In vivo assessment of trabecular bone structure using fractal analysis of distal radius radiographs

Our purpose in this study was (i) to measure trabecular bone structure using fractal analysis of distal radius radiographs in subjects with and without osteoporotic hip fractures, and (ii) to compare these measures with bone mineral density (BMD) as well as with measures of trabecular bone structure derived from high resolution magnetic resonance (MR) images. Distal radius radiographs were obtained using semi-industrial films (55 kVp, 400 mAs) in 30 postmenopausal patients, who had suffered osteoporotic hip fractures (74.8+/-8.2 years) in the last 24 months and 27 postmenopausal age-matched (74.6+/-6.6 yr) normal volunteers. Radiographs were digitized at 50 microm. A Fourier power spectrum-based fractal dimension (FD) characterizing the trabecular pattern was measured in a region of interest proximal to the joint line. The fractal dimension was calculated over two spatial frequency (f) ranges: FD1 was calculated over 0.5相似文献   

Fractal analysis of radiographs: assessment of trabecular bone structure and prediction of elastic modulus and strength.

The purpose of this study was to determine whether fractal dimension of radiographs provide measures of trabecular bone structure which correlate with bone mineral density (BMD) and bone biomechanics, and whether these relationships depend on the technique used to calculate the fractal dimension. Eighty seven cubic specimen of human trabecular bone were obtained from the vertebrae and femur. The cubes were radiographed along all three orientations--superior-inferior (SI), medial-lateral (ML), and anterior-posterior (AP), digitized, corrected for background variations, and fractal based techniques were applied to quantify trabecular structure. Three different techniques namely, semivariance, surface area, and power spectral methods were used. The specimens were tested in compression along three orientations and the Young's modulus (YM) was determined. Compressive strength was measured along the SI direction. Quantitative computed tomography was used to measure trabecular BMD. High-resolution magnetic-resonance images were used to obtain three-dimensional measures of trabecular architecture such as the apparent bone volume fraction, trabecular thickness, spacing, and number. The measures of trabecular structure computed in the different directions showed significant differences (p<0.05). The correlation between BMD, YM, strength, and the fractal dimension were direction and technique dependent. The trends of variation of the fractal dimension with BMD and biomechanical properties also depended on the technique and the range of resolutions over which the data was analyzed. The fractal dimension showed varying trends with bone mineral density changes, and these trends also depended on the range of frequencies over which the fractal dimension was measured. For example, using the power spectral method the fractal dimension increased with BMD when computed over a lower range of spatial frequencies and decreased for higher ranges. However, for the surface area technique the fractal dimension increased with increasing BMD. Fractal measures showed better correlation with trabecular spacing and number, compared to trabecular thickness. In a multivariate regression model inclusion of some of the fractal measures in addition to BMD improved the prediction of strength and elastic modulus. Thus, fractal based texture analysis of radiographs are technique dependent, but may be used to quantify trabecular structure and have a potentially valuable impact in the study of osteoporosis.     

Microstructural trabecular bone from patients with osteoporotic hip fracture or osteoarthritis: Its relationship with bone mineral density and bone remodelling markers

Osteoporosis (OP) and osteoarthritis (OA) are the most prevalent musculoskeletal disorders in the elderly but the relationship between them is unclear. The purposes of this study are to analyze the bone turnover markers (BTM), bone mineral density (BMD) and the structural and mechanical properties of trabecular bone in patients with OP and OA, and to explore the relationship between these two diseases. We studied 12 OP patients and 13 OA patients. We analyzed BTM (β-CrossLaps and PINP), BMD and microstructural and biomechanical parameters (micro-CT). Our results were: OP group has higher levels of β-CrossLaps and lower BMD at the femoral neck. Also, OP patients have a decreased volume of trabecular bone and less trabecular number, with architecture showing prevalence of rod-like trabeculae and worse connectivity than OA patients. The biomechanical parameters were worse in OP patients. BMD was correlated with almost all the structural and biomechanical parameters. Moreover, β-CrossLaps was negatively correlated with hip BMD and with bone surface density and positively with trabecular separation. BTM, BMD and bone microstructural changes in osteoporosis are opposite to those of OA. These findings justify a less resistant bone with higher risk of fragility fractures in OP patients. These histomorphometric and biomechanical changes may be suspected by measuring of BMD and β-CrossLaps levels.     

