What the difference between crack and fracture?

Same: This typically is one in the same. A fracture is a "crack in the bone" whether it be complete or incomplete.

Same: We are often asked what the difference is between a fracture and a break - or, in this case, a crack. There is no difference - it all means the same thing: a broken bone. A fracture can be further described according to angulation, displacement, whether it's open or not, etc.