Bone densitometry: current status and future prospects

The Lichfield bone study: the skeletal response to exercise in healthy young men

The skeletal response to short-term exercise training remains poorly described. We thus studied the lower limb skeletal response of 723 Caucasian male army recruits to a 12-wk training regime. Femoral bone volume was assessed using magnetic resonance imaging, bone ultrastructure by quantitative ultrasound (QUS), and bone mineral density (BMD) using dual-energy X-ray absorptiometry (DXA) of the hip. Left hip BMD increased with training (mean ± SD: 0.85 ± 3.24, 2.93 ± 4.85, and 1.89 ± 2.85% for femoral neck, Ward's area, and total hip, respectively; all P < 0.001). Left calcaneal broadband ultrasound attenuation rose 3.57 ± 0.5% (P < 0.001), and left and right femoral cortical volume by 1.09 ± 4.05 and 0.71 ± 4.05%, respectively (P = 0.0001 and 0.003), largely through the rise in periosteal volume (0.78 ± 3.14 and 0.59 ± 2.58% for right and left, respectively, P < 0.001) with endosteal volumes unchanged. Before training, DXA and QUS measures were independent of limb dominance. However, the dominant femur had higher periosteal (25,991.49 vs. 2,5572 mm(3), P < 0.001), endosteal (6,063.33 vs. 5,983.12 mm(3), P = 0.001), and cortical volumes (19,928 vs. 19,589.56 mm(3), P = 0.001). Changes in DXA, QUS, and magnetic resonance imaging measures were independent of limb dominance. We show, for the first time, that short-term exercise training in young men is associated not only with a rise in human femoral BMD, but also in femoral bone volume, the latter largely through a periosteal response.

Characterization of controlled bone defects using 2D and 3D ultrasound imaging techniques

Ultrasound is emerging as an attractive alternative modality to standard x-ray and CT methods for bone assessment applications. As of today, however, there is a lack of systematic studies that investigate the performance of diagnostic ultrasound techniques in bone imaging applications. This study aims at understanding the performance limitations of new ultrasound techniques for imaging bones in controlled experiments in vitro. Experiments are performed on samples of mammalian and non-mammalian bones with controlled defects with size ranging from 400 microm to 5 mm. Ultrasound findings are statistically compared with those obtained from the same samples using standard x-ray imaging modalities and optical microscopy. The results of this study demonstrate that it is feasible to use diagnostic ultrasound imaging techniques to assess sub-millimeter bone defects in real time and with high accuracy and precision. These results also demonstrate that ultrasound imaging techniques perform comparably better than x-ray imaging and optical imaging methods, in the assessment of a wide range of controlled defects both in mammalian and non-mammalian bones. In the future, ultrasound imaging techniques might provide a cost-effective, real-time, safe and portable diagnostic tool for bone imaging applications.

Osteoporosis after spinal cord injury

Osteoporosis is a known consequence of spinal cord injury (SCI) and occurs in almost every SCI patient. It manifests itself as an increase in the incidence of lower extremity fractures. The pattern of bone loss seen in SCI patients is different from that usually encountered with endocrine disorders and disuse osteoporosis. In general, there is no demineralization in supralesional areas following SCI. Several factors appear to have a major influence on bone mass in SCI individuals, such as the degree of the injury, muscle spasticity, age, sex and duration after injury. At the lumbar spine, bone demineralization remains relatively low compared to that of the long bones in the sublesional area. A new steady state level between bone resorption and formation is reestablished about 2 years after SCI. SCI may not only cause bone loss, but also alter bone structure and microstructure. Trabecular bone is more affected than cortical bone in the SCI population. Numerous clinical series have reported a high incidence ranging from 1 to 34% of lower extremity fractures in SCI patients. The pathogenesis of osteoporosis after SCI remains complex and perplexing. Disuse may play an important role in the pathogenesis of osteoporosis, but neural factors also appear to be important. SCI also leads to impaired calcium and phosphate metabolism and the parathyroid hormone (PTH)-vitamin D axis. Pharmacologic intervention for osteoporosis after SCI includes calcium, phosphate, vitamin D, calcitonin and biphosphonates. However, the concomitant prescription of bone-active drugs for the prevention and treatment of osteoporosis remains low, despite the availability of effective therapies. Functional stimulated exercises may contribute to the prevention of bone loss to some extent. In addition, many unanswered questions remain about the pathogenesis of osteoporosis and its clinical management.

