Elaine
Back surgery was done on my brother-in-law when he was 14. To this day, he cannot move certain ways. But the surgery was done ages ago and maybe back surgery today has come further, allowing better movement. If they use the steel spike in the back, he won't have too much bending movement for the flips. I would consult with the specialist and ask what they use today. If he is wearing a brace now, that usually helps straighten things out nicely without surgery. My husband wore the brace for 3 years and his back is very straight now. If it were my child and he is that active in sports and needs the flexibility of the swimming flips, I would not restrict him with the surgery. You have to spend 10 months or more in a body cast, so that wouldn't be fun for him at all. Hope this helps. Keep wearing the brace! :>)