Influence of cup orientation on the wear performance of metal-on-metal hip replacements

Abstract

There are a number of factors that determine the overall outcome of total hip replacement (THR) surgery, some of which appear to be related to the surgical procedure. In particular, the inclination angle at which the acetabular component is placed has been reported to influence the long-term successful performance of THR. The present study assessed the influence of cup orientation on the wear of 40 mm diameter metal-on-metal (MoM) hip bearings tested in a hip simulator. The bearings had a mean radial clearance of 150 μm; the cups oriented at 35°, 50°, and 60° to the horizontal were loaded for up to 6×106 cycles. In each test the wear rates during the run-in phase were higher than in the steady state phase; the wear rates during the run-in phase were not significantly different for each cup orientation. However, at cup angles of 50° and 60°, the steady state wear rates were 0.69 mm3/106 cycles and 1.7 mm3/106 cycles respectively, significantly higher than at 35° (0.24 mm3/106 cycles). The results indicated that larger cup inclination angles not only move the position of the wear scar but also, more significantly in MoM bearings, increase the wear rates and total wear volume generated.