FIG. 1.

Kinetics of CD34⁺ cells in bone fracture. When bone fracture occurred, CD34⁺ cells (endothelial progenitor cell-rich population) are mobilized from bone marrow into peripheral blood, and they are recruited to the fracture site through circulation. Then, recruited CD34⁺ cells at the injured site develop a favorable environment for fracture healing by releasing vascular endothelial growth factor (VEGF) differentiating osteoblasts and endothelial cells. These combined mechanisms finally enhance vasculogenesis/angiogenesis and osteogenesis, leading to accelerate bridging callus formation and functional recovery from fracture. Color images available online at www.liebertpub.com/teb