Age-related hypermineralization in the female proximal human femur

Bone mineral density modeling via random field: Normality, stationarity, sex and age dependence

BACKGROUND AND OBJECTIVE

Capturing the population variability of bone properties is of paramount importance to biomedical engineering. The aim of the present paper is to describe variability and correlations in bone mineral density with a spatial random field inferred from routine computed tomography data.

METHODS

Random fields were simulated by transforming pairwise uncorrelated Gaussian random variables into correlated variables through the spectral decomposition of an age-detrended correlation matrix. The validity of the random field model was demonstrated in the spatiotemporal analysis of bone mineral density. The similarity between the computed tomography samples and those generated via random fields was analyzed with the energy distance metric.

RESULTS

The random field of bone mineral density was found to be approximately Gaussian/slightly left-skewed/strongly right-skewed at various locations. However, average bone density could be simulated well with the proposed Gaussian random field for which the energy distance, i.e., a measure that quantifies discrepancies between two distribution functions, is convergent with respect to the number of correlation eigenpairs.

CONCLUSIONS

The proposed random field model allows the enhancement of computational biomechanical models with variability in bone mineral density, which could increase the usability of the model and provides a step forward in in-silico medicine.

Effects of Osteoporosis on Bone Morphometry and Material Properties of Individual Human Trabeculae in the Femoral Head

Osteoporosis is the most common bone disease and is conventionally classified as a decrease of total bone mass. Current diagnosis of osteoporosis is based on clinical risk factors and dual energy X‐ray absorptiometry (DEXA) scans, but changes in bone quantity (bone mass) and quality (trabecular structure, material properties, and tissue composition) are not distinguished. Yet, osteoporosis is known to cause a deterioration of the trabecular network, which might be related to changes at the tissue scale—the material properties. The goal of the current study was to use a previously established test method to perform a thorough characterization of the material properties of individual human trabeculae from femoral heads in cyclic tensile tests in a close to physiologic, wet environment. A previously developed rheological model was used to extract elastic, viscous, and plastic aspects of material behavior. Bone morphometry and tissue mineralization were determined with a density calibrated micro‐computed tomography (μCT) set‐up. Osteoporotic trabeculae neither showed a significantly changed material or mechanical behavior nor changes in tissue mineralization, compared with age‐matched healthy controls. However, donors with osteopenia indicated significantly reduced apparent yield strain and elastic work with respect to osteoporosis, suggesting possible initial differences at disease onset. Bone morphometry indicated a lower bone volume to total volume for osteoporotic donors, caused by a smaller trabecular number and a larger trabecular separation. A correlation of age with tissue properties and bone morphometry revealed a similar behavior as in osteoporotic bone. In the range studied, age does affect morphometry but not material properties, except for moderately increased tissue strength in healthy donors and moderately increased hardening exponent in osteoporotic donors. Taken together, the distinct changes of trabecular bone quality in the femoral head caused by osteoporosis and aging could not be linked to suspected relevant changes in material properties or tissue mineralization. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Intra-skeletal vascular density in a bipedal hopping macropod with implications for analyses of rib histology

Human ribs are thought to be less affected by mechanical strain at the microscopic level than limb bones, implying that rib remodelling better reflects bone physiological homeostasis. Here, we test the hypothesis that rib tissue will be well vascularized and thus enhance susceptibility to metabolic influence. An intra-skeletal comparison of bone vascular canal density was conducted using a macropod animal model adapted to bipedal habitual hopping. The right humerus, ulna, radius, femur, tibia, fibula, a mid-thoracic and upper-thoracic rib of an eastern grey kangaroo (Macropus giganteus) were sectioned at the midshaft, from which histological sections were prepared. Bone vascularity from a maximum of 12 mm² of sub-periosteal parallel-fibred and lamellar bone was recorded, resulting in a total of 2047 counted vessels. Vascular canal density data were corrected by cortical width, maximum length, and midshaft circumference robusticity indices computed for each bone. The fibula consistently had the highest vascular canal density, even when corrected for maximum length, cortical width and midshaft circumference robusticities. This was followed by the mid- and upper-thoracic ribs. Vascularity differences between bones were relatively consistent whether vascular canal density was controlled for by cortical width or midshaft circumference robusticities. Vascular canal density and robusticity indices were also positively and negatively correlated (p < 0.05). Results confirm that the ribs are well vascularized, which facilitates bone metabolic processes such as remodelling, but the fibula also appears to be a well vascularized bone. Future research investigating human bone metabolism will benefit from examining thoracic rib or fibula samples.

Globular structure of the hypermineralized tissue in human femoral neck

Bone becomes more fragile with ageing. Among many structural changes, a thin layer of highly mineralized and brittle tissue covers part of the external surface of the thin femoral neck cortex in older people and has been proposed to increase hip fragility. However, there have been very limited reports on this hypermineralized tissue in the femoral neck, especially on its ultrastructure. Such information is critical to understanding both the mineralization process and its contributions to hip fracture. Here, we use multiple advanced techniques to characterize the ultrastructure of the hypermineralized tissue in the neck across various length scales. Synchrotron radiation micro-CT found larger but less densely distributed cellular lacunae in hypermineralized tissue than in lamellar bone. When examined under FIB-SEM, the hypermineralized tissue was mainly composed of mineral globules with sizes varying from submicron to a few microns. Nano-sized channels were present within the mineral globules and oriented with the surrounding organic matrix. Transmission electron microscopy showed the apatite inside globules were poorly crystalline, while those at the boundaries between the globules had well-defined lattice structure with crystallinity similar to the apatite mineral in lamellar bone. No preferred mineral orientation was observed both inside each globule and at the boundaries. Collectively, we conclude based on these new observations that the hypermineralized tissue is non-lamellar and has less organized mineral, which may contribute to the high brittleness of the tissue.

Extracellular matrix composition during bone regeneration in the human dental alveolar socket

Within the dental alveolar socket, the sequence of events following tooth extraction involves deposition of a provisional connective tissue matrix that is later replaced by woven bone and eventually by lamellar bone. Bone regeneration within the dental alveolar socket is unique since the space occupied by the root(s) of a tooth does not originally contain any bone. However, extracellular matrix composition of the healing alveolar socket has not previously been investigated. Here, alveolar bone biopsies representing early (7-46 months, < 4y) and late (48-60 months; 4-5y) healing periods were investigated using Raman spectroscopy, X-ray micro-computed tomography and backscattered electron scanning electron microscopy. Partially or completely edentulous individuals and those with a smoking habit were not excluded. Between < 4y and 4-5y, mineral crystallinity and bone mineral density increase, phenylalanine, proline/hydroxyproline, and bone surface-to-volume ratio decrease, while the carbonate-to-phosphate ratio, the mineral-to-matrix ratio, and the collagen crosslink ratio remain relatively unchanged. Observed exclusively at 4-5y, hypermineralised osteocyte lacunae contain spherical and rhomboidal mineral nodules. Spearman correlation analysis reveals several significant, high (ρ = 0.7-0.9; p ≤ 0.01) and moderate (ρ = 0.5-0.7; p ≤ 0.01) correlations. Mineral crystallinity and proline/hydroxyproline, the carbonate-to-phosphate ratio and phenylalanine, mineral crystallinity and bone surface-to-volume ratio, the carbonate-to-phosphate ratio and bone surface-to-volume ratio, proline/hydroxyproline and bone mineral density, and bone mineral density and bone surface-to-volume ratio are negatively correlated. Mineral crystallinity and bone mineral density, and proline/hydroxyproline and bone surface-to-volume ratio are positively correlated. Although bone regeneration in the dental alveolar socket follows typical bone healing patterns, the compositional and microstructural patterns reveal mature bone at <4y with indications of better mechanical competence at 4-5y.

