Here's a good account of a disc replacement with some x rays that show the new discs and pictures of the surgical procedure. My spinal cord looked very similar to this patients(in the initial MRI) with the disc pinching the cord down to a very narrow dimension. I had the same symptoms of electric shocks down my arms.
http://www.spinalneurosurgery.com/CR_aritificial_disc.htm
I've seen x-rays of two level disc replacments in the neck and I think I may have heard of a three level, but never a four level.