Multi-axial fatigue failure of orthopedic bone cement - experiments with tubular specimens.

Bone cement is subjected to multi-axial cyclic loading when used to fixate orthopedic prostheses for joint arthroplasty. In this study, tubular specimens of poly(methylmethacrylate) (PMMA) bone cement are subjected to internal pressure and cyclic axial loading to ascertain the influence of multi-axial loading on fatigue life. As expected, it was found that the probability of survival of specimens under multi-axial loading was very much reduced relative to specimens loaded uniaxially. Furthermore, the variability of the fatigue life was increased by multi-axial loading. In conclusion, the results point to the importance of characterizing the behavior of bone cements under the multi-axial fatigue experienced in vivo, and of the importance of accounting for the multi-axial stress state when predicting implant longevity.