title: Fretting crevice corrosion of stainless steel stem-CoCr femoral head connections: comparisons of materials, initial moisture, and offset length.
abstract: Modular tapers continue to be used in a wide variety of orthopedic implants. In this study, stainless steel (ASTM F-1568) femoral hip stems combined with Co-Cr-Mo alloy heads (SS/CoCr) were tested in an in vitro fretting corrosion test set-up to assess the propensity for mechanically assisted corrosion. Three different aspects of the modular design were evaluated in this study: (1) material combination compared to CoCr/CoCr, (2) wet versus dry assembly for SS/CoCr couples, and (3) 0- and 6-mm head offset for SS/CoCr couples. Fretting corrosion tests over a range of cyclic loads up to 3300 N were performed, and continuous cyclic loading at 3300 N for 1 M cycles were performed on each group (n = 5). Fretting micromotion was measured as a function of cyclic load on select couples to detect the nature and extent of motion present. The results showed that SS/CoCr couples were more susceptible to fretting corrosion than CoCr/CoCr couples, that dry assembly does not prevent fretting corrosion from taking place but raises the onset load, and that 6-mm offset heads had higher visual evidence of fretting damage but showed mixed statistical results in terms of onset loads and OCP shifts and currents compared to the 0-mm offset samples. Current and voltage excursions over 1 million cycles tended to diminish towards their unloaded control levels but did not fully recover until cyclic loading ceased. Micromotion measurements indicated fretting motions in the range of 10-25 microm where 0-mm heads tended to piston on the trunion, while 6 mm heads tended to rock.
authors.affiliation: Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, New York 13244, USA. gilbert@syr.edu
authors.forename: Jeremy L
authors.initials: JL
authors.lastname: Gilbert
authors.forename: Manav
authors.initials: M
authors.lastname: Mehta
authors.forename: Bryan
authors.initials: B
authors.lastname: Pinder
mesh_terms: D002857:Chromium / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D003343:Corrosion; D004563:Electrochemistry; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005270:Femur Head / Q000473:pathology*; D006622:Hip Prosthesis; D006801:Humans; D008422:Materials Testing; D009068:Movement; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013193:Stainless Steel / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D002857:Chromium; D013193:Stainless Steel; D003035:Cobalt