I'd give someone else a try.
Get second opinions before going back to the other guy.
Unless he is the best option you have.

But sometimes they can’t do much, other than pain control.
Meds, TENS, injections/blocks etc?
SCS might be something to consider if more surgery is not an option.

I don't know if poor posture can affect fused areas?
Also slouching/slumping might compress the nerves/blood flow as they travel thru the neck/chest junction, and that may cause arm symptoms. (collarbone/brachial plexus)
Internal scar tissue can occur also creating problems.

Have you tried any PT to see if they can help w/pain & symptoms?