There is no difference at all between a break and a fracture in bones. A fracture is a medical condition wherein there is a break in the continuity of the bone. These two both terms are used in describing bone injuries. They only differ in the severity of damage.
Geologically speaking a fracture is the way a brittle, non-planar rock would break. Chemically speaking, since bone is made from calcium and other similar elements, these fall into the brittle metals section of the periodic table. In other words calcium is a non-planar mineral that fractures rather than cleaves. Basically a break is a fracture is a break.