The Influence of Stem Design and Fixation Methods on the Lifetime of Total Hip Replacement

Total hip replacement is one of the most common surgical procedures performed both in the UK
and worldwide, with aseptic loosening cited as the primary reason for revision. Aseptic loosening
is attributed to the wear debris generated by wear of the components. Recently, as great progress has been achieved in reducing wear at the head–cup interface, there has been a shift of research interest to other load bearing surfaces.

The main purpose of this thesis is to study fretting wear mechanisms at the polished femoral stem–bone cement interface.

The initial studies have investigated the bond strength at the stem–cement interface using seven
brands of bone cement and femoral stems with different surface finishes. It can be confirmed that debonding at this interface is inevitable, which subsequently facilitates generation of fretting wear on the stem surface.

A new test methodology has been developed to reproduce fretting wear clinically seen on polished stems through in vitro wear simulations, and it shows great success in comparison with previous attempts. In addition, migration of the stem within the cement mantle has been investigated, and it has been indicated that the simulation setup more realistically mimics clinical situations.

The influence of two factors on generation of fretting wear, i.e. the duration of in vivo service of the hip implant and bone cement brand, has been studied. A potential fretting wear initiator that is concerned with polymerisation of bone cement has been identified, with both experimental (the results of wear simulations) and theoretical (finite element analysis) evidence being provided.

In summary, the overall contribution of this research is that it has gained a deep insight into the fretting wear mechanism between polished femoral stem and bone cement.