A friend of mine broke my arm in high school. Both bones snapped in half, and the muscles and tendons then pulled the upper portion down towards my elbow. (think snapping a pencil in half and then putting the two pieces side by side)
The break itself was loud and somewhat disturbing, but didn't really hurt. Just ached pretty bad, and swelled up with fluid to a pretty grotesque proportion.
At the hospital (where I sat in the waiting room for 6 hours) the doctor gave me 13 anesthetic shots up and down my arm in an effort to dull what he said would be "a possibly significant" amount of pain during the resetting process. Apparently the extended period of time between the breakage and resetting process had caused both the muscles and tendons to "contract and become lazy", and everything would need a great deal of coaxing and stretching before the bones could be pulled out to the point where they could be snapped back together.
A nurse wheeled a metal rack into the room with a medieval looking wire glove attached to it, strapped my hand into it, and without giving a warning so I could attempt to steel myself, both she and the doctor proceeded to yank, pull, tug, push, crank, (and other cruel verbs as well) my arm downwards for the next 20 minutes of testicle imploding, soul shattering agony.
There's really no way to know exactly how much the anesthesia helped, but assuming that it did and based upon how much pain I felt anyway, I'm pretty sure that without it I would have died.