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<v ->And I'm gonna start this

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by discussing briefly septic arthritis.

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There are four basic mechanisms

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by way infections will reach joints.

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So I just wanna kind of summarize those mechanisms for you.

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And I'm gonna use some of my diagrams

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on the right side of these slides.

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The first of these is hematogenous cause

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of septic arthritis.

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And there are two subgroups here that you have to consider.

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The first is that through the bloodstream,

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organisms may be deposited directly

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into the synovial membrane.

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The second is that certain sites, there is in fact,

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vascular continuity between the epiphysis

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and the synovial membrane so that infections

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can first begin in the bone and then extend directly

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by blood flow into the synovial membrane.

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Whether you're dealing with the first or the second

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of these two possibilities, typically the synovium

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is contaminated before the joint fluid.

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So at least classically,

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you could do a joint aspiration that would not be positive,

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and yet the synovium could be contaminated at that stage.

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Now, as I talked about on day one of this course

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that if you're dealing with a synovitis from infection

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as with rheumatoid, the marginal or bare area of the joint

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is often the earliest site of involvement.

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Here's another example of changes in the bone

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in the marginal region not protected

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by articular cartilage.

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And here's a further example

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showing you hematogenous septic arthritis,

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presumably the organisms deposited directly

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within the synovial membrane with a joint effusion,

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all right, marginal erosions, that are very, very large

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and secondary osteomyelitis, which can be seen.

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And when you do have a joint effusion,

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yes, you can have a drooping shoulder,

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but there are many causes of a drooping shoulder

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including deltoid muscle acne.

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Following an injury, if you see a drooping shoulder

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is more likely not an effusion,

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but muscle atrophy involving the deltoid muscle.