Bone mineralization density distribution in health and disease

Age-dependence of power spectral density and fractal dimension of bone mineralized matrix in atomic force microscope topography images: potential correlates of bone tissue age and bone fragility in female femoral neck trabeculae

There is an increasing interest in bone nano-structure, the ultimate goal being to reveal the basis of age-related bone fragility. In this study, power spectral density (PSD) data and fractal dimensions of the mineralized bone matrix were extracted from atomic force microscope topography images of the femoral neck trabeculae. The aim was to evaluate age-dependent differences in the mineralized matrix of human bone and to consider whether these advanced nano-descriptors might be linked to decreased bone remodeling observed by some authors and age-related decline in bone mechanical competence. The investigated bone specimens belonged to a group of young adult women (n = 5, age: 20-40 years) and a group of elderly women (n = 5, age: 70-95 years) without bone diseases. PSD graphs showed the roughness density distribution in relation to spatial frequency. In all cases, there was a fairly linear decrease in magnitude of the power spectra with increasing spatial frequencies. The PSD slope was steeper in elderly individuals (-2.374 vs. -2.066), suggesting the dominance of larger surface morphological features. Fractal dimension of the mineralized bone matrix showed a significant negative trend with advanced age, declining from 2.467 in young individuals to 2.313 in the elderly (r = 0.65, P = 0.04). Higher fractal dimension in young women reflects domination of smaller mineral grains, which is compatible with the more freshly remodeled structure. In contrast, the surface patterns in elderly individuals were indicative of older tissue age. Lower roughness and reduced structural complexity (decreased fractal dimension) of the interfibrillar bone matrix in the elderly suggest a decline in bone toughness, which explains why aged bone is more brittle and prone to fractures.

Osteocyte regulation of bone mineral: a little give and take

Osteocytes actively participate in almost every phase of mineral handling by bone. They regulate the mineralisation of osteoid during bone formation, and they are also a major RANKL-producing cell. Osteocytes are thus able to liberate bone mineral by regulating osteoclast differentiation and activity in response to a range of stimuli, including bone matrix damage, bone disuse and mechanical unloading, oestrogen deficiency, high-dose glucocorticoid and chemotherapeutic agents. At least some of these activities may be regulated by the osteocyte-secreted product, sclerostin. There is also mounting evidence that in addition to regulating phosphate homeostasis systemically, osteocytes contribute directly to calcium homeostasis in the mature skeleton. Osteocyte cell death and the local loss of control of bone mineralisation may be the cause of focal hypermineralisation of bone and osteopetrosis, as seen in aging and pathology. The sheer number of osteocytes in bone means that "a little give and take" in terms of regulation of bone mineral content translates into a powerful whole organism effect.

Mineralization pattern of vertebral bone material following fragility fracture of the spine

Little is known whether trabecular bone matrix mineralization is altered at the site of osteoporotic vertebral fractures. Bone mineralization density distribution (BMDD) was assessed in trabecular bone of acute, single-level compression fractures of the spine at various stages of fracture repair using quantitative backscattered electron imaging (qBEI). The grading of the repair stage was performed by histological methods. From 20 patients, who underwent either kyphoplasty (n=18) or vertebroplasty (n=2), a vertebral bone biopsy was taken prior to cement augmentation. Six patients took bisphosphonates (BP) prior to fracture. Three study groups were formed: N1=early-, N2=late-healing and B=BP treatment at late healing stage. In general, all groups had an altered BMDD when compared to historical normative reference data. Mean matrix mineralization (CaMean) was significantly (p<0.001) lower in all groups (N1: -5%, N2: -16%, and B2: -16%). In N2, CaMean was -13.1% (p<0.001) lower than N1. At this stage, deposition of new bone matrix and/or formation of woven bone are seen, which also explains the more heterogeneous matrix mineralization (CaWidth). Moreover, BP treatment (B2) led to a significant reduction in CaWidth (-28.5%, p<0.001), when compared to N2. Bone tissue from vertebrae with acute compression fractures reveals a large variation in matrix mineralization depending on the stage of repair. Bisphosphonate treatment does affect the mineralization pattern of tissue repair. The low mineralization values found in early stage of repair suggest that altered bone material properties may play a role in the occurrence of fragility fractures of the spine.

Analysis of retrieved hip resurfacing arthroplasties reveals the interrelationship between interface hyperosteoidosis and demineralization of viable bone trabeculae

Retrieved hip resurfacing arthroplasties (HRA) revised for causes other than osteonecrosis enable further insights into bone-cement interactions within the interface with only minimal biomechanical stresses. Our primary objective was to investigate the mineralization changes at the trabecular bone interface in retrieved hips using bright field and polarized light microscopy and by quantitative backscattered electron imaging. Because superficial seams of non-mineralized bone tissue varied substantially, we defined hyperosteoidosis as an osteoid seam of more than 20 µm thickness. We hypothesized that interface hyperosteoidosis might be caused by the demineralization of previously mineralized bone tissue. One hundred and thirty-one retrieved HRAs with viable bone remnant tissue were analyzed. Bone mineral density distribution obtained from backscattered signal intensities of the trabecular bone at the bone-cement interface was assessed in cases with and without interface hyperosteoidosis. In cases with interface hyperosteoidosis, the degree of trabecular mineralization was also analyzed in deeper areas of the femoral remnants. Thirty-four cases showed hyperosteoidosis at the bone-cement interface, mostly in female patients. Bone trabeculae with hyperosteoidosis displayed a mineral density distribution pattern suggestive of the demineralization of a previously mineralized bone matrix. Our results demonstrate the localized disorder of the mineralization pattern of bone trabeculae at the bone-cement interface in a group of retrieved HRAs. In previously well-fixed femoral components, potential adverse effects on the load-bearing bone due to a decreased degree of mineralization at the bone-cement interface may affect the durability of the implant's function.

Correlative light and scanning X-ray scattering microscopy of healthy and pathologic human bone sections

Scanning small and wide angle X-ray scattering (scanning SWAXS) experiments were performed on healthy and pathologic human bone sections. Via crystallographic tools the data were transformed into quantitative images and as such compared with circularly polarized light (CPL) microscopy images. SWAXS and CPL images allowed extracting information of the mineral nanocrystalline phase embedded, with and without preferred orientation, in the collagen fibrils, mapping local changes at sub-osteon resolution. This favorable combination has been applied for the first time to biopsies of dwarfism syndrome and Paget's disease to shed light onto the cortical structure of natural bone in healthy and pathologic sections.

X-ray vector radiography for bone micro-architecture diagnostics

The understanding of large biophysical systems at the systems level often depends on a precise knowledge of their microstructure. This is difficult to obtain, especially in vivo, because most imaging methods are either limited in terms of achievable field of view, or make use of penetrating ionizing radiations such as x-rays, in which case the resolution is severely limited by the deposited dose. Here, we describe a new method, x-ray vector radiography (XVR), which yields various types of information about the local orientation, anisotropy and average size of the sample microstructures. We demonstrate the feasibility by showing first experimental XVRs of human vertebra bone samples, giving information on the trabecular structures even with a pixel resolution of half a millimetre, much larger than the structures themselves. This last point is critical for the development of low-dose measurement methods which will allow for in vivo studies and potentially in the future for new medical diagnostics methods of bone metabolic disorder diseases such as osteoporosis.

Assessment of lamellar level properties in mouse bone utilizing a novel spherical nanoindentation data analysis method

In this work, we demonstrate the viability of using our recently developed data analysis procedures for spherical nanoindentation in conjunction with Raman spectroscopy for studying lamellar-level correlations between the local composition and local mechanical properties in mouse bone. Our methodologies allow us to convert the raw load-displacement datasets to much more meaningful indentation stress-strain curves that accurately capture the loading and unloading elastic moduli, the indentation yield points, as well as the post-yield characteristics in the tested samples. Using samples of two different inbred mouse strains, A/J and C57BL/6J (B6), we successfully demonstrate the correlations between the mechanical information obtained from spherical nanoindentation measurements to the local composition measured using Raman spectroscopy. In particular, we observe that a higher mineral-to-matrix ratio correlated well with a higher local modulus and yield strength in all samples. Thus, new bone regions exhibited lower moduli and yield strengths compared to more mature bone. The B6 mice were also found to exhibit lower modulus and yield strength values compared to the more mineralized A/J strain.

