The wear of PTFE against stainless steel in a multi-directional pin-on-plate wear device

The aim of this work was to see if a multi-directional pin-on-plate wear device was able to reproduce the wear factors reported for hip prostheses which employed polytetrafluoroethylene (PTFE) acetabular cups articulating against stainless steel counterfaces. The influence of type of motion and protein concentration of the bovine serum lubricant on wear, were investigated. Tests involved a four-station pin-on-plate rig, two stations had a standard reciprocation-only motion, while the other two stations had a rotational element added to the test pins. Tests were done at 100, 50, 25, 10 and 0% bovine serum, the remaining lubricant being made up with distilled water. One hundred percent bovine serum was equivalent to a protein content of 52 g/l. Reciprocation plus rotation applied to the test pins produced mean wear factors which increased with protein concentration, as reported for PTFE rubbing against a metal counterface in hip simulators. With reciprocation-only motion, this trend was not clear. At zero protein content, wear was negligible. With reciprocation plus rotation applied to the test pins, wear factors in the range (2.3–5.2)×10−5 mm3/Nm were measured, which compare with a calculated clinical wear factor of 3.7×10−5 mm3/Nm.