Correlation of ultrasound bone velocity with dual-energy X-ray bone absorptiometry in rat bone specimens

Extracorporeal shock waves alone or combined with raloxifene promote bone formation and suppress resorption in ovariectomized rats

Osteoporosis is a metabolic skeletal disease characterized by an imbalance between osteoclast-mediated bone resorption and osteoblast-mediated bone formation. We examined the beneficial effect of shock waves (SW) alone or in combination with raloxifene (RAL) on bone loss in ovariectomized rats (OVX). Sixteen weeks after surgery, OVX were treated for five weeks with SW at the antero-lateral side of the right hind leg, one session weekly, at 3 Hz (EFD of 0.33 mJ/mm²), or with RAL (5 mg/kg/die, per os) or with SW+RAL. Sera, femurs, tibiae and vertebrae were sampled for following biochemical and histological analysis. SW, alone or combined with RAL, prevented femur weight reduction and the deterioration of trabecular microarchitecture both in femur and vertebrae. All treatments increased Speed of Sound (SoS) values, improving bone mineral density, altered by OVX. Serum parameters involved in bone remodeling (alkaline phosphatase, receptor activator of nuclear factor kappa-B ligand, osteoprotegerin) and osteoblast proliferation (PTH), altered by ovariectomy, were restored by SW and RAL alone or in combination. In tibiae, SW+RAL significantly reduced cathepsin k and TNF-α levels, indicating the inhibition of osteoclast activity, while all treatments significantly increased runt-related transcription factor 2 and bone morphogenetic-2 expression, suggesting an increase in osteoblastogenic activity. Finally, in bone marrow from tibiae, SW or RAL reduced PPARγ and adiponectin transcription, indicating a shift of mesenchymal cells toward osteoblastogenesis, without showing a synergistic effect. Our data indicate SW therapy, alone and in combination with raloxifene, as an innovative strategy to limit the hypoestrogenic bone loss, restoring the balance between bone formation and resorption.

Different diagnostic techniques for the assessment of cortical bone on osteoporotic animals

The aim of this study was to assess the capability of ultrasonography and densitometry to predict the mechanical competence of cortical bone in healthy and osteopenic rats, respectively. Thirty 10-month-old Sprague-Dawley retired breeder female rats were used and randomized into three groups of 10 animals each. A group underwent bilateral ovariectomy by dorsal approach (Ovx), another group underwent a simulated ovariectomy (Sham-Ovx), and the last group served as a sham-aged control group (Control). Sixteen weeks after surgery, the animals were euthanized and the femurs of each rat excised for ultrasonographic and densitometric measurements, and mechanical analyses. The Ovx Group had a significantly decreased amplitude dependent speed of sound (AD-SoS-about 7-8%) when compared to the other groups (p<0.0005). For Ovx animals compared with Sham-Ovx and Control rats, significant decreases in densitometric data were observed (6-13%), as well as significant decreases in femoral Max. Load (about 18%) and flexural rigidity (about 30%). The best correlation (R2=0.55, p<0.0005) found was between SoS and femoral shaft bone mineral density (SBMD). The regression coefficient R2 increased when power-law fits were used, particularly from 0.34 (p<0.001) to 0.36 (p<0.0005) in the correlation between SoS and Max. Load and from 0.21 (p<0.05) to 0.25 (p<0.01) in the correlation between SBMD and Max. Load. The ability of QUS or DXA to accurately predict the actual mechanical characteristics of bone, and in particular bone elasticity, remained relatively poor and the improvement of the power-law model did not describe exhaustively the relationships between the variables tested. The DXA and QUS capability to discriminate between ovariectomized and non-ovariectomized rats did not improve when tested together.

Effect of uterine horn ligation on bone mass: an experimental study in rats

OBJECTIVE

After tubal ligation, normal bone mass in the presence of gonadal deficit has been reported. These incongruent results motivated us to examine the topic.

STUDY DESIGN

Bone mass was assessed by densitometry and ultrasonography 60 days after surgery on 100-day-old female Wistar rats. Fifteen Wistar rats with uterine horn ligation (TL) were compared with 15 unoperated, 15 with a sham uterine horn ligation (Sham-TL), and 15 ovariectomized (OVX), using ANOVA and a correlation test to determine the relations between results.

RESULTS

Femoral and vertebral bone mass were significantly lower in the OVX y TL groups than in unoperated and controls groups (P<0.0001).

CONCLUSIONS

Our study revealed significantly lower axial and peripheral bone mass in rats with uterine horn ligation.

