A hip joint simulator study of the performance of metal-on-metal joints: Part II: design.

The separate and combined roles of head diameter and clearance were studied experimentally in simulator tests and also theoretically. Head diameters ranging from 16-54 mm and various clearances were studied. Effective mixed-film lubrication achieved through careful design and manufacture greatly reduced wear. The running-in wear volumes were very low for larger-diameter heads and smaller clearances; but because the subsequent steady-state wear rate was much smaller than the running-in wear rate, the former contributed significantly to the total volume of wear debris even over very long periods of time. The design study has shown that head diameters should be as large as possible and diametral clearances as low as practicable, to ensure that the joints operate well into the mixed lubrication regime.