How does a fracture hematoma form after a bone breaks?

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Internal structure of a human long bone — bone A long bone of the human body, showing a magnified cross section of the interior.

When a bone breaks, the blood vessels within the bone tissue rupture. The resulting bleeding causes blood to collect at the site of the injury, which is known as a fracture hematoma. This accumulation of blood leads to swelling at the fracture site and often causes skin discoloration.1

The pressure from this bleeding distends the nerve endings in the periosteum, which is why movement or pressure on a broken bone is painful. The formation of the fracture hematoma is the initial stage of the healing process; it is subsequently invaded by cellular elements, eventually leading to the formation of a callus that bridges the fracture.1