Yes, the lidocaine shot is definitely a diagnostic tool. It can also be done on the SI joint. In fact, my surgeon performed this same procedure on me to verify that dermatome pain I was having was in fact SI instead of coming from a nerve root in my l-spine. My results were immediate and led to my SI joint fusion 3 months later. As an aside, I'm also fused from L4-S1 and have degenerative changes of varying degrees caused by my disease from T12-L5.

Ablation of the SI joint has a good success rate. It's relatively easy for the specialist to hit the correct nerve that causes the majority of SI joint pain. When compared to the tight quarters of lumbar and sacral spine ablation, as far as I understand it.

I've seen a few friends undergo the SI joint ablation, one a medical doctor. Relief seems to last a minimum of a year and up to three or four years anecdotally. I don't know what the actual statistics are but I would be they are easy to find.

Maybe something to discuss with your doctor?

One last thing, don't let yourself get locked in with one surgeon without getting at least one other opinion. Backs are tough and as my ortho surgeon once told me after a nerve conduction study came back negative, "nerves are weird." My left leg was numb on the L5 and S1 dermatomes, I had a pronounced foot drop and leg drag and was no longer able to drive or even walk much past the mailbox. My nerve roots were absolutely covered in scar tissue and adhered to various tissues: disk, bone, ligaments. I had major nerve root compression for over a decade. I was a mess but the MRIs weren't picking up the extent to which my back was damaged. Took 17 more years to get diagnosed with my autoimmune condition. Two years ago.

All this explanation to say that I've been where you are. Don't give up and don't settle for vague answers.

I'm happy to help if you have more questions. I'll answer as best as I can or point you in a direction where you can find more answers.