Abstract
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.
The abstracts were prepared by David P. Davlin. Correspondence should be addressed to him at the Orthopedic Clinic Bulovka, Budínova 2, 18081 Prague 8, Czech Republic.
