Calcium citrate: a new biomaterial that can enhance bone formation in situ

To investigate the effect of a new biomaterial combining calcium citrate and recombinant human bone morphogenetic protein-2 (rhBMP-2) on bone regeneration in a bone defect rabbit model.

Totally 30 male New Zealand white rabbits were randomly and equally divided into calcium citrate-rhBMP-2 (CC-rhBMP-2) group and rhBMP-2 only group. Two 10 mm-long and 5 mm-deep bone defects were respectively created in the left and right femoral condyles of the rabbits. Subsequently 5 pellets of calcium citrate (10 mg) combined with rhBMP-2 (2 mg) or rhBMP-2 alone were implanted into the bone defects and compressed with cotton swab. Bone granules were obtained at 2, 4 and 6 weeks after procedure and received histological analysis. LSD t-test and a subsequent t-test were adopted for statistical analysis.

Histomorphometric analysis revealed newly formed bones, and calcium citrate has been absorbed in the treatment group. The percent of newly formed bone area in femoral condyle in control group and CC-rhBMP-2 group was respectively 31.73%+/-1.26% vs 48.21%+/-2.37% at 2 weeks; 43.40%+/-1.65% vs 57.32%+/-1.47% at 4 weeks, and 51.32%+/-7.80% vs 66.74%+/-4.05% at 6 weeks (P less than 0.05 for all). At 2 weeks, mature cancellous bone was observed to be already formed in the treatment group.

From this study, it can be concluded that calcium citrate combined with rhBMP-2 signifcantly enhances bone regeneration in bone defects. This synthetic gelatin matrix stimulates formation of new bone and bone marrow in the defect areas by releasing calcium ions.