TRANSVERSE ISOTROPIC ELASTIC PROPERTIES OF VERTEBRAL TRABECULAR BONE MATRIX MEASURED USING MICROINDENTATION UNDER DRY CONDITIONS (EFFECTS OF AGE, GENDER, AND VERTEBRAL LEVEL)

The mechanical properties of bone extracellular matrix have become of increasing interest for the understanding of vertebral fracture risk. Depth-sensing indentation techniques allow the measurement of directional elastic properties of trabecular bone ex vivo with a high spatial resolution. Transverse isotropic elastic properties of vertebral trabecular bone obtained from two orthogonal directions were investigated using microindentation under dry conditions focusing on the influence of microanatomical location, age, gender, vertebral level, and anatomic direction on these properties. Biopsies were obtained from 104 human vertebrae (T1–L3) with a median age of 65 (21–94) years. Significantly, higher indentation moduli were found for indentations on axial than on transverse cross-sections of trabeculae (p < 0.01). Indentation moduli in the core were 1.05 to 1.12 times higher than in the periphery (p < 0.01). No difference in stiffness could be detected between males and females (p > 0.05) and different ages (p > 0.5). Vertebral level showed a weak correlation (p = 0.073, r2 ≈ 0.17). These results provide insights in the transverse isotropic properties of trabecular bone matrix related to age, gender, microanatomical location, and anatomic direction for a broad spectrum of human vertebrae.

Bone mineralization in celiac disease

Evidence indicates a well-established relationship between low bone mineral density (BMD) and celiac disease (CD), but data on the pathogenesis of bone derangement in this setting are still inconclusive. In patients with symptomatic CD, low BMD appears to be directly related to the intestinal malabsorption. Adherence to a strict gluten-free diet (GFD) will reverse the histological changes in the intestine and also the biochemical evidence of calcium malabsorption, resulting in rapid increase of BMD. Nevertheless, GFD improves BMD but does not normalize it in all patients, even after the recovery of intestinal mucosa. Other mechanisms of bone injury than calcium and vitamin D malabsorption are thought to be involved, such as proinflammatory cytokines, parathyroid function abnormalities, and misbalanced bone remodeling factors, most of all represented by the receptor activator of nuclear factor B/receptor activator of nuclear factor B-ligand/osteoprotegerin system. By means of dual-energy X-ray absorptiometry (DXA), it is now rapid and easy to obtain semiquantitative values of BMD. However, the question is still open about who and when submit to DXA evaluation in CD, in order to estimate risk of fractures. Furthermore, additional information on the role of nutritional supplements and alternative therapies is needed.

No evidence of circulating autoantibodies against osteoprotegerin in patients with celiac disease

AIM: To investigate risk factors for low bone mineral density (BMD) in celiac disease (CD) patients, focusing on circulating autoantibodies against osteoprotegerin (OPG).

METHODS: Seventy asymptomatic CD adult patients on gluten-free diet (GFD) and harbouring persistent negative CD-related serology were recruited. Conventional risk factors for osteoporosis (e.g., age, sex, menopausal status, history of fractures, smoke, and body mass index) were checked and BMD was assessed by dual energy X ray absorptiometry. Serum calcium and parathyroid hormone (PTH) levels were evaluated. Thirty-eight patients underwent repeat duodenal biopsy. Serum samples from a selected sub-group of 30 patients, who were also typed for human leukocyte antigen (HLA) DQ2 and DQ8 haplotype, were incubated with homodimeric recombinant human OPG and tested by western blotting with an anti-OPG antibody after immunoprecipitation.

RESULTS: Despite persistent negative CD-related serology and strict adherence to GFD, 49 out of the 70 (74%) patients displayed low BMD. Among these patients, 13 (24%) showed osteoporosis and 36 (76%) osteopenia. With the exception of age, conventional risk factors for osteoporosis did not differ between patients with normal and low BMD. Circulating serum calcium and PTH levels were normal in all patients. Duodenal mucosa healing was found in 31 (82%) out of 38 patients who underwent repeat duodenal biopsy with 20 (64%) still displaying low BMD. The remaining 7 patients had an incomplete normalization of duodenal mucosa with 6 (84%) showing low BMD. No evidence of circulating antibodies against OPG was found in the serum of 30 celiac patients who were tested for, independent of BMD, duodenal histology, and HLA status.

CONCLUSION: If any, the role of circulating autoantibodies against OPG in the pathogenesis of bone derangement in patients with CD is not a major one.

Deterioration of bone quality in the tibia and fibula in growing mice during skeletal unloading: gender-related differences

Skeletal unloading causes bone loss in both men and women; however, only a few studies have been performed on the effects of gender differences on bone quality during skeletal unloading. Moreover, although the fibula also plays an important role in load bearing and ankle stability, the effects of unloading on the fibula have been rarely investigated. The present study aimed to investigate the effects of skeletal unloading on bone quality of the tibia and fibula in growing animals and to determine whether differences existed between genders. Six-week-old female and male mice were randomly allocated into two groups. The right hindlimb of each mouse in the skeletal unloading group was subjected to sciatic neurectomy. After two weeks of skeletal unloading, the structural characteristics of the tibia and fibula in both genders were worsened. In addition, the bone mineralization density distribution (MDD) of the tibia and fibula in both genders were altered. However, the magnitude of deterioration and alteration of the MDD in the bones of females were larger than in those of males. These results demonstrate that skeletal unloading diminishes bone quality in the tibia and fibula, leading to an increase in bone fracture risks, particularly in females.

Significant deterioration in nanomechanical quality occurs through incomplete extrafibrillar mineralization in rachitic bone: evidence from in-situ synchrotron X-ray scattering and backscattered electron imaging

Bone diseases such as rickets and osteoporosis cause significant reduction in bone quantity and quality, which leads to mechanical abnormalities. However, the precise ultrastructural mechanism by which altered bone quality affects mechanical properties is not clearly understood. Here we demonstrate the functional link between altered bone quality (reduced mineralization) and abnormal fibrillar-level mechanics using a novel, real-time synchrotron X-ray nanomechanical imaging method to study a mouse model with rickets due to reduced extrafibrillar mineralization. A previously unreported N-ethyl-N-nitrosourea (ENU) mouse model for hypophosphatemic rickets (Hpr), as a result of missense Trp314Arg mutation of the phosphate regulating gene with homologies to endopeptidase on the X chromosome (Phex) and with features consistent with X-linked hypophosphatemic rickets (XLHR) in man, was investigated using in situ synchrotron small angle X-ray scattering to measure real-time changes in axial periodicity of the nanoscale mineralized fibrils in bone during tensile loading. These determine nanomechanical parameters including fibril elastic modulus and maximum fibril strain. Mineral content was estimated using backscattered electron imaging. A significant reduction of effective fibril modulus and enhancement of maximum fibril strain was found in Hpr mice. Effective fibril modulus and maximum fibril strain in the elastic region increased consistently with age in Hpr and wild-type mice. However, the mean mineral content was ∼21% lower in Hpr mice and was more heterogeneous in its distribution. Our results are consistent with a nanostructural mechanism in which incompletely mineralized fibrils show greater extensibility and lower stiffness, leading to macroscopic outcomes such as greater bone flexibility. Our study demonstrates the value of in situ X-ray nanomechanical imaging in linking the alterations in bone nanostructure to nanoscale mechanical deterioration in a metabolic bone disease.

