I have terrible back bend flexibility, but good flexibility most other places. I never broke a tailbone, but recently bruised it during a skate fall. My hips have been slightly crooked for many years, I just never did anything about it. As I trained more heavily in dance these last 2 years, I built up uneven muscle tone due to my hips being out of line. This created scar tissue and limited mobility in my lower spine, making it feel "compressed" with every back bend, and making the places between my shoulder blades feel so tight, even slight bends done with good form. I tried to correct my hip problem by counter balancing (as in, my right hip dropped, making my whole body tilt, though my legs are exactly the same length) so I recognized I crossed my legs right over left for years and tried to correct by consciously crossing left over right. Well, now I'm even more twisty lol.
I am currently seeing a Chiropractor because of the pain after the skating injury (the one I hurt my tailbone in.) I am AMAZED at the difference I feel after just two visits. The first day, I got in my car, and almost thought I had gotten in the wrong car because the pedals were like an automatic. Then I realized my whole bottom half had shifted toward correctness, and that I was pushing the clutch, thinking it was the brake, and there was no clutch lol. It really was weird, I mean, you climb in your car, your foot placement is second nature, untill an adjustment. The sciatic nerve pain in my back is decreasing by day, increasing mobility in my lower back. I've been told to avoid muscle and flexibility training and anything with impact until we can get me straightened out as much as possible, and then start building small again to put muscles evenly around my core to keep the alignment. I'm more normal structured than before, but because of that, it FEELS like my right leg is longer than my left now. Something I'll get used to. Doc says I'll be better balanced and better protected in any future falls from such injuries.
The only reason I even know I had the hip problem for a long time is from X-rays done back then, and it was suggested then that I see a Chiro, but I wasn't convinced. Years later, here I am. Have you tried a chiro? I can't WAIT until I heal a bit and get back into training. I can already feel that I finally have an even arabesque on both legs. AMAZING. Good luck!