Hypermineralization in the femoral neck of the elderly

Hip fragility depends on the decline in bone mass as well as changes in bone microstructure and the properties of bone mineral and organic matrix. Although it is well-established that low bone mass or osteoporosis is a key factor in hip fracture risk, it is striking to observe that 92% of 24 patients who have sustained an intracapsular hip fracture showed hypermineralization at the superior-anterior quadrant, a critical region associated with increased hip fracture risk. In-depth material studies on a total of 12 human cadaver femurs revealed increased degree of mineralization in the hypermineralized tissue: calcium weight percentage as measured by quantitative backscattered electron imaging increased by approximately 15% compared with lamellar bone; mineral-to-matrix ratio obtained by Raman microspectroscopy imaging also increased. Immunohistochemistry revealed localized type II collagen in the hypermineralized region, implying its cartilaginous nature. At the ultrastructural level, X-ray scattering revealed significantly smaller (on average 2.3 nm thick and 15.6 nm long) and less ordered bone minerals in the hypermineralized tissue. Finally, the hypermineralized tissue was more brittle than lamellar bone under hydrated state - cracks propagated easily in the hypermineralized region but stopped at the lamellar boundary. This study demonstrates that hypermineralization of femoral neck cortical bone is a source of bone fragility which is worth considering in future fracture risk assessment when the origin of hip fracture is unclear based on current evaluation standards. STATEMENT OF SIGNIFICANCE: Hypermineralization of femoral cortical bone in older adults might occur in many more hip fracture cases than presently known. Yet, this tissue remains largely unknown to the orthopedic community possibly due to coarse resolution of clinical imaging. The current study showed the hypermineralized tissue had reduced fracture resistance which could be attributed to the material changes in mineral content, organic matrix, and mineral platelets properties. It thus could be a source for fracture initiation. Consequently, we believe hypermineralization of femoral neck cortical bone should be considered in hip fragility assessment, especially when low bone mass cannot be identified as a primary contributor to hip fracture.

Brief communication: Test of a method to identify double-zonal osteon in polarized light microscopy

OBJECTIVES

Double-zonal osteons (DZ) have been of interest in paleopathological research because they might be linked to physiological pathology. DZ are thought to be evidence of arrested osteon formation with a brief but abrupt increase in mineralization of lamellae occurring during bone remodeling. Originally identified from microradiographs as hypermineralized rings, recent studies have identified DZ from linear polarized light microscopy (PLM). However, PLM does not guarantee the adequate detection of DZ since PLM captures bone birefringence and not hyper-mineralization. Scanning electron microscopy with backscatter electrons (BSE-SEM) allows observation of DZ by detecting differences in mineralization. The purpose of this study is to investigate whether DZ, as identified by BSE-SEM, can indeed be identified with PLM.

MATERIALS AND METHODS

The sample consists of an archaeological collection of adult midshaft femurs (n = 30) from St. Matthew cemetery, Quebec City (1771-1860). DZ were identified and counted independently with PLM and BSE-SEM for the same sections. Results from both methods were compared.

RESULTS

Chi-square test shows that there was no significant difference between the two methods (p = 0.404). No significant bias was found on Bland-Altman analysis and Cohen's kappa shows a substantial agreement between the two methods (Κ = 0.66). PLM shows a good accuracy (sensitivity 79%, specificity 99.4%) and reliability (Positive Predictive Value: 86.71%; Negative Predictive Value: 99.45%).

DISCUSSION

These findings indicate that the two methods are interchangeable. PLM, using our proposed protocol, is reliable to accurately identify DZ. We discuss how PLM and BSE-SEM that measure different features of the bone tissue can converge on the identification of DZ.

Sealed osteons in animals and humans: low prevalence and lack of relationship with age

Sealed osteons are unusual variants of secondary osteons that have received little attention, especially in non-human bones. Sealed osteons are characterized by central canals that are plugged with bone tissue. As with other variants of secondary osteons (e.g. drifting, dumbbell, multi-canal), understanding how and why sealed osteons form can shed light on the mechanisms that regulate normal bone remodeling and how this process can be perturbed with aging and some diseases. In a recent microscopic evaluation of human tibiae obtained after traumatic amputations, 4-5% of the osteons were sealed. It is suggested that this high prevalence reflects occasional localized microscopic ischemia from normal osteonal remodeling; hence sealed osteons are implicated in human skeletal fragility. Therefore, osteon prevalence would be expected to correlate with the bone remodeling seen with aging; for example, showing positive relationships between sealed osteons and the population density of typical secondary osteons (OPD). We evaluated the prevalence of partially sealed (80-99% sealed) and fully sealed osteons with respect to age and variations in OPD in 10 adult human femora (34-71 years) and in various non-human appendicular bones of mature animals that were not of advanced age, including deer calcanei, equine radii and equine third metacarpals. An additional sample of 10 bilateral human femora with unilateral non-cemented total hip replacements (F,+HR) and non-implanted contralateral femora (F,-HR) were evaluated (10 patients; 52-94 years). In non-human bones, sealed + partially sealed osteons were rare (~0.1%) even when having relatively high OPD. When considering sealed + partially sealed osteons in femora from patients without any HR, results showed that 1.6% of the osteons were sealed or partially sealed, which was much lower than anticipated, but this is 10- to 20-fold more than in any of the non-human bones. Additionally, in all bones, sealed + partially sealed osteons were significantly smaller than typical secondary osteons (mean diameters: 125 vs. 272 μm; P < 0.005). In the patients with HR, the percentage of sealed + partially sealed osteons: (i) did not correlate with age, (ii) showed no significant difference between F,-HR and F,+HR (1.9 vs. 2.1%; P = 0.2), and (iii) was positively correlated with OPD (r = 0.67, P = 0.001), which differs from the very weak or lack of correlations in the non-human bones and the other human femur sample. The lack of an age-related relationship, in addition to the very low prevalence of sealed + partially sealed osteons are inconsistent with the idea that they contribute to reduced bone quality seen in aging humans. The small size of sealed and partially sealed osteons, regardless of species affiliation, suggests that they represent closing cones at the termini of some osteons. Available evidence suggests that osteons of primates might have a greater capacity for branching that is associated with closing cones, which might explain the 10-20 times higher prevalence of sealed + partially sealed osteons in the human bones examined in this study.

Clinical hip fracture is accompanied by compression induced failure in the superior cortex of the femoral neck

Hip fractures pose a major health problem throughout the world due to their devastating impact. Current theories for why these injuries are so prevalent in the elderly point to an increased propensity to fall and decreases in bone mass with ageing. However, the fracture mechanisms, particularly the stress and strain conditions leading to bone failure at the hip remain unclear. Here, we directly examined the cortical bone from clinical intra-capsular hip fractures at a microscopic level, and found strong evidence of compression induced failure in the superior cortex. A total of 143 sections obtained from 24 femoral neck samples that were retrieved from 24 fracturing patients at surgery were examined using laser scanning confocal microscopy (LSCM) after fluorescein staining. The stained microcracks showed significantly higher density in the superior cortex than in the inferior cortex, indicating a greater magnitude of strain in the superior femoral neck during the failure-associated deformation and fracture process. The predominant stress state for each section was reconstructed based on the unique correlation between the microcrack pattern and the stress state. Specifically, we found clear evidence of longitudinal compression and buckling as the primary failure mechanisms in the superior cortex. These findings demonstrate the importance of microcrack analysis in studying clinical hip fractures, and point to the central role of the superior cortex failure as an important aspect of the failure initiation in clinical intra-capsular hip fractures.

