0:00

The last layer that we're gonna look at is gonna be the

0:03

extra synovial fat.

0:05

There are three areas of fat that we wanna look at.

0:09

The large HFA fat pad, the triangular, pre femoral,

0:14

uh, supra, patellar fat pad,

0:16

and the pre, uh, femoral fat pad.

0:19

And those are the three areas.

0:22

They're all designed to cushion the articular surfaces.

0:26

Interestingly, they release synovial fluid during motion

0:30

and are thought to improve, uh, homeostasis.

0:33

So they have mechanical as well as endocrine, um, uh,

0:38

and nutritional, uh, effects within the joint.

0:41

Now the pathologies we see here are not that common,

0:45

and they really fall into just a couple of categories.

0:48

Uh, before I get into that, just, uh, outline

0:51

of their anatomy again, uh, the, uh, fat pads.

0:56

Uh, the one that we are gonna see fluid

0:58

inside the most is gonna be the PHA fat pad.

1:01

And it has two clefts within it, a vertical cleft superiorly

1:06

and a horizontal cleft inferiorly.

1:09

These are normal, and you don't want to confuse those

1:12

with areas of synovitis

1:14

or of, uh, tearing, uh, of the, uh, the fat pad.

1:18

Those are just the normal, uh, clefts within that area.

1:21

This is a tear. Uh, this patient has a torn patella tendon,

1:25

and as the patella went up, you can see

1:27

that the hoffa fat pad is also torn.

1:30

The joint fluid is leaking.

1:32

We don't have any effusion in the joint,

1:34

and everything is presenting anterior, uh, to the knee,

1:38

and it looks like a pre patella arm bursitis.

1:40

But when you look at it carefully,

1:42

the fluid is actually derived, uh, from the articulation.

1:46

Now, it's rare to see these full thickness fat pads,

1:49

like I'm showing you, but partial tearing is very common

1:53

after patellar dislocation.

1:55

And, uh, it is managed conservatively.

1:58

I have never seen anybody go in

1:59

and repair one of these fat pads, uh,

2:02

but just be aware that it does occur.

2:05

Now, in terms of inflammation, there is this disease known

2:09

as PHAs disease.

2:11

It's rather nebulous.

2:13

Uh, and, uh, it's not really clear what causes this.

2:16

Uh, hoffa's disease is an idiopathic synovitis

2:21

of the joint, but the more important feature,

2:24

rather than the snow bium is the infiltration

2:26

and edema that we see in Hoffa's fat pad.

2:30

And it can be very, very painful.

2:32

And I, you know, I, I describe this

2:35

and normally we don't see the cause for it.

2:37

It's generally idiopathic.

2:39

Some of the things to consider are in patients who have aids

2:43

that are being treated with heart therapy.

2:46

The lipoatrophy can be associated with this finding.

2:50

I've seen this in graft versus host disease.

2:53

For some reason that seems to like the front of the knee

2:57

as well as the soft

2:58

Tissues. Posteriorly

2:59

you can consider infection,

3:02

though, that's uncommon.

3:04

Uh, and, uh, trauma as, uh, as I showed you earlier,

3:08

this is a two different patients, uh, with, uh, aids,

3:13

uh, who were on treatment showing you this emus, uh,

3:18

reaction to the antiretrovirals and the fat pad.

3:21

The patient on the right also had, uh, osteonecrosis,

3:25

and we wrote this up many years ago,

3:27

but at that point, weren't aware of, uh,

3:30

lipoatrophy associated with these drugs.

3:33

Uh, now we know that this is likely related to HIV,

3:37

uh, lipo atrophy.

3:40

Now, the other thing you want

3:42

to think about when this focal is fat pad impingement.

3:46

So focal edema, this is common,

3:48

but it's not like the hoffa's disease I just showed you.

3:52

Here. We have edema that is limited

3:55

to the sup lateral fat pad.

3:57

And this is generally going to be seen in patients

4:01

who have some sort of patellar tracking dysfunction.

4:04

And in a nice paper by Christine, many years ago,

4:07

they looked at a number of patients

4:09

who had this focal pattern of fat pad edema,

4:13

and noted that the vast majority

4:16

of them had some underlying tracking dysfunction.

4:19

So I always look at this area when I'm looking

4:22

for patellar tracking disorders to look for this edema.

4:26

A couple of other entities that you're going

4:28

to see in the fat pads, but less common.

4:31

This is focal nodular fibrosis.

4:34

Uh, it has a similar appearance

4:36

to pigmented nodular synovitis,

4:39

which is the diffuse form that can involve the entire joint.

4:43

When you have the focal form, it's often more nodular

4:47

and it can be seen in a number of locations around the knee,

4:51

the most common of which is at the edge of the fat pad.

4:55

But it can also occur in the, uh, SAP patella pouch,

4:59

often intimate with the pre femoral fat pad

5:02

or in the intracon or notch,

5:04

or really anywhere, uh, within the joint.

5:07

So it's histologically very similar to PBNS,

5:10

but much less aggressive.

5:12

And a has a lower recurrence rate following, uh, excision,

5:17

uh, the interarticular disorders.

5:19

Unfortunately, I'm not going to have any time, uh,

5:22

during this, uh, presentation to discuss any of those,

5:25

but they will be covered in the rest of the lecture.

5:29

So that's the layered approach that I like to use

5:32

for anterior uh, knee pain.