Understanding basic multicellular unit activity in cortical bone through 3D morphological analysis: New methods to define zones of the remodeling space

The activity of basic multicellular units (BMU) in cortical bone is classically described as a sequential order of events- resorption, reversal and formation. This simplified portrayal of the remodeling process is pervasive despite the reported variability in remodeling space morphology. These variations may reflect meaningful nuances in BMU activity but methods to quantify 3D remodeling space morphology within the context of the cellular activity are currently lacking. This study developed new techniques to define zones of BMU activity based on the 3D morphology of remodeling spaces in rabbit cortical bone and integrated morphological data with the BMU longitudinal erosion rate (LER) to elucidate the spatial-temporal coordination of BMUs and estimate mineral apposition rate (MAR). The tibiae of New Zealand white rabbits (n = 5) were imaged in vivo using synchrotron radiation and two weeks later ex vivo with desktop microCT. The in vivo and ex vivo datasets were co-registered, and 27 remodeling spaces were identified at both timepoints. A radial profile representing the 3D morphology was the platform for partitioning the remodeling spaces into resorption, reversal and formation zones. Manual, automated and semi-automated partitioning approaches were compared, and the zone-segmentations were used to calculate the length, change in radius and slope of each zone. The manual approach most accurately defined the zones of idealized remodeling spaces with known dimensions (relative error = 0.9-9.2 %) while the semi-automated method reliably defined the zones in rabbit remodeling spaces (ICC = 0.85-1.00). Combining LER and the manually derived zone dimensions indicated that a BMU passes through a cross-section in approximately 18.8 days with resorption, reversal and formation taking 4.1, 2.2, and 12.5 days, respectively. MAR estimated by the 3D analysis was not significantly different than that determined with classic histomorphometry (p = 0.48). These techniques have the potential to assess dynamic parameters of bone resorption and formation, eliminate the need for fluorochrome labeling and provide a more comprehensive perspective of the remodeling process.

Daily administration of parathyroid hormone slows the progression of basic multicellular units in the cortical bone of the rabbit distal tibia

Basic Multicellular Units (BMUs) conduct bone remodeling, a critical process of tissue turnover which, if imbalanced, can lead to disease, including osteoporosis. Parathyroid hormone (PTH 1-34; Teriparatide) is an osteoanabolic treatment for osteoporosis; however, it elevates the rate of intra-cortical remodeling (activation frequency) leading, at least transiently, to increased porosity. The purpose of this study was to test the hypothesis that PTH not only increases the rate at which cortical BMUs are initiated but also increases their progression (Longitudinal Erosion Rate; LER). Two groups (n = 7 each) of six-month old female New Zealand white rabbits were both administered 30 μg/kg of PTH once daily for a period of two weeks to induce remodeling. Their distal right tibiae were then imaged in vivo by in-line phase contrast micro-CT at the Canadian Light Source synchrotron. Over the following two weeks the first group (PTH) received continued daily PTH while the second withdrawal group (PTHW) was administrated 0.9 % saline. At four weeks all animals were euthanized, their distal tibiae were imaged by conventional micro-CT ex vivo and histomorphometry was performed. Matching micro-CT datasets (in vivo and ex vivo) were co-registered in 3D and LER was measured from 612 BMUs. Counter to our hypothesis, mean LER was lower (p < 0.001) in the PTH group (30.19 ± 3.01 μm/day) versus the PTHW group (37.20 ± 2.77 μm/day). Despite the difference in LER, osteonal mineral apposition rate (On.MAR) did not differ between groups indicating the anabolic effect of PTH was sustained after withdrawal. The slowing of BMU progression by PTH warrants further investigation; slowed resorption combined with elevated bone formation rate, may play an important role in how PTH enhances coupling between resorption and formation within the BMU. Finally, the prolonged anabolic response following withdrawal may have utility in terms of optimizing clinical dosing regimens.

MRI overestimates articular cartilage thickness and volume compared to synchrotron radiation phase-contrast imaging

Accurate evaluation of morphological changes in articular cartilage are necessary for early detection of osteoarthritis (OA). 3T magnetic resonance imaging (MRI) has highly sensitive contrast resolution and is widely used clinically to detect OA. However, synchrotron radiation phase-contrast imaging computed tomography (SR-PCI) can also provide contrast to tissue interfaces that do not have sufficient absorption differences, with the added benefit of very high spatial resolution. Here, MRI was compared with SR-PCI for quantitative evaluation of human articular cartilage. Medial tibial condyles were harvested from non-OA donors and from OA patients receiving knee replacement surgery. Both imaging methods revealed that average cartilage thickness and cartilage volume were significantly reduced in the OA group, compared to the non-OA group. When comparing modalities, the superior resolution of SR-PCI enabled more precise mapping of the cartilage surface relative to MRI. As a result, MRI showed significantly higher average cartilage thickness and cartilage volume, compared to SR-PCI. These data highlight the potential for high-resolution imaging of articular cartilage using SR-PCI as a solution for early OA diagnosis. Recognizing current limitations of using a synchrotron for clinical imaging, we discuss its nascent utility for preclinical models, particularly longitudinal studies of live animal models of OA.

The various meanings and uses of bone "remodeling" in biological anthropology: A review

OBJECTIVES

In modern bone biology, the term "remodeling" generally refers to internal bone turnover that creates secondary osteons. However, it is also widely used by skeletal biologists, including biological anthropologists as a catch-all term to refer to different skeletal changes. In this review, we investigated how "remodeling" is used across topics on skeletal biology in biological anthropology to demonstrate potential problems with such pervasive use of a generalized term.

METHODS

Using PubMed and Google Scholar, we selected and reviewed 205 articles that use the term remodeling to describe skeletal processes and have anthropological implications. Nine edited volumes were also reviewed as examples of collaborative work by different experts to demonstrate the diverse and extensive use of the term remodeling.

RESULTS

Four general meanings of bone "remodeling" were identified, namely, internal turnover, functional adaptation, fracture repair, and growth remodeling. Additionally, remodeling is also used to refer to a broad array of pathological skeletal changes.

DISCUSSION

Although we initially identified four general meanings of bone remodeling, they are not mutually exclusive and often occur in combination. The term "remodeling" has become an extensively used catch-all term to refer to different processes and outcomes of skeletal changes, which inevitably lead to misunderstanding and a loss of information. Such ambiguity and confusion are potentially problematic as the field of biological anthropology becomes increasingly multidisciplinary. Therefore, we advocate for precise, context-specific definitions and explanations of bone remodeling as it continues to be used across disciplines within and beyond biological anthropology.

Printing tissue-engineered scaffolds made of polycaprolactone and nano-hydroxyapatite with mechanical properties appropriate for trabecular bone substitutes

BACKGROUND

Bone tissue engineering, based on three-dimensional (3D) printing technology, has emerged as a promising approach to treat bone defects using scaffolds. The objective of this study was to investigate the influence of porosity and internal structure on the mechanical properties of scaffolds.

METHODS

We fabricated composite scaffolds (which aimed to replicate trabecular bone) from polycaprolactone (PCL) reinforced with 30% (wt.) nano-hydroxyapatite (nHAp) by extrusion printing. Scaffolds with various porosities were designed and fabricated with and without an interlayer offset, termed as staggered and lattice structure, respectively. Mechanical compressive testing was performed to determine scaffold elastic modulus and yield strength. Linear regression was used to evaluate mechanical properties as a function of scaffold porosity.

RESULTS

Different relationships between mechanical properties and porosities were noted for the staggered and lattice structures. For elastic moduli, the two relationships intersected (porosity = 55%) such that the lattice structure exhibited higher moduli with porosity values greater than the intersection point; vice versa for the staggered structure. The lattice structure exhibited higher yield strength at all porosities. Mechanical testing results also indicated elastic moduli and yield strength properties comparable to trabecular bone (elastic moduli: 14-165 MPa; yield strength: 0.9-10 MPa).

CONCLUSIONS

Taken together, this study demonstrates that scaffolds printed from PCL/30% (wt.) nHAp with lattice and staggered structure offer promise for treating trabecular bone defects. This study identified the effect of porosity and internal structure on scaffold mechanical properties and provided suggestions for developing scaffolds with mechanical properties for substituting trabecular bone.

Investigation into relationships between design parameters and mechanical properties of 3D printed PCL/nHAp bone scaffolds

BACKGROUND

Scaffolds are of great importance in tissue engineering applications as they provide a mechanically supportive environment for cellular activity, which is particularly necessary for hard tissues such as bone. Notably, the mechanical properties of a scaffold vary with differing design parameters such as those related to scaffold height and internal structure. Thus, the present study aimed to explore the relationship between design parameters and mechanical properties of composite polycaprolactone (PCL) and nano-hydroxyapatite (nHAp) scaffolds fabricated by three-dimensional (3D) printing.

METHODS

We designed and printed scaffolds with different internal structures (lattice and staggered) and varying heights (4, 6, 8 and 10 layers), and consistent porosity (50%) for the purpose of comparison. Then, we examined the scaffold microstructure (pore size and penetration between layers) using scanning electron microscopy (SEM) and mechanical properties (elastic modulus and yield strength) using compressive testing.

