Finite element analysis on interlocking intramedullary nail and locking compression plate in treating older children with fracture of femoral shaft

Objective To compare and analyze biomechanical characteristics of interlocking intramedullary nail and locking compression plate in treating older children with transverse fracture of femoral shaft. Methods Two kinds of finite element models for internal fixation of fractures were established. Axial compression experiment, four-point bending experiment and torsion experiment were conducted, and the stress as well as displacement of the models in the experiments were analyzed. Results The maximum stress values and average stress values of the interlocking intramedullary nail in the axial compression test and four-point bending test were larger than those of the locking compression plate. In the torsion test, the maximum and average stress values of interlocking intramedullary nail were less than that of locking compression plate. In fracture model with internal fixation of locking compression plate, the stress at the femoral fracture line was greater than that in fracture model with internal fixation of interlocking intramedullary nail, so the stress shielding of interlocking intramedullary nail was greater. The maximum femoral displacement in the internal fracture fixation model of locking compression plate was larger. Conclusion Compared with the internal fixation of locking compression plate, the internal fixation of interlocking intramedullary nail has larger stress shielding in fracture site, but it is more powerful to resist bending and torsion, has less operative wound and slight influence upon - the femoral blood supply. The static fixation can be changed to dynamic fixation at the late stage of the healing, thereby making the stress distribution more conform to the original biomechanical characteristics of the femur. Therefore, for the transverse fracture of femoral shaft of the older children, the internal fixation of interlocking intramedullary nail can be taken as a preferred treatment.