I have recently had a triple ankle fusion. I did fine for the 4 days in hospital, When I came out I had constant mini flares.
I think you should prepare for that, a chat with your GP or hospital team.
I am 4 months in and just come out of plaster. The flares are stopping.
It seems that when I have pain in other places, or my body is in shock over surgery, the Fibro joins the party.
Good luck with the surgery. My friend has just had one and she is a new woman ❤️