As soon as I posted Fred Couples, I recalled Jack Nicholas also has serious, chronic back problems.
Back problems limited Nicholas time in the senior tour to the point he only played the majors in later years (Masters, etc.) where he has a lifetime exemption due to being a past champion of all four. Nicholas has made far more $$$ designing golf courses in his later years.
I remember just a few years ago Couples was leading the Senior PGA Championship in the final round over Bernhard Langer when his back went out and he had to have two people more or less carry him in to the medical tent, ending his tournament!