Low dosage of native allogeneic bone morphogenetic protein in repair of sheep calvarial defects.

A sheep skull trephine defect model was used to test the efficacy of allogeneic partially purified sheep bone morphogenetic protein (sBMP), extracted using a low-cost alternative technique based on 60% ammonium sulphate saturation of the guanethidine-HCI extract of pulverized bone matrix. Eight mg of partially purified sBMP was implanted in six 22-mm right-side sheep calvarial critical-size defects trephined in the diploë area using a midline incision; left-side defects implanted with an equal amount of type IV collagen served as controls. After 16 weeks the sheep were killed and the defects removed. Formation of new bone was evaluated using radiomorphometry and histomorphometry. The healing percentage in sBMP-implanted defects was 60.8 +/- 8.1% and in controls 49.8 +/- 6.7% (P < 0.05) as assessed by radiomorphometry. In cross-sectional histomorphometry, newly formed bone regenerated 50.9 +/- 15.1% in the defects with sBMP and 16.1 +/- 10.6% in controls (P < 0.01). The good result, considering the low dosage of sBMP, can be explained by the strong osteoinductivity and low immunogenicity of native allogeneic sBMP.