Using a patterned microtexture to reduce polyethylene wear in metal-on-polyethylene prosthetic bearing couples

Abstract

The longevity of metal-on-polyethylene prosthetic hip joint bearings, in which a CoCrMo femoral head articulates with a polyethylene liner, is often limited by polyethylene wear and osteolysis caused by polyethylene wear particles. Current approaches to reduce polyethylene wear include improving the mechanical properties of the polyethylene liner, and/or manufacturing ultra-smooth articulating surfaces. In contrast, this experimental work shows that adding a patterned microtexture of concave "dimples" to a polished CoCrMo surface significantly reduces polyethylene wear by promoting the formation of an elastohydrodynamic lubricant film, which reduces contact between the CoCrMo and polyethylene bearing surfaces. Using a gravimetric method to measure polyethylene pin wear during pin-on-disc experiments, it was demonstrated that microtextured CoCrMo caused reduced polyethylene wear compared to polished CoCrMo surfaces. Wear was quantified for different polyethylene materials currently used in commercial prosthetic hip joint bearings, and for several microtexture geometries. It was also documented by correlating polyethylene wear with surface topography measurements that the patterned microtexture reduced contact between the articulating bearing surfaces.

Figure 1

Schematic of five-station pin-on-disc tester. Inset shows detail of polyethylene pin articulating with CoCrMo disc.

Figure 2

Polyethylene wear as a function of number of cycles for (a) UHMWPE GUR 1050, (b) HXPE, and (c) VEXPE UHMWPE, articulating with microtextured and polished CoCrMo discs. The data points show the average of ten wear measurements, whereas the error bars show the extreme wear measurement results.

Figure 3

Polyethylene wear rate as a function of number of cycles for (a) UHMWPE GUR 1050, (b) HXPE, and (c) VEXPE UHMWPE, articulating with microtextured and polished CoCrMo discs

Figure 4

Surface topography of UHMWPE GUR 1050 (a) before a wear experiment, (b) after wear experiment with Disc 4, and (c) with Disc 1.

Figure 5

Average surface roughness R_a before and after wear testing for (a) UHMWPE GUR 1050, (b) HXPE, and (c) VEXPE UHMWPE