rhBMP-2 not alendronate combined with HA-TCP biomaterial and distraction osteogenesis enhance bone formation

The long treatment duration of distraction osteogenesis (DO) usually causes some complications such as re-fracture, non-union. We have previously demonstrated that the combined use of biomaterial with distraction osteogenesis technique can enhance bone formation and consolidation. This study further tested whether the use of biological agents such as rhBMP-2 or alendronate together with biomaterials in DO will further promote bone formation.

A 1.0-cm tibial shaft was removed in the left tibia of 30 rabbits. The 1.0-cm defect gap was reduced to 0.5 cm and the remaining 0.5-cm defect gap was filled with 0.5-cm restorable hydroxyapatite/tri-calcium phosphates (HA/TCP) cylindrical block. The animals were divided into three groups with the following added on the HA/TCP block: Group A 50 μl of saline, Group B 75 μg rhBMP-2 in 50 μl of saline, Group C 250 μg alendronate in 50 μl saline. The tibia was then fixed with unilateral lengthener and lengthening started 7 days after at a rate of 1.0 mm/day for 5 days. All animals were terminated at day 37 following surgery. The excised bone specimens were subject to micro-CT, mechanical testing and histological examinations.

Bone mineral density and content were significantly higher in Groups A and B compared to Group C and the mechanical properties of the regenerates in Group B were highest. Micro-CT and histological examinations also confirmed that the regenerates in Group B had the most advanced bone formation, consolidation and remodeling comparing to other groups.

The combined use of rhBMP-2 with HA-TCP biomaterial in DO has significantly enhanced bone formation and consolidation than using the HA-TCP biomaterials alone, whereas the use of alendronate has inhibitory effects on bone formation.