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Crouzon syndrome is a congenital craniofacial disorder caused by mutations in the Fibroblast Growth Factor Receptor 2 (FGFR2). It is characterized by the premature fusion of cranial sutures, leading to a brachycephalic head shape, and midfacial hypoplasia. The aim of this study was to investigate the effect of the FGFR2 mutation on the microarchitecture of cranial bones at different stages of postnatal skull development, using the FGFR2C342Y mouse model. Apart from craniosynostosis, this model shows cranial bone abnormalities. High-resolution synchrotron microtomography images of the frontal and parietal bone were acquired for both FGFR2C342Y/+ (Crouzon, heterozygous mutant) and FGFR2+/+ (control, wild-type) mice at five ages (postnatal days 1, 3, 7, 14 and 21, n = 6 each). Morphometric measurements were determined for cortical bone porosity: osteocyte lacunae and canals. General linear model to assess the effect of age, anatomical location and genotype was carried out for each morphometric measurement. Histological analysis was performed to validate the findings. In both groups (Crouzon and wild-type), statistical difference in bone volume fraction, average canal volume, lacunar number density, lacunar volume density and canal volume density was found at most age points, with the frontal bone generally showing higher porosity and fewer lacunae. Frontal bone showed differences between the Crouzon and wild-type groups in terms of lacunar morphometry (average lacunar volume, lacunar number density and lacunar volume density) with larger, less dense lacunae around the postnatal age of P7-P14. Histological analysis of bone showed marked differences in frontal bone only. These findings provide a better understanding of the pathogenesis of Crouzon syndrome and will contribute to computational models that predict postoperative changes with the aim to improve surgical outcome.
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BACKGROUND: Endoscopic strip craniectomy followed by helmet therapy (ESCH) is a minimally invasive approach for correcting sagittal craniosynostosis. The treatment involves a patient-specific helmet designed to facilitate lateral growth while constraining sagittal expansion. In this study, finite element modelling was used to predict post-treatment head reshaping, improving our comprehension of the necessary helmet therapy duration. METHOD: Six patients (aged 11 weeks to 9 months) who underwent ESCH at Connecticut Children's Hospital were enrolled in this study. Day-1 post-operative 3D scans were used to create skin, skull, and intracranial volume models. Patient-specific helmet models, incorporating areas for growth, were designed based on post-operative imaging. Brain growth was simulated through thermal expansion, and treatments were modelled according to post-operative Imaging available. Mechanical testing and finite element modelling were combined to determine patient-specific mechanical properties from bone samples collected from surgery. Validation compared simulated end-of-treatment skin surfaces with optical scans in terms of shape matching and cranial index estimation. RESULTS: Comparison between the simulated post-treatment head shape and optical scans showed that on average 97.3 ± 2.1 % of surface data points were within a distance range of -3 to 3 mm. The cranial index was also accurately predicted (r = 0.91). CONCLUSIONS: In conclusion, finite element models effectively predicted the ESCH cranial remodeling outcomes up to 8 months postoperatively. This computational tool offers valuable insights to guide and refine helmet treatment duration. This study also incorporated patient-specific material properties, enhancing the accuracy of the modeling approach.
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Craniossinostoses , Dispositivos de Proteção da Cabeça , Humanos , Craniossinostoses/cirurgia , Craniossinostoses/diagnóstico por imagem , Lactente , Masculino , Feminino , Craniotomia , Simulação por Computador , Análise de Elementos Finitos , Endoscopia/métodos , Cabeça/diagnóstico por imagem , Cabeça/cirurgiaRESUMO
Age-related muscle loss poses a significant health concern in an aging population. This study aimed to assess the impact of a home Full-Body in-Bed Gym protocol on quality of life, pain and risk of sarcopenia in elderly subjects. A total of 22 subjects with a median age of 71.90 years were included in the study. Patients participating in the Full-Body in-Bed Gym program, with a frequency of three times a week for two months, demonstrated a significant enhancement in their quality of life, as indicated by the 12-Item Short Form Health Survey (SF-12) Mental Component Summary (p = 0.04), and an improvement in pain levels (p = 0.03). Although not statistically significant, there was also an improvement in sarcopenia risk. Patients were given the freedom to decide whether to continue treatment after the evaluation of outcomes. Patient compliance with the exercise protocol over six months indicated its feasibility and sustainability, even in the long term. These findings suggest that the Full-Body in-Bed Gym protocol may play a valuable role in mitigating age-related muscle loss, emphasizing the importance of further investigation into such rehabilitation and prevention strategies.
