I believe he has only missed 1 game in his career, he is a tough qb and has proven he can take a beating.
But it's very possible that he was forced into playing hurt (by himself and the coaches) because the alternative has always been Brunell. Unfortunately Sanchez at 50% was better than Brunell.
Now that presents an interesting scenario, if he starts taking a pounding does Tebow come in or do they go with a battered Sanchez. Not saying he is injury prone but he has been beaten up over the last few years and has always gotten up and stuck it out.