An experimental analogue to model the fibrous tissue layer in cemented hip replacements

Fibrous tissue at the bone-cement interface of cemented joint replacements has been reported frequently in cases of revisions made necessary by aseptic loosening. This work describes the development of in vitro specimens suitable for biomechanical modeling of cemented femoral hip replacements with a fibrous tissue layer at the bone-cement interface. In particular, a series of uniaxial compression tests were performed on silicone elastomer specimens to identify a suitable analogue with similar mechanical characteristics to those reported for the fibrous tissue layer. A method was developed to apply the silicone elastomer at the bone-cement interface. This was examined for two types of cemented hip replacements implanted in composite femurs. The selected thickness of the elastomer layers was in the range of those found in clinical cases of aseptic loosening. Specimens produced by these methods could be used in preclinical biomechanical tests (such as stability or stress shielding tests) to assess the effects of a soft-tissue layer, to model in vitro a long-term-implant scenario, and to provide validation for similar finite element studies.