Evaluation of the Microstructural Characteristics of Bone Surrounding Anchor Screws Placed under a Horizontal Load by Exploring the Orientation of Biological Apatite Crystals and Collagen Fiber Anisotropy

The objective of this study was to carry out quantitative evaluations of the microstructural characteristics of bone surrounding anchor screws placed under a horizontal load and the microstructural characteristics of bone on the compressed and non-compressed sides of anchor screws by investigating the orientation of biological apatite (BAp) crystals and colla-gen fiber anisotropy. Anchor screws were implanted in the femurs of adult rats. They were divided into those placed under a horizontal load (horizontal loading group, n = 4), those not placed under a horizontal load (unloaded group, n = 4), and a sham group of rats that did not undergo femoral anchor screw implantation. In addition to histological observations, BAp crystal orientation and collagen fiber anisotropy were also analyzed. Osteocytes adjacent to anchor screws on the compressed side in the horizontal loading group were rounder in shape than those in normal femurs, the unloaded group, and on the non-compressed side in the horizontal loading group. Collagen fibers showed anisotropy on the non-compressed side in the horizontal loading group. BAp crystals also showed a uniaxial preferential orientation in the direction of traction on the compressed side in the horizontal loading group. These results demonstrated that the osteogenesis of bone around anchor screws placed under a sustained horizontal load gave this bone structural characteristics that differed in some respects from those of normal bone. They also showed that this bone acquired micro/nanostructural characteristics adapted to its new mechanical environment.