The apparent fracture toughness of acrylic bone cement: effect of three variables.

In cemented arthroplasties, pores are almost invariably present at one or more of the so-called 'weak-link' zones (namely, the bone-cement interface, the cement mantle and the cement-implant interface). In the clinical milieu, arthroplasties are frequently subjected to cyclical loading. These conditions underscore the significance of the apparent fracture toughness (KISR) of the cement. The present work is an investigation of the effect of three variables on KISR of three commercial formulations of bone cement (namely, CMW3, PalacosR and Osteopal) measured using straight-sided chevron notched short rod specimens. For CMW3, the effect of mixing method was studied, with all cement constituents having been stored at ambient laboratory environment prior to being mixed. The highest KISR was obtained from material that was obtained from exposing the cement constituents to a passive vacuum for 20 s and then mixing them in a machine that subjected them to simultaneous mechanical mixing and centrifugation. For Palacos R, the effects of two variables [storage temperature of the cement constituents prior to being mixed (4 degrees C versus 21 degrees C) and mixing method (hand mixing versus vacuum mixing)] (taken individually) were studied. It was found that only mixing method exerts a significant effect on KISR. When room-temperature stored constituents were vacuum mixed, the KISR values for a low-viscosity cement (Osteopal) and a medium-viscosity cement of very similar composition (Palacos R) are not significantly different, indicating that the fracture resistance of bone cement is influenced more by its composition than its viscosity.