I hardly ever do songs with lots of 9ths, once when doing a song with too many big stretches, my hand got a strange lump by the knuckle - doctor said it was nothing, but I've been leery of doing too BIG of a piece since then! (It did go away.)
Oooh, that sounds bad! I know a woman piano teacher who developed a 'trigger finger'. I think that's what it is called. Her finger got stuck in a bent shape and she could not move or straighten it. She got a cortisone shot in the finger and then was able to move it, again. But still - things like that are scary.