A finite element model to study the torsional fracture strength of a composite tibia

Abstract

Screws are common orthopaedic hardware used to secure a fractured bone. After the bone has healed, the screws may be removed, and the vacant screw holes introduce a potential site for re-fracture, which is a known complication. The current study simulated a laboratory torsional fracture test of a composite analogue tibia with vacant screw holes by using a finite element (FE) model, and the results from the simulation were compared to those obtained experimentally. Variations of the FE model were also analyzed to investigate the effects of failure model, screw holes, element size, rotation direction, and simplification of the model's geometry. This FE model was set up the same as the experimental torsion test, with a section from the distal portion of the tibia. The proximal end of the section was subjected to an axial load and rotated, while the distal end was fixed. The FE model contained 102,126 first order tetrahedral elements and 24,817 nodes, and it utilized an isotropic linear elastic material law with material properties obtained from the composite analogue manufacturer. Comparisons between the FE model variations considered the fracture torque, fracture angle, torsional stiffness, principal stress contour, and maximum shear stress contour. The results predicted a fracture torque within the standard deviation of the experimental data, and the percent of strength reduction caused by the screw holes agreed with experimental data.