Papers by Keyword: Preferential Alignment

Abstract: The quantity and quality of regenerated bone strongly depends on the direction and amplitude of in vivo principal stress; therefore, in vivo stress distribution near bone implants should be optimized on the basis of the morphology of the interface between an implant and bone tissue. In this study, grooves were created on the implant surface in order to improve the surface morphology of the implant for optimizing in vivo stress distribution near the implant. The preferential alignment of the biological apatite (BAp) c-axis, which is a parameter of bone quality and controls the mechanical function of bones, is closely related to stress distribution; therefore, the direction of principal stress should be matched with the direction of the groove on the implant surface. Hip implants were prepared with grooves aligned at different angles from the surface; the grooves were located on the stem portion. These implants were inserted in a beagle femur to investigate the dependency of the quantity and quality of newly formed bone in the grooves on the groove angle. The degree of preferential alignment of the BAp c-axis of the regenerated bone in the grooves strongly depends on the angle of the groove to the principal stress vector that was estimated previously to an animal experiment. The regenerated bone forms anisotropic BAp orientation in response to the principal stress in the grooves; therefore, the direction of the grooves has to be designed on the basis of the stress distribution near the implant.

Abstract: Absorption and formation of hard tissues are repeated in vivo by the activity of osteoclast and osteoblast, respectively. The preferential alignment of BAp or collagen fibril is thought to be closely related to the activity of the bone cells. In this study, changes in bone mineral density (BMD) and preferential alignment of biological apatite (BAp) were examined focusing on the role of osteoblast using the model of osteopetrotic (op/op) mice in which osteoblast activity was normal but the expression of osteoclast was reduced. Osteopetrotic (op/op) mice and their normal littermates aged 5, 12 and 24 weeks were analyzed. The BMD and BAp texture of femoral diaphysis were measured using peripheral quantitative computed tomography (pQCT) and a microbeam X-ray diffractometer system with a 50 µmφ diameter beam spot respectively. The decrease in osteoclast expression induced both the reduction of the skeletal system and calcification of the medullary cavity, which are typical features of osteopetrosis. As a result, the shape, BMD and preferential BAp alignment of the femur in the op/op mice were remarkably different from those in the control group. At the center of the femoral diaphysis, BMD in the cortical area showed no significant difference between the two groups, but preferential alignment of the BAp c-axis in the op/op mice group had a lower value than that in the control group. This suggests that the decrease in the number of osteoclasts suppresses normal remodeling, resulting in a decrease in bone quality, especially the preferential alignment of the BAp c-axis.