Mechanical changes linked to embrittlement at the wear surface ofpolyethylene implants in hip joints

Abstract

A study of microhardness at the wear surface of polyethylene implants before and after use is reported. The microhardness values supportprevious electron microscopic observations of an embrittled region extending into used implants by showing that, after use, the hardness ofpolyethylene implants increases above the initial value the nearer the wear surface is approached. It is shown that these changes accompany ahardening of the surface layer and are related to an increase in the crystallinity of the polymer. The increasing hardness towards the edge ofthe concave surface of the implant is discussed in terms both of the local variation of crystallinity and changes in the interlamellar regions.