Original Full Length ArticleComposition and microarchitecture of human trabecular bone change with age and differ between anatomical locations
Highlights
► Molecular composition and microarchitecture of human trabecular bone in the femoral neck, greater trochanter and calcaneus was quantified and compared. ► Micro-computed tomography and Fourier transform infrared spectroscopy were used to evaluate the microarchitecture and molecular composition, respectively. ► We found significant differences in the molecular composition and microarchitecture of trabecular bone between different anatomical locations.
Introduction
Trabecular bone microarchitecture is adapted to the local mechanical environment according to Wolff's law [1], [2]. Moreover, the microarchitecture also changes as the individual ages [3]. Trabecular bone is a metabolically very active tissue, resulting in possible changes in the composition due to loading or aging [4], [5]. Hence, the molecular composition and microarchitecture of trabecular bone may vary between different anatomical locations due to different mechanical loading and remodeling rates.
Dual energy X-ray absorptiometry (DXA) provides a measure of the areal bone mineral density (BMD). However, the effects of bone thickness and the degree of mineralization cannot be directly distinguished by DXA. Therefore, BMD measured by DXA alone cannot fully depict or predict bone mechanical properties or fracture risk [6], [7], [8]. Other important factors for predicting fracture risk include, e.g. geometry [9], [10], micro-damage [11], composition [12], [13] and trabecular bone microarchitecture [14], [15]. The combined effect of all of these factors defines the bone quality, which depends on the structural and compositional parameters as well as the mechanical properties [16]. Thus, to understand the mechanisms that affect bone strength, it is important to understand both the microarchitecture and the molecular composition.
Micro-computed tomography (μCT) can be used to quantify the microarchitecture of trabecular bone [17], [18], [19]. The evaluation of three-dimensional morphology of trabecular bone provides an estimation of several indices, such as bone volume fraction (BV/TV), average trabecular thickness (Tb.Th), separation (Tb.Sp) and number (Tb.N) as well as information about the trabecular plate-rod-like shape (structural model index, SMI) and the degree of anisotropy (DA). These indices have been used to examine human trabecular bone in different anatomical locations, e.g. vertebrae, iliac crest, proximal femur and calcaneal bone [3], [19], [20], [21], [22].
Fourier transform infrared (FTIR) microspectroscopy represents a tool for fast measurements of the spatial molecular composition of bone [4], [5], [23]. In FTIR transmission spectroscopy, a wide band of infrared (IR) light is guided through the sample. The different molecular bonds absorb IR light of different wavelengths and thus an absorption spectrum is created. Several compositional parameters can be calculated from the bone IR spectra. Mineralization can be evaluated from the mineral/matrix ratio (M/M), whereas carbonate substitution is evaluated from the carbonate/phosphate (C/P) ratio [24], [25]. In addition, collagen maturity (C.Mat) [26], and crystallinity [27], [28] can be evaluated through second derivative peak fitting.
The femoral neck has to withstand continuous high compressive and shear forces. During standing these are roughly 1 × BW (body weight), but they can be higher during physical activities (Fig. 1A) [29]. The greater trochanter is mainly subjected to tensile forces from the muscles (e.g. gluteus maximus, medius and minimus) [29] (Fig. 1A), whereas in the calcaneus tensile forces act through the Achilles tendon, plantar fascia and plantar ligaments [30] (Fig. 1B). Since the weight is divided between the heel and forefoot, the calcaneus does not experience as high static compressive loading as the femoral neck. However, the calcaneus has to withstand impact loading during e.g. walking and running, which may be up to 10 × BW [30]. Bone adaptation is driven by dynamic loading [31] which typically increases bone strength through increased cross-sectional area of bone [32], [33]. However, it is possible that concomitant changes in composition occur during adaptation, e.g., the mineral/matrix ratio increases without an increase in cross-sectional area [34]. However, these changes in bone quality have been investigated much more rarely. Hence, trabecular bone adapts to loading environments through modeling and remodeling, which alter its microarchitecture. Moreover, the molecular composition is also altered, at least temporarily, during the process of remodeling [28], [35]. Thus, local compositional and structural evaluations can provide important information about normal development of trabecular bone and its adaptation to different loading environments.
