An experimental and computational investigation of bone cement residual stresses

Hip arthroplasty is a common orthopaedic procedure with considerable success in alleviating hip joint pain and disability. To transfer loads from the prosthesis to the contiguous bone, self-curing polymethyl methacrylate, often referred to as bone cement, is routinely used. Residual stresses due to shrinkage of the bone cement during and after polymerisation have been implicated in the formation of cement mantle cracks before any functional loading. Contemporary cemented hip arthroplasties involve mixing the bone cement under vacuum and applying bone cement pressurisation in situ. However vacuum-mixed bone cement has been linked with increased cement shrinkage and theoretically linked with greater residual stress. In this thesis, experimental work was performed to investigate the effect of vacuum mixing and pressurisation with respect to bone cement residual stress. Also, two commercial brands of bone cement were compared against each other. Results revealed that vacuum mixing did not appreciably alter the residual stress levels compared with cement mixed under atmospheric conditions. Likewise, negligible residual stress difference was measured between CMW® 1 Gentamicin and SmartSet® HV Gentamicin bone cements. However, pressurisation of the curing bone cement mass had a significant effect on the residual stress magnitudes. Finite element analysis was implemented to quantify the bone cement residual stresses for the experimental construct. Differential scanning calorimetry and dilatometry experimentation was performed to quantify the bone cement’s exotherm and linear coefficient of thermal expansion properties respectively. Both the transient thermal and residual stress predictions were directly comparable with the experimental measurements. Utilising the same finite element methodology, the transient thermal and residual stresses were predicted for a representative in vivo scenario. The representative in vivo stresses for the rehabilitation activity of walking was also predicted. Predictions revealed the residual stresses were significant and should be included to establish the cement mantle stress magnitude and distribution for the early portion of the artificial hip replacement lifetime