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<v ->Let's talk a bit about synovial cysts

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and kind of compare them to ganglion cysts.

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So the classic definition of a synovial cyst

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is a juxta-articular fluid-filled lesion

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lined by synovial cells.

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People have argued through the years, why do they develop?

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But the general philosophy is

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that you develop a synovial cyst

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because there's something in the joint

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that is elevating intraarticular pressure.

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So you can imagine if you're gonna treat a synovial cyst

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you might have to consider treating what's in the joint

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rather than treating what's in the cyst itself.

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So if you think of elevated interarticular pressure

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there are three ways that I think of immediately

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how you can decrease the pressure, all right?

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One of them would be to communicate with or enlarge

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an opening with a surrounding synovial sac .

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That would be a synovial cyst.

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Another would be to drive the fluid

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through the cartilage subchondral bone plate

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and subjacent bone creating enlarging

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intracia cyst within the bone

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and the third and something we saw in rheumatoid arthritis

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were sinus tracts that would develop from the diseased joint

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and lead to the skin surface.

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All three of these could decompress the joint.

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Look at this one. This is from an old article.

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I was about three years old when I wrote this one.

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And basically it shows you a dispopliteal cyst

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which eventually created a sinus tract

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at the level of the ankle joint.

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The classic place we find a synovial cyst you all know,

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is the posterior aspect of the knee.

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The most common cause of a popliteal cyst,

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that's in this region.

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A small one is an internal derangement.

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The most common cause of a large popliteal cyst

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is synovitus particularly rheumatoid arthritis.

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But did you ever think of how complicated the pathway

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that allows the joint fluid to leave the joint

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and to reach this versa between the gastrocnemius

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and the semimembranosus?

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I did. I thought about how complicated the pathway,

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so I provide you with this sagittal section.

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So here is the joint lumen, the posterior recess,

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and you go here to an area that is a ball valve mechanism

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allowing fluid to move in only one direction

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from inside out.

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So the fluid then enters a second space,

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so it's gone from the recess number one

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to the second space labeled number two.

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This is beneath the gastrocnemius medial head

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of the gastrocnemius muscle

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so it is the sub gasstrocnemius bursa

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and then it makes a major turn.

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It ends up in a bursa between the gastrocnemius

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and seminmembranosus muscles and tendons.

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So that's the course that it has to take.

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Now, many of you may not think of this then as three spaces,

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one, the joint space, two the sub gastrocnemius bursa,

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three the gastrocnemius semimemosus bursa

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but you may want to think about it because you see,

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the pattern of fluid distribution varies.

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And I'll show it with this particular case.

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So if you go ahead and look at

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we can see fluid here within the joint.

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This is the second space,

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the sub gastrocnemius space okay.

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You can see that here.

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And when fluid extends in that space,

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more often than not it extends in a transverse direction.

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It can turn vertically.

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We can see that here,

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but look at the transverse direction of the fluid.

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And it goes all the way over to the region

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of the popliteal vessels.

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So you could imagine that such fluid in space two

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might irritate those popliteal vessels

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and there are descriptions of pathology

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with none of those vessels related

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to the sub gastrocnemius component of a popliteal cyst.

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Then it makes the turn into the bursa,

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that I talked about earlier,

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and there, it goes more often in a vertical direction.

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So there are various locations of fluid

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that are associated with your classic popliteal cyst

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Here, for example, is another phenomenon we see

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that when you're dealing with filling of that

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semimembranosus, gastrocnemius bursa,

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the fluid may not stay in soft tissues

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it may stay in or extend into bone.

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There's probably no added clinical meaning when this occurs.

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There are two muscles that are involved.

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The ones that you would expect,

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the medial head of the gastrocnemius,

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muscle shown in this particular case.

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And in this case, the other muscle,

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the semimembranosus muscle, the fluid extending

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into that muscle as well associated with a popliteal cyst.

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Now I've had an interest for some time

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about these cysts that develop about the knee.

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And there's another one that I've seen rather frequently

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that I want to call your attention to.

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It's shown here in one of a few cases that I've seen.

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We're looking at midline saggatal sections.

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So this is escape of fluid, not in the area

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of a popliteal cyst, but through the posterior capsule

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here in a more central location, complex fluid.

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Now the reason it probably extends through that part

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of the capsule is that we arteries entering

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and veins exiting that region of the capsule

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as well as nerves supplying the capsule.

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And because of that, there is a weak area

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presumably within the posterior capsule that can allow

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fluid like this to escape.

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But there is another theory that says,

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this is not escaping through defects in the capsule

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it's escaping through nerves or vessels.

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And in some of the articles, and by the way,

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if you ever wanna read about intraneural ganglion cysts

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this is the name that you wanna Google, Spinner.

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He's written so many articles on this subject

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but he's also included intravascular ganglion cysts.

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And I, it belief that cysts like this probably relate to

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the vessels that are supplying the capsule

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and the knee joint that the ganglion cysts develop in them

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and escape through larger vessels

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such as the middle genicular artery.

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That is one of the theories that he has.

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Here's another one, kind of interesting.

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On the fluid sensitive sequence,

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we see this, it kind of looks like a ganglion cyst

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or synovial cyst.

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We did an arthogram and the contrast leaks

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from the knee joint proving it's communicating this cyst

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with the knee joint and you'll note

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that it extends around the popliteal vessels.

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And indeed there are cases of cystic musinous degeneration

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of popliteal artery and popliteal vein related to ganglion

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and synovial cysts that look just like this.