Clodronate reduces plate osteopenia in the rabbit.

An osteosynthesis with a four-hole AO/ASIF-DCP plate was performed on the right tibia of 40 rabbits. Clodronate (50 mg/kg s.c.) was given once a week, resulting in a mean bone concentration of 509 micrograms/g in 2 hours. Plate fixation caused a decrease in mean net cross-sectional area of compact cortical bone of 17 percent at 9 weeks and 46 percent at 18 weeks. This resulted from bone resorption in bone under the plate, from pronounced cavitation in the plated bone (about 5 percent of cortical bone area at 9 weeks and 15 percent at 18 weeks), and from the fact that the medullary space was increased by 15 percent at 18 weeks. The total cross-sectional area of the diaphysis was increased by 31 percent at 9 weeks and by 17 percent at 18 weeks. Clodronate treatment reduced cortical porosity to about half of the mean values in the placebo group. Clodronate increased both the calcium content in the retained bone and the cross-sectional area of compact cortical bone, but induced only an insignificant increase in the area of periosteal new bone. Clodronate treatment seems not to be contraindicated in conjunction with rigid osteosynthesis, and may even slow down the osteopenic response occurring under the rigid plate.