Lebanese guidelines for osteoporosis assessment and treatment: who to test? What measures to use? When to treat?

With the demographic explosion of the population worldwide, the human, social, and economic costs of osteoporosis will continue to rise. It is estimated that the magnitude of the problem might be even larger in developing countries, including those in the Middle East. Although several organizations and countries have developed or adapted guidelines to their local needs, as of today there are no guidelines for osteoporosis assessment in the Middle East. In April 2002, a panel of osteoporosis experts met and discussed practice guidelines for osteoporosis assessment and treatment in Lebanon. The process, which involved an overview of international guidelines as well as local data on osteoporosis, resulted in a draft for Lebanese guidelines that addressed three main questions: "Who to test?" "What measures to use?" and "When to treat?". Representatives from five major Lebanese societies (Endocrinology, Rheumatology, Orthopedics, Obstetrics and Gynecology, and Radiology) subsequently reviewed, discussed, and officially endorsed the guidelines after revisions. The Lebanese guidelines were also endorsed by the Eastern Mediterranean branch of the World Health Organization.

A simple non invasive computerized method for the assessment of bone repair within osteoconductive porous bioceramic grafts

Single energy X-ray imaging, due to its low cost and flexibility, is one of the most used and common technique to assess bone state and bone remodeling over time. Standardized X-ray images are needed to compare sets of radiographs for semi-quantitative analyses of tissue remodeling. However, useful mathematical modeling for the analysis of high level radiographic images are not easily available. In order to propose a useful evaluation tool to a wide clinical scenario, we present an innovative calibration algorithm for a semi-quantitative analysis of non-standardized digitized X-ray images. For calibration on a unique standardization scale, three time invariant regions (ROI) of radiographs were selected and analyzed. The accuracy of the normalization method for X-ray films was successfully validated by using an aluminum step wedge for routine X-ray exposures as tool to standardize serial radiographs (Pearson correlation test: R(2) = 0.96). This method was applied to investigate the progression of the new bone deposition within ceramic scaffolds used as osteoconductive substitute in large bone defects taking advantage of a large animal model. This innovative image-processing algorithm allowed the identification and semi-quantification of the bone matrix deposited within the implant. The osteo-integration at the bone-implant interface was also investigated. A progressively increasing bone tissue deposition within the porous bioceramic implant and a progressive osteo-integration was observed during the 12 months of the trial.

Influence of age and osteoporosis on calcaneus trabecular bone structure: a preliminary in vivo MRI study by quantitative texture analysis

Recent developments in high-resolution MR imaging techniques have opened up new perspectives for structural characterization of trabecular bone by non-invasive methods. In this study, 3-D MR imaging was performed on 17 healthy volunteers and 6 osteoporotic patients. Two different MR sequences were used to evaluate the impact on MR acquisition on texture analysis results. Images were analyzed with four automated methods of texture analysis (grey level histogram, cooccurrence, runlength and gradient matrices) enabling quantitative analysis of grey level intensity and distribution within three different regions of interest (ROI). Texture analysis is not very frequently used since the interpretation of the large number of calculated parameters is difficult. We applied multiparametric data analyses such as principal component analysis (CFA) and hierarchical ascending classification (HAC) to determine the relevant parameters to differentiate between three sets of images (healthy young volunteers, healthy postmenopaused and osteoporotic patients). The results suggest that relevant texture information (depending on the ROI localization in the calcaneus) can be extracted from calcaneus MR images to evaluate osteoporosis and age effects on trabecular bone structure if strictly the same acquisition sequences are used for all patients' examination.

Optical biopsy of bone tissue: a step toward the diagnosis of bone pathologies

In vivo absorption and reduced scattering spectra of the human calcaneous from 650 to 1000 nm were assessed using a laboratory system for time-resolved transmittance spectroscopy. Measurements were performed on the calcaneous of seven female volunteers ranging from 26 to 82 years of age. The analysis of the absorption spectra, using a linear combination of the key tissue absorbers (bone mineral, water, lipids, oxy- and deoxyhemoglobin), revealed a general decrease in bone mineral content and an increase in lipids with age, which is in agreement with the aging transformations that occur in bone tissues. The scattering spectra were less effective in detecting such changes in older subjects, showing only a minor decrease in the coefficient for these subjects. The capability to noninvasively quantify bone tissue composition suggests a possible use of optical biopsy for the diagnosis of bone pathologies such as osteoporosis, which are characterized by a progressive reduction and transformation of the mineral in the bone matrix.

