Cysts in the joints of your back? Or in the back of your fingers? Sorry.. I didn't understand what you meant? (I guess you would mean between the discs of the spine? I'm not up on my back anatomy).
(I have these weird nodes forming in the backs of my fingers, .. a few of them anyway. I have no idea what they are.. they're small still, but white, just under the surface, and visible enough if my fingers are straight.)
Do they cause you a lot of pain?