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<v ->Another question that has come up

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is the relationship of osteonecrosis and marrow edema.

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So let's address that for a minute.

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It is clear that it is often that you will see marrow edema

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sometimes extensive in patients who have osteonecrosis

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whereas in other patients or in other instances,

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here it's the opposite side,

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marrow edema may not be very prominent.

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What is well known is that

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the marrow edema elevates intramedullary pressure.

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So it correlates with pain

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and also with the necrotic volume.

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But the question that is not clear

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is it a precursor to osteonecrosis

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or does it occur after the onset of osteonecrosis?

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And here, for example are two articles

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that argue those two possibilities.

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So when it occurs with relationship

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to osteonecrosis is not clear

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but clearly it can produce pain.

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There is an unusual pattern of osteonecrosis

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that involves the femoral head that I call segmental

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because only one quadrant of the femoral head

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may be involved.

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The best cases of this that I saw were from years ago,

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so the image quality is not very good,

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but here is an area of segmental osteonecrosis,

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and often these were kind of crescent shaped or V-shaped

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when we studied them with CT.

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I think they look a little bit like the infarcts

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you can see within the lung.

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So this is segmental or minimal osteonecrosis

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of the femoral head.

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Here's another example.

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Note, by the way, that although this is not involving

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a lot of the femoral head

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the characteristics of a serpentine like border

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of low signal and entrapped fat

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can be seen within that area.