They said that somehow the blood supply is cut off. I asked if it had anything to do with the accessory nerve thing and he said no. They are going to do a procedure called core decompression where they drill a few holes into the bone in hopes that when it repairs itself it will establish new blood supply to the dying bone. I am at stage 2 AVN which means it does not show up on an x-ray. The MRI clearly shows a density change at the humeral head. (shoulder)
The sooner you have it done the better. Getting old sucks!