To determine whether there is a maximum trabecular thickness, after which trabecular tunneling takes place, we analyzed the distribution of trabecular thickness in the epiphysis of all rats at all time points. The scanner software provides outputs of counts per bin and trabecular thickness was categorized in bins of 15 μm. Prediction of gain in bone mass after PTH treatment We hypothesized that several structural properties may predict the gain in bone mass after PTH, such as bone selleck kinase inhibitor surface at the start of PTH treatment, bone mass at the start of PTH treatment, bone mass before ovariectomy, and amount of bone mass loss after

ovariectomy. Therefore, a linear correlation was determined between several structural parameters and the gain in bone mass, gain in bone volume fraction, final bone mass, and final bone volume fraction Selumetinib purchase after PTH treatment. This was done for the PTH-treated rats only. Three-point bending of tibiae After sacrifice, all tibiae were dissected and frozen

in phosphate buffered saline solution at −20°C. They were thawed prior to three-point bending. The tibia was placed on the lateral surface on two rounded supporting bars with a distance of 2.4 cm. A preload of 1 N was applied (ZWICK, Z020) at the medial surface CP673451 mw of the diaphysis by lowering a third rounded bar. A constant displacement rate of 6 mm/min was applied until failure. Displacement was measured from the actuator displacement transducer of the testing machine. From the force–displacement

curve, the following mechanical parameters were determined: (1) ultimate load, defined as the maximum load, (2) displacement at ultimate load, which was corrected for the toe region, (3) extrinsic stiffness, calculated as the slope in the linear region between 40% and 80% of the ultimate load, and (4) energy to ultimate load, defined as the area under the curve until ultimate load. Statistics A one-way analysis Bumetanide of variance (ANOVA) with repeated measures was performed to compare the PTH-treated and OVX groups during treatment between weeks 8 and 14. A one-way ANOVA with a Bonferroni post hoc test was used to determine differences between the groups at certain time points, for all parameters. Furthermore, a one-way ANOVA with repeated measures was performed to compare the OVX and SHAM groups between weeks 0 and 8. Finally, an ANOVA with repeated measures was performed in the SHAM group to determine effects of aging. All p values below 0.05 were considered significant. Results Metaphyseal structural parameters At week 8, the ovariectomized groups displayed loss of BV/TV, Conn.D, Tb.N, and Tb.Th and an increase in SMI and Tb.Sp, indicating the development of osteopenia (Fig. 2). Beyond 8 weeks, the untreated OVX group showed further deterioration of bone structure except for Tb.Th, which increased. Fig.