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The middle ear is part of the ear in all terrestrial vertebrates. It provides an interface between two media, air and fluid. How does it work? In mammals, the middle ear is traditionally described as increasing gain due to Helmholtz's hydraulic analogy and the lever action of the malleus-incus complex: in effect, an impedance transformer. The conical shape of the eardrum and a frequency-dependent synovial joint function for the ossicles suggest a greater complexity of function than the traditional view. Here we review acoustico-mechanical measurements of middle ear function and the development of middle ear models based on these measurements. We observe that an impedance-matching mechanism (reducing reflection) rather than an impedance transformer (providing gain) best explains experimental findings. We conclude by considering some outstanding questions about middle ear function, recognizing that we are still learning how the middle ear works.
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About 70% of people with osteogenesis imperfecta (OI) experience hearing loss. There is no cure for OI, and therapies to ameliorate hearing loss rely on conventional treatments for auditory impairments in the general population. The success rate of these treatments in the OI population with poor collagenous tissues is still unclear. Here, we conduct a systematic review and meta-analysis on the efficacy of treatments addressing hearing loss in OI. This study conforms to the reporting standards of the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). Data sources include published articles in Medline via PubMed, Web of Science, Scopus, and Embase, from their inception to November 2020. Studies included individuals with OI undergoing a hearing loss treatment, having pre- and postoperative objective assessment of hearing function at a specified follow-up length. Our search identified 1144 articles, of which 67 were reviewed at full-text screening. A random-effects meta-analysis was conducted on the selected articles (n = 12) of people with OI that underwent stapes surgery. Success was assessed as the proportion of ears with a postoperative Air-Bone Gap (ABG) ≤ 10 dB. A systematic review was conducted on the remaining articles (n = 13) reporting on other treatments. No meta-analysis was conducted on the latter due to the low number of articles on the topic and the nature of single case studies. The meta-analysis shows that stapes surgeries have a low success rate of 59.08 (95% CI 45.87 to 71.66) in the OI population. The systematic review revealed that cochlear implants, bone-anchored hearing aids, and other implantable hearing aids proved to be feasible, although challenging, in the OI population, with only 2 unsuccessful cases among the 16 reviewed single cases. This analysis of published data on OI shows poor clinical outcomes for the procedures addressing hearing loss. Further studies on hearing loss treatments for OI people are needed. Notably, the mechanisms of hearing loss in OI need to be determined to develop successful and possibly non-invasive treatment strategies.
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Implante Coclear , Surdez , Perda Auditiva , Osteogênese Imperfeita , Cirurgia do Estribo , Surdez/cirurgia , Perda Auditiva/cirurgia , Perda Auditiva/terapia , Humanos , Osteogênese Imperfeita/complicações , Osteogênese Imperfeita/terapiaRESUMO
There is no cure for osteogenesis imperfecta (OI), and current treatments can only partially correct the bone phenotype. Stem cell therapy holds potential to improve bone quality and quantity in OI. Here, we conduct a systematic review and meta-analysis of published studies to investigate the efficacy of stem cell therapy to rescue bone brittleness in mouse models of OI. Identified studies included bone marrow, mesenchymal stem cells, and human fetal stem cells. Effect size of fracture incidence, maximum load, stiffness, cortical thickness, bone volume fraction, and raw engraftment rates were pooled in a random-effects meta-analysis. Cell type, cell number, injection route, mouse age, irradiation, anatomical bone, and follow up time were considered as moderators. It was not possible to investigate further parameters due to the lack of standards of investigation between the studies. Despite the use of oim mice in the majority of the investigations considered and the lack of sham mice as control, this study demonstrates the promising potential of stem cell therapy to reduce fractures in OI. Although their low engraftment, cell therapy in mouse models of OI had a beneficial effect on maximum load, but not on stiffness, cortical thickness and bone volume. These parameters all depend on bone geometry and do not inform on its material properties. Being bone fractures the primary symptom of OI, there is a critical need to measure the fracture toughness of OI bone treated with stem cells to assess the actual efficacy of the treatment to rescue OI bone brittleness.
