Influence of test specimen fabrication method and cross-section configuration on tension-tension fatigue life of PMMA bone cement.

Different cyclic loading modes have been used in in vitro fatigue studies of PMMA bone cement. It is unclear which loading mode is most appropriate from the perspective of the in vivo loading experienced by the cement in a cemented arthroplasty. Also, in different in vitro fatigue studies, different test specimen configurations have been used. The present work considers the influence of test specimen fabrication method (direct moulding vs moulding followed by machining) and cross-section shape (rectangular vs circular) on the tension-tension fatigue performance of two bone cement brands (SmartSet GHV and CMW1), under force control conditions. Two trends were consistent: 1) for each of the cements, for moulded specimens, a longer fatigue life was obtained with circular cross-sectioned specimens and, 2) for either rectangular or circular CMW1 specimens, a longer fatigue life was obtained using machined specimens. A comparison of the present results to those reported in our previous work on fully-reversed tension-compression loading under force control showed that, regardless of the test specimen fabrication method or cross-section configuration used, the fatigue life was considerably shorter under tension-compression than tension-tension loading. This finding highlights the fact that the presence of the compression portion in the loading cycle accelerates fatigue failure.