Sorry, but I was out of the country.
Fatty infiltration of the muscles (“My last MRI showed heavy marbling of FAT INFILTRATION in the cervical muscles”) is normally a sign of disuse or even neurological disconnection (nerve loss). It would be the opposite of recovery.
I suspect your current symptoms are possibly from a lack of fusion of a 4-level ACDF. 4 levels is a lot to have to expect that all levels would fuse. Also, the long lever arm on the lowest level (the open C6-7) could wear this level out prematurely.
Your symptoms are more focal and significant that what I would expect from Fibromyalgia (“The muscles are cramping in the right side of my neck. The pain is so severe that I can stand or sit for only about 15 minutes before I have to rest my head back”).
I would say that a new set of x-rays including flexion/extension are necessary and if any questions, a CT scan of your neck could be in order.
Dr. Corenman