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I'd like to introduce the concept of on track and

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off track shoulder imaging in unstable shoulders.

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And I'd like to start out with this basic diagram

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of the humerus sitting on the glenoid cup.

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The anterior glenoid cup is truncated,

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and we are at the N range of stability.

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I'll explain what I mean by that.

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So the capsuloligamentous structures, especially the

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capsule and inferior glenohumeral ligament, are the main

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stabilizers with the arm in the end range of movement.

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So when your arm is in this position, the so called

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Hebert position or behind the head, an abduction,

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an external rotation with the elbow up, this is the

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position that makes the green capsule here taut and

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prevents the shoulder from being displaced anteriorly.

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Now there are other helpers that stabilize,

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including the shape of the glenoid cup, the

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depth of the cup, for if the cup is flat.

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You know, you're less likely to

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keep the humeral head in place.

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If the cup is too deep, then you

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could have diminished range of motion.

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There are two types of glenoid bone loss.

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There's glenoid bone loss from wear, from

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being ground down, from repetitive dislocation.

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And that will often look something like this.

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It'll be a little more rounded and a little more subtle.

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Then there's glenoid bone loss

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that is in the form of a fragment.

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That's usually pretty serrated.

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And then you actually will see the fragment.

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Often with medullary bone with high T1 signal inside it.

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Now four out of every five patients that are actual

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dislocators have both a Hill Sachs and a Bankert lesion.

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And this is known as a bipolar lesion.

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And when the arm is in this, this end range of motion or

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movement, which I have displayed for you, for you here.

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And there are varying degrees of abduction

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and external rotation from patient to

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patient, depending upon their sport.

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the glenoid with the humeral head.

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And this contact zone is known as the glenoid track.

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Now, the contact zone is usually between the mid and

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posterior humerus, articular surface, and the glenoid.

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Now, a Hill Sachs lesion that stays on this track, so that

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there's continuous articular contact, so called glenoid.

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on track lesion, cannot get stuck on or engage

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with the glenoid and cause a dislocation.

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I'll explain what I mean by that in a subsequent diagram,

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since many of you may not be able to conceptualize this.

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I'm gonna, I'm gonna I'm going to keep it simple,

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but that's just an introduction for right now.

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On the other hand, if you have a Hill Sachs lesion,

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which is off the glenoid track, this has a high risk of

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engagement, in other words, getting stuck and dislocation.

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I probably can draw it pretty simply.

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If I come out of this position, this, this extreme

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position, and I start to move my arm forward.

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What may happen is, I might have a defect in the humerus.

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And I'll just randomly draw a defect.

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I'm going to make my defect, um, green.

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So here's my defect.

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So my defect gets stuck on the anterior edge of the glenoid

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and it engages and as I continue to come out of my extreme

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position this entire humeral head will fulcrum forward

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basically be levered out of the glenoid by this defect.

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Remember, this is a triangular shaped defect, and

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the glenoid is kind of seated into it, like that.

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It'll be clear in a moment.

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Now here we have glenoid bone loss.

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But yet, we don't really have a defect

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here for the glenoid to prolapse into.

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And this is still a patient that is going to

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have an on track morphology, because there's

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always going to be articular contact, even though

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you've lost a fair amount of glenoid tissue.

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And we're going to teach you some different ways

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and methods to make that assessment in unipolar,

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And, but especially bipolar lesions, where you

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have both the glenoid abnormality and the humeral

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abnormality, which is 80 percent of all of them.

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Now this is clinically validated stuff.

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Um, I mean this concept that you can reliably predict

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somebody who's going to be a recurrent dislocator by

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looking at this engagement on track, off track phenomenon.

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is supported, clinically invalidated.

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Uh, it's important because for off track lesions,

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the treatment may, may have to be different.

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You may have to use bone blocks and grafts and

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capsulography and something called remplissage,

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which we'll define a little bit later on.

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And these procedures, in addition to a

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Bankert, or instead of a Bankert, may

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decrease your risk of recurrent dislocation.

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So, let's move on now to another simple demonstration

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of on track, off track morphology diagrammatically.