Methods of treatment of femoral fractures still remain controversial in adolescent age when the patients are too young for adult-type stabilization. This study examines the possibilities for improving the mechanical parameters of the bone-nail interface in flexible intramedullary nailing.

Mathematical models, which simulate different fractures, have been created by using the finite elements method. The stabilizing construction with two 4,00 mm Ender nails was performed in two versions:

standard divergent “C” configuration (3 points of pressure);

Each version has been tested towards the deforming forces – bending in frontal and sagital plane; torsion and axial loading. Strength coefficient of the nails has been calculated as well as the stiffness of the configuration. The comparative analysis of the results found out that under the angular and torsional forces the mechanical parameters of the two types of configurations are equivalent. However, under axial loading, the divergent “S” configuration shows definitely better mechanical characteristics. The strength coefficient is 30% higher and the stiffness of the configuration is twice as strong. The specific intramedullary cohesion enables more considerable resistance towards the transverse displacement in telescoping of the fragments.

Proceeding from the presented data, it could be considered that the divergent “S” configuration creates much more sufficient length control. Its implementation in axial unstable femoral fractures could enable an earlier mobilization, respectively – an earlier weight-bearing loading.

The purpose of our study was to compare the mechanical nature of nails with different cross-sections in order to optimise the elasticity-stability ratio. There is no doubt that elastic intramedullary osteosynthesis is a successful choice for treating femoral shaft fractures in children. However, misalignment is a potential problem connected with stability of the fixation.

The mechanics of two types of nails with the same type of surface, but with different kind of cross sections – a circle (Ender) and an ellipse – was examined using the “finite elements” method.

The standard configuration of the two nails was put under four kinds of deforming forces: bending in the frontal plane and the sagital plane, torsion, and axial compression. Strength coefficient and stiffness were calculated in each particular situation.

In respect to angular stability (frontal plane) and axial compression, the mechanical characteristics of the two types of nails are similar. The stability of the elliptical nail is higher in bending in the sagital plane and in torsion. The elliptical implant has better intramedullary cohesion because the large half-axis is perpendicular to the sagital plane.

Nails with an elliptical cross section provide the opportunity for redistribution of stiffness. As a result, better mechanical properties are achieved. The elliptical cross section assures better intramedullary cohesion.