In vitro wear simulation on the RandomPOD wear testing system as a screening method for bearing materials intended for total knee arthroplasty

Abstract

The 16-station RandomPOD wear test system, previously validated for prosthetic hip wear, was used in the simulation of knee wear mechanisms with a ball-on-flat test configuration. This consisted of a CoCr pin with a ground and polished spherical bearing surface (radius 28mm) against a conventional, gamma-sterilized UHMWPE disk in serum lubrication. The biaxial motion, consisting of x and y translations, and the load was non-cyclic. Relative to the disk, the center of contact wandered within a circle of 10mm diameter, and the average sliding velocity was 15.5mm/s (ranging from 0 to 31mm/s). The load varied non-cyclically between 0 and 142N (average 73N). In the 60-day test with 16 similar wear couples, moderate adhesive wear, the principal wear mechanism of a well-functioning prosthetic knee, dominated. This showed as a burnished, circular wear mark (diameter 13.2mm, area 137mm2). The wear factor was 2.04±0.03×10−6mm3/Nm (mean±95 percent confidence limit). For the first time a truly multidirectional, realistic and uniform, large capacity pin-on-disk simulation of knee wear mechanisms was implemented.