When a teacup is broken, we can mend it with glue. Depending on how carefully we hunt down the pieces, how carefully we adjust and align them, how delicately we apply the glue, the mend may be nearly invisible and the teacup good as new. I've mended cups and bowls well enough to make the fractures invisible and to allow them to hold liquids without leaking.
Hearts break just so, especially young ones, and mend, usually, with as little effort.
A broken arm is mendable as well, and the damage typically is confined to internal parts, the bones. With proper attention, it will eventually appear whole again. The skin, if it wasn't punctured, will show no signs. If the bones were set correctly, the arm will move and display correctly. And the accepted wisdom is that bone scar tissue is harder and stronger than the original it replaces.