Topology-based orientation analysis of trabecular bone networks

After bone mineral density, orientation is the major determinant of trabecular bone strength and is thus of significant interest in understanding the clinical implications of osteoporotic bone loss. The methods used to measure orientation and anisotropy of the trabecular bone have largely relied on deriving global measures along test lines, computing the best-fit ellipsoid, and decomposing to eigenvalue-eigenvector pairs that yield the mean orientation and anisotropy of the region. These techniques ignore the differences between measuring the orientation of trabecular plates versus rods, and do not provide insight into the relationship between local orientation and biomechanical stresses. Digital topological analysis allows a unique determination of each voxel's topological class as belonging to a plate, rod, or junction. The digital topology-based orientation analysis (DTA-O) method extracts the voxels belonging to plates and determines the local surface normal by fitting a plane through the local neighborhood BVF map. Modeling regional distributions of these vectors allows assessment of anisotropy measures, such as mean and variance of the orientation distribution. High-resolution microcomputed tomography, synthetic, and in vivo images were used for a validation of the new method and compare the results with the mean intercept length (MIL) technique. The results indicate that DTA-O is a better measure of trabecular orientation and anisotropy than MIL. Applying DTA-O to a recently completed study on the distal radius of 82 subjects [F.W. Wehrli et al., J. Bone Min. Res. 16, 1520 (2001)] shows that the mean orientation and anisotropy at the medial and lateral sides in the distal radius mataphyseal trabecular network are consistent with the mechanical stresses acting on the radius during common tasks.     

Osseous microarchitecture of the scaphoid: Cadaveric study of regional variations and clinical implications

Bone strength and structure are closely associated with fracture and screw fixation, however osseous micro architecture on scaphoid has not been clearly addressed. We conducted histomorphometric study of the scaphoid using micro CT to find regional variations and differences in the scaphoid to provide better understanding of fracture mechanism and suggest optimal screw position. We divided scaphoid into eight regions and collected regional data from eleven different cadaveric scaphoids. A computer program was used to measure parameters, which includes mean subchondral bone thickness, bone mineral density for bone density parameters, and tissue mineral density, trabecular thickness, trabecular spacing, trabecular number and bone volume fraction for bone quality parameters. All bone strength parameters were measured the maximum value in the regions where scaphoid articulates with radius. Articular regions presented higher bone strength parameters and thicker subchondral bone. The minimum value of trabecular number was in midcarpal side of waist portion. There was trend of higher subchondral bone thickness in the scaphoid which articulates with capitate and radius. This histomorphometric study showed regional variation of the scaphoid in terms of bone density and quality parameters. Waist portion presented thick subchondral and trabecular bone for high cross section moment of inertia against bending. Three point bending for scaphoid fracture and vertical screw placement are suggested based on these variations.     