Morphological and Microstructural Alterations of the Articular Cartilage and Bones during Treadmill Exercises with Different Additional Weight-Bearing Levels

The aim of this study was to investigate the morphological and microstructural alterations of the articular cartilage and bones during treadmill exercises with different exercise intensities. Sixty 5-week-old female rats were randomly divided into 10 groups: five additional weight-bearing groups (WBx) and five additional weight-bearing with treadmill exercise groups (EBx), which were subjected to additional weight bearing of x% (x = 0, 5, 12, 19, and 26) of the corresponding body weight of each rat for 15 min/day. After 8 weeks of experiment, the rats were humanely sacrificed and their bilateral intact knee joints were harvested. Morphological analysis of the cartilages and microcomputed tomography evaluation of bones were subsequently performed. Results showed that increased additional weight bearing may lead to cartilage damage. No significant difference was observed among the subchondral cortical thicknesses of the groups. The microstructure of subchondral trabecular bone of 12% and 19% additional weight-bearing groups was significantly improved; however, the WB26 and EB26 groups showed low bone mineral density and bone volume fraction as well as high structure model index. In conclusion, effects of treadmill exercise on joints may be associated with different additional weight-bearing levels, and exercise intensities during joint growth and maturation should be selected reasonably.

Cortical Bone Mineralization in the Human Femoral Neck in Cases and Controls from Synchrotron Radiation Study

To compare the degree and distribution of mineralization in femoral neck cortex from 23 women with hip fractures (age 65-96 years) and 17 female controls (age 72-103 years), we obtained 3D data by synchrotron radiation microtomography (SRμCT). Variables were degree of mineralization of bone (DMB) in total cortex (cDMBSRMEAN), osteons (oDMBSRMEAN), and pure interstitial tissue (intDMBSRMEAN). The cortex on SRμCT images was divided into nine to twelve 50-μm zones from the periosteum to the endosteum; cDMBSRMEAN, oDMBSRMEAN, and intDMBSRMEAN were measured in each zone. We used descriptive statistics and t tests, general linear model analyses to compare DMBSR values across zones and individuals, one-way analysis of variance for within-group comparisons of zones. In patients, the variance of mineral content value was not different than in controls, but mean values of degree of mineralization varied across zones. These cross-sectional data suggest that bone fragility may be related to a greater heterogeneity of the distribution of mineralization in femoral neck cortex.

From restoration to regeneration: periodontal aging and opportunities for therapeutic intervention

With the march of time our bodies start to wear out: eyesight fades, skin loses its elasticity, teeth and bones become more brittle and injuries heal more slowly. These universal features of aging can be traced back to our stem cells. Aging has a profound effect on stem cells: DNA mutations naturally accumulate over time and our bodies have evolved highly specialized mechanisms to remove these damaged cells. Whilst obviously beneficial, this repair mechanism also reduces the pool of available stem cells and this, in turn, has a dramatic effect on tissue homeostasis and on our rate of healing. Simply put: fewer stem cells means a decline in tissue function and slower healing. Despite this seemingly intractable situation, research over the past decade now demonstrates that some of the effects of aging are reversible. Nobel prize-winning research demonstrates that old cells can become young again, and lessons learned from these experiments-in-a-dish are now being translated into human therapies. Scientists and clinicians around the world are identifying and characterizing methods to activate stem cells to reinvigorate the body's natural regenerative process. If this research in dental regenerative medicine pans out, the end result will be tissue homeostasis and healing back to the levels we appreciated when we were young.

Ancient Human Bone Microstructure in Medieval England: Comparisons between Two Socio-Economic Groups

Understanding the links between bone microstructure and human lifestyle is critical for clinical and anthropological research into skeletal growth and adaptation. The present study is the first to report correspondence between socio-economic status and variation in bone microstructure in ancient humans. Products of femoral cortical remodeling were assessed using histological methods in a large human medieval sample (N = 450) which represented two distinct socio-economic groups. Osteonal parameters were recorded in posterior midshaft femoral sections from adult males (N = 233) and females (N = 217). Using univariate and multivariate statistics, intact, fragmentary, and osteon population densities, Haversian canal area and diameter, and osteon area were compared between the two groups, accounting for sex, age, and estimated femoral robusticity. The size of osteons and their Haversian canals, as well as osteon density, varied significantly between the socio-economic groups, although minor inconsistencies were observed in females. Variation in microstructure was consistent with historical textual evidence that describes differences in mechanical loading and nutrition between the two groups. Results demonstrate that aspects of ancient human lifestyle can be inferred from bone microstructure.

Trends in trabecular architecture and bone mineral density distribution in 152 individuals aged 30-90 years

The strength of trabecular bone depends on its microarchitecture and its tissue level properties. However, the interrelation between these two determinants of bone quality and their relation to age remain to be clarified. Iliac crest bone cores (n=152) from individuals aged 30-90 years were analyzed by quantitative backscattered electron imaging. Univariate and multivariate analyses were conducted to determine whether epidemiological parameters (age, sex or BMI), structural histomorphometrical variables (BV/TV, Tb.Th, Tb.N and Tb.Sp) and osteoid-related indices (OV/BV, OS/BS or O.Th) predict the degree of bone mineralization. While sex and BMI were not associated with bone mineralization, age was positively correlated with the most frequently occurring calcium concentrations (Ca peak), the percentage of highly mineralized bone areas (Ca high) and, in the case of adjusted covariates, also the mean calcium content (Ca mean). Bone volume fraction and trabecular thickness were both negatively correlated with Ca mean. However, trabecular thickness was additionally associated with Ca peak, Ca high as well as the amount of low mineralized bone (Ca low) and was the only structural parameter predicting bone mineralization independent of age. Furthermore, our analyses demonstrated that osteoid variables - within a normal range (<2% OV/BV) - were significantly associated with all mineralization parameters and represent the only predictor for the mineralization heterogeneity (Ca width). Taken together, we showed that elevated trabecular bone mineralization correlates with aging and bone loss. However, these associations are attributable to trabecular thinning that comes along with high bone mineralization due to the loss of low mineralized bone surfaces. Therefore, we demonstrated that the degree of areally resolved bone mineral is primarily associated with the amount of physiological osteoid present and the thickness of mineralized bone in trabeculae.

Multi-frequency axial transmission bone ultrasonometer

The last decade has seen a surge in the development of axial transmission QUS (Quantitative UltraSound) technologies for the assessment of long bones using various modes of acoustic waves. The condition of cortical bones and the development of osteoporosis are determined by numerous mechanical, micro-structural, and geometrical or macro-structural bone properties like hardness, porosity and cortical thickness. Such complex manifestations of osteoporosis require the evaluation of multiple parameters with different sensitivities to the various properties of bone that are affected by the disease. This objective may be achieved by using a multi-frequency ultrasonic examination The ratio of the acoustic wavelength to the cortical thickness can be changed by varying the frequency of the ultrasonic pulse propagating through the long bone that results in the change in composition of the induced wave comprised of a set of numerous modes of guided, longitudinal, and surface acoustic waves. The multi-frequency axial transmission QUS method developed at Artann Laboratories (Trenton, NJ) is implemented in the Bone Ultrasonic Scanner (BUSS). In the current version of the BUSS, a train of ultrasonic pulses with 60, 100, 400, 800, and 1200 kHz frequencies is used. The developed technology was tested on a variety of bone phantoms simulating normal, osteopenic, and osteoporotic bones. The results of this study confirm the feasibility of the multi-frequency approach for the assessment of the processes leading to osteoporosis.

