Non-linear explicit micro-FE models accurately predict axial pull-out force of cortical screws in human tibial cortical bone

Screws are the most frequently used implants for treatment of bone fractures and play an essential role in determining fixation stability. Robust prediction of the bone-screw interface failure would enable development of improved fixation strategies and implant designs, ultimately reducing failure rates and improving outcomes of bone fracture treatments. This study aimed to compare the accuracy of micro-computed tomography image based bone volume measures, linear micro-finite element (FE) and non-linear micro-FE simulations in predicting pull-out force of 3.5 mm screws in human cadaveric tibial cortical bone. Axial pull-out experiments were performed in forty samples harvested from a single human tibia to measure ultimate force, which was correlated with bone volume around the screw and the predictions by both linear micro-FE and non-linear explicit micro-FE models. Correlation strength was similar for bone volume around the screw (R2 = 0.866) and linear micro-FE (R2 = 0.861), but the explicit non-linear micro-FE models were able to capture the experimental results more accurately (R2 = 0.913) and quantitatively correctly. Therefore, this technique may have potential for future in silico studies aiming at implant design optimization.