Elsevier

Bone

Volume 32, Issue 3, March 2003, Pages 316-323
Bone

Regular article
Constant mineralization density distribution in cancellous human bone

https://doi.org/10.1016/S8756-3282(02)00973-0Get rights and content

Abstract

The degree of mineralization of bone matrix is an important factor in determining the mechanical competence of bone. The remodeling and modeling activities of bone cells together with the time course of mineralization of newly formed bone matrix generate a characteristic bone mineralization density distribution (BMDD). In this study we investigated the biological variance of the BMDD at the micrometer level, applying a quantitative backscattered electron imaging (qBEI) method. We used the mean calcium concentration (CaMean), the most frequent calcium concentration (CaPeak), and full width at half maximum (CaWidth) to characterize the BMDD. In none of the BMDD parameters were statistically significant differences found due to ethnicity (15 African–American vs. 27 Caucasian premenopausal women), skeletal site variance (20 ilium, 24 vertebral body, 13 patella, 13 femoral neck, and 13 femoral head), age (25 to 95 years), or gender. Additionally, the interindividual variance of CaMean and CaPeak, irrespective of biological factors, was found to be remarkably small (SD < 2.1% of means). However, there are significant changes in the BMDD in the case of bone diseases (e.g., osteomalacia) or following clinical treatment (e.g., alendronate). From the lack of intraindividual changes among different skeletal sites we conclude that diagnostic transiliac biopsies can be used to determine the BMDD variables of cancellous bone for the entire skeleton of the patient. In order to quantify deviations from normal mineralization, a reference BMDD for adult humans was calculated using bone samples from 52 individuals. Because we find the BMDD to be essentially constant in healthy adult humans, qBEI provides a sensitive means to detect even small changes in mineralization due to bone disease or therapeutic intervention.

Introduction

The mechanical properties of bone are established by the structural organization at different hierarchical levels, including organ, tissue, and material level [1]. It has been shown that bone diseases can affect different levels of bone structure, such as trabecular architecture in osteoporosis [2], [3], the degree of mineralization in osteomalacia [4], and the nanostructure of the composite material in osteogenesis imperfecta [5], [6], [7], [40]. Clinical evaluations of biochemical markers, radiography, DEXA, QCT, pQCT, and NMR are not always sufficient to make correct clinical diagnoses. In such cases, bone biopsies (usually transiliac bone) are taken from the patients for histological studies. Additionally, these bone biopsies provide the opportunity to examine the bone quality at different hierarchical levels by other physical methods, e.g., (a) μCT and magnetic resonance microimaging (MRμI) [3], [8], [41], which are powerful tools to evaluate 3D-structural parameters of trabecular bone, (with a spatial resolution down to 15 μm achievable by commercially available CT-scanners); (b) microradiography [9], [10], [11], [12] and quantitative backscattered electron imaging (qBEI) [4], [13], [14], [15], which quantify the degree of mineralization within sectioned bone regions; (c) synchrotron radiation microtomography, which permits the analysis of the 3D structure together with degree of mineralization [16] in bone; (d) scanning small angle X-ray scattering (scanning-SAXS) [17], [18], which enables the determination of mineral particle size, shape, and orientation; (e) Fourier transform infrared microspectroscopy (microFTIR) [19], [20], [21], which can provide local information on variations in mineral:matrix ratios, in carbonate:phosphate ratios of the mineral, in crystallinity, and in collagen cross-linking; and (f) Raman spectroscopy [22], which provides insight into molecular variations in the structure of the mineral. We focus on the assessment of the local calcium distribution within the trabecular bone matrix using qBEI [4], [23]. The degree of mineralization is a crucial factor for bone quality, because it modifies the elastic modulus of the matrix material—the higher the degree of mineralization, the higher the stiffness of the material [24].

