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<v ->Now the question does arise,

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how do you tell the a part

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osteonecrosis and insufficiency fractures?

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And the reason this becomes important will become obvious

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if we go back and we review some of the information

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that has appeared with showing the difficulty

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of differentiating osteoarthritis

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from subchondral insufficiency fractures.

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This is a very important article again

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by Yamamoto and Peter Bullough

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from the Hospital for Special Surgery in New York.

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It was published in 1999, it was a retrospective review

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of over 450 surgically removed femoral heads

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with subchondral collapse in elderly persons.

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And if, when they reviewed it

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they realized that in about 10 of those femoral heads,

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they had originally diagnosed this

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as osteonecrosis of the femoral head.

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But later on, indeed, they changed the diagnosis

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to an insufficiency fracture.

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So it can be difficult not only by imaging

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but even by histology to distinguish

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between osteonecrosis of the femoral head

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and an insufficiency fracture.

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What's been pointed out is the morphology

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of the insufficiency fractures

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that involve the femoral head.

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Three types have been identified in a couple of articles,

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one of which has been cited here.

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The first is a parallel arrangement, okay,

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of an insufficiency fracture.

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And you can see it here separated

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from the subchondral bone plate

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by a small area of normal fat.

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The second suggested the convex appearance

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of the insufficiency fracture with the convex appearance

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pointing toward the center of the femoral head.

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And that's shown here in this particular drawing.

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And the third was described as serpiginous,

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kind of an undulating appearance

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to the insufficiency fracture.

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This is an example showing that.

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Well we have not found

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this particular morphologic classification very useful.

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When we look at our insufficiency fractures

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we can see characteristic of,

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the more of than one type here.

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We see linear and more globular appearance

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of an insufficiency fracture.

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But the location of insufficiency factors may help you.

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The vast majority of insufficiency fractures

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that involve the femoral head involve two areas.

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They involve the anterior aspect of the femoral head

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or what is designated the anteromedial aspect

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of the femoral head.

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So when you see things more posteriorly,

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the likelihood of an insufficiency fracture becomes less.

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Here's an example taken from this article showing you

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the anteromedial pattern of insufficiency fracture

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in the femoral head.

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Now, this I think is a very important slide.

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This is a slide that is taken from a scientific exhibit

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from a group from Belgium in, at the RSNA in 2016.

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And what they tried to decide are

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what are the characteristics of an insufficiency fracture,

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for example, in the femoral head

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and the crescent sign of osteonecrosis.

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And what they found is that the classic location

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of an insufficiency fracture is below

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the subchondral bone plate.

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It later on may merge with the subchondral bone plate

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but it does not occur within the subchondral bone plate,

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so here's a beautiful example of that.

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And what they found with regard to the crescent sign

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is the fractures occur within

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the subchondral bone plate or,

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and that's shown here, or they occur below it.

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So when you see fractures extending

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up into the subchondral bone plate

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and then into the cartilage, as I talked about before,

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it is far more likely you're dealing with osteonecrosis

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than with an insufficiency fracture.

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But by no means is it an easy differential diagnosis.