Mechanical strength of trabecular bone at the knee

Interest in the biomechanical properties of trabecular bone has expanded in response to the problems related to total and partial joint replacement with the knee joint constituting a main focus of attention. This relatively recent development has left a number of fundamental problems unanswered, especially related to the machining, storage and testing of trabecular bone specimens. Nevertheless, these studies have contributed to the understanding of the mechanical function of trabecular bone. Regarding the role of trabecular bone at the knee joint, the following conclusions may be emphasized (conclusions drawn from the author's previous studies (I-X) are shown in italics): (1) Trabecular bone is almost exclusively responsible for the transmission of load at the proximal tibial epiphysis from the knee joint to the metaphysis. The peripheral shell surrounding the epiphysis is not composed of cortical bone and plays a negligible role in load transmission. (2) The compressive strength and stiffness of trabecular bone is primarily dependent upon the apparent density, trabecular architecture and the strength of the bone material. Direct and indirect sources suggest that the true material strength of trabecular bone is less than that of cortical bone. The epiphyseal trabecular architecture, featuring a marked polarity with alignment of primary trabeculae at right angles to the joint surface, is responsible for functional anisotropy which points to the axial compressive properties as the more important mechanical parameters. (3) Tensile and shear properties are of special relevance to mechanical loosening of implants. These properties may be derived from the apparent density, and a close empirical relation to the axial compressive strength and stiffness is suggested. (4) The foam-like structure of trabecular bone is the basis for the large energy absorptive capacity. (5) The pattern of axial compressive stiffness and strength at the normal proximal tibia differs little among individuals. Supporting the medial tibial plateau is a large high strength area with maximal strength centrally and slightly anteriorly, while laterally there is a restricted area of relatively high strength posteriorly with a lower maximal value than medially. Bone strength is significantly reduced within ten millimeters of the subchondral bone plate, and this reduction continues distally at the lateral condyle. At both condyles strength is reduced towards the periphery with very low values being obtained at the margins of the condyles and at the intercondylar region. Absolute bone strength values are influenced by the level of physical activity.(ABSTRACT TRUNCATED AT 400 WORDS)     

A review of anatomical and mechanical factors affecting vertebral body integrity

Background: The aetiology of osteoporotic vertebral fracture is multifactorial and may be conceptualised using a systems framework. Previous studies have established several correlates of vertebral fracture including reduced vertebral cross-sectional area, weakness in back extensor muscles, reduced bone mineral density, increasing age, worsening kyphosis and recent vertebral fracture. Alterations in these physical characteristics may influence biomechanical loads and neuromuscular control of the trunk and contribute to changes in subregional bone mineral density of the vertebral bodies. Methods: This review discusses factors that have received less attention in the literature, which may contribute to the development of vertebral fracture. A literature review was conducted using electronic databases including Medline, Cinahl and ISI Web of Science to examine the potential contribution of trabecular architecture, subregional bone mineral density, vertebral geometry, muscle force, muscle strength, neuromuscular control and intervertebral disc integrity to the aetiology of osteoporotic vertebral fracture. Interpretation: A better understanding of factors such as biomechanical loading and neuromuscular control of the trunk may help to explain the high incidence of subsequent vertebral fracture after sustaining an initial vertebral fracture. Consideration of these issues may be important in the development of prevention and management strategies.     

Prediction of mechanical properties of trabecular bone using quantitative MRI

Techniques for quantitative magnetic resonance imaging (MRI) have been developed for non-invasive estimation of the mineral density and structure of trabecular bone. The R*(2) relaxation rate (i.e. 1/T*(2)) is sensitive to bone mineral density (BMD) via susceptibility differences between trabeculae and bone marrow, and by binarizing MRI images, structural variables, such as apparent bone volume fraction, can be assessed. In the present study, trabecular bone samples of human patellae were investigated in vitro at 1.5 T to determine the ability of MRI-derived variables (R*(2) and bone volume fraction) to predict the mechanical properties (Young's modulus, yield stress and ultimate strength). Further, the MRI variables were correlated with reference measurements of volumetric BMD and bone area fraction as determined with a clinical pQCT system. The MRI variables correlated significantly (p < 0.01) with the mechanical variables (r = 0.32-0.46), BMD (r = 0.56) and bone structure (r = 0.51). A combination of R*(2) and MRI-derived bone volume fraction further improved the prediction of yield stress and ultimate strength. Although pQCT showed a trend towards better prediction of the mechanical properties, current results demonstrate the feasibility of combined MR imaging of marrow susceptibility and bone volume fraction in predicting the mechanical strength of trabecular bone and bone mineral density.     

