Quantitative measurement of the stresses induced during polymerisation of bone cement

When bone cement cures, residual stresses due to bulk and thermal shrinkage will result. Present finite element (FE) simulations of implanted constructs often do not account for these stresses as an initial condition; this may lead to overestimations of the fatigue life of the cement. In the present study, an instrumented stem equipped with strain gauges and a thermocouple was employed to experimentally quantify the residual stresses induced as a result of bone cement curing within a simulated bone/cement/stem construct. Residual stresses as high as 10 MPa were observed in the cement mantle. Residual stresses of this magnitude are potentially high enough to initiate damage within the cement mantle or at the stem/cement interface immediately post-implantation. The acoustic emission technique has demonstrated that cracking and sliding mechanisms are occurring during curing, resulting in partial relaxation of these stresses. The implications for FE simulations of the implanted construct are discussed.