NUMERICAL MODELLING OF THE ACETABULAR CONSTRUCT FOLLOWING IMPACTION GRAFTING A.T.M. Phillips 1 , P. Pankaj 2 , A.S. Usmani 2 , C.R. Howie 3 1. ABSTRACT The study uses 2D and 3D finite element models to examine the behaviour of the acetabular construct following revision hip arthroplasty, carried out using the ‘Slooff- Ling’ impaction grafting technique. In all models loading was applied to the acetabular construct through a femoral head using smooth sliding surfaces. In 2D the non-linear elastic-plastic material behaviour of the bone graft was defined, and the effect of using different acetabular cup sizes for a reference cavitory defect was investigated. The study suggests that clinical benefits may be gained by using the largest practical size of acetabular cup. In 3D the elastic displacement of the acetabular construct subject to walking, sitting down and standing up loading cycles was investigated. The study suggests that activities such as sitting down and standing up may be more critical to cup migration than walking. 2. INTRODUCTION Hip arthroplasty is one of the most successful operations carried out by orthopaedic surgeons, resulting in significant improvement in quality of life for the patient. The number of hip arthroplasties performed worldwide is now in excess of 800,000 per year. However prosthetic components used in hip arthroplasty are subject to wear at prosthesis-prosthesis and prosthesis-bone interfaces. The generation of wear particles can lead to bone resorption. Thus skeletal structures deteriorate causing loosening of the prosthesis requiring revision surgery. Around 17% of hip arthroplasties carried out are revision operations. The ‘Slooff-Ling’ impaction grafting technique for cavitory femoral and acetabular defects has found favour with many orthopaedic surgeons carrying out revision operations. The technique uses morselised bone allograft, which is impacted into the skeletal defects to form a bed onto which the new prosthetic components are cemented. If short-term stability of the components is achieved, over time bone graft incorporation into the host skeleton can be seen, ensuring long-term stability. A common cause of failure in revision hip arthroplasties is the loss of structural stability in the acetabular construct, and in particular in the bone graft. Experimental studies have indicated that the behaviour of bone graft can be improved by using an appropriate particle size distribution, and by washing [1,2]. However there has been a general lack of research into the development of structural instability in the bone graft used in the acetabular construct. Keywords: hip arthroplasty, bone graft, impaction grafting, acetabular, cup rotation 1 PhD Research Student, 2 Senior Lecturer, School of Engineering and Electronics, The University of Edinburgh, Alexander Graham Bell Building, Kings Buildings, EH9 3JL 3 Consultant Orthopaedic Surgeon and Honorary Senior Lecturer, Royal Infirmary of Edinburgh and Department of Orthopaedics, The University of Edinburgh, Little France, Old Dalkeith Road, EH16 4SA