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<v ->Now unfortunately, the talus is a site of stress fracture,

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particularly of the insufficiency type.

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And either end of the talus

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may show you a subchondral insufficiency fracture.

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Here is one involving the talar head.

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And I wanna call your attention

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to the fluid-sensitive sequence,

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the thickening and slight flattening

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of the subchondral bone plate

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typical of subchondral insufficiency fractures.

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And at the other end, here's another example

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of marrow edema of the talus with an insufficiency fracture.

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But it doesn't answer the question, which comes first?

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And again I really feel strongly it's the marrow edema

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that occurs before the insufficiency fracture.

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So let's begin a little bit of a chart

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that I'm going to actually extend further

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in subsequent lectures today.

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I've put some numbers on there.

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I'm gonna read the six things that I've written here.

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Number one,

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radiographically evident juxta-articular osteopenia,

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whether it's transient osteoporosis of the hip

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or regional migratory osteoporosis,

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is accompanied by and likely preceded by marrow edema.

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So I'm showing you that here,

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this link between these two entities.

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Number two, insufficiency fractures are a frequent finding

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in transient osteoporosis of the hip,

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transient marrow edema,

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but it is not clear if the fracture causes or results

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from the edema and osteopenia.

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I believe it occurs after the edema and osteopenia.

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Number three, all right, number three, you can see

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insufficiency fractures are infrequent

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in regional migratory osteoporosis or marrow edema.

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Number four, shown here, based on the architecture

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of the subchondral bone,

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marrow edema leads to elevated marrow pressure.

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Number five, which you can see here and here,

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elevated marrow pressure may lead

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to vascular abnormalities with subsequent ischemia,

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osteonecrosis, and bone collapse.

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And number six, which I'm not gonna answer yet,

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I'll answer later.

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What is the stimulus for this cascade of events

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that may progress to osteopenia, marrow edema, and ischemia?