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PURPOSE OF THE REVIEW: Bone's ability to withstand load resisting fracture and adapting to it highly depends on the quality of its matrix and its regulators. This review focuses on the contribution of bone quality to fracture resistance and possible therapeutic targets for skeletal fragility in aging and disease. RECENT FINDINGS: The highly organized, hierarchical composite structure of bone extracellular matrix together with its (re)modeling mechanisms and microdamage dynamics determines its stiffness, strength, and toughness. Aging and disease affect the biological processes regulating bone quality, thus resulting in defective extracellular matrix and bone fragility. Targeted therapies are being developed to restore bone's mechanical integrity. However, their current limitations include low tissue selectivity and adverse side effects. Biological and mechanical insights into the mechanisms controlling bone quality, together with advances in drug delivery and studies in animal models, will accelerate the development and translation to clinical application of effective targeted-therapeutics for bone fragility.
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Densidade Óssea/fisiologia , Matriz Óssea/patologia , Remodelação Óssea/fisiologia , Fraturas Ósseas/etiologia , Fraturas Ósseas/prevenção & controle , Matriz Óssea/metabolismo , HumanosRESUMO
Bone adapts its architecture to the applied load; however, it is still unclear how bone mechano-adaptation is coordinated and why potential for adaptation adjusts during the life course. Previous animal models have suggested strain as the mechanical stimulus for bone adaptation, but yet it is unknown how mouse cortical bone load-related strains vary with age and sex. In this study, full-field strain maps (at 1 N increments up to 12 N) on the bone surface were measured in young, adult, and old (aged 10, 22 weeks, and 20 months, respectively), male and female C57BL/6J mice with load applied using a noninvasive murine tibial model. Strain maps indicate a nonuniform strain field across the tibial surface, with axial compressive loads resulting in tension on the medial side of the tibia because of its curved shape. The load-induced surface strain patterns and magnitudes show sexually dimorphic changes with aging. A comparison of the average and peak tensile strains indicates that the magnitude of strain at a given load generally increases during maturation, with tibias in female mice having higher strains than in males. The data further reveal that postmaturation aging is linked to sexually dimorphic changes in average and maximum strains. The strain maps reported here allow for loading male and female C57BL/6J mouse legs in vivo at the observed ages to create similar increases in bone surface average or peak strain to more accurately explore bone mechano-adaptation differences with age and sex. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.
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Osteogenesis imperfecta (OI or brittle bone disease) is a group of genetic disorders of the connective tissues caused mainly by mutations in the genes encoding collagen type I. Clinical manifestations of OI include skeletal fragility, bone deformities, and severe functional disabilities, such as hearing loss. Progressive hearing loss, usually beginning in childhood, affects approximately 70% of people with OI with more than half of the cases involving the inner ear. There is no cure for OI nor a treatment to ameliorate its corresponding hearing loss, and very little is known about the properties of OI ears. In this study, we investigate the morphology of the otic capsule and the cochlea in the inner ear of the oim mouse model of OI. High-resolution 3D images of 8-week old oim and WT inner ears were acquired using synchrotron microtomography. Volumetric morphometric measurements were conducted for the otic capsule, its intracortical canal network and osteocyte lacunae, and for the cochlear spiral ducts. Our results show that the morphology of the cochlea is preserved in the oim ears at 8 weeks of age but the otic capsule has a greater cortical thickness and altered intracortical bone porosity, with a larger number and volume density of highly branched canals in the oim otic capsule. These results portray a state of compromised bone quality in the otic capsule of the oim mice that may contribute to their hearing loss.
