The effects of fibrous hydroxyapatite on the process of bone formation was studied in histological and biomechanical animal experiments. First, fibrous hydroxyapatite was implanted in a hole made in the midfemur of a white rabbit. Second, after midf emoral transverse osteotomies were performed on mongrel canines, fibrous hydroxyapatite was implanted in the osteotomized site, and then fixed with a dynamic axial fixation system. At 3 weeks after osteotomy, axial dynamization, histological observations, and bone histomorphometric analysis were performed in some animals. Third, after a window was made in the lateral midfemur of a canine, fibrous hydroxyapatite was implanted, and a three-point bending test was performed. In the hydroxyapatite group, osteoprogenitor cells gathered soon after surgery showing active osteoid hyperplasia. Trabecular bone specific volume (tVsp) and fractional formation surface (FrFS) remained higher throughout the entire process. In the dynamization group, features of mature bone accompanied by a decrease in the number of osteoids were evident in the early stage. In a three-point bending test, the stiffness and maximum load increased sharply, particularly after 4 weeks. These findings suggest that, in the process of bone formation, fibrous hydroxyapatite acts as an osteoconduction material, which accelerates bone maturation under the influence of axial dynamization. It also provides mechanical stability from an early stage.
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