Biomechanical analysis of the sliding hip screw, cannulated screws and Targon® FN in intracapsular hip fractures in cadaver femora

BackgroundInternal fixation is one of the main options for treating displaced intracapsular hip fractures. However, controversy remains over which osteosynthesis is the best choice. Using a simulated displaced intracapsular hip fracture model, we compared the mechanical stability of three types of osteosynthesis: the sliding hip screw (SHS), three cannulated screws and the Targon® FN. We also assessed whether bone mineral density (BMD) influenced the stability of the fixation.MethodsUnstable/displaced intracapsular hip fractures were induced in a total of 12 pairs of fresh-frozen cadaver femora. Each fracture was fixed at random on the left or right side with an SHS or three cannulated screws (six bone pairs; study 1), or with an SHS or the Targon® FN implant (six bone pairs; study 2). All femoral heads were exposed to cyclic combined axial and torque loads until failure. The failure mechanism, the maximal load-to-failure and the dual-energy X-ray absorptiometry (DEXA) values of the femoral heads were determined and their relationships were analysed.ResultsThere was no significant difference in the maximal load-to-failure between the SHS and the three cannulated screws. The load-to-failure was significantly higher for the Targon® FN than for the SHS. There was a high correlation between the bone mineral densities (BMDs) of the femoral heads and maximal load-to-failure in the Targon® FN group only.InterpretationBasing the implant choice on preimplantation BMD measurements does not ensure the best biomechanical outcome. We found that the combination of a fixed-angle device and multiple sliding neck screws (Targon® FN) enhances the mechanical strength of reconstructions in unstable/displaced intracapsular hip fractures.