Measurement of intrinsic bone quality in vivo by reflection ultrasound: correction of impaired quality with slow-release sodium fluoride and calcium citrate

The Effects of Claw Health and Bone Mineral Density on Lameness in Duroc Boars

To investigate the effects of claw lesion types and bone mineral density on lameness in boars, the data of claw lesion score, gait score, and bone mineral density, measured by a Miniomin ultrasound bone densitometer, were collected from a total of 739 Duroc boars. Firstly, we discovered that the prevalence of claw lesions was as high as 95.26% in boars. The percentage of lameness of boars with SWE was higher than those with other claw lesions. Meanwhile, the results showed that the probability of lameness was higher in boars with lower bone mineral density (p < 0.05). Logistic regression models, including variables of boar age, body weight, serum mineral level, and housing type, were used to identify the influencing factors of bone mineral density in this study. The results found that bone mineral density increases with age before reaching a maximum value at 43 months of age, and begins to decrease after 43 months of age. Elevated serum Ca levels were significantly associated with an increase in bone mineral density (p < 0.05). Aside from the above findings, we also made an interesting discovery that boars in the individual pen model significantly increased bone mineral density compared to those in the individual stall model. In conclusion, claw lesions and bone mineral density were significantly associated with lameness. Age, serum Ca, and housing type are the potential influencing factors for bone mineral density in boars.

Radial anatomic variation of ultrasonic velocity in human cortical bone

Quantitative ultrasound techniques can be used to retrieve cortical bone quality. The aim of this study was to investigate the anatomic variations in speed of sound (SOS) in the radial direction of cortical bone tissue. SOS measurements were realized in 17 human cortical bone samples with a 3.5-MHz transverse transmission device. The radial dependence of SOS was investigated in a direction perpendicular to the periosteum. For each sample, bone porosity was measured using an X-ray micro-computed tomography device. The mean SOS was 3586 ± 255 m/s. For 16 of 17 specimens, similar radial variations in SOS were observed. In the periosteal region, SOS first decreased in the direction of the endosteum and reached a minimum value approximately in the middle of the cortical bone. SOS then increased, moving to the endosteal region. A significant negative correlation was obtained between SOS and porosity (R = -0.54, p = 0.02).

Ultrasound and the biomechanical competence of bone

Ultrasound is a mechanical wave and consequently has a unique potential to characterize the mechanical properties of bone. In some applications, such as determination of the anisotropic elastic constants of cortical bone specimens, this potential has been realized. In other applications, including the hugely important field of clinical measurements, current ultrasonic techniques struggle to provide information directly relating to mechanical properties. This article reviews the successes and shortcomings of ultrasound as a tool for determination of bone mechanical properties and highlights those new developments likely to bring progress in the future.

Instrumentation for in vivo ultrasonic characterization of bone strength

Although it has been more than 20 years since the first recorded use of a quantitative ultrasound (QUS) technology to predict bone fragility, the field has not yet reached its maturity. QUS has the potential to predict fracture risk in several clinical circumstances and has the advantages of being nonionizing, inexpensive, portable, highly acceptable to patients, and repeatable. However, the wide dissemination of QUS in clinical practice is still limited and suffering from the absence of clinical consensus on how to integrate QUS technologies in bone densitometry armamentarium. Several critical issues need to be addressed to develop the role of QUS within rheumatology. These include issues of technologies adapted to measure the central skeleton, data acquisition, and signal processing procedures to reveal bone properties beyond bone mineral quantity and elucidation of the complex interaction between ultrasound and bone structure. This article reviews the state-of-the art in technological developments applied to assess bone strength in vivo. We describe generic measurement and signal processing methods implemented in clinical ultrasound devices, the devices and their practical use, and performance measures. The article also points out the present limitations, especially those related to the absence of standardization, and the lack of comprehensive theoretical models. We conclude with suggestions of future lines and trends in technology challenges and research areas such as new acquisition modes, advanced signal processing techniques, and modelization.