Human bone material characterization: integrated imaging surface investigation of male fragility fractures

The interrelation of calcium and phosphorus was evaluated as a function of bone material quality in femoral heads from male fragility fracture patients via surface analytical imaging as well as scanning microscopy techniques. A link between fragility fractures and increased calcium to phosphorus ratio was observed despite normal mineralization density distribution.

INTRODUCTION

Bone fragility in men has been recently recognized as a public health issue, but little attention has been devoted to bone material quality and the possible efficacy in fracture risk prevention. Clinical routine fracture risk estimations do not consider the quality of the mineralized matrix and the critical role played by the different chemical components that are present. This study uses a combination of different imaging and analytical techniques to gain insights into both the spatial distribution and the relationship of phosphorus and calcium in bone.

METHODS

X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry imaging techniques were used to investigate the relationship between calcium and phosphorus in un-embedded human femoral head specimens from fragility fracture patients and non-fracture age-matched controls. The inclusion of the bone mineral density distribution via backscattered scanning electron microscopy provides information about the mineralization status between the groups.

RESULTS

A link between fragility fracture and increased calcium and decreased phosphorus in the femoral head was observed despite normal mineralization density distribution. Results exhibited significantly increased calcium to phosphorus ratio in the fragility fracture group, whereas the non-fracture control group ratio was in agreement with the literature value of 1.66 M ratio in mature bone.

CONCLUSIONS

Our results highlight the potential importance of the relationship between calcium and phosphorus, especially in areas of new bone formation, when estimating fracture risk of the femoral head. The determination of calcium and phosphorus fractions in bone mineral density measurements may hold the key to better fracture risk assessment as well as more targeted therapies.

Mineral heterogeneity has a minor influence on the apparent elastic properties of human cancellous bone: a SRμCT-based finite element study

At the tissue level, the local material properties of human cancellous bone are heterogeneous due to constant remodelling. Since standard high-resolution computed tomography scanning methods are unable to capture this heterogeneity in detail, local differences in mineralisation are normally not incorporated in computational models. To investigate the effects of heterogeneous mineral distribution on the apparent elastic properties, 40 cancellous bone samples from the human femoral neck were scanned by means of synchrotron radiation microcomputed tomography (SRμCT). SRμCT-based micromechanical finite element models that accounted for mineral heterogeneity were compared with homogeneous models. Evaluation of the apparent stiffness tensor of both model types revealed that homogeneous models led to a minor but significant (p < 0.05) overestimation of the elastic properties of heterogeneous models by 2.18 ± 1.89%. Variation of modelling parameters did not affect the overestimation to a great extent. It was concluded that the heterogeneous mineralisation has only a minor influence on the apparent elastic properties of human cancellous bone.

Do regional modifications in tissue mineral content and microscopic mineralization heterogeneity adapt trabecular bone tracts for habitual bending? Analysis in the context of trabecular architecture of deer calcanei

Calcanei of mature mule deer have the largest mineral content (percent ash) difference between their dorsal 'compression' and plantar 'tension' cortices of any bone that has been studied. The opposing trabecular tracts, which are contiguous with the cortices, might also show important mineral content differences and microscopic mineralization heterogeneity (reflecting increased hemi-osteonal renewal) that optimize mechanical behaviors in tension vs. compression. Support for these hypotheses could reveal a largely unrecognized capacity for phenotypic plasticity - the adaptability of trabecular bone material as a means for differentially enhancing mechanical properties for local strain environments produced by habitual bending. Fifteen skeletally mature and 15 immature deer calcanei were cut transversely into two segments (40% and 50% shaft length), and cores were removed to determine mineral (ash) content from 'tension' and 'compression' trabecular tracts and their adjacent cortices. Seven bones/group were analyzed for differences between tracts in: first, microscopic trabecular bone packets and mineralization heterogeneity (backscattered electron imaging, BSE); and second, trabecular architecture (micro-computed tomography). Among the eight architectural characteristics evaluated [including bone volume fraction (BVF) and structural model index (SMI)]: first, only the 'tension' tract of immature bones showed significantly greater BVF and more negative SMI (i.e. increased honeycomb morphology) than the 'compression' tract of immature bones; and second, the 'compression' tracts of both groups showed significantly greater structural order/alignment than the corresponding 'tension' tracts. Although mineralization heterogeneity differed between the tracts in only the immature group, in both groups the mineral content derived from BSE images was significantly greater (P < 0.01), and bulk mineral (ash) content tended to be greater in the 'compression' tracts (immature 3.6%, P = 0.03; mature 3.1%, P = 0.09). These differences are much less than the approximately 8% greater mineral content of their 'compression' cortices (P < 0.001). Published data, suggesting that these small mineralization differences are not mechanically important in the context of conventional tests, support the probability that architectural modifications primarily adapt the tracts for local demands. However, greater hemi-osteonal packets in the tension trabecular tract of only the mature bones (P = 0.006) might have an important role, and possible synergism with mineralization and/or microarchitecture, in differential toughening at the trabeculum level for tension vs. compression strains.

Delayed bone regeneration and low bone mass in a rat model of insulin-resistant type 2 diabetes mellitus is due to impaired osteoblast function

Patients with diabetes mellitus have an impaired bone metabolism; however, the underlying mechanisms are poorly understood. Here, we analyzed the impact of type 2 diabetes mellitus on bone physiology and regeneration using Zucker diabetic fatty (ZDF) rats, an established rat model of insulin-resistant type 2 diabetes mellitus. ZDF rats develop diabetes with vascular complications when fed a Western diet. In 21-wk-old diabetic rats, bone mineral density (BMD) was 22.5% (total) and 54.6% (trabecular) lower at the distal femur and 17.2% (total) and 20.4% (trabecular) lower at the lumbar spine, respectively, compared with nondiabetic animals. BMD distribution measured by backscattered electron imaging postmortem was not different between diabetic and nondiabetic rats, but evaluation of histomorphometric indexes revealed lower mineralized bone volume/tissue volume, trabecular thickness, and trabecular number. Osteoblast differentiation of diabetic rats was impaired based on lower alkaline phosphatase activity (-20%) and mineralized matrix formation (-55%). In addition, the expression of the osteoblast-specific genes bone morphogenetic protein-2, RUNX2, osteocalcin, and osteopontin was reduced by 40-80%. Osteoclast biology was not affected based on tartrate-resistant acidic phosphatase staining, pit formation assay, and gene profiling. To validate the implications of these molecular and cellular findings in a clinically relevant model, a subcritical bone defect of 3 mm was created at the left femur after stabilization with a four-hole plate, and bone regeneration was monitored by X-ray and microcomputed tomography analyses over 12 wk. While nondiabetic rats filled the defects by 57%, diabetic rats showed delayed bone regeneration with only 21% defect filling. In conclusion, we identified suppressed osteoblastogenesis as a cause and mechanism for low bone mass and impaired bone regeneration in a rat model of type 2 diabetes mellitus.

Lathyrism-induced alterations in collagen cross-links influence the mechanical properties of bone material without affecting the mineral

In the present study a rat animal model of lathyrism was employed to decipher whether anatomically confined alterations in collagen cross-links are sufficient to influence the mechanical properties of whole bone. Animal experiments were performed under an ethics committee approved protocol. Sixty-four female (47 day old) rats of equivalent weights were divided into four groups (16 per group): Controls were fed a semi-synthetic diet containing 0.6% calcium and 0.6% phosphorus for 2 or 4 weeks and β-APN treated animals were fed additionally with β-aminopropionitrile (0.1% dry weight). At the end of this period the rats in the four groups were sacrificed, and L2-L6 vertebra were collected. Collagen cross-links were determined by both biochemical and spectroscopic (Fourier transform infrared imaging (FTIRI)) analyses. Mineral content and distribution (BMDD) were determined by quantitative backscattered electron imaging (qBEI), and mineral maturity/crystallinity by FTIRI techniques. Micro-CT was used to describe the architectural properties. Mechanical performance of whole bone as well as of bone matrix material was tested by vertebral compression tests and by nano-indentation, respectively. The data of the present study indicate that β-APN treatment changed whole vertebra properties compared to non-treated rats, including collagen cross-links pattern, trabecular bone volume to tissue ratio and trabecular thickness, which were all decreased (p<0.05). Further, compression tests revealed a significant negative impact of β-APN treatment on maximal force to failure and energy to failure, while stiffness was not influenced. Bone mineral density distribution (BMDD) was not altered either. At the material level, β-APN treated rats exhibited increased Pyd/Divalent cross-link ratios in areas confined to a newly formed bone. Moreover, nano-indentation experiments showed that the E-modulus and hardness were reduced only in newly formed bone areas under the influence of β-APN, despite a similar mineral content. In conclusion the results emphasize the pivotal role of collagen cross-links in the determination of bone quality and mechanical integrity. However, in this rat animal model of lathyrism, the coupled alterations of tissue structural properties make it difficult to weigh the contribution of the anatomically confined material changes to the overall mechanical performance of whole bone. Interestingly, the collagen cross-link ratio in bone forming areas had the same profile as seen in actively bone forming trabecular surfaces in human iliac crest biopsies of osteoporotic patients.