The fragile elderly hip: mechanisms associated with age-related loss of strength and toughness

Every hip fracture begins with a microscopic crack, which enlarges explosively over microseconds. Most hip fractures in the elderly occur on falling from standing height, usually sideways or backwards. The typically moderate level of trauma very rarely causes fracture in younger people. Here, this paradox is traced to the decline of multiple protective mechanisms at many length scales from nanometres to that of the whole femur. With normal ageing, the femoral neck asymmetrically and progressively loses bone tissue precisely where the cortex is already thinnest and is also compressed in a sideways fall. At the microscopic scale of the basic remodelling unit (BMU) that renews bone tissue, increased numbers of actively remodelling BMUs associated with the reduced mechanical loading in a typically inactive old age augments the numbers of mechanical flaws in the structure potentially capable of initiating cracking. Menopause and over-deep osteoclastic resorption are associated with incomplete BMU refilling leading to excessive porosity, cortical thinning and disconnection of trabeculae. In the femoral cortex, replacement of damaged bone or bone containing dead osteocytes is inefficient, impeding the homeostatic mechanisms that match strength to habitual mechanical usage. In consequence the participation of healthy osteocytes in crack-impeding mechanisms is impaired. Observational studies demonstrate that protective crack deflection in the elderly is reduced. At the most microscopic levels attention now centres on the role of tissue ageing, which may alter the relationship between mineral and matrix that optimises the inhibition of crack progression and on the role of osteocyte ageing and death that impedes tissue maintenance and repair. This review examines recent developments in the understanding of why the elderly hip becomes fragile. This growing understanding is suggesting novel testable approaches for reducing risk of hip fracture that might translate into control of the growing worldwide impact of hip fractures on our ageing populations.

Effects of ageing, prolonged estrogen deficiency and zoledronate on bone tissue mineral distribution

The quantity and distribution of bone tissue mineral are key determinants of bone strength. Recent research revealed altered mineral distribution within sheep femora following estrogen deficiency. Rapid increases in bone remodeling occur at the onset of estrogen deficiency and abate over time. Therefore, altered tissue mineralization might be a transient characteristic of osteoporosis. Bisphosphonates reduce fracture incidence by 40-60% but increases in bone mineral density are insufficient to explain such changes. In this study the hypotheses that bone tissue mineralization is altered over prolonged estrogen depletion and bisphosphonate treatment were tested. Quantitative backscattered imaging (qBEI) was used to quantify bone mineral density distribution (BMDD) parameters (mean, FWHM) in trabeculae from the proximal femora of an ovariectomized sheep model that underwent estrogen deficiency for 31 months, an ovariectomized group administered with Zoledronic acid and age-matched controls. To assess the effects of normal ageing and prolonged estrogen deficiency, data were compared to BMDD data from sheep that were estrogen deficient for 12 months and age-matched controls. This study reports that normal ageing increases mean mineralization and mineral heterogeneity at a trabecular level. In contrast, prolonged estrogen deficiency leads to significantly decreased mean mineralization and further exacerbates increases in mineral heterogeneity. Interestingly, ZOL treatment of OVX sheep significantly reduced tissue mineral variability, both at a trabecular level and between femoral regions. Together, these findings indicate that ZOL treatment acts to reverse the increased mineral heterogeneity occurring during estrogen deficiency, which may contribute to its capacity to reduce osteoporotic fractures.

Bone mineralization is elevated and less heterogeneous in adults with type 2 diabetes and osteoarthritis compared to controls with osteoarthritis alone

PURPOSE

The purpose of this study was to determine whether trabecular bone mineralization differed in adults with type 2 diabetes compared to adults without type 2 diabetes.

METHODS

Proximal femur specimens were obtained following a total hip replacement procedure from men and women ≥65 years of age with and without type 2 diabetes. A scanning electron microscope was used for quantitative backscattered electron imaging (qBEI) analysis of trabecular bone samples from the femoral neck. Gray scale images (pixel size=5.6 μm(2)) were uploaded to ImageJ software and gray level (GL) values were converted to calcium concentrations (weight [wt] % calcium [Ca]) using data obtained with energy dispersive X-ray spectrometry. The following bone mineralization density distribution (BMDD) outcomes were collected: the weighted mean bone calcium concentration (CaMEAN), the most frequently occurring bone calcium concentration (CaPEAK) and mineralization heterogeneity (CaWIDTH). Differences between groups were assessed using the Student's t-test for normally distributed data and Mann-Whitney U-test for non-normally distributed data. An alpha value of <0.05 was considered significant.

RESULTS

Thirty-five Caucasian participants were recruited (mean [standard deviation, SD] age, 75.5 [6.5]years): 14 adults with type 2 diabetes (years since type 2 diabetes diagnosis, 13.5 [7.4]years) and 21 adults without type 2 diabetes. In the adults with type 2 diabetes, bone CaMEAN was 4.9% greater (20.36 [0.98]wt.% Ca versus 19.40 [1.07]wt.% Ca, p=0.015) and CaWIDTH was 9.4% lower (median [interquartile range] 3.55 [2.99-4.12]wt.% Ca versus 3.95 [0.71]wt.% Ca, p<0.001) compared to controls. There was no between-group difference in CaPEAK (21.12 [0.97]wt.% Ca for type 2 diabetes versus 20.44 [1.30]wt.% Ca for controls, p=0.121).

CONCLUSION

The combination of elevated mean calcium concentration in bone and lower mineralization heterogeneity in adults with type 2 diabetes may have deleterious effects on the biomechanical properties of bone. These microscopic alterations in bone mineralization, which may be mediated by suppressed bone remodeling, further elucidate higher fracture risk in adults with type 2 diabetes.

Anatomical distribution of the degree of mineralization of bone tissue in human femoral neck: impact on biomechanical properties

Osteoporotic hip fractures represent a major public health problem associated with high human and economic costs. The anatomical variation of the tissue mineral density (TMD) and of the elastic constants in femoral neck cortical bone specimens is an important determinant of bone fragility. The purpose of this study was to show that a Synchrotron radiation microcomputed tomography system coupled with a multiscale biomechanical model allows the determination of the 3-D anatomical dependence of TMD and of the elastic constants (i.e. the mechanical properties of an anisotropic material) in human femoral neck. Bone specimens from the inferior femoral neck were obtained from 18 patients undergoing standard hemiarthroplasty. The specimens were imaged using 3-D synchrotron micro-computed tomography with a voxel size of 10.13 μm, leading to the determination of the anatomical distributions of porosity and TMD. The elastic properties of bone tissue were computed using a multiscale model. The model uses the experimental data obtained at the scale of several micrometers to estimate the components of the elastic tensor of bone at the scale of the organ. Statistical analysis (ANOVA) revealed a significant effect of the radial position on porosity and TMD and a significant effect of axial position on TMD only. Porosity was found to increase in the radial direction moving from the periosteum inwards (p<10(-5)). At any given distance from the periosteum, porosity does not vary noticeably along the bone axis. TMD was found to be significantly higher (p<10(-5)) in the periosteal region than in other bone locations and decreases from the periosteal to the endosteal region with an average slope of 10.05 g.cm(-3).m(-1), the decrease being faster in the porous part of the samples (average slope equal of 30.04 g.cm(-3).m(-1)) than in dense cortical bone. TMD was found to decrease from the distal to the proximal part of the femur neck (average slope of 6.5 g.cm(-3).m(-1)). Considering TMD variations in the radial direction induces weak changes of bone properties compared to constant TMD. TMD variations in the axial direction are responsible for a significant variation of elastic constants. These results demonstrate that the anatomical variations of TMD affect the bone elastic properties, which could be explained by the complex stress field in bone affecting bone remodeling. TMD spatial variations should be taken into account to properly describe the spatial heterogeneity of elastic coefficients of bone tissue at the organ scale.

