Influence of the intramedullary nail length on a fracture site: Biomechanical evaluation with the finite element method

Introduction: Intramedullar locking nails have been widely preferred in femoral shaft fractures, however, design of the nails cause some problems. If the length of the nail and the distance of the distal locking screws to the fracture site are not considered, negative side effects may be observed. In order to understand the side effect of the distance between fructure gap and the distal locking pin, effect of the nail length were aimed to investigate in this study. Material and Method: Two intramedullary nails with different lengths were compared. One nail was 301 mm and the other nail was 251 mm in length. The nails were inserted into the 1/3 proximal fractured femur with the support of computer aided design (CAD) software. Comparative Static analyses were performed on the 3D models. Results: Different equivalent (von-Mises) stress results were observed on the fructure sides of the two models which were 2.0204e+009 Pa and 3.1925e+007 Pa respectively. Consequently, the stress on the fracture surface decreases as the distance between the distal locking side and the fracture side, decreases. Discussion and Conclusion: Clinically, the shorter nail must be prefered to decrease the stress on the fructure side. Meanwhile, the other factors like diameter, angle of the fixation pin, and material properties should be considered while choosing nails