From EurekAlert!: "transplantation of adult stem cells enriched with a bone-regenerating hormone can help mend bone fractures that are not healing properly. ... stem cells manufactured with the regenerative hormone insulin-like growth factor (IGF-I) become bone cells and also help the cells within broken bones repair the fracture, thereby speeding the healing. ... A deficiency of fracture healing is a common problem affecting an estimated 600,000 people annually in North America. ... This problem is even more serious in children with osteogenesis imperfecta, or brittle bone disease, and in elderly adults with osteoporosis, because their fragile bones can easily and repeatedly break, and bone graft surgical treatment is often not successful or feasible. ... Fractures that do not mend within the normal timeframe are called non-union fractures. Using an animal model of a non-union fracture, a 'knockout' mouse that lacks the ability to heal broken bones, Spagnoli and her colleagues studied the effects of transplanting adult stem cells enriched with IGF-I. They took mesenchymal stem cells (adult stem cells from bone marrow) of mice and engineered the cells to express IGF-I. Then they transplanted the treated cells into knockout mice with a fracture of the tibia, the long bone of the leg. Using computed tomography (CT) scanning, the researchers showed that the treated mice had better fracture healing than did mice either left untreated or treated only with stem cells. Compared with controls left to heal on their own or recipients of stem cells only, treated mice had more bone bridging the fracture gap, and the new bone was three to four times stronger."