RESULTS

Our results illustrated that the microstructural parameters were related to scaffold design. At higher heights, pore size increased while penetration between layers decreased; thus, mechanical properties were affected. Results of mechanical testing demonstrated that for lattice scaffolds, elastic modulus was similar for 6 vs 4, and 8 vs 4 layers but ~33% lower for 10 layers vs 4 layers. Similarly, yield strength was comparable for 6 vs 4, and 8 vs 4 layers but ~27% lower for 10 layers vs 4 layers. With staggered scaffolds, when compared to 4-layer results, elastic modulus was similar for 6 layers but was ~43% lower for 8 layers and ~38% lower for 10 layers. Staggered scaffolds had ~38%, ~51%, and ~76% lower yield strength when the number of layers were increased from 4 to 6, 8, and 10 layers, respectively. When comparing lattice and staggered scaffolds with the same layer number, elastic modulus was similar, apart from 8-layer scaffolds where the staggered design was ~42% lower than lattice. Yield strength was similar between 4-layer staggered and lattice scaffolds, while staggered scaffolds with 6, 8, and 10 number of layers showed ~43%, ~45%, ~68% lower strength, respectively, than those found in lattice scaffolds with the same layer numbers.

CONCLUSIONS

Mechanical properties of 3D printed scaffolds depended on scaffold height for both lattice and staggered internal structures. Staggered scaffolds had lower mechanical properties than the lattice scaffolds with the same height and were more sensitive to the change in scaffold height. Taken together, lattice scaffolds demonstrated the advantages of more stable mechanical properties over staggered scaffolds. Also, scaffolds with lower height were more promising in terms of mechanical properties compared to scaffolds with greater height.

Low-density tissue scaffold imaging by synchrotron radiation propagation-based imaging computed tomography with helical acquisition mode

Visualization of low-density tissue scaffolds made from hydrogels is important yet challenging in tissue engineering and regenerative medicine (TERM). For this, synchrotron radiation propagation-based imaging computed tomography (SR-PBI-CT) has great potential, but is limited due to the ring artifacts commonly observed in SR-PBI-CT images. To address this issue, this study focuses on the integration of SR-PBI-CT and helical acquisition mode (i.e. SR-PBI-HCT) to visualize hydrogel scaffolds. The influence of key imaging parameters on the image quality of hydrogel scaffolds was investigated, including the helical pitch (p), photon energy (E) and the number of acquisition projections per rotation/revolution (N_p), and, on this basis, those parameters were optimized to improve image quality and to reduce noise level and artifacts. The results illustrate that SR-PBI-HCT imaging shows impressive advantages in avoiding ring artifacts with p = 1.5, E = 30 keV and N_p = 500 for the visualization of hydrogel scaffolds in vitro. Furthermore, the results also demonstrate that hydrogel scaffolds can be visualized using SR-PBI-HCT with good contrast while at a low radiation dose, i.e. 342 mGy (voxel size of 26 µm, suitable for in vivo imaging). This paper presents a systematic study on hydrogel scaffold imaging using SR-PBI-HCT and the results reveal that SR-PBI-HCT is a powerful tool for visualizing and characterizing low-density scaffolds with a high image quality in vitro. This work represents a significant advance toward the non-invasive in vivo visualization and characterization of hydrogel scaffolds at a suitable radiation dose.

A multimodal 3D imaging approach of pore networks in the human femur to assess age-associated vascular expansion and Lacuno-Canalicular reduction

Cellular communication in the mechanosensory osteocyte Lacuno-Canalicular Network (LCN) regulates bone tissue remodeling throughout life. Age-associated declines in LCN size and connectivity dysregulate mechanosensitivity to localized remodeling needs of aging or damaged tissue, compromising bone quality. Synchrotron radiation-based micro-Computed Tomography (SRμCT) and Confocal Laser Scanning Microscopy (CLSM) were employed to visualize LCN and vascular canal morphometry in an age series of the anterior femur (males n = 14, females n = 11, age range = 19-101, mean age = 55). Age-associated increases in vascular porosity were driven by pore coalescence, including a significant expansion in pore diameter and a significant decline in pore density. In contrast, the LCN showed significant age-associated reductions in lacunar volume fraction, mean diameter, and density, and in canalicular volume fraction and connectivity density. Lacunar density was significantly lower in females across the lifespan, exacerbating their age-associated decline. Canalicular connectivity density was also significantly lower in females but approached comparable declining male values in older age. Our data illuminate the trajectory and potential morphometric sources of age-associated bone loss. Increased vascular porosity contributes to bone fragility with aging, while an increasingly reduced and disconnected LCN undermines the mechanosensitivity required to repair and reinforce bone. Understanding why and how this degradation occurs is essential for improving the diagnosis and treatment of age-related changes in bone quality and fragility.

Effects of PTH glandular and external dosing patterns on bone cell activity using a two-state receptor model-Implications for bone disease progression and treatment

Temporal aspects of ligand specificity have been shown to play a significant role in the case of pulsatile hormone secretion, as exemplified by parathyroid hormone (PTH) binding to its receptor (PTH1R), a G-protein-coupled receptor expressed on surfaces of osteoblasts and osteocytes. The latter binding reaction regulates intracellular signalling and subsequently modulates skeletal homeostasis via bone remodelling. PTH glandular secretion patterns dictate bone cellular activity. In healthy humans, 70% of PTH is secreted in a tonic fashion, whereas 30% is secreted in low-amplitude and high-frequency bursts occurring every 10-20 min, superimposed on the tonic secretion. Changes in the PTH secretion patterns have been associated with various bone diseases. In this paper, we analyse PTH glandular secretion patterns for healthy and pathological states and their link to bone cellular responsiveness (αR). We utilise a two-state receptor ligand binding model of PTH to PTH1R together with a cellular activity function which is able to distinguish various aspects of the stimulation signal including peak dose, time of ligand exposure, and exposure period. Formulating and solving several constrained optimisation problems, we investigate the potential of pharmacological manipulation of the diseased glandular secretion and via clinical approved external PTH injections to restore healthy bone cellular responsiveness. Based on the mean experimentally reported data, our simulation results indicate cellular responsiveness in healthy subjects is sensitive to the tonic baseline stimulus and it is 28% of the computed maximum responsiveness. Simulation results for pathological cases of glucocorticoid-induced osteoporosis, hyperparathyroidism, initial and steady state hypocalcemia clamp tests indicate αR values significantly larger than the healthy baseline (1.7, 2.2, 4.9 and 1.9-times, respectively). Manipulation of the pulsatile glandular secretion pattern, while keeping the mean PTH concentration constant, allowed restoration of healthy baseline values from these catabolic bone diseases. Conversely, PTH glandular diseases that led to maximum bone cellular responsiveness below the healthy baseline value can't be restored to baseline via glandular manipulation. However, external PTH injections allowed restoration of these latter cases.

Towards novel measurements of remodeling activity in cortical bone: implications for osteoporosis and related pharmaceutical treatments

Bone remodelling is performed by basic multicellular units (BMUs) that resorb and subsequently form discrete packets of bone tissue. Normally, the resorption and formation phases of BMU activity are tightly coupled spatially and temporally to promote relatively stable bone mass and bone quality. However, dysfunctional remodelling can lead to bone loss and is the underlying cause of osteoporosis. This review surveys how BMU activity is altered in postmenopausal, disuse and glucocorticoid-induced osteoporosis as well as the impact of anabolic and anti-resorptive pharmaceutical treatments. The dysfunctional remodelling observed during disease and following medical intervention bares many testable hypotheses regarding the regulation of BMU activity and may provide novel insights that challenge existing paradigms of remodelling dynamics, particularly the poorly understood BMU coupling mechanisms. Most bone remodelling research has focused on trabecular bone and 2D analyses, as technical challenges limit the direct assessment of BMU activity in cortical bone. Recent advances in imaging technology present an opportunity to investigate cortical bone remodelling in vivo. This review discusses innovative experimental methods, such as 3D and 4D (i.e. time- lapsed) evaluation of BMU morphology and trajectory, that may be leveraged to improve the understanding of the spatio-temporal coordination of BMUs in cortical bone.

3D Bioprinted Scaffolds for Bone Tissue Engineering: State-Of-The-Art and Emerging Technologies

Treating large bone defects, known as critical-sized defects (CSDs), is challenging because they are not spontaneously healed by the patient’s body. Due to the limitations associated with conventional bone grafts, bone tissue engineering (BTE), based on three-dimensional (3D) bioprinted scaffolds, has emerged as a promising approach for bone reconstitution and treatment. Bioprinting technology allows for incorporation of living cells and/or growth factors into scaffolds aiming to mimic the structure and properties of the native bone. To date, a wide range of biomaterials (either natural or synthetic polymers), as well as various cells and growth factors, have been explored for use in scaffold bioprinting. However, a key challenge that remains is the fabrication of scaffolds that meet structure, mechanical, and osteoconductive requirements of native bone and support vascularization. In this review, we briefly present the latest developments and discoveries of CSD treatment by means of bioprinted scaffolds, with a focus on the biomaterials, cells, and growth factors for formulating bioinks and their bioprinting techniques. Promising state-of-the-art pathways or strategies recently developed for bioprinting bone scaffolds are highlighted, including the incorporation of bioactive ceramics to create composite scaffolds, the use of advanced bioprinting technologies (e.g., core/shell bioprinting) to form hybrid scaffolds or systems, as well as the rigorous design of scaffolds by taking into account of the influence of such parameters as scaffold pore geometry and porosity. We also review in-vitro assays and in-vivo models to track bone regeneration, followed by a discussion of current limitations associated with 3D bioprinting technologies for BTE. We conclude this review with emerging approaches in this field, including the development of gradient scaffolds, four-dimensional (4D) printing technology via smart materials, organoids, and cell aggregates/spheroids along with future avenues for related BTE.

