The Four Stages of Healing a Fractured Bone
1) Formation of Hematoma at The Break
When a bone breaks, blood flows from the vessels torn by the fracture. These blood vessels
could be in the periosteum, osteons, and/or the medullary cavity. A blood clot forms in the area where the broken bone occurred. The blood begins to clot, and about six to eight hours after the fracture, the clotting blood has formed a fracture hematoma (Figure A). The hematoma contains a meshwork of proteins that provide a temporary plug to fill the gap created by the broken one. The disruption of blood flow to the bone results in the death of bone cells around the fracture.
The immune system takes action and starts the inflammatory response, which is the first part of healing. Inflammation triggers stem cells from the surrounding tissues, bone marrow, and blood to migrate to the fracture. The cells start two vital processes: bone formation and cartilage formation.
2) The Formation of a Fibrocartilaginous Callus
Within 48 hours after the fracture, chondrocytes from the endosteum have created an internal callus (plural= calli) by secreting a fibrocartilaginous matrix between the two ends of the broken bone. While the periosteal chondrocytes and osteoblasts form an external callus of hyaline cartilage and bone, around the outside of the break (Figure B), this stabilizes the broken bone.
3) Formation of a Bony Callus
Over the next few weeks, osteoclasts resorb the dead bone, osteogenic cells are activated,
divide, and differentiate into osteoblasts. The cartilage in the calli is replaced by trabecular bone via endochondral ossification (Figure C).
4) Remodeling and Addition of Compact Bone.
After about six to eight weeks, the internal and external calli unite, compact bone replaces
spongy bone at the outer boundaries of the fracture, and healing is completed. A bulging may remain on the outer surface of the bone, but over time that area is remodeled (Figure D), and no external evidence of the fracture remains. The healing time, however, could be extended significantly If you have multiple breaks, ligament, tendon, or muscle damage.
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