Analysis of push-out test data based on interfacial fracture energy

Push-out testing is frequently used to assess the interfacial shear strengt h developed at a bone-biomaterial interface during in vivo experiments. The aim of the present research was to assess the in vivo performance of a nov el substrate/coating combination and to introduce a more rigorous fracture mechanics analysis of the push-out test data. An adhesively bonded hydroxya patite (HA), and a Ti-6Al-4V alloy plasma sprayed with HA, were implanted i n female New Zealand white rabbits for up to 6 months in duration. After de ath, push-out tests were carried out and the shear strength was calculated in the conventional way, together with microscopical examination of crack p aths. A finite element model was drawn up representing four potential failu re mechanisms. The measured "failure shear strengths" in conventional analy sis were approximately equal for the two coatings. However, J(C) at failure calculated from the model was 210 J m(-2) at the novel adhesively bonded H A/bone interface and 5 J m(-2) at a conventional titanium/plasma-sprayed HA interface. The conventional shear strength approach is strongly test depen dent, and we believe that the fracture energy approach represents a more ri gorous analysis of the real failure criterion in the implant/host tissue st ructure. (C) 1999 Kluwer Academic Publishers.