Nitinol is commonly used as a retention clip to prevent backout of fixation screws in spinal anterior cervical plates (ACP). During implantation, however, there is metallic contact between the screw and retention clip. The effects of this surface damage on corrosion resistance of the Nitinol clip have not been thoroughly investigated and may be dependent on the level of screw-clip interference in the construct design. Therefore, the goal of this study is to characterize the effects on the Nitinol corrosion resistance using varying levels of screw-clip interference in a modified ACP assembly.

The use of superelastic Nitinol in implants continues to grow as physicians, scientists, and engineers design more novel medical devices to utilize its unique characteristics. As many of these devices are expected to be long-term implants, it becomes critically important to increase our understanding of Nitinol fatigue mechanisms beyond 10 7 cycles. In this study, the fatigue behavior of Nitinol wire in rotary bend testing was characterized by experimental methods and computational modeling. Fractures occurred in high strain regions as predicted by computational modeling. Furthermore, fractures beyond 10 7 or 10 8 cycles were observed and seem to have been initiated by nonmetallic inclusions.