Of course prayers are going out. Broken, or crushed, he's looking at around 6-8 weeks healing time. A lot of pain. Even hurts to wiggle your toes!
I'm assuming that he was driving an older car (without airbags)?
Broken - rib is broken in one place (bad)
Crushed - multiple fractures of the same rib (serious)
Flail - multiple adjacent ribs are broken in multiple places, separating a segment, so a part of the chest wall moves independently (really serious).
Biggest complication is infection. Many patients are unable to take a deep breath because it hurts. If you don't breathe deep enough, mucous and moisture can build up in the lungs and lead to an infection such as pneumonia.
Calgon - my friend is a physician (you know - those who make the worst patients!!!). No - he was stopped for a red light, and was driving a 2003 BMW. I don't know all the details, such as whether the front airbags deployed or not since it was a rear-end collision. I hope I never have to find out, but I would have thought the impact of being hit at 45mph would have jolted all the airbags. I honestly have no idea if airbags, if deployed, could have mitigated that great an impact.