Comparative examination of human proximal tibiae in vitro by ultrasonic guided waves and pQCT

The velocity of ultrasonic guided waves in long bones is dependent upon two determinants of bone strength: the cortical thickness and the material properties. In this study, six human proximal tibiae in vitro were examined to test the efficacy of an ultrasonic method based on guided waves. Peripheral quantitative computed tomography (pQCT) was used as the comparative reference modality. The guided wave velocity (c(F)) was derived from two-dimensional (2-D) spatial-temporal waveform profiles formed by multiple ultrasonic signals acquired along the bones at 100 kHz frequency and passed wavelet processing. The ultrasonic profiles from the examined bones were ranged according to pQCT measurements of cortical thickness (CTh), and cortical bone mineral density (CBMD). Strong correlations between c(F) and CTh (r(S) = 0.83, p < 0.0001) and CBMD (r(S) = 0.88, p < 0.0001) resulted. The study confirmed a potential for guided waves to assess atrophic changes of the proximal tibia.

Bone targeting for the treatment of osteoporosis

Osteoporosis represents a major public health burden especially considering the aging populations worldwide. Drug targeting will be important to better meet these challenges and direct the full therapeutic potential of therapeutics to their intended site of action. This review has been organized in modules, such that scientists working in the field can easily gain specific insight in the field of bone targeting for the drug class they are interested in. We review currently approved and emerging treatment options for osteoporosis and discuss these in light of the benefit these would gain from advanced targeting. In addition, established targeting strategies are reviewed and novel opportunities as well as promising areas are presented along with pharmaceutical strategies how to render novel composites consisting of a drug and a targeting moiety responsive to bone-specific or disease-specific environmental stimuli. Successful implementation of these principles into drug development programs for osteoporosis will substantially contribute to the clinical success of anti-catabolic and anabolic drugs of the future.

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.

Trabecular packet-level lamellar density patterns differ by fracture status and bone formation rate in white females

Spatial patterns of mineralization for human iliac crest cancellous bone were measured from images obtained by quantitative backscattered electron microscopy. Biopsies collected from vertebral fracture patients and healthy individuals with high or low bone formation rate (BFR(s)) were examined (fracture/low BFR(s): N=12, fracture/high BFR(s): N=10, normal/low BFR(s): N=12, normal/high BFR(s): N=15). 20 by 20 pixel square areas or smaller were sampled from superficial and deep remodeling packets. Mean (Z(mean)) and standard deviation (SD) of mineralization were measured, and coefficients of variation (CV=SD/Z(mean)) were calculated. Fast Fourier transform analysis was used to quantify the distribution of the mineral in the packets. "FFT_ratio" was defined as the ratio magnitude of the principal spatial frequency to the average atomic number density. A higher FFT_ratio occurred in specimens with more pronounced alternating layers of light and dark as visible in the backscattered electron image, which was defined as lamellar patterning. Two-way ANOVA revealed that the coefficients of variation of mineralization for both superficial and deep packets were significantly lower in fracture patients than in normal individuals. However, the interaction between turnover rate and group (fracture/non-fracture) indicated that the difference in packet CV occurred among the low turnover individuals and not among those with high turnover. Mean mineralization levels and CV between deep and superficial packets were highly correlated. Regressions of packet CV of mineralization and FFT_ratio were highly significant (p<0.001) for all packets pooled and for packets divided by group (fracture/normal). However, analyses of packet CV and FFT_ratio by individual were variable (R(2) from 0.00338 to 0.700). Packet-level mineralization variability may be associated with fracture toughness, and fracture patients had less variable packet-level mineralization. The result that the packet CV varied significantly between fracture and non-fracture individuals with low turnover suggests that for low turnover subjects without fracture, high variability in mineralization may have a protective effect. In high turnover patients, the accelerated turnover may prevent the lamellar variability from developing over time. Strong correlations between CV and Z(mean) for both superficial and deep packets imply that newly formed bone is created similarly to older bone within an individual. Fourier transform results show that the mineralization variability found within packets is associated with lamellar patterning. Lamellar structure has been hypothesized to guide microcrack propagation in order to optimize bone strength and toughness. Osteoporotics with fracture had less pronounced lamellation than healthy normals and may be more prone to fracture.

The degree and distribution of cortical bone mineralization in the human femoral shaft change with age and sex in a microradiographic study

BACKGROUND

The incidence of osteoporotic hip fractures increases with age, more sharply in women than in men, as a result of qualitative and quantitative bone alterations. Mineralization (a qualitative parameter) showed no differences with age or sex in cancellous bone in earlier studies. Few studies assessed such differences in cortical bone, a major contributor to femoral bone strength. The aim of this in vitro cross-sectional study of a large group of human femoral midshafts was to look for age- and sex-related differences in the degree and distribution of cortical mineralization that might be implicated in bone fragility.

METHODS

Cortical bone specimens from 193 femurs were studied using quantitative microradiography, with an aluminum step-wedge reference. The femurs were from 99 females and 94 males in a Caucasian anthropological collection covering a broad age spectrum. We determined the mean degree of mineralization of osteons (On.DMB-Al), interstitial tissue (Int.DMB-Al), and total bone (Tt.DMB-Al), and representative parameters of density histograms. Results were expressed as relative values. Age- and sex-related differences in DMB-Al values were evaluated using non-parametric tests.

RESULTS

Degree of tissue mineralization (Tt.DMB-Al) decreased significantly with age in females (r=-0.257; P=0.010) but did not change in males. Tt.DMB-Al was higher in females than males until 50 years of age (P=0.001) but was lower in elderly females than elderly males (P=0.016). DMB-Al distribution varied significantly with sex and age. The first DMB-Al quartiles in osteons and interstitial tissue were not different between males and females, but the third quartile and interquartile range differed significantly (P=0.032 and P=0.000, respectively). The mineralization difference between the two tissues indicated greater bone heterogeneity in females than males (P=0.000).

CONCLUSIONS

In this in vitro cross-sectional study of anterior midfemoral cortical specimens, the degree and distribution of mineralization varied with age and sex. In females, mineralization started at a higher level than in males but was lower in the sixth decade, falling below the level in males. Mineralization was far more stable throughout life in males. In elderly females, the lower degree and greater heterogeneity of mineralization may have consequences on bone strength and the risk of fracture.

Probabilistic failure analysis of bone using a finite element model of mineral-collagen composites

Microdamage accumulation is a major pathway for energy dissipation during the post-yield deformation of bone. In this study, a two-dimensional probabilistic finite element model of a mineral-collagen composite was developed to investigate the influence of the tissue and ultrastructural properties of bone on the evolution of microdamage from an initial defect in tension. The probabilistic failure analyses indicated that the microdamage progression would be along the plane of the initial defect when the debonding at mineral-collagen interfaces was either absent or limited in the vicinity of the defect. In this case, the formation of a linear microcrack would be facilitated. However, the microdamage progression would be scattered away from the initial defect plane if interfacial debonding takes place at a large scale. This would suggest the possible formation of diffuse damage. In addition to interfacial debonding, the sensitivity analyses indicated that the microdamage progression was also dependent on the other material and ultrastructural properties of bone. The intensity of stress concentration accompanied with microdamage progression was more sensitive to the elastic modulus of the mineral phase and the nonlinearity of the collagen phase, whereas the scattering of failure location was largely dependent on the mineral to collagen ratio and the nonlinearity of the collagen phase. The findings of this study may help understanding the post-yield behavior of bone at the ultrastructural level and shed light on the underlying mechanism of bone fractures.

