Correlation between densitometric and hystomorphometric values in isolated vertebrae of Sprague-Dawley rats

Comparison insight dual X-ray absorptiometry (DXA), histomorphometry, ash weight, and morphometric indices for bone evaluation in an animal model (the orchidectomized rat) of male osteoporosis

We have compared the measurements obtained by different methods: dual energy X-ray absorptiometry (DXA), histomorphometry, ash weight, and two morphometric indices (robusticity and bone weight/bone length index) in the orchidectomized (ORX) rat model of male osteoporosis. We examined 144 male wistar rats: 48 sham-operated, 48 ORX, and 48 ORX-treated with a bisphosphonate (risedronate) 2 or 10 mg/kg/day, 5 days per week. Rats were sacrificed at 2, 4, 8, or 16 weeks after the beginning of the study. DXA was performed on a Hologic QDR 2000 on the whole body, whole tibia, and tibial metaphysis. Bone volumes (C.BV/C.TV, and BV/TV) were measured by histomorphometry on the proximal tibial. A significant correlation was obtained between weight measured by DXA and scale (r = 0.993, P <0.000001). However, DXA underestimated weight by 0.3%. This discrepancy was dependent on the rat's weight. The weight bone length (WL) index was linearly correlated with BMD (r = 0.86), BMC (r = 0.96), and ash weight (r = 0.97). Correlation with robusticity was lower than with the WL index. A significant correlation was found between BMC of the metaphyseal region and the bone volumes but this explained only 27% of the variance; correlation with BMD was poorer (r = 0.40). BMC and ash weight were highly correlated (r = 0.992, P <0.000001). However, DXA overestimated BMC by 11% and the overestimation was found to be clearly dependent on the net mineral content of the bone.

Texture analysis of X-ray radiographs is a more reliable descriptor of bone loss than mineral content in a rat model of localized disuse induced by the Clostridium botulinum toxin

Botulism is a generalized paralyzing disease caused by the toxin of Clostridium botulinum (BTX). The toxin acts 3-4 days after injection by blocking the release of acetylcholine to the muscle. Six Wistar rats received a 2-U injection of BTX in the right quadriceps. Six rats were similarly injected with saline and were used as control. Paralysis of the quadriceps was obtained 4-5 days after the injection. Animals were killed 4 weeks after the BTX injection. The bone mineral content (BMC) was measured by dual-energy X-ray absorptiometry (DXA) on the femur and tibia. No side-to-side difference was observed for BMC on the whole tibia and femur in the BTX group. When subregions were selected in the bones, a significant decrease in BMC was obtained on the proximal tibia (-17.4 +/- 2.5%, p < 0.02). No significant difference could be observed on the proximal or distal femur, nor on the diaphyseal shafts. Numeric X-rays were done and a region of interest was transferred to an image analyzer. The texture of the trabecular bone was analyzed by the run length and fractal methods (skyscrapers and blanket). Significant differences were obtained on the proximal tibia for all methods except with fractal skyscrapers. On the distal femur, significant differences were obtained with the run length method, and the skyscrapers and the blanket method in the vertical direction. No differences were obtained with any method on the tibia and femur from control animals. Bone is a highly anisotropic material and its architecture at the microscopic level is conditioned by strains. The trabecular pattern differs in the proximal tibia than in the distal femural. Depending on the trabecular anisotropy, the algorithms can be more or less pertinent. BTX induced a significant bone loss on the bony subparts that are directly influenced by disuse. Texture analysis of X-ray images can reveal differences that were not evidenced by naked eyes. However, a combination of several methods appears necessary to appreciate the bone loss.

Cross-sectional study of osteopenia with quantitative MR imaging and bone densitometry

PURPOSE

To evaluation the cancellous bone-induced intravoxel spin dephasing rate (R2') and its relationship to bone mineral density and marrow fat and to examine these parameters as predictors of vertebral fracture status.

MATERIALS AND METHODS

R2' and R2, the rate constants for reversible and irreversible spin dephasing, and marrow fat fraction were measured in the lumbar vertebrae and proximal femur. One hundred thirty-nine subjects (mean age, 62.4 years +/- 11.4 [SD]; 33 men, 106 women) had spinal dual-energy x-ray absorptiometric bone mineral density (BMD) T scores ranging from +3 to -5. R2', BMD, and bone marrow composition as determinants of vertebral fracture status were examined.

RESULTS

Strongest single predictors of fracture status for BMD and R2' were the Ward triangle (r(2) = 0.48) and trochanter (r(2) = 0.37), respectively. Combined, the two parameters and sites increased fracture prediction (r(2) = 0. 62), whereas the combination of multiple BMD sites did not. Multivariate regression involving marrow fat fraction further improved fracture status prediction. R2' was correlated with BMD at all sites, although slopes differed by a factor of up to 2.5, which reflected differences in trabecular orientation relative to the static field. R2, the true transverse relaxation rate, was negatively correlated with marrow fat fraction. A non-age-related increase in marrow fat fraction in osteoporosis parallels earlier findings in animal models.

CONCLUSION

Cancellous bone marrow R2' measured in the proximal femur provides information, which, with BMD, improves prediction of vertebral fracture status.

Specific evaluation of localized bone mass and bone loss in the rat using dual-energy X-ray absorptiometry subregional analysis

Dual-energy X-ray absorptiometry (DXA), together with the use of ultra-high resolution software, recently appeared as an accurate method for determining bone mineral density (BMD) in the rat. In order to assess the ability of this technique to detect changes in bone mass in the rat rapidly and precisely, we measured BMD at various sites of the femur using DXA subregional analysis. In particular, we studied the BMD of the metaphyseal part of the femur (M-BMD) rich in trabecular bone, and compared the values obtained with the cancellous bone volume measured by histomorphometry. In short-term ovariectomized animals (experiment 1), M-BMD was the only parameter to differentiate statistically between 10 ovariectomized (OVX) and 10 SHAM-operated (SHAM) rats (-11.2%, p < 0.01) 9 days after surgery. M-BMD still expressed the greatest variation between OVX and SHAM rats 42 days following ovariectomy (experiment 2) (-16.1%, p < 0.001 v -6.2%, p < 0.01 for the total femur BMD) and confirmed previous data demonstrating a greater loss of cancellous than cortical bone after cessation of ovarian activity. M-BMD was highly correlated with cancellous bone volume (BV) in normal (r = 0.82, p < 0.001, n = 30), OVX (r = 0.77, p < 0.001, n = 22) and SHAM (r = 0.88, p < 0.001, n = 21) rats.(ABSTRACT TRUNCATED AT 250 WORDS)