Welcome

I had back surgery in Jan 07 but wasnt a fusion, I was out of action for about eight months.
I didnt have fusion, my lowest disc had burst through my spine and was crushing the ciatic<<spelling nerve. I couldnt walk for longer than 50m at a time and I didnt sleep for longer than an hour at a time

I hit the pools every day after my operation (had to wait six weeks) walking and swimming. I think this helped alot, also beach walking is excelent for lower back.
You will get back in the water and dont give up on shortboarding, just focus on what you want and you will get there. I did, Im not as flexible and I dont go out in surf that Im not comfortable in.
Hope that help