Standardized bending and breaking test for the normal and osteoporotic metaphyseal tibias of the rat: Effect of estradiol, testosterone, and raloxifene

Introduction: Osteoporosis becomes manifest predominantly in the metaphyseal rat tibia. The anti-osteoporotic character of substances should, therefore, be tested (mechanically) in this bone area. Materials and Methods: We evaluated a new three-point bending test for the metaphyseal tibia in rats in a right-left trial. In an animal experiment, we studied the change of bone quality under estradiol (E)-, raloxifene (R)-, and testosterone (T)-supplemented food and compared it with trabecular BMD (qCT). Results: In the right-left comparison, the mean difference between the metaphyseal loads of both tibias in 37 rats was 8.43% for the maximum load (F-max) and 6.46% for the failure load (fL). These results show the high reproducibility of the test, because they are close to the usual intraindividual difference of the two extremities. In a second experiment, four groups of 11 3-month-old male orchidectomized rats were fed with soy-free food only (C) or with the additives E, T, or R for 1.2 weeks. E and R were similar for F-max and fL. There were significant differences in the stiffness (E = 406.92 N/mm versus R = 332.08 N/mm),. the yield load (yL; E = 99.17 N versus R = 83.33 N), and the ratio between yL and F-max (E = 86.33% versus R = 76.37%). T was similar to the controls concerning F fL, and stiffness. There were significant differences in yL (T = 49.00 N versus C = 39.5N) and the ratio between yL and F-max (T = 64.28% versus C = 51.28%). Conclusions: Estradiol is superior to raloxifene concerning stiffness and yield load, and both are superior to testosterone. We conclude that the described three-point bending test for the metaphyseal tibia is a highly sensitive method to study hormones and substances with regard to their osteoprotective character. The precision and the low SD of the presented results are superior to the data from qCT and the calculated index of stiffness (SSI).