My sister broke her back years ago and never got it healed properly, she is still dealing with insane pain and doesn't take the steps *I* would take to fix it.
My brother broke his back twice while serving in Iraq, he deals with insane pain from that and loss of feeling from the waist down on occassion. Again, he doesn't push as hard as I would to get it fixed.
My husband had knee surgery and was back to playing softball 4 weeks later - no shock that he sat out most of that season and this last season as well.
You can't force people to get the help *you* think they need. He's likely dealt with this his whole life and you can't change his mindset on his pain.
Aside from you offering to give him back rubs, suggesting a doctor, and just being there for him, there's not much else I can think of.