chick with broken leg

[skittles1]

i have 4 chicks in a box, they are about 16 to 20 days old. all was fine until this morning, it appears the one chick has a broken leg, she is still able to get to the food and water, however it is not pretty.
any one have an idea on what to do for this poor baby.
for the life of me i can not figure out what she did to break her leg?

 

[skittles1]

oops sorry new to this game, i did not realize i was still in geese,when i posted about my chicken