Wear simulation of UHMWPE for total hip replacement with a multidirectional motion pin-on-disk device: effects of counterface material, contact area, and lubricant.

Abstract

The wear of nonirradiated ultra-high molecular weight polyethylene (UHMWPE) was studied with a circularly translating pin-on-disk (CTPOD) device. With this simple device, the wear of the acetabular cup is simulated. Two shapes of a polyethylene pin were used: flat wear faces of 3.0 and 8.9 mm in diameter. The load was always 70.7 N. Tests were done against stainless steel plates in serum, albumin, and gamma-globulin lubricants and against alumina plates in serum. With 3.0-mm-in-diameter wear faces, the wear factors were an order of magnitude lower than the average clinical wear factors of polyethylene acetabular cups. With 8.9-mm-in-diameter wear faces, the wear factors and wear mechanisms were consistent with clinical ones. The mean wear factor against stainless steel in serum was 1.46 times higher than that against alumina, and the difference was statistically significant. The mean wear factors in albumin and gamma globulin were close to that in serum; the differences were not statistically significant. The results indicate that albumin and gamma globulin are the fractions of synovia that influence the wear of polyethylene. A practical test parameter combination for the CTPOD device has now been established for future studies of modified and new materials and of lubricants.