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We're talking about the extensor digitorum longus

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and extensor compartment on MRI.

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Some pitfalls you should be aware of.

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First, an easy one.

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Here are two oblique components

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of the extensor retinaculum.

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Look at how this one sidles right up to the

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medial free edge of the extensor digitorum.

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It creates a somewhat fuzzy appearance

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to it, which shouldn't be confused with

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fraying or an injury, or an abnormality.

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Another really important pitfall

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you ought to be familiar with, is the sinus

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tarsi, or subtalar space, has this inferolateral

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retinaculum, also called the stem ligament.

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And there's a stem ligament bursa,

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and a capsule associated with that bursa.

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So you can get a bursal cyst,

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or a ganglion pseudocyst.

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It'll come right out of here, and dissect into the

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individual tendon leaflets, or between the tendons

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of the extensor digitorum, and kind of weave its

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way around inside the tendons after they split.

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So when they split down lower, you may have

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a white object weaving in and out of these,

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thinking you're dealing with tenosynovitis,

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when actually you're dealing with a

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single mass that came out of here,

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either a bursal cyst or a ganglion pseudocyst.

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One last pitfall.

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As you follow the extensor digitorum from

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up high, and I've done this before,

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I've often confused the halluses as the medial

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free edge of the extensor digitorum.

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So as we come down, we see the halluses separate.

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That's the digitorum.

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And then as we come down,

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the digitorum's pretty flat.

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And then all of a sudden,

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it'll get a little bulbous.

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Right before it decides to split.

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Do not confuse this bulbous,

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sort of grayish appearance of the

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extensor digitorum with tendinosis.

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This is a normal physiologic bundling of

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the tendon before it splits into its four

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individual rootlets that will come to insert

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on the extensor components of the digits.

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Those are the pitfalls for the EDL.

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Here's a plantar flexed, uh,

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group of images of the foot.

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PD spur T2 and T1 highlighting.

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Delicate structures, namely the

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extensor retinacular mechanism in the

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extensor compartment of the foot on MR.

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So we're up pretty high.

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tibia.

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Let's look at our friends Tom, Dick, and Harry.

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Tibialis anterior, extensor halluces,

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actually Tom, Harry, and Dick.

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Extensor halluces for Harry, and Dick,

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the extensor digitorum longus, which

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travels with the peroneus tertius,

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which hasn't gotten a lot of attention.

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play on our vignettes, yet.

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By the way, deep to those sits the

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neurovascular bundle, and right there, and

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there, is going to be the deep peroneal nerve.

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But that will be a story for another day.

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So, let's focus on the retinaculum.

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And, right about here, we see the

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extensor retinaculum, and there's often

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a separate little loop above the ankle

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joint that surrounds the tibialis anterior

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to help secure it a little bit further.

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And that loop, or separation, or split,

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is Now let's talk for a moment about

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the inferior extensor retinaculum.

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So the inferior extensor retinaculum

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is below the ankle joint.

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As stated, the superior one, which is more

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simple, and may form its own loop around

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the tibialis anterior, is the superior one.

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So here's the superior retinaculum.

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You kind of lose it for a little bit.

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And then as you get down

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here, it kind of makes an X.

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There's a deep oblique component of it, and

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there's a more superficial component of it.

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And there is an oblique supramedial, an

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oblique inframedial, and a variable oblique

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supralateral limb below the ankle joint.

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Here's one of the oblique limbs back here.

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So, not of critical importance to you right now.

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What I'd like to do is turn

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our attention to the stem.

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So the stem, specifically the medial root

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of the inferior retinaculum, helps support,

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in somewhat of a sling-like fashion, to The

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tertius complex, which is right here and here.

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So there's the stem, stem, and stem.

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And here is the superficial retinaculum.

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So superficial portion of the

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sling, deep portion of the sling.

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And these can continue on around for a

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variable distance and provide support to

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the other extensor compartment tendons.