Abstract
In spinal instrumentation for the treatment of vertebral fractures, it is common to loosen for screws which are inserted into vertebrae and strongly immobilized by a rigid rod. Therefore, we have been proposed an improved rod with a damper structure to increase freedom of movement of the rod and allow more flexible fixation of the spine. Because one of the factors of the occurrence of the loosening is decrease of fixity due to morphological change of trabecular bone by remodeling around screw, it is important to elucidate the relationship between the improved structure of rod and morphological change of bone around the screw. In this study, first, in order to identify loading condition of vertebral body for bone remodeling, we elucidated the relationship between morphological change in trabecular bone of vertebral body and tightening force by annulus fibrous using our remodeling simulation framework. Second, we performed remodeling simulation around the inserted screw in vertebral model to clarify relationship between trabecular morphology and apparent stiffness of the damper part of the proposed rod. As results, bone formation in the horizontal axis occurred more active as magnitude of the tightening force was stronger, suggesting that the tightening force strongly affected trabecular bone morphology by remodeling. In addition, number of trabecular bone around inserted screw kept high in remodeling process in the flexible fixation because mechanical stimulus was transferred to trabecular bone below the inserted screw, suggesting that the loosening risk of screw was low in the flexible fixation.
