when does the healing process of a fractured bone begin
Bone healing After fracture, blood cells accumulate adjacent to the injury site. Soon after fracture, blood vessels constrict, stopping further bleeding. Within a few hours, the extravascular blood cells form a clot called a hematoma[5] that acts as a template for callus formation. These cells, including macrophages, release inflammatory mediators such as cytokines (tumor necrosis factor alpha (TNFα), interleukin-1 family (IL-1), interleukin 6 (IL-6), 11 (IL-11), and 18 (IL-18)) and increase blood capillary permeability. Inflammation peaks by 24 hours and completes by seven days. Through tumor necrosis factor receptor 1 (TNFR1) and tumor necrosis factor receptor 2, TNFα mediates the differentiation of mesenchymal stem cell (originated from the bone marrow) into osteoblast and chondrocytes. Stromal cell-derived factor 1 (SDF-1) and CXCR4 mediate recruitment of mesenchymal stem cells. IL-1 and IL-6 are the most important cytokines for bone healing. IL-1 promotes formation of callus and of blood vessels. IL-6 promotes differentiation of osteoblasts and osteoclasts.[4] All cells within the blood clot degenerate and die. Within this area, the fibroblasts replicate. Within 7-14 days, they form a loose aggregate of cells, interspersed with small blood vessels, known as granulation tissue.[5] Osteoclasts move in to reabsorb dead bone ends, and other necrotic tissue is removed.[6]