Friction-induced squeaking has been reported in 1–20% of patients who have a ceramic on ceramic total hip replacement, which is a subject of annoyance. Friction induced stick-slip phenomenon is the driving force behind squeaking. Stick-slip occurs when the film lubrication is broken. Fluid film lubrication is a function of sliding speed, lubricating fluid viscosity, bearing roughness, clearance, and contact pressure. A breakdown of fluid film lubrication may result from edge loading, presence of third bodies (wear particles) during articulation, damage to the articular surface (increased roughness), mismatched bearing diameters, etc. In the present study, influence of variation in relative densities of the biofluid and femoral head is mathematically investigated when the spheres are initially subjected to an impulse (start-up condition: initial contact to pre-swing phase of the gait cycle). The parametric analysis also looks at the influence of initial impulse speed, and time of approach of the femoral head to the outer shell.

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