Endosteal Surface Research Articles

Developing long bones respond to surrounding tissues by trans-pairing of periosteal osteoclasts and endocortical osteoblasts.

Developing long bones alter their shape while maintaining uniform cortical thickness via coordinated activity of bone-forming osteoblasts and bone-resorbing osteoclasts at periosteal and endosteal surfaces, a process we designate trans-pairing. Two types of trans-pairing shift cortical bone in opposite orientations: peri-forming trans-pairing (peri-t-p) increases bone marrow space and endo-forming trans-pairing (endo-t-p) decreases it, via paired activity of bone resorption and formation across the cortex. Here, we focused on endo-t-p in growing bones. Analysis of endo-t-p activity in the cortex of mouse fibulae revealed osteoclasts under the periosteum compressed by muscles, and expression of RANKL in periosteal cells of the cambium layer. Furthermore, mature osteoblasts were localized on the endosteum, while preosteoblasts were at the periosteum and within cortical canals. X-ray tomographic microscopy revealed the presence of cortical canals more closely associated with endo- than with peri-t-p. Sciatic nerve transection followed by muscle atrophy and unloading induced circumferential endo-t-p with concomitant spread of cortical canals. Such canals likely supply the endosteum with preosteoblasts from the periosteum under endo-t-p, allowing bone shape to change in response to mechanical stress or nerve injury.

Bone of contention: Intra-element variability in remodelling of human femora based on histomorphometric and isotope analyses.

The volume of human carbon (δ13C) and nitrogen (δ15N) isotope data produced in archaeological research has increased markedly in recent years. However, knowledge of bone remodelling, its impact on isotope variation, and the temporal resolution of isotope data remains poorly understood. Varied remodelling rates mean different elements (e.g., femur and rib) produce different temporal signals but little research has examined intra-element variability. This study investigates human bone remodelling using osteon population density and the relationship with carbon and nitrogen isotope data at a high resolution, focusing on variation through femoral cross-sections, from periosteal to endosteal surfaces. Results demonstrate considerable differences in isotope values between cross-sectional segments of a single fragment, by up to 1.3‰ for carbon and 1.8‰ for nitrogen, illustrating the need for standardised sampling strategies. Remodelling also varies between bone sections, occurring predominantly within the endosteal portion, followed by the midcortical and periosteal. Therefore, the endosteal portion likely reflects a shorter period of life closer to the time of death, consistent with expectations. By contrast, the periosteal surface provides a longer average, though there were exceptions to this. Results revealed a weak negative correlation between osteon population density and δ15N or δ13C, confirming that remodelling has an effect on isotope values but is not the principal driver. However, a consistent elevation of δ15N and δ13C (0.5‰ average) was found between the endosteal and periosteal regions, which requires further investigation. These findings suggest that, with further research, there is potential for single bone fragments to reconstruct in-life dietary change and mobility, thus reducing destructive sampling.

Extracellular matrices of stromal cell subtypes regulate phenotype and contribute to the stromal microenvironment in vivo

BackgroundBone marrow stromal cells (BMSCs) are highly heterogeneous, which may reflect their diverse biological functions, including tissue maintenance, haematopoietic support and immune control. The current understanding of the mechanisms that drive the onset and resolution of heterogeneity, and how BMSCs influence other cells in their environment is limited. Here, we determined how the secretome and importantly the extracellular matrix of BMSCs can influence cellular phenotype.MethodsWe used two immortalised clonal BMSC lines isolated from the same heterogeneous culture as model stromal subtypes with distinct phenotypic traits; a multipotent stem-cell-like stromal line (Y201) and a nullipotent non-stem cell stromal line (Y202), isolated from the same donor BMSC pool. Label-free quantitative phase imaging was used to track cell morphology and migration of the BMSC lines over 96 h in colony-forming assays. We quantified the secreted factors of each cell line by mass spectrometry and confirmed presence of proteins in human bone marrow by immunofluorescence.ResultsTransfer of secreted signals from a stem cell to a non-stem cell resulted in a change in morphology and enhanced migration to more closely match stem cell-like features. Mass spectrometry analysis revealed a significant enrichment of extracellular matrix (ECM) proteins in the Y201 stem cell secretome compared to Y202 stromal cells. We confirmed that Y201 produced a more robust ECM in culture compared to Y202. Growth of Y202 on ECM produced by Y201 or Y202 restored migration and fibroblastic morphology, suggesting that it is the deficiency of ECM production that contributes to its phenotype. The proteins periostin and aggrecan, were detected at 71- and 104-fold higher levels in the Y201 versus Y202 secretome and were subsequently identified by immunofluorescence at rare sites on the endosteal surfaces of mouse and human bone, underlying CD271-positive stromal cells. These proteins may represent key non-cellular components of the microenvironment for bona-fide stem cells important for cell maintenance and phenotype in vivo.ConclusionsWe identified plasticity in BMSC morphology and migratory characteristics that can be modified through secreted proteins, particularly from multipotent stem cells. Overall, we demonstrate the importance of specific ECM proteins in co-ordination of cellular phenotype and highlight how non-cellular components of the BMSC microenvironment may provide insights into cell population heterogeneity and the role of BMSCs in health and disease.

