Volume 3, Issue 7 (July 2006)
Slip Velocity Direction Impacts Wear in Total Knee Arthropolasty
Total knee arthroplasties are subjected to high slip velocities and constantly changing velocity vector directions, as they mimic the anatomical conditions of the natural joint. Together with fluid film thickness and applied load, the velocity difference between the two bodies defines the amount of energy that is induced into the contact. Particularly for polyethylene (PE), it is known that the angle describing the difference in motion direction is an important variable for material loss. In this study, a wheel-on-flat simulator scenario was used to apply a slip velocity vector with a constant magnitude and changing direction over the length of a polyethylene sample. The difference in vector orientation ranged from zero to 20.4°, while a constant axial load of 1600 N was applied, and the contact area was submersed in physiological testing fluid. After 500k cycles, the surface of the PE specimen was visually examined and scanned with a video-based measurement system to analyze the wear profile. Polishing was the predominant wear pattern, and minor striations were found in the end zone of the wear area. The wear depth increased with higher velocity angles—this relationship appeared to be linear. This study supports earlier publications that reported a correlation between cross-shear motion and wear. The presented experimental results will help in attempts to numerically simulate wear generation.