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21-year-old man jammed his wrist

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two months ago, now with wrist pain.

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Let's look at the coronal projection,

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T1 fat-weighted, and in the center,

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water-weighted, fat-suppressed image.

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Let's start our general search pattern.

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Carpal bones, check, but not in the

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proper orientation of one another.

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For instance, the capitate looks like it's

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a little proximal, but obviously, there's

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a huge gap, the so-called Terry Thomas

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sign, between the scaphoid and the lunate.

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There's evidence of scapholunate dissociation.

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How about the lunotriquetral interval?

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There is a ligament present, although there is swelling

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in the LT interval, so it's not completely normal.

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There are some other indirect signs of lunotriquetral

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interval microinstability, such

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as arthritis with erosions, and there is

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an ossicle, or a bony structure, sitting at

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the base of the lunotriquetral ligament.

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So, all is not well on the ulnar side of the wrist,

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but let's return to the radial side of the wrist.

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So, we, we quickly assess our bony architecture,

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we assess our alignment, we also look at the

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distal radioulnar articulation, as well as the

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shape of the ulnar styloid, which is a little bit

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irregular, and the shape of the radial styloid,

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which is moderately irregular and hypertrophic.

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That's signed immediately.

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Tells us that the radius is being remodeled

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by something, and what is that something?

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It's the scaphoid rubbing, irritating, and pressing

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against the radius, producing radial styloid hypertrophy.

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And the only way that can happen is if there's scaphoid

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micro or macro instability, even though this is a static

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image, so we are immediately suspicious of

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scapholunate instability with scapholunate collapse

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or scapholunate advanced collapse, called SLAC wrist.

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And this is one of the earliest signs of SLAC

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wrist, namely radial styloid hypertrophy.

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Now, with this widening or dissociation, the next thing

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I would do as part of my search pattern and practice

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would be to look at some of the extrinsic ligaments.

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The first one I would focus on is the one that

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comes off the radial styloid right here, which

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is the radioscaphocapitate, or sling ligament.

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It's still present.

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But the radiolunotriquetral ligament, which is the

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other V-shaped structure in the palmar aspect of the

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wrist that goes from the notch of the radius, crosses

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the lunate over to the triquetrum, in other words,

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another band underneath this band, it's missing.

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So that might contribute to instability

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of the lunate with fine movements.

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What else should we search

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for in the coronal projection?

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The degree of synovial

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inflammation or capsular swelling.

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Well, there's general high signal

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intensity throughout the carpus.

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I would describe it subjectively as mild.

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The number of erosions, scattered and mild,

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although concentrated at the LT interval.

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I'd look at the triangular fibrocartilage, which

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has some ill-defined signal, but rather non-focal, a

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little bit of irregularity and arthritis at the radioulnar

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articulation, and the peripheral attachments

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to the styloid and to the fovea are still present.

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So let's turn our attention back to this

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finding and go to the sagittal projection.

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In the sagittal projection, let's scroll.

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And as we scroll, you see a

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few lines that have been made.

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One line through the scaphoid.

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Now, the scaphoid should be standing up a little taller.

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And one of the things we do is we look at the

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relationship of the scaphoid to the lunate.

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So if we extract this line to this image, and then draw

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a perpendicular line through the lunate, let's do that.

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Here's our perpendicular line through the lunate.

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Here's our scaphoid line.

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Even though we don't see the scaphoid,

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we look at this angle, and if we measure

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this angle, it's about 85 degrees.

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What is it?

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Normally?

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30 to 60 degrees.

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Anytime this angle is over 70 degrees, you are assessing

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with dorsal intercalary segmental instability, or DISI.

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Another name for this is a dorsal facing lunate.

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DISI is associated with scapholunate dissociation.

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There are a number of causes of DISI.

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It can occur with a scaphoid fracture.

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It can occur with scapholunate dissociation.

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It can also occur with interruption

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of other ligamentous structures of the

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wrist, including some of the extrinsic

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stabilizers on the radial side of the wrist.

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So, in summary, we've got a patient with

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scapholunate dissociation, which means

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the scapholunate ligament is compromised.

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It's gone.

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The lunate is starting to migrate over towards

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the ulnar side of the wrist, where there's

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some ulnar translocation of the lunate.

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There's evidence of dorsal intercalary,

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segmental instability, or DISI.

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Note that the capitate is sitting a bit

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posterior, which is another feature of DISI.

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And we would add that there's evidence of micro

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instability and arthritis at the LT interval.

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And then add to our conclusion generalized

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capsulitis with early signs of slack wrist

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as evidenced by hypertrophy of the radial styloid.