The Inflammatory Stage
When a bone breaks, the body sends out signals for special cells to come to the injured area. Some of these special cells cause the injured area to become inflamed (red, swollen, and painful). This tells the body to stop using the injured part so it can heal.
Other cells that come to the area during this stage form a hematoma (blood clot) around the broken bone. This is the first bridge between the pieces of the broken bone.
The Reparative Stage
The reparative stage starts within about a week of the injury. A soft callus (a type of soft bone) replaces the blood clot that formed in the inflammatory stage. The callus holds the bone together, but isn't strong enough for the body part to be used.
Over the next few weeks, the soft callus becomes harder. By about 2–6 weeks, this hard callus is strong enough for the body part to be used.
The Remodeling Stage
The remodeling stage starts around 6 weeks after the injury. In this stage, regular bone replaces the hard callus. If you saw an X-ray of the healing bone, it would look uneven. But over the next few months, the bone is reshaped so that it goes back to looking the way it did before the injury.