On-Track/Off-Track: Stable Hill-Sachs Lesions
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Let's take a look at stable Hill-Sachs defects.
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I mean, this is a deep hatchet job, if you will.
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But yet, no matter whether you're in the mid-range,
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where the capsule is lax, or you're in the end range
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with the arm in abduction and external rotation,
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there is always contact between the surface of
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the humerus and the glenoid articular surface.
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Even though there's laxity here, which is very common,
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and in fact there's usually some anterior translation
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of the humerus when you're in the mid-range position.
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In other words, when you're not fully
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abducted and externally rotated.
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Now in some athletes, the amount of translation that you
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might see here would be greater than the average person.
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In fact, some people in the mid-range, even without a
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Hill-Sachs, And without a glenoid lesion, may be able
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to sublux and even dislocate the shoulder spontaneously.
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Further contributing to the failure of dislocation,
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or helping to support the shoulder, is the
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concavity, as we've said before, of the glenoid cup.
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So you're much more likely to spontaneously
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dislocate with anterior laxity, with or without
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a Hill-Sachs, if the cup is completely flat.
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And that's why you must pay attention to this conformity
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and the fit between the humeral head and the glenoid
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cup, even though the humeral head is a heck of a lot
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bigger, and that's why this joint is prone to dislocation.
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Now the glenoid socket is twice as deep in the
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cranial caudate, or superior to inferior direction,
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as it is in the anterior to posterior direction.
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As a result, the force necessary to translate
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the humeral head under constant compressive
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force is twice as large in the supero inferior
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direction than it is in the AP direction.
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And that's why AP dislocations dominate
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more over direct inferior dislocations.
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The anteroinferior capsule and inferior dislocations,
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as you would expect, are at high risk, and this is
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what may generate your haggle, your bagel, your raggle,
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and your gaggle.
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So, this is an example of mid-range shoulder positioning
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with capsular laxity and end-range abduction external
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rotation with the anterior capsule taut that get this
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patient translating a little bit but not dislocating
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even in the face of a good size Hill-Sachs laxative.
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
ProScan Imaging
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