Noninvasive estimation of bone mass in ancient vertebrae

Histomorphometry is useful in the assessment of trabecular bone mass (TBM), and thus, in the estimation of the prevalence and intensity of osteopenia in ancient population groups. However, it is a destructive method. It is therefore necessary to explore the accuracy of nondestructive approaches, such as radiography, bone mineral density (BMD) assessed by double-energy X-ray absorptiometry (DEXA), bone density (BD), or optical density (OD) in the diagnosis of osteopenia. We selected 51 vertebrae out of a total sample composed of 333 T12, L1, and L2 vertebrae belonging to adult pre-Hispanic inhabitants from El Hierro. These vertebrae underwent histomorphometrical analysis, a fine-grained film radiography with assessment of trabecular pattern following standard methods, OD, DEXA-assessed BMD, and BD. The presence of biconcave vertebrae and wedge-shaped vertebrae was also assessed by measuring anterior height (a), posterior height (p), and height at the middle point of the vertebral body (m), and further calculating the indices 2m/(a + p) ("spine score") and a/p. Significant correlations were observed between TBM and BMD (r=0.43), TBM and BD (r=0.49), TBM and OD (r=0.52), BMD and OD (r=0.51), and BMD and BD (r=0.36), but not between TBM and the indices 2m/(a + p) and a/p. In the stepwise multiple correlation analysis between TBM and BMD, BD, and OD, OD entered into first place and BD into second place, whereas BMD became displaced; the multiple correlation coefficient was 0.63, with a standard error of 3.78. A BMD greater than 0.60 g/cm2, or a bone density greater than 0.60 g/cm3, excluded osteopenia (TBM <15%) with a specificity greater than 90%, whereas a BMD value less than 0.35 g/cm2, a BD less than 0.35 g/cm3, or optical density >1.6 excluded a normal bone mass (TBM >20%) with a specificity greater than 90%. Based on radiographic criteria on the total sample, we also conclude that the overall prevalence of vertebral fractures in the adult pre-Hispanic population of El Hierro of any age is 7.5%.

Osteoporosis: What a clinician expects to learn from a patient's bone density examination

Osteoporosis has lately become recognized as an important disease on two accounts. On one hand, demographic change has resulted in a greatly increased and increasing burden of morbidity and mortality due to osteoporotic fracturing. On the other hand, lifestyle changes and preventive measures have become recognized as important factors in prevention of both osteoporosis and osteoporotic fractures, while several effective drug treatments have recently become available to treat osteoporosis by increasing bone density and reducing fracture incidence. Because bone density is, with age, the best predictor of fracture risk, its measurement has become central to the care of those potentially at risk. When a clinician refers a person for a bone density examination, the clinician should be concerned less with an "imaging diagnosis" than with the requirement that the laboratory has procedures in place for rigorous quality assurance and precision measurements, as well as for education of the staff involved. Implementation of these measures and an understanding of their clinical relevance in diagnosis and follow-up, as well as communication with clinicians in this context, are more important than any diagnostic insight that might be provided by "interpreting" a bone density study.

Electrical and dielectric properties of bovine trabecular bone--relationships with mechanical properties and mineral density

Interrelationships of trabecular bone electrical and dielectric properties with mechanical characteristics and density are poorly known. While electrical stimulation is used for healing fractures, better understanding of these relations has clinical importance. Furthermore, earlier studies have suggested that bone electrical and dielectric properties depend on the bone density and could, therefore, be used to predict bone strength. To clarify these issues, volumetric bone mineral density (BMDvol), electrical and dielectric as well as mechanical properties were determined from 40 cylindrical plugs of bovine trabecular bone. Phase angle, relative permittivity, loss factor and conductivity of wet bovine trabecular bone were correlated with Young's modulus, yield stress, ultimate strength, resilience and BMDvol. The reproducibility of in vitro electrical and dielectric measurements was excellent (standardized coefficient of variation less than 1%, for all parameters), especially at frequencies higher than 1 kHz. Correlations of electrical and dielectric parameters with the bone mechanical properties or density were frequency-dependent. The relative permittivity showed the strongest linear correlations with mechanical parameters (r > 0.547, p < 0.01, n = 40, at 50 kHz) and with BMDvol (r = 0.866, p < 0.01, n = 40, at 50 kHz). In general, linear correlations between relative permittivity and mechanical properties or BMDvol were highest at frequencies over 6 kHz. In addition, a significant site-dependent variation of electrical and dielectric characteristics, mechanical properties and BMDvol was revealed in bovine femur (p < 0.05, Kruskall-Wallis H-test). Based on the present results, we conclude that the measurement of electrical and dielectric properties provides quantitative information that is related to bone quantity and quality.

