0:00

We're talking the extensor compartment and

0:02

focusing on the extensor digitorum longus.

0:07

Let's go up pretty high where we see the

0:10

extensor digitorum myotendinous unit sitting

0:13

next to the EHL, the extensor hallucis longus.

0:17

Now this tendon arises up higher from the

0:20

lateral tibial condyle, the proximal three

0:23

fourths of the fibula, so tibia and fibula, and

0:26

the interosseous membrane, and the deep fascia.

0:29

And the intramuscular septum.

0:32

It then goes down and sits behind the

0:35

extensor retinaculum, which we can barely

0:37

see as a thin linear membrane over the top.

0:41

There is the extensor digitorum.

0:43

And it's going to divide into, eventually,

0:46

four slips that go into the phalanges.

0:50

Now, as we get further down,

0:52

something very interesting happens.

0:54

Here we are dividing the extensor

0:56

digitorum up into at least two slips.

1:00

We're seeing a little bit of

1:02

the anterolateral retinaculum.

1:06

And then, what is that?

1:08

That is actually the sinus tarsi

1:11

space infralateral retinaculum.

1:14

Some people will refer to it as the stem ligament.

1:17

And it comes out and sits kind

1:19

of underneath these tendons.

1:21

And the retinaculum sits on top of these tendons.

1:24

And it forms a sling.

1:26

There is the underbelly of the sling right there.

1:29

Coming out from the subtalar space.

1:32

And here is the superficial retinaculum.

1:35

The extensor digitorum is

1:36

going to slip right in between.

1:39

In the sagittal projection, not as easy to see.

1:42

However, the inferior retinaculum

1:44

and stem ligament is easy to see.

1:47

There it is.

1:48

There it is.

1:49

Coursing obliquely, superiorly, anteriorly.

1:53

And coming to rest right

1:55

underneath the extensor digitorum.

1:57

Although you can't see it, the

1:58

superficial retinaculum is on top.

2:01

This is on the bottom, and so

2:02

it thusly forms that sling.

2:06

Now the extensor digitorum, as it comes down,

2:08

let's look at it in the coronal projection.

2:10

Because we get a very nice look anteriorly.

2:13

Let me see if I can find it.

2:14

Right here, there's the extensor digitorum.

2:18

And there are some slips of the

2:21

oblique extensor retinaculum.

2:24

And these slips may huddle up right next

2:27

to the extensor digitorum and create a

2:29

little kind of fuzzy, uh, appearance to it.

2:33

It'll eventually exit, uh, from these, uh, slips.

2:36

It'll traverse the foot and it will insert

2:39

on the dorsal aspect of the middle and distal

2:43

phalanges two through five, two through five

2:46

digits in the extensor expansion sheaths.

2:49

This tendon functions primarily as a

2:53

phalangeal extensor, but also contributes

2:55

a little bit of extension to the foot

2:58

along with the tibialis anterior.

3:00

This coronal projection is a very nice view of

3:03

the oblique course of the extensor retinacula.

3:07

And you can see how they kind of huddle

3:08

over the top of the extensor hallucis,

3:11

as well as, uh, huddling over the

3:13

top of the extensor digitorum longus.

3:16

Again, this sagittal shows the stem

3:18

ligament coming out from the sinus tarsi.

3:21

Forming the undersurface of the sling that

3:24

surrounds the extensor digitorum longus.