Do ultrasound measurements reflect bone microarchitecture rather than bone mass?: An in vitro study of the rat femur with the use of ultrasound, densitometry, and histomorphometry

RATIONALE AND OBJECTIVES

In an experimental study in 40 rat femurs, the authors correlated the amplitude-dependent speed of bone ultrasound (Ad-SOS) with the bone mineral content and density and with the bone trabecular connectivity: trabecular bone volume, trabecular number, trabecular thickness, and trabecular separation to evaluate and compare the usefulness of the Ad-SOS to determine bone quantity and/or quality.

METHODS

Bone mineral content and density were determined with dual-energy x-ray absorptiometry. Trabecular connectivity was determined with histomorphometric techniques.

RESULTS

There was a strong correlation between the Ad-SOS and the other parameters studied, with a particularly high positive correlation with trabecular bone volume and trabecular thickness, and an inverse correlation with trabecular separation. The correlation was weaker with the bone mineral content and bone mineral density and with the trabecular number. For the trabecular separation, the correlation was significant in all cases, but it was negative.

CONCLUSIONS

Bone ultrasound, in this case Ad-SOS, defines the quality of the bone in terms of trabecular architecture rather than bone density; however, this conclusion is valid only for the rat femur model that the authors used.

Influence of bone tissue density and elasticity on ultrasound propagation: an in vitro study

Ultrasound (US) waves are mechanical vibrations that are applied to a material--bone tissue--in order to study its properties, that is, density, elasticity, and structure. In this study we evaluated in which way density and elasticity of the spongy bone influenced the transmission of 1.25 MHz US pulses. Twelve cylindrical specimens (diameter, 8 mm; height, 5 mm) excised from phalanxes of pig were decalcified with 0.5 M EDTA for different times (0, 2, and 5 days). During these periods, the samples underwent the following investigations: US transmission, density, and elasticity measurements. To assess the homogeneity of decalcification, the cross-sections of some samples were microradiographed. A detailed analysis of the US signal received was performed using velocity, Fourier analysis, and some parameters typical of signal processing technique. A good correlation was found between US velocity and density (r2 = 0.70); a lower correlation was found between velocity and elasticity (r2 = 0.59). If density and elasticity are considered simultaneously, the correlation with the US velocity improves significantly (r2 = 0.84). Fourier analysis enabled us to observe a shift of the main frequency toward lower values as the decalcification process advanced. We also observed that in the regressions weighted for density, US velocity correlated poorly with elasticity (r2 = 0.16), whereas signal processing parameters maintain a good correlation with elasticity (ultrasound peak amplitude [UPA], r2 = 0.48; slope, r2 = 0.62). In this study, it has been observed that when using a signal processing technique to analyze US pulses, it is possible to identify some parameters that are related in different ways to density and to elastic properties of bone. Our results show the potentiality of US technique to separate information on bone density and elasticity that X-ray-based densitometric methods do not provide.

Speed of sound, bone mineral density and bone strength in oophorectomized rats

BACKGROUND

The aim of this study was to determine the sensitivity of bone mineral density (BMD), ultrasounds (SOS) and resistance to torsion (T) to detect experimental osteopenia induced in rats 3 and 6 months after ooforectomy.

MATERIALS AND METHODS

Seventy-four rats were used, divided into four groups, ooforectomized rats analysed 3 and 6 months after the operation and their respective control groups, in which BMD (Hologic QDR 1000 S/N 277), SOS (DBM Sonic 1200) and T (adapted test machine) were determined in the right femur.

RESULTS

The results of the three techniques distinguished the ooforectomized groups from the controls, both 3 and 6 months after the ooforectomy, obtaining more significant differences with BMD (P = 0.0006, P = 0. 001, respectively) than SOS and T, where a significance of only P = 0.05 was obtained. In the correlation study among the three techniques, a significant correlation was observed between BMD and SOS (r = 0.39, P = 0.0008), as well as between BMD and T (r = 0.31, P = 0.03). However, significance was not observed between the SOS and T tests.

CONCLUSION

In the study of sensitivity and specificity of the techniques used to detect the osteopenia caused by the ooforectomy, by means of calculation of the area under the receiver operation characteristic (ROC) curve, it was proven that although the three techniques distinguished between the two analysed populations, BMD presented an area under the ROC curve that was superior (0.87, 0.85) to that obtained with SOS (0.73, 0.67) and T (0.73, 0.68), both 3 and 6 months after the operation.

Discriminant capacity of quantitative ultrasound versus dual X-ray absorptiometry to determine cancellous bone loss in ovariectomized rats

The capacity of dual x-ray absorptiometry and quantitative ultrasound to discriminate bone loss and to predict the mechanical and microarchitectural properties of cancellous bone in an animal model of osteopenia was evaluated. Thirty-five female Sprague-Dawley rats (10 months old) were randomized into three groups: baseline group, 10 rats killed at the beginning of the study; ovx group, 15 rats ovariectomized; and sham group, 10 rats sham operated. At the beginning and end of the study, all the animals underwent osteosonography to record the proximal tail (C3 vertebra) bone speed of sound. Sixteen weeks after surgery, the animals were euthanized and the L5-6 lumbar vertebrae of each rat were excised for densitometric, biomechanical (compression test), and histomorphometric studies. Significant differences were found among the groups for final speed of sound (p = 0.01). The L5 bone mineral density of the ovx group decreased by 12.1% (p = 0.049) and 12.6% (p = 0.035) compared, respectively, with baseline and sham groups. The biomechanical parameters of the ovx group decreased by 15-47% compared with the other groups, showing significant differences between the ovx and sham groups both for maximal stress (p = 0.026) and elastic modulus (p = 0.013). Histomorphometric parameters of the ovx group showed significant decreases in comparison with other groups. Logistic regression analysis showed that dual X-ray absorptiometry and quantitative ultrasound discriminate ovariectomized and healthy rats with a similar capacity, classifying correctly all rats used in the model in a range of 61-70%. This similar capacity seems to derive from two different capacities to detect bone changes. Dual X-ray absorptiometry, depending on bone mineralization and density, is able to detect modifications in bone stiffness and strength, confirmed also by the correlation with biomechanical data. On the contrary, quantitative ultrasound seems to depend more on cancellous bone microarchitecural changes because it is correlated to histomorphometric parameters.

Impact of weight in obese subjects on bone speed of sound

RATIONALE AND OBJECTIVES

The authors determined the effect of obesity on measurements of amplitude-dependent speed of bone ultrasound (Ad-SOS [m/sec]) and compared them to the total body bone mineral content (TBBMC/g).

METHODS

A total of 25 women were studied (mean age 41.8 +/- 10.2 years). In all the subjects, body mass index (BMI) exceeded 30 kg/m2 (range, 31.12-47.47 kg/m2); mean body weight was 104 +/- 17 kg. Ad-SOS was measured at the proximal phalanges and TBBMC in whole body with dual-energy x-ray absorptiometry.

RESULTS

Correlation study (Fisher's r to z) showed that Ad-SOS correlated negatively with weight (r = -0.85, P < 0.0001) and with TBBMC (r = -0.71, P < 0.0001). The correlation between TBBMC and weight was r = 0.76, P < 0.0001. Body fat percentage correlated partially with TBBMC (r = 0.40, P < 0.05) and negatively with Ad-SOS (r = -0.75, P < 0.0001). When the correlation test was adjusted for weight (partial correlation), the correlation between Ad-SOS and TBBMC was not significant (r = -0.21, P = NS), and the correlation between Ad-SOS and weight continued to be inversely significant (r = -0.67, P < 0.0001).

CONCLUSIONS

The results showed a clearly negative effect of weight on Ad-SOS measurements and indicated the limitations of this technique when employed in overweight and obese patients. Broad-band ultrasound attenuation and speed of sound, two commonly measured variables in bone ultrasound studies, may be differently affected by soft tissue.

Influence of soft tissue (fat and fat-free mass) on ultrasound bone velocity: an in vivo study

RATIONALE AND OBJECTIVES

The authors determine the relative effect of soft-tissue compartments, body fat (percent [%Bfat] and weight [Bfat kg]) and fat-free mass (FFM kg), on measurements of ultrasound bone velocity (UBV m/second).

METHODS

The authors measured UBV in proximal phalanxes and body fat and fat-free mass by near infrared interactance in 40 healthy premenopausal women (mean age +/- standard deviation 28.2 +/- 3.8 years).

RESULTS

Correlation study (Fisher's r to z) showed that UBV correlated negatively with %Bfat (r = -0.61, P < 0.0001), Bfat kg (r = -0.56, P = 0.0001) and marginally with body weight (r = -0.33, P = 0.0403), but did not correlate with FFM kg or H2O L (both r = -0.08, P not significant). When the correlation test was adjusted for weight and age (partial correlation), the negative correlation between UBV and %Bfat persisted (r = -0.54, P < 0.0005; and r = -0.63, P < 0.0001, respectively) and the correlation with FFM kg, adjusted for weight, became positive and significant (r = 0.55, P < 0.0005).

CONCLUSIONS

These results, to our knowledge, are the first to be obtained by in vivo evaluation of UBV in relation to body fat and fat-free mass. Body fat, but not fat-free mass, was the main factor affecting UBV. This confirms the deficiency of UBV measurements, considering that obesity is a protective factor for bone mass.