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Infectious arthritis | Muscular-skeletal diseases | NCLEX-RN | Khan Academy

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– [Voiceover] Infectious
arthritis is where you have an infection in the
joint, usually bacterial. And we think of how a joint is
one bone then the other bone, some cartilage in the middle
and with this joint capsule that closes off the space. Usually the synovial
fluid in here is sterile. This is not open to the environment, and it's sterile and clean in there. And an infectious arthritis happens when the bacteria gets in
there and causes an infection, just like it can in the rest of the body. Now, the two bacteria that
are most commonly the culprit for infectious arthritis
are Neisseria gonorrhoeae, gonorrhoeae, that's the first one. And then Staph aureus is the second one.

And I've drawn this knee here because infectious
arthritis usually happens or most commonly happens in the knee. And it's just one knee. It's not systemic, so there's no reason for both sides to be affected. It's usually just in one joint. And this joint that's affected here would be red and swollen and painful, just like having an infection
anywhere in the body. This local inflammation will be there. Now, especially with
Neisseria gonorrhoeae, you might be thinking,
well, that sounds familiar. We talked about Reiter’s syndrome, which is one of the auto-immune
arthritis illnesses. And you're right, gonorrhoeae
is involved in Reiter's in the sense that after a
local infection of gonorrhoeae, Reiter's syndrome can
develop in the joints. But just to point out really quickly, in Reiter's, first of all the
gonorrhoeae infection itself does not have to be local in the joint. It can be in the body in general. Reiter's. And also, we talked about
in an auto-immune disease, the infection is in the blood, the orange dots being the bacteria. And then our body synthesizes these green, I think of like green soldiers
fighting off the infection.

And that's our immune system. And over time, after the original gonorrhoeae infection is gone, there's no more orange crystals
in there, no more bacteria. But the immune system is still present. And the immune system is confused
about what it's attacking. And it starts attacking this joint, which had nothing to do with
gonorrhoeae in the first place. Now, this is a completely
different process, and that's why it's called auto-immune, because our body's own immune system is causing the damage on our own tissue.

But in infectious arthritis it's different because the gonorrhoeae is
one locally in the knee. I'll draw the orange crystals here. It's not elsewhere in the body. And it's an active infection,
meaning it's not been cleared. And the immune system is trying
to get rid of it locally. That's why infectious arthritis is not an auto-immune disease.

It's simply an infection in the body. So aside from the fact that it affects usually one joint at a
time, usually the knee, also if we look at the onset of time, this being the time and this being the symptoms, it's gonna start very abruptly. So as you go along,
suddenly the symptoms begin, as opposed to auto-immune diseases having a waxing and waning,
up and down kind of course. The diagnosis of infectious arthritis should be pretty straightforward. When you're seeing a
swollen, red knee like this, infection should always be
one of the possibilities. And you do a fluid analysis. So you take a needle,
go into the joint space, draw the fluid, and you can
just test it for bacteria.

If it's infectious arthritis, the bacteria will grow from the fluid. But also, a person having
an infection anywhere is gonna have an increased
white blood cell count. This is a sign that the
immune system has responded. And whether you have an
infection in your knee or in your finger or in
your lungs or in your gut, it's gonna drive this up.

So it's not specific, but it tells you that an infection is going on. Now, what we want to prevent
in cases of all infections, including this one, is prevent
it from becoming sepsis. And that's when the
infection becomes systemic. It leaks into the blood. If you have septic arthritis, that's a step up in the severity. So if you have septic arthritis, this person would be very sick overall.

They should have fevers and symptoms that are not limited to just one joint. And in this case when
you do a blood culture, you should be able to
grow bacteria from that. But honestly, we want to try to keep it from becoming septic arthritis because the treatment,
the treatment for this is very simple, actually,
just antibiotics. We know how to deal with infections. And that's why don't want
to miss diagnosing this because the treatment is straightforward. Now, granted, infectious
arthritis is not the only disease where we can have a red,
swollen, and painful joint.

But because of the fact that it can do a lot of permanent damage
and it's easy to treat, we routinely take out
the fluid from the knee just to analyze it. And the fluid content will tell us a lot. And by the way, just to be complete, Staph aureus is a bacteria
that we have on our skin. All of us have it. And it's usually not harmful
on the surface of our skin. But if it gets into a sterile
area, it can cause infection. And Neisseria gonorrhoeae is associated with sexually transmitted infections.

And that's why in terms of
the people who get this, Staph aureus seems to be in older people or in older children, while gonorrhoeae is more
likely in young adults. So infectious arthritis, not auto-immune, but does involve the immune system in the way that every
infection in the body does. And the treatment is antibiotics..

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