Currently, data on the variation in the composition of trabecular bone at several anatomic sites within the same donor is limited [36]. Specifically, the composition at the femoral neck, greater trochanter and calcaneus within the same donor has not been studied. Thus, in the present study, we quantified and compared the molecular composition and microarchitecture of trabecular bone in the femoral neck, greater trochanter and calcaneus in human donors with healthy bones. Additionally, changes in and relationships between molecular composition and microarchitecture of trabecular bone with age during adult life were investigated.
Section snippets
Experimental overview
Trabecular bone samples were harvested from the femoral neck, greater trochanter and calcaneus of male human cadavers (age range 17–82 years, n = 20) with permission from the National Authority for Medicolegal Affairs (TEO, 5783/04/044/07) (Fig. 1). Medical records were available and none of the cadavers had any known metabolic bone diseases. First, DXA measurements were conducted on the intact proximal femur and calcaneus. Thereafter, two trabecular bone samples (diameter 10 mm, length 10–15 mm)
Results
In order to compare the relative difference in compositional and structural parameters between different anatomical locations within each individual, all parameters were first normalized to the corresponding parameter value in the femoral neck (Fig. 3). Any of the locations could have been selected. The non-normalized values of all parameters are presented in Table 1. For BMD, significant differences (p < 0.01) were found between each anatomical location. BMD was highest in femoral neck and
Discussion
In the present study, the composition and microarchitecture of trabecular bone in the human femoral neck, greater trochanter and calcaneus were studied using FTIR microspectroscopy and micro-computed tomography, and then compared with BMD measurements from the clinical gold standard DXA. The anatomical location and age dependency in these parameters were investigated. Significant differences in the composition and the microarchitecture of trabecular bone were detected between the anatomical
Conclusion
Little is known about the variation in molecular composition of bone across anatomical locations. This study supplements other recent studies investigating this important topic [36], [50]. Moreover, the understanding of the interplay between molecular composition and microarchitecture is still limited. No previous study has addressed the composition of trabecular bone from the human femur neck, greater trochanter and calcaneus. In the present study, significant differences were identified in
Acknowledgments
The research was supported by the strategic funding of the University of Eastern Finland, the Academy of Finland (128863), Kuopio University Hospital (EVO project 5031342, PY 120 musculoskeletal disorders) and the National Doctoral Programme of Musculoskeletal Disorders and Biomaterials (TBDP). We want to acknowledge Ewen MacDonald for wording revision.
References (56)
- et al.
Bone mineralization density distribution in health and disease
Bone
(2008) - et al.
Long-term voluntary exercise of male mice induces more beneficial effects on cancellous and cortical bone than on the collagenous matrix
Exp Gerontol
(2009) Three-dimensional methods for quantification of cancellous bone architecture
Bone
(1997)- et al.
Assessment of trabecular bone structure of the calcaneus using multi-detector CT: correlation with microCT and biomechanical testing
Bone
(2009) - et al.
FT-IR imaging of native and tissue-engineered bone and cartilage
Biomaterials
(2007) - et al.
Novel infrared spectroscopic method for the determination of crystallinity of hydroxyapatite minerals
Biophys J
(1991) Three rules for bone adaptation to mechanical stimuli
Bone
(1998)- et al.
Non-invasive axial loading of mouse tibiae increases cortical bone formation and modifies trabecular organization: a new model to study cortical and cancellous compartments in a single loaded element
Bone
(2005) - et al.
Fabric and elastic principal directions of cancellous bone are closely related
J Biomech
(1997) - et al.
A physical, chemical, and mechanical study of lumbar vertebrae from normal, ovariectomized, and nandrolone decanoate-treated cynomolgus monkeys (Macaca fascicularis)
Bone
(2000)