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We're going to start out with a basic overview of

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wrist instability and you will be able to drill deeper

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when we get into our complex instability series.

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But as I start, I rely on the coronal AP projection.

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Basic, basic.

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All the carpal bones are there.

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And if you are a plain film aficionado,

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you will remember the arcs of Galula.

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And let's look at those arcs momentarily.

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Even though they're drawn on plain film, they include

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a proximal arc through the base of the proximal carpal

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row and those should line up proximal-distal with

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each other. They sort of do, although the lunate is

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migrating towards the east coast. Then the second arc

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will make green; that's going to be along the distal

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aspects of these bones and we see how they line up

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with one another. And our third arc is going to be along

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the proximal aspect of the capitate and the hamate.

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Let's make that one blue. And these are

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the same three arcs you would use on

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conventional radiography to evaluate somebody

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for lunate and perilunate dislocation.

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Another basic, basic tenet.

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The zones of failure.

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Let's use a different color.

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Let's use something that's sort of peachy or orange.

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If I draw an inverted arc like this through the

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scaphoid and through the triquetrum, and through the

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base of the capitate, if you've got an instability

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that's related to bony failure, it will often

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interrupt these bony structures in this orientation.

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Not all of them, one of them, or more than one

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of them, depending upon the type of injury.

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That's called the greater inverted arc.

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The lesser inverted arc, if there's a

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greater one, there's got to be a lesser one.

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The lesser inverted one, I'll use yellow,

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is going to be centered around the scaphoid.

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And it's going to include failures in this

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distribution that include the scaphoid-lunate

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ligament, the lunate-triquetral ligament, and some

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other important ligaments like the radioscapho-

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capitate or sling ligament and a few others.

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So this lesser yellow arc would

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refer to the distribution or arc of

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failure for pure ligamentous injuries.

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Bony injuries, ligamentous injuries.

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The arcs of Galula, all three of them, used

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on conventional radiography to look at the

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alignment of the wrist in the AP projection.

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Let's move on, shall we?