General anaesthetics reduce acute lymphoblastic leukaemia malignancies in vitro and in vivovia CXCR4 and osteopontin mediated mechanisms.

Acute lymphoblastic leukaemia (ALL) is a common type of cancer in children. General anaesthetics are often used on patients undergoing painful procedures during ALL treatments but their effects on ALL malignancy remain unknown. Herein, we aim to study the effect of propofol and sevoflurane on the migration, homing and chemoresistance of ALL cells. NALM-6 and Reh cells were treated with propofol (5 and 10 μg/ml) or sevoflurane (3.6%) in vitro for six hours. Then, cells were harvested for adhesion assay and migration assay in vitro. In in vivo experiments, GFP-NALM-6 cells were pre-treated with propofol (10 μg/ml) or sevoflurane (3.6%) for six hours. Then, cells were injected intravenously to C57BL/6 female mice followed by intravital microscopy. For chemoresistance study, cells were treated with rising concentrations of Ara-c (0.05-50 nM) plus 10μg/ml of propofol or Ara-C plus 3.6% of sevoflurane for 4 hours, followed by the assessment of cell viability via CCK-8 assay and detection of autophagy via flow cytometry. Both anaesthetics reduced in vivo migration and in vivo homing as exemplified by 1) the reduction in the number of cells entering the bone marrow and 2) the disturbance in homing location in relation to endosteal surface. Our results indicated that general anaesthetics reduced the surface CXCR4 expression and the adhesion of leukaemia cells to thrombin cleaved osteopontin (OPN) was reduced. Those changes might result in the alterations in migration and homing. In addition, both anaesthetics sensitised ALL cells to Ara-c possibly through CXCR4 mediated mechanisms. Propofol but not sevoflurane enhanced chemo-related cell death via inducing cytotoxic autophagy. Together, our data suggest that both propofol and sevoflurane could reduce ALL migration, and homing in vivo and in vitro via CXCR4 and OPN mediated mechanisms. Both anaesthetics could sensitise ALL cells to chemotherapy possibly via CXCR4 mediated mechanisms.

Cortical thickness adaptation to combined mechanical loading and parathyroid hormone treatments is site specific and synergistic in the mouse tibia model

In this study, we aimed to quantify the localised effects of mechanical loading (ML), low (20 μg/kg/day), moderate (40 μg/kg/day) or high (80 μg/kg/day) dosages of parathyroid hormone (PTH), and combined (PTHML) treatments on cortical bone adaptation in healthy 19-week old female C57BL/6 mice. To this end, we utilise a previously reported image analysis algorithm on μCT data of the mouse tibia published by Sugiyama et al. (2008) to measure changes in cortical area, marrow cavity area and local cortical thickness measures (ΔCt.Ar, ΔMa.Ar, ΔCt.Th respectively), evaluated at two cross-sections within the mouse tibia (proximal-middle (37 %) and middle (50 %)), and are compared to a superposed summation (P + M) of individual treatments to determine the effectiveness of combining treatments in vivo. ΔCt.Ar analysis revealed a non-linear, synergistic interactions between PTH and ML in the 37 % cross-section that saturates at higher PTH dosages, whereas the 50 % cross-section experiences an approximately linear, additive adaptation response. This coincided with an increase in ΔMa.Ar (indicating resorption of the endosteal surface), which was only counteracted by combined high dose PTH with ML in the middle cross-section. Regional analysis of ΔCt.Th changes reveal localised cortical thinning in response to low dose PTH treatment in the posteromedial region of the middle cross-section, signifying that PTH does not provide a homogeneous adaptation response around the cortical perimeter. We observe a synergistic response in the proximal-middle cross-section, with regions of compressive strain experiencing the greatest adaptation response to PTHML treatments, (peak ΔCt.Th of 189.32, 213.78 and 239.30 μm for low, moderate and high PTHML groups respectively). In contrast, PTHML treatments in the middle cross-section show a similar response to the superposed P + M group, with the exception of the combined high dose PTHML treatment which shows a synergistic interaction. These analyses suggest that, in mice, adding mechanical loading to PTH treatments leads to region specific bone responses; synergism of PTHML is only achieved in some regions experiencing high loading, while other regions respond additively to this combined treatment.

