Frustration

The Mister is experiencing lots of pain recently.
For about 15 years he was a mechanic--lots of bending over cars, twisting the body in uncomfortable positions....
Once he finally stopped being a mechanic, and moved to more of a desk job, it was a big relief for his body.  However, the stress on his body has come back to haunt him.
First it was his right shoulder.  He's right-handed, so most of the tough work was likely done with that arm.  He somehow ended up with a torn labrum a few years ago.  If he hadn't had surgery, his bicep could've detached from his shoulder and fallen like a limp noodle to his elbow (if I'm remembering correctly).
The surgery fixed the tear, but he still experiences pain in his shoulder.
All the bending over lead to lots of back pain in recent years.  Not necessarily a bulged disc, but nerve pain.  The kind of pain that doesn't show up on an MRI because you can't really see nerves...I know, because I had lower back/hip pain for months and my MRI showed nothing wrong with my lower spine.  The worst part is, so many doctors will either throw strong pain meds at the problem and not treat the cause, or they tell you the pain is all in your head.  Sure, it's the "center" of the central nervous system, but until they come up with some way to "shut off" the brain to pain, I don't see any other helpful treatment except to ease the pain.
The whole thing is very hard to see because I can't help him.  His pain threshold is higher than mine, and as a kid growing up with migraines, he was given lots of pain killers--which lead to a high tolerance to those as well.  So most medications that help him would knock an elephant on it's ass.  And those medications are highly addictive.

Why can't they just fix the cause at the source so he doesn't have to worry about the pain anymore!?