Increasing strut porosity in silicate-substituted calcium-phosphate bone graft substitutes enhances osteogenesis.

Synthetic, porous silicate-substituted calcium phosphate bone graft matrices (SiCaP; 0.8 wt % Si) with varying strut porosity were applied to ovine critical-sized defect sites as either 1-2 mm microgranules (SiCaP-23G, SiCaP-32G, and SiCaP-46G) or 1-2 mm microgranules in an aqueous poloxamer carrier (SiCaP-23P, SiCaP-32P, and SiCaP-46P). Defect sites treated with SiCaP-23G or SiCaP-23P showed evidence of bone formation at 8 and 12 weeks in central zones. More advanced neovascularization and increased bone contact was observed for graft materials with higher strut porosities. At 12 weeks, graft materials with higher strut porosities (32% and 46%) had statistically significantly higher absolute bone volumes (p < 0.05) versus those with a strut porosity of 23%. Absolute bone volume in defects treated with grafts of matched strut porosities as microgranules, or microgranules with poloxamer carrier, were similar at 12 weeks. Absolute graft volume for SiCaP-46 reduced over 12 weeks (not statistically significant). In conclusion, bone formation patterns in critically-sized defects confirm strut porosity to be a clinically relevant property of porous silicate-substituted calcium phosphate bone grafts in promoting osteogenesis. Increasing graft matrix strut porosity encouraged earlier neovascularization and increased the absolute equilibrium volume of bone growth within the graft without compromising graft stability.