Recently developed in vivo animal high-resolution micro-CT scanners offer the possibility to monitor longitudinal changes in bone microstructure of small rodents, but may impose high radiation doses that could damage bone tissue. The goal of this study was to determine the effects on the bone of 8 weeks of in vivo scanning of the proximal tibia in female Wistar rats. Eight weekly CT scans were made of the right proximal tibia of nine female, 30-week-old, retired-breeder, Wistar rats. Two weeks after the last weekly scan, a final scan was made. The left leg was only scanned during first and final measurements and served as a control. A two-way ANOVA with repeated measures was performed on the first and last measurements of left and right tibiae for six bone structural parameters. Bone marrow cells were flushed out and tested for cell viability. No significant difference was found between left and right for any of the bone structural parameters ( p > 0.05). Structure model index and trabecular separation significantly changed as a result of aging, while none of the other parameters did. No significant difference was found between left and right in absolute and percentage number of cell viability. We did not find any indication that the applied scanning regime, in combination with the particular settings used, would affect the results of in vivo bone structural measurements in long-term studies using aged, female Wistar rats. However, careful consideration should be made when determining the number of scans, particularly when a different experimental design is used. ß

Bisphosphonates are antiresorptive drugs commonly used to treat osteoporosis. It is not clear, however, what the influence of the time point of treatment is. Recently developed in vivo micro-computed tomographic (CT) scanners offer the possibility to study such effects on bone microstructure in rats. The aim of this study was to determine the influence of early and late zoledronic acid treatment on bone in ovariectomized rats, using in vivo micro-CT. Twenty-nine female Wistar rats were divided into the following groups: ovariectomy (OVX, n = 5), OVX and zoledronic acid (ZOL) at week 0 (n = 8), OVX and ZOL at week 8 (n = 7), and sham (n = 9). CT scans were made of the proximal tibia at weeks 0, 2, 4, 8, 12, and 16; and bone structural parameters were determined in the metaphysis. Two fluorescent labels were administered to calculate dynamic histomorphometric parameters. At week 16, all groups were significantly different from each other in bone volume fraction (BV/TV), connectivity density, and trabecular number (Tb.N), except for the early ZOL and control groups which were not significantly different for any structural parameter. After ZOL treatment at week 8, BV/TV, structure model index, Tb.N, and trabecular thickness significantly improved in the late ZOL group. The OVX and ZOL groups showed, respectively, higher and lower bone formation rates than the control group. Early ZOL treatment inhibited all bone microstructural changes seen after OVX. Late ZOL treatment significantly improved bone microstructure, although the structure did not recover to original levels. Early ZOL treatment resulted in a significantly better microstructure than late treatment. However, late treatment was still significantly better than no treatment.Keywords Osteoporosis Á Bisphosphonate Á In vivo micro-computed tomography Á Rat Postmenopausal osteoporosis affects millions of women worldwide and results in loss of bone mass and bone microstructural changes, which lead to reduced bone strength. It remains unknown how exactly the microstructure is affected over the time course of osteoporosis development and to what extent this structure can be recovered by drug treatment. Since the assessment of bone structure in humans is still limited to a few peripheral sites, the ovariectomized rat is used in many studies as an animal model for osteoporosis in cross-sectional evaluations. Numerous cross-sectional studies have determined the loss of trabecular bone in the proximal tibia in rats following ovariectomy (OVX) at different time points by measuring bone structural parameters [1][2][3]. OVX has been shown to decrease bone volume fraction, connectivity, and trabecular number and to increase trabecular separation and structure model index, which indicates that trabecular bone changes from plate-like to more rod-like in the proximal tibial metaphysis of the female rat. However, conflicting results were found for the effects of OVX on trabecular thickness, showing increases, decreases, or no response at