Derivation, validation, and prediction of loading-induced mineral apposition rates at endocortical and periosteal bone surfaces based on fluid velocity and pore pressure

The capacity of bone to optimize its structure in response to mechanical loads has been widely observed. The mechanical load acting on a bone at the macroscopic level influences the bone cells, particularly osteocytes within the lacunae canalicular network (LCN). Osteocytes are responsive to a range of physical signals, including strain, interstitial fluid flow, and pore pressure. However, physiological tissue strain is known to be typically smaller than that required to directly induce bone formation. On the other hand, as per evidence provided by this study from the literature, models based on fluid flow alone cannot simultaneously predict bone formation at both the periosteal and endocortical surfaces. This suggests that another component of the osteocyte's mechanical environment, such as pore pressure, may play an essential role in bone adaptation, either alone or in combination with other stimuli, such as tissue strain and/or interstitial fluid flow. In vitro experiments have also confirmed that osteocytes respond to cyclic pore pressure and, thus, have a mechanism to sense the pressure, possibly because of its viscoelasticity.In this work, dissipation energy density, being irreversible work done per unit volume, has been successfully used as a greater stimulus to incorporate all of the parameters of mechanical environments of the LCN, such as waveforms of both fluid velocity and pore pressure, number of loading cycles. Mineral Apposition Rate (MAR) has also been mathematically derived to be proportional to the square root of the dissipation energy density minus its reference value. A hypothesis is accordingly proposed and successfully tested/validated for both endocortical and periosteal surfaces with respect to an in-vivo study on mouse tibia available in the literature. The constant of proportionality and the reference/threshold value of the dissipation energy density are determined through a nonlinear curve fitting. The mathematical/computational method thus developed is then successfully used to predict MAR at both endocortical and periosteal surfaces induced by a different loading condition.Computational implementation of the mathematical model has been done through a poroelastic finite element analysis of bone, where bone is assumed to be porous and filled with fluid, with a boundary condition that the periosteum is impermeable to the fluid and the endosteal surface maintains a reference zero pressure. This work also provides evidence for these assumptions to be true based on the state-of-the-art literature on related experimental studies. The currently developed model shows that the bone uses these conditions (assumptions) to its advantage, as the greater stimulus, i.e., the dissipation energy due to both fluid flow and pore pressure, are of a similar order at both the surfaces, and hence osteogenesis of the same order at both the surfaces.As a bottom line, the resulting model is the first of its kind as it has been able to correctly predict MAR at both endocortical and periosteal surfaces. This study thus significantly advances the modeling of cortical bone adaptation to exogenous mechanical loading.

Agomelatine alleviates steroid-induced osteoporosis by targeting SIRT1/RANKL/FOXO1/OPG signalling in rats.

One of the major contributors to secondary osteoporosis is long-term glucocorticoid usage. Clinically used antidepressant agomelatine also has anti-inflammatory properties. Our research aimed to inspect the probable defensive effect of agomelatine against steroid-promoted osteoporosis. There were four groups of rats; group I had saline as a negative control; rats of group II had dexamethasone (0.6 mg/kg, s.c.), twice weekly for 12 weeks; rats of group III had agomelatine (40 mg/kg/day, orally), as a positive control, daily for 12 weeks; and rats of group IV had dexamethasone + agomelatine in the same previous doses combined for 12 weeks. Finally, biochemical as well as histopathological changes were evaluated and dexamethasone treatment caused osteoporosis, as evidenced by discontinuous thin cancellous bone trabeculae, minor fissures and fractures, irregular eroded endosteal surface with elevated alkaline phosphate, tartarate resistant acid phosphate (TRACP) and osteocalcin levels. Osteoprotegerin (OPG), calcium, and phosphorus levels decreased with disturbed receptor activator of nuclear factor κ B ligand (RANKL), forkhead box O1 (FOXO1), and silent information regulator 1 (SIRT1)protein expression. However, treatment with agomelatine restored the normal levels of biochemical parameters to a great extent, supported by SIRT activation with an improvement in histopathological changes. Here, we concluded that agomelatine ameliorates steroid-induced osteoporosis through a SIRT1/RANKL/FOXO1/OPG-dependent pathway.

