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<v ->We turn our attention next to

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digital osteoarthrosis or digital osteoarthritis.

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Clearly recognize this

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it involves the interphalangeal joints.

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The only abnormality that you will see

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typically at a metacarpal phalangeal joint

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in ordinary osteoarthrosis is joint space narrowing.

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Here I'm showing you inflammatory OA

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but you can see a bit of joint space narrowing.

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So right away, you see our radiographic rules.

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If you have radiographs that show erosions

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of the metacarpal phalangeal joints, it's not OA.

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If you have radiographs that show large osteophytes

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of the metacarpal phalangeal joints, it's not OA.

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The only finding we see there is joint space loss.

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Now in ordinary osteoarthrosis we see two findings,

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joint space narrowing and marginal osteophytes.

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But the remarkable thing about ordinary OA in the digits

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is the interdigitation of one bone with its neighbor.

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They fit together like the pieces of a puzzle.

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All right.

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And so be aware of that finding.

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Now inflammatory osteoarthritis,

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and some people as we've heard call it erosive OA,

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is painted on a background of ordinary osteoarthrosis.

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So you can see joints

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that look like ordinary OA,

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and now we come across a joint

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that looks a little bit more aggressive.

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You can see here the degree of collapse centrally

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is more prominent and this joint too may be involved.

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In inflammatory OA it is not marginal erosions you see.

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What you see is central collapse, it's mechanical in nature.

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It's the pressure of one bone against the other

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leading to depression of the subchondral bone plate.

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One final point as I look at this,

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in rheumatoid arthritis there is dorsal volar subluxations,

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like boutonniere and swan neck.

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In OA, it is radial ulnar deviations.

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So you can see how you get horizontal plane deviations,

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that's a difference from rheumatoid arthritis.

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And now we come to the part we kind of mentioned before,

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what do you do when a patient

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with ordinary OA comes in with inflammation?

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Well, you know, the typical patient with ordinary OA

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of the fingers is a woman middle-aged or elderly

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not much pain, but palpable bumps.

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Those are Heberden's nodes, Bouchard's nodes.

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And often, as they say no pain,

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but then they come back and they have pain.

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And your differential diagnosis

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is inflammatory osteoarthritis one.

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But in addition, I wanna remind you

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you can indeed have secondary crystal deposition

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in these joints.

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Calcium pyrophosphate, basic calcium phosphate,

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rarely calcium oxalate and also uncommonly

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but certainly reported. secondary gout

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involving these joints.

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And here's an example,

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I don't have too many to show you so not beautiful image,

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but this is now urate involvement of a joint

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that was involved in digital OA.