I'm so sorry...
I guess that they did check the rest of your spine and sacrum, too?
I'm really reaching here, but maybe an orthopedic doctor might have an idea? A new angle to consider?

Winter- I'm dreading it, too. Maybe the el nino snow will be pretty to see out the window, at least. (Now, that last comment was really stretching the limits of believe-ability. ha!)

It's discouraging when the docs admit they don't know, isn't it? In addition to my arm/hand issue, the left side of my face, tongue and eyelids get numb, and they (neurologist and ear, nose and throat doc) don't know why. ENT guesses that it's from my autoimmune disease. I'm fortunate that it isn't painful yet, just annoying and really strange and unsettling mentally. You truly have my sympathy!
I hope that some of the other folks here have some good ideas for you.
Have you seen "Inspiring Quotes" and "Just for a Laugh" (or similar names) sections here on Mayo? They help me a lot.