Double-energy X-ray absorptiometry in the diagnosis of osteopenia in ancient skeletal remains

Bone mineral density (BMD) assessed by double-energy X-ray absorptiometry (DEXA) accurately estimates the bone mass in living individuals, and is thus the method usually employed in the diagnosis and follow-up of osteopenia. It is preferred, in clinical settings, to the more invasive and destructive histomorphometrical assessment of trabecular bone mass in undecalcified bone samples. This study was performed in order to examine the value of DEXA-assessed BMD at the proximal end of the right tibia, either alone or in combination with the cortico-medullary index at the midshaft point of the right tibia (CMI), in the diagnosis of osteopenia in a prehistoric sample composed of 95 pre-Hispanic individuals from Gran Canaria. Age at death could be estimated in 34 cases. Diagnosis of osteopenia was performed by histomorphometrical assessment of trabecular bone mass (TBM) in an undecalcified bone section of a small portion of the proximal epiphysis of the right tibia. A high prevalence of osteopenia was found among the population of Gran Canaria. Both TBM and BMD were significantly lower in the older individuals than in younger ones, and BMD was also significantly lower in female individuals. BMD was moderately correlated with TBM (r = +0.51); the correlation was higher if CMI was included (multiple r = +0.615). BMD values lower than 0.7 g/cm2 showed a high specificity (>93%) at excluding normal TBM values. These methods were prospectively applied in a further sample of 21 right tibiae from Gran Canaria, Tenerife, and El Hierro. The results were similar to those obtained in the larger sample. Thus, DEXA-assessed BMD combined with CMI (noninvasive procedures) may be useful in detecting osteopenia in ancient populations.

Optimizing the assessment of age-related changes in trabecular bone

The goal of this study was to develop an optimal procedure to determine age-related changes in trabecular bone. The investigations were based on two-dimensional images of the human vertebral trabecular bone specimens. The following indices of trabecular structure were considered: bone volume/total volume, star volume of the marrow cavity, Euler number and the probability of disconnection (straightforwardly connected with the number of separated parts of the network). To follow precisely the changes in the trabecular structure with age, a computer simulation model was used. Up to 35 years of physiological remodelling were simulated. The validation of the model calculations was based on a quantitative comparison with the data measured for older individuals. The simulations confirmed that the description of the age-related changes in the trabecular bone by means of the architectural parameter (star volume) constitutes a promising tool for subjects older than approximately 50 years. For individuals younger than approximately 50 years bone mineral density (bone volume/total volume) seems to be the best suited descriptor. The results suggest that the optimal diagnostic procedure is age-dependent and should not be limited to the bone mineral density measurement. The clinical usefulness of the procedure has been validated by examination of the CT images.

Quantitative ultrasound of the calcaneus: an in vivo comparison with dual-energy X-ray absorptiometry and magnetic resonance imaging

The current study was performed in a clinical setting and aimed to evaluate the relationship between quantitative ultrasound (QUS) of the calcaneus with bone mineral density (BMD) assessed with dual-energy X-ray absorptiometry (DXA) and with variables derived from magnetic resonance imaging (MRI). Thirty-two postmenopausal women (mean age 61 years) were studied at the level of the nondominant calcaneus. QUS was performed using a DTU-one device including parametric imaging and yielded speed of sound (SOS) and broadband ultrasound attenuation (BUA) data. DXA was performed at a matched region of interest (ROI) in the calcaneus, using a Hologic QDR 4500 device. MRI, also performed at a matched ROI, yielded, using a Siemens Magnetom Vision device, the inverse of the transverse relaxation time (1/T(2)(*)) and the phase standard deviation (PSD). The strongest relationship between QUS and the other variables involved BUA and BMD (r &equals: 0.677, p < 0.001); 1/T(2)(*) showed a trend to correlation with SOS (r = 0.359, p = 0. 044) and with BMD (r = 0.364, p = 0.040), while the relationship between 1/T(2)(*) and BUA, PSD and BUA, PSD and SOS, PSD and BMD remained far from significance. Regression analysis of QUS, DXA, and MRI variables against age showed a trend to significant decline only for 1/T(2)(*) (r = -0.409, p = 0.020). In conclusion, this study shows that BUA of the calcaneus has the best correlation with BMD, and that, at least in a clinical setting, the ability of QUS to give information about bone structure is limited.

