Just a thought, why don't we go back in the horses training and see what is broken. Everyone seems to want to look for a mechanical fix to the situation. I do not want to take anything away from the person that trained this horse, but something in the foundation is lacking.
I have been training for years, and to blame the horse is human nature. We all have time constraints, "Git her done" but that usually comes back and bites us on the ass. This is an example and I am very sorry you got hurt.
What if we go back and look at the basic training, something there is slightly out. Maybe the horse got the idea was not pushed hard enough to make it go pop so we could fix it. When we train we need to push our horses to find out what sets them off. This does not need to be mean or nasty, it is more about setting them up so we can correct.
Years ago I had a mustang gelding I was training, he was a huge brute that was well trained. What he was was a ticking time bomb. So long as he wanted to do what you wanted to do he was a great horse. The instant he got bored, he headed home and there was nothing anyone could do.
Gor three days I rode this horse in a corral, doing the exact oppisite of what it wanted to do. If it wanted to walk we went to the trott, or lope. It wanted to go left we went right. You get the idea.
At the end of the three days this big old boy lost it, it5 was the explosion from hell. He reared, took off on his back feet and I was not sure if he was going all the way. When he decided to come back down, he was the nicest boy you could want. To this day those folk still think I created some miracle. All I did was piss their horse off and showed him that I was still there. Soon as he realized I was not going away he stopped all the attitude.