Elemental Bioimaging of Sheep Bone and Articular Cartilage After Single Application of Gadolinium-Based Contrast Agents.

Gadolinium-based contrast agents (GBCAs) are applied to enhance magnetic resonance imaging. Gadolinium (Gd), a rare earth metal, is used in a chelated form when administered as GBCA to patients. There is an ongoing scientific debate about the clinical significance of Gd retention in tissues after administration of GBCAs. It is known that bone serves as Gd reservoir, but only sparse information on localization of Gd in bone is available. The aim of this study was to compare Gd tissue concentration and spatial distribution in femoral epiphysis and diaphysis 10 weeks after single-dose injection of linear and macrocyclic GBCAs in a large animal model. In this prospective animal study, Swiss-Alpine sheep (n = 36; age range, 4-10 years) received a single injection (0.1 mmol/kg) of macrocyclic (gadobutrol, gadoteridol, and gadoterate meglumine), linear (gadodiamide and gadobenate dimeglumine) GBCAs, or saline. Ten weeks after injection, sheep were killed, and femur heads and shafts were harvested. Gadolinium spatial distribution was determined in 1 sample of each treatment group by laser ablation-inductively coupled plasma-mass spectrometry. All bone specimens were analyzed histopathologically. Injection of GBCAs in female Swiss-Alpine sheep (n = 36) resulted in Gd localization at the endosteal and periosteal surface and in a subset of GBCAs additionally at the cement lines and the bone cartilage junction. No histopathological alterations were observed in the investigated tissue specimens. Ten weeks after single injection of a clinically relevant dose in adult sheep, both linear species of GBCA resulted in considerably higher accumulation than macrocyclic GBCAs. Gadolinium deposits were restricted to distinct bone and cartilage compartments, such as in bone linings, cement lines, and bone cartilage junctions. Tissue histology remained unaffected.

Optical coherence tomography application for assessing variation in bone mineral content: a preclinical study.

Optical Coherence Tomography (OCT) is a non-invasive imaging technique that produces cross-sectional images through biological tissues, allowing three-dimensional reconstruction and analysis. Aim was to evaluate if OCT may discriminate among tissues with different bone density and composition, by measuring the depth of light penetration in porcine and rat bone samples. Two carpal bone samples (2 cm length) were harvested from the porcine forelimb and fixed overnight in 3.7% buffered formal saline. Following fixation, one sample was decalcified in a 1:1 mixture of 8% hydrochloric acid and 8% formic acid solution for three days, with solution changes each day. Samples were imaged using an OCT microscope. Furthermore, the calvaria, ulnar, alveolar and basal bone of the mandible of 6 male and 6 female rats were cleared of overlying soft tissues and scanned under OCT. The light penetration depth in each sample was measured using the software Image J, and Scattering Attenuation Microscopy. In the mineralized bone the average depth (µm) and standard deviation (SD) of light penetration were 790.1±18.05 and 410.4±21.7 for periosteal and endosteal surface, respectively, and 507.3±21.03 for cross-section surfaces, while it was 858.4±32.03 for periosteal surface, 1150±26.9 for endosteal, and 627.3±31.8 for cross-section bone surfaces in demineralized porcine bone. There was a significant difference (p<0.001) in depth of light penetration between normal and de-mineralized bone for all regions evaluated. No systematic significant difference in light penetration depth between-gender was found at any site evaluated, while there were variations between sites (p<0.001). The OCT detected differences in bone mineral and porosity among gender (p<0.0001) CONCLUSIONS: This study suggests that OCT may represent a valuable technique to estimate local variations in bone mineral content.

Csf1 from marrow adipogenic precursors is required for osteoclast formation and hematopoiesis in bone.

