Britannica Sources used in this answer

How does callus help a fractured bone heal?

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

Medical illustration of a human knee joint in a parasagittal section just lateral to the midline, labeling ligaments, cartilage, meniscus, patella, synovial structures, and surrounding muscles and fat pads. — joint The ligaments and cartilage in a knee joint.

A callus is a bridge of bony and cartilaginous material that forms to repair a fracture by connecting the broken ends of a bone.1

Within one to two weeks of an injury, a provisional callus develops to envelop the fracture site. During this process, osteoblasts—specialized bone-forming cells located in the periosteum—proliferate and form collars around the fracture ends, growing toward each other to unite the fragments.1

As healing progresses, a definitive callus forms as the initial cartilage is resorbed and replaced by bone tissue. By two to three weeks post-injury, strong bony extensions successfully join the fractured ends, allowing the bone to regain its organized structure. Over a period of months to years, the callus is gradually resorbed as the bone completes its remodeling process.1