Relationship Between Fatigue Parameters and Fatigue Crack Growth in PMMA Bone Cement

Poly(methyl methacrylate) (PMMA) bone cement is used to anchor the majority of total joint replacements (TJRs). Many brands of cement are used, both with and without the addition of antibiotics to reduce the risk of infection. The present study involved determination of various parameters in tensile fatigue loading: (1) energy absorbed (U) vs number of loading cycles (N) and creep strain (epsilon) vs N, during fatigue tests on specimens of an antibiotic-containing cement (SmartSet GHV) and a plain cement (CMW1) and (2) crack length (a) vs fatigue loading cycles (N) and crack growth rate (da/dN) vs Mode I stress intensity factor range (Delta K-1), during Fatigue Crack Propagation (FCP) tests. In the fatigue tests, four different sample types (round, machined; round, directly moulded; rectangular, machined, and rectangular, directly moulded) and tension-tension loading were used. In the FCP tests, compact tension specimens under tension-tension loading were used. It was found that there were limited effects of sample type, except at the highest stress levels, but that these two cements had different rates of crack propagation. These differences were reflected in the fracture surfaces with SmartSet GHV showing accumulation of opacifier around the particles and crack progression around the initial beads, while for CMW1 the opacifier was evenly distributed and the cracks went through the initial beads.