Are Distributions of Secondary Osteon Variants Useful for Interpreting Load History in Mammalian Bones?

BACKGROUND/AIMS

In cortical bone, basic multicellular units (BMUs) produce secondary osteons that mediate adaptations, including variations in their population densities and cross-sectional areas. Additional important BMU-related adaptations might include atypical secondary osteon morphologies (zoned, connected, drifting, elongated, multiple canal). These variants often reflect osteonal branching that enhances toughness by increasing interfacial (cement line) complexity. If these characteristics correlate with strain mode/magnitude-related parameters of habitual loading, then BMUs might produce adaptive differences in unexpected ways.

METHODS

We carried out examinations in bones loaded in habitual torsion (horse metacarpals) or bending: sheep, deer, elk, and horse calcanei, and horse radii. Atypical osteons were quantified in backscattered images from anterior, posterior, medial, and lateral cortices. Correlations were determined between atypical osteon densities, densities of all secondary osteons, and associations with habitual strain mode/magnitude or transcortical location.

RESULTS

Osteon variants were not consistently associated with 'tension', 'compression', or neutral axis ('shear') regions, even when considering densities or all secondary osteons, or only osteon variants associated with relatively increased interfacial complexity. Similarly, marrow- and strain-magnitude-related associations were not consistent.

CONCLUSION

These data do not support the hypothesis that spatial variations in these osteon variants are useful for inferring a habitual bending or torsional load strain history.

Young-elderly differences in bone density, geometry and strength indices depend on proximal femur sub-region: a cross sectional study in Caucasian-American women

Fragility fractures at the trochanter (TR) and the femoral neck (FN) have distinct etiologies, but the underlying age-related structural changes at these proximal femoral sub-regions are poorly understood. 28 young (41+/-3 years) and 124 elderly (74+/-3 years) healthy Caucasian women underwent volumetric quantitative computed tomography at the hip. Integral (i), cortical (c) and trabecular (t) bone mineral density and content (BMD, BMC) were measured. Geometric parameters included cross sectional area (CSA), and volumes of the integral, cortical and trabecular regions (VOL). Structural measures included indices of compressive (Compstr) and bending (BSI) strength. After adjusting for height and weight, an F-test was used to compare the TR and the FN mean values between young and elderly and to test for interaction to compare logarithmic difference of young and elderly (log(Young)-log(Elderly), Y/Ed) between the FN and the TR in an ANOCOVA model. All BMC, iBMD and tBMD values were significantly lower in elderly than in young women, with the largest Y/Ed in the FN tBMC and tBMD (P<0.0011 and P<0.0001). cBMD in young and elderly groups was not significantly different at the TR while at the FN it was greater (P=0.0075) in elderly than young women, showing significant Y/Ed (P=0.0003) dependence on skeletal site. Elderly women had significantly larger iVOL and CSA values (0.0001<P<0.0051), except for the FN iVOL. cVOL values were smaller in elderly than young women (P<0.0001). Y/Ed in bone geometry differed by sub-region only for cVOL measures (P=0.0267). Despite larger CSA and iVOL measures in elderly, the younger women had greater Compstr (P<0.0001) and BSI (P=0.0051). Thus, although both the TR and the FN appear to increase in size with age, this enlargement is insufficient to protect against loss of bone strength.

The Pathomechanics of Plantar Fasciitis

Plantar fasciitis is a musculoskeletal disorder primarily affecting the fascial enthesis. Although poorly understood, the development of plantar fasciitis is thought to have a mechanical origin. In particular, pes planus foot types and lower-limb biomechanics that result in a lowered medial longitudinal arch are thought to create excessive tensile strain within the fascia, producing microscopic tears and chronic inflammation. However, contrary to clinical doctrine, histological evidence does not support this concept, with inflammation rarely observed in chronic plantar fasciitis. Similarly, scientific support for the role of arch mechanics in the development of plantar fasciitis is equivocal, despite an abundance of anecdotal evidence indicating a causal link between arch function and heel pain. This may, in part, reflect the difficulty in measuring arch mechanics in vivo. However, it may also indicate that tensile failure is not a predominant feature in the pathomechanics of plantar fasciitis. Alternative mechanisms including 'stress-shielding', vascular and metabolic disturbances, the formation of free radicals, hyperthermia and genetic factors have also been linked to degenerative change in connective tissues. Further research is needed to ascertain the importance of such factors in the development of plantar fasciitis.

Use of multiple acoustic wave modes for assessment of long bones: model study

Multiple acoustic wave mode method has been proposed as a new modality in axial bone QUS. The new method is based on measurement of ultrasound velocity at different ratio of wavelength to the bone thickness, and taking into account both bulk and guided waves. It allows assessment of changes in both the material properties related to porosity and mineralization as well as the cortical thickness influenced by resorption from inner layers, which are equally important in diagnostics of osteoporosis and other bone osteopenia. Developed method was validated in model studies using a dual-frequency (100 and 500 kHz) ultrasound device. Three types of bone phantoms for long bones were developed and tested: (1) tubular specimens from polymer materials to model combined changes of material stiffness and cortical wall thickness; (2) layered specimens to model porosity in compact bone progressing from endosteum towards periosteum; (3) animal bone specimens with both cortical and trabecular components. Observed changes of the ultrasound velocity of guided waves at 100 kHz followed gradual changes in the thickness of the intact cortical layer. On the other hand, the bulk velocity at 500 kHz remained nearly constant at the different cortical layer thickness but was affected by the material stiffness. Similar trends were observed in phantoms and in fragments of animal bones.

Variation of long-lived free radicals responsible for the EPR native signal in bone of aged or diseased human females and ovariectomized adult rats

The purpose of this study was to gain insights into the variations seen in the electron paramagnetic resonance (EPR) spectroscopy of the native signals of teeth and bones used for retrospective dosimetry measurements. We determined that changes occur in the long-lived free radicals responsible for the native signal of cortical bone in aging or diseased human females and aged ovariectomized rats. This was done by measuring the magnitude of the broad (BC) and narrow (NC) components of the native EPR signal of bone following chemical extraction, aging, crushing and thermal annealing. Bone from the upper midshaft of femora of young (17-34 years old, n=5) and elderly (70-92 years old, n=18) females was examined. The results showed that the elderly women had significantly higher BC than the younger women (P<0.01). A similar interpretation was made of the data from an aging female rat osteoporosis model. The results for the NC signals were similar. Finally, dramatic decreases in both NC and BC signals were seen in HIV positive and uncontrolled diabetic (one each) patients indicating the need for studying this signal for a broad spectrum of metabolic disorders. Experiments were performed which strongly indicate that iron liganded with organic molecules is the source of the BC signal. Finally, the accuracy achieved in this study indicates that resolving the dosimetric signal (g=2.0018) should be improved by subtraction of the deconvoluted NC and BC signals from the original spectrum.

