Abstract
Following hip arthroplasty carried out using the Slooff-Ling impaction grafting technique micro-motion of the acetabular cup is frequently seen within the bone graft bed. In some cases this can lead to gross migration and rotation of the acetabular cup, resulting in failure of the arthroplasty. The movement of the cup is thought to be due to the irrecoverable deformation of bone graft under shear and compressive forces. Previous experimental studies have addressed ways in which the behaviour of the bone graft material may be improved, for example through washing and the use of improved particle size distribution. However there has been a limited amount of research carried out into assessing the behaviour of the acetabular construct in-vivo.
This study presents a 3D finite element model of the acetabular construct and hemi-pelvis following impaction grafting of a cavitory defect. A sophisticated elasto-plastic material model was developed based on research carried out by the group to describe the bone graft bed. The material model includes the non-linear stiffness response, as well as the shear and consolidation yield response of the graft. Loading associated with walking, sitting down, and standing up is applied to the model. Distinct patterns of migration and rotation are observed for the different activities. When compared in a pseudo-quantitative manner with clinical observations results were found to be similar. Walking is found to account for superior migration, and rotation in abduction of the acetabular cup, while sitting down and standing up are found to account for posterior migration, and lateral rotation. The developed 3D model can be used in the assessment of cup designs and fixation devices to reduce the rate of aseptic failure in the acetabular region.
Correspondence should be addressed to Mr Carlos Wigderowitz, Senior Lecturer, University Department of Orthopaedic and Trauma Surgery, Ninewells Hospital and Medical School, Dundee DD1 9SY.
