How do broken bones heal?
Bone tissue has the ability to rebuild itself. Only hours after a bone has been broken, young tissue cells start to appear to begin the repairing process.
The cells multiply quickly and are filled with calcium. About 72 hours after the break, these cells form the tissue that will unite the ends of the broken bone. More calcium is deposited to harden the bone and over the following months a normal bone is developed. The plaster cast is applied to a broken limb to make sure that the edges of the bone are kept in alignment. Tell Me How?, Chancellor Press