Microcracks colocalize within highly mineralized regions of cortical bone tissue

While much work has been performed to quantify the extent of bone damage, its effects on the mechanical integrity of the tissue and its biological impact, the set of factors which gives forth to microdamage are nebulous, particularly the compositional properties local to microdamage. In this context, the current study tested the hypothesis that microcracks initiate within more mineralized regions of bone. Cortical bone specimens were taken from human male donors aged 31, 38, 53, 64, 71, and 84 years at the mid femoral diaphysis in a plane parallel to the osteonal orientation. The mineralization was assessed in a spatially resolved manner using Raman microspectroscopy. Arrays of measurements were taken over the entire area (i.e. global scans) of each sample followed by measurements in the vicinity of microcracks (i.e. local scans). Histograms of mineralization were constructed for global and local scans to determine whether the mineralization of damaged loci differed from the mean overall mineralization. Statistical analysis of this data revealed that the mean mineralization of damaged loci was significantly greater (P < 0.05) than the overall mineralization for each donor, indicating that there exists a highly-mineralized 'brittle volume' in bone. The presence of this damage prone 'brittle volume' has future implications for the assessment of fracture susceptibility.

Human femoral neck has less cellular periosteum, and more mineralized periosteum, than femoral diaphyseal bone

Periosteal expansion enhances bone strength and is controlled by osteogenic cells of the periosteum. The extent of cellular periosteum at the human femoral neck, a clinically relevant site, is unclear. This study was designed to histologically evaluate the human femoral neck periosteal surface. Femoral neck samples from 11 male and female cadavers (ages 34-88) were histologically assessed and four periosteal surface classifications (cellular periosteum, mineralizing periosteum, cartilage, and mineralizing cartilage) were quantified. Femoral mid-diaphysis samples from the same cadavers were used as within-specimen controls. The femoral neck surface had significantly less (P<0.05) cellular periosteum (18.4+/-9.7%) compared to the femoral diaphysis (59.2+/-13.8%). A significant amount of the femoral neck surface was covered by mineralizing periosteal tissue (20-70%). These data may provide an alternate explanation for the apparent femoral neck periosteal expansion with age and suggest the efficiency of interventions that stimulate periosteal expansion may be reduced, albeit still possible, at the femoral neck of humans.

Cortical bone in the human femoral neck: three-dimensional appearance and porosity using synchrotron radiation

A high-resolution CT system using synchrotron radiation allowed visualization of the 3D cortical bone microarchitecture and measurement of intracortical porosity of femoral neck cortical bone specimens from 19 female cadavers imaged at 10.13-microm resolution. 3D reconstruction of specimens showed osteonal system arrangement. Mean porosity was 15.88%. This technique will provide insights into the mechanisms involved in osteoporotic hip fractures.

INTRODUCTION

The purpose of this study was to show that a high-resolution CT system using synchrotron radiation (SR) allows visualization of the 3D cortical bone microarchitecture of the human femoral neck and quantification of intracortical porosity.

MATERIALS AND METHODS

Bone specimens from the inferior femoral neck were obtained from 19 female cadavers with no hip fracture (mean, 86.9 +/- 8.3 years). The specimens, consisting of embedded approximately 7 x 7 x 12-mm cortical bone parallelepipeds, were imaged using SR at 10.13-microm resolution. Commercial software was used to visualize both the 660 x 660 x 660-voxel volumes and the 2D axial slices through each volume. Qualitative examination of 2D axial slices focused on the appearance of the vessel canal system, presence of small bright zones (fully mineralized tissue) in the osseous matrix, and presence of cracks. A method was developed to automatically measure 3D intracortical porosity after separating pure bone from pores and cortical bone from trabecular bone.

RESULTS AND CONCLUSIONS

3D reconstruction of the specimens showed the entire structure and arrangement of the osteonal systems, parallel to the axis of the femoral neck. Bright zones were seen in the outer cortex. No cracks were observed. Porosity values varied widely from 4.96% to 38.87% (mean, 15.88 +/- 9.87%). This study establishes that SR microtomography can be used to display the 3D bone microstructure of the human femoral neck cortex and to quantify intracortical porosity. This technique will provide insights into the mechanisms involved in cortical bone loss and osteoporotic hip fractures.

Remodeling capacity of calcified fibrocartilage of the hip

It is well known that the incidence of hip fractures increases exponentially with age and that hip fractures can be a major cause of morbidity and morality among elderly humans; this has prompted substantial research on hip fractures. The majority of research on hip fractures has focused on morphological changes of the proximal femur with age. Recently calcified fibrocartilage in the proximal femur has been shown to increase in fractional area with age and can ultimately make up to 60% of the fractional area of the cortex. However, the capacity of the tissue to remodel and heal is currently unknown. The purpose of the present study was to determine the remodeling capacity of calcified fibrocartilage on the proximal femur compared to the underlying cortical bone. The remodeling capacity of calcified fibrocartilage and cortical bone was assessed in adult female sheep by means of tetracycline labeling. The number of double and single labels within each tissue type was quantified and analyzed with a paired t-test. The data showed very few labels in the calcified fibrocartilage compared to the cortical bone. This indicated that calcified fibrocartilage lacked a capacity to remodel in a manner similar to bone. The results of this investigation demonstrate that while the underlying cortical bone was actively remodeling, the calcified fibrocartilage appeared to have no remodeling capacity similar to that of cortical bone.

Microvascularization of the hypermineralized calcified fibrocartilage and cortical bone in the sheep proximal femur

It is well known that the incidence of hip fractures is increasing as the population ages, and that vascularity is one of the most important characteristics for any tissue (the proximal femur being no exception). Additionally, calcified fibrocartilage from tendon and ligament insertions comprises a significant portion of the fractional area of the proximal femur's cortical shell. The goal of the present investigation was to quantify and compare the microvascularity of the cortical bone and calcified fibrocartilage of the proximal femur in a sheep model. There were no regional differences in the vascular density of the cortical bone. However, the calcified fibrocartilage from tendon and capsular insertions were determined to be avascular, and regions of the proximal femur with insertions lacked a vascularized periosteum. If a vessel was present in the calcified fibrocartilage, it was located within an isolated region of bone tissue or osteoid. Since blood vessels appear to be a significant contributor to the health and remodeling of mineralized tissue, it is hypothesized that the large areas of avascular calcified fibrocartilage present on the elderly femoral neck may predispose these regions to damage accumulation. Therefore future research should examine the role of the vascularity to the proximal femur in the mechanisms of numerous pathological conditions, such as avascular necrosis, osteopenia, and hip fractures.

The skeletal attachment of tendons--tendon "entheses"

Tendon entheses can be classed as fibrous or fibrocartilaginous according to the tissue present at the skeletal attachment site. The former can be "bony" or "periosteal", depending on whether the tendon is directly attached to bone or indirectly to it via the periosteum. At fibrocartilaginous entheses, the uncalcified fibrocartilage dissipates collagen fibre bending and tendon narrowing away from the tidemark; calcified fibrocartilage anchors the tendon to the bone and creates a diffusion barrier between the two. Where there are additional fibrocartilaginous specialisations in the tendon and/or bone next to the enthesis, an "enthesis organ" is created that reduces wear and tear. Little attention has been paid to bone at entheses, despite the obvious bearing this has on the mechanical properties of the interface and the clinical importance of avulsion fractures. Disorders at entheses (enthesopathies) are common and occur in conditions such as diffuse idiopathic skeletal hyperostosis and the seronegative spondyloarthropathies. They are also commonly seen as sporting injuries such as tennis elbow and jumper's knee.

