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Lateral ankle tendon anatomy, peroneus longus.

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It's bigger.

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It's badder.

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It's fatter.

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It's more convoluted in the

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number of turns it takes.

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It tears hypertrophically, unlike the

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peroneus brevis, which is usually in front of it in the

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inframalleolar position, which tears atrophically.

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You may or may not have noticed that

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the axial is not a straight axial.

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It's actually an oblique axial,

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even though we're talking anatomy.

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Because that's how you best image these two

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tendons and avoid magic angle phenomenon.

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It's even better if you can plantar flex the foot.

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The number one cause of making a mistake on the

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peroneus longus and/or brevis in diagnosis is

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not having the proper angle and slight, maybe

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20 degrees or more, plantar flexion of the foot.

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So if we look at the brevis and longus,

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they're gonna have a similar course.

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They both like to go behind the

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fibula and this groove of the fibula

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is usually slightly convex forward.

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In other words, it's shaped like, like this.

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And that's about 82% of the time.

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11% of the time it's just flat.

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And about 7% of the time,

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in normal individuals, it's convex backwards,

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which is not optimal because then

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it's pressing pretty hard against

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the peroneus longus and brevis.

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But spurs can serve as a very prominent irritant

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to either peroneus longus or brevis.

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Now, something else we didn't discuss

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previously about the peroneus longus and brevis but this is

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a good time to do it, is their security.

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We've already said that they are secured

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by a lateral retinaculum above the

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ankle joint, called superior lateral,

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below the ankle joint, inferolateral.

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But there's also another important,

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securing structure, and that is

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this little attachment right here.

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It looks almost like a little limbus thorn.

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Some people call it a fibrous ridge.

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And from that fibrous ridge emanates

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the retinaculum that helps secure what

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I would call the peroneus complex.

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Now the peroneus longus has

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three turns as it descends.

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So let's go back and demagnify our image.

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The first turn is going to be at the malleolus.

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So I think you can see that

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nicely in the sagittal.

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It's making a curve.

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So, it's prone to injury at this

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level, and at this level we have the

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securing superior retinaculum.

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The second place where it is prone

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to injury is where it makes the turn

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about the peroneal calcaneal tubercle.

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Some people call this the

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trochlear process of the calcaneus.

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And if the patient has a large spur or a bifid

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tubercle or tuberculum bifidum, that restricts the

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movement of the peroneus longus, produces excessive

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shear forces and it may cause it to tear.

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So that's another, a second vulnerable point.

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And finally, the last vulnerable point,

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the point where it makes its last

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turn, or major turn, is when it goes

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into the cuboid tunnel, right there.

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Now, a very common mistake, here we are entering

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the cuboid tunnel in the axial projection.

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Here we are coronally, let's follow it.

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There it goes, curving around

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into the cuboid tunnel.

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There we go, there's the cuboid.

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Here it's going into the tunnel,

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and now it's in the plantar aspect of the foot,

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foot, headed towards the west coast.

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It's headed towards the left.

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It's headed towards its insertion

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site, which we'll discuss in a moment.

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So these are the three major important turns.

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Let's review them again.

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One, retromalleolar.

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Two, at the level of the trochlear

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protuberance or calcaneal tubercle.

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And finally, three, at the level of the

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cuboid tunnel, where it passes in the

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tunnel in this small little arcuate curve.

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Now this is also where you're going to find

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an accessory ossicle known as an os peroneum.

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The ossicle is in the tendon.

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It is not uncommon to have micro- or

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macro-separations of the distal aspect

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of the tendon from the ossicle itself.

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And that is one of the more

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commonly, but sophisticated,

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missed tears of the peroneus longus.

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Now as far as the insertion sites,

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there's a triple insertion in the first

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metatarsal base, the first cuneiform,

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and the first dorsal interosseous muscle.

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The most important of these, though, is the one

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that inserts on the base of the first metatarsal.

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So let's follow our peroneus longus.

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There it is.

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It's a little more inferior to the brevis.

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Let's keep following our longus.

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Here it is coming around the curve.

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There it is.

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We kind of lose it for a little bit.

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And now, we're at the base of the first metatarsal.

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We actually didn't quite reach it,

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because we're not distal enough.

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But you'll see when we get into the forefoot.

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And the midfoot, that the first metatarsal

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base is a very important locus of

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insertion, and it can be traced quite

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nicely in the short-axis projection.

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Let's see how far we can follow it in the axial.

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Here it is.

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There it is.

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And now it's exhibited magic angle

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effect, so we've kind of lost it,

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and we haven't gone quite distal enough

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to see its distal insertion point.

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Triple insertion.

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First metatarsal base.

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First cuneiform, first dorsal interosseous muscle

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coming to a theater near you in the forefoot.