Segmentation of bone CT images and assessment of bone structure using measures of complexity

A nondestructive and noninvasive method for numeric characterization (quantification) of the structural composition of human bone tissue has been developed and tested. In order to quantify and to compare the structural composition of bones from 2D computed tomography (CT) images acquired at different skeletal locations, a series of robust, versatile, and adjustable image segmentation and structure assessment algorithms were developed. The segmentation technique facilitates separation from cortical bone and standardizes the region of interest. The segmented images were symbol-encoded and different aspects of the bone structural composition were quantified using six different measures of complexity. These structural examinations were performed on CT images of bone specimens obtained at the distal radius, humeral mid-diaphysis, vertebral body, femoral head, femoral neck, proximal tibia, and calcaneus. In addition, the ability of the noninvasive and nondestructive measures of complexity to quantify trabecular bone structure was verified by comparing them to conventional static histomorphometry performed on human fourth lumbar vertebral bodies. Strong correlations were established between the measures of complexity and the histomorphometric parameters except for measures expressing trabecular thickness. Furthermore, the ability of the measures of complexity to predict vertebral bone strength was investigated by comparing the outcome of the complexity analysis of the CT images with the results of a biomechanical compression test of the third lumbar vertebral bodies from the same population as used for histomorphometry. A multiple regression analysis using the proposed measures including structure complexity index, structure disorder index, trabecular network index, index of a global ensemble, maximal L-block, and entropy of x-ray attenuation distribution revealed an excellent relationship (r=0.959, r2=0.92) between the measures of complexity and compressive bone strength. In conclusion, the image segmentation techniques and the assessment of bone architecture by measures of complexity have been successfully applied to analyze high-resolution peripheral quantitative computed tomography (pQCT) and CT images obtained from the distal radius, humeral mid-diaphysis, third and fourth lumbar vertebral bodies, proximal femur, proximal tibia, and calcaneus. The proposed approach is of broad interest as it can be applied for the quantification of structures and textures originating from different imaging modalities in other fields of science.     

A comparison of the texture of computed tomography and projection radiography images of vertebral trabecular bone using fractal signature and lacunarity.

The structural integrity of trabecular bone is an important factor characterizing the biomechanical strength of the vertebra, and is determined by the connectivity of the bone network and the trabeculation pattern. These can be assessed using texture measures such as the fractal signature and lacunarity from a high resolution projection radiograph. Using central sections of lumbar vertebrae we compared the results obtained from high-resolution transverse projection images with those obtained from spatially registered low-resolution images from a conventional clinical CT scanner to determine whether clinical CT data can provide useful structural information. Provided the power spectra of the CT images are corrected for image system blurring, the resulting fractal signature is similar for both modalities. Although the CT images are blurred relative to the projection images, with a consequent reduction in lacunarity, the estimated trabecular separation obtained from the lacunarity plots is similar for both modalities. This suggests that these texture measures contain essential information on trabecular microarchitecture, which is present even in low resolution CT images. Such quantitative texture measurements from CT or MRI images are potentially useful in monitoring bone strength and predicting future fracture risk.     

Vertebral Osteoporosis and Trabecular Bone Quality

Vertebral fractures due to osteoporosis commonly occur under non-traumatic loading conditions. This problem affects more than 1 in 3 women and 1 in 10 men over a lifetime. Measurement of bone mineral density (BMD) has traditionally been used as a method for diagnosis of vertebral osteoporosis. However, this method does not fully account for the influence of changes in the trabecular bone quality, such as micro-architecture, tissue properties and levels of microdamage, on the strength of the vertebra. Studies have shown that deterioration of the vertebral trabecular architecture results in a more anisotropic structure which has a greater susceptibility to fracture. Transverse trabeculae are preferentially thinned and perforated while the remaining vertical trabeculae maintain their thickness. Such a structure is likely to be more susceptible to buckling under normal compression loads and has a decreased ability to withstand unusual or off-axis loads. Changes in tissue material mechanical properties and levels of microdamage due to osteoporosis may also compromise the fracture resistance of vertebral trabecular bone. New diagnostic techniques are required which will account for the influence of these changes in bone quality. This paper reviews the influence of the trabecular architecture, tissue properties and microdamage on fracture risk for vertebral osteoporosis. The morphological characteristics of normal and osteoporotic architectures are compared and their potential influence on the strength of the vertebra is examined. The limitations of current diagnostic methods for osteoporosis are identified and areas for future research are outlined.     

