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.
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.