The effect of preparatory technique on the compressive properties of morsellised bone graft

Fabrication and mechanical testing of porous calcium phosphate bioceramic granules

Porous hydroxyapatite/tricalcium phosphate (HA/TCP) granules were fabricated by a novel technique of vacuum impregnation of reticulated polyurethane (PU) foams with ceramic slip. The resultant granules had 5-10% interconnected porosity with controlled pore sizes necessary to allow bone ingrowth combined with good mechanical properties. Using PU foams with a different number of pores per inch (ppi), porous HA/TCP granules in the size range of 2-8 mm were successfully manufactured. Dieplunger tests were used to compare the compression and relaxation properties of the granules with those of a commercially available bone graft product, BoneSave. The results of the die-plunger testing showed that the experimental granules were stiffer than the BoneSave materials and had less of a tendency to crumble to powder after testing. This therefore suggests that these experimental granules would be useful for impaction grafting and space filling applications.

A comparison of the viscoelastic properties of bone grafts

BACKGROUND

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.

METHODS

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 120s. 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.

RESULTS

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.

INTERPRETATION

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.