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

A study of microhardness at the wear surface of polyethylene implants befor e and after use is reported. The microhardness values support previous elec tron microscopic observations of an embrittled region extending into used i mplants by showing that, after use, the hardness of polyethylene implants i ncreases above the initial value the nearer the wear surface is approached. It is shown that these changes accompany a hardening of the surface layer and are related to an increase in the crystallinity of the polymer. The inc reasing hardness towards the edge of the concave surface of the implant is discussed in tl:rms both of the local variation of crystallinity and change s in the interlamellar regions. (C) 2000 Elsevier Science Ltd. All rights r eserved.