"...fighting for his life..."
Huh?
Ankle = life?
For a horse, movement is life. Yes, it's life threatening if they can't repair it enough for him to walk.
Thoroughbreds cannot recuperate well from a leg break. They will smash the casts or, if anesthetized, will not do well when forced to lay down (bad for their internal organs). All in all, it would be unusal for this great horse champion to make it through this. I hope he does...