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<v ->Now to complete our story

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of these restraining systems that keep tendons in place,

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I wanted to spend just a moment

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talking about the flexor tendons of the finger and,

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the fingers and thumb, by the way

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and the existence of two types of pulleys,

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annular pulleys labeled A here

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and cruciate pulleys labeled C.

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And as you all know, if we deal with the four fingers,

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rather than the thumb, you end up with five annular pulleys

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and three cruciate pulleys.

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And they're labeled here in this particular drawing.

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And these are taken from an article

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that one of our fellows did years ago.

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Now of these pulleys, you can see the location,

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A1, A3 and A5 are located at the joints

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A2 and A4 are located between the joints.

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The most important and strongest

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of these pulleys are A2 and A4.

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The most common finger that is involved

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in an injury is the middle finger, next to the ring finger

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than the others.

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The most typical pulley that is involved is the A2 pulley,

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then the A3, then the A4, rarely A1 pulley abnormalities.

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And in the normal situation, owing to these pulleys,

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here we see A2 as this thin black line.

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Here's A4, these flexor tendons are held tightly

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against the phalanges

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but when there is a pulley injury,

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this is an A2 pulley injury.

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there is a bow string deformity and an increased distance

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at the level of the injured pulley

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between it, the tendon and the phalanges.

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And so be aware of that.

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There are ways of doing the MR imaging for these.

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Some people suggest stress views, holding a ball.

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When you do MR imaging.

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I'll show you one further example.

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This was in a cadaver.

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We created the lesion.

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You can see the bow stringing here

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and you can see the specimen.

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And these were lesions of the A2 and A3 pulleys.