Reduction in normalized bone elasticity following long-term bisphosphonate treatment as measured by ultrasound critical angle reflectometry

Using an improved version of ultrasound critical angle reflectometry, the bone quality of cortical and trabecular bone was assessed in vivo by measuring elastic moduli (normalized for bone density) at both principal axes, referred to as the minimum and maximum normalized elasticities. The measurements were made in 30 normal premenopausal women, 30 normal postmenopausal women, 22 untreated postmenopausal women with osteoporosis, 74 postmenopausal women with osteoporosis or osteopenia on bisphosphonate treatment, and 32 patients with renal transplantation (16 women and 16 men) taking steroids. Cortical elasticity was higher than trabecular elasticity; both declined slightly and non-significantly with age in normal women. Among untreated postmenopausal women with osteoporosis, cortical maximum normalized elasticity (E(cmax)) remained within 95% prediction intervals of normal women. Among patients on bisphosphonate, E(cmax) was low in the majority of patients. E(cmax) was significantly more depressed among those taking the drug > or =3 years than <3 years (22.1% below normal premenopausal women versus 17.2%, P =0.001), and among those with incident non-spinal fractures than without (75.9 vs. 81.5%, P =0.008). E(cmax) was independent of bone mineral density at the calcaneus. Most patients with renal transplantation had low E(cmax), with a mean 20.8% below the normal premenopausal mean. Qualitatively similar findings were found with cortical minimum elasticity and with trabecular minimum and maximum elasticities. Thus, the material bone quality of cortical and trabecular bone may be impaired following bisphosphonate treatment, as in renal transplantation on steroids.

Limited diagnostic agreement of quantitative sonography of the radius and phalanges with dual-energy x-ray absorptiometry of the spine, femur, and radius for diagnosis of osteoporosis

OBJECTIVE

The aim of our study was to evaluate the diagnostic agreement of quantitative sonography of the radius and proximal phalanx and dual-energy X-ray absorptiometry (DXA) of the radius, lumbar spine, and femoral neck for the detection of osteoporosis.

MATERIALS AND METHODS

In 95 women (mean age, 53 +/- 13 years) and 26 men (mean age, 53 +/- 13 years), DXA measurements of the lumbar spine (posterior-anterior, L1-L4) and the femoral neck, as well as quantitative sonography of the radius and proximal phalanx of the third finger were obtained. The percentage of patients below a given threshold was calculated for each imaging technique. A T score of less than -2.5 indicated presence of osteoporosis. Diagnostic agreement in identifying individuals with osteoporosis was assessed using kappa scores.

RESULTS

Between 14% and 22% of the patients were classified as osteoporotic after DXA of the various regions of interest of the radius, 31% after DXA of the spine, 43% after DXA of the femoral neck, 32% after quantitative sonography of the distal radius, and 34% after quantitative sonography of the phalanx of the third finger. Correlation coefficients between T values for quantitative sonography and those for DXA varied between not significant and 0.54 at the different regions. Kappa analysis showed the diagnostic agreement among quantitative sonography and DXA to be fair to moderate (kappa = 0.38-0.48). The highest agreement was between quantitative sonography of the proximal phalanx of the third finger and DXA of the total radius (kappa 0.48; p < 0.05).

CONCLUSION

Considerable diagnostic disagreement exists between quantitative sonography and DXA of the forearm, as is true for most quantitative techniques in the assessment of skeletal status. The lack of correlation makes quantitative sonography impractical for routine diagnostic use but might characterize different parameters related to bone quality.

Transmission scanning acoustic imaging of human cortical bone and relation with the microstructure

OBJECTIVE

To investigate and compare the spatial distribution of velocity with that of the microstructural properties (dimension of the haversian canal, percentage of porosity) on cross section of cortical bone.

DESIGN

Experimental investigations permitted to quantify variation of acoustic properties related with that of the microstructural properties.

BACKGROUND

Transmission ultrasonic techniques have been used in vitro and in vivo to assess the elastic and acoustic properties of Human bone, but few investigated the relationship between their variation with that of the microstructure.

METHODS

Two scanning techniques (in transmission with a focused transducer at 5 MHz and an environmental scanning electronic microscope at 20 KV) enabled to obtain the spatial distribution of relative acoustic velocities and the microstructural properties (pore size and porosity).