Variation of trabecular microarchitectural parameters in cranial, caudal and mid-vertebral regions of the ovine L3 vertebra

The lumbar vertebrae are major load-bearing structures within the spinal column. The current understanding of the microstructure of these bodies and their full role in load-bearing is incomplete. There is a need to develop our understanding of these issues to improve fracture prediction in musculoskeletal diseases such as osteoporosis. The lumbar vertebrae consist primarily of trabecular bone enclosed in a thin cortical shell, but little is known about how microstructural parameters vary within these structures, particularly in relation to the trabecular compartment. The specific aim of this study was to use micro-computed tomography to characterize the trabecular microarchitecture of the ovine L3 vertebra in cranial, mid-vertebra and caudal regions. The L3 vertebra was obtained from skeletally mature ewes ( n  = 18) more than 4 years old. Three-dimensional reconstructions of three pre-defined regions were obtained and microarchitectural parameters were calculated. Whereas there was no difference in bone volume fraction or structural model index between regions, trabecular number, thickness, spacing, connectivity density, degree of anisotropy and bone mineral density all displayed significant regional variations. The observed differences were consistent with the biomechanical hypothesis that in vivo loads are distributed differently at the endplates compared with the mid-vertebra. Thus, a more integrative approach combining biomechanical theory and anatomical features may improve fracture risk assessment in the future.     

Spatial autocorrelation and mean intercept length analysis of trabecular bone anisotropy applied to in vivo magnetic resonance imaging

Osteoporosis is characterized by bone loss and deterioration of the trabecular bone (TB) architecture that leads to impaired overall mechanical strength of the bone. Bone mineral density (BMD) measured by dual-energy x-ray absorptiometry is currently the standard clinical metric assessing bone integrity but it fails to capture the structural changes in the TB. Recent research suggests that structure contributes to bone strength in a manner complementary to BMD. Besides parameters of scale such as the mean TB thickness and mean bone volume fraction, parameters describing the anisotropy of the trabecular architecture play an important role in the characterization of TB since trabeculae are preferentially oriented along the direction of local loading. Therefore, the degree of structural anisotropy is of pivotal importance to the bone's mechanical competence. The most common method for measuring structural anisotropy of TB is the mean-intercept length (MIL). In this work we present a method, based on the three-dimensional spatial autocorrelation function (ACF), for mapping of the full structural anisotropy ellipsoid of both TB thickness and spacing and we examine its performance as compared to that of MIL. Not only is the ACF method faster by several orders of magnitude, it is also considerably more robust to noise. Further, it is applicable at lower spatial resolution and is relatively insensitive to image shading. The chief reason for ACF's superior performance is that it does not require binarization, which is difficult to achieve in the limited spatial regime of in vivo magnetic resonance imaging. MIL and ACF have been applied to high-resolution magnetic resonances images of the tibia in a group of ten healthy postmenopausal women by comparing the structural anisotropy and principal direction of the computed fabric tensor for each method. While there is fair agreement between the two methods, ACF analysis yielded greater anisotropy than MIL for both TB thickness and spacing. There was good agreement between the two techniques as far as the eigenvectors of the fabric ellipsoids were concerned, which parallel the bone's macroscopic axis.     

骨生物力学特性在骨质疏松症中的改变

骨质疏松症是一种以系统骨量、骨强度及骨微结构损害为特征常导致骨折风险增加的疾病,是绝经后妇女常见且严重的情况。骨的生物力学特性取决于骨材料数量、质量及其空间结构,主要受骨皮质、骨松质和骨胶原蛋白的影响。当骨质疏松症发生时,骨皮质、骨松质和骨胶原蛋白均发生相应改变,从而导致骨生物力学特性的变化。重点对骨质疏松时骨皮质、骨小梁和胶原蛋白的变化加以概述,以全面认识骨生物力学特性在骨质疏松症中的改变。     

Segmentation techniques for analysis of bone by three-dimensional computed tomographic imaging.

