How can thyroid surgery affect vocal production?

I had my thyroid removed due to a cancerous tumor. I'm a singer and was also a speaker through my job. I have noticed my singing range has been diminished, in particular my higher range. The most troublesome problem is I can no longer sustain a steady tone. I now experience a very unsteady vibrato or tremolo when singing and this situation may keep me from any future performing as I have always done in the past. Rumor has it that not all surgeons are careful to protect
the vocal mechanism when performing the surgery. And I was even sure to tell my surgeon a number of times that I had serious concerns regarding my voice. I have been scoped and polyps have been ruled out as a possible cause. Are there other things that can be done to help improve my situation?