Britannica Sources used in this answer

How does the body repair a broken bone with a callus?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Front and back views of the human skeleton are shown side by side, with labeled bones including the skull, spine, ribs, pelvis, arms, legs, hands, and feet. Insets detail the bones of the foot and hand, highlighting major bone groups and anatomical terms. — human skeleton Front and back views of the human skeleton.

When a bone suffers a fracture, the body initiates a repair process by forming a callus, which acts as a bridge of bony and cartilaginous material to reconnect the broken segments.1

The process unfolds in several stages:

Provisional Callus Formation: Within one to two weeks of the injury, osteoblasts—cells responsible for creating new bone—proliferate rapidly in the periosteum. They form collars around the fracture ends that grow toward each other to unite the fragments.1
Definitive Callus Formation: As the injury heals, the initial cartilage is resorbed and replaced by bone tissue. By two to three weeks, strong bony extensions successfully join the fractured ends.1
Remodeling: Over a period ranging from months to years, the callus is gradually resorbed. Through the process of bone remodeling, the bone restores its original structure and organized appearance.12