title: Effect of mixed alloy combinations on fretting corrosion performance of spinal screw and rod implants.
abstract: Spinal implants are made from a variety of materials to meet the unique mechanical demands of each application. However, the medical device community has raised concern about mixing dissimilar metals in an implant because of fear of inducing corrosion. There is a lack of systematic studies on the effects of mixing metals on performance of spinal implants, especially in fretting corrosion conditions. Hence, the goal was to determine whether mixing stainless steel (SS316L), titanium alloy (Ti6Al4V) and cobalt chromium (CoCrMo) alloy components in a spinal implant leads to any increased risk of corrosion degradation. Spinal constructs consisting of single assembly screw-connector-rod components were tested using a novel short-term cyclic fretting corrosion test method. A total of 17 alloy component combinations (comprised of SS316L, Ti6Al4V-anodized and CoCrMo alloy for rod, screws and connectors) were tested under three anatomic orientations. Spinal constructs having all SS316L were most susceptible to fretting-initiated crevice corrosion attack and showed higher average fretting currents (∼25 - 30 µA), whereas constructs containing all Ti6Al4V components were less susceptible to fretting corrosion with average fretting currents in the range of 1 - 6 µA. Mixed groups showed evidence of fretting corrosion but they were not as severe as all SS316L group. SEM results showed evidence of severe corrosion attack in constructs having SS316L components. There also did not appear to be any galvanic effects of combining alloys together. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1169-1177, 2017.
authors.affiliation: Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, New York.|Syracuse Biomaterial Institute, Syracuse University, Syracuse, New York.
authors.forename: Sachin A
authors.initials: SA
authors.lastname: Mali
authors.affiliation: Medtronic Spinal and Biologics, Memphis, Tennessee.
authors.forename: Vaneet
authors.initials: V
authors.lastname: Singh
authors.affiliation: Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, New York.|Syracuse Biomaterial Institute, Syracuse University, Syracuse, New York.
authors.forename: Jeremy L
authors.initials: JL
authors.lastname: Gilbert
mesh_terms: D000497:Alloys; D001863:Bone Screws; D003343:Corrosion; D006801:Humans; D020007:Implants, Experimental; D013131:Spine; D013193:Stainless Steel; D014025:Titanium; D014800:Vitallium
chemical_list: D000497:Alloys; D013193:Stainless Steel; D014800:Vitallium; C031462:titanium alloy (TiAl6V4); D014025:Titanium
keywords: corrosion; fretting corrosion; mixed alloy corrosion; performance testing; spinal screw-connector-rod implants