What Do Numbness And Tingling Sensation In The Left Arm Indicate?

I had a 2 level fusion in my neck 5 months ago. Before the surgery I had lost the use of my left arm and hand. I had severe muscle atrophy in my forearm and bicep. I still have numbness and tingling in my arm and hand. I also have pain at times like the tissue is being stripped out of my arm. A very painful pulling sensation. However I have slowly regained my strength since surgery, This past week I am experiencing frequent muscle spasams in my bicep. Any idea why? Thanks