TENSILE-STRENGTH OF THE CEMENT-BONE INTERFACE DEPENDS ON THE AMOUNT OF BONE INTERDIGITATED WITH PMMA CEMENT

An experimental investigation was performed to (1) determine the gener al mechanical behavior and in particular, the post-yield behavior of t he cement-bone interface under tensile loading, (2) determine where in terface failure occurs, and (3) determine if the mechanical properties of the interface could be related to the density of bone at the inter face and/or the amount of cement-bone interdigitation. Seventy-one cem ent-bone test specimens were machined from human proximal femurs that had been broached and cemented using contemporary cementing techniques . The amount of cement-bone interdigitation was documented and the qua ntitative computed tomography equivalent mineral density (QCT density) of the bone with cement was measured. Specimens were loaded to failur e in tension under displacement control and exhibited linear elastic b ehavior with some reduction in stiffness until the peak tensile stress was reached (1.28 +/- 0.79 MPa). A substantial amount of strain softe ning (negative tangent stiffness) with an exponential-type decay was f ound after the peak stress and continued until there was complete debo nding of the specimens (at 0.93 +/- 0.44 mm displacement). Interfacial failure most often occurred at the extent of cement penetration into the bone (56% of specimens) or with small spicules of cement left in t he bone (38% of specimens). The results showed that the post-yield ten sile behavior contributes substantially to the energy required to caus e failure of the cement-bone interface, but the post-yield behavior wa s not well correlated with the amount of interdigitation or density of bone. Linear regression analysis revealed a moderate (r(2) = 0.499, p < 0.0001) positive relationship between the tensile strength of the c ement-bone interface and the quantity of bone interdigitated with the cement. (C) 1997 Elsevier Science Ltd.