Experimental confirmation of the sheep model for studying the role of calcified fibrocartilage in hip fractures and tendon attachments

Research has shown that there is a dramatic increase in the fractional area of calcified fibrocartilage from tendon and capsular insertions on the human femoral neck (Vajda and Bloebaum, 1999; Shea et al., 2001b). Additional information regarding the properties of the proximal femur's cortical shell, gained from the use of an animal model, may result in a better understanding of elderly hip fracture since the cortical shell is a significant contributor to the strength of the proximal femur. The objective of the present study was to determine if the greater trochanter's tendon insertions of the human, rat, and sheep differ in terms of morphology and mineralization. The tendons of the greater trochanter of the human, rat, and sheep were observed to insert via a fibrocartilage insertion. The mineral content of the human and sheep calcified fibrocartilage was significantly higher than that of the rat calcified fibrocartilage (P < 0.01). Additionally, the mineral content of the rat cortical bone was significantly higher than that of the human cortical bone (P < 0.01). The mineral content of the calcified fibrocartilage and bone of the human and sheep were not statistically different from each other. There were also more similarities between the bone structure and lacunae density of the human and sheep than between the human and the rat. This suggests that the tendon insertions of the sheep are a better model than the tendon insertions of the rat for the investigation of calcified fibrocartilage in elderly hip fractures.

Three-dimensional reconstructions of the Achilles tendon insertion in man

The distribution of type II collagen in sagittal sections of the Achilles tendon has been used to reconstruct the three-dimensional (3D) shape and position of three fibrocartilages (sesamoid, periosteal and enthesis) associated with its insertion. The results showed that there is a close correspondence between the shape and position of the sesamoid and periosteal fibrocartilages--probably because of their functional interdependence. The former protects the tendon from compression during dorsiflexion of the foot, and the latter protects the superior tuberosity of the calcaneus. When the zone of calcified enthesis fibrocartilage and the subchondral bone are mapped in 3D, the reconstructions show that there is a complex pattern of interlocking between pieces of calcified fibrocartilage and bone at the insertion site. We suggest that this is of fundamental importance in anchoring the tendon to the bone, because the manner in which a tendon insertion develops makes it unlikely that many collagen fibres pass across the tissue boundary from tendon to bone. When force is transmitted to the bone from a loaded tendon, it is directed towards the plantar fascia by a series of highly orientated trabeculae that are clearly visible in 3D in thick resin sections.

The anatomical basis for disease localisation in seronegative spondyloarthropathy at entheses and related sites

The 2 major categories of idiopathic inflammatory arthritis are rheumatoid arthritis and the seronegative spondyloarthropathies. Whilst the synovium is the primary site of joint disease in the former, the primary site in the latter is less well defined. However, it has recently been proposed that enthesitis-associated changes in the spondyloarthropathies are primary and that all other joint manifestations are secondary. Nevertheless, some of the sites of disease localisation have not been adequately explained in terms of enthesitis. This article summarises current knowledge of the structure, function, blood supply, innervation, molecular composition and histopathology of the classic enthesis (i.e. the bony attachment of a tendon or ligament) and introduces the concept of 'functional' and articular 'fibrocartilaginous' entheses. The former are regions where tendons or ligaments wrap-around bony pulleys, but are not attached to them, and the latter are synovial joints that are lined by fibrocartilage rather than hyaline cartilage. We describe how these 3 types of entheses relate to other, and how all are prone to pathological changes in spondyloarthropathy. We propose that the inflammatory responses characteristic of spondyloarthropathies are triggered at these seemingly diverse sites, in genetically susceptible individuals, by a combination of anatomical factors which lead to higher levels of tissue microtrauma, and the deposition of microbes.

Distribution of intracortical porosity in human midfemoral cortex by age and gender

The purpose of this study was to describe the age-specific distribution of midfemoral intracortical porosity throughout the cortical width in males and females. Microradiography and an automated image analysis system were used to study midfemoral cortical bone specimens from 163 white people, including 77 males and 86 females, in a recent anthropological collection covering a broad age range. In each specimen, porosity (percentage of the cortical bone area occupied by pores), pore number, and pore size were measured throughout the entire cortex and in three cortical subregions of equal width labeled the periosteal, midcortical, and endosteal subregions. For each gender, relationships linking age to porosity, pore number, and mean pore size were assessed using regression analysis. In addition, age- and site-related changes in these three variables were tested for significance using two-way analysis of variance (ANOVA). Age explained 52% of the porosity variance in females and 13.5% in males. In each gender, there were significant age- and site-related differences in porosity, pore number, and pore size. In adults aged 60 years or younger, both pore size and pore number increased with increasing age, whereas in adults older than 60 years, pore size continued to increase but pore number decreased. In males, the age-related changes in pore size and pore number were proportionally similar in the three cortical subregions. In females, in contrast, the changes predominated in the endosteal subregion and resulted in significant cortical thinning.

Exploring the effects of hypermineralisation in bone tissue by using an extreme biological example

The properties of bone tissue with very high or very low mineral levels attract attention because they allow researchers to comprehend more fully the mechanics, interaction and effects of mineral on collagen through a greater range of compositions than that found in the "ordinary". The bone tissue of the rostrum of the whale Mesoplodon densirostris is the densest bone known. We examined the composition, static and fatigue strength, hardness and toughness of this tissue and compared them to those of other less mineralised analogues. The rostrum bone has remarkably little organic matter and retains very little water in its native state, but its basic mineral stoichiometry is very similar to that of other bones. We present here updated versions of the microhardness vs. modulus and microhardness vs. mineral fraction relationships, which thanks to the rostrum have been produced for a considerably wider range than in the past. We found the rostrum to be extremely brittle with a toughness ratio in two perpendicular directions (along and across its length) similar to that of tissue of other "ordinary" long bones and we discuss the possible significance of our findings.

Evidence of a hypermineralised calcified fibrocartilage on the human femoral neck and lesser trochanter

Femoral neck fractures are a major cause of morbidity and mortality in elderly humans. In addition to the age-related loss of cancellous bone, changes to the microstructure and morphology of the metaphyseal cortex may be a contributing factor in osteoporotic hip fractures. Recent investigations have identified a hypermineralised tissue on the neck of the femur and trochanteric region that increases in fractional area with advancing age in both males (Boyce & Bloebaum, 1993) and females (Vajda & Bloebaum, 1999). The aim of this study was to determine if the hypermineralised tissue previously observed on the proximal femur is calcified fibrocartilage. Regional variations in the fractional area of hypermineralised tissue, cortical bone, and porosity of the cortical bone along the neck of the femur and lesser trochanter were also quantified. Comparison of back scattered electron and light microscope images of the same area show that regions of hypermineralised tissue correlate with the regions of calcified fibrocartilage from tendon and capsular insertions. The hypermineralised tissue and calcified fibrocartilage had similar morphological features such as the interdigitations of the calcified fibrocartilage into the bone, lacunar spaces, and distinctly shaped pores adjacent to the 2 tissues. Regions of the neck that did not contain insertions were covered with periosteum. There were no regional differences (P > 0.05) on the superior and inferior femoral neck in terms of the percentage area of hypermineralised calcified fibrocartilage, cortical bone, or cortical bone porosity. The lesser trochanter exhibited regional differences in the fractional area of hypermineralised calcified fibrocartilage (P = 0.007) and cortical bone (P = 0.007) but not porosity of the cortical bone (P > 0.05). The effects of calcified fibrocartilage on femoral neck periosteal expansion, repair, and mechanics are unknown, but may play a role in osteoporotic fractures and intracapsular fracture healing.