His bones must have fused together, thats the only way his back is still getting fukked up.
I had back problems a few years back and blew out my back 3x. Went to see a surgeon and he told me surgery for your back is really only to help your legs (sciatic nerve). Theres 3 stages of subluxation (misalignment of your vertebrae). The 1st stage is just minor pain and swelling. The 2nd (which is what I had) is really painful and your bones are beginning to fuse together. Theres supposed to be even spacing between each vertebrae but the back problems cause the spacing to condense and puts a ton of pressure on your lower back. When mine was bad I was basically paralyzed. Literally couldn't stand up or support any weight. Stage 2 is treatable. I went to a chiropractor for two years and he fixed my issue. Haven't had a blown back in 4 years now.
The last stage, and where I'm guessing Tiger is at, is stage 3. Its where your vertebrae has been fukked up for so long that your bones literally fuse together. You lose the proper spacing between each one and that creates swelling, sciatic pain in your legs, and basically makes you a cripple for the rest of your life. Its not fixable through surgery so if you've hit stage 3, your sports career is done and your real life is gonna be tough.