I got this article on Wikipedia, and I still don't know what thoracic outlet syndrome is. https://en.m.wikipedia.org/wiki/Thoracic_outlet_syndrome My wife had a rib excised because of it several years ago. It's basically when blood vessels or nerves get pinched funny...in my wife's case between a rib and another bone (I don't remember all of the details at this point). In her case, she had tingling in her arm, and pain in her funny bone and back area. She was actually dealing with it, not thinking much of it, but a neurologist she goes to for another condition noticed muscle loss in her left hand, and it eventually was traced back to this. Once she had the rib excised, she's had no problems.