Optimization of Connecting Rod Design Parameters for External Fixation System: A Biomechanical Study

The role of connecting rod in healing process of a fractured bone has always been of significant importance for surgeons. Adding a connecting rod to the fixator would be a secure option for increasing stability without increasing infection rate. The roles of 4 design parameters of the connecting rod (ie, connecting rod diameter, elevation, material, and configuration) were assessed by using finite element models to calculate axial stiffness and interfragmentary strain at the fracture gap. Taguchi method was used to achieve an optimal design set for maximizing stability with regard to connecting rod variables. Also, analysis of variance (ANOVA) approach was employed to determine contribution percentage of each design parameter on outputs. For optimizing connecting rod design parameters, an optimal set of variables consisting of 11 mm, 40 mm, 200 GPa, and Type 3 external fixator were determined by Taguchi for connecting rod diameter, elevation, modulus of elasticity, and configuration, respectively. However, as Type 3 external fixator stability is a little more than Type 2, it would be better if Type 3 external fixator in Taguchi suggestion be replaced by Type 2 external fixator to be as minimally invasive as possible. Furthermore, ANOVA results revealed that the connecting rod configuration is the most important parameter with 95% and 96% effectiveness on the interfragmentary strain and axial stiffness.