RESULTS

Increase of the velocities is related with the decrease of pore size and porosity. Around the periphery of the sections, the velocities were found to be significantly lower in the posterior side with a significant increase along the length. Radial variations are correlated to the spatial distribution of the microstructure where the endocortical region is more porous compared to the periosteal region.

CONCLUSION

Significant alterations of the microstructural properties of the cortical bone reflect small variation of velocity suggesting that the velocities are not so sensitive to microstructural changes.

RELEVANCE

These results are of importance for the clinicians and researchers to get a better understanding (advantages and limitation) of the use of ultrasound technique to assess material and structural properties of cortical bone. Our study suggested that velocity could be an index of porosity. Then it would be of interest to improve the clinical assessment of bone quality by describing bone both by a mineralization index and a microstructural index.

Spatial distribution of acoustic and elastic properties of human femoral cortical bone

The purpose of this study is to quantify the spatial distribution of acoustic velocities and elastic properties (elastic constants) on Human femoral cortical bone. Four cross sections (average thickness of 2.09+/-0.27 mm) have been cut transversally between 40% and 70% of the total length and between them parallelepiped samples in each quadrant have been cut. Ultrasonic technique in transmission with immersion focused transducers at 5 MHz and contact transducers 2.25 MHz were used on the cross sections and parallelepiped samples, respectively. The first technique allows relative spatial distribution of velocities to be obtained, meanwhile the second technique allows the direct assessment of elastic constants. For both techniques, bulk velocities were found to be lower at the posterior side with an increase along the length (from 40% to 70% total length) (p < 0.05). Densities and elastic constants show equivalent pattern of variation. These variations are mainly due the cortical porosity related to vascularisation environment. The spatial distribution of velocities exhibits significant radial variation from the endosteal to the periosteal region. This is in agreement with variation of the porosity at that location. Same range of velocities was obtained with both techniques. The range of longitudinal velocities values varies from 3548 to 3967 m/s and between 18.5 and 33.1 GPa for the bulk velocities and axial elastic constants, respectively. Our results are within the range with those found in the literature. However, it must be noted that the range of acoustic and elastic properties variation is concerning the same bone. So, our new results show the ability of the technique to quantify accurately local variation of acoustic and elastic properties (within the section and along the length) of human cortical bone. Furthermore, our immersion technique could be used to assess the spatial distribution of the elastic constants with the knowledge of spatial distribution of densities.

Assessment of bone status using speed of sound at multiple anatomical sites

Studies in vitro and in vivo have shown that quantitative ultrasound (QUS) is a valid tool for the assessment of bone status. Current QUS methods using the transmission technique are limited to one peripheral bone site. A new system, Sunlight Omnisense (Omnisense, Sunlight Medical Ltd., Rehovot, Israel), measures speed of sound (SOS, in m/s) along the surface of the bone based on an axial transmission technique. The Omnisense can measure SOS at several anatomical sites. This study evaluated the SOS at different anatomical sites in a healthy population. A total of 334 adult women from three research centers in the USA and Canada with a mean (+/- SD) age of 48.8 (+/- 17.4) years were enrolled in this study. SOS was measured at the proximal third phalanx, distal one third radius, midshaft tibia, and fifth metatarsal. The mean SOS (+/- SD) values for the phalanx, radius, tibia and metatarsal were 3984 (+/- 221), 4087 (+/- 147), 3893 (+/- 150) and 3690 (+/- 246) m/s, respectively. Each anatomical site SOS was significantly different (p < 0.001) from that of the other sites. SOS at the different anatomical sites was modestly, but significantly, correlated (r = 0.31 to 0.56, p < 0.001). Similar correlation coefficients were obtained for the T scores. The mean T scores for subjects over the age of 60 years were -1.94, -2.01, -0.97 and -1.42 for the phalanx, radius, tibia and metatarsal, respectively. The age of peak SOS and the rate of change thereafter varied with anatomical site, implying that the prevalence of osteopenia and osteoporosis was site-dependent if only one T score cut-off point was used. Comparing individuals, 10% to 17% of patients had T scores that differed by more than a factor of 2 between sites. Weight and age were some of the contributing factors to this heterogeneity. The Omnisense provides an opportunity to assess bone status at different anatomical sites. Whether or not combining measurements from all these anatomical sites will improve osteoporosis management still needs to be determined.

