Abstract
Introduction
MDM implants can enhance stability in total hip replacement (THR), but complications include malseated liners and corrosion between the cobalt-chrome liner and titanium acetabular shell increased systemic metal ion levels. The liner-shell junction has the potential for fretting corrosion, and the corrosion could be exacerbated in malseated liners. We determined the potential for fretting corrosion in malseated versus well-seated liners using a mechanical electrochemical corrosion chamber.
Methods
Four pristine MDM liners and shells were tested. Two liners were well-seated into their shells; two were canted at 6°. The liner-shell couples were assembled with a 2kN force after wetting the surfaces to promote a crevice environment conducive to corrosion. Couples were fixed in an electrochemical chamber at 40° inclination/20° anteversion to the load axis. The chamber was filled with phosphate buffered saline and setup as a three-electrode configuration: the shell as the working, a saturated calomel electrode as the reference, and a carbon rod as the counter electrode. A potentiostat held the system at −50mV throughout testing. After equilibration, couples underwent cyclic loading of increasing magnitudes from 100 to 3400N at 3 Hz. Fretting current was measured throughout, and the onset load for fretting was determined from the increase in average current.
Results
Well-seated liners showed lower fretting current values at all peak compressive loads greater than 800 N (p<0.05). Canted liners demonstrated a fretting onset load of 2400 N, and fretting currents at greater than 2400 N were larger than those at lower peak compressive loads (p<0.05).
Conclusion
The clinical consequences of MDM liner malseating remain unknown, but our results demonstrate earlier fretting current onset at lower peak loads when compared to well-seated liners. The onset loads were consistent with physiologic loads for daily activities. Our findings are significant given the potential for metallosis and adverse local tissue reactions.
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