0:01

Knee anatomy on MRI, posteromedial corner,

0:05

focusing on the semimembranosus and its

0:08

expansions. Semimembranosus is a large muscle.

0:13

The semitendinosus rides along its posterior margin

0:16

or back up more approximately.

0:18

And as it comes down, it has

0:21

a very deep component known as the direct arm.

0:25

And this is the one you frequently

0:27

see attaching to the tuberculum tendinous along

0:30

the posteromedial aspect of the tibia.

0:35

It'll bifurcate into two structures

0:39

that one sees one anteriorly, not labeled here.

0:44

It's underneath the POL and the deep

0:46

portion of the superficial MCL, or superficial

0:51

portion of the deep MCL. Also known

0:53

as the tibial collateral ligament.

0:56

And here is the anterior reflected arm underneath, called the pars reflexa.

1:04

So you'll probably be able to see that.

1:06

You'll also be able to see the

1:08

distal continuation of the direct arm or

1:12

deep arm, more distally along the posteromedial aspect of the tibia.

1:17

More variable and often not seen on MRI

1:20

is the inferior (popliteal arm), which goes in between these two.

1:26

And then more posteriorly is the distal attachment of the inferior arm.

1:29

This goes a long ways down, and because of that,

1:32

it's sometimes more easily identifiable because of its distal extension.

1:37

And then, supporting the posteromedial capsule of the knee,

1:41

a little more in the front though,

1:43

is the capsular arm.

1:45

And then all the way in the back, becoming the oblique poploteal ligament,

1:51

is the OPL extension of the semimembranosus.

1:55

So the semimembranosus provides support

1:59

to the entire posterior capsule running from posteromedial

2:04

to posterolateral, along the back of the knee.

2:08

It's a little hard to appreciate on

2:09

this oblique projection, but you'll see what

2:12

we mean on other vignettes.

2:14

So those are the major expansion heads

2:17

of the semimembranosus.

2:19

As you can see, we've added an

2:20

important division here, the pars reflexa, which runs

2:23

anteriorly underneath the POL and the direct

2:27

arm, which runs more oblique inferior

2:31

and inserts on the tuberculum tenderness

2:33

a little protrusion or bony protrusion along the

2:36

posteromedial edge of the tibia.

The Posteromedial Corner: Semimembranosus Expansions

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0:01

Knee anatomy on MRI, posteromedial corner,

0:05

focusing on the semimembranosus and its

0:08

expansions. Semimembranosus is a large muscle.

0:13

The semitendinosus rides along its posterior margin

0:16

or back up more approximately.

0:18

And as it comes down, it has

0:21

a very deep component known as the direct arm.

0:25

And this is the one you frequently

0:27

see attaching to the tuberculum tendinous along

0:30

the posteromedial aspect of the tibia.

0:35

It'll bifurcate into two structures

0:39

that one sees one anteriorly, not labeled here.

0:44

It's underneath the POL and the deep

0:46

portion of the superficial MCL, or superficial

0:51

portion of the deep MCL. Also known

0:53

as the tibial collateral ligament.

0:56

And here is the anterior reflected arm underneath, called the pars reflexa.

1:04

So you'll probably be able to see that.

1:06

You'll also be able to see the

1:08

distal continuation of the direct arm or

1:12

deep arm, more distally along the posteromedial aspect of the tibia.

1:17

More variable and often not seen on MRI

1:20

is the inferior (popliteal arm), which goes in between these two.

1:26

And then more posteriorly is the distal attachment of the inferior arm.

1:29

This goes a long ways down, and because of that,

1:32

it's sometimes more easily identifiable because of its distal extension.

1:37

And then, supporting the posteromedial capsule of the knee,

1:41

a little more in the front though,

1:43

is the capsular arm.

1:45

And then all the way in the back, becoming the oblique poploteal ligament,

1:51

is the OPL extension of the semimembranosus.

1:55

So the semimembranosus provides support

1:59

to the entire posterior capsule running from posteromedial

2:04

to posterolateral, along the back of the knee.

2:08

It's a little hard to appreciate on

2:09

this oblique projection, but you'll see what

2:12

we mean on other vignettes.

2:14

So those are the major expansion heads

2:17

of the semimembranosus.

2:19

As you can see, we've added an

2:20

important division here, the pars reflexa, which runs

2:23

anteriorly underneath the POL and the direct

2:27

arm, which runs more oblique inferior

2:31

and inserts on the tuberculum tenderness

2:33

a little protrusion or bony protrusion along the

2:36

posteromedial edge of the tibia.

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Description

Faculty

Stephen J Pomeranz, MD

Chief Medical Officer, ProScan Imaging. Founder, MRI Online

ProScan Imaging

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Case Review: Supporting Structure Injuries

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Pivot Shift Injuries and Meniscal Pathology

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More Meniscus Tears with Case Examples

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Applying What You've Learned

The Posteromedial Corner: Semimembranosus Expansions