need some really bizarre color like light blue.

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And this capsule right here, which can insert right at

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the base of the labrum, like this, frequently does this.

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It inserts more medial.

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And sometimes, especially in athletic individuals

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and people that need a lot of plasticity, it will

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even insert along the scapular ridge, or more

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medially, or even along the scapular concavity.

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That being said, some patients

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will develop capsular stripping.

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And so, that may be a normal physiologic

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response or an abnormal response.

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In summary though, the takeoff of the capsule from

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the anterior glenoid is very variable from more

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lateral to more medial, and it's most commonly

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seen here, away from the base of the labrum.

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And then we'll reflect off the

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labrum as it courses more laterally.

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Now, in the back, the story is different.

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In the back, let's pick something

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that is easy to see, like, um, purple.

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And you always have a, an apparent take off

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of the capsule from the tip of the labrum.

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However, that capsule becomes very thin.

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Let's see if I can make it thinner.

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Creatively becomes very thin and rides along

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the back of the labrum and then merges with the

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periosteum and continues on for a variable distance.

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But the apparent takeoff is always going to

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be on point at the apex of the posterior.

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A couple of other points, actually one other major point.

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The position.

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of the humeral head, is something that I tap

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into in all of my posterior instability cases.

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So I will visually, I won't do this with, with a pen, or

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I won't do this with any kind of marker, cause I'm plowing

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through a lot of work during the day, just like all of you.

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My eye will gravitate to the center of the

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humeral head, it'll gravitate to the center of

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the glenoid, and I like to see these line up.

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So I don't like to see the humeral head translating back.

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People that have humeral heads that translate

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back have a higher incidence, at some

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point, of clinical instability, posteriorly.

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Generally, about 5 to 10 millimeters of displacement

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is when you start to get significantly concerned.

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Now, on the other hand, let's

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look at the glenoid for a moment.

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The glenoid plays a role in posterior stability.

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Let's do some more drawing.

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We're running out of colors, but,

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uh, let's go with a deep purple.

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And I like to take a line and draw it straight

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down the barrel of the scapular spine.

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And then I like to take a line

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and draw it from cortex to cortex.

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And then I also like to take another line that is

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absolutely perpendicular to this long purple line.

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So I'm going to use a different color.

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I'm going to use blue.

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And I want to be absolutely perpendicular,

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or 90 degrees, to this purple line.

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So this is my perpendicular line.

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The purple one is my cortex to cortex

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line, and that's going to give us an angle.

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And that's called the version angle.

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Now that version angle should be somewhere

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around 3 to 6 degrees or no more.

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But what happens if your anterior

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glenoid looks something like this.

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Your anterior glenoid comes jutting out much

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more than the posterior portion of the labrum.

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Now, your purple line, which is over here, from

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cortex to cortex, let's pretend this is cortex.

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In fact, I'll color it in brown,

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just to give you the effect.

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Okay, that's all cortex and medullary bone.

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We'll pretend the green is cortex.

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Now I'll draw my other line, which In

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aquamarine, actually I'll draw it in purple.

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And I'll go cortex to cortex.

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And now look what happens.

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Now look at the intersection between my

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blue line and my cortex to cortex line.

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Now I have a pretty big angle right there.

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And that is going to be the retroversion angle.

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So let's do it one more time.

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Right down the barrel of the scapula.

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Great.

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Perpendicular to that, great.

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Cortex to cortex might look something

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like that, 3 to 6 degrees, fine.

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Cortex to cortex, it might also look

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something like that, 3 to 6 degrees, fine.

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But when those angles get big, 6, 10, 15 degrees, we

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could have the situation of retroversion, or the opposite.

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Antiversion, which we're not going to talk about right now.

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So, those are the take home points from this diagram.

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Variable take off of the capsule from the front.

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Consistent take off from the back.

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The humeral head can start to translate

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passively when the patient lies down in

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cases of micro instability above 5 to 5.

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8 millimeters, I start to get nervous.

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And we've shown you how to evaluate

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visually and even with measurements.

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Retroversion, and if you want to, Antiversion.

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So now, as a companion vignette, with this vignette, you

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can stop right now, or you can go on to the next vignette

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where I'll diagrammatically show you some labral pathology.

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Let's move on, shall we?