Insights into biogenic and diagenetic lead exposure in experimentally altered modern and archaeological bone: Synchrotron radiation X-ray fluorescence imaging

Bones represent a valuable biological archive of environmental lead (Pb) exposure for modern and archaeological populations. Synchrotron radiation X-ray fluorescence imaging (SR-XFI) generates maps of Pb in bone on a microstructural scale, potentially providing insights into an individual's history of Pb exposure and, in the context of archaeological bone, the biogenic or diagenetic nature of its uptake. The aims of this study were to (1) examine biogenic spatial patterns for Pb from bone samples of modern cadavers compared with patterns observed archaeologically, and (2) test the hypothesis that there are spatial differences in the distribution of Pb for diagenetic and biogenic modes of uptake in bone. To address these aims, this study used inductively coupled plasma-mass spectrometry (ICP-MS) and SR-XFI on unaltered and experimentally altered cadaveric bone samples (University of Saskatchewan, Saskatoon, SK) and archaeological bone samples from 18th to 19th century archaeological sites from Antigua and Lithuania. Bone concentrations of modern individuals are relatively low compared to those of archaeological individuals. SR-XFI results provide insights into modern Saskatchewan Pb exposure with some samples demonstrating a pattern of relatively low Pb exposure with higher levels of Pb exposure occurring in bone structures of a relatively older age that formed earlier in life, likely during the era of leaded gasoline (pre-1980s), and other samples demonstrating a pattern of fairly consistent, low-level exposure. Results support hypotheses for the spatial distribution of Pb corresponding to biogenic vs. diagenetic uptake. Diagenetic Pb is mainly confined to the periosteal surface of each sample with some enrichment of cracks and sub-periosteal canals. This may be useful in the future for differentiating diagenetic from biogenic Pb accumulation, analyzing environmental contamination, and informing sampling strategies in archaeological or fossil bone.

Bone microstructure and bone mineral density are not systemically different in Antarctic icefishes and related Antarctic notothenioids

Ancestors of the Antarctic icefishes (family Channichthyidae) were benthic and had no swim bladder, making it energetically expensive to rise from the ocean floor. To exploit the water column, benthopelagic icefishes were hypothesized to have evolved a skeleton with “reduced bone,” which gross anatomical data supported. Here, we tested the hypothesis that changes to icefish bones also occurred below the level of gross anatomy. Histology and micro‐CT imaging of representative craniofacial bones (i.e., ceratohyal, frontal, dentary, and articular) of extant Antarctic fish species specifically evaluated two features that might cause the appearance of “reduced bone”: bone microstructure (e.g., bone volume fraction and structure linear density) and bone mineral density (BMD, or mass of mineral per volume of bone). Measures of bone microstructure were not consistently different in bones from the icefishes Chaenocephalus aceratus and Champsocephalus gunnari, compared to the related benthic notothenioids Notothenia coriiceps and Gobionotothen gibberifrons. Some quantitative measures, such as bone volume fraction and structure linear density, were significantly increased in some icefish bones compared to homologous bones of non‐icefish. However, such differences were rare, and no microstructural measures were consistently different in icefishes across all bones and species analyzed. Furthermore, BMD was similar among homologous bones of icefish and non‐icefish Antarctic notothenioids. In summary, “reduced bone” in icefishes was not due to systemic changes in bone microstructure or BMD, raising the prospect that “reduced bone” in icefish occurs only at the gross anatomic level (i.e., smaller or fewer bones). Given that icefishes exhibit delayed skeletal development compared to non‐icefish Antarctic fishes, combining these phenotypic data with genomic data might clarify genetic changes driving skeletal heterochrony.

Timing of Mouse Molar Formation Is Independent of Jaw Length Including Retromolar Space

For humans and other mammals to eat effectively, teeth must develop properly inside the jaw. Deciphering craniodental integration is central to explaining the timely formation of permanent molars, including third molars which are often impacted in humans, and to clarifying how teeth and jaws fit, function and evolve together. A factor long-posited to influence molar onset time is the jaw space available for each molar organ to form within. Here, we tested whether each successive molar initiates only after a minimum threshold of space is created via jaw growth. We used synchrotron-based micro-CT scanning to assess developing molars in situ within jaws of C57BL/6J mice aged E10 to P32, encompassing molar onset to emergence. We compared total jaw, retromolar and molar lengths, and molar onset times, between upper and lower jaws. Initiation time and developmental duration were comparable between molar upper and lower counterparts despite shorter, slower-growing retromolar space in the upper jaw, and despite size differences between upper and lower molars. Timing of molar formation appears unmoved by jaw length including space. Conditions within the dental lamina likely influence molar onset much more than surrounding jaw tissues. We theorize that molar initiation is contingent on sufficient surface area for the physical reorganization of dental epithelium and its invagination of underlying mesenchyme.

The physiopathology of osteoarthritis: Paleopathological implications of non-articular lesions from a modern surgical sample

OBJECTIVES

This research focused on osteoarthritis (OA) lesions on modern patients to 1) identify consistently observed lesions not included within current paleopathological measures of OA, 2) assess the correspondence of bone and cartilage lesions with clinical OA diagnostic criteria, and 3) discuss the correspondence of bone lesions with sources of pain reported in clinical literature.

MATERIALS

Tibial plateaus from 62 patients undergoing total knee replacement surgery due to OA were examined.

METHODS

Plateaus were scored for several non-standard OA criteria, including non-articular and X-ray visible lesions and pre-maceration cartilage lesions, as well as articular surface criteria standard in paleopathology.

RESULTS

Proliferative bone in the intercondylar region was present in 95 % of specimens, while areas of dense trabecular bone and lytic defects, both on the inferior side of the plateaus, were present in 98 % and 83 %, respectively.

CONCLUSIONS

The inferior lytic defects may be physical evidence of bone marrow lesions (BML), a clinical OA indicator visible via MRI. Previous research has linked BML to pain, inflammation, and ligament pathology. The latter conditions have also been associated with intercondylar enthesophytes and third intercondylar tubercle of Parsons (TITP), both of which were observed in the intercondylar regions.

SIGNIFICANCE

Several non-articular lesions not currently included in paleopathological measures of OA were consistently observed.

SUGGESTIONS FOR FUTURE RESEARCH

A similar analysis of a control sample of non-OA tibial plateaus would better contextualize these results.

LIMITATIONS

The sample's high average age (65.8 years) and severe OA stage may hamper generalizability to archaeological collections.

Evaluation of La(XT), a novel lanthanide compound, in an OVX rat model of osteoporosis

Purpose

The purpose of this study was to evaluate the efficacy and toxicity of a novel lanthanum compound, La(XT), in an ovariectomized (OVX) rat model of osteoporosis.

Methods

Twenty-four ovariectomized female Sprague Dawley rats were divided into 3 groups receiving a research diet with/without treatment compounds (alendronate: 3 mg/kg; La(XT) 100 mg/kg) for three months. At the time of sacrifice, the kidney, liver, brain, lung and spleen were collected for histological examination. The trabecular bone structure of the tibiae was evaluated using micro-CT and a three-point metaphyseal mechanical test was used to evaluate bone failure load and stiffness.

Results

No significant differences were noted in plasma levels of calcium, phosphorus, creatinine, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) between the La(XT) treatment compared to the non-treated OVX group. Alendronate-treated animals (positive control) showed higher BV/TV, Tb.N and lower Tb.Th and Tb.Sp when compared to the non-treated OVX group. Mechanical analysis indicated that stiffness was higher in the alendronate (32.88%, p = 0.04) when compared to the non-treated OVX group. Failure load did not differ among the groups.

Conclusions

No kidney or liver toxicities of La(XT) treatments were found during the three-month study. The absence of liver and kidney toxicity with drug treatment for 3 months, as well as the increased trabecular bone stiffness are encouraging for the pursuit of further studies with La(XT) for a longer duration of time.

3D printing PCL/nHA bone scaffolds: exploring the influence of material synthesis techniques

Background

It is known that a number of parameters can influence the post-printing properties of bone tissue scaffolds. Previous research has primarily focused on the effect of parameters associated with scaffold design (e.g., scaffold porosity) and specific scaffold printing processes (e.g., printing pressure). To our knowledge, no studies have investigated variations in post-printing properties attributed to the techniques used to synthesize the materials for printing (e.g., melt-blending, powder blending, liquid solvent, and solid solvent).

Methods

Four material preparation techniques were investigated to determine their influence on scaffold properties. Polycaprolactone/nano-hydroxyapatite 30% (wt.) materials were synthesized through melt-blending, powder blending, liquid solvent, and solid solvent techniques. The material printability and the properties of printed scaffolds, in terms of swelling/degradation, mechanical strength, morphology, and thermal properties, were examined and compared to one another using Kruskal-Wallis nonparametric statistical analysis.

Results

Material prepared through the liquid solvent technique was found to have limited printability, while melt-blended material demonstrated the highest degree of uniformity and lowest extent of swelling and degradation. Scaffolds prepared with powder-blended material demonstrated the highest Young’s modulus, yield strength, and modulus of resilience; however, they also demonstrated the highest degree of variability. The higher degree of inhomogeneity in the material was further supported by thermal gravimetric analysis. While scaffolds printed from melt-blended, powder-blended, and solid solvent materials demonstrated a high degree of micro-porosity, the liquid solvent material preparation technique resulted in minimal micro-porosity.

