Setrusumab for the Treatment of Osteogenesis Imperfecta: 12-Month Results from the Phase 2b Asteroid Study.

Osteogenesis imperfecta (OI) is a rare genetic disorder commonly caused by variants of the type I collagen genes COL1A1 and COL1A2. OI is associated with increased bone fragility, bone deformities, bone pain, and reduced growth. Setrusumab, a neutralizing antibody to sclerostin, increased areal bone mineral density (aBMD) in a 21-week phase 2a dose escalation study. The phase 2b Asteroid (NCT03118570) study evaluated the efficacy and safety of setrusumab in adults. Adults with a clinical diagnosis of OI type I, III, or IV, a pathogenic variant in COL1A1/A2, and a