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<v ->Now another finding that we see

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in osteoarthrosis or subchondral cysts,

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these dominate in the joints of the lower extremity,

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and they occur in the stress part of the joint.

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So when we think about hip osteoarthrosis,

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the most common characteristic

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is cartilage loss, superiorly.

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This is the stress portion.

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So cystic lesions and bone sclerosis dominate here

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not along this aspect of the joint.

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The theory about why these cysts occur,

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there are several theories, but in most cases

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the cysts communicate with the joint

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as shown here in some pictures

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taken from a scientific exhibit of the RSNA.

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And so it may be the elevated pressure within the joint

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driven through the cartilage abnormality

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reaching the subchondral bone

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creating these cystic lesions.

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I have seen the greatest cysts in certain locations

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including the proximal femur,

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and as I show you here, the proximal humerus.

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Exactly why the cystic lesions accompanying joint disease

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of the glenohumeral joint can extend far

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down the humerus is not clear.

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But I think it's likely related

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to very little resistance produced

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by the few trabeculae that exists in the central portion

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of the humeral neck and proximal shaft.

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So we do see, and we have seen cases

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of extreme cysts formation involving the proximal humerus

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in patients who have OA.

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When we have cysts...

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Lemme just one, excuse me.

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(nose blowing)

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When we have cysts, we may have gas originating

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in the joint that extends into the cysts.

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Here's an example of what we would see

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with degenerative involving the intervertebral disc

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with gas extension into cysts within the vertebral body.

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But the same phenomenon is seen elsewhere

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particularly when we deal with osteoarthrosis

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of the sacroiliac joint.

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And typically in most cases those cysts called pneumatocyst

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dominate in the illum aspect of the sacroiliac joint.

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They have no added significance

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to the cartilage loss that characterizes osteoarthrosis.