Effect of Recombinant Human Bone Morphogenetic Protein 7 on Bone Density During Distraction Osteogenesis of the Rabbit Mandible

Objectives: To examine whether the quality of bone generation in distraction osteogenesis of the rabbit mandible is enhanced by administering recombinant human bone morphogenetic protein 7 (rhBMP-7) to the lengthened site at the end of the distraction phase.

Study Design: Prospective randomized study of 24 rabbits undergoing distraction osteogenesis of the mandible, followed by injection of rhBMP-7 or a lactate buffer.

Settings: McGill University animal care facility.

Methods: Twenty-four white New Zealand rabbits underwent unilateral mandibular osteotomy and application of an Orthofix uniplanar M-100 fixator (Orthofix Inc., Verona, Italy) to the mandible. Mandibular distraction was carried out for 3 weeks. The animals were divided into three groups: group 1 (eight rabbits), control group: distraction, no injection; group 2 (eight rabbits), study group: distaction + injection of 200 microg of rhBMP7-lactate buffer; group 2 (eight rabbits), comparison group: distraction + injection of lactate buffer. All rabbits were sacrificed 7 weeks after surgery. The mandibles underwent radiology and bone densitometry analysis.

Main Outcome Measures: Radiology assessment of bone generation within distracted segments and objective analysis of bone mineral density.

Results: Radiology confirmed the presence of bone generate within distraction sites. Densitometry showed a difference in bone mineral density among the three groups (p < .05).

Conclusion: Local injection of a single dose of 200 microg of rhBMP-7 did enhance bone density when compared with the control group, although not in a statistically significant way when analyzed by an x-ray bone densitometer. This study serves as a starting point for future studies in bone tissue engineering by guiding the strategic administration of rhBMPs and the use of new state-of-the-art technologies, such as micro CT scanning, to analyze in a more detailed way, the effects of rhBMP administration.