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Orelha Interna/diagnóstico por imagem , Orelha Interna/fisiopatologia , Osteogênese Imperfeita/fisiopatologia , Animais , Densidade Óssea , Cóclea/diagnóstico por imagem , Cóclea/fisiopatologia , Modelos Animais de Doenças , Tomografia com Microscopia Eletrônica/métodos , Ósteon/diagnóstico por imagem , Ósteon/fisiopatologia , Masculino , Camundongos Mutantes , Osteogênese Imperfeita/etiologia , SíncrotronsRESUMO
This technical note describes synchrotron x-ray fluorescence microscopy (XFM) as a method for measuring the concentrations of different elements in cross-sections of the ear at extremely high resolution. This method could be of great importance for addressing many open questions in hearing research. XFM uses synchrotron radiation to evoke emissions from many biologically relevant elements in the tissue. The intensity and wavelength of the emitted radiation provide a fingerprint of the tissue composition that can be used to measure the concentration of the elements in the sampled location. Here, we focus on energies that target biologically-relevant elements of the periodic table between magnesium and zinc. Since a highly focused x-ray beam is used, the spot size is well below 1 µm and the samples can be scanned at a nanometer lateral resolution. This study shows that measurement of the concentrations of different elements is possible in a mid-modiolar cross-section of a mouse cochlea. Images are presented that indicate potassium and chloride "hot spots" in the spiral ligament and the spiral limbus, providing experimental evidence for the potassium recycling pathway and showing the cochlear structures involved. Scans of a section obtained from the incus, one of the middle ear ossicles, in a developing mouse have shown that zinc is not uniformly distributed This supports the hypothesis that zinc plays a special role in the process of ossification. Although limited by sophisticated sample preparation and sectioning, the method provides ample exciting opportunities, to understand the role of genetics and epigenetics on hearing mechanisms in ontogeny and phylogeny.
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Orelha Interna/metabolismo , Íons/metabolismo , Microscopia de Fluorescência , Espectroscopia por Absorção de Raios X , Fatores Etários , Animais , Camundongos Endogâmicos C57BL , SíncrotronsRESUMO
Vein grafts for coronary artery bypass are not available in more than 30% of patients due to prior use or systemic vascular diseases. Tissue engineered vascular grafts (TEVGs) have shown promise, but intimal hyperplasia and graft thrombosis are still concerns when grafted in small-diameter arteries. In this study, we utilized the peritoneal cavity as an "in vivo" bioreactor to recruit autologous cells to electrospun conduits enclosed within porous pouches to improve the response after grafting. Specifically, we designed a new poly (ethylene glycol)-based pouch to avoid adhesion to the peritoneal wall and still allow the necessary peritoneal fluid to reach the enclosed conduit. The pouch mechanics in compression and bending were determined through experiments and finite element simulations to optimize the pouch design. This included poly (ethylene glycol) concentration, pore density, and pouch size. We demonstrated that the optimized pouch was able to withstand the estimated forces applied in the rat peritoneal cavity and it allowed maturation of the enclosed electrospun conduit. This pouch significantly reduced peritoneal adhesion formation compared to polytetrafluoroethylene pouches that have been used previously, which overcomes this potential limitation to clinical translation. After aortic grafting of pre-conditioned conduits, patent grafts with limited intimal hyperplasia were observed. Overall, this study demonstrated a new pouch design that allows the in vivo bioreactor strategy to be used for vascular tissue engineering without the potential side effect of peritoneal adhesion formation.
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Prótese Vascular , Enxerto Vascular , Animais , Humanos , Politetrafluoretileno , Porosidade , Ratos , Engenharia TecidualRESUMO
Mechanoadaptation maintains bone mass and architecture; its failure underlies age-related decline in bone strength. It is unclear whether this is due to failure of osteocytes to sense strain, osteoblasts to form bone or insufficient mechanical stimulus. Mechanoadaptation can be restored to aged bone by surgical neurectomy, suggesting that changes in loading history can rescue mechanoadaptation. We use non-biased, whole-bone tibial analyses, along with characterisation of surface strains and ensuing mechanoadaptive responses in mice at a range of ages, to explore whether sufficient load magnitude can activate mechanoadaptation in aged bone. We find that younger mice adapt when imposed strains are lower than in mature and aged bone. Intriguingly, imposition of short-term, high magnitude loading effectively primes cortical but not trabecular bone of aged mice to respond. This response was regionally-matched to highest strains measured by digital image correlation and to osteocytic mechanoactivation. These data indicate that aged bone's loading response can be partially recovered, non-invasively by transient, focal high strain regions. Our results indicate that old murine bone does respond to load when the loading is of sufficient magnitude, and bones' age-related adaptation failure may be due to insufficient mechanical stimulus to trigger mechanoadaptation.
