Interactive Transcript
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21-year-old man who fell with wrist pain.
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Simple search pattern involving the
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skeleton demonstrates a wide gap between
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the scaphoid and the lunate immediately.
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There's no secret that this patient
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has scapholunate dissociation.
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But there's more.
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There is hypertrophy of the radial styloid due
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to arthritis of the distal pole of the scaphoid
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as it rubs abnormally against the distal radial
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styloid, causing its hypertrophic response.
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This is one of the earliest signs of scapholunate
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advanced collapse, or slack wrist.
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In fact, it's considered stage one.
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There's a little inflammatory reaction around it.
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Slack wrist, by the way, is the most common
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cause of degenerative arthritis of the wrist,
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and Watson and Ballet coined the term in 1984.
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Oh, but there's more.
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We're not done looking simply at the skeleton
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of the wrist in the coronal AP projection.
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What is stage 2 slack wrist?
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In this scenario, stage 2, there is arthritis
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between the entire scaphoid and the radius.
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Now it doesn't have to be every inch of it,
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but let's look at the base of the scaphoid.
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Oh, there's an erosion there.
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There's narrowing of the joint space.
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So the proximal aspect of the joint is involved,
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and the distal aspect of the joint is involved.
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Now, frequently, in slack wrist, you may
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see erosions all the way from proximal to
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distal on the radial side in its fossa.
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That's not the case here.
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But there is involvement of
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more than just the distal pole.
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What would be stage 3 slack wrist?
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We would see narrowing, sclerosis, irregularity,
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and erosions of the capitolunate articulation,
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and we do, right there on the T1-weighted image,
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right there on the water-weighted image, with joint
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space narrowing at the lunate and the capitate.
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And in stage 4, which this patient does
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not manifest, there would be generalized
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degeneration in the intercarpal space,
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and perhaps involvement in the
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remaining radial carpal articulation
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and the radial ulnar articulation,
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which in this case is relatively spared.
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So we have features of stages one, two, and
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three slack wrist that we have demonstrated.
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Now, as said previously, with scapholunate
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dissociation, there is a high risk of
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DISSI, or dorsal intercalary segmental
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instability, which this patient has.
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Although we haven't mentioned it, there
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are four causes or basic types of DISSI.
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It can occur as a result of a scaphoid fracture.
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This is known as bony DISSI.
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Distal radius fracture, compensatory DISSI, radius
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malunion, known as adaptive DISSI, and this type,
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dissociation of the scaphoid and lunate, so-called
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ligamentous DISSI, producing a dorsal-facing lunate.
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And if we look at the angle between the lunate and this
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angle is the long axis of the radius, let's scroll it.
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Actually, we won't scroll it.
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You'll have to take my word for it.
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This is the long axis of the radius.
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Sorry.
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The long axis of the scaphoid.
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This is the perpendicular axis of the lunate.
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And we look at this angle.
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This angle should be less than
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60 degrees. Over 70 degrees,
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it's almost always DISSI.
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And this angle will be markedly decreased in the
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opposite, ventral-facing lunate, so-called VISSI.
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So now, we've highlighted
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the manifestations of slack wrist in a patient
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with scapholunate dissociation and DISSI,
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giving you the four progressive stages of
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slack wrist, originally described in 1984.
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