The influence of clodronate on the torsional strength of the growing rat tibia in immobilization osteoporosis.

The purpose was to investigate whether the reduction in bone mechanical strength induced by immobilization could be prevented by a bisphosphonate compound, clodronate. The torsional breaking strength of the tibia was measured using a specially constructed torsion machine. Maximum torque capacity, maximum angle of deformation, and rigidity of the bone were calculated from a load-deformation curve. The study was performed in two experiments, one with rats having their right hind leg immobilized, the other with freely moving animals. In both experiments, the rats were treated with either clodronate or pure vehicle. Thus, the following groups, consisting of growing male Sprague-Dawley rats, were included: immobilized groups receiving clodronate (20 rats), immobilized group receiving vehicle only (20 rats), nonimmobilized group receiving clodronate (10 rats), and nonimmobilized group receiving vehicle only (10 rats). The rats to receive clodronate were injected daily with clodronate tetrahydrate s.c., 10 mg/kg body weight for 21 days, the others having the same volume of 0.9% NaCl (2 ml/kg body weight). On the third day of injection the right hind leg of the rats in the immobilization groups were immobilized with a plaster cast. Eighteen days later the animals were sacrificed, the tibias were submitted to torsional testing, and the ash weights of the femurs were determined. Clodronate treatment had an increasing effect on immobilized bone ash weight and all mechanical parameters, in the contralateral leg on ash weight, and maximum torque capacity, when compared with the respective leg of the immobilized, vehicle-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)