Growth factors are triggering and/or signaling molecules that regulate not only growth but also musculoskeletal repair and regeneration. Bone morphogenetic proteins (BMPs), which regulate cellular proliferation, differentiation and extracellular matrix production, were first described by Dr. Marshall Urist in 1965 [22], and are the most well-known and researched of the musculoskeletal growth factors. They also function in apoptosis [13] and reshaping the extracellular matrix. The membrane receptors and intracellular signaling mechanisms of these growth factors are well-defined [2]. Not only osteoblasts and chondrocytes but also osteoclasts [19] contain these membrane receptors, which indicates growth factors have a key role in the homeostasis of the musculoskeletal system. The externally administered local therapeutic quantity and duration that is required to trigger and/or control the event is, however,substantially higher than that of the endogenous dose. Responsive cells are essential at the administration site to have an optimal healing effect. BMP producing and marketing sources indicate that injecting or implanting these growth factors attracts stem cells. The mechanism of how BMPs work at atrophic nonunions where such cells are lacking needs further investigation. Recent preclinical and clinical studies including those published in this symposium will give insight into these mechanisms.
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