Colony-stimulating factor 1 (Csf1) is an essential growth factor for osteoclast progenitors and an important regulator for bone resorption. It remains elusive which mesenchymal cells synthesize Csf1 to stimulate osteoclastogenesis. We recently identified a novel mesenchymal cell population, marrow adipogenic lineage precursors (MALPs), in bone. Compared to other mesenchymal subpopulations, MALPs expressed Csf1 at a much higher level and this expression was further increased during aging. To investigate its role, we constructed MALP-deficient Csf1 CKO mice using AdipoqCre. These mice had increased femoral trabecular bone mass, but their cortical bone appeared normal. In comparison, depletion of Csf1 in the entire mesenchymal lineage using Prrx1Cre led to a more striking high bone mass phenotype, suggesting that additional mesenchymal subpopulations secrete Csf1. TRAP staining revealed diminished osteoclasts in the femoral secondary spongiosa region of Csf1 CKOAdipoq mice, but not at the chondral-osseous junction nor at the endosteal surface of cortical bone. Moreover, Csf1 CKOAdipoq mice were resistant to LPS-induced calvarial osteolysis. Bone marrow cellularity, hematopoietic progenitors, and macrophages were also reduced in these mice. Taken together, our studies demonstrate that MALPs synthesize Csf1 to control bone remodeling and hematopoiesis.

Postnatal Osterix but not DMP1 lineage cells significantly contribute to intramembranous ossification in three preclinical models of bone injury.

Murine models of long-bone fracture, stress fracture, and cortical defect are used to discern the cellular and molecular mediators of intramembranous and endochondral bone healing. Previous work has shown that Osterix (Osx+) and Dentin Matrix Protein-1 (DMP1+) lineage cells and their progeny contribute to injury-induced woven bone formation during femoral fracture, ulnar stress fracture, and tibial cortical defect repair. However, the contribution of pre-existing versus newly-derived Osx+ and DMP1+ lineage cells in these murine models of bone injury is unclear. We addressed this knowledge gap by using male and female 12-week-old, tamoxifen-inducible Osx Cre_ERT2 and DMP1 Cre_ERT2 mice harboring the Ai9 TdTomato reporter allele. To trace pre-existing Osx+ and DMP1+ lineage cells, tamoxifen (TMX: 100mg/kg gavage) was given in a pulse manner (three doses, 4weeks before injury), while to label pre-existing and newly-derived lineage Osx+ and DMP1+ cells, TMX was first given 2weeks before injury and continuously (twice weekly) throughout healing. TdTomato positive (TdT+) cell area and cell fraction were quantified from frozen histological sections of injured and uninjured contralateral samples at times corresponding with active woven bone formation in each model. We found that in uninjured cortical bone tissue, Osx Cre_ERT2 was more efficient than DMP1 Cre_ERT2 at labeling the periosteal and endosteal surfaces, as well as intracortical osteocytes. Pulse-labeling revealed that pre-existing Osx+ lineage and their progeny, but not pre-existing DMP1+ lineage cells and their progeny, significantly contributed to woven bone formation in all three injury models. In particular, these pre-existing Osx+ lineage cells mainly lined new woven bone surfaces and became embedded as osteocytes. In contrast, with continuous dosing, both Osx+ and DMP1+ lineage cells and their progeny contributed to intramembranous woven bone formation, with higher TdT+ tissue area and cell fraction in Osx+ lineage versus DMP1+ lineage calluses (femoral fracture and ulnar stress fracture). Similarly, Osx+ and DMP1+ lineage cells and their progeny significantly contributed to endochondral callus regions with continuous dosing only, with higher TdT+ chondrocyte fraction in Osx+ versus DMP1+ cell lineages. In summary, pre-existing Osx+ but not DMP1+ lineage cells and their progeny make up a significant amount of woven bone cells (particularly osteocytes) across three preclinical models of bone injury. Therefore, Osx+ cell lineage modulation may prove to be an effective therapy to enhance bone regeneration.