Analysis of bone demineralization due to the use of exoprosthesis by comparing Young's modulus of the femur in unilateral transfemoral amputees

BACKGROUND

There is a relation between Hounsfield units obtained from computed tomography (CT) scans and bone density. The density of the bones can be used to establish its mechanical properties and therefore to assess the bone mechanical condition using CT images.

OBJECTIVES

To identify the effect of the transfemoral amputation and the use of external lower limb prosthesis in the bone properties, by comparing Young's modulus.

STUDY DESIGN

Young's modulus comparison.

METHODS

Comparison of bone density between the healthy femur and the amputated bone of 20 unilateral transfemoral amputees was done by generating three histograms of the Hounsfield units at different parts of the femur. The histograms were created based on images obtained by CT and the Hounsfield units were translated to Young's modulus to establish the comparison.

RESULTS

The results show a significant difference (p-value <0.05) between the mean value of Young's modulus of healthy and amputated bone.

CONCLUSIONS

There is clearly a direct association between the use of external prosthesis and the bone demineralization due the stress shielding phenomenon. The Young's modulus comparison using information from CT images can be a suitable tool to analyze the bone demineralization due to the use of exoprosthesis.

Increased strontium uptake in trabecular bone of ovariectomized calcium-deficient rats treated with strontium ranelate or strontium chloride

Based on clinical trials showing the efficacy to reduce vertebral and non-vertebral fractures, strontium ranelate (SrR) has been approved in several countries for the treatment of postmenopausal osteoporosis. Hence, it is of special clinical interest to elucidate how the Sr uptake is influenced by dietary Ca deficiency as well as by the formula of Sr administration, SrR versus strontium chloride (SrCl(2)). Three-month-old ovariectomized rats were treated for 90 days with doses of 25 mg kg(-1) d(-1) and 150 mg kg(-1) d(-1) of SrR or SrCl(2) at low (0.1% Ca) or normal (1.19% Ca) Ca diet. Vertebral bone tissue was analysed by confocal synchrotron-radiation-induced micro X-ray fluorescence and by backscattered electron imaging. Principal component analysis and k-means clustering of the acquired elemental maps of Ca and Sr revealed that the newly formed bone exhibited the highest Sr fractions and that low Ca diet increased the Sr uptake by a factor of three to four. Furthermore, Sr uptake in bone of the SrCl(2)-treated animals was generally lower compared with SrR. The study clearly shows that inadequate nutritional calcium intake significantly increases uptake of Sr in serum as well as in trabecular bone matrix. This indicates that nutritional calcium intake as well as serum Ca levels are important regulators of any Sr treatment.

Skeletal mineralization defects in adult hypophosphatasia--a clinical and histological analysis

Histomorphometry and quantitative backscattered electron microscopy of iliac crest biopsies from patients with adult hypophosphatasia not only confirmed the expected enrichment of non-mineralized osteoid, but also demonstrated an altered trabecular microarchitecture, an increased number of osteoblasts, and an impaired calcium distribution within the mineralized bone matrix.

INTRODUCTION

Adult hypophosphatasia is an inherited disorder of bone metabolism caused by inactivating mutations of the ALPL gene, encoding tissue non-specific alkaline phosphatase. While it is commonly accepted that the increased fracture risk of the patients is the consequence of osteomalacia, there are only few studies describing a complete histomorphometric analysis of bone biopsies from affected individuals. Therefore, we analyzed iliac crest biopsies from eight patients and set them in direct comparison to biopsies from healthy donors or from individuals with other types of osteomalacia.

METHODS

Histomorphometric analysis was performed on non-decalcified sections stained either after von Kossa/van Gieson or with toluidine blue. Bone mineral density distribution was quantified by backscattered electron microscopy.

RESULTS

Besides the well-documented enrichment of non-mineralized bone matrix in individuals suffering from adult hypophosphatasia, our histomorphometric analysis revealed alterations of the trabecular microarchitecture and an increased number of osteoblasts compared to healthy controls or to individuals with other types of osteomalacia. Moreover, the analysis of the mineralized bone matrix revealed significantly decreased calcium content in patients with adult hypophosphatasia.

CONCLUSIONS

Taken together, our data show that adult hypophosphatasia does not solely result in an enrichment of osteoid, but also in a considerable degradation of bone quality, which might contribute to the increased fracture risk of the affected individuals.

Effect of high phosphorus diet on tooth microstructure of rodent incisors

Enamel hypoplasia and disruption of dentinogenesis are the most common abnormalities of development and mineralization of human teeth. Several reports are available in the literature on the influence of dietary calcium on the formation of human and rodent tooth; however, the information about the influence of dietary phosphorus on the tooth formation is scarce. The aim of the present investigation was to examine the chronic effect of high phosphorus diet and improper dietary calcium to phosphorus ratio on the mandibular incisor microstructure in a hystricomorph rodent--Octodon degu--using macroscopic observation, histopathological examination, transmission and scanning electron microscopy. The present study shows that enamel and dentin development is disturbed under high phosphorus diet and improper calcium to phosphorus ratio. Disturbed mineral metabolism resulted in enamel depigmentation, enamel hypoplasia, enamel pitting and altered dentin morphology. The results suggest that more attention should be focused on dietary phosphorus content when facing altered tooth structure in young patients with deciduous or permanent dentition. Furthermore, we showed that degus can be used as an experimental animal model for the study of the developmental teeth disturbances.

Trabecular reorganization in consecutive iliac crest biopsies when switching from bisphosphonate to strontium ranelate treatment

BACKGROUND

Several agents are available to treat osteoporosis while addressing patient-specific medical needs. Individuals' residual risk to severe fracture may require changes in treatment strategy. Data at osseous cellular and microstructural levels due to a therapy switch between agents with different modes of action are rare. Our study on a series of five consecutively taken bone biopsies from an osteoporotic individual over a six-year period analyzes changes in cellular characteristics, bone microstructure and mineralization caused by a therapy switch from an antiresorptive (bisphosphonate) to a dual action bone agent (strontium ranelate).

METHODOLOGY/PRINCIPAL FINDINGS

Biopsies were progressively taken from the iliac crest of a female patient. Four biopsies were taken during bisphosphonate therapy and one biopsy was taken after one year of strontium ranelate (SR) treatment. Furthermore, serum bone markers and dual x-ray absorptiometry measurements were acquired. Undecalcified histology was used to assess osteoid parameters and bone turnover. Structural indices and degree of mineralization were determined using microcomputed tomography, quantitative backscattered electron imaging, and combined energy dispersive x-ray/µ-x-ray-fluorescence microanalysis.