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Adaptação Fisiológica , Envelhecimento/patologia , Osso Cortical/patologia , Estresse Mecânico , Animais , CamundongosRESUMO
Tissue inhibitor of metalloproteinases-3 (TIMP-3) maintains a healthy extracellular matrix by regulating matrix metalloproteinases (MMP), disintegrin-metalloproteinases (ADAM), and disintegrin-metalloproteinases with ThromboSpondin-like motifs (ADAMTS) activity. Currently, there is a need for a comprehensive understanding of the effects of TIMP-3 on the bone quality and integrity. In this study, we examined the mechanical, morphological, and compositional properties of TIMP-3 knock out (Timp-3 -/-) mouse bone. We hypothesize that the lack of TIMP-3 plays an important role in maintaining the overall bone integrity. Mechanical properties of humeri, lumbar vertebrae, and femurs from Timp-3 -/- mice were determined using 3-point bending, compression, and notched 3-point bending, respectively. Morphological properties of the humeral cortical and trabecular bone and the caudal vertebrae cortical bone were evaluated using micro-computed tomography, while the composition of the femoral cortical and trabecular bone was examined using Fourier transform infrared spectroscopic imaging. Our results revealed that the integrity of the Timp-3 -/- bone is compromised due to changes in its composition, structure, and mechanics. Reductions in the yield and ultimate load and stress capacity, and loss in bone fracture toughness were attributed to reduced density and thickness, and increased porosity of cortical bone. Thin trabeculae were dense, highly connected, and closely packed in Timp-3 -/- bone. Furthermore, altered cortical and trabecular bone mineralization and increased compositional heterogeneity were found in Timp-3 -/- bone, all being indicative of high bone remodeling. In conclusion, this study suggests that the lack of TIMP-3 is detrimental to bone development and maintenance.
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Densidade Óssea/fisiologia , Osso e Ossos/metabolismo , Inibidor Tecidual de Metaloproteinase-3/metabolismo , Animais , Feminino , Fraturas Ósseas/metabolismo , Camundongos Endogâmicos C57BL , Camundongos Knockout , Inibidor Tecidual de Metaloproteinase-3/deficiênciaRESUMO
This study aimed at using eXtended finite element method (XFEM) to characterize crack growth through bone's intra-cortical pores. Two techniques were compared using Abaqus: (1) void material properties were assigned to pores; (2) multiple enrichment regions with independent crack-growth possibilities were employed. Both were applied to 2D models of transverse images of mouse bone with differing porous structures. Results revealed that assigning multiple enrichment regions allows for multiple cracks to be initiated progressively, which cannot be captured when the voids are filled. Therefore, filling pores with one enrichment region in the model will not create realistic fracture patterns in Abaqus-XFEM.
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Análise de Elementos Finitos , Fraturas Ósseas/patologia , Animais , Fenômenos Biomecânicos , Modelos Animais de Doenças , Fraturas Ósseas/fisiopatologia , Camundongos , Modelos Teóricos , Osteogênese Imperfeita/patologia , Osteogênese Imperfeita/fisiopatologia , PorosidadeRESUMO
Bone development and length relies on the growth plate formation, which is dependent on degradative enzymes such as MMPs. Indeed, deletion of specific members of this enzyme family in mice results in important joint and bone abnormalities, suggesting a role in skeletal development. As such, the control of MMP activity is vital in the complex process of bone formation and growth. We generated a transgenic mouse line to overexpress TIMP3 in mouse chondrocytes using the Col2a1-chondrocyte promoter. This overexpression in cartilage resulted in a transient shortening of growth plate in homozygote mice but bone length was restored at eight weeks of age. However, tibial bone structure and mechanical properties remained compromised. Despite no transgene expression in adult osteoblasts from transgenic mice in vitro, their differentiation capacity was decreased. Neonates, however, did show transgene expression in a subset of bone cells. Our data demonstrate for the first time that transgene function persists in the chondro-osseous lineage continuum and exert influence upon bone quantity and quality.
