I had that done about 10 years ago, just one fusion. It really helped the back problem except then I had problems with my SI joint because the stress was put on to that joint. The doctor told me that I would be good for about 10 years and then the stress on the vertebrae above it would start causing problems and I may have to have another fusion. It's been just about 10 years and my back is starting to give me problems again but for 10 years it was good!
The plus side of it was that the cut they made from one hip to the other hip across the front made my skin numb. When I was in the hospital for covid they kept having to give me shots in my belly so I had them put it in the area where the scar was and there was no pain at all lol! (If you can call that a plus)