Background: Calcium phosphate cements (CPCs) have been widely used as an alternative to biological grafts as they present excellent biocompatibility and osteoconductive properties. Novel work has successfully introduced Bioglass (BG) into (ⅰ) hydroxyapatite, (ⅱ) octacalcium phosphate and (ⅲ) fluorohydroxyapatite cements without compromising the setting time. The aim of this study was to investigate bone formation and contact to these three novel BG/CPC cements following implantation in an ovine femoral condyle critical-sized defect. Our hypothesis was that the novel cements would augment bone formation to equal amounts when compared with a commercially available calcium phosphate cement (Hydroset™). Methods: Twenty-four 8 × 15 mm deep defects were created In the medial femoral condyles of 6 female, skeletally mature commercially cross-bred sheep. Cements investigated were BG/CPC composites, however the calcium phosphate component was composed of either (1) OCP/Brushite (OCP), (2) a fluorohydroxyapatite (FHA) or (3) hydroxyapatite (HA). Groups were compared with (4) Hydroset™, a commercially available calcium phosphate cement. Cements remained in vivo for 12 weeks (n=6). Fluorochrome markers were used to measure bone apposition rates and following retrieval, specimens were processed for undecalcified histology. A thin section was made through the centre of each defect and image analysis techniques used to quantify bone apposition rates and bone-implant contact at 12 weeks post surgery. The compressive strength (MPa) of each of the cements was tested using an indentation method (Zwick Praline 500) following retrieval. Mann Whitney U tests were used for statistical analysis where p＜0.05 was considered significant. Results: Results showed that significantly increased apposition rates were measured in the Hydroset™ group (mean, 1.191 ± 0.345 μm/day-1) when compared with OCP filled (mean, 0.740 ± 0.156 μm/day-1) (p = 0.028) and FHA defects (mean, 0.839 ± 0.141 μm/day-1) (p = 0.047). No significant difference was found when Hydroset™ and HA samples were compared. Significantly increased bone turnover rates were measured adjacent to the HA cement (mean, 1.151 ± 0.274 μm/day-1) when compared with OCP samples (p - 0.028). No other significant differences were found. The greatest amount of bone-cement contact was measured in the OCP group (mean, 95.47 ± 3.22%). Lowest bone-cement contact values were measured in HA samples (mean, 93.02 ± 2.32%). Significantly less bone contact was measured in HA samples when compared with FHA samples (mean, 94.55 ± 1.77%) (p = 0.014). No other significant differences were found (Figure 1). Mechanical testing showed the compressive strength of cements in each of the groups were similar (Figure 2).. Light and backscattered scanning electron microscopy showed mature lamellar bone in contact with all cement surfaces (Figure 3). Conclusion: The incorporation of fluoride within the hydroxyapatite lattice and the formation of OCP/Brushite BG/CPCs were seen to be as bioactive as the commercially available calcium phosphate cement Hydroset™. These cements are able to be injected and their compressive strength once set, and after 12 weeks in vivo, indicates that they may be excellent bone void fillers and may have potential uses for vertebroplasty applications. Further work is needed to assess the resorbability of the cements over time.
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