CONCLUSIONS/SIGNIFICANCE

Microstructural data revealed a notable increase in bone volume fraction after one year of SR treatment compared to the bisphosphonate treatment period. Indices of connectivity density, structure model index and trabecular bone pattern factor were predominantly enhanced indicating that the architectural transformation from trabecular rods to plates was responsible for the bone volume increase and less due to changes in trabecular thickness and number. Administration of SR following bisphosphonates led to a maintained mineralization profile with an uptake of strontium on the bone surface level. Reactivated osteoclasts designed tunneling, hook-like intratrabecular resorption sites. The appearance of tunneling resorption lacunae and the formation of both mini-modeling units and osteon-like structures within increased plate-like cancellous bone mass provides additional information on the mechanisms of strontium ranelate following bisphosphonate treatment, which may deserve special attention when monitoring a treatment switch.

New laboratory tools in the assessment of bone quality

Bone quality is a complex set of intricated and interdependent factors that influence bone strength. A number of methods have emerged to measure bone quality, taking into account the organic or the mineral phase of the bone matrix, in the laboratory. Bone quality is a complex set of different factors that are interdependent. The bone matrix organization can be described at five different levels of anatomical organization: nature (organic and mineral), texture (woven or lamellar), structure (osteons in the cortices and arch-like packets in trabecular bone), microarchitecture, and macroarchitecture. Any change in one of these levels can alter bone quality. An altered bone remodeling can affect bone quality by influencing one or more of these factors. We have reviewed here the main methods that can be used in the laboratory to explore bone quality on bone samples. Bone remodeling can be evaluated by histomorphometry; microarchitecture is explored in 2D on histological sections and in 3D by microCT or synchrotron. Microradiography and scanning electron microscopy in the backscattered electron mode can measure the mineral distribution; Raman and Fourier-transformed infra-red spectroscopy and imaging can simultaneously explore the organic and mineral phase of the matrix on multispectral images; scanning acoustic microscopy and nanoindentation provide biomechanical information on individual trabeculae. Finally, some histological methods (polarization, surface staining, fluorescence, osteocyte staining) may also be of interest in the understanding of quality as a component of bone fragility. A growing number of laboratory techniques are now available. Some of them have been described many years ago and can find a new youth; others having benefited from improvements in physical and computer techniques are now available.

Whole bone mechanics and bone quality

BACKGROUND

The skeleton plays a critical structural role in bearing functional loads, and failure to do so results in fracture. As we evaluate new therapeutics and consider treatments to prevent skeletal fractures, understanding the basic mechanics underlying whole bone testing and the key principles and characteristics contributing to the structural strength of a bone is critical.

QUESTIONS/PURPOSES

We therefore asked: (1) How are whole bone mechanical tests performed and what are the key outcomes measured? (2) How do the intrinsic characteristics of bone tissue contribute to the mechanical properties of a whole bone? (3) What are the effects of extrinsic characteristics on whole bone mechanical behavior? (4) Do environmental factors affect whole bone mechanical properties?

METHODS

We conducted a PubMed search using specific search terms and limiting our included articles to those related to in vitro testing of whole bones. Basic solid mechanics concepts are summarized in the context of whole bone testing and the determinants of whole bone behavior.

RESULTS

Whole bone mechanical tests measure structural stiffness and strength from load-deformation data. Whole bone stiffness and strength are a function of total bone mass and the tissue geometric distribution and material properties. Age, sex, genetics, diet, and activity contribute to bone structural performance and affect the incidence of skeletal fractures.

CONCLUSIONS

Understanding and preventing skeletal fractures is clinically important. Laboratory tests of whole bone strength are currently the only measures for in vivo fracture prediction. In the future, combined imaging and engineering models may be able to predict whole bone strength noninvasively.

Methods for assessing bone quality: a review

BACKGROUND

Bone mass, geometry, and tissue material properties contribute to bone structural integrity. Thus, bone strength arises from both bone quantity and quality. Bone quality encompasses the geometric and material factors that contribute to fracture resistance.

QUESTIONS/PURPOSES

This review presents an overview of the methods for assessing bone quality across multiple length scales, their outcomes, and their relative advantages and disadvantages.

METHODS

A PubMed search was conducted to identify methods related to bone mechanical testing, imaging, and compositional analysis. Using various exclusion criteria, articles were selected for inclusion.

RESULTS

Methods for assessing mechanical properties include whole-bone, bulk tissue, microbeam, and micro- and nanoindentation testing techniques. Outcomes include structural strength and material modulus. Advantages include direct assessment of bone strength; disadvantages include specimen destruction during testing. Methods for characterizing bone geometry and microarchitecture include quantitative CT, high-resolution peripheral quantitative CT, high-resolution MRI, and micro-CT. Outcomes include three-dimensional whole-bone geometry, trabecular morphology, and tissue mineral density. The primary advantage is the ability to image noninvasively; disadvantages include the lack of a direct measure of bone strength. Methods for measuring tissue composition include scanning electron microscopy, vibrational spectroscopy, nuclear magnetic resonance imaging, and chemical and physical analytical techniques. Outcomes include mineral density and crystallinity, elemental composition, and collagen crosslink composition. Advantages include the detailed material characterization; disadvantages include the need for a biopsy.

CONCLUSIONS

Although no single method can completely characterize bone quality, current noninvasive imaging techniques can be combined with ex vivo mechanical and compositional techniques to provide a comprehensive understanding of bone quality.

Infrared assessment of bone quality: a review

BACKGROUND

Bone strength depends on both bone quantity and quality. The former is routinely estimated in clinical settings through bone mineral density measurements but not the latter. Bone quality encompasses the structural and material properties of bone. Although its importance is appreciated, its contribution in determining bone strength has been difficult to precisely quantify partly because it is multifactorial and requires investigation of all bone hierarchical levels. Fourier transform infrared spectroscopy provides one way to explore these levels.

QUESTIONS/PURPOSES

The purposes of our review were to (1) provide a brief overview of Fourier transform infrared spectroscopy as a way to establish bone quality, (2) review the major bone material parameters determined from Fourier transform infrared spectroscopy, and (3) review the role of Fourier transform infrared microspectroscopic analysis in establishing bone quality.

METHODS

We used the ISI Web of Knowledge database initially to identify articles containing the Boolean term "infrared" AND "bone." We then focused on articles on infrared spectroscopy in bone-related journals.

RESULTS

Infrared spectroscopy provides information on bone material properties. Their microspectroscopic versions allow one to establish these properties as a function of anatomic location, mineralization extent, and bone metabolic activity. It provides answers pertaining to the contribution of mineral to matrix ratio, mineral maturity, mineral carbonate substitution, and collagen crosslinks to bone strength. Alterations of bone material properties have been identified in disease (especially osteoporosis) not attainable by other techniques.

CONCLUSIONS

Infrared spectroscopic analysis is a powerful tool for establishing the important material properties contributing to bone strength and thus has helped better understand changes in fragile bone.

Greater tissue mineralization heterogeneity in femoral neck cortex from hip-fractured females than controls. A microradiographic study

In addition to bone quantity, bone quality affects bone strength. Bone quality depends in part on the degree of mineralization of bone tissue (DMB). The relationship between the DMB distribution and the risk of osteoporotic hip fractures remains incompletely investigated. Here, our aim was to compare DMB distribution in femoral neck cortex specimens from 23 women with hip fractures (age, 65-96 years) and 14 control women (age, 75-103 years). Mineralization was determined using quantitative microradiography. We evaluated the following parameters of DMB frequency histograms, for both osteons and interstitial tissue: mode (oDMB(Al)mode and intDMB(Al)mode, respectively); 25th (oDMB(Al)q25, intDMB(Al)q25), 50th (oDMB(Al)q50, intDMB(Al)q50), and 75th (oDMB(Al)q75, intDMB(Al)q75) percentiles; and interquartile range (oDMB(Al)iqr, intDMB(Al)iqr). For each specimen, we also calculated the variance of pixel mineral content for osteons and interstitial tissue (oDMB(Al)var and intDMB(Al)var). We used nonparametric tests to compare frequency histogram parameters between hip-fractured women and controls and Fisher's test to compare variances between groups. All frequency histogram parameters for osteons and interstitial tissue except the 25th percentile, and the variances of pixel mineral content in osteons and interstitial tissue, were significantly different between hip-fractured women and controls, indicating greater heterogeneity of mineralization in the hip-fracture patients than in the controls. These cross-sectional data suggest that bone fragility may be related to greater DMB heterogeneity in osteons and interstitial tissue.

