Biomedical Engineering Reference
In-Depth Information
Fig. 5.38
TiN Ceramic Coated Titanium Alloy B-P Femoral Stem
TiN ceramic finished stems provide enhanced biocompatibility. TiN is inert in
vivo [143]. It shields the surface of the implant, particularly the porous coated region
with its high surface area, against metallic ion release. The extreme hardness, and
abrasion resistance, of TiN ceramic coatings has been shown to eliminate the
metallosis observed in both uncoated titanium and Co-Cr alloy prostheses [144, 145].
This is because much less abrasion debris is generated, and the debris is inert and
consists of nontoxic Ti and N ions. As a result, TiN ceramic finished titanium stems
represent mechanically and biologically compatible femoral stems.
Retrieved specimens of femoral stems with modular heads have shown a
disturbing degree of corrosion at the taper connection interface. This corrosion is the
result of micro motion in the interface (fretting corrosion) and is present in both
mixed and similar metal combinations [146. 147].
Much of the micro motion in this interface is the result of excessive tolerances
used in the manufacture of the tapers. The orthopaedic implant industry generally
