Objective To evaluate the effects of locked plates with different screw layouts on stability of the internal fixation system for femoral shaft fracture, so as to provide guidance for clinical study on screw layout of the internal fixation system for femoral shaft fracture. Methods Orthogonal test design method was used with 4 groups of screws at 3 parametric levels. Biomechanical properties of the internal fixation system for femoral shaft fracture under 9 screw layouts were analyzed respectively by the finite element method, and 4 inspection indices, namely, the maximum equivalent stress of the plate, the screw and the femur, and the maximum axial displacement of the internal fixation system were obtained from each group of the experiment, and the orthogonal test weight matrix analysis method was conducted for data analysis. Results The influences of different screw parameters on stability of the internal fixation system varied, and the maximum weights of the 4 sets of screw parameters in stability of the internal fixation system were 13.86%, 7.57%, 7.53% and 5.91%, respectively. Conclusions The best scheme for screw layout in orthogonal test is the screw with none-fixed threaded holes in the first group, the single cortical screws with fixed threaded holes in the second group and the double cortical screws with fixed threaded holes in the third and fourth group.

Objective To explore the effects of screw configurations on bone healing, so as to provide the basis for related fracture treatment. Methods The process of bone healing under different screw configurations was studied by finite element method, and the change in the process of callus growth during healing periods was simulated by interfragmentary strain theory (IFS). The iterative process for renewing callus modulus in every finite element was conducted by the second-developed ABAQUS based on Python scripting language, thus the process of fracture healing was simulated. Results The effect from different numbers of screws on bone healing was smaller than that from different working length of bone plates. On the premise of stable fixation, given the certain working length of bone plates, the effect from different screw numbers on stress distributions in plates or screws was relatively small, while the effect from different working length on stress distributions in plates or screws was relatively large, and the stress distribution in plates was larger than that in screws at different working length. Conclusions It is necessary to take more consideration on working length of bone plates than the number of screws when they are under a stable fixed situation, and it is a wise choice to reduce the screw numbers and choose a suitable working length for bone healing process.