Friction between a polyethylene pin and a microtextured CoCrMo disc, and its correlation to polyethylene wear, as a function of sliding velocity and contact pressure, in the context of metal-on-polyethylene prosthetic hip implants

Abstract

The longevity of metal-on-polyethylene prosthetic hip implant bearings, in which a polished CoCrMo femoral head articulates with a polyethylene liner, is limited by mechanical instability or inflammation resulting from osteolysis caused by polyethylene wear debris. We use pin-on-disc experiments to measure friction and wear of a polyethylene pin that articulates with different microtextured CoCrMo surfaces, covering a wide range of operating conditions including sliding velocity and contact pressure. We determine how the lubrication regime changes as a function of operating conditions, and show that the microtexture accelerates the transition from boundary to elastohydrodynamic lubrication. Additionally, we illustrate that the microtexture could enable tailoring the hip implant to the specific patient needs based on activity level, gender, and age.

Keywords: Microtexture; patient-specific; prosthetic hip implant.

Figure 1

Schematic of single-station POD tester. Inset shows detail of polyethylene pin articulating with CoCrMo disc.

Figure 2

Friction coefficient between the virgin polyethylene pins and the CoCrMo Discs 1–6 under in-vivo prosthetic hip implant operating conditions versus sliding parameter S.

Figure 3

Friction coefficient of virgin polyethylene pins articulating with Disc 1 and Disc 4 versus time, under two extreme in-vivo operating conditions: (1) contact pressure 2 MPa, cycle frequency 1.0 Hz (low S), and (2) contact pressure 1 MPa, cycle frequency 1.8 Hz (high S).

Figure 4

Friction coefficient as a function of polyethylene wear rate for three types of retrieved polyethylene pins after 2 million wear cycles (GUR 1050 UHMWPE, HXPE, and VEXPE) articulating with microtextured CoCrMo discs in the elastohydrodynamic/hydrodynamic lubrication regime. Linear regression and R² value calculated for each retrieved polyethylene pin type is also shown.