General anaesthetics reduce acute lymphoblastic leukaemia cell migration and homing in vitro and in vivo via CXCR4 and osteopontin mediated mechanisms

Background: Acute lymphoblastic leukaemia (ALL) is the most common type of cancer in children. General anaesthetics are often used on patients undergoing painful procedures during ALL treatments but their effects on ALL malignancy remain unknown. Herein, we aim to study the effect of two commonly used general anaesthetics, intravenous propofol and inhalational sevoflurane, on the migration and homing of ALL cells in vitro and in vivo. Methods: NALM-6 cells were treated with propofol (5 and 10 μg/ml) or sevoflurane (3.6%) in vitro for six hours. Then, cells were harvested for flow cytometry analysis. For in vitro migration experiments, NALM-6 cells were pre-treated with propofol and sevoflurane for six hours before being loaded onto the upper chamber of a migration chamber and cells were collected in the lower chamber after six hours of migration. For in vivo adhesion assays, NALM-6 cells were pre-treated with propofol and sevoflurane before an adhesion assay was carried out. In in vitro experiments, GFP-NALM-6 cells were pre-treated with propofol (10 μg/ml) or sevoflurane (3.6%) for six hours. Then, cells were injected intravenously to C57BL/6 female mice followed by intravital microscopy. Results: Both anaesthetics reduced in vitro migration, in vivo migration and in vivo homing as exemplified by 1) the reduction in the number of cells entering the bone marrow and 2) the disturbance in homing location in relation to the nearest endosteal surface. Our results indicated that general anaesthetics reduced the surface CXCR4 expression. In addition, the adhesion of leukaemia cells to thrombin cleaved osteopontin (OPN) was reduced by general anaesthetics. Those changes might result in the alterations in migration and homing. Conclusion: Together, our data suggest that both propofol and sevoflurane could reduce ALL migration and homing in vivo and in vitro via CXCR4 and OPN mediated mechanisms.

Tracking changes of individual cortical pores over 1 year via HR-pQCT in a small cohort of 60-year-old females

IntroductionHigh-resolution peripheral quantitative computed tomography (HR-pQCT) is a powerful tool that has revolutionized 3D longitudinal assessment of bone microarchitecture. However, cortical porosity, a common characteristic of cortical bone loss, is still often determined by static evaluation of overall porosity at one timepoint. Therefore, we sought to 1) describe a technique to evaluate individual cortical pore dynamics in aging females over one year using HR-pQCT imaging and 2) determine whether formation and expansion of pores would exceed contraction and infilling of pores. MethodsHR-pQCT (60.7 μm resolution) images were acquired one year apart at the distal tibia and distal radius in seven female volunteers (60–72 years of age). Baseline and one-year images were registered at each bone site and a custom software was used to quantify dynamic activity of individual cortical pores using the following categories: developed, infilled, expanded, contracted, and static. ResultsOver the one-year period, cortical pores actively developed, contracted, expanded, and infilled. More pores expanded and developed vs. infilled or contracted leading to increased pore area in both tibial and radial sites (p = 0.0034 and p = 0.0474, respectively). Closed pores in the tibia, those that were not connected to the endosteal or periosteal surfaces, were the most dynamic of any pores type (open/closed) at either bone site. ConclusionThis study demonstrates an approach to longitudinally track individual cortical pore activity in tibial and radial sites. These data expand conventional parameters for assessing cortical porosity and show increased porosity in one year of aging is caused by newly developed pores and expansion of existing pores.

Elemental Imaging of Long-term Gadolinium Retention in Rodent Femur.

Background The use of gadolinium-based contrast agents (GBCAs) is linked to gadolinium retention in the skeleton of healthy individuals. The mechanism of gadolinium incorporation into bone tissue is not fully understood and requires spatially resolved analysis to locate the gadolinium. Purpose To compare the quantitative distribution of gadolinium retained over time in rodent femur following the administration of gadodiamide and gadobutrol at three different time points. Materials and Methods In this animal study conducted between May 2018 and April 2020, 108 9-week-old healthy rats were repeatedly injected with either gadodiamide, gadobutrol, or saline solution and were killed 1, 3, or 12 months after the last injection. The femurs of six female and six male rats per each group and time point were collected. Quantitative elemental imaging of gadolinium in longitudinal thin sections was performed on one sample per sex with use of laser ablation inductively coupled plasma mass spectrometry (ICP-MS). Gadolinium concentration was determined with use of ICP-MS on the samples of all animals (six per group). Mann-Whitney U tests were applied on pairwise comparisons to determine potential sex effect and GBCA effect on gadolinium concentrations. Results The highest gadolinium retention was observed in the gadodiamide group (concentration, 97-200 nmol · g-1), exceeding the mean concentration in the gadobutrol group (6.5-17 nmol · g-1). However, the gadolinium distribution pattern was similar for both contrast agents, showing prominent gadolinium retention at endosteal surfaces, in the bone marrow, and in small tissue pores. Gadolinium distribution in cortical bone changed over time, initially showing a thin rim of higher concentration close to the periosteum, which appeared to grow wider and move toward the interior of the femur over 1 year. Conclusion For both gadolinium-based contrast agents, gadolinium retention in rat bone was initially located close to the periosteum and bone cavities and changed with bone remodeling processes. The relevance to long-term storage of gadolinium in humans remains to be determined. © RSNA, 2022 Online supplemental material is available for this article.

