Biomedical Engineering Reference
In-Depth Information
7.6 (a) Schematic of the surface modification of Zr alloy to produce Oxinium
bearing surface; (b) microstructure of Oxinium bearing; (c) Oxinium bearings
for total knee arthroplasty; (d) Oxinium femoral head for total hip arthroplasty.
(Courtesy of Smith & Nephew, Memphis, TN.)
modification of the surface of a metal to form a ceramic has been successfully
used in the manufacture of THA and TKA bearings. In this approach, a zir-
conium alloy (Zr±2.5%Nb) is oxidized by thermal diffusion to create a 5±10m
oxidized zirconium layer (Laskin, 2003). The ZrO
2
-based ceramic surface forms
the articulating surface of the femoral head, whereas the metal substrate pro-
vides the strength and ductility to resist fracture (Fig. 7.6). Oxidized zirconium,
manufactured by Smith & Nephew, Memphis, TN, under the trade name
Oxinium, has had a successful clinical experience when used as an articulating
bearing against UHMWPE, providing favorable reduction in wear when com-
pared with CoCr (Good et al., 2003; Spector et al., 2001). However, oxidized
zirconium is not intended for use in hard-on-hard bearing applications.
Furthermore, recent reports (Evangelista et al., 2007; Kop et al., 2007) have
expressed concerns about surface damage or breakdown of the ZrO
2
-based
surface on Oxinium femoral heads, particularly subsequent to dislocation.
Damage features included general scratching, indentation, and large gouges,
