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

Background: Internal 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.

Methods: Unstable/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.

Results: There 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.

Interpretation: Basing 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.