Bone material ultrasound velocity is predictive of whole bone strength

In humans, bone strength is assessed indirectly by the noninvasive measurement of structure or mass. Recent clinical application of an ultrasonic critical-angle reflectometry technique (UCR) has demonstrated the measurement of the regional and directional distribution of mechanical stiffness. This study investigates the specific question: are these measurements of a local material level property predictive of the strength of whole bone? Maximum values of pressure wave velocity and breaking strength were recorded at two locations (midshaft and base of neck) on rat femurs from growing rats. The results demonstrate a strong empirical relationship between material-level ultrasound (US) velocity and whole bone mechanical strength. However, the US velocity at a specific bone site can be used to assess bone strength at that site only, explaining discrepancies in other published studies that negate a relationship between strength and US velocity. The results indicate an important role for US velocity measurement in clinical evaluation of bone health.

Bone material elasticity in a murine model of osteogenesis imperfecta

To investigate the source of bone brittleness in the disease osteogenesis imperfecta (OI), biomechanical properties have been measured in the femurs from a homozygous (oim/oim) mutant mouse model of OI, its heterozygous littermates, and wild-type animals. The novel technique of ultrasound critical-angle reflectometry (UCR) was used to determine bone material elasticity matrix from measurements of the pressure and shear wave velocity at different orientations about selected points of the bone specimens. This nondestructive method is the only available means for obtaining measurements of this nature from a single surface. The ultrasound pressure wave velocity showed an increased isotropy in the homozygous compared to the wild-type specimens. This was reflected in a significant decrease in the principal elastic modulus measured along the length of the oim/oim bones (E33) while the modulus along the width (E11) did not change significantly, compared to wild-type specimens. The Poisson's ratio, v12, also had a significantly increased value in oim/oim bones. Measurements of these parameters in heterozygous animals generally fell between those from homozygous and control mice. The differences in the elasticity components in oim/oim bones indicate an altered stress distribution and a modified elastic response to loads, compared to normal bone.

Fluoride for treating postmenopausal osteoporosis

OBJECTIVES

To assess the efficacy of fluoride therapy on bone loss, vertebral and non-vertebral fractures and side effects in postmenopausal women.

SEARCH STRATEGY

We searched Medline, Current Contents and the Cochrane Controlled Trial Registry up to December 1998.

SELECTION CRITERIA

Two independent reviewers selected RCTs which met predetermined inclusion criteria.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data using predetermined forms and assessed the methodological quality of the trials using a validated scale. For dichotomous outcomes, relative risks (RR) were calculated and for continuous outcomes, weighted mean differences (WMD) of percentage change from baseline were calculated. Where heterogeneity existed (determined by a chi-square test) a random effects model was used.

MAIN RESULTS

Eleven studies (1429 subjects) met the inclusion criteria. The increase in lumbar spine bone mineral density (BMD) was found to be higher in the treatment group than in the control group with a WMD 8.1% (95%CI: 7.15,9.09) after two years of treatment and 16.1%(95%CI: 14.65,17.5) after four years. The RR for new vertebral fractures was not significant at two years [0.87 (95%CI: 0.51,1.46)] or at four years [0.9(95%CI: 0.71,1.14)]. The RR for new non-vertebral fractures was not significant at two years 1.2(95%CI: 0.68,2.1) but was increased at four years in the treated group 1.85(95%CI: 1.36,2.5), especially if used at high doses and in a non slow release form. The RR for gastrointestinal side effects was not significant at two years 2.18(95%CI: 0.86,1.21) but was increased at four years in the treated group 2.18(95%CI: 1.69,4.57) especially if fluoride was used at high doses and in a non slow release form. The number of withdrawals and dropouts was not different between treated and control groups at two and four years.

REVIEWER'S CONCLUSIONS

Although fluoride has an ability to increase BMD at lumbar spine, it does not result in a reduction of vertebral fractures. In increasing the dose of fluoride, one increases the risk of non-vertebral fracture and gastrointestinal side effects without any effect on the vertebral fracture rate.