Conclusions

Study results indicate that specific techniques used to prepare materials influence the printing process and post-printing scaffold properties. Among the four techniques examined, melt-blended materials were found to be the most favorable, specifically when considering the combination of printability, consistent mechanical properties, and efficient preparation. Techniques determined to be favourable based on the properties investigated should undergo further studies related to biological properties and time-dependent properties beyond 21-days.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40824-021-00204-y.

Historical overview and new directions in bioarchaeological trace element analysis: a review

Given their strong affinity for the skeleton, trace elements are often stored in bones and teeth long term. Diet, geography, health, disease, social status, activity, and occupation are some factors which may cause differential exposure to, and uptake of, trace elements, theoretically introducing variability in their concentrations and/or ratios in the skeleton. Trace element analysis of bioarchaeological remains has the potential, therefore, to provide rich insights into past human lifeways. This review provides a historical overview of bioarchaeological trace element analysis and comments on the current state of the discipline by highlighting approaches with growing momentum. Popularity for the discipline surged following preliminary studies in the 1960s to 1970s that demonstrated the utility of strontium (Sr) as a dietary indicator. During the 1980s, Sr/Ca ratio and multi-element studies were commonplace in bioarchaeology, linking trace elements with dietary phenomena. Interest in using trace elements for bioarchaeological inferences waned following a period of critiques in the late 1980s to 1990s that argued the discipline failed to account for diagenesis, simplified complex element uptake and regulation processes, and used several unsuitable elements for palaeodietary reconstruction (e.g. those under homeostatic regulation, those without a strong affinity for the skeleton). In the twenty-first century, trace element analyses have been primarily restricted to Sr and lead (Pb) isotope analysis and the study of toxic trace elements, though small pockets of bioarchaeology have continued to analyse multiple elements. Techniques such as micro-sampling, element mapping, and non-traditional stable isotope analysis have provided novel insights which hold the promise of helping to overcome limitations faced by the discipline.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12520-020-01262-4.

Assessment of romosozumab efficacy in the treatment of postmenopausal osteoporosis: Results from a mechanistic PK-PD mechanostat model of bone remodeling

This paper introduces a theoretical framework for the study of the efficacy of romosozumab, a humanized monoclonal antibody targeting sclerostin for the treatment of osteoporosis. We developed a comprehensive mechanistic pharmacokinetic-pharmacodynamic (PK-PD) model of the effect of drug treatment on bone remodeling in postmenopausal osteoporosis (PMO). We utilized a one-compartment PK model to represent subcutaneous injections of romosozumab and subsequent absorption into serum. The PD model is based on a recently-developed bone cell population model describing the bone remodeling process at the tissue scale. The latter accounts for mechanical feedback by incorporating nitric oxide (NO) and sclerostin (Scl) as biochemical feedback molecules. Utilizing a competitive binding model, where Wnt and Scl compete for binding to LRP5/6, allows to regulate anabolic bone remodeling responses. Here, we extended this model with respect to romosozumab binding to sclerostin. For the currently approved monthly injections of 210 mg, the model predicted a 6.59%, 10.38% and 15.25% increase in BMD at the lumbar spine after 6, 12 and 24 months, respectively. These results are in good agreement with the data reported in the literature. Our model is also able to distinguish the bone-site specific drug effects. For instance, at the femoral neck, our model predicts a BMD increase of 3.85% after 12 months of 210 mg injections, which is consistent with literature observations. Finally, our simulations indicate rapid bone loss after treatment discontinuation, indicating that some additional interventions such as use of bisphosphonates are required to maintain bone mass.

Biodistribution of strontium and barium in the developing and mature skeleton of rats

Bone acts as a reservoir for many trace elements. Understanding the extent and pattern of elemental accumulation in the skeleton is important from diagnostic, therapeutic, and toxicological perspectives. Some elements are simply adsorbed to bone surfaces by electric force and are buried under bone mineral, while others can replace calcium atoms in the hydroxyapatite structure. In this article, we investigated the extent and pattern of skeletal uptake of barium and strontium in two different age groups, growing, and skeletally mature, in healthy rats. Animals were dosed orally for 4 weeks with either strontium chloride or barium chloride or combined. The distribution of trace elements was imaged in 3D using synchrotron K-edge subtraction micro-CT at 13.5 µm resolution and 2D electron probe microanalysis (EPMA). Bulk concentration of the elements in serum and bone (tibiae) was also measured by mass spectrometry to study the extent of uptake. Toxicological evaluation did not show any cardiotoxicity or nephrotoxicity. Both elements were primarily deposited in the areas of active bone turnover such as growth plates and trabecular bone. Barium and strontium concentration in the bones of juvenile rats was 2.3 times higher, while serum levels were 1.4 and 1.5 times lower than adults. In all treatment and age groups, strontium was preferred to barium even though equal molar concentrations were dosed. This study displayed spatial co-localization of barium and strontium in bone for the first time. Barium and strontium can be used as surrogates for calcium to study the pathological changes in animal models of bone disease and to study the effects of pharmaceutical compounds on bone micro-architecture and bone remodeling in high spatial sensitivity and precision.

Homogeneous hydroxyapatite/alginate composite hydrogel promotes calcified cartilage matrix deposition with potential for three-dimensional bioprinting

Calcified cartilage regeneration plays an important role in successful osteochondral repair, since it provides a biological and mechanical transition from the unmineralized cartilage at the articulating surface to the underlying mineralized bone. To biomimic native calcified cartilage in engineered constructs, here we test the hypothesis that hydroxyapatite (HAP) stimulates chondrocytes to secrete the characteristic matrix of calcified cartilage. Sodium citrate (SC) was added as a dispersant of HAP within alginate (ALG), and homogeneous dispersal of HAP within ALG hydrogel was confirmed using sedimentation tests, electron microscopy, and energy dispersive spectroscopy. To examine the biological performance of ALG/HAP composites, chondrocyte survival and proliferation, extracellular matrix production, and mineralization potential were evaluated in the presence or absence of the HAP phase. Chondrocytes in ALG/HAP constructs survived well and proliferated, but also expressed higher levels of calcified cartilage markers compared to controls, including Collagen type X secretion, alkaline phosphatase (ALP) activity, and mineral deposition. Compared to controls, ALG/HAP constructs also showed an elevated level of mineralized matrix in vivo when implanted subcutaneously in mice. The printability of ALG/HAP composite hydrogel precursors was verified by 3D printing of ALG/HAP hydrogel scaffolds with a porous structure. In summary, these results confirm the hypothesis that HAP in ALG hydrogel stimulates chondrocytes to secrete calcified matrix in vitro and in vivo and reveal that ALG/HAP composites have the potential for 3D bioprinting and osteochondral regeneration.

A wavelet gradient sparsity based algorithm for reconstruction of reduced-view tomography datasets obtained with a monochromatic synchrotron-based X-ray source

High-resolution synchrotron computed tomography (CT) is very helpful in the diagnosis and monitor of chronic diseases including osteoporosis. Osteoporosis is characterized by low bone mass and cortical bone porosity best imaged with CT. Synchrotron CT requires a large number of angular projections to reconstruct images with high resolution for detailed and accurate diagnosis. However, this poses great risks and challenges for serial in-vivo human and animal imaging due to a large amount of X-ray radiation dose required that can damage living specimens. Also, longer scan times are associated with increased risk of specimen movement and motion artifact in the reconstructed images. We developed a wavelet-gradient sparsity based algorithm to be utilized as a synchrotron tomography reconstruction technique allowing accurate reconstruction of cortical bone porosity assessed for in-vivo preclinical study which significantly reduces the radiation dose and scan time required while maintaining satisfactory image resolution for diagnosis. The results of our study on a rat forelimb sample imaged in the Biomedical Imaging and Therapy Bending Magnet (BMIT-BM) beamline at the Canadian Light Source show that the proposed algorithm can produce satisfactory image quality with more than 50 percent X-ray dose reduction as indicated by both visual and quantitative-based performance.

Franklin expedition lead exposure: New insights from high resolution confocal x-ray fluorescence imaging of skeletal microstructure

In the summer of 1845, under the command of Sir John Franklin, 128 officers and men aboard Royal Navy ships HMS Erebus and HMS Terror sailed into Lancaster Sound and entered the waters of Arctic North America. The goal of this expedition was to complete the discovery of a northwest passage by navigating the uncharted area between Barrow Strait and Simpson Strait. Franklin and his crew spent the first winter at Beechey Island, where three crewmen died and were buried. In September 1846, the ships became stranded in ice off the northwest coast of King William Island, where they remained until April 1848. At that time, the crew, reduced to 105, deserted the ships and retreated south along the island's western and southern shores in a desperate attempt to reach the mainland and via the Back River, to obtain aid at a Hudson's Bay Company Post. Sadly, not one individual survived. Previous analyses of bone, hair, and soft tissue samples from expedition remains found that crewmembers' tissues contained elevated lead (Pb) levels, suggesting that Pb poisoning may have contributed to their demise; however, questions remain regarding the timing and degree of exposure and, ultimately, the extent to which the crewmembers may have been impacted. To address this historical question, we investigated three hypotheses. First, if elevated Pb exposure was experienced by the crew during the expedition, we hypothesized that those sailors who survived longer (King William Island vs. Beechey Island) would exhibit more extensive uptake of Pb in their bones and vice versa. Second, we hypothesized that Pb would be elevated in bone microstructural features forming at or near the time of death compared with older tissue. Finally, if Pb exposure played a significant role in the failure of the expedition we hypothesized that bone samples would exhibit evidence of higher and more sustained uptake of Pb than that of a contemporary comparator naval population from the 19th century. To test these hypotheses, we analyzed bone and dental remains of crew members and compared them against samples derived from the Royal Navy cemetery in Antigua. Synchrotron-based high resolution confocal X-ray fluorescence imaging was employed to visualize Pb distribution within bone and tooth microstructures at the micro scale. The data did not support our first hypothesis as Pb distribution within the samples from the two different sites was similar. Evidence of Pb within skeletal microstructural features formed near the time of death lent support to our second hypothesis but consistent evidence of a marked elevation in Pb levels was lacking. Finally, the comparative analysis with the Antigua samples did not support the hypothesis that the Franklin sailors were exposed to an unusually high level of Pb for the time period. Taken all together our skeletal microstructural results do not support the conclusion that Pb played a pivotal role in the loss of Franklin and his crew.