Appositional long bone growth: Implications for measuring cross‐sectional geometry

AbstractObjectivesAs growth at the periosteal and endosteal surfaces varies with age, cross‐sectional geometric (CSG) properties derived from periosteal (“solid”) contours may not produce comparable results to those from endosteal and periosteal contours (“true”), contrary to findings from adults. Error in CSG properties derived from the “solid” sections is compared with “true” sections in a sample of archeologically derived skeletons with estimated dental ages ranging from 1.5 months to 23.5 years.Materials and MethodsCross sections were extracted from 3D surface models, and endosteal contours were located from biplanar radiographs for 56 femora and 59 humeri. Polar second moment of area (J), cross‐sectional shape (Imax/Imin), and polar section modulus (Zp) were calculated from solid and true sections. Relationships between solid and true properties were examined with least squares regression. Multiple regression examined the effect of age and % cortical area on solid section CSG error.ResultsWhile correlations were high (R2 = 0.72–0.99, all p &lt; 0.001), the results indicate that solid CSG properties are not within an acceptable error range (%SEE of ≤8.0, and %PE of ≤5.0) of true CSG. Error was most affected by %CA, while estimated age was not correlated with %CA, %PE, or percent difference of true‐solid CSG.DiscussionPeriosteal contours alone should not be used to calculate CSG properties from individuals during the period of growth and development. Variation in bone growth and/or adaptive responses independent of age may account for the inconsistent age effects.

The Morphometric analysis of accessory sutural bones with an emphasis on association with parietal emissary foramina

Background: The sutural bones and fontanelle of the skull display unique morphological characters. Sutural bones are also called supernumerary bones or ossicles or Wormian bones (WB). These are irregular and develop from the independent ossification centers present along the cranial sutures. They appear on periosteal and endosteal surfaces of the skull with variations in size, number, shape, and location. In the present study, we aimed to determine the morphological characteristics of sutural bones and emphasize the significance of the same. One interesting entity of skull near the posterior fontanelle is the presence of Inca bones. Methods: The present study was done on 128 dry human skulls by a convenient sampling method. The skulls were collected from the Department of Anatomy and significant characteristic features of Inca and Wormian bones like shape, number, size and location were recorded. Results: Of the 128 dry skulls examined Wormian bones were seen in 13.2 % of skulls and Inca bones in 5.4 % of skulls. Incorporation of Wormian bones in lambdoid suture was noted in 12.5 % in sagittal suture in 0.7 % skulls respectively. The Wormian bones were found frequently on the left side (n=12) as compared to the right side (n=5). The morphometry of the accessory bones showed quadrilateral as the most common shape (n=9, 37.5 %) followed by triangular (n=4, 16.6 %). Radiological examination of all 24 skulls with accessory bones showed a zigzag pattern of accessory suture lines. Conclusions: The presence of Wormian and Inca bones can be easily confused with fractures of the related bony regions. The surgeons need to be aware of this fact in order to make a proper and accurate diagnosis. The knowledge regarding these bones is highly beneficial to the clinician, radiologist, and neurosurgeon.

Prediction of cortical bone mineral apposition rate in response to loading using an adaptive neuro-fuzzy inference system

Daily activities such as aerobic movements and athletic events found effective in mitigating bone loss as it promotes osteogenesis. Computational model considered normal strain, or strain energy density as a stimulus to predict site specific osteogenesis. This model, however, fails to predict site specific osteogenesis as cortical bone surfaces exhibit different remodelling rate to mechanical loading. Remodelling rate or mineral apposition rate depends upon the loading parameters such as loading cycle, frequency, and magnitude of strain. Therefore, the present study aims to develop an adaptive neuro-fuzzy inference system (ANFIS) model for finding a robust relationship between loading parameters like strain magnitude, frequency, and cycle, and a bone remodelling parameter i.e. mineral apposition rate (MAR). The model is trained, tested, and checked with the experimental data. The results indicate that ANFIS model outperformed state of the art Artificial Neural Network (ANN) models during the prediction of MAR at periosteal and endosteal surface. A strong corelation R2 = 0.92 and R2 = 0.97 was observed at 70% of the input data at periosteal and endosteal surface respectively. Result concludes that endosteal surface was more promisable as compared to periosteal surface in predicting accurate MAR. The outcomes of present study may be used to precisely predict site-specific osteogenesis in cortical bone as function of loading parameters.

