Effects of a fixation screw on trabecular structural changes in a vertebral body predicted by remodeling simulation.

Computational simulation of trabecular surface remodeling was conducted to investigate the effects of a spinal fixation screw on trabecular structural changes in a vertebral body. By using voxel-based finite elements, computational models of the bone and screw were constructed in two structural scales of a vertebral body with an implanted screw and a bone-screw interface. In the vertebral body, the implantation of the fixation screw caused changes in the mechanical environment in cancellous bone, leading to trabecular structural changes at the cancellous level. The effects of the screw on trabecular orientation were greater in the regions above and below the screw than in those in front of the screw. In the case of the bone-screw interface, trabecular structural changes depended on the direction of load applied to the screw. It was suggested that the bone resorption predicted in the pull-out loading case is a candidate cause of the loosening of the screw. The results indicate that the effects of the implanted screw on trabecular structural changes are more important for longer-term fixation.