Sliding of the load carrier in third-generation intramedullary nails for proximal femur fractures: an in vitro mechanical comparison study.

Dynamic osteosynthesis of proximal femur fractures facilitates compression at the fracture site through distal glide of the femoral head load carrier in the intramedullary nail. Modern implants are currently designed according to diverse gliding principles. The aim of this study was to compare the sliding mechanisms of different types of nails. As in other similar mechanical studies the load patterns occurring around the femoral head load carrier and the intramedullary nail under full load were simulated for three different types of intramedullary nail - PFNA, Targon PFT and Trigen Intertan. The load necessary to trigger distal displacement of the femoral head implant in the nail was determined. The lengths of the load carriers were varied. For the three lengths of load carrier, mechanical testing showed that the Targon PFT started to slide at a significantly lower load compared to the other two implants. Comparison of the PFNA and Trigen Intertan in terms of load to dynamization for 77 mm carriers revealed a significantly lower load for the PFNA. Slide efficacy for the PFNA and the Trigen Intertan was found to improve as the length of the blade/screw was shortened. The dynamization properties of the Targon PFT with its cylindrical sliding mechanism, similar to the DHS, were far better compared to the PFNA and the Trigen Intertan that have more complex sliding actions. Since theoretical considerations indicate that a less efficient gliding action leads to a higher complication rate, implants of the next generation should be optimized in this regard. © IMechE 2015.