The long term objective of this study is to improve understanding of fatigue failure in the cement mantle of Total Hip Replacements (THR). The proposed imaging technique will provide a new direction for research within the ongoing project of definition and control of the mechanical factors that lead to aseptic loosening of cemented THR. Specifically, a three dimensional map of cement crack surfaces, along with associated stem and endosteal bone morphology, will be generated using an automated high-resolution serial grinding and imaging technique. Currently there are two widely used competing design principles for femoral stems: 'taper slip'/'force closure', and 'minimal subsidence'/shape closure'. The proposed technique will be used to compare the response to in vitro fatigue loading of these two stem types. The serial grinding technique will be used in combination with measurements of stem micro-motions, bone quality and degree of cement/bone interdigitation. Pairs of cadaveric femora will be subjected to cyclic 'stair climbing' loads, with contralateral bones receiving 'taper slip' style and 'minimal subsidence' style implants. The effect of fatigue on these stem/cement/femur complexes will be explored by quantifying fatigue crack surfaces and correlating these data with stem micro-motions and the morphology of stem, cement and endosteal bone. The following hypotheses will be tested: 1) that the magnitudes of stem micro-motions are proportional to the quantity of cement mantle fatigue damage; 2) that 'taper slip' and 'minimal subsidence' stem types have different cement fatigue fracture patterns; 3) that subsidence of 'taper slip' stems requires fatigue failure of the cement mantle; 4) that under cyclic loading, permanent subsidence steps of 'taper slip' stems are associated with reductions in cyclic micro-motions. The results of this study will have immediate clinical relevance by enabling surgeons to make more informed decisions concerning which stem type might be most appropriate for each individual patient. The imaging technique will also facilitate development of stem designs to improve longevity of cement mantles. In addition, the crack imaging system will be used in a pilot study of stem/cement/femur complexes recovered at post-mortem. It is anticipated that successful implementation of the imaging technique will facilitate further studies, including the analysis of recovered stem/cement/femur complexes, which will assist with the NIAMS research goal of 'Development and use of an implant retrieval analysis registry to elucidate the mechanisms of failure'.
| Mann, Kenneth A; Damron, Leatha A; Miller, Mark A et al. (2007) Stem-cement porosity may explain early loosening of cemented femoral hip components: experimental-computational in vitro study. J Orthop Res 25:340-50 |
| Race, Amos; Miller, Mark A; Clarke, Michael T et al. (2005) Cement-implant interface gaps explain the poor results of CMW3 for femoral stem fixation: A cadaver study of migration, fatigue and mantle morphology. Acta Orthop 76:679-87 |
| Race, Amos; Miller, Mark A; Ayers, David C et al. (2003) Early cement damage around a femoral stem is concentrated at the cement/bone interface. J Biomech 36:489-96 |
