You might want to post this in Orthopedics...

But it my opinion, the bone will fuse wherever it is still attached, severely broken or no. If the fracture is breaking the skin, left untreated, I'm sure gangrene would eventually take over and it would have to be amputated. Some hairline fractures can repair themselves if the person takes care not to put any sort of strain upon it until it is healed. It is more likely to successfully repair itself in babies and young children than in adults. Some broken bones, such as bones in the foot, sometimes are left untreated.

http://homeemergency.wordpress.com/2007/06 /28/fractures-broken-bones/

untreated fractures could leave bone marrow exposed and release fat emboli which can cause inter cranial pressure, strokes, different blood clots and ultimately death.

I heard this man in Denver can heal broken bone. He claimed he can heal it in two week. Anyone want to try. I doubt it work but he pretty confidence the magic work. He'll do some chanting, light incenses and dip the incenses into a bowl of water. He then use the water to sprinkle over the area when it broke. He claimed this work. He charge $$$ for it. I am skeptical and much question it. No test has ever be done and he said two week but unlikely- bone in children takes about 4 - 6 weeks and for adult longer. Wish people would test it out and shut him up.