The effect of growth rate on the three-dimensional orientation of vascular canals in the cortical bone of broiler chickens

Vascular canals in cortical bone during growth and development typically show an anisotropic pattern with canals falling into three main categories: circumferential, radial, and longitudinal. Two major hypotheses attempt to explain the preferred orientations in bone: that vascular canal orientation is optimized to resist a predominant strain direction from functional loading, or that it reflects growth requirements and velocity. We use a controlled growth experiment in broiler chickens to investigate the effect of growth rate on vascular canal orientation. Using feed restriction we set up a fast growing control group and a slow growing restricted group. We compared the microstructure in the humerus and the femur at 42 days of age using synchrotron micro‐computed tomography (micro‐CT), a three‐dimensional (3D) method that visualizes the full canal network. We measured the 3D orientation of each canal in the whole cross‐section of the bone cortex using a set of custom imagej scripts. Using these orientations we compute laminar, radial, and longitudinal indices that measure the proportion of circumferential, radial, and longitudinal canals, by unit of length, in the cortex. Following previous studies we hypothesized that vascular canal orientation is related to growth, with radial canals linked to a faster growth rate and related to functional loading through a high laminar index in flight bones which reflects torsional loading resulting from active flight. The control group had final body weights that were nearly twice the final weights of the restricted group and higher absolute growth rates. We found consistent patterns in the comparison between the humerus and the femur in both groups, with the humerus having higher laminar and longitudinal indices, and a lower radial index than the femur. The control group had higher radial indices and lower laminar and longitudinal indices in both the humerus and the femur than the restricted group. The higher radial indices in our control group point to a link between radial canals and faster growth, and between laminar canals and slower growth, while the higher laminar indices in the humerus point to a link between circumferential canals and torsional loading. Overall, our results indicate that the orientation of the cortical canal network in a bone is the consequence of a complex interaction between the growth rate of that bone and functional loading environment.

Interpreting the three-dimensional orientation of vascular canals and cross-sectional geometry of cortical bone in birds and bats

Cortical bone porosity and specifically the orientation of vascular canals is an area of growing interest in biomedical research and comparative/paleontological anatomy. The potential to explain microstructural adaptation is of great interest. However, the determinants of the development of canal orientation remain unclear. Previous studies of birds have shown higher proportions of circumferential canals (called laminarity) in flight bones than in hindlimb bones, and interpreted this as a sign that circumferential canals are a feature for resistance to the torsional loading created by flight. We defined the laminarity index as the percentage of circumferential canal length out of the total canal length. In this study we examined the vascular canal network in the humerus and femur of a sample of 31 bird and 24 bat species using synchrotron micro-computed tomography (micro-CT) to look for a connection between canal orientation and functional loading. The use of micro-CT provides a full three-dimensional (3D) map of the vascular canal network and provides measurements of the 3D orientation of each canal in the whole cross-section of the bone cortex. We measured several cross-sectional geometric parameters and strength indices including principal and polar area moments of inertia, principal and polar section moduli, circularity, buckling ratio, and a weighted cortical thickness index. We found that bat cortices are relatively thicker and poorly vascularized, whereas those of birds are thinner and more highly vascularized, and that according to our cross-sectional geometric parameters, bird bones have a greater resistance to torsional stress than the bats; in particular, the humerus in birds is more adapted to resist torsional stresses than the femur. Our results show that birds have a significantly (P = 0.031) higher laminarity index than bats, with birds having a mean laminarity index of 0.183 in the humerus and 0.232 in the femur, and bats having a mean laminarity index of 0.118 in the humerus and 0.119 in the femur. Counter to our expectation, the birds had a significantly higher laminarity index in the femur than in the humerus (P = 0.035). To evaluate whether this discrepancy was a consequence of methodology we conducted a comparison between our 3D method and an analogue to two-dimensional (2D) histological measurements. This comparison revealed that 2D methods significantly underestimate (P < 0.001) the amount of longitudinal canals by an average of 20% and significantly overestimate (P < 0.001) the laminarity index by an average of 7.7%, systematically mis-estimating indices of vascular canal orientations. In comparison with our 3D results, our approximated 2D measurement had the same results for comparisons between the birds and bats but found significant differences only in the longitudinal index between the humerus and the femur for both groups. The differences between our 3D and pseudo-2D results indicate that differences between our findings and the literature may be partially based in methodology. Overall, our results do not support the hypothesis that the bones of flight are more laminar, suggesting a complex relation between functional loading and microstructural adaptation.

Superhydrophobicity from the Inside

The nature of trapped air on submersed ultra-water-repellent interfaces has been investigated. These gaseous layers (plastrons) can last from hours to, in some examples such as the Salvinia molesta fern, months. The interface of submerged superhydrophobic surfaces with carefully controlled micropatterned surface roughness has been probed using synchrotron-based high-resolution X-ray phase tomography. This technique looks in situ, through the aqueous/gas interface in three dimensions. Long-term plastron stability appears to correlate with the appearance of scattered microdroplets <20 μm in diameter that are sandwiched within the 30 μm thick gaseous interfacial layer. These microdroplets are centered on defects or damaged sections within the substrate surface approximately 20-50 μm apart. Such irregularities represent heterogeneous micro/nano-hierarchical structures with varying surface structures and chemistry. The stability of microdroplets is governed by a combination of electrostatic repulsion, contact angle limitations, and a saturated vapor pressure, the latter of which reduces the rate of diffusion of gas out of the air layer, thus increasing underwater longevity. Homogenous surfaces exhibiting purely nano- or micro-regularity do not support such microdroplets, and, as a consequence, plastrons can disappear in <20 h compared with >160 h for surfaces with scattered microdroplets. Such behavior may be a requirement for long-term nonwetting in any system.

Lacunar-canalicular network in femoral cortical bone is reduced in aged women and is predominantly due to a loss of canalicular porosity

The lacunar-canalicular network (LCN) of bone contains osteocytes and their dendritic extensions, which allow for intercellular communication, and are believed to serve as the mechanosensors that coordinate the processes of bone modeling and remodeling. Imbalances in remodeling, for example, are linked to bone disease, including fragility associated with aging. We have reported that there is a reduction in scale for one component of the LCN, osteocyte lacunar volume, across the human lifespan in females. In the present study, we explore the hypothesis that canalicular porosity also declines with age. To visualize the LCN and to determine how its components are altered with aging, we examined samples from young (age: 20–23 y; n = 5) and aged (age: 70–86 y; n = 6) healthy women donors utilizing a fluorescent labelling technique in combination with confocal laser scanning microscopy. A large cross-sectional area of cortical bone spanning the endosteal to periosteal surfaces from the anterior proximal femoral shaft was examined in order to account for potential trans-cortical variation in the LCN. Overall, we found that LCN areal fraction was reduced by 40.6% in the samples from aged women. This reduction was due, in part, to a reduction in lacunar density (21.4% decline in lacunae number per given area of bone), but much more so due to a 44.6% decline in canalicular areal fraction. While the areal fraction of larger vascular canals was higher in endosteal vs. periosteal regions for both age groups, no regional differences were observed in the areal fractions of the LCN and its components for either age group. Our data indicate that the LCN is diminished in aged women, and is largely due to a decline in the canalicular areal fraction, and that, unlike vascular canal porosity, this diminished LCN is uniform across the cortex.

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The lacunar-canalicular network (LCN) is reduced by 40.6% in aged women

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The lacunar density (lacunae number per given area of bone) is reduced by 21.4% in aged women

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The reduction in LCN in aged women is primarily due to a 44.6% loss of canaliculi

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No endosteal vs. periosteal regional differences were observed in the LCN and its components in either young or aged women

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A reduction in canaliculi with age may contribute to bone fragility in aged women

Accounting for spatial variation of trabecular anisotropy with subject-specific finite element modeling moderately improves predictions of local subchondral bone stiffness at the proximal tibia

INTRODUCTION

Previously, a finite element (FE) model of the proximal tibia was developed and validated against experimentally measured local subchondral stiffness. This model indicated modest predictions of stiffness (R²=0.77, normalized root mean squared error (RMSE%)=16.6%). Trabecular bone though was modeled with isotropic material properties despite its orthotropic anisotropy. The objective of this study was to identify the anisotropic FE modeling approach which best predicted (with largest explained variance and least amount of error) local subchondral bone stiffness at the proximal tibia.

METHODS

Local stiffness was measured at the subchondral surface of 13 medial/lateral tibial compartments using in situ macro indentation testing. An FE model of each specimen was generated assuming uniform anisotropy with 14 different combinations of cortical- and tibial-specific density-modulus relationships taken from the literature. Two FE models of each specimen were also generated which accounted for the spatial variation of trabecular bone anisotropy directly from clinical CT images using grey-level structure tensor and Cowin's fabric-elasticity equations. Stiffness was calculated using FE and compared to measured stiffness in terms of R² and RMSE%.

