Abstract 29

AN ANALYSIS OF BONE GRAFT SUBSTITUTES IN A CRITICAL SIZE DEFECT MODEL

Smitham P, Auld J, Langdown A, Butler A, Vizesi F, Stephens, P, Bruce W, Walsh W

Orthopaedic Research Laboratory, Universtity of New South Wales, Sydney

The in vivo response of a new class of micro and macro porous hydroxyapatite materials was examined in a standard rabbit tibial defect.

Bilateral anteromedial critical size defects (5mm by 15mm) were created in sixty, 12 week old, NZ white rabbits using a standard model. The defects were filled with hydroxyapatite(HA) based materials of varying porosity (Apapore 60% and 80% porous), a biphasic HA -tricalcium phosphate material (Osatura 80% porous) or a silicate substituted HA material (Pore Si). Radiographic, torsional testing, histomophometric analyses and light microscopy were performed at 2, 4 and 12 weeks to assess healing, mechanical properties and percentages of bone, implant and void. Data was compared to ProOsteon 200R examined in the same model using the same endpoints.

No differences were noted between groups at each time with respect to radiographic appearance or mechanical data. The biphasic HA material demonstrated implant resorption by 12 weeks unlike the HA materials. The incorporation of silicate to the HA material increased bone formation within the defect. Comparison of the HA based materials to ProOsteon 200R (calcium carbonate and HA) revealed increased bone formation in this class of bone graft substitutes at 12 weeks.

Porosity and material composition play an important role in the in vivo performance of bone graft substitutes. Pure HA materials resorb at a slower rate compared to biphasic HA materials. Increasing porosity had a positive effect on new bone formation.

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