Microscopic Analysis of Fractured Screws Used as Implants in Bone Fixation

The increase of life expectancy and risk of accidents, thereby causing a higher incidence of surgeries, has led to a growing use of implants. The reliability of these implants, either for bone fracture correction or for joint replacement, thus used in applications of considerable responsibility, depends on the characteristics of the materials, as well as on the conditions of manufacture. By using some techniques, mainly optical microscopy and scanning electron microscopy tests, this work has as purpose the identification of the possible causes of failure of screws used in plates for bone fixation, considering the fracture surface aspects and microstructural characteristics of the austenitic stainless steel used in their manufacture, which is essential for this application. The results obtained in this study allowed the identification of the main causes of the failure, primarily related to fatigue fracture, associated to the presence of surface cracks, generated by stress concentration, which was probably caused by grooves left by improper machining.