Post natal expression of Prx1 labels appendicular restricted progenitor cell populations of multiple tissues.

Currently, there is no consensus whether there is a single or multiple postnatal stem cell population(s) that contribute to skeletal homeostasis and postnatal bone formation. A known population of cells that express Prx1 contributes to postnatal bone formation. Prx1 expression also connotes calvaria and appendicular tissues during embryonic development. A transgenic tamoxifen inducible Prx1 reporter mouse was used for lineage tracking, to characterize the postnatal contribution of Prx1 expressing cells in skeletal homeostasis and bone formation. Under homeostatic conditions Prx1 labeling gave rise to a transient yet rapid turnover cell population at the periosteal and endosteal surfaces, along muscle fibers, and within the medial layers of vessels both within the muscle and marrow compartments of the appendicular skeleton. Fracture and ectopic bone formation of both fore and hind limbs showed recruitment and expansion of Prx1-derived cells in newly formed bone tissues. Prx1 labeled cells were limited or absent at axial skeletal sites during both homeostasis and after induction of bone formation. Last, Prx1-derived cells differentiated into multiple cell lineages including vascular smooth muscle, adipose, cartilage, and bone cells. These results show that Prx1 expression retained its embryonic tissue specification and connotes a stem/progenitor cell populations of mesenchymal tissue progenitors.

Sfrp4 and the Biology of Cortical Bone.

Periosteal apposition and endosteal remodeling regulate cortical bone expansion and thickness, both critical determinants of bone strength. Yet, the cellular characteristics and local or paracrine factors that regulate the periosteum and endosteum remain largely elusive. Here we discuss novel insights in cortical bone growth, expansion, and homeostasis, provided by the study of Secreted Frizzled Receptor Protein 4 (Sfrp4), a decoy receptor for Wnt ligands. SFRP4 loss-of function mutations cause Pyle disease, a rare skeletal disorder characterized by cortical bone thinning and increased fragility fractures despite increased trabecular bone density. On the endosteal surface, Sfrp4-mediated repression of non-canonical Wnt signaling regulates endosteal resorption. On the periosteum, Sfrp4 identifies as a critical functional mediator of periosteal stem cell/progenitor expansion and differentiation. Analysis of signaling pathways regulating skeletal stem cells/progenitors provides an opportunity to advance our understanding of the mechanisms involved in cortical bone biology.

Effect of Intramedullary Nailing Patterns on Interfragmentary Strain in a Mouse Femur Fracture: A Parametric Finite Element Analysis.

Delayed long bone fracture healing and nonunion continue to be a significant socioeconomic burden. While mechanical stimulation is known to be an important determinant of the bone repair process, understanding how the magnitude, mode, and commencement of interfragmentary strain (IFS) affect fracture healing can guide new therapeutic strategies to prevent delayed healing or nonunion. Mouse models provide a means to investigate the molecular and cellular aspects of fracture repair, yet there is only one commercially available, clinically-relevant, locking intramedullary nail (IMN) currently available for studying long bone fractures in rodents. Having access to alternative IMNs would allow a variety of mechanical environments at the fracture site to be evaluated, and the purpose of this proof-of-concept finite element analysis study is to identify which IMN design parameters have the largest impact on IFS in a murine transverse femoral osteotomy model. Using the dimensions of the clinically relevant IMN as a guide, the nail material, distance between interlocking screws, and clearance between the nail and endosteal surface were varied between simulations. Of these parameters, changing the nail material from stainless steel (SS) to polyetheretherketone (PEEK) had the largest impact on IFS. Reducing the distance between the proximal and distal interlocking screws substantially affected IFS only when nail modulus was low. Therefore, IMNs with low modulus (e.g., PEEK) can be used alongside commercially available SS nails to investigate the effect of initial IFS or stability on fracture healing with respect to different biological conditions of repair in rodents.