Adhesion and reliability of interfaces in cemented total joint arthroplasties

Debonding of the prosihctielpolymelhylmcthacrylate interface has been implicated in the initial failure process of cemented total hip arthroplasties. However, little quantitative understanding of the debonding process, as well as of the optimum interface morphology for enhanced resistance to debonding, exists. Accordingly, a fracture-mechanics approach has been used in which adhesion at the interface is characterized in terms of the interface fracture energy. G (J/m²), and shown to be a strong function of the morphology, debonding length, and loading mode of the interface. Double-cantilever-beam and four-point-flexure fracture-mechanics samples containing four clinically relevant prosthetic surface preparations were prepared to survey a range of interface roughness and loading modes. Adhesion at the interface could not be characterized with a single-valueu material property but was found to exhibit resistance-curve behavior in which resistance to debonding increased with both the initialdebond extension and the roughness of the interface. Values of debonding. initiation. G_o, were relatively insensitive to the roughness of the surface and the loading mode, whereas steady-state fracture resistance of the interface. G_ss, increased significantly with the roughness and shear loading of the interface. These quantitative results suggest that debonding of the prosthetic/polymethyl methacrylate interface may be primarily attributed to surface interactions such as interlocking and the pullout of rough asperities thai occur behind the debond tip. A simple mechanics analysis of such interactions was performed and revealed increases in the fracture resistance of the interface that were consistent with experimentally measured values.