RESULTS

The uniform anisotropic FE model explained 53-74% of the measured stiffness variance, with RMSE% ranging from 12.4 to 245.3%. The models which accounted for spatial variation of trabecular bone anisotropy predicted 76-79% of the variance in stiffness with RMSE% being 11.2-11.5%.

CONCLUSIONS

Of the 16 evaluated finite element models in this study, the combination of Synder and Schneider (for cortical bone) and Cowin's fabric-elasticity equations (for trabecular bone) best predicted local subchondral bone stiffness.

Evaluating differential nuclear DNA yield rates and osteocyte numbers among human bone tissue types: A synchrotron radiation micro-CT approach

Molecular human identification has conventionally focused on DNA sampling from dense, weight-bearing cortical bone tissue, typically from femora or tibiae. A comparison of skeletal elements from three contemporary individuals demonstrated that elements with high quantities of cancellous bone yielded nuclear DNA at the highest rates, suggesting that preferentially sampling cortical bone may be suboptimal (Mundorff & Davoren, 2014). Despite these findings, the reason for the differential DNA yields between cortical and cancellous bone tissues remains unknown. The primary goal of this work is to ascertain whether differences in bone microstructure can be used to explain differential nuclear DNA yield among bone tissue types observed by Mundorff and Davoren (2014), with a focus on osteocytes and the three-dimensional (3D) quantification of their associated lacunae. Osteocytes and other bone cells are recognized to house DNA in bone tissue, thus examining the density of their lacunae may explain why nuclear DNA yield rates differ among bone tissue types. Lacunae were visualized and quantified using synchrotron radiation-based micro-Computed Tomographic imaging (SR micro-CT). Volumes of interest (VOIs) from cortical and cancellous bone tissues (n=129) were comparatively analyzed from the three skeletons sampled for Mundorff and Davoren's (2014) study. Analyses tested the primary hypothesis that the abundance and density of osteocytes (inferred from their lacunar spaces) vary between cortical and cancellous bone tissue types. Results demonstrated that osteocyte lacunar abundance and density vary between cortical and cancellous bone tissue types, with cortical bone VOIs containing a higher lacunar abundance and density. We found that the osteocyte lacunar density values are independent of nuclear DNA yield, suggesting an alternative explanation for the higher nuclear DNA yields from bones with greater quantities of cancellous bone tissue. The use of SR micro-CT allowed for a scale of analysis that revealed a high range of variation in lacunar abundance in both tissue types. Moreover, high-resolution SR micro-CT imaging revealed potential soft tissue remnants within marrow spaces not visible macroscopically. It is hypothesized that soft tissue remnants observed among the trabeculae of skeletal elements with high quantities of cancellous bone tissue are responsible for the high nuclear DNA yields. These findings have significant implications for bone-sample selection for nuclear DNA analysis in a forensic context when skeletal remains are recovered from the ground surface.

A sparsity-based iterative algorithm for reconstruction of micro-CT images from highly undersampled projection datasets obtained with a synchrotron X-ray source

Synchrotron X-ray Micro Computed Tomography (Micro-CT) is an imaging technique which is increasingly used for non-invasive in vivo preclinical imaging. However, it often requires a large number of projections from many different angles to reconstruct high-quality images leading to significantly high radiation doses and long scan times. To utilize this imaging technique further for in vivo imaging, we need to design reconstruction algorithms that reduce the radiation dose and scan time without reduction of reconstructed image quality. This research is focused on using a combination of gradient-based Douglas-Rachford splitting and discrete wavelet packet shrinkage image denoising methods to design an algorithm for reconstruction of large-scale reduced-view synchrotron Micro-CT images with acceptable quality metrics. These quality metrics are computed by comparing the reconstructed images with a high-dose reference image reconstructed from 1800 equally spaced projections spanning 180°. Visual and quantitative-based performance assessment of a synthetic head phantom and a femoral cortical bone sample imaged in the biomedical imaging and therapy bending magnet beamline at the Canadian Light Source demonstrates that the proposed algorithm is superior to the existing reconstruction algorithms. Using the proposed reconstruction algorithm to reduce the number of projections in synchrotron Micro-CT is an effective way to reduce the overall radiation dose and scan time which improves in vivo imaging protocols.

Cortical Bone Porosity: What Is It, Why Is It Important, and How Can We Detect It?

There is growing recognition of the role of micro-architecture in osteoporotic bone loss and fragility. This trend has been driven by advances in imaging technology, which have enabled a transition from measures of mass to micro-architecture. Imaging trabecular bone has been a key research focus, but advances in resolution have also enabled the detection of cortical bone micro-architecture, particularly the network of vascular canals, commonly referred to as 'cortical porosity.' This review aims to provide an overview of what this level of porosity is, why it is important, and how it can be characterized by imaging. Moving beyond a 'trabeculocentric' view of bone loss holds the potential to improve diagnosis and monitoring of interventions. Furthermore, cortical porosity is intimately linked to the remodeling process, which underpins bone loss, and thus a larger potential exists to improve our fundamental understanding of bone health through imaging of both humans and animal models.

Spectral K-edge subtraction imaging of experimental non-radioactive barium uptake in bone

PURPOSE

To evaluate the feasibility of using non-radioactive barium as a bone tracer for detection with synchrotron spectral K-edge subtraction (SKES) technique.

METHODS

Male rats of 1-month old (i.e., developing skeleton) and 8-month old (i.e., skeletally mature) were orally dosed with low dose of barium chloride (33mg/kg/day Ba²⁺) for 4weeks. The fore and hind limbs were dissected for imaging in projection and computed tomography modes at 100μm and 52μm pixel sizes. The SKES method utilizes a single bent Laue monochromator to prepare a 550eV energy spectrum to encompass the K-edge of barium (37.441keV), for collecting both 'above' and 'below' the K-edge data sets in a single scan.

RESULTS

The SKES has a very good focal size, thus limits the 'crossover' and motion artifacts. In juvenile rats, barium was mostly incorporated in the areas of high bone turnover such as at the growth plate and the trabecular surfaces, but also in the cortical bone as the animals were growing at the time of tracer administration. However, the adults incorporated approximately half the concentration and mainly in the areas where bone remodeling was predominant and occasionally in the periosteal and endosteal layers of the diaphyseal cortical bone.

CONCLUSIONS

The presented methodology is simple to implement and provides both structural and functional information, after labeling with barium, on bone micro-architecture and thus has great potential for in vivo imaging of pre-clinical animal models of musculoskeletal diseases to better understand their mechanisms and to evaluate the efficacy of pharmaceuticals.

Three-dimensional labeling of newly formed bone using synchrotron radiation barium K-edge subtraction imaging

Bone is a dynamic tissue which exhibits complex patterns of growth as well as continuous internal turnover (i.e. remodeling). Tracking such changes can be challenging and thus a high resolution imaging-based tracer would provide a powerful new perspective on bone tissue dynamics. This is, particularly so if such a tracer can be detected in 3D. Previously, strontium has been demonstrated to be an effective tracer which can be detected by synchrotron-based dual energy K-edge subtraction (KES) imaging in either 2D or 3D. The use of strontium is, however, limited to very small sample thicknesses due to its low K-edge energy (16.105 keV) and thus is not suitable for in vivo application. Here we establish proof-of-principle for the use of barium as an alternative tracer with a higher K-edge energy (37.441 keV), albeit for ex vivo imaging at the moment, which enables application in larger specimens and has the potential to be developed for in vivo imaging of preclinical animal models. New bone formation within growing rats in 2D and 3D was demonstrated at the Biomedical Imaging and Therapy bending magnet (BMIT-BM) beamline of the Canadian Light Source synchrotron. Comparative x-ray fluorescence imaging confirmed those patterns of uptake detected by KES. This initial work provides a platform for the further development of this tracer and its exploration of applications for in vivo development.

Role of endocortical contouring methods on precision of HR-pQCT-derived cortical micro-architecture in postmenopausal women and young adults

Precision errors of cortical bone micro-architecture from high-resolution peripheral quantitative computed tomography (pQCT) ranged from 1 to 16 % and did not differ between automatic or manually modified endocortical contour methods in postmenopausal women or young adults. In postmenopausal women, manually modified contours led to generally higher cortical bone properties when compared to the automated method.

INTRODUCTION

First, the objective of the study was to define in vivo precision errors (coefficient of variation root mean square (CV%RMS)) and least significant change (LSC) for cortical bone micro-architecture using two endocortical contouring methods: automatic (AUTO) and manually modified (MOD) in two groups (postmenopausal women and young adults) from high-resolution pQCT (HR-pQCT) scans. Second, it was to compare precision errors and bone outcomes obtained with both methods within and between groups.

METHODS

Using HR-pQCT, we scanned twice the distal radius and tibia of 34 postmenopausal women (mean age ± SD 74 ± 7 years) and 30 young adults (27 ± 9 years). Cortical micro-architecture was determined using AUTO and MOD contour methods. CV%RMS and LSC were calculated. Repeated measures and multivariate ANOVA were used to compare mean CV% and bone outcomes between the methods within and between the groups. Significance was accepted at P < 0.05.

RESULTS

CV%RMS ranged from 0.9 to 16.3 %. Within-group precision did not differ between evaluation methods. Compared to young adults, postmenopausal women had better precision for radial cortical porosity (precision difference 9.3 %) and pore volume (7.5 %) with MOD. Young adults had better precision for cortical thickness (0.8 %, MOD) and tibial cortical density (0.2 %, AUTO). In postmenopausal women, MOD resulted in 0.2-54 % higher values for most cortical outcomes, as well as 6-8 % lower radial and tibial cortical BMD and 2 % lower tibial cortical thickness.

