Effect of Risedronate on Bone Resorption during the Consolidation Phase of Distraction Osteogenesis: A Rabbit Model

Abstract

Purpose. To evaluate the effects of continuous local injection of risedronate in the prevention of bone resorption in a lengthened segment. Methods. 11 male rabbits underwent subperiosteal osteotomy of the left tibia and an external fixator was applied anteromedially. After a lag phase of one week, a 2-week distraction phase and a 5-week consolidation phase followed. Risedronate was continuously injected into the centre of the distracted segment at a rate of 10 μg/kg/day during the first 14 days of consolidation by a subcutaneously implanted osmotic pump. A control group received purified buffer solution (PBS) using the same protocol. The lengthened bone segments were evaluated using radiography, quantitative computed tomography, and 3-point bending mechanical test. Results. Risedronate injection prevented osteopenia as compared to PBS injection. The mean bone mineral content, volumetric density and cross-sectional area of the lengthened segments were significantly higher in the risedronate group than in controls (as much as 65%, 30%, and 25%, respectively). There was no significant difference between the 2 groups regarding the ultimate load to failure. Conclusion. Continuous local injection of risedronate into the lengthened segment can prevent osteopenia during distraction osteogenesis but fails to enhance mechanical strength of newly distracted segments.