Osteoblast Origins in Fracture Healing: Two Key Cellular Sources

Fracture repair relies on osteoblasts from two primary sources:

1. Local Osteoprogenitor Cells: Reside on bone surfaces (periosteum, endosteum). Fracture signals activate them to differentiate into osteoblasts, producing new bone matrix at the fracture site.
2. Bone Marrow Stromal Cells (Mesenchymal Stem Cells): Multipotent cells in marrow cavity. Injury signals (growth factors, cytokines) drive their differentiation into osteoblasts, contributing to callus formation and bridging.

Both populations are essential for successful fracture union. Their recruitment and differentiation are tightly regulated by mechanical and biochemical cues at the injury site.