Summary Using in vivo microcomputed tomography (micro-CT), we found in parathyroid hormone (PTH)-treated osteopenic rats linear increases in cortical and trabecular, due to increased trabecular thickness and number, bone mass. Bone was formed in cavities, leading to restoral of nearly cleaved trabeculae. For the first time, effects in PTH-treated rats were analyzed longitudinally. Introduction Our aims were to over time (1) determine changes in trabecular thickness and number after PTH, (2) compare responses to PTH between the meta-and epiphysis, (3) determine effects of PTH on mineralization and mechanical properties, (4) determine locations of new bone formation due to PTH on a microlevel, and (5) determine the predictive value of bone structural properties for gain in bone mass after PTH. Methods Adult rats were divided into ovariectomy (OVX; n=8), SHAM-OVX (n=8), and OVX and PTH treatment (n=9). Between weeks 8 and 14, PTH rats received daily subcutaneous PTH injections (60 μg/kg/day).At weeks 0, 8, 10, 12, and 14, in vivo micro-CT scans were made of the proximal and diaphyseal tibia. After sacrifice, all tibiae were tested in three-point bending.Results PTH increased bone volume fraction linearly over time in meta-and epiphysis, accompanied by increased trabecular thickness in both and increased trabecular number only in the latter one. CT-estimated mineralization increased in trabecular and remained constant in cortical bone. Ultimate load and energy were increased and ultimate displacement and stiffness unaltered compared to SHAM rats. For those trabeculae analyzed, bone was formed initially on places where it was most beneficial for increasing their strength and later on to all surfaces.

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Daily low-amplitude, high-frequency whole-body vibration (WBV) treatment can increase bone formation rates and bone volume in rodents. Its effects vary, however, with vibration characteristics and study design, and effects on 3D bone microstructure of ovariectomized animals over time have not been documented. Our goal was to determine the effects of WBV on tibial bone of ovariectomized, mature rats over time using an in vivo micro-CT scanner. Adult rats were divided into: ovariectomy (OVX) (n ¼ 8), SHAM-OVX (n ¼ 8), OVX and WBV treatment (n ¼ 7). Eight weeks after OVX, rats in the vibration group were placed on a vibrating platform for 20 min at 0.3 g and 90 Hertz. This was done 5 days a week for six weeks, twice a day. Zero, 8, 10, 12 and 14 weeks after OVX, in vivo micro-CT scans were made (vivaCT 40, Scanco Medical AG) of the proximal and diaphyseal tibia. After sacrifice, all tibiae were dissected and tested in three-point bending. In the metaphysis between 8 to 12 weeks after OVX, WBV treatment did not alter structural parameters compared to the OVX group and both groups continued to show deterioration of bone structure. In the epiphysis, structural parameters were not altered. WBV also did not affect cortical bone and its bending properties. To summarize, no substantial effects of 6 weeks of low-magnitude, high-frequency vibration treatment on tibial bone microstructure and strength in ovariectomized rats were found. Keywords: vibration; rats; ovariectomy; in vivo micro-CT Mechanical stimulation of bone by vibration has been shown in vivo to have a potential osteogenic effect, contributing to a structure more resistant to habitual loads. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] These mechanical signals are often applied in high-frequency, low-acceleration mode, and commonly result in small strains (<10 microstrain) in the bone, that are orders of magnitude lower than strains resulting from daily loads.1,7 As they are apparently harmless to the body, they may provide a potential treatment for bone-debilitating diseases like osteoporosis.In a study performed in sheep, 1 year of daily vibrations resulted in an increase of trabecular bone volume fraction of 32%. 8 In a study in which teenagers with low bone mineral density (BMD) were put on a vibration plate for 10 min a day for a year, a small increase in trabecular BMD in lumbar vertebrae was found as well as an increase in femoral cortical bone area. 13 However, in the first study on the effects of vibration in a small cohort of osteoporotic women, no significant effect on bone mineral density of the spine, hip, or distal radius was found after 1 year of treatment. 9A significant effect of treatment compliance was shown though in that study, and effects in patients of the highest quartile of compliance almost reached significance. These results thus demonstrate the potential osteogenic effect of mechanical vibration, but also suggest that the effects might be site and species dependent.To further elucidate the effects of low-magnitude, ...