In cemented hip implant, the polymethyl methacrylate (PMMA) also called bone cement is used as grouting material between the implant and the bone. During the operation, the bone cement still in a liquid form is inserted between the femoral component and the bone. During polymerisation of the cement, residual stresses are generated in the bulk cement. The process of cement curing is a complex solidification phenomenon where transient stresses are generated and the residual stresses vary with different boundary conditions during curing (Ahmed et al., 1982). In particular, normal stresses are generated at the implant-PMMA interface resulting in a press-fit problem. The cement does not have a chemical bond with the stem nor the bone, however it fills completely the space between the two and serves to distribute the load being transferred from the stem to the bone. An experiment has been devised to measure directly the residual stresses of the bone cement to reproduce the in-vivo behaviour of the prosthesis. An idealized prosthesis (19-mm diameter) is used. A subminiature load cell (9.5-mm diameter) is inserted inside the stem to measure directly the radial residual stresses of the PMMA on the stem. Bone cement polymerizes between the stem and the synthetic bone (40-mm outside diameter). The tests are conducted at body temperature of 37°C.

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