Subperiosteal Cysts in Shoulder

[David Smith]

Stephen mentions imaging the RC tendon enthesis and checking for subperiosteal cysts. Steve, can you describe a bit more what that looks like on US and maybe include a few images? Thanks.

[Stephen Bird]

Hi David,

Absolutely,

When I teach someone to scan the supraspinatus tendon I ask them to look at the enthesis first with their eyes and the tendon second. Most SST tears are enthesis based and when the collagen is pulled from the enthesis it disturbs the bony architecture. Remember the bony architecture of the enthesis is not like regular bone, it consists of collagen in the tendon transitioning to unossified fibrocartilage then transitioning into calcified fibrocartilage, then transitioning to cortical bone. The echogenic line we see as the bone causing an acoustic shadow is actually the ossified fibrocartilage, not cortical bone. The tearing of the SST virtually always destroys the calcified fibrocartilage and often causes damage to the underlying cortical bone and hence it produced sub-periosteal cysts which we see on plain radiographs and ultrasound. The correlation between the presence of these bony changes and a tendon tear is very high. So if someone is measuring a black area in a tendon and the underlying enthesis is beautiful and normal I suspect they are doing what I call MSU (making shit up) (please excuse my phrase).
Check out the images below,

Steve

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[Stephen Bird]

You can see on the images that the enthesis when normal has bright collagen turning into almost anechoic unossified fibrocartilage, then smooth bony looking calcified fibrocartilage.
In the abnormal ones you can see the bony irrecularity and the way the ultrasound seems to get into the bone. This is due to the destruction of the enthesis. Once you see this if you look at the adjacent tendon it is going to be abnormal!

Steve

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