My theory is that after about 20,000 cycles (steps running) the rib and cartilidge were weaker due to fatigue and that slight twist was enough to break it. I did not run Monday because it hurt that much and only ran six miles Tuesday. This morning it felt ok again. I think I am a fast healer. I know that when I run a lot mmy body reacts to injuries and muscle tears by recovering very fast. I think that is what is happening to fix my rib. While Sunday and Monday were terribly painful, Tuesday was ok and today has gone well.
It is such an odd injury. Who breaks a rib? There is basically no way to fix it, besides surgery and putting metal plates in me but that is not practical unless I am in danger of internal bleeding. So I live with this constant feeling of what feels like a stick is jabbed in my side. This too shall pass.