CONCLUSIONS

Results suggest that AUTO and MOD endocortical contour methods provide comparable repeatability. In postmenopausal women, manual modification of endocortical contours led to generally higher cortical bone properties when compared to the automated method, while no between-method differences were observed in young adults.

Three-dimensional reconstruction of Haversian systems in human cortical bone using synchrotron radiation-based micro-CT: morphology and quantification of branching and transverse connections across age

This study uses synchrotron radiation-based micro-computed tomography (CT) scans to reconstruct three-dimensional networks of Haversian systems in human cortical bone in order to observe and analyse interconnectivity of Haversian systems and the development of total Haversian networks across different ages. A better knowledge of how Haversian systems interact with each other is essential to improve understanding of remodeling mechanisms and bone maintenance; however, previous methodological approaches (e.g. serial sections) did not reveal enough detail to follow the specific morphology of Haversian branching, for example. Accordingly, the aim of the present study was to identify the morphological diversity of branching patterns and transverse connections, and to understand how they change with age. Two types of branching morphologies were identified: lateral branching, resulting in small osteon branches bifurcating off of larger Haversian canals; and dichotomous branching, the formation of two new osteonal branches from one. The reconstructions in this study also suggest that Haversian systems frequently target previously existing systems as a path for their course, resulting in a cross-sectional morphology frequently referred to as 'type II osteons'. Transverse connections were diverse in their course from linear to oblique to curvy. Quantitative assessment of age-related trends indicates that while in younger human individuals transverse connections were most common, in older individuals more evidence of connections resulting from Haversian systems growing inside previously existing systems was found. Despite these changes in morphological characteristics, a relatively constant degree of overall interconnectivity is maintained throughout life. Altogether, the present study reveals important details about Haversian systems and their relation to each other that can be used towards a better understanding of cortical bone remodeling as well as a more accurate interpretation of morphological variants of osteons in cross-sectional microscopy. Permitting visibility of reversal lines, synchrotron radiation-based micro-CT is a valuable tool for the reconstruction of Haversian systems, and future analyses have the potential to further improve understanding of various important aspects of bone growth, maintenance and health.

3-D localization of non-radioactive strontium in osteoarthritic bone: Role in the dynamic labeling of bone pathological changes

The study objective was to visualize regions of bone that undergo pathological mineralization and/or remodeling during pathogenesis of osteoarthritis, by employing non-radioactive strontium as a dynamic tracer of bone turnover. Post traumatic osteoarthritis was surgically induced in skeletally mature rats, followed by in vivo micro-CT imaging for 12 weeks to assess bone micro-structural changes. Rats either received strontium ranelate daily for the entire course of study or only last 10 days before euthanization. Distribution of strontium in bone was assessed in two and three dimensions, using electron probe micro-analysis (EPMA) and synchrotron dual energy K-edge subtraction micro-CT (SRμCT), respectively. Considerable early formation of osteophytes around the collateral ligament attachments and margins of articulating surfaces were observed, followed by subchondral sclerosis at the later stages. Accordingly, strontium was heavily incorporated by mineralizing osteophytes at 4, 8, and 12 weeks post-surgery, whereas subchondral bone only incorporated strontium between weeks 8-12.This study showed low dose stable strontium can effectively serve as a dynamic tracer of bone turnover to study pathological bone micro-structural changes, at resolution higher than nuclear medicine. Co-administration of strontium during therapeutic drug intervention may show enormous utility in assessing the efficacy of those compounds upon adaptive bone physiology.

Does 3D orientation account for variation in osteon morphology assessed by 2D histology?

The primary microstructural unit of cortical bone, the secondary osteon or Haversian system, is widely assumed to have a cylindrical shape. It is generally accepted that osteons are roughly circular in cross-section and deviations from circularity have been attributed to deviations from longitudinal orientation. To our knowledge this idealized geometric relationship, which assumes osteons are perfect cylinders, has not been rigorously explored. As such, we sought to explore two research questions: (i) Does the orientation of osteons in 3D explain variation in shapes visualized in 2D? (ii) Can differences in osteon 3D orientation explain previously reported age-related differences observed in their 2D cross-sectional shape (e.g. more circular shape and decreased area with age)? To address these questions we utilized a combination of 2D histology to identify osteon shape and superimposed micro-computed tomography data to assess osteon orientation in 3D based upon the osteonal canal. Shape was assessed by the inverse of Aspect Ratio (On.AspR(-1), based on a fitted ellipse) - which ranged from 0 (infinitely elongated shape) to 1 (perfectly circular). A sample (n = 27) of human female anterior femoral cortical bone samples from across the human lifespan (20-87 years) were included in the analysis, which involved 1418 osteons. The overall mean measure of On.AspR(-1) was 0.703 (1.42 Aspect Ratio). Mean osteon orientation was 79.1° (90° being longitudinal). While we anticipated a positive relation between orientation and On.AspR(-1), we found the opposite - a weak negative correlation (with more oblique 3D osteon alignment, the 2D shape became more circular as reflected by increased On.AspR(-1)). When analysis of covariance was performed with age and orientation as covariates, the negative relation with orientation was replaced by a significant relation with age alone. This relation with age accounted for 41% of the variation of On.AspR(-1). The results revealed that osteons, on average, are not circular in cross-section and that 3D orientation cannot account for deviation from circular shape. Osteons thus are strictly speaking not cylinders, as they tend to have elliptical cross-sections. We observed that osteons did become less elliptical in cross-section with age independent of orientation - suggesting this is a real change in morphology.

Adolescent physical activity and bone strength at the proximal femur in adulthood

INTRODUCTION

Physical activity (PA) enhances bone structural strength at the proximal femur in adolescence, but whether these benefits are maintained into early adulthood remains unknown. The purpose of this study was to investigate whether males and females, described as active, average, and inactive during adolescence, display differences in structural strength at the proximal femur in early adulthood (20-30 yr).

METHODS

One hundred four participants (55 males and 49 females) from the Pediatric Bone Mineral Accrual Study (PBMAS) were categorized into adolescent PA groupings (inactive, average, and active) using the Physical Activity Questionnaire for Adolescents. Cross-sectional area and section modulus (Z) at the narrow neck, intertrochanter, and femoral shaft (S) sites of the proximal femur were assessed using hip structural analysis in young adulthood from femoral neck dual-energy x-ray absorptiometry scans. Group differences were assessed using ANCOVA, controlling for adult height (Ht), adult weight (Wt), adolescent bone geometry, sex, percentage adult total body lean tissue (LTM%), and adult PA levels.

RESULTS

Active adolescents had significantly greater adjusted bone geometric measures at all sites than their inactive classified peers during adolescence (P < 0.05). In adulthood, when adjusted for Ht, Wt, adolescent bone geometry, sex, LTM%, and adult PA levels, adolescent participants categorized as active had significantly greater adjusted adult bone geometric measures at the proximal femur than adult participants who were classified as inactive during adolescence (P < 0.05).

CONCLUSIONS

Skeletal advantages associated with adolescence activity appear to confer greater geometric bone structural strength at the proximal femur in young adulthood.

Modalities for Visualization of Cortical Bone Remodeling: The Past, Present, and Future

Bone's ability to respond to load-related phenomena and repair microdamage is achieved through the remodeling process, which renews bone by activating groups of cells known as basic multicellular units (BMUs). The products of BMUs, secondary osteons, have been extensively studied via classic two-dimensional techniques, which have provided a wealth of information on how histomorphology relates to skeletal structure and function. Remodeling is critical in maintaining healthy bone tissue; however, in osteoporotic bone, imbalanced resorption results in increased bone fragility and fracture. With increasing life expectancy, such degenerative bone diseases are a growing concern. The three-dimensional (3D) morphology of BMUs and their correlation to function, however, are not well-characterized and little is known about the specific mechanisms that initiate and regulate their activity within cortical bone. We believe a key limitation has been the lack of 3D information about BMU morphology and activity. Thus, this paper reviews methodologies for 3D investigation of cortical bone remodeling and, specifically, structures associated with BMU activity (resorption spaces) and the structures they create (secondary osteons), spanning from histology to modern ex vivo imaging modalities, culminating with the growing potential of in vivo imaging. This collection of papers focuses on the theme of "putting the 'why' back into bone architecture." Remodeling is one of two mechanisms "how" bone structure is dynamically modified and thus an improved 3D understanding of this fundamental process is crucial to ultimately understanding the "why."

