Material dependent fretting corrosion in spinal fusion devices: Evaluation of onset and long-term response.

Posterior spinal fusion implants include number of interconnecting components, which are subjected to micromotion under physiological loading conditions inducing a potential for fretting corrosion. There is very little known about the fretting corrosion in these devices in terms of the minimum angular displacement (threshold) necessary to induce fretting corrosion or the amount of fretting corrosion that can arise during the life of the implant. Therefore, the first goal was to evaluate the threshold fretting corrosion in three anatomical orientations and second the long-term fretting corrosion for the three different material types of spinal implants under physiological loading conditions. In threshold test, axial rotation exhibited highest changes in open circuit potential (V-OCP in mV) and induced fretting currents (I-frett in mu A) for cobalt chrome (V-OCP: 24.71 +/- 5.53; I-frett: 4.03 +/- 0.51) and stainless steel (V-OCP: 28.21 +/- 6.97; I-frett: 2.98 +/- 0.42) constructs whereas it was flexion-extension for titanium constructs (V-OCP: 4.51 +/- 2.48; I-frett: 0.38 +/- 0.12). Long-term test indicated that the titanium (V-OCP:101 +/- 0.06; I-frett: 0.07 +/- 0.02) and cobalt chrome (V-OCP: 140.67 +/- 0.04; I-frett: 0.12 +/- 0.05) constructs were more resistant to the fretting corrosion compared to stainless steel (V-OCP: -135.33 +/- 0.31; I-frett: 2.63 +/- 1.06). (c) 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2858-2868, 2018.