I started to get the Synvasic shots just after my RNY, 4 years ago. The surgeon told me that if they don't work he would give me the steroid. Because I have lymphedma, the Synvasic shot caused a reaction, so I went over to the steroids. I must admit the first year ( a shot in each knee every 3 months) I didn't feel there was that much relief, and then I noticed there was as I started taking Aleve, along with other pain relievers, but it was the shot that was helping. I now have to get the shots every 2 months to have the best relief. I also started taking Celebrex and have also started back on losing more weight. Because of my lymphedma I can only get one knee done at a time. I am also getting steroid shots in my heel for a spur that starting acting up.
Good luck, I know how painful siatica can be. I really hope the shots work for you.