Improved methods for evaluation and quantification of the three-dimensional (3D) architecture of bone are needed in order to more fully understand the role of trabecular architecture in bone strength. Computed tomography (microCT) is capable of examining bone at resolutions below 30 microm (isotropic), with collection of a three-dimensional data set which can then be subjected to image analysis. In this paper, we discuss automated methods for important steps in this analysis, including methods for (1) segmenting the image into bone and background; (2) defining the volume of interest for determination of structural parameters; and (3) segmenting the bone into trabecular and cortical components. Evaluation of bone structure using these techniques provides new information about the 3D architecture of bone tissue, and may be useful for evaluation of structural changes in bone caused by aging, disease, or drug treatment.     

Quantification of the degree of mineralization of bone in three dimensions using synchrotron radiation microtomography

The availability of three-dimensional measuring techniques coupled to specific image processing methods opens new opportunities for the analysis of bone structure. In particular, synchrotron radiation microtomography may provide three-dimensional images with spatial resolution as high as one micrometer. Moreover, the use of a monoenergetic synchrotron beam, which avoids beam-hardening effects, allows quantitative measurements of the degree of mineralization in bone samples. Indeed, the reconstructed gray levels of tomographic images correspond directly to a map of the linear attenuation coefficient within the sample. Since the absorption depends on the amount of mineral content, we proposed a calibration method to evaluate the three-dimensional distribution of the degree of mineralization within the sample. First a theoretical linear relationship modeling the linear attenuation coefficient as a function of the hydroxyapatite concentrations was derived. Then, an experimental validation on phantoms confirmed both the accuracy of the image processing tools and the experimental setup used. Finally, the analysis of the degree of mineralization in four iliac crest bone biopsy samples was reported. Our method was compared to the reference microradiography technique, currently used for this quantification in two dimensions. The concentration values of the degree of mineralization were found with both techniques in the range 0.5-1.6 g of mineral per cubic centimeter of bone, both in cortical and in trabecular region. The mean difference between the two techniques was around 4.7%, and was slightly higher in trabecular region than in cortical bone.     

仙灵骨葆对尾悬吊拟失重大鼠骨量丢失的抑制

背景：以淫羊藿苷为主要成分的中药制剂仙灵骨葆具有促进骨形成的作用。 目的：观察仙灵骨葆对尾悬吊拟失重大鼠骨量丢失的抑制作用及机制。 方法：将SD大鼠随机分为正常对照组、拟失重组、仙灵骨葆组,后两组大鼠采用尾悬吊法模拟失重,仙灵骨葆组悬吊同时灌胃给予仙灵骨葆250 mg/(kg•d),拟失重组悬吊同时灌胃给予双蒸水,4周后取右侧股骨行骨密度、三点弯曲生物力学及骨组织形态计量学检测。 结果与结论：正常对照组骨密度、胫骨近端骨小梁相对体积、骨小梁厚度、骨小梁数量、生物力学最大载荷显著高于拟失重组、仙灵骨葆组(P < 0.05)。仙灵骨葆组胫骨远端1/4骨密度、胫骨近端骨小梁相对体积显著高于拟失重组(P < 0.05),生物力学最大载荷也高于拟失重组,但差异无显著性意义。说明仙灵骨葆灌胃干预可促进松质骨的骨形成,部分阻止拟失重大鼠骨量的丢失。      

A synchrotron radiation microtomography system for the analysis of trabecular bone samples.

