Determination of the biomechanical properties of intramedullary nails by experimental and numerical methods

Intramedullary nailing is a fixation method which has been often preferred by surgeons in the treatment of long bone fractures. There are studies to develop different distal locking system in order to avoid the disadvantages of cortical locking screws which are used as a standard for distal locking of standard intramedullary nailing. In this thesis, the mechanical behavior of intramedullary nails with different distal locking system was investigated experimentally and numerically, and research was conducted to develop a new alternative nail design that eliminates the use of distal cortical locking screw and to determine its mechanical properties by numerical methods. Firstly, the mechanical behavior of standard locking intramedullary nail, clawed intramedullary nail and new expandable wedge locked intramedullary nail on the femur with subtrochanteric fracture were compared with simple finite element analyzes and it was observed that the expandable wedge locked intramedullary nail provided a secure fixation. Afterwards, with the detailed parametric finite element analyzes, the appropriate values of the connection parameters affecting the fixation safety in the expandable wedge-locked intramedullary nail fixation were determined and it was seen that the model with a wedge tightening torque of 3 Nm and a friction coefficient of 0.7 at the wedge-bone interface was the safest model. In the experimental studies carried out within the scope of the thesis, the mechanical properties of the fixations of standard locking and clawed intramedullary nails on subtrochanteric and intertrochanteric fractured femurs were examined under compression loads and it was concluded that standard locking nails withstand higher loads and exhibit higher stiffness than clawed nails. Following the experiments, the finite element models of the fixations examined in the experiments were validated with the experimental data. In the validation of the finite element models, experimental strains and fixation stiffnesses taken from the samples were used as validation parameters. With validated models of subtrochanteric fracture fixation, strain values can be estimated with an error of up to 10%. On the other hand, the fact that the stiffness value obtained from the numerical study is higher than the experimental stiffness should be considered. When the strain measurement taken from the second strain gauge in neon fixation is ignored, strain estimations can be made with an error of up to 15%. In the thesis, subtrochanteric and intertrochanteric fracture fixations of the expandable wedge locked intramedullary nail were analyzed via validated finite element models and its mechanical behavior was investigated. The most important conclusion to be drawn from the thesis is that the expandable wedge locked intramedullary nail fixation, which is proposed, detailed in design, and examined by numerical methods, can be used as a new alternative to the standard locking intramedullary nail fixation. However, further experimental studies are required to say this clearly. Another important conclusion that can be drawn from the thesis is that when fixing long bone fractures with Navy nails, especially for individuals with high bone quality, the claws must be completely deployed in contact with the cortical bone and must stick in the bone at a significant amount. Additionally, the preference of distal locking with claws in the distal third of the femur should be avoided.