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Osso e Ossos/fisiologia , Cartilagem/metabolismo , Lâmina de Crescimento/fisiologia , Inibidor Tecidual de Metaloproteinase-3/metabolismo , Animais , Osso e Ossos/patologia , Células Cultivadas , Colágeno Tipo II/genética , Fêmur/diagnóstico por imagem , Fêmur/fisiologia , Lâmina de Crescimento/patologia , Humanos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos CBA , Camundongos Transgênicos , Osteoblastos/citologia , Osteoblastos/metabolismo , Osteogênese , Regiões Promotoras Genéticas , Resistência à Tração , Tíbia/diagnóstico por imagem , Tíbia/fisiologia , Inibidor Tecidual de Metaloproteinase-3/genéticaRESUMO
Osteogenesis imperfecta (OI), commonly known as brittle bone disease, is a genetic disease characterized by extreme bone fragility and consequent skeletal deformities. This connective tissue disorder is caused by mutations in the quality and quantity of the collagen that in turn affect the overall mechanical integrity of the bone, increasing its vulnerability to fracture. Animal models of the disease have played a critical role in the understanding of the pathology and causes of OI and in the investigation of a broad range of clinical therapies for the disease. Currently, at least 20 animal models have been officially recognized to represent the phenotype and biochemistry of the 17 different types of OI in humans. These include mice, dogs, and fish. Here, we describe each of the animal models and the type of OI they represent, and present their application in clinical research for treatments of OI, such as drug therapies (ie, bisphosphonates and sclerostin) and mechanical (ie, vibrational) loading. In the future, different dosages and lengths of treatment need to be further investigated on different animal models of OI using potentially promising treatments, such as cellular and chaperone therapies. A combination of therapies may also offer a viable treatment regime to improve bone quality and reduce fragility in animals before being introduced into clinical trials for OI patients.
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Joint morphogenesis is an important phase of prenatal joint development during which the opposing cartilaginous rudiments acquire their reciprocal and interlocking shapes. At an early stage of development, the prenatal hip joint is formed of a deep acetabular cavity that almost totally encloses the head. By the time of birth, the acetabulum has become shallower and the femoral head has lost substantial sphericity, reducing joint coverage and stability. In this study, we use a dynamic mechanobiological simulation to explore the effects of normal (symmetric), reduced and abnormal (asymmetric) prenatal movements on hip joint shape, to understand their importance for postnatal skeletal malformations such as developmental dysplasia of the hip (DDH). We successfully predict the physiological trends of decreasing sphericity and acetabular coverage of the femoral head during fetal development. We show that a full range of symmetric movements helps to maintain some of the acetabular depth and femoral head sphericity, while reduced or absent movements can lead to decreased sphericity and acetabular coverage of the femoral head. When an abnormal movement pattern was applied, a deformed joint shape was predicted, with an opened asymmetric acetabulum and the onset of a malformed femoral head. This study provides evidence for the importance of fetal movements in the prevention and manifestation of congenital musculoskeletal disorders such as DDH.
