Your bones heal by creating new bone tissue. The new bone is called the external callus. This callus begins to form shortly after the bone is broken. At first it’s not like normal bone — it’s soft and does not provide any protection for the underlying break. But it grows stronger as it calcifies and develops into normal bones over weeks to months.
Compound fractures heal in three stages:
Inflammation stage: Your body starts to heal right after the fracture. The cells of your immune system rush to the injured area instantly. One of the things they do is increase blood flow to the area, and that can cause the skin around the compound fracture to swell and turn red. This swelling and redness can continue for some time as your body tries to ensure healing.
Repair stage: During this stage — which can last from weeks to months — your fractured bone will be kept still (immobilized) in a cast. It’s vital that your broken bones don’t move while they heal. Your body will create new bone tissue during this stage. The external callus (the new bone) can be easily damaged, so it needs protection.
Remodeling stage: The remodeling stage can take several months. During this time, the external callus gets stronger because it grows thicker and calcifies. As your bones remodel, they become a more normal shape and are less fragile.