Development and validation of a second-generation metal-on-metal bearing: laboratory studies and analysis of retrievals.

This paper summarizes hip simulator and retrieval studies that were done to optimize 1 design of a second-generation metal-on-metal hip replacement. It was determined that clearance is the first key parameter controlling wear behaviour. The clearance should be as small as possible while as large as necessary to avoid any equatorial contact leading to clamping of the articulation. The minimum clearance should be investigated for each different design. Carbon concentration should be in the range 0.20-0.25% as high carbon concentration alloys have systematically a lower wear rate than low carbon alloys. The wear of clinically retrieved implants confirms the predicted low wear of this implant and confirms the importance of the clearance and the type of cobalt-chrome alloy.