ABSTRACT
Bone is three times lighter than iron but ten times more flexible, although bone and iron have the same tensile strength. Bone is, nevertheless, anisotropic and has a modulus of around 18 giganewtons/m2. Fractures can be caused by direct or indirect trauma. The latter type can be traction, angulation, rotational, or compression fractures, or fractures caused by a combination of these forces.[1]
Biology of Bone Healing
The immediate reaction to fracture is an inflammatory phase that lasts up to 72 hours. The ends of the fractured bone do not actively participate in this process, but are in fact dead. They play only a passive role in the bridging process between the more distant living bone edges. Injured tissues and platelets release vasoactive mediators (which induce vasodilatation) and cytokines. Cytokines influence migration and proliferation of mesenchymal stem cells and their differentiation to osteoprogenitor cells, as well as matrix synthesis (i.e., members of the Tissue Growth Factor-b superfamily, such as Bone Morphogenetic Proteins 2 and 7, Platelet-Derived Growth Factor, Fibroblast Growth Factor, Insulin Growth Factor, and Interleukins 1 and 7). During this process macrophages remove the dead tissue.
