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This study was designed to determine the modulatory effect of estrogen on mechanical stimulation in bone. Trabecular and cortical bone compartments of ovariectomized rats exposed to whole-body vibration of different amplitudes were evaluated by peripheral quantitative computed tomographic (pQCT) analysis and histomorphometry and compared to controls not exposed to vibration. Rats underwent whole-body vibration (20 minutes/day, 5 days/week) on a vibration platform for 2 months. The control rats were placed on the platform without vibration for the same time. We divided rats into six groups: a sham control (SHAM); a sham vibrated (SHAM-V) at 30 Hz, 0.6 g; a SHAM-V at 30 Hz, 3g; an ovariectomized control (OVX); an ovariectomized vibrated (OVX-V) at 30 Hz, 0.6 g; and an OVX-V at 30 Hz, 3g. In vivo, pQCT analyses of the tibiae were performed at the start of the experiment and after 4 and 8 weeks. After 8 weeks the tibiae were excised for histomorphometric and for in vitro pQCT analyses. In the SHAM-V group, vibration had no effect upon the different bone parameters. In the OVX-V group, vibration induced a significant increase compared to the OVX group of the cortical and medullary areas (P < 0.01) and of the periosteal (P < 0.01) and endosteal (P < 0.05) perimeters at the 3 g vibration. The strain strength index increased in the OVX-V group significantly (P < 0.01) at the higher vibration. The results showed that low-amplitude, high-frequency whole-body vibration is anabolic to bone in OVX animals. The osteogenic potential is limited to the modeling of the bone cortex and depends on the amplitude of the vibration.

At cortical sites, the precision for the densitometric and geometric variables ranged from 0.4% to 4.3%, and was similar for the radius, tibia and femur. At trabecular locations, the reproducibility of the density measurements ranged from 1.8% to 2.5% at the radius, and from 3.2% to 5.9% at the femur and tibia. The intersite correlation of the total bone mineral content ranged from 0.87 and 0.97 at cortical sites, and from 0.63 to 0.85 at trabecular locations. The trabecular density showed a higher similarity between the tibia and femur (r=0.68-0.78) than between the radius and the lower extremity (r=0.41-0.45). The results demonstrate a substantial heterogeneity of trabecular bone in elderly individuals and advocate measurements directly at the site of clinical or scientific interest.

The purpose of the present study was to evaluate the accuracy of peripheral quantitative computed tomography (pQCT) in measuring the thickness of the radial cortex. Thirty left forearm specimens were scanned on an XCT 960 Stratec pQCT device using a 2.5 mm thick slice at the junction of the middle and the distal third of the radius. Cortical and trabecular areas were assessed using a threshold procedure; cortical thickness was subsequently calculated assuming a circular ring model for the radius. Cortical thickness was also measured on the true shape of bone using an iterative contour detection procedure. Subsequently 2.5 mm thick resin-embedded cylindrical radial specimens, matched with the site of pQCT examination, were obtained and contact radiographs were performed. After tenfold magnification, the cortical and trabecular areas of the specimens were measured using computerized planimetry and cortical thickness was calculated assuming a circular ring model. The cortical thickness could be assessed by pQCT in all cases using the threshold algorithm (mean (SD) 2.51 (0.58) mm) and in 21 cases could be directly measured on the true shape of bone (2.62 (0.32) mm). The cortical thickness of the specimens showed good correlation and high proportionality with that measured using pQCT with either the threshold algorithm (r = 0.941, slope = 0.976) or the iterative contour detection procedure (r = 0.883, slope = 0.987). In conclusion, pQCT is able to assess the thickness of the radial cortex, at the junction of the middle and the distal third, with high accuracy.

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