Respective roles of organic and mineral components of human cortical bone matrix in micromechanical behavior: an instrumented indentation study

Bone is a multiscale composite material made of both a type I collagen matrix and a poorly crystalline apatite mineral phase. Due to remodeling activity, cortical bone is made of Bone Structural Units (BSUs) called osteons. Since osteon represents a fundamental level of structural hierarchy, it is important to investigate the relationship between mechanical behavior and tissue composition at this scale for a better understanding of the mechanisms of bone fragility. The aim of this study is to analyze the links between ultrastructural properties and the mechanical behavior of bone tissue at the scale of osteon. Iliac bone biopsies were taken from untreated postmenopausal osteoporotic women, embedded, sectioned and microradiographed to assess the degree of mineralization of bone (DMB). On each section, BSUs of known DMB were indented with relatively high load (~500 mN) to determine local elastic modulus (E), contact hardness (H(c)) and true hardness (H) of several bone lamellae. Crystallinity and collagen maturity were measured by Fourier Transform InfraRed Microspectroscopy (FTIRM) on the same BSUs. Inter-relationships between mechanical properties and ultrastructural components were analyzed using multiple regression analysis. This study showed that elastic deformation was only explained by DMB whereas plastic deformation was more correlated with collagen maturity. Contact hardness, reflecting both elastic and plastic behaviors, was correlated with both DMB and collagen maturity. No relationship was found between crystallinity and mechanical properties at the osteon level.

Fragility fractures in men with idiopathic osteoporosis are associated with undermineralization of the bone matrix without evidence of increased bone turnover

The pathogenesis of primary osteoporosis in younger individuals is still elusive. An important determinant of the biomechanical competence of bone is its material quality. In this retrospective study we evaluated bone material quality based on quantitative backscattered electron imaging to assess bone mineralization density distribution (BMDD) in bone biopsies of 25 male patients (aged 18-61 years) who sustained fragility fractures but were otherwise healthy. BMDD of cancellous bone was compared with previously established adult reference data. Complementary information was obtained by bone histomorphometry. The histomorphometric results showed a paucity of osteoblasts and osteoclasts on the bone surface in the majority of patients. BMDD revealed a significant shift to lower mineralization densities for cancellous bone values: CaMean (weighted mean Ca content, -5.9%), CaPeak (mode of the BMDD, -5.6%), and CaHigh (portion of fully mineralized bone, -76.8%) were decreased compared to normative reference; CaWidth (heterogeneity in mineralization, +18.5%) and CaLow (portion of low mineralized bone, +68.8; all P < 0.001) were significantly increased. The shift toward lower mineral content in the bone matrix in combination with reduced indices of bone formation and bone resorption suggests an inherent mineralization defect leading to undermineralized bone matrix, which might contribute to the susceptibility to fragility fractures of the patients. The alteration in bone material might be related to osteoblastic dysfunction and seems fundamentally different from that in high bone turnover osteoporosis with a negative bone balance.

Severe osteoporosis with multiple vertebral fractures after gender reassignment therapy - is it male or female osteoporosis?

OBJECTIVE

We report about a 49-years-old patient with severe osteoporosis and multiple vertebral fractures after male-to-female reassignment therapy. The patient had 12 years of hormone replacement therapy (HRT) with very low serum levels of estradiol and testosterone at the time the fractures occurred. The reasons are currently not known. Most likely the patient seems to be non-compliant with the HRT intake.

RESULTS

Bone mineral density (BMD) measurements showed highly decreased T-Scores between -3.5 and -4.5. All routine laboratory parameters, especially the markers of bone turnover, were within the normal range. μ-CT 3D-structural analysis of the bone biopsy showed a highly reduced trabecular connectivity (Conn.Dens.). Bone mineral density distribution (BMDD), measured by quantitative backscattered electron imaging (qBEI), showed a BMDD within normal range, except heterogeneity index (Ca(WIDTH)) and fraction of highly mineralised bone (Ca(HIGH)), which were increased.

CONCLUSIONS

We conclude that our patient has a cross-sex hormonal therapy induced total imbalance of bone homeostasis, because of the long lasting under monitored hormone therapy which led to severe interferences in physiological maturities. Male-to-female transsexuals without an adequate estrogen treatment are at increased risk of developing osteoporosis.

Variability of tissue mineral density can determine physiological creep of human vertebral cancellous bone

Creep is a time-dependent viscoelastic deformation observed under a constant prolonged load. It has been indicated that progressive vertebral deformation due to creep may increase the risk of vertebral fracture in the long-term. The objective of this study was to examine the relationships of creep with trabecular architecture and tissue mineral density (TMD) parameters in human vertebral cancellous bone at a physiological static strain level. Architecture and TMD parameters of cancellous bone were analyzed using microcomputerized tomography (micro-CT) in specimens cored out of human vertebrae. Then, creep and residual strains of the specimens were measured after a two-hour physiological compressive constant static loading and unloading cycle. Creep developed (3877 ± 2158 με) resulting in substantial levels of non-recoverable post-creep residual strain (1797 ± 1391 με). A strong positive linear correlation was found between creep and residual strain (r = 0.94, p < 0.001). The current results showed that smaller thickness, larger surface area, greater connectivity of trabeculae, less mean tissue mineral density (TMD, represented by gray levels) and higher variability of TMD are associated with increasing logarithmic creep rate. The TMD variability (GL(COV)) was the strongest correlate of creep rate (r = 0.79, p < 0.001). This result suggests that TMD variability may be a useful parameter for estimating the long-term deformation of a whole vertebral body. The results further suggest that the changes in TMD variability resulting from bone remodeling are of importance and may provide an insight into the understanding of the mechanisms underlying progressive failure of vertebral bodies and development of a clinical fracture.

COL1 C-propeptide cleavage site mutations cause high bone mass osteogenesis imperfecta

Osteogenesis imperfecta (OI) is most often caused by mutations in the type I procollagen genes (COL1A1/COL1A2). We identified two children with substitutions in the type I procollagen C-propeptide cleavage site, which disrupt a unique processing step in collagen maturation and define a novel phenotype within OI. The patients have mild OI caused by mutations in COL1A1 (Patient 1: p.Asp1219Asn) or COL1A2 (Patient 2: p.Ala1119Thr), respectively. Patient 1 L1-L4 DXA Z-score was +3.9 and pQCT vBMD was+3.1; Patient 2 had L1-L4 DXA Z-score of 0.0 and pQCT vBMD of -1.8. Patient BMD contrasts with radiographic osteopenia and histomorphometry without osteosclerosis. Mutant procollagen processing is impaired in pericellular and in vitro assays. Patient dermal collagen fibrils have irregular borders. Incorporation of pC-collagen into matrix leads to increased bone mineralization. FTIR imaging confirms elevated mineral/matrix ratios in both patients, along with increased collagen maturation in trabecular bone, compared to normal or OI controls. Bone mineralization density distribution revealed a marked shift toward increased mineralization density for both patients. Patient 1 has areas of higher and lower bone mineralization than controls; Patient 2's bone matrix has a mineral content exceeding even classical OI bone. These patients define a new phenotype of high BMD OI and demonstrate that procollagen C-propeptide cleavage is crucial to normal bone mineralization.

