Effects of wear, structural supports and transient operating conditions on fluid film lubrication in metal-on-metal hip implants

Effects of wear, structural supports, and transient operating conditions on fluid film lubrication in metal-on-metal hip implants were analyzed. Three different MOM hip implants were taken: a thick-walled acetabular cup (7mm), a metasul bearing with a polyethylene backing underneath a metallic cup, and an original thin-walled McKee-Farrar cup. The geometry modification of the original spherical bearing surfaces due to wear was considered by assuming a spherical worn area, characterized by an angle and a maximum linear wear depth. It was found that the effect of the transient operating condition increased the lubricant film thickness significantly, as compared with the steady-state prediction based on the average load and speed.