Specifically, on Thursday & Friday, Stu was in the hospital for pain (and other symptoms that I don't want to detail). For a while the doctors were baffled, but we think the source of the pain was found in the final procedure done.
The likely source: scarring from kidney stones... which Stu last had over 15 years ago.
Stu has passed kidney stones twice in his life. The first time, I took him to a shitty hospital (which later closed) and his stone was never captured & analyzed. The second time, we went to a better hospital, and the stone was caught, analyzed, and with the help of the book No More Kidney Stones, Stu has never had a problem with kidney stones since.
It seems the scar tissue from the old injury to the ureter (the tube from the kidney to the bladder... where most of the pain in "passing" the stones comes from, I believe) can grow over time and cause similar pain as kidney stones themselves.
The treatment was a stent in the ureter, and it seems to have done the trick (that said, it's not even been 24 hours, and the stent comes out on Monday).
Anyway, this is just a warning to my friends who have had kidney stones -- even if you're not getting stones any more due to dietary changes, you can still have trouble from them years later. Just be aware.