Fractures: Bone Repair

A fractured bone undergoes three stages of repair— reactive, reparative, and remodeling.

The initial reactive phase seals the damaged blood vessels forming a blood clot called fracture hematoma. It disrupts circulation, leading to the death of bone cells near the fracture.

The resulting cell debris causes swelling and inflammation, recruiting the phagocytes and osteoclasts to the injury site.

As the debris is cleared, new blood vessels extend into the hematoma, starting the reparative phase.

Fibroblasts and chondroblasts migrate from the undamaged regions of the bone into the fractured gap.

They form collagen fibers and fibrocartilage to bridge the broken ends, using a fibrocartilage repair tissue called soft callus.

As repair progresses, osteoprogenitor cells from the healthy regions of the bone differentiate into osteoblasts.

These osteoblasts begin forming spongy bone trabeculae at the fracture margins of the bone.

Gradually, the fibrocartilage around the external edges of the break is replaced with spongy bone or the hard callus.

During the final phase, osteoclasts and osteoblasts remodel and replace the peripheral spongy bone with compact bone, repairing the shaft wall.