The effects of androgens on the mechanical properties of primate bone

Feral adult female cynomolgus monkeys were divided into three groups and treated for two years: (1) normal controls; (2) weak androgenic treatment (androstenedione+estrone); and (3) strong androgenic treatment (testosterone). The tibiae and the trabecular bone of femoral head from each group were tested mechanically. There were no significant changes in the elastic modulus and shear modulus of the tibiae, measured by three point bending and torsion tests, among the three groups. Significant increases in energy absorption capacity (+45% for testosterone) and maximum shear stress (+19.4% for androstenedione and +39% for testosterone) of the tibiae, measured by torsion tests, and the cortical bone density (+5.5% for androstenedione and +8.7% for testosterone), were observed. Testosterone treatment significantly increased torsional rigidity (+23%) and bending stiffness (+15%) of the tibiae while androstenedione did not change any of these structural properties. The results of compression tests of the trabecular bone samples indicated significant increases in their elastic modulus after androstenedione (+88%) or testosterone (+107%) treatment. The maximum compressive stress of the testosterone treated samples was significantly higher than those of both normal (+28%) and androstenedione treated groups (+26%). The trabecular bone density increased after both androgenic treatments. This increase was significant for the testosterone treated group (+8.6%). We conclude that in the young cynomolgus monkey, long-term androgenic treatment significantly improves some of the mechanical properties of both cortical and trabecular bones, increases bone density, and the stronger the androgen, likely, the more pronounced is the effect.