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Let's focus on the shoulder.

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Stabilization in the sagittal projection.

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We've got an axial reference on the left with

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an arthrogram and a sagittal on the right.

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The sagittal is orthogonal in its acquisition.

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So the dynamic stabilizers of

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the shoulder are pretty simple.

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They include things like the rotator cuff

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complex, which includes the supraspinatus,

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the infraspinatus, as well as the oft ignored.

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Along the top of the humerus, biceps, long head, which

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comes off the superior tubercle of the glenoid, and

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then we can follow it anteriorly as it exits the joint

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space and becomes extra-articular, but intra-synovial.

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It is bounded in the front by a

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stabilizer, the coracohumeral ligament.

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Now, the coracohumeral ligament frequently bifurcates

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and merges with the belly of the supraspinatus.

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But most of the fibers go underneath and form

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the deepest layer of the anterior margin of the

1:01

rotator cuff, which is a dynamic stabilizer.

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And we're here to talk about instability, not rotator

1:07

cuff pathology, but it does play a role in stability.

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As does other muscles, like the

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pec major, the latissimus dorsi,

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and the periscapular muscles.

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So you can't ignore those.

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And that's why patients that have lots of

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muscular atrophy and fatty infiltration are

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at risk for various types of instability.

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Now the passive stabilizers include the glenoid rim, which

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is discussed in a separate section along with the labra.

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And do go back to that vignette

1:37

that talks about the, the glenoid.

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And we will talk about, separately, the

1:43

labrum and the capsuloligamentous reflection.

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So that's going to be in the next upcoming

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vignette, a companion to this one.

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At extremes of motion, the glenohumeral

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ligaments contribute the most to stability.

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So when you're all the way forward and

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adducted with your arm across your body,

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the posterior structures come into play.

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When your arm is at your side in abduction and

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extremes of external rotation, the inferior

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glenohumeral ligament is taut, and it comes into play.

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And together with this structure, the CHL, and together

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with this structure, right here, the CHL, the superior

2:28

glenohumeral ligament, which we can see in the sagittal

2:31

projection up higher, the middle glenohumeral ligament,

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and the inferior glenohumeral ligament, we've got

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passive restraints to translation of the humerus.

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So let's talk about these passive restraints.

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First, the SGHL.

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Here's the SGHL in the axial.

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Where is it in the sagittal?

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Right there.

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Now let's scroll a little bit.

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Because the biceps is a good indicator of

2:57

where you can find the rest of the SGHL.

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Here I see some of it here.

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There it is right there.

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That's SGHL.

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Now here's our biceps.

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This is CHL and SGHL, hard to detect, but

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it's starting to come underneath the biceps.

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SGHL now looping under the biceps, and now SGHL merging and

3:18

blending with the biceps and the subscapularis upper border.

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This is a restraint to inferior translation of

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the adducted shoulder, the shoulder at the side.

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What about the MGHL?

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Let's go ahead and find that.

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Here's our condensed MGHL,

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and there's part of the MGHL right here.

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Here's the rest of the MGHL, which is

3:44

a pretty thick cord-like structure.

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It's got variable descent.

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It can be horizontal, oblique, or

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straight, up and down, vertical.

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This one's more oblique, although we are catching a

3:56

vertical portion of it, and a horizontal portion of it.

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If we follow it on down, that's still part of the

4:03

MGHL, and these are some condensed portions of the

4:07

deeper capsule, so-called pseudo MGHL structures.

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It limits. The MGHL limits anterior translation

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when the shoulder is externally rotated and

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moderately abducted away from the body.

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That leads us to the most important, the granddaddy

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of them all, the IGHL, especially the anterior band.

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And look at that thing.

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Oh, she's a big one.

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And there are some senechii extending from it, some

4:41

bands extending from it to the humerus.

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The IGHL is the most important stabilizer of the shoulder.

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It's got an anterior band, an

4:53

axillary band, and a posterior band.

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There's the posterior band right

4:58

here coming onto the humerus.

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Let's get to the humerus.

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Well, we actually have trouble seeing it.

5:04

Right there is a portion of the posterior band of the IGHL.

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It's much less well-developed.

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Than the axillary band, which is much less

5:13

well-developed than the anterior band.

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The anterior band is the one that's best seen

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in all projections, and it's the thickest, and

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in this case, it is split into two components,

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an anterior anterior band component, and a more

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dominant anterior posterior band component.

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We're not low enough to see the axillary band.

5:32

And we're seeing the upper portion

5:34

of the posterior band of the IGHL.

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It is critical to passive joint stabilization.

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And it is critical to resisting

5:42

anterior translation of the shoulder.

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In other words, preventing the shoulder from

5:47

doing this when your arm is in this position.

5:51

So that concludes our discussion of

5:54

the dynamic and passive stabilizers

5:57

in the sagittal projection.