As is shown by microradiography [10], [11], [12] and backscattered electron imaging [4], [13], [15], [23], the bone matrix is not uniformly mineralized, but exhibits a range of mineral concentration, which is determined primarily by the duration of secondary mineralization of the individual bone packets. The differences in the degree of mineralization within a certain bone region can be quantified by measurement of the frequency distributions of calcium concentrations detected. We designated such a distribution as the bone mineralization density distribution (BMDD), synonymous to bone mineral density distribution used previously [4]. For the reasons noted above, BMDD indirectly provides information on the bone turnover rate. For instance, a high bone turnover rate will result in a higher contribution of less mineralized matrix and will shift the distribution to lower mineral concentration values. Additionally, the distribution will get broader, because of the increase in the heterogeneity in mineralization [25], [26]. In contrast, when bone turnover is reduced, e.g., by treatment with an antiresorptive drug [19], [27], [28], the distribution shifts to higher calcium concentration values and becomes more narrow, the sharpening indicating that the mineralization is more homogeneous.

To gain insight into the mineralization pattern of normal bone and to establish the BMDD as a diagnostic tool to detect deviations from normality, we studied the BMDD of trabecular bone from different skeletal sites from healthy individuals of variable ethnicity, gender, and age by quantitative backscattered electron imaging (qBEI) [4] in the scanning electron microscope.

Section snippets

Samples

Human bone biopsies were obtained from the sources listed below. No evidence of metabolic bone disease or post mortal alterations in mineralized tissue was present in any of the groups of bone samples designated P1 to P4 in the following: P1: transiliac bone samples from autopsies of 20 individuals (7 males, 13 females, ages 30–85 years) from a previous study [4]; P2: L4-vertebral samples from autopsies of 24 individuals (16 males, 11 females, ages 5–95 years); and P3: transiliac biopsies from

Interindividual variance

The BMDD variables for 27 premenopausal white females (group P3) of approximately the same age, similar weights, and with similar health status were determined at the same skeletal site (iliac crest) and were averaged (Table 1). The standard deviations were less than 2.3% for CaMean and CaPeak, and less than 12.5% for CaWidth for this group of individuals.

Ethnic origin influence

A group of 27 white and 14 black (age range 26 to 37 years) premenopausal females (group P3) was analyzed. Fig. 2 compares the average BMDD

Discussion

Numerous studies at organ and tissue levels have shown that bone variables like bone mineral density (BMD), bone mineral content (BMC), cortical bone area relative to trabecular area, bone volume, trabecular thickness, osteoid perimeter, and thickness can exhibit distinct variations with ethnicity [31], [32], [33], [34], gender [2], [35], age [2], [31], [32], [36], and menopausal status [31], [32]. In contrast, at the material level, we found that the BMDD is strikingly constant for trabecular

Acknowledgements

We thank G. Dinst and P. Messmer for excellent technical assistance, and Dr. B.M. Grabner for very helpful discussions of the manuscript. Supported in part by National Institutes of Health Grants AR-31991 and DK-32333.

References (42)

  • A. Laib et al.

    Ridge number densitya new parameter for in vivo bone structure analysis

    Bone

    (1997)
  • J.D. Currey

    The Mechanical Adaptations of Bones

    (1984)
  • A.M. Parfitt et al.

    Relationships between surface, volume, and thickness of iliac trabecular bone in aging and in osteoporosis

    J Clin Invest

    (1983)
  • F.W. Wehrli et al.

    Digital topological analysis of in vivo magnetic resonance microimages of trabecular bone reveals structural implications of osteoporosis

    J Bone Miner Res

    (2001)
  • N.P. Camacho et al.

    The material basis for reduced mechanical properties in oim mice bones

    J Bone Miner Res

    (1999)
  • P. Fratzl et al.

    Bone mineralization in an osteogenesis imperfecta mouse model studied by small-angle X-ray scattering

    J Clin Invest

    (1996)
  • B. Borah et al.

    Three-dimensional microimaging (MRμI and μCT), finite element modeling, and rapid prototyping provide unique insights into bone architecture in osteoporosis

    Anat Rec (new anat)

    (2001)
  • G. Boivin et al.

    The degree of mineralization of bone tissue measured by computerized quantitative contact microradiography

    Calcified Tiss Int

    (2002)
  • J. Eschberger et al.

    Microradiography

  • J. Jowsey

    Variations in bone mineralization with age and disease

  • S.A. Reid et al.

    Changes in the mineral density distribution in human bone with ageimage analysis using backscattered electrons in the SEM

    J Bone Miner Res

    (1987)
  • Cited by (230)

    View all citing articles on Scopus
    View full text