Patient-Specific Finite Element Models of Posterior Pedicle Screw Fixation: Effect of Screw’s Size and Geometry

Pedicle screw fixation is extensively performed to treat spine injuries. Post-operative complications may arise from this surgery leading to back pain or revisions. Finite element (FE) models could be used to predict the outcomes of surgeries and test the effect of different screw’s sizes.

The aim of this study was to generate patient-specific Computed Tomography (CT)-based FE models of human vertebrae with two pedicle screws, verify the models, and use them to evaluate the effect of the screws’ size and geometry on the mechanical properties of the screws-vertebra structure.

We found that changes in screw’s length resulted in significantly lower differences in peak stress in the screws, mean strain in the bone around the screw and maximum deflection of the structure with respect to changes in screw’s diameter. In addition, the maximum deflection predicted with realistic or simplified screws correlated very well, while the peak stress in screws with realistic or simplified design correlated well but simplified models underestimated the peak stress.

In conclusion, the results showed that the diameter of the screw has a major role on the mechanics of the screw-vertebral structure for each patient. Simplified screws can be used to estimate the mechanical properties of the implanted vertebrae, but the systematic underestimation of the peak stress should be considered when interpreting the results from the FE analyses.

Sensale, M., Vendeuvre, T., Schilling, C., Grupp, T., Rochette, M., & Dall’Ara, E. (2021). Patient-specific finite element models of posterior pedicle screw fixation: effect of screw’s size and geometry. Frontiers in Bioengineering and Biotechnology, 9, 175.