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Let's talk about the MR imaging

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features of the extensor compartment.

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We're going to focus on the

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tibialis anterior tendon.

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Do you remember that the achilles doesn't have

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a true sheath and has a fibrous rim called

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paratenon, whereas the remaining structures,

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the remaining tendons of the foot have

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tenosynovial sheaths around them.

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However, anteriorly, the anterior

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tendons do not have fluid around them.

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So even a small amount of fluid

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anteriorly is considered abnormal.

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Whereas a small amount of fluid, about a

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millimeter in thickness, around, say,

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the posterior tibial tendon, that is often normal.

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The tibialis anterior arises from the

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proximal third of the lateral tibia. It's the

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most medial extensor muscle of the ankle.

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It also arises from the lateral tibial condyle,

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the interosseous membrane, and the deep deep fascia and intermuscular septum.

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The proximal AT tendon is surrounded by a

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synovial sheath of variable length, and the last

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few insertional centimeters of the tendon are

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invested by a more fibrous, thicker peritenon.

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And you see as we come down here sagittally

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on our lateral projection, kind of spreads out a little

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bit and becomes flatter due not only to its

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footprint, but also due to this peritenon.

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It's retained anteriorly by three separate

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what I would call fibro-osseous tunnels that

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include the superior extensor retinaculum.

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Let's go up and have a look at it.

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It's pretty hard to see

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until you get up really high.

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This very small...I'm gonna

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magnify it a little bit for you.

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This very small, thin structure right here.

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It's part of the superior,

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extensor retinaculum.

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And then down lower we have oblique

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superomedial and oblique inferomedial bands.

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So here's the oblique superomedial band.

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And then let's get down even lower and you'll

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see the oblique inferomedial band, all serving

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to secure the tibialis anterior tendon.

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Now this tendon has a bifid insertion.

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The major slip is to the medial cuneiform.

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So let's follow it again.

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There's the TA, the tibialis anterior.

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Let's watch it go on to the medial cuneiform.

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And it's a little hard to appreciate, but there's

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a small slip going to the base of the first.

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I think that's better appreciated if we

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slide over to the sagittal projection.

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Let's look at our tibialis anterior.

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There she blows.

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Remember, she's gonna be secured by

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the retinaculum, both above the ankle

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joint and below the ankle joint.

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Here it's coming down, getting

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a little more fan shaped.

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Touching, inserting on the

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medial cuneiform, right there.

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There's the footprint.

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And now a tiny little slip going to

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the base of the first, right there.

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Base of the first, medial cuneiform.

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That is the footprint of the AT tendon.

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It's responsible for about 80% of foot dorsiflexion.

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72 00:03:09,549 --> 00:03:11,559 So if you lose it, you're in trouble.

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Usually injuries to it are in athletic

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individuals, particularly people that

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do a lot of uphill and downhill running,

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people that do a lot of overuse activities.

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We also see it in women between

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the ages of, say, 50 and 70.

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It's not uncommon to see hypertrophic

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tendinosis of this tendon without a tear,

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especially in overweight and obese individuals.

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It hypertrophies in some ways a lot

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like the posterior tibial tendon.

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And the classic mechanism of rupture is a

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sudden, say, eversion of the foot tendon

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with plantar flexion and then forced dorsiflexion

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of the foot with the tendon kind of pulling

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against the foot as the foot tries to lift

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itself out of the plantar flexion position.

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So that's our summary of the AT tendon.

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It's a pretty simple tendon.

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It has a pretty straight

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line from proximal to distal.

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It has a bifid insertion on the medial

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cuneiform and the base of the first metatarsal.