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The long-term fixation of cemented femoral components may be jeopardised by the presence of a fibrous tissue layer at the bone–cement interface. This study used both experimental and finite element (FE) methods to investigate the load transfer characteristics of two types of cemented hip replacements (Lubinus SPII and Mu¨ller-Curved) with a fibrous tissue layer.The experimental part investigated six stems of each type, where these were implanted in composite femurs with a specially selected silicone elastomer modelling the soft interfacial layer. Two fibrous tissue conditions were examined: a layer covering the full cement mantle, representing a revision condition; and a layer covering the proximal portion of the cement mantle, representing a non-revised implant with partial debonding and fibrous tissue formation. The FE method was used to model the full fibrous tissue layer condition, for both implants. The layer was modelled as a homogeneous, linearly isotropic material. A cross-comparison was performed of the experimental and FE findings.Agreement between experimental and FE models was verified to be within 15%. Varying the stiffness parameter of the FE soft tissue layer had little influence on the cortical bone strains, though had considerable effect on the cement strains. Stress shielding occurred for both stems under both fibrous tissue conditions, with the greatest reduction around the calcar. However, the cortical bone strains were generally larger than those for the equivalent well-fixed stems. The fibrous tissue layer was not found to increase the general strain pattern of the cement mantle, though localised regions of high stress were detected. [Copyright &y& Elsevier]

Objective. To determine the load transfer patterns of femurs in the intact, immediate post-operative and long-term (remodelled) post-operative implanted conditions for Lubinus SPII and Mu¨ller-Curved cemented hip prostheses, and to examine to what extent remodelling may influence the long-term outcome.Design. Experimental and finite element (FE) methods were applied to composite femurs under loads representing the heel-strike phase of gait, determining cortical bone and cement strains for the different femur conditions.Background. The authors previously developed protocols to measure bone and cement strains, and to produce remodelled femur specimens, yet these have not been applied together to compare strain patterns of different femur conditions. The Lubinus SPII is clinically more successful than the Mu¨ller-Curved stem, with failure mainly due to aseptic loosening.Methods. Cortical bone strains were determined in intact femurs. Six femurs each were implanted with the two stem types and cortical bone and cement strains were measured. Bone remodelling was recreated using a validated CAD–CAM procedure to remove a layer of proximal cortical bone, replicating a typical scenario found in stable clinical retrievals. Strains were remeasured. FE methods were used to compliment the experiments.Results. Stress shielding was reduced with remodelling, though bone strains did not return to their intact values, particularly around the calcar. Cement strains increased with remodelling. Differences occurred between the two stems; the Mu¨ller-Curved produced a more severe strain transition.Conclusions. Procedures were successfully combined together to investigate in vitro the performance of two cemented stems, in immediate and long-term post-operative conditions. The increase of cement strains with remodelling is a potential indicator for in vivo cement failure.RelevanceThe consequences of femoral bone remodelling on the long-term success of joint replacements are not well understood, where remodelling may lead to increased bone and cement stresses. [Copyright &y& Elsevier]