The influence of phospholipid concentration in protein-containing lubricants on the wear of ultra-high molecular weight polyethylene in artificial hip joints

There is considerable interest in the wear of polyethylene and the resultin g wear-debris-induced osteolysis in artificial hip joints. Proteins play an important role as boundary lubricants in vivo in the pseudosynovial fluid, and these are reproduced in in vitro tests through the use of bovine serum . Little is known, however, about the effect of phospholipid concentrations within proteinaceous solutions on the wear of ultra-high molecular weight polyethylene (UHMWPE). The effects of protein-containing lubricants with 0. 05, 0.5 and 5 per cent (w/v) phosphatidyl choline concentrations on the wea r of ultra-high molecular weight polyethylene (UHMWPE) were compared with 2 5 per cent (v/v) bovine serum which had 0.01 per cent (w/v) lipid; the effe cts were compared in a hip joint simulator with smooth (n = 4) and scratche d (n = 3) femoral heads. The control bovine serum lubricant produced UHWMPE wear of 55 and 115 mm(3)/10(6) cycles on the smooth and rough heads respec tively. The increased phospholipid concentration significantly reduced the wear rate. At the higher concentration (5%;, w/v phosphatidyl choline) the average wear was reduced to less than 2 mm(3)/10(6) cycles. Even with the r elatively low concentrations of 0.05% w/v phosphatidyl choline the wear was reduced by at least threefold compared with the bovine serum tests for bot h the smooth and rough femoral heads. There may be considerable differences in the phospholipid concentrations in patients' synovial fluid and this is highly likely to produce considerable variation in wear rates. In vitro, d ifferences in the phospholipid concentration of lubricants may also cause v ariation in wear rates between different simulator tests.