Simulação do comportamento mecânico de placas volares de aço inoxidável e da liga de titânio Ti-6Al-4V

Abstract

Fractures in the distal region of the radius are the most frequent injuries to the human body. The treatment of these fractures through the use of volar plates has become popular in recent decades. The present work seeks to study, via finite elements, the mechanical behavior of a system composed of a fractured radius, a volar plate (one of 316L stainless steel and the other of Ti-6Al-4V alloy) and fixation screws, applying loads compressive and tractive. To obtain the radius geometry, an STL (Stereolithography) file was used in a database, containing the external surface of the bone. The inner surface was generated by offsetting the outer surface. Each of the surfaces was formed by areas, which together generated the volumes that came to form the different parts of the bone. The volar plate was defined by splines that connected the key points to form the implant contour. The screws were represented by beam elements of 2.8 mm in diameter. Traction and compression simulations were carried out with the structure composed of the radius, the volar plate and the fixation screws, with loads of at most 600 N. However, for the calculation of stiffness, loads of up to 300 N were considered, following the norms ACGIH (American Conference of Governmental Industrial Hygienists, USA) and NIOSH (National Institute for Occupational Safety and Health, USA). There was a difference of 5.5% between the simulated models. Furthermore, there was a considerable influence of the implant material and the type of loading imposed in relation to the magnitude of the system's rigidity. The titanium alloy plate proved to be safer than the stainless steel one, due to the fact that the former did not enter the plastic deformation regime. In addition, for both systems, two stiffness values were found (initial and final), and for the titanium plate the final stiffness was higher than the stiffness of the stainless steel plate, while for the initial stiffness the opposite was observed, since for loads above 300 N the stainless steel entered the permanent deformation regime.