A comparison of the viscoelastic properties of bone grafts

The expansion in joint arthroplasty surgery in the 1970s has resulted in a large group of patients who require revision arthroplasty for aseptic loosening. Impaction bone grafting to deal with bone stock loss has become an increasingly popular procedure in revision hip surgery. The results of this revision surgery are variable and very much dependent on the grafting techniques adopted at the time of surgery. In vitro testing of impaction bone grafting methods can constitute an important tool to improve long-term clinical results. The increasing clinical demand for human allograft limits its availability for use in in vitro laboratory studies therefore suitable experimental alternatives are required. Human, porcine and ovine cancellous bone grafts were morsellised and prepared for in vitro laboratory testing following a standard operative technique. Each graft type was compressed using a die plunger test. After compression to a predetermined level the graft was left to relax for 120 s. A comparison of the compression moduli and of the relaxation characteristics for each graft preparation was performed. In addition, the effects of washing the graft and of cartilage removal from the graft mixture were investigated. This study has demonstrated that there is no statistical difference in the compression modulus or relaxation percentage between human and ovine graft preparations. The effect of removing cartilage and washing the graft mixtures were inconsistent with regard to alterations in the viscoelastic properties of the grafts. On the basis of the experiments performed we recommend the use of ovine bone graft as a suitable substitute for human allograft for in vitro testing of impaction bone grafting methods. The properties of ovine graft were similar for both compression moduli and relaxation properties to human allograft.