Comparison of the Dynamic Cut-Out Failure Modes of Common Proximal Femoral Fixation Devices Using a Mesh-Free Computational Method.

Abstract

Migration and cut-out are commo n failures observed in internal fixation of intertrochanteric fractures. This study compares the performance of four typical devices under dynamic loading using benchtop and computer-simulated fracture models. The dynamic hip screw (DHS), Gamma3, proximal femoral nail anti-rotation (PFNA-II), and TFN-Advanced (TFNA) were inserted into a solid rigid 10 pounds per cubic foot (PCF) polyurethane bone foam mimicking a reduced unstable intertrochanteric fracture model. Static and dynamic loading tests using a double-peak loading curve based on natural walking gait were conducted. The blade devices had higher resistance to the onset of implant migration under physical dynamic loading in comparison to the screw devices. However, as dynamic loading progressed, no implant showed clear superior performance. Mesh-free simulations of the physical tests were then conducted to visualize stress and failure patterns within the bone foam during migration and cut-out, using an experimentally validated porous foam material model. The mean concordance correlation coefficient between load to cut-out for the physical and simulated tests was 0.953 and 0.858 under static and dynamic loading, respectively. Under simulated dynamic loading, the volumes of yielding and failed bone foam were 15%, 32%, and 25% higher for Gamma3, PFNA-II, and TFNA than for DHS, suggesting that devices with similar forces at cut-out may produce relatively large differences in the volume of damaged bone tissue. Accurate simulation of material damage during dynamic loading may offer a useful alternative method for differentiating device performance in support of clinical decision-making around implant selection.