Stress distribution in vertebral bone and pedicle screw and screw-bone load transfers among various fixation methods...

This paper examines the stress distribution in the posterior fusion fixation, spinal range of motion (ROM), and the screw-bone interaction force obtained from various fixation methods of short-segment spine surgical alignment (SA) under five loading conditions (axial compression, flexion, extension, lateral bending, and axial rotation) provided by a FE spine model. The implant-instrumented FE spine model was validated against the experimental data in the literature. Among different fixation methods, fusing more spinal segments might help distribute the spinal load on the pedicle-screw to reduce the stress, screw force, and instability of the spine (range of motion). With longer rods, the additional intermediate screws are suggested to provide additional anchoring effect to the fixation device. However, the fact that inserting more screws also increases the stress concentration points on the rods should also be considered. Further this study supports the clinical observation that interbody cage can provide anterior support to the spine and reduce the loads on the posterior fixation devices. In both single-level and two-level fusion, IB reduced ROM, rod stress, and screw/bone interaction force.