The effect of acetabular cup position on wear of a large-diameter metal-on-metal prosthesis studied with a hip joint simulator

Clinically, malposition of the acetabular cup in large-diameter metal-on-metal prosthetic hip designs is associated with high wear, adverse reaction to metal debris and early failure. A steep angle of the cup (>60°) may lead to poor tribological performance. Large-diameter CoCr-on-CoCr prostheses were run in the HUT-4 hip joint simulator so that a steep angle was included. With a correct position, the tribological behaviour was excellent, the wear rate being 0.1 mm3/106 cycles. In the steepest position, lubrication failed and the wear rate was two orders of magnitude higher. This study stresses the importance of rigorous pre-clinical testing.

► Clinical failures of large-diameter metal-on-metal hip prostheses have occurred.
► Failures are associated with a steep angle of acetabular cup causing high wear.
► Correct and steep angles were compared in a hip joint simulator.
► Low wear took place with correct position but steep angle caused a high wear rate.
► Rigorous pre-clinical wear testing is important in preventing clinical disasters.