Prevalence and risk factors of low quantitative ultrasound values of calcaneus in Korean elderly women

Quantitative ultrasound (QUS) of bone is a new radiation-free, low-cost method that measures both bone mass and bone quality. This study was performed to establish the normative data of QUS for Korean women and to determine the prevalence and risk factors of low quantitative ultrasound values in a Korean elderly population. We studied 238 healthy women aged 20-29 years working at a hospital, and 552 women over 50 years of age living in six villages of Chung-Up district, a rural area of South Korea, using QUS measurement of bone. Broadband ultrasound attenuation and speed of sound were measured at the calcaneus, and an index combining these factors (stiffness index) was calculated. T-score was calculated from the data of young normal subjects. Of the 552 elderly women, 34.2% had T-scores between -1.0 and -2.5, and 11.8% had T-scores below -2.5. The prevalence of low quantitative ultrasound values increased with older age, longer duration following menopause, lower body mass index, younger age at menopause and smoking. In multiple logistic regression analysis, age (odds ratio = 1.40 per 5 years, P < 0.05), duration following menopause (odds ratio = 1.35 per 5 years, P < 0.05) and body mass index (odds ratio = 0.78 per quartile, P < 0.05) were independently associated with low quantitative ultrasound values. These results suggested that quantitative ultrasound measurement of the calcaneus could be a useful tool for epidemiological surveys of bone mass.

Computer simulations for the optimization of magnetic resonance phase imaging applied in the study of trabecular bone

A new technique for the evaluation of bone trabeculation using magnetic resonance (MR) phase images has been recently presented. This technique calculates the phase variance in a region of interest (ROI) on the phase images of a gradient echo sequence. In this study, a computer program was developed which simulates the phase distribution in gradient echo acquired phase images of a structure that mimics trabecular bone, consisting of a three-dimensional connected network of orthogonal bone struts. Several tests were performed in order to assess the influence of imaging parameters such as the echo time, the pixel size and the slice width on phase variance. The results from this work show that with selection of appropriate imaging parameters, phase variance strongly reflects variations in trabecular bone density. Representative MR experiments were performed in the distal radius to verify the simulation results.

Determination of a standard site for the measurement of bone mineral density of the human calcaneus

Ultrasound of the calcaneus may be used as a cheap, ionising radiation-free and easy to use indicator of skeletal status, and hence of osteoporotic fracture risk. At present ultrasound is not widely used as it suffers from high precision errors. As ultrasound parameters are determined in part by bone mineral density (BMD), an increase in the accuracy and precision of BMD measurements should reduce the precision error associated with ultrasound measurements. The aim of this study was to define an anatomical site on the calcaneus at which accurate and precise measurements of BMD can be made. Ten dry calcanei and 10 cadaveric feet were scanned using a DXA scanner; 9 anatomically defined regions (1 cm2) were selected in the posterior part of the calcaneus for analysis. The centre of region 1 was positioned halfway along the line joining the anterior border of the calcaneal tubercle and the peak of the posterior superior tubercle, and the remaining 8 regions were placed around this central area. The BMD in these 9 regions was compared with the whole bone BMD and the variability of BMD within each of the 9 regions was measured. The reproducibility of the technique was assessed by taking 10 repeated measurements of 2 bone and 2 cadaveric specimens, each specimen being removed and repositioned between measurements. Region 1 was found to be the most representative of total BMD in cadaveric feet. This region also showed the least variability of BMD and consistently gave the lowest coefficients of variation in the reproducibility study both in the bone and the cadaveric specimens. This region is hence the most suitable site on the calcaneus for measuring absolute values of and changes in BMD. The surface position of region 1 was found to be consistently 5/9 along the line at 45 degrees to the vertical, from the lateral malleolus to the heel. The identification of the surface location of region 1 relative to anatomical landmarks of the foot has enabled the same anatomical site to be measured in all subjects. This allows meaningful intersubject comparisons to be made. Preliminary data suggest that precision errors using ultrasound are also reduced when measurements are taken at this region of the calcaneus. The reduction in the precision error of ultrasound assessment of skeletal status may provide a cheap and safe way to identify individuals at risk from osteoporotic fracture.