title: In vitro assessment of strength, fatigue durability, and disassembly of Ti6Al4V and CoCrMo necks in modular total hip replacements.
abstract: Modularity in total hip replacement offers advantages with regard to biomechanical adjustments and leg lengths. Recently, modular femoral necks were introduced as an added advantage to head modularity permitting further adjustments in femoral version as well as offset and ease of revision. Currently, most necks are made of Ti6Al4V for which cases of in vivo fractures and inseparable neck-stem junctions have been reported. Therefore, we investigated CoCrMo head-Ti6Al4V stem hip replacements with necks made of CoCrMo as an alternative to Ti6Al4V. We compared the two materials with respect to (1) compressive load bearing capacity; (2) fatigue durability; and (3) component distraction. We performed in vitro fatigue-pull-off, microscopy, fatigue durability and compression investigations. The CoCrMo neck showed a load bearing capacity of 18 kN, 38% higher than 13 kN for the Ti6Al4V neck. A fatigue load of 11.2 kN for 1 million cycle failure was achieved with CoCrMo translating into nearly 1000 times longer fatigue life compared to Ti6Al4V necks. The neck-stem distraction force showed large statistical variation and was similar for both neck materials. Overall, the results suggest a superiority of CoCrMo over Ti6Al4V as neck material with regard to mechanical behavior. However, the corrosion behavior was not appropriately assessed and necessitates additional investigations.
authors.affiliation: Department of Mechanical Engineering, University of Ottawa, 161 Louis-Pasteur, Ottawa, ON K1N 6N5, Canada. mnganbe@uottawa.ca
authors.forename: Michel
authors.initials: M
authors.lastname: Nganbe
authors.forename: Usman
authors.initials: U
authors.lastname: Khan
authors.forename: Hakim
authors.initials: H
authors.lastname: Louati
authors.forename: Andrew
authors.initials: A
authors.lastname: Speirs
authors.forename: Paul E
authors.initials: PE
authors.lastname: Beaulé
mesh_terms: D000497:Alloys; D019644:Arthroplasty, Replacement, Hip; D006622:Hip Prosthesis; D006801:Humans; D008422:Materials Testing; D014025:Titanium; D014800:Vitallium
chemical_list: D000497:Alloys; D014800:Vitallium; C031462:titanium alloy (TiAl6V4); D014025:Titanium