Normal variation in cortical osteocyte lacunar parameters in healthy young males

The most abundant cell in bone, osteocytes form an interconnected system upon which the regulation of healthy bone relies. Although the complete nature of the role of osteocytes has yet to be defined, they are generally accepted to play a part in the sensing of load and the initiation of damage repair. A previous study conducted by our group identified variation of up to 30% in osteocyte lacunar density and morphological parameters between regions of a single cross-section of human femoral shaft; that study, however, was limited to a single individual. The aim of the current study was to determine whether this pattern consistently occurs in healthy young male femora. Anterior, posterior, medial and lateral blocks were prepared from the proximal femoral shaft of seven males and synchrotron radiation micro-CT imaged. Average lacunar densities (± SD) from the anterior, posterior, medial and lateral regions were 23 394 ± 1705, 30 180 ± 4860, 35 946 ± 5990 and 29 678 ± 6081 lacunae per mm(3) of bone tissue, respectively. These values were significantly different between the anterior and both the medial and posterior regions (P < 0.05). The density of the combined anterior and posterior regions was also significantly lower (P = 0.006) than the density of the combined medial and lateral regions. Although no difference was found in predominant orientation, shape differences were found; with the combined anterior-posterior regions having lacunae that were significantly more elongated and less flat than the combined medial-lateral values (P < 0.001). As expected, in this larger study, there was a dramatic difference in lacunar density between the medial and anterior region (up to ~ 54%). The study clearly demonstrates that the high variation seen in osteocyte lacunar density as well as other lacunar parameters, noted in a number of biomechanical, age and pathology studies, are well within the range of normal variation; however, the reasons for and consequences of this variation remain unclear. Lacunar parameters including abundance and shape are being increasingly incorporated into computational modeling of bone biology and this paper represents a more comprehensive description of normal healthy lacunae.

Technique: imaging earliest tooth development in 3D using a silver-based tissue contrast agent

Looking in microscopic detail at the 3D organization of initiating teeth within the embryonic jaw has long-proved technologically challenging because of the radio-translucency of these tiny un-mineralized oral tissues. Yet 3D image data showing changes in the physical relationships among developing tooth and jaw tissues are vital to understand the coordinated morphogenesis of vertebrate teeth and jaws as an animal grows and as species evolve. Here, we present a new synchrotron-based scanning solution to image odontogenesis in 3D and in histological detail using a silver-based contrast agent. We stained fixed, intact wild-type mice aged embryonic (E) day 10 to birth with 1% Protargol-S at 37°C for 12-32 hr. Specimens were scanned at 4-10 µm pixel size at 28 keV, just above the silver K-edge, using micro-computed tomography (µCT) at the Canadian Light Source synchrotron. Synchrotron µCT scans of silver-stained embryos showed even the earliest visible stages of tooth initiation, as well as many other tissue types and structures, in histological detail. Silver stain penetration was optimal for imaging structures in intact embryos E15 and younger. This silver stain method offers a powerful yet straightforward approach to visualize at high-resolution and in 3D the earliest stages of odontogenesis in situ, and demonstrates the important of studying the tooth organ in all three planes of view.

Variation in osteocyte lacunar morphology and density in the human femur--a synchrotron radiation micro-CT study

In recent years there has been growing interest in the spatial properties of osteocytes (including density and morphology) and how these potentially relate to adaptation, disease and aging. This interest has, in part, arisen from the availability of increasingly high-resolution 3D imaging modalities such as synchrotron radiation (SR) micro-CT. As resolution increases, field of view generally decreases. Thus, while increasingly detailed spatial information is obtained, it is unclear how representative this information is of the skeleton or even the isolated bone. The purpose of this research was to describe the variation in osteocyte lacunar density, morphology and orientation within the femur from a healthy young male human. Multiple anterior, posterior, medial and lateral blocks (2 mm × 2 mm) were prepared from the proximal femoral shaft and SR micro-CT imaged at the Advanced Photon Source. Average lacunar densities (± standard deviation) from the anterior, posterior, medial and lateral regions were 27,169 ± 1935, 26,3643 ± 1262, 37,521 ± 6416 and 33,972 ± 2513 lacunae per mm(3) of bone tissue, respectively. These values were significantly different between the medial and both the anterior and posterior regions (p<0.05). The density of the combined anterior and posterior regions was also significantly lower (p=0.001) than the density of the combined medial and lateral regions. Although no difference was found in predominant orientation, shape differences were found; with the combined anterior and posterior regions having more elongated (p=0.004) and flattened (p=0.045) lacunae, than those of the medial and lateral regions. This study reveals variation in osteocyte lacunar density and morphology within the cross-section of a single bone and that this variation can be considerable (up to 30% difference in density between regions). The underlying functional significance of the observed variation in lacunar density likely relates to localized variations in loading conditions as the pattern corresponds well with mechanical axes. Lower density and more elongate shapes being associated with the antero-posterior oriented neutral axis. Our findings demonstrate that the functional and pathological interpretations that are increasingly being drawn from high resolution imaging of osteocyte lacunae need to be better situated within the broader context of normal variation, including that which occurs even within a single skeletal element.

Age-related differences in collagen-induced arthritis: clinical and imaging correlations

Arthritis is among the most common chronic diseases in both children and adults. Although intraarticular inflammation is the feature common among all patients with chronic arthritis there are, in addition to age at onset, clinical characteristics that further distinguish the disease in pediatric and adult populations. In this study, we aimed to demonstrate the utility of microCT (μCT) and ultrasonography in characterizing pathologic age-related differences in a collagen-induced arthritis (CIA) rat model. Juvenile (35 d old) and young adult (91 d old) male Wistar rats were immunized with bovine type II collagen and incomplete Freund adjuvant to induce polyarthritis. Naïve male Wistar rats served as controls. All paws were scored on a scale of 0 (normal paw) to 4 (disuse of paw). Rats were euthanized at 14 d after the onset of arthritis and the hindpaws imaged by μCT and ultrasonography. Young adult rats had more severe signs of arthritis than did their juvenile counterparts. Imaging demonstrated that young adult CIA rats exhibited more widespread and severe skeletal lesions of the phalanges, metatarsals, and tarsal bones, whereas juvenile CIA rats had more localized and less proliferative and osteolytic damage that was confined predominantly to the phalanges and metatarsals. This report demonstrates the utility of imaging modalities to compare juvenile and young adult rats with CIA and provides evidence that disease characteristics and progression differ between the 2 age groups. Our observations indicate that the CIA model could help discern age-related pathologic processes in inflammatory joint diseases.

Prolonged unloading in growing rats reduces cortical osteocyte lacunar density and volume in the distal tibia

Bone dynamically adapts its structure to the environmental demands placed upon it. Load-related stimuli play an important role in this adaptation. It has been postulated that osteocytes sense changes in these stimuli and initiate adaptive responses, across a number of scales, through a process known as mechanotransduction. While much research has focused on gross and tissue-level adaptation, relatively little is known regarding the relation between cellular-level features (e.g. osteocyte lacunar density, volume and shape) and loading. The increasing availability of high resolution 3D imaging modalities, including synchrotron-based techniques, has made studying 3D cellular-level features feasible on a scale not previously possible. The primary objective of this study was to test the hypothesis that unloading (sciatic neurectomy) during growth results in altered osteocyte lacunar density in the tibial diaphysis of the rat. Secondarily, we explored a potential effect of unloading on mean lacunar volume. Lacunar density was significantly (p<0.05) lower in immobilized bones (49,642 ± 11,955 lacunae per mm(3); n=6) than in control bones (63,138 ± 1956 lacunae per mm(3); n=6). Mean lacunar volume for immobilized bones (209 ± 72 μm(3); n=6) was significantly smaller (p<0.05) than that for the control bones (284 ± 28 μm(3); n=6). Our results demonstrate that extreme differences in loading conditions, such as those created by paralysis, do indeed result in changes in osteocyte lacunar density and volume. Further investigation is warranted to examine relations between these measures and more subtle variation in loading as well as pathological states, which have been linked to alterations in mechanotransduction.

Three dimensional mapping of strontium in bone by dual energy K-edge subtraction imaging

The bones of many terrestrial vertebrates, including humans, are continually altered through an internal process of turnover known as remodeling. This process plays a central role in bone adaptation and disease. The uptake of fluorescent tetracyclines within bone mineral is widely exploited as a means of tracking new tissue formation. While investigation of bone microarchitecture has undergone a dimensional shift from 2D to 3D in recent years, we lack a 3D equivalent to fluorescent labeling. In the current study we demonstrate the ability of synchrotron radiation dual energy K-edge subtraction (KES) imaging to map the 3D distribution of elemental strontium within rat vertebral samples. This approach has great potential for ex vivo analysis of preclinical models and human tissue samples. KES also represents a powerful tool for investigating the pharmokinetics of strontium-based drugs recently approved in many countries around the globe for the treatment of osteoporosis.

Maturational timing does not predict HSA estimated adult bone geometry at the proximal femur

Late maturational timing is documented to be detrimental to bone strength primarily at the distal radius. Studies at the proximal femur have focused on bone mass and the results remain controversial. The purpose of this study was to examine the long term relationship between the onset of maturation and the development of estimated cross sectional area (CSA) and section modulus (Z) at the proximal femur. Two hundred and twenty six individuals (108 males and 118 females) from the Saskatchewan Pediatric Bone Mineral Accrual Study (PBMAS) were classified into maturity groups based on age of attainment of peak height velocity. CSA and Z were serially assessed at the narrow neck (NN), intertrochanter (IT) and proximal shaft (S) sites using hip structural analysis (HSA). Multilevel models were constructed to examine the development of CSA and Z by maturity group. Cross sectional observations indicated that during adolescence, early maturing males had significantly greater CSA and Z than late maturing males at all sites of the proximal femur, while early maturing females had greater Z at the NN and S, and greater CSA at the NN, IT and S sites compared to late maturing females. When age, body size, body composition, physical activity and dietary intake were controlled no significant effects of maturational timing were found at the NN, IT or S regions (p>0.05) in either males or females. In this population of healthy individuals there appears to be no effect of the onset of maturation on estimated CSA and Z development at the proximal femur in both males and females. This may be a result of the proximal femur's loading environment. Future research is required to determine the role of loading on the relationship between maturational timing and bone structure and strength development at the proximal femur.