Does combining the results from multiple bone sites measured by a new quantitative ultrasound device improve discrimination of hip fracture?

There is a growing interest in the use of quantitative ultrasound (QUS) measurements as an alternative to current radiation-based bone densitometry techniques for the noninvasive assessment of fracture risk. While most of the commercialized ultrasound devices measure only single predefined peripheral skeletal sites, the Omnisense prototype (Sunlight Ltd., Israel) can be used on multiple bones, including the spinous processes. In this study, we examined the ability of speed of sound measured at the calcaneus, distal third and ultradistal radius, proximal third phalanx, metacarpal, capitate, patella, and the posterior process of the thoracic spine to differentiate subjects with hip fractures from normal controls. Seventy-nine postmenopausal Caucasian Israeli women who had sustained an atraumatic fracture of the proximal femur within the last 6 months were recruited from the local population (mean age 80 +/- 8.9 years). As controls, 295 postmenopausal Caucasian Israeli women without osteoporotic fractures were also included (mean age 70 +/- 8.7 years). Discrimination of hip fractures with QUS at all ultrasound sites was highly statistically significant (p < 0.01) (odds ratios [ORs] = 1.4-3.0; area under the ROC curve [AUC] 77-92%), except for the hand metacarpal. Distal radius and calcaneus measurements (ORs = 2.4 and 3.0) were the best discriminators of hip fracture patients from controls. Using a forward selective linear regression model, the discriminator values of combined assessment at two sites were investigated. There was moderate improvement in diagnostic value, but the best combination was the calcaneus with the distal radius, which improved the AUC by 3% and raised both the sensitivity and specificity to 94%. These data demonstrate the encouraging potential of improving discrimination of hip fracture by using multiple-site ultrasonic measurements.

Bone elasticity and ultrasound velocity are affected by subtle changes in the organic matrix

The mechanical competence of bone can be studied through the measurement of the components of its material elasticity, a property which can vary both in magnitude and in dependence upon orientation (anisotropy). While it is known that the elasticity is largely determined by the mineral constituents of the bone matrix, it is nonetheless clear that it must be also dependent upon the remaining constituents of bone material. In this work, the influence of organic components on the elasticity is explored by altering specific constituents of the bone matrix to varying degrees. This study addresses two questions: first, are the resulting changes in elasticity strongly or weakly dependent upon direction, and second, are they substantially dependent upon the nature and magnitude of the induced matrix alteration? To answer these questions, we performed different chemical manipulations of the bone matrix and measured the changes in elasticity and velocity using the technique of ultrasound critical angle reflectometry. Altering the properties of the organic matrix resulted in substantial and complex changes in the elasticity of bone. The observed changes were strongly dependent upon direction, could not be explained by changes in density alone, and varied strongly with the specific chemical treatment of the matrix. Immersion in urea selectively affected protein components of the organic matrix and resulted in reversible changes in velocity and elasticity, while removal of collagen caused anisotropic decreases and removal of all organic matter caused a collapse of all components of the elasticity. In conclusion, this study confirms that the organic matrix exerts a profound influence on the elasticity and indicates that the measurement of elastic properties at multiple directions is necessary in the assessment of bone mechanical competence.

Reflection ultrasound velocities and histomorphometric and connectivity analyses: correlations and effect of slow-release sodium fluoride

