Computational comparison of tibial diaphyseal fractures fixed with various degrees of prebending of titanium elastic nails and with and without end caps

Abstract

Introduction: Elastic stable intramedullary nailing (ESIN) is a treatment strategy for the management of diaphyseal long-bone fractures in adolescents and children, but few studies have investigated the mechanical stability of tibial diaphyseal fractures treated with various degrees of prebending of the elastic nails. Therefore, the aim of this study was to compare the mechanical stability, including the gap deformation and nail dropping, of a tibia fracture with various fracture sites and fixed with various degrees of prebending of the elastic nails by the finite element method. Furthermore, the contribution of end caps to stability was taken into consideration in the simulation.

Methods: A tibia model was developed with a transverse fracture at the proximal, middle and distal parts of the diaphysis, and fixed with three degrees of prebending of elastic nails, including those equal to, two times and three times the diameter of the intramedullary canal. The outer diameter of the nail used in the computation was 3.5mm, and the fractured tibia was fixed with two elastic double C-type nails. Furthermore, the proximal end of each nail was set to free or being tied to the surrounding bone by a constraint equation to simulate with or without using end caps.

Results: The results indicated that using end caps can prevent the fracture gap from collapsing by stopping the ends of the nails from dropping back in all prebending conditions and fracture patterns, and increasing the prebending of the nails to a degree three times the diameter of the canal reduced the gap shortening and the dropping distance of the nail end in those without using end caps under axial compression and bending. Insufficient prebending of the nails and not using end caps caused the gap to collapse and the nail to drop back at the entry point under loading.

Conclusions: Using end caps or increasing the prebending of the nails to three times the diameter of the canal is suggested to stop the nail from dropping back and thus produce a more stable structure, with less gap deformation, in the management of a simulated tibial diapyhseal fracture by using titanium elastic nails with a double C-shape.

Keywords: Elastic stable intramedullary nail; End cap; Finite element (FE) method; Prebending of the nail; Tibial diaphyseal fracture.