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Luxação Congênita de Quadril/fisiopatologia , Articulação do Quadril/fisiopatologia , Acetábulo/embriologia , Acetábulo/patologia , Fenômenos Biomecânicos , Simulação por Computador , Feminino , Cabeça do Fêmur/embriologia , Cabeça do Fêmur/patologia , Luxação Congênita de Quadril/embriologia , Articulação do Quadril/embriologia , Articulação do Quadril/patologia , Humanos , Modelos Biológicos , Morfogênese , Movimento , Gravidez , Amplitude de Movimento ArticularRESUMO
Bone fragility is a concern for aged and diseased bone. Measuring bone toughness and understanding fracture properties of the bone are critical for predicting fracture risk associated with age and disease and for preclinical testing of therapies. A reference point indentation technique (BioDent) has recently been developed to determine bone's resistance to fracture in a minimally invasive way by measuring the indentation distance increase (IDI) between the first and last indentations over cyclic indentations in the same position. In this study, we investigate the relationship between fracture toughness KC and reference point indentation parameters (i.e. IDI, total indentation distance (TID) and creep indentation distance (CID)) in bones from 38 mice from six types (C57Bl/6, Balb, oim/oim, oim/+, Phospho1(-/-) and Phospho1 wild type counterpart). These mice bone are models of healthy and diseased bone spanning a range of fracture toughness from very brittle (oim/oim) to ductile (Phospho1(-/-)). Left femora were dissected, notched and tested in 3-point bending until complete failure. Contralateral femora were dissected and indented in 10 sites of their anterior and posterior shaft surface over 10 indentation cycles. IDI, TID and CID were measured. Results from this study suggest that reference point indentation parameters are not indicative of stress intensity fracture toughness in mouse bone. In particular, the IDI values at the anterior mid-diaphysis across mouse types overlapped, making it difficult to discern differences between mouse types, despite having extreme differences in stress intensity based toughness measures. When more locations of indentation were considered, the normalised IDIs could distinguish between mouse types. Future studies should investigate the relationship of the reference point indentation parameters for mouse bone in other material properties of the bone tissue in order to determine their use for measuring bone quality.
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Doenças Ósseas/diagnóstico , Técnicas e Procedimentos Diagnósticos , Fraturas Ósseas , Animais , Modelos Animais de Doenças , Camundongos , Fatores de RiscoRESUMO
Bone fracture is a health concern for those with aged bone and brittle bone diseases. Mouse bone is widely used as a model of human bone, especially to investigate preclinical treatment strategies. However, little is known about the mechanisms of mouse bone fracture and its similarities and differences from fracture in human bone. In this work we present a methodology to investigate the fracture toughness during crack initiation and crack propagation for mouse bone. Mouse femora were dissected, polished on their periosteal surface, notched on the posterior surface at their mid-diaphysis, and tested in three-point bending under displacement control at a rate of 0.1mm/min using an in situ loading stage within an environmental scanning electron microscope. We obtained high-resolution real-time imaging of the crack initiation and propagation in mouse bone. From the images we can measure the crack extension at each step of the crack growth and calculate the toughness of the bone (in terms of stress intensity factor (K) and work to fracture (Wf)) as a function of stable crack length (Δa), thus generating a resistance curve for the mouse bone. The technique presented here provides insight into the evolution of microdamage and the toughening mechanisms that resist crack propagation, which are essential for preclinical development of treatments to enhance bone quality and combat fracture risk.
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Osso e Ossos/patologia , Fraturas Ósseas/patologia , Animais , Fenômenos Biomecânicos , Modelos Animais de Doenças , Fêmur/patologia , Consolidação da Fratura , Masculino , Camundongos , Camundongos Transgênicos , Microscopia Eletrônica de Varredura , Osteogênese Imperfeita/genética , Osteogênese Imperfeita/patologia , Estresse Mecânico , Resistência à TraçãoRESUMO
Previous studies introduced the digital image correlation (DIC) as a viable technique for measuring bone strain during loading. In this study, we investigated the sensitivity of a DIC system in determining surface strains in a mouse tibia while loaded in compression through the knee joint. Specifically, we examined the effect of speckle distribution, facet size and overlap, initial vertical alignment of the bone into the loading cups, rotation with respect to cameras, and ex vivo loading configurations on the strain contour maps measured with a DIC system. We loaded tibiae of C57BL/6 mice (12 and 18 weeks old male) up to 12 N at 8 N/min. Images of speckles on the bone surface were recorded at 1N intervals and DIC was used to compute strains. Results showed that speckles must have the correct size and density with respect to the facet size of choice for the strain distribution to be computed and reproducible. Initial alignment of the bone within the loading cups does not influence the strain distribution measured during peak loading, but bones must be placed in front of the camera with the same orientation in order for strains to be comparable. Finally, the ex vivo loading configurations with the tibia attached to the entire mouse, or to the femur and foot, or only to the foot, showed different strain contour maps. This work provides a better understanding of parameters affecting full field strain measurements from DIC in ex vivo murine tibial loading tests.