0:00

Knee anatomy, tendons on MRI. We begin with the medial compartment,

0:08

looking at the sausage shaped sartorius muscle, which becomes a tendon.

0:14

Muscles become tendons which insert on bone. Ligaments go from bone to bone,

0:20

or occasionally from a ligament to bone. So we've got a trident shaped

0:24

group of tendons, the sartorius, the gracilis, and the semitendinosus, known

0:29

as the pes anserinus. Let's cross reference the pes anserinus in the sagittal

0:36

projection. Look at how far posterior it is, and then as we go

0:41

more medially, we see it swing around and have a fairly distal insertion

0:46

footprint on the tibia. It is far more distal and far more anterior

0:52

than its kissing cousin, the semimembranosus. For a moment, let's just take

0:57

a look at the pes anserinus in the coronal projection. Here it is,

1:01

and as we follow it distally, look at how far down and distal

1:05

it inserts on the tibia. Way lower than the semimembranosus, which in the

1:11

coronal is up here. So let's tackle the semimembranosus. In the sagittal

1:15

projection, it's a large, thick structure, oft underappreciated, as it's

1:21

a posteromedial stabilizer with five expansions sitting immediately behind

1:27

the meniscocapsular reflection. Where is it actually? It's right here.

1:33

It comes from a very large muscle. Riding on the back of that

1:36

muscle is the semitendinosus, which becomes part of the pes. But the semimembranosus

1:42

goes down and inserts along the back of the tibia with,

1:47

to be discussed later on, its five expansions.

1:52

Now let's go to the back of the knee, where we have the

1:55

high takeoff of the gastrocnemius medial head on the medial side,

2:00

co mingling with the capsule, a common site for ganglion pseudocysts to

2:04

occur. And on the lateral side, also a pretty high takeoff of the

2:09

gastrocnemius lateral head, with a small, separate, linear, dark structure

2:14

just deep to it, the origin of the plantaris. This is also another

2:19

common site where ganglia may occur. Now let's take on the popliteus tendon,

2:26

which unlocks the screw home mechanism in the knee. It has a fairly

2:32

circuitous course. Let's go to the popliteus hiatus. In this patient,

2:37

it's identified by a little bit of fluid with the origin footprint of

2:40

the popliteus tendon. And then we can follow the popliteus tendon down,

2:44

and sometimes that is easier to do in the coronal projection.

2:47

So let's do it. We go to the popliteus hiatus, which by the

2:50

way is below the origin of the FCL, or fibular collateral ligament.

2:55

We follow our tendon down. It makes a little curve and then has

2:59

an antero infero medial course as the obliquely oriented popliteus muscle.

3:06

Here is the popliteus tendon in the sagittal projection. We'll see later

3:11

on it has important attachments to the tibia and fibula. The biceps femoris

3:18

comes from a large muscle with long and short heads. You can see

3:23

two separate segments of the biceps femoris right here. And it inserts on

3:27

the fibular head as the conjoined tendon along with the fibular collateral

3:32

ligament. Even though conjoined tendon is somewhat of a misnomer, they come

3:36

together to form this fairly broad footprint along the lateral aspect of

3:42

the fibular head. Let's see if we can identify the biceps femoris in

3:46

the sagittal projection. Here it is right here.

3:49

It's got a fairly posterior position. There's a little bit of signal inside

3:54

it. That's not pathologic, probably from just simply wear and tear.

3:58

But you see the relatively broad footprint of the biceps femoris,

4:02

which merges imperceptibly with some fibers of the fibular collateral ligament.

4:08

Now let's go to the front where we've got the quadriceps tendon,

4:12

which is somewhat striated. Let's look at it sagittally. It's striated because

4:17

it's made up of four structures, the rectus femoris, the vastus intermedius,

4:24

the vastus lateralis, and the vastus medialis. So sometimes you'll see a

4:27

little bit of fat inside it. It oft has a little bit of

4:31

linear streaky fluid inside it. And you may see a little bit of

4:36

hyperintensity around it. It then continues on as the prepatellar plate.

4:42

Here's your plate. An oft overlooked structure that may get injured when

4:46

you fall. And then continues on as the patellar tendon, inserting on the

4:50

tibial tubercle. And as we go down, here's our patellar tendon with an

4:54

oval shape, convex anterior, concave posterior, connected to

5:00

the inferomedial parapatellar retinaculum and the inferolateral parapatellar

5:07

retinaculum. Let's look at these structures in the coronal projection. Here's

5:10

the quadriceps with its striated appearance above the patella. And here

5:15

is the patellar tendon, the plate hard to see because we're tangent or

5:19

on foss to this structure. And then a couple of less important structures

5:24

down lower. The tibialis anterior and the peroneus, which are going to insert

5:29

on the tibia. And that concludes our discussion of the major tendons of

5:36

the knee.