Trabecular bone remodelling simulated by a stochastic exchange of discrete bone packets from the surface

Human bone is constantly renewed through life via the process of bone remodelling, in which individual packets of bone are removed by osteoclasts and replaced by osteoblasts. Remodelling is mechanically controlled, where osteocytes embedded within the bone matrix are thought to act as mechanical sensors. In this computational work, a stochastic model for bone remodelling is used in which the renewal of bone material occurs by exchange of discrete bone packets. We tested different hypotheses of how the mechanical stimulus for bone remodelling is integrated by osteocytes and sent to actor cells on the bone's surface. A collective (summed) signal from multiple osteocytes as opposed to an individual (maximal) signal from a single osteocyte was found to lead to lower inner porosity and surface roughness of the simulated bone structure. This observation can be interpreted in that collective osteocyte signalling provides an effective surface tension to the remodelling process. Furthermore, the material heterogeneity due to remodelling was studied on a network of trabeculae. As the model is discrete, the age of individual bone packets can be monitored with time. The simulation results were compared with experimental data coming from quantitative back scattered electron imaging by transforming the information about the age of the bone packet into a mineral content. Discrepancies with experiments indicate that osteoclasts preferentially resorb low mineralized, i.e. young, bone at the bone's surface.

Spatial-temporal mapping of bone structural and elastic properties in a sheep model following osteotomy

The course of bone healing in animal models is conventionally monitored by morphologic approaches, which do not allow the determination of the material properties of the tissues involved. Mechanical characterization techniques are either dedicated to the macroscopic evaluation of the entire organ or to the microscopic evaluation of the tissue matrix. The latter provides insight to regionally specific alterations at the tissue level in the course of healing. In this study, quantitative scanning acoustic microscopy was used at 50 MHz to investigate microstructural and elastic alterations of mineralized callus and cortical tissue after transverse osteotomy in sheep tibiae. Analyses were performed after 2, 3, 6 and 9 weeks of consolidation with stabilization by either a rigid or a semi-rigid external fixator. Increased stiffness and decreased porosity were observed in the callus tissue over the course of the healing process, which was dependent on the fixator type. In the adjacent cortical tissue, stiffness decreased during the first 3 weeks. Cortical porosity increased over time but the time-dependence was different between the two fixator types. The changes of stiffness of cortical and callus tissues were measured with respect to the distance to the periosteal cortex-callus boundary. Stiffness of cortex and callus tissue smoothly decreased as a function of the distance from the inner cortical region. The data obtained in this study can help to understand the processes involved in tissue maturation during endogenous bone healing.

Decrease in the osteocyte lacunar density accompanied by hypermineralized lacunar occlusion reveals failure and delay of remodeling in aged human bone

Aging decreases the human femur's fatigue resistance, impact energy absorption, and the ability to withstand load. Changes in the osteocyte distribution and in their elemental composition might be involved in age-related bone impairment. To address this question, we carried out a histomorphometric assessment of the osteocyte lacunar distribution in the periosteal and endosteal human femoral cortexes of 16 female and 16 male donors with regard to age- and sex-related bone remodeling. Measurements of the bone mineral density distribution by quantitative backscattered electron imaging and energy dispersive X-ray analysis were taken to evaluate the osteocyte lacunar mineral composition and characteristics. Age-dependent decreases in the total osteocyte lacunar number were measured in all of the cases. This change signifies a risk for the bone's safety. Cortical subdivision into periosteal and endosteal regions of interest emphasized that, in both sexes, primarily the endosteal cortex is affected by age-dependent reduction in number of osteocyte lacunae, whereas the periosteal compartment showed a less pronounced osteocyte lacunar deficiency. In aged bone, osteocyte lacunae showed an increased amount of hypermineralized calcium phosphate occlusions in comparison with younger cases. With respect to Frost's early delineation of micropetrosis, our microanalyses revealed that the osteocyte lacunae are subject to hypermineralization. Intralacunar hypermineralization accompanied by a decrease in total osteocyte lacunar density may contribute to failure or delayed bone repair in aging bone. A decreased osteocyte lacunar density may cause deteriorations in the canalicular fluid flow and reduce the detection of microdamage, which counteracts the bone's structural integrity, while hypermineralized osteocyte lacunae may increase bone brittleness and render the bone fragile.

Microstructure and nanomechanical properties in osteons relate to tissue and animal age

Material property changes in bone tissue with ageing are a crucial missing component in our ability to understand and predict age-related fracture. Cortical bone osteons contain a natural gradient in tissue age, providing an ideal location to examine these effects. This study utilized osteons from baboons aged 0-32 years (n=12 females), representing the baboon lifespan, to examine effects of tissue and animal age on mechanical properties and composition of the material. Tissue mechanical properties (indentation modulus and hardness), composition (mineral-to-matrix ratio, carbonate substitution, and crystallinity), and aligned collagen content (aligned collagen peak height ratio) were sampled along three radial lines in three osteons per sample by nanoindentation, Raman spectroscopy, and second harmonic generation microscopy, respectively. Indentation modulus, hardness, mineral-to-matrix ratio, carbonate substitution, and aligned collagen peak height ratio followed biphasic relationships with animal age, increasing sharply during rapid growth before leveling off at sexual maturity. Mineral-to-matrix ratio and carbonate substitution increased 12% and 6.7%, respectively, per year across young animals during growth, corresponding with a nearly 7% increase in stiffness and hardness. Carbonate substitution and aligned collagen peak height ratio both increased with tissue age, increasing 6-12% across the osteon radii. Indentation modulus most strongly correlated with mineral-to-matrix ratio, which explained 78% of the variation in indentation modulus. Overall, the measured compositional and mechanical parameters were the lowest in tissue of the youngest animals. These results demonstrate that composition and mechanical function are closely related and influenced by tissue and animal age.

Atypical subtrochanteric and diaphyseal femoral fractures: report of a task force of the American Society for Bone and Mineral Research

Reports linking long-term use of bisphosphonates (BPs) with atypical fractures of the femur led the leadership of the American Society for Bone and Mineral Research (ASBMR) to appoint a task force to address key questions related to this problem. A multidisciplinary expert group reviewed pertinent published reports concerning atypical femur fractures, as well as preclinical studies that could provide insight into their pathogenesis. A case definition was developed so that subsequent studies report on the same condition. The task force defined major and minor features of complete and incomplete atypical femoral fractures and recommends that all major features, including their location in the subtrochanteric region and femoral shaft, transverse or short oblique orientation, minimal or no associated trauma, a medial spike when the fracture is complete, and absence of comminution, be present to designate a femoral fracture as atypical. Minor features include their association with cortical thickening, a periosteal reaction of the lateral cortex, prodromal pain, bilaterality, delayed healing, comorbid conditions, and concomitant drug exposures, including BPs, other antiresorptive agents, glucocorticoids, and proton pump inhibitors. Preclinical data evaluating the effects of BPs on collagen cross-linking and maturation, accumulation of microdamage and advanced glycation end products, mineralization, remodeling, vascularity, and angiogenesis lend biologic plausibility to a potential association with long-term BP use. Based on published and unpublished data and the widespread use of BPs, the incidence of atypical femoral fractures associated with BP therapy for osteoporosis appears to be very low, particularly compared with the number of vertebral, hip, and other fractures that are prevented by BPs. Moreover, a causal association between BPs and atypical fractures has not been established. However, recent observations suggest that the risk rises with increasing duration of exposure, and there is concern that lack of awareness and underreporting may mask the true incidence of the problem. Given the relative rarity of atypical femoral fractures, the task force recommends that specific diagnostic and procedural codes be created and that an international registry be established to facilitate studies of the clinical and genetic risk factors and optimal surgical and medical management of these fractures. Physicians and patients should be made aware of the possibility of atypical femoral fractures and of the potential for bilaterality through a change in labeling of BPs. Research directions should include development of animal models, increased surveillance, and additional epidemiologic and clinical data to establish the true incidence of and risk factors for this condition and to inform orthopedic and medical management.

