In reply to Rigid Raider:
Having "broken my back" a few years ago, i would suggest that it encompasses a few different fractures, some more serious than others.
A friend bust one of the processes on a vertebra, the bit where a muscle attaches. He was in agony but he left hospital that day with a box of painkillers.
I crushed a thorasic vertebra. Stable fracture, so kicked out of hospital 2 days later with painkillers.
Another friend fell off a crag and blew two vertebra to bits. That is probably what people think of as "breaking your back". Said friend spent 17 wks in hospital and had several ops. And he could still climb better than me =D>
I guess that most of the tour riders have fractures like my first two examples, rather than the third.