Introduction and Objective

Trochanteric fractures are associated with increasing incidence and represent serious adverse effect of osteoporosis. Their cephalomedullary nailing in poor bone stock can be challenging and associated with insufficient implant fixation in the femoral head. Despite ongoing implant improvements, the rate of mechanical complications in the treatment of unstable trochanteric fractures is high. Recently, two novel concepts for nailing with use of a helical blade – with or without bone cement augmentation – or an interlocking screw have demonstrated advantages as compared with single screw systems regarding rotational stability and cut-out resistance. However, these two concepts have not been subjected to direct biomechanical comparison so far. The aims of this study were to investigate in a human cadaveric model with low bone density (1) the biomechanical competence of cephalomedullary nailing with use of a helical blade versus an interlocking screw, and (2) the effect of cement augmentation on the fixation strength of the helical blade.

Background. Femur fracture fixation systems depend on the stability of the supporting cortical screws, inside the host bone. Only a few works have studied the stability of cortical screws in femur shafts and compared their results with previous studies. Methods. In present study, five different cortical screw types are assessed using artificial femurs, under equated testing conditions. The maximum force needed to cause screw-bone inter face failure was measured, for each screw type by pullout tests. The obtained results were normalised according to traditional methods and cross-compared. The best performer was searched for and the effect of screw dimensions on the screw performance was investigated. To make the pullout tests solely dependent on screw dimensions, the effect of the bicortical bone thickness was eliminated by equating the conditions of screw insertion. Results. Evaluation of the test results proved that the non-locking screws with larger diameter and pitch depth required larger pullout forces to be extracted, thus showed statistically superior performance compared to locking screws with smaller dimensions. However, the observed statistical differences between the absolute pullout forces were diminished, after the traditional normalisation of the results. But, traditional normalisation was challenged due to its known short comings. A new normalisation method was proposed based on a solid geometric reasoning, which is supported by true observations. Conclusion. This novel approach showed that a screw type that appeared to show average performance; in fact, did not have significantly different results than the top performers. The outcome of the comparisons pointed out that surgeons are not obliged to prefer larger dimension screws, in small dimension host bones. Level of Evidence. Level 5. Disclosure. The authors declare that no conflict of interests were associated with the present study