Effect of Screw Distribution on Stability and Interfragmentary Strain of Lower Tibial Fractures: A Finite Element Analysis.

OBJECTIVE

The aim of this study was to explore the influence of working length (determined by the screw position) on the stiffness and interfragmentary strain (IFS) of femoral locking compression plate (LCP) external fixators for lower tibial fractures under full weight-bearing conditions, with the goal of providing a reference basis for clinical applications.

METHODS

Finite element analysis software was used to construct a model of a lower tibial fracture with external femoral LCP fixation. The models were divided into four groups according to the different working lengths (external femoral locking plate fixation 1 [EF1], EF2, EF3, and EF4). Stress distribution clouds, fracture end displacements, stiffness and IFS were tested for each model group at different loads.

RESULTS

Compared with those in the EF1 group, the stiffnesses in the EF2, EF3, and EF4 groups decreased by 28%, 31%, and 37%, respectively, under axial compression loading. Compared with those in the EF1 group, the stiffnesses in the EF2, EF3, and EF4 groups decreased by 19%, 33%, and 35%, respectively, under axial torsion loading. Compared with those in the EF1 group, the stiffnesses in the EF2, EF3, and EF4 groups decreased by 32%, 33%, and 35%, respectively, under a three-point bending load. The IFS of the four finite element models increased with the working length of the plate, with EF1 (76%) < EF2 (107%) < EF3 (110%) < EF4 (122%). Finite element analysis revealed that under full weight-bearing conditions, the structural stiffness of the femoral LCP external fixator decreased with increasing working length, leading to an increase in the IFS, which resulted in an IFS that exceeded the ideal range required for secondary healing.

CONCLUSION

For unstable lower tibial fractures, screws in the femoral LCP external fixator should be placed as close to the fracture end as possible to increase stability and promote fracture healing.