I Have Had A 2 Level Fusion L4-L5, L5-L6 I

I have had a 2 level fusion L4-L5, L5-L6 I have also had one in thoracic and a neauro simulator in my back for left leg pain. I have since had SI joint problems I do walk with a cane.
Doctor has suggested having an ablation on my L4-L5 and the joint of the SI. I would like to know what to expect and if everything will be numb? How far down my leg.