X-ray computed microtomography is particularly well suited for studying trabecular bone architecture, which requires three-dimensional (3-D) images with high spatial resolution. For this purpose, we describe a three-dimensional computed microtomography (microCT) system using synchrotron radiation, developed at ESRF. Since synchrotron radiation provides a monochromatic and high photon flux x-ray beam, it allows high resolution and a high signal-to-noise ratio imaging. The principle of the system is based on truly three-dimensional parallel tomographic acquisition. It uses a two-dimensional (2-D) CCD-based detector to record 2-D radiographs of the transmitted beam through the sample under different angles of view. The 3-D tomographic reconstruction, performed by an exact 3-D filtered backprojection algorithm, yields 3-D images with cubic voxels. The spatial resolution of the detector was experimentally measured. For the application to bone investigation, the voxel size was set to 6.65 microm, and the experimental spatial resolution was found to be 11 microm. The reconstructed linear attenuation coefficient was calibrated from hydroxyapatite phantoms. Image processing tools are being developed to extract structural parameters quantifying trabecular bone architecture from the 3-D microCT images. First results on human trabecular bone samples are presented.     

Accuracy of high-resolution peripheral quantitative computed tomography for measurement of bone quality

The introduction of three-dimensional high-resolution peripheral in vivo quantitative computed tomography (HR-pQCT) (XtremeCT, Scanco Medical, Switzerland; voxel size 82 μm) provides a new approach to monitor micro-architectural bone changes longitudinally. The accuracy of HR-pQCT for three important determinants of bone quality, including bone mineral density (BMD), architectural measurements and bone mechanics, was determined through a comparison with micro-computed tomography (μCT) and dual energy X-ray absorptiometry (DXA). Forty measurements from 10 cadaver radii with low bone mass were scanned using the three modalities, and image registration was used for 3D data to ensure identical regions were analyzed.

The areal BMD of DXA correlated well with volumetric BMD by HR-pQCT despite differences in dimensionality (R² = 0.69), and the correlation improved when non-dimensional bone mineral content was assessed (R² = 0.80). Morphological parameters measured by HR-pQCT in a standard patient analysis, including bone volume ratio, trabecular number, derived trabecular thickness, derived trabecular separation, and cortical thickness correlated well with μCT measures (R² = 0.59–0.96). Additionally, some non-metric parameters such as connectivity density (R² = 0.90) performed well. The mechanical stiffness assessed by finite element analysis of HR-pQCT images was generally higher than for μCT data due to resolution differences, and correlated well at the continuum level (R² = 0.73).

The validation here of HR-pQCT against gold-standards μCT and DXA provides insight into the accuracy of the system, and suggests that in addition to the standard patient protocol, additional indices of bone quality including connectivity density and mechanical stiffness may be appropriate to include as part of a standard patient analysis for clinical monitoring of bone quality.     

Effect of human trabecular bone composition on its electrical properties

Mechanical properties of bone are determined not only by bone mineral density (BMD), but also by tissue trabecular structure and organic composition. Impedance spectroscopy has shown potential to diagnose trabecular bone BMD and strength, however, the relationships between organic composition and electrical and dielectric properties have not been systematically investigated. To investigate these issues organic composition of 26 human trabecular bone samples harvested from the distal femur and proximal tibia was determined and compared with relative permittivity, loss factor, conductivity, phase angle, specific impedance and dissipation factor measured at wide range (50 Hz to 5 MHz) of frequencies. A strong linear correlation was found between the relative permittivity at 1.2 MHz and trabecular bone fat content (r = -0.85, p<0.01, n=26). On the other hand, relative permittivity measured at 200 Hz served as a good predictor of water content (r = 0.83). Phase angle, specific impedance and especially conductivity were strongly related to the trabecular bone dry density and water content (|r| > or = 0.69). Variation in bone tissue collagen content was strongly related to the relative permittivity measured at 1.2 MHz (r = 0.64), but only moderately to other parameters. Glycosaminoglycan content showed no significant relations with any investigated electrical parameters. The present study indicates that if the trabecular bone composition is known, the relationships presented in this study could facilitate calculation of current field distribution, e.g. during electrical stimulation of osteogenesis. On the other hand, our results suggest that permittivity measured at low (<1 kHz) or high (>100 kHz) frequencies could be used, e.g. during implant surgery, for prediction of trabecular bone water or fat contents, respectively.