Periosteal osteoprogenitor cells and mesenchymal stem cells will proliferate in the area of the fracture.
At the ends of the fracture where the blood vessels have receded, oxygen supply will be at its greatest, and in these areas osteoprogenitor cells will differentiate into osteoblasts, and begin producing new bone (a process resembling intramembranous ossification).
- Meanwhile, in the areas where blood supply is low or absent (in the center of the blood clot, for instance) mesenchymal stem cells will differentiate into chondroblasts and begin producing a rudimentary fibrocartilage
- in roughly the middle of the fracture site.
- Osteoclastic activity will begin
- breaking down the fractured and damaged bone.