What Causes Numbness In My Arm Along With Tightness In Shoulder?

I had a spinal fusion C5-C7 back in June 2010. I'm having problems now with my thumb and arm going numb. I've also noticed that my muscle in my upper arm and shoulder stays tight and won't let down. I've been to a neurologist and had MRI's, he just puts me off as though I'm full of it. All I want to know is what this is and how to fix the problem. I can't even trust my hand to hold anything without it falling.