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We're talking about the MR anatomy

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of the extensor compartment.

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And let's focus on the extensor

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hallucis longus, which sits right

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next to our tibialis anterior tendon.

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The big fat one, also known as Tom.

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Tom is responsible for 80 percent

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of the dorsiflexion of the foot.

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We've got Harry, the extensor hallucis,

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and it's gonna go to the big toe.

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It originates from the middle half of the

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fibula, and adjacent interosseous membrane.

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And then it descends vertically between the

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tibialis anterior, and just lateral to it, the

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extensor digitorum, longest tendon and muscles.

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And it becomes tendinous around

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the distal third of the tibia.

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It's kind of got an oblique

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course, and it is secured.

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You can see the security provided somewhat

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by the inferior extensor retinaculum.

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If we go up higher, you'll see very nicely the

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superior extensor retinaculum securing the EHL.

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And each EHL will eventually insert

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medially onto the dorsal surface of the

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hallux of the distal phalangeal base.

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Or, the distal portion of the great toe.

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When it does so, it kind of spreads

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out in a poneurotic fashion.

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So it's kind of triangular, and sometimes it's

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even referred to as a triangular ligament.

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And it covers the dorsal surface

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of the distal phalangeal base.

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Some variations of this tendon

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include one to three muscle bellies

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and tendons, and a shared muscle slip.

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Sometimes it'll actually share

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a muscle slip with the adjacent

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extensor digitorum.

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And here we've actually got

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retinaculum and a shared muscle slip

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between the two, blending together.

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So that is not uncommon.

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Having multiple muscle bellies

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up higher is not uncommon.

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So this can get a little bit confusing.

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So if we look at the sagittal projection,

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let's go over to our easy-to-see, because we

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identified the medial cuneiform tibialis anterior.

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And we follow it back, we follow it back.

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Now the next long tendon that we run into, there

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it is, is gonna be the extensor hallucis longus.

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And this very thin thread right there

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represents the retinaculum, uh, over top.

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And then we can follow the hallucis all

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the way up into its, uh, muscular portion.

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Again, multiple muscle bellies may

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be present in the muscular portion.

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That's our discussion regarding

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the extensor hallucis longus.