I read CyclingNews about Cavendish crashing at Ghent and leaving on a stretcher, two broken ribs and a collapsed lung.  I feel for him.  Been there.  Next thought - probably a moment of bad riding on somebody's part.  (After all, the track.  No potholes, leaves, dogs, unruly spectators on the roadway.)  It was the track, or rather, moisture on it.  Another rider saw the moisture the lap before but at Madison speeds, how do you convey this to the infield?

I wonder if this was a matter of poor sweat management by a rider.

As for Cavendish - if my experience applies, he'll get over this just fine but it will take some time.  Painful!  And the deep breaths that are such a godsend to speedy healing cause the biggest and sharpest pain.  I'm guessing he'll figure out early that to sleep, he needs in addition to his bed, a comfortable couch or armchair.  (I used both and kept pillows and comforters by each.  Rolling over was way, way too painful.  I just got up and moved.)