On-Track/Off-Track: The Hill-Sachs Concept
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So we have a diagram of a patient with a Hill Sachs
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lesion in the mid range position where the capsule,
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seen here in green, is lax, as it normally will be.
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And then with the patient in extreme abduction,
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external rotation, where the capsule is taut.
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And in neither of these cases is the
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shoulder unstable, despite the fact that
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we have a deep focal Hill Sachs lesion.
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Now the prevalence of Hill Sachs lesions is
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about 70 percent after initial dislocation.
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It's about 85 to 95 percent with recurrent dislocations.
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It may even be a little higher than that.
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The Hill Sax lesions Can't appreciate it here, but
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let's draw the greater tuberosity, and then this
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would be the medial humerus, and then the neck, so
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this would be, uh, lateral, and this would be medial.
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And if you were, you were to look at a Hillsack's
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lesion that is contentious, the contentious
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ones are usually more medially positioned.
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And they course from supralateral to
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inframedial, so they kind of look like this.
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They have this course to them.
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And you'll sometimes see that.
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on a coronal water weighted
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sequence on the posterior slices.
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And when you do see that in the medial quadrant
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of the humerus, you should be highly suspicious
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that you have an off track, gauging scenario.
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Now typically, most Tilsax lesions occur not right at
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the exact apex, but slightly off the apex, laterally.
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Anywhere from, say, 2 to 5 millimeters.
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But the actual range is more like 2
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to 24 millimeters off to the side.
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So, that's probably a pretty good set of numbers to use.
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But the more medialized the hillsacks The greater
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the hairs on the back of your neck should stand up.
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So, small Hill Sachs lesions on the medial side
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may be a lot more contentious than really big
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ones that are seen near the greater tuberosity.
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So this is something you have to be aware of on CT and MRI.
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The, the Hill Sachs lesion that we have here never engages.
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the capsule is lax, it never engages the point.
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of the glenoid.
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In other words, it's pretty much displaced away
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from the anterior margin of the glenoid cup, so
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there really isn't the opportunity for engagement.
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Now, if the Hill-Sachs was all the way over
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here, that would be a different story.
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But it's not.
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So, the position of the Hill-Sachs, the size of
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the Hill-Sachs, has a great bearing on whether
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you have engagement in either the mid-range or
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extreme abduction external rotation position.
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
ProScan Imaging
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