Friction and wear - Orthopaedic Biomaterials in Research and Practice - page 274

FIGUre 11.13 Wear of femoral head of thr (ti6ai4v).

Although it apparently occurs quite rarely, it produces sufficient volumes
of wear debris to require revision surgery for pain relief.
Polymers wear at much higher rates than metals (see Table 11.3),
and large material removal may occur, as seen in the UHMWPE tibial
liner shown in Figure 11.14. This damage reflects both wear and creep.
Therefore, in such cases of polymeric wear, care must be taken to dis-
tinguish between wear and creep; microstructural examination of the
material below the surface may be necessary to resolve the relative con-
tributions when such questions arise.
When third-body wear occurs in a joint replacement, it is frequently
accompanied by the presence of embedded debris in the polymeric com-
ponent (metal, poly(methyl methacrylate), bone chips, etc.) and asso-
ciated score marks on the metal component. Figure 11.15 shows the
appearance of a UHMWPE acetabular liner cup removed after 12 years.
The darker spot near the top is a fragment of bone, while wear, delami-
nation, and local fatigue breakdown are all visible as well.

FIGUre 11.14 (See color insert.) Wear of tibial plateau (uhmWPe).