Effects of 1 year of daily teriparatide treatment on iliacal bone mineralization density distribution (BMDD) in postmenopausal osteoporotic women previously treated with alendronate or risedronate

Anabolic treatment with teriparatide of postmenopausal osteoporotic patients previously treated with bisphosphonates is a new therapeutic approach. However, its effects on the bone mineralization density distribution (BMDD) are unknown. We studied paired transiliac bone biopsy samples taken before and after 1 year of treatment with recombinant human parathyroid hormone peptide 1-34 (teriparatide) from 16 osteoporotic women treated with either alendronate (priorALN) or risedronate (priorRIS) for at least 2 years and subsequently treated for 12 months with teriparatide. Cancellous (Cn.) and cortical (Ct.) BMDD values were measured using quantitative backscattered electron imaging. At baseline, BMDD values of priorALN and priorRIS women were similar and within the normal range. One year of teriparatide treatment caused significant effects on the BMDD. Analyzing changes from baseline for each bisphosphonate group separately, priorALN patients revealed increases in the portion of low mineralized bone areas (Cn.Ca(Low) +25.9%, Ct.Ca(Low) +62.0%, both p < .05) and Ct. heterogeneity of mineralization (Ct.Ca(Width) +22.8%, p < .001). PriorRIS patients showed increased mineralization heterogeneity (Cn.Ca(Width) +14.8%, p < .05, and Ct.Ca(Width) +15.8%, p < .001). Analysis of the influence of the prior bisphosphonate treatment showed that the BMDD response to 1 year of teriparatide treatment did not depend on the type of prior bisphosphonate. In consequence, priorALN and priorRIS groups were combined. The pooled groups revealed increased Cn.Ca(Width) and Ct.Ca(Width) (+10.7%, p < .01, and +19.6%, p < .001, respectively) as well as increased Cn.Ca(Low) and Ct.Ca(Low) (+18.2%, p < .05, and +36.6%, p < .01, respectively). In summary, our findings indicate a significant effect of teriparatide on BMDD when administered subsequent to a bisphosphonate in agreement with teriparatide's anabolic action.

Effect of risedronate on osteocyte viability and bone turnover in paired iliac bone biopsies from early postmenopausal women

It is unclear whether standard clinical doses of risedronate affect osteocyte viability. This study examined osteocyte viability and bone remodeling rate in early postmenopausal women (1-5 years after menopause) who were treated with a standard clinical dose of risedronate (5 mg/day, orally) for 1 year. Paired transiliac bone biopsies were obtained from 19 postmenopausal women at baseline and after 1-year treatment with placebo (n = 8, mean age 52.9 ± 3.4 years) or risedronate 5 mg/day (n = 11, mean age 52.5 ± 3.4 years). In these samples, we measured osteocyte- and bone remodeling-related variables in trabecular bone. In both the placebo and risedronate groups, empty lacunae were significantly decreased after 1-year treatment compared to baseline. There were no significant differences in osteocyte-related variables between placebo and risedronate. Risedronate significantly reduced bone-remodeling indices including mineralizing surface (MS/BS), bone formation rate (BFR/BS), and activation frequency (Ac.f). Risedronate treatment caused significantly lower MS/BS and Ac.f than placebo administration. In conclusion, risedronate 5 mg/day effectively inhibited bone remodeling but did not significantly reduce osteocyte viability in trabecular bone.

Scanning small-angle X-ray scattering analysis of the size and organization of the mineral nanoparticles in fluorotic bone using a stack of cards model

A model describing the size and arrangement of mineral particles in bone tissues is used to analyse the results of a scanning small-angle X-ray scattering (SAXS) experiment on a pathological bone biopsy. The overall description assumes that the nanometre-sized mineral platelets are arranged in a parallel fashion with possible fluctuations in their relative position, orientation and thickness. This method is tested on a thin sample section obtained from the biopsy of an osteoporotic patient treated with a high cumulative dose of NaF. The mineralization pattern of fluorotic bone is known to exhibit significant differences as compared to healthy bone in terms of density, particle size and organization. This is the first attempt to provide quantitative indicators of the degree of regularity in the packing of the mineral platelets in human pathological bone. Using scanning SAXS with a synchrotron microbeam of 15 µm allows discrimination between pathological and healthy bone at the tissue level. Additionally, the benefits of this method are discussed with respect to the accuracy of particle size determination using SAXS.

Current and emerging treatments for the management of osteogenesis imperfecta

Osteogenesis imperfecta (OI) is the most common bone genetic disorder and it is characterized by bone brittleness and various degrees of growth disorder. Clinical severity varies widely; nowadays eight types are distinguished and two new forms have been recently described although not yet classified. The approach to such a variable and heterogeneous disease should be global and therefore multidisciplinary. For simplicity, the objectives of treatment can be reduced to three typical situations: the lethal perinatal form (type II), in which the problem is survival at birth; the severe and moderate forms (types III-IX), in which the objective is 'autonomy'; and the mild form (type I), in which the aim is to reach 'normal life'. Three types of treatment are available: non-surgical management (physical therapy, rehabilitation, bracing and splinting), surgical management (intramedullary rod positioning, spinal and basilar impression surgery) and medical-pharmacological management (drugs to increase the strength of bone and decrease the number of fractures as bisphosphonates or growth hormone, depending on the type of OI). Suggestions and guidelines for a therapeutic approach are indicated and updated with the most recent findings in OI diagnosis and treatment.

Altered bone matrix mineralization in a patient with Rett syndrome

Rett syndrome (RTT) is a common X-linked neurodevelopmental disorder caused by mutations in the coding region of methyl-CpG-binding 2 (MECP2) gene. Patients with RTT have a low bone mineral density and increased risk of fracture. However, very little is known if bone matrix mineralization is altered in RTT. A 17-year-old girl with a classical form of RTT with a heterozygous nonsense mutation in exon 3 in the MECP2-gene was treated in our hospital. Her femoral neck BMD is 43.3% below the 3rd percentile when compared to age and sex-matched controls. She underwent surgery for correction of her scoliosis, which provided a unique opportunity to obtain bone tissue to study bone matrix mineralization (Bone Mineralization Density Distribution-BMDD) using quantitative backscattered electron imaging (qBEI) and histomorphometry. BMDD outcomes were compared to recently published normative reference data for young individuals. qBEI analysis showed a significant shift to lower matrix mineralization despite histomorphometric indices indicate a low bone turnover. There was a reduction in CaMean (-7.92%) and CaPeak (-3.97%), which describe the degree of mineralization. Furthermore the fraction of low mineralized matrix (CaLow: +261.84%) was dramatically increased, which was accompanied with an increase in the heterogeneity of mineralization (CaWidth: +86.34%). Our findings show a significantly altered bone matrix mineralization of a typical patient with RTT. This may partly explain the low bone density seen in these patients. These results also warrant further studies on the molecular role of MECP2 in bone matrix mineralization.

The role of mineral content in determining the micromechanical properties of discrete trabecular bone remodeling packets

In trabecular bone, each remodeling event results in the resorption and/or formation of discrete structural units called 'packets'. These remodeling packets represent a fundamental level of bone's structural hierarchy at which to investigate composition and mechanical behaviors. The objective of this study was to apply the complementary techniques of quantitative backscattered electron microscopy (qBSEM) and nanoindentation to investigate inter-relationships between packet mineralization, elastic modulus, contact hardness and plastic deformation resistance. Indentation arrays were performed across nine trabecular spicules from 3 human donors; these spicules were then imaged using qBSEM, and discretized into their composite remodeling packets (127 in total). Packets were classified spatially as peripheral or central, and mean contact hardness, plastic deformation resistance, elastic modulus and calcium content calculated for each. Inter-relationships between measured parameters were analysed using linear regression analyses, and dependence on location assessed using Student's t-tests. Significant positive correlations were found between all mechanical parameters and calcium content. Elastic modulus and contact hardness were significantly correlated, however elastic modulus and plastic deformation resistance were not. Calcium content, contact hardness and elastic modulus were all significantly higher for central packets than for peripheral, confirming that packet mineral content contributes to micromechanical heterogeneity within individual trabecular spicules. Plastic deformation resistance, however, showed no such regional dependence, indicating that the plastic deformation properties in particular, are determined not only by mineral content, but also by the organic matrix and interactions between these two components.