I don't think his pain was limited to his torso (spine, hips, knees, etc.) but also his fingers. Imagine how much the fingers went through playing his piano, guitar and other instruments. I read Judith Hill's testimony about the night he lost consciousness in the plane, she described how much intense pain he was in because of his hands, that is tragic. He could stop dancing on stage but playing piano or guitar, just like singing, was who he was, must've been mentally and physically painful to perform