Yeah, Chris Duffin posted something about hanging, where he's using it for his elbow (and grip). Ido Portal posted some stuff about hanging; he had some "challenge" where you were supposed to get some number of minutes a day cumulative hanging. And this orthopedist guy wrote this book on it.
I went through the Amazon reviews one night, and out of the people who actually tried his protocol, it looked like there was only one person who didn't have success with it. Everyone else ended up either significantly or completely better, anywhere from 8 days to 8 weeks of doing it. It sounded too good to be true, but I'm giving it a shot. This was for all sorts of shoulder issues too.
You don't necessarily have to hang for all 10 minutes, but yeah, 10 minutes where you're alternately hanging and resting. It's a long time.
When I first started doing it, my body hung pretty unevenly and was fairly twisted. That has pretty much evened itself out now, which I think is kind of cool.
Here's his basic theory though as far as impingement is concerned.
There's two bony bits of the shoulder blade that stick out to the front of the body; the coracoid process and the acromion. There's also a ligament that runs between them. All three create the "coracoacromial arch". Impingement occurs when tendons get pinched between the humerus (upper arm bone) and that arch.
The theory with the hanging is that it puts pressure on the ligament and the acromion, and, over time, actually causes the bone to reshape itself and make that arch bigger. That way there's more room for those tendons and less chance of impingement.
Basically it's like braces... exert enough pressure, over enough time, and the bone will remodel how you want it.
Fluoroscopic imaging is pretty cool: