Numerical modelling of the pelvis and acetabular construct following hip arthroplasty
Phillips, Andrew T M
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The study presents finite element models of the acetabular construct and the pelvis. Particular attention is given to investigating the behaviour of the acetabular construct following revision hip arthroplasty, carried out using the Slooff-Ling impaction grafting technique. Mechanical tests are carried out on bone graft, and constitutive models are developed to describe its non-linear elasto-plastic behaviour, for inclusion in finite element analyses. Impaction of bone graft was found to have a significant effect in reducing subsequent development of consolidation plastic strains. A novel approach for the inclusion of muscles and ligaments, in finite element analyses, to provide boundary conditions similar to those found in vivo is also presented. 2D analyses of the acetabular construct, following revision hip arthroplasty, carried out using impaction grafting, indicate that for idealised load cases, rotation of the acetabular cup increases, as the depth of the bone graft bed increases. This indicates that it is advantageous to use the largest practical diameter of acetabular cup. Results from 3D analyses of the hemi pelvis, following revision arthroplasty, indicate that different patterns of migration and rotation of the acetabular cup, within the bone graft bed are associated with different physiological activities. For example walking is seen to cause migration of the cup in the superior direction, and rotation of the cup in abduction. Results from 3D analyses of the pelvis indicate that the inclusion of muscles and ligaments, in place of fixed boundary conditions cause significant changes to the stress distribution observed in the cortical bone, but comparatively minor changes to the stresses in the trabecular bone, and bone graft in the acetabular region.