Assessment of a porous hydroxyapatite graft expander in revision hip arthroplasty
Introduction: Impaction allografting has proved a successful means of restoring deficient bone stock during revision athroplasty of the hip. Mechanical and clinical studies were performed to investigate the role of IG-Pore, a synthetic hydroxyapatite Graft expander, in impaction grafting. Methods: 32 synthetic femoral models underwent impaction grafting using allograft mixed with varying proportions of IG-Pore (0%, 50%, 70% and 90% IG-Pore). The cyclical displacements induced by repetitive loading on an Instron were measured, and overall migration of the prosthesis was determined using radiostereometric analysis (RSA). A randomised controlled clinical trial comparing impaction grafting using pure allograft and a 1:1 mixture of allograft and IG-Pore is also described. Migration of the revised femoral and acetabular components was determined using RSA, and clinical outcomes were monitored. A preliminary analysis of the first 14 patients in this study with follow-up of up to six months is presented. Results: The mechanical data indicate that IG-Pore confers a greater resistance to subsidence (p=0.034) and cyclical movement (p=0.005). In particular, subsidence at the prosthesis-cement interface is lower than with pure allograft (p=0.019). The clinical study shows similar patterns of migration, although it is too early for definite conclusions. Movement of individual graft particles is greater with IG-Pore, however, and graft handling may be more difficult. Discussion: Synthetic hydroxyapatite graft expanders may indeed be beneficial in impaction grafting, and the clinical study which is described herein should, in due course, definitely characterise their role.