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 micro g/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.
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 micro g/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.