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MRI, sagittal projection, wrist anatomy, focusing on

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the position of the bones relative to one another.

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We're talking about the central column first,

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the simple alignment of the third metacarpal,

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with the capitate, the lunate, and the radius.

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Sometimes, if the technologist positions

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the wrist in the scanner in ulnar

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deviation, it'll alter the position of the

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lunate such that the lunate will rotate.

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Face dorsally.

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This is known as pseudo DISI.

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Similarly, if the technologist accidentally puts

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the wrist in the scanner in radial deviation,

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then the lunate will face in a palmar orientation.

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So-called pseudo VISI.

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Now, if there's a pseudo DISI and a pseudo VISI,

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that means there must be a real DISI and a real VISI.

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So what does that mean in a real DISI, the lunate.

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It's properly placed in the scanner such that the

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wrist is in a neutral position, but the lunate

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is still tilted dorsally, it's dorsal facing.

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Why does that happen?

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Because there is injury to the stabilizers of

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the scaphoid and the scapholunate ligament.

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If the lunate were to face in the palmar

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orientation, the opposite direction, we'd say

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that the patient then has VISI, which stands

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for Volar Intercalary Segmental Instability.

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Those patients have abnormalities of the lunotriquetral

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ligament and often of the palmar

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ligaments, the so-called inverted V ligaments.

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So you can have DISI or pseudo DISI

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from malpositioning, VISI or

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pseudo VISI from malpositioning.

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What's another alignment feature we might look at?

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Simply in the sagittal projection.

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The overall position of the scaphoid.

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The scaphoid should look like

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it stands up a little bit.

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So that if we make a line, which I already have

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drawn on here, but I'll draw over it again.

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Make a line down the long axis or barrel of the radius.

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And then a long axis line along the scaphoid.

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This angle should be about 60 degrees.

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If the stabilizers of the scaphoid are compromised.

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The scaphoid is going to start to rotate

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downward, and this angle, labeled number

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two, is going to increase in size.

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So those are the two major observations we

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make alignment wise in the sagittal projection.

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There is a third minor, but still

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important observation, and that is

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one you're used to making on an x-ray.

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The position of the ulna.

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Relative to the radius.

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The back of the ulna should not be

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more than a centimeter to the back

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margin of the cortex of the radius.

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And if the ulna looks like it's sagging

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too far back, it's often because there

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is radial ulnar ligamentous instability.

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The best way to confirm that, if you're unsure,

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is to pull down a short axis projection.

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So let's do that.

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Pull down the short axis projection, and

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we see that there is congruence between the

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dorsal-ventral position of the ulna and the

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dorsal-ventral position of the radius and that

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the ulna fits nicely in the sigmoid notch.

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So this is not one of my favorite views to

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analyze the position of the ulna, but it is a

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view that you have to make that observation on.

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You're much better off analyzing the radial

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ulnar relationship in the short axis projection.