Quantification of the Contact Area at the Head-Stem Taper Interface of Modular Hip Prostheses.
Corrosion of modular taper junctions of hip implants may be associated with clinical failure. Taper design parameters, as well as the intraoperatively applied assembly forces, have been proposed to affect corrosion. Fretting corrosion is related to relative interface shear motion and fluid ingress, which may vary with contact force and area. It was hypothesised in this study that assembly forces modify the extent and distribution of the surface contact area at the taper interface between a cobalt chrome head and titanium stem taper with a standard threaded surface profile. Local abrasion of a thin gold coating applied to the stem taper prior to assembly was used to determine the contact area after disassembly. Profilometry was then used to assess permanent deformation of the stem taper surface profile. With increasing assembly force (500 N, 2000 N, 4000 N and 8000 N) the number of stem taper surface profile ridges in contact with the head taper was found to increase (9.2±9.3%, 65.4±10.8%, 92.8±6.0% and 100%) and the overall taper area in contact was also found to increase (0.6±0.7%, 5.5±1.0%, 9.9±1.1% and 16.1±0.9%). Contact was inconsistently distributed over the length of the taper. An increase in plastic radial deformation of the surface ridges (-0.05±0.14 μm, 0.1±0.14 μm, 0.21±0.22 μm and 0.96±0.25 μm) was also observed with increasing assembly force. The limited contact of the taper surface ridges at lower assembly forces may influence corrosion rates, suggesting that the magnitude of the assembly force may affect clinical outcome. The method presented provides a simple and practical assessment of the contact area at the taper interface.
Institute of Biomechanics, TUHH Hamburg University of Technology, 21073 Hamburg, Germany.
Florian
F
Witt
Institute of Biomechanics, TUHH Hamburg University of Technology, 21073 Hamburg, Germany.
Julian
J
Gührs
Institute of Biomechanics, TUHH Hamburg University of Technology, 21073 Hamburg, Germany.
Michael M
MM
Morlock
Institute of Biomechanics, TUHH Hamburg University of Technology, 21073 Hamburg, Germany; Faculty of Life Sciences, HAW Hamburg University of Applied Sciences, Ulmenliet 20, 21033 Hamburg, Germany.
Nicholas E
NE
Bishop
D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D002858:Chromium Alloys / Q000737:chemistry; D003343:Corrosion; D006622:Hip Prosthesis; D008422:Materials Testing / Q000295:instrumentation; D011474:Prosthesis Design / Q000295:instrumentation*; D011475:Prosthesis Failure; D013314:Stress, Mechanical; D014025:Titanium / Q000737:chemistry
D002858:Chromium Alloys; D014025:Titanium