If you look at my signature, you'll see that I had a displaced tailbone (coccyx) which was found w/ a simple xray of the coccyx area.
I had coccygeal manipulations done twice, along w/ caudal steroid injections which helped w/ the sitting length tremendously. Unfortunately, I have other problems, too ... so I'm still going to docs. If it were only the tailbone, I feel pretty certain I would have my life back by now!
Good luck...and if you have any other questions, please let me know!