Biomechanical stability analysis of transpedicular screws combined with sublaminar hook-rod system using the finite element method

Aim To develop and test a new posterior stabilization system by augmenting the posterior hook-rod system with screws and rods. Methods A biomechanical analysis was performed using the finite element method. The anatomical structures were modeled based on computed tomography data. Instrumentation (hooks, rods, and screws) was modeled based on the data obtained by 3D scanning. The discretized model was verified by converging solutions and validated against data from a previously published experiment. A Th12-L1 spinal segment was modeled and modified by removing the body of the L1 vertebra (corpectomy) and the entire L1 vertebra (spondylectomy). The model was additionally modified by incorporating stabilization systems: i) posterior stabilization (transpedicular screws and rods); ii) combined posterior stabilization with sublaminar hooks; and iii) combined anterior (titanium cage) and posterior (sublaminar hooks) stabilization. The rotation angles in each group, and the strains on each part of the three stabilization constructs, were analyzed separately. Results The combined anterior and posterior stabilization system was the stiffest, except in the case of lateral bending, where combined posterior stabilization was superior. Stress analysis showed that the posterior stabilization system was significantly unloaded when augmented with a hook-rod system. A significant strain concentration was calculated in the cranially placed hooks. Conclusion Stiffness analysis showed comparable stiffness between the tested and proposed stabilization construct. Stress analysis showed luxation tendency of the cranially placed hooks, which would most likely lead to system failure.