To better understand how structural and functional bone properties contribute to the changes in bone biomechanical properties revealed by ultrasound critical angle reflectometry (UCR) analysis, we measured both UCR velocities and histomorphometric properties in bone biopsy specimens from 33 osteoporotic patients before and following intermittent slow-release sodium fluoride (SRNaF) and continuous calcium citrate administration. Mean skeletal fluoride exposure was 17 months, and mean skeletal fluoride content was 0.203 +/- 0.088 SD% bone ash. Intermittent SRNaF and continuous calcium citrate promoted significant increases in trabecular thickness (122 +/- 18 SD microm to 131 +/- 20, p = 0.020), mineral apposition rate (0.79 +/- 0.26 to 1.05 +/- 0.40 microm/day, p = 0.014), and a significant decline in eroded surface (3.9 +/- 1.6 to 2.8 +/- 1.4%, p = 0.002). There were also significant increases in node number (0.193 +/- 0.100 to 0.368 +/- 0.245, p < 0.01) and node-to-node strut length (0.076 +/- 0.087 to 0.191 +/- 0.173, p < 0.01) relative to total cancellous area. Cortical UCR velocity did not change but cancellous velocity significantly increased by 97 m/s following therapy (p = 0.0005). When compared against the significant changes in bone histomorphometry and connectivity, the sum of both cancellous and cortical ultrasound velocities was significantly correlated with node number/area (R2 = 0.305, p < 0.0001) and node-to-node strut length/area (R2 = 0.372, p < 0.0001) and to a lesser extent with mineral apposition rate (R2 = 0.106, p = 0.032). Multiple regression analysis demonstrated that 40% of the variance in the sum of the UCR velocities can be accounted for by the variability in these histomorphometric and connectivity parameters. There were no significant correlations between the sum of cortical and cancellous ultrasound velocities and cancellous bone volume (R2 = 0.014, p = 0533), trabecular thickness (R2 = 0.012, p = 0.47), or bone mineral density (R2 = 0.003, p = 0.80). These observations indicate that velocity measurements with the UCR methodology show an improvement in bone elasticity associated, in part, with an improvement in the rate of bone mineralization and an improvement in bone quality at the structural level as shown by microarchitecture.

Utility of ultrasound to assess risk of fracture

Traditional assessments of bone properties have utilized densitometry techniques such as Dual Energy X-ray Absorptiometry (DXA). Recently, quantitative ultrasound (QUS) has been introduced as an alternative method of assessing bone properties. Advantages of QUS over X-ray techniques include low costs, portability, and nonionizing radiation. Proponents of QUS have claimed that this technology can provide information not only about the density but also about the structure and mechanical properties of bone. There are two major questions that need to be answered for those who seek to diagnose bone disorders with ultrasound: (1) what does quantitative ultrasound actually measure, and, even more importantly, (2) what is its clinical utility? In this review we will briefly examine the first question and will focus on the utility of ultrasound in clinical trials to discriminate between fractures and non-fractures and to predict the risk of fractures.

Ultrasound critical-angle reflectometry (UCR): a new modality for functional elastometric imaging

This paper discusses the measurement of velocity in a solid based on the analysis of the amplitude and phase of ultrasound waves reflected by a solid, a technique called ultrasound critical-angle reflectometry (UCR). To this end, the complete formulation of ultrasound wave reflection and refraction from a liquid-solid interface is described. Differences between this formulation and previously published ones are briefly discussed. Based on this analysis it is in particular possible to measure by this technique not only pressure but also, for the first time in such studies, shear wave velocities, an experimentally confirmed result. The measurement of the complete stiffness matrix of a transversely isotropic solid, specifically cortical bone, by applying UCR elastometry to any point on the solid's surface is demonstrated. Finally this method is extended to functional elastometric imaging. The techniques presented in this paper offer new opportunities for applications of UCR imaging to the assessment of bone metabolism, formation and disease and also the analysis of composite materials in general.

Measurement of shear-wave velocity by ultrasound critical-angle reflectometry (UCR)

There exists a growing body of research that relates the measurement of pressure-wave velocity in bone to different physiological conditions and treatment modalities. The shear-wave velocity has been less studied, although it is necessary for a more complete understanding of the mechanical properties of bone. Ultrasound critical-angle reflectometry (UCR) is a noninvasive and nondestructive technique previously used to measure pressure-wave velocities both in vitro and in vivo. This note describes its application to the measurement of shear-wave velocity in bone, whether directly accessible or covered by soft tissue.

