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So let's begin our discussion

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of articular cartilage going over a little bit of

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its anatomy with a histologic slide on your left

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and my drawing somewhat three dimensional on your right.

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You can see here the noncalcified articular

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cartilage in light blue.

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Here are the various cellular rows.

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We'll be talking more about them a little bit

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later as we proceed.

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Down to the bottom of the noncalcified cartilage,

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we find a histologic landmark known

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as the tide mark shown here,

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which separates the noncalcified cartilage from the

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calcified cartilage.

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Below that, there is a layer of compact bone shown

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by the gray in my drawing, and below that shown here.

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And here we have the subcon bone.

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Now to that particular diagram,

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I'm now adding some additional features

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and these are the collagen bundles.

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At the surface, we can see parallel layers of collagen.

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This is the lamina Splendas.

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It's right at the surface of the articular cartilage.

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And below that, we can see these arcades described years

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ago by benninghoff.

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They extend down in a curve linear fashion

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through the tide mark into the calcified cartilage,

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anchoring the cartilage to the subcon bone, compact bone,

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and the SubCal bone.

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Now I wanna make an important point.

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This is the layer of compact bone right here.

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It's a thin layer.

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Indeed, there are two types of compact bone

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that we see in the skeleton.

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The first of these is properly called cortex.

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Here you can see a yellow arrow pointing to the cortex

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in the proximal radius.

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Cortex, by definition, is compact bone formed

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by the periosteal membrane.

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The process of fancy one intramembranous bone formation.

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The second pattern of compact bone occurs at the

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end of the bone.

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This is compact bone formed by articular cartilage.

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This is not cortex.

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When you see a white line on a conventional radiograph on a

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ct, when you see a low single intensity line on MR at

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the end of a bone, that is not cortex.

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The proper term for that is a subcon bone plate,

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and you're gonna hear that term a lot

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during this particular lecture.

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Now let's look at electron microscopy showing you those

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layers of collagen.

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At the top, the lamins splendid,

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and here we see the arcades of bending off, extending down,

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becoming almost vertical in the lower portion

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of the articular cartilage.