The influence of porosity and pore size on the ultrasonic properties of bone investigated using a phantom material

Ultrasonic propagation in bone has been investigated using the Leeds Ultrasonic Bone Phantom Material. Phantoms were produced with different porosities in the range of 45-83% and pore sizes of 1.3 and 0.6 mm. The phase velocity at 600 kHz was found to follow a second-order polynomial as a function of porosity. Phase velocity values between 1545 and 2211 m s-1 were measured and found to be largely independent of pore size for a given porosity. The slope of the phase velocity as a function of frequency (dispersion) decreases with increasing porosity. The values obtained from samples having different pore sizes were also similar. The attenuation coefficient and normalized broadband ultrasonic attenuation (nBUA) reached a maximum at about 50%. The normalized attenuation ranged from 6 to 25 dB cm-1 over the porosity range available and consistently showed higher values for the larger pore size. Similarly, the nBUA values were found to be between 14 and 53 dB MHz-1 cm-1, with the values for the larger pore size being roughly 10 dB MHz-1 cm-1 greater than those for the smaller pore size. These findings demonstrate that the Leeds phantom can be used to investigate the effect of structural changes in bone and to aid the understanding of quantitative ultrasound. The results support the assumption that the velocity in trabecular bone is not dependent on pore size but is influenced by the mechanical properties of the bone's constituents and the overall framework, whereas the attenuation and BUA are also influenced by structure.

Reductions in bone strength after fluoride treatment are not reflected in tissue-level acoustic measurements

Acoustic velocity measurements are used to estimate tissue-level bone strength after fluoride therapy for osteoporosis. However, acoustic measurements provide information about elasticity, not strength, and bone elasticity does not necessarily correlate with bone strength at a tissue level. The current study was undertaken to evaluate the effects of fluoride treatment on tissue-level acoustic velocities, and to determine the relationship between acoustic velocity and bone strength measured in the femur, femoral neck, and spine. Young adult rabbits were treated with either 0 or 100 parts per million of fluoride in their drinking water for six months. After treatment, the bones were harvested for measurement of tissue fluoride, bone strength, and acoustic properties. Acoustic velocities were measured in the femoral midshaft using an acoustic microscope with a 50 MHz transducer. Both longitudinal and transverse velocities were measured. After the initial acoustic measurements the bone specimens were treated to remove either the organic matrix or mineral, and the acoustic measurements were repeated. Fluoride treatment increased bone fluoride levels 7-8 fold and reduced all biomechanical parameters. Most notably the fracture force of the femoral neck was reduced by 25% (p < 0.005), and the fracture stress of the L-5 vertebra was reduced by 19% (p < 0.05). Fluoride treatment had no significant effect on any of the measured acoustic velocities. The elastic anisotropy of the bone was decreased by demineralization (p < 0.0001) and increased by removal of the organic matrix (p < 0.0001), but unaffected by fluoride treatment. Acoustic measurements were not correlated with bone strength in the femoral neck or femoral midshaft. There was a positive correlation between the longitudinal velocity measured in the femur and the vertebral fracture stress, but this was the only positive association between acoustic velocities and strength measurements. These data cast doubt on the utility of high frequency (>2 MHz) acoustic measurements for evaluating the efficacy of fluoride therapy, especially in the hip.

Quantitative ultrasound bone measurements: normal values and comparison with bone mineral density by dual X-ray absorptiometry

Normative data for qualitative ultrasound (QUS) measurements: speed of sound (SOS), broadband ultrasound attenuation (BUA), and stiffness were established in 118 healthy women aged 20-86 years and in 42 healthy men aged 22-76 years. The relations between age, weight, height, and QUS were studied. QUS measurements were negatively correlated with age in both sexes. In women, age was accepted as first factor (R2 = 0.39 for SOS, 0.35 for BUA, and 0.45 for stiffness, P < 0.001); weight was accepted as second factor for BUA (R2 = 0.44, P < 0.001). In men, age was the only significant parameter (R2 = 0.41 for SOS, 0.39 for BUA, 0.43 for stiffness, P < 0.001). QUS measurements of the right and left feet were highly correlated unless unilateral foot pathology such as algodystrophy was present. Significant correlations were found between QUS of the calcaneus and dual X-ray absorptiometry (DXA) of the lumbar spine (R = 0.67, P < 0.01 for SOS; R = 0.57, P < 0.02 for BUA; R = 0.65, P < 0.01 for stiffness).

Effects of high levels of fluoride on bone formation: an in vitro model system

In order to develop an in vitro model for the study of the effects of different agents on biomineralization, a three-dimensional cell culture system was investigated at different levels of fluoride. Rat fetal osteoblasts were seeded onto collagen discs and maintained in a culture medium for 40 days. Results showed that, at 40 days, the cultured matrices had a Ca:P ratio, mineral content and Fourier transform infrared (FTIR) spectrum that were close to those seen for normal rat bone. Viable cells, observed by light microscopy, were present in the matrix at 40 days. The formation of a mineralized matrix in this experimental set-up provided a model for exploring in vitro the effects of high levels of fluoride on bone. The fluoride content of the mineral formed in the cultures showed a dose-dependent increase in fluoride content with time. Also, an increase in the crystallinity of the apatite in the presence of fluoride, was observed by FTIR. The Ca:P ratio and percentage mineral by weight showed no apparent differences among the groups. The three-dimensional model used for this study has the potential to be a powerful tool in the study of time-dependent effects of drugs and other factors on osteoblast cell functions and subsequently on matrix mineralization.

A comparison of reflection and transmission ultrasonic techniques for measurement of cancellous bone elasticity

A reflection ultrasonic technique, which offers several advantages over transmission ultrasonic techniques, has been described for elastic property measurement of bone. Ultrasonic velocities from specimens of cancellous bone were compared using a reflection ultrasound technique and the more traditional transmission ultrasonic technique. The two techniques were found to yield velocities which were reasonably well correlated (r2 = 0.74). However, a statistical difference was found between the line of identity and the regression between transmission and reflection velocities (due to an offset in the intercept). In spite of differences in intercept between velocities measured by the two techniques, significant correlation was found between the two methods, suggesting that the reflection technique can measure wave velocities meaningful to bone elasticity.

Quantitative ultrasound of the heel: correlation with densitometric measurements at different skeletal sites

To assess the utility of quantitative ultrasound (QUS) of the heel for osteoporosis screening, we studied a group of 170 early postmenopausal women using both QUS of the heel and dual-energy X-ray absorptiometry (DXA) at the spine, hip, forearm, and whole body. On the basis of the linear regression results between QUS and DXA, a 95% bone mineral density (BMD) estimate confidence range was defined. Correlation coefficients between the QUS measurements and DXA ranged from 0.26 to 0.63. The confidence ranges for the estimated BMD based on a QUS measurement of the heel were large, such that an estimation of skeletal BMD at any of the DXA sites measured was not possible. For example, an estimate of the normative anteroposterior spine BMD (i.e. the T-score or the Z-score) based on a calcaneal ultrasound reading would have an error of +/- 1.9 standard deviations. Results for predicting the normative BMD of the other DXA regions were similar, with expected errors ranging from +/- 1.4 to +/- 2.0 standard deviations. We therefore conclude that QUS is not suited for the screening of early postmenopausal women for low axial or peripheral BMD. However, QUS may have a role as an independent predictor of fracture by measuring skeletal properties in addition to bone density.

Ultrasound study of bone in vitro

Ultrasound has been investigated as a tool for characterizing the biomechanical competence of bone. The rationale for using ultrasound rests on two points. First, its interaction with tissues can be used to measure their density, velocity, and structure, and thus to characterize the elasticity and to infer the strength of bone. Second, ultrasound may be used to characterize tissue properties over a wide range of spatial dimensions and organizational levels, ranging from its constituents (e.g., trabeculae for cancellous bone) to the entire organ. Different ultrasound techniques can be used to investigate diverse bone properties, but two techniques have emerged as having the potential for providing useful information on problems of current biomedical interest. These measure two parameters, density and velocity, which correlate with the elastic and ultimate properties of bone. In particular, the elasticity E is formally related to the product of density and velocity squared, E = rho v2. Moreover, it has been shown by mechanical testing that there is a single linear correlation between elasticity and strength at all orientations, both in cortical and in cancellous bone, materials with a strong intrinsic anisotropy. At the tissue level, it may therefore be expected that the ultrasound parameters will prove to be useful predictors of bone strength and of its dependence on orientation. In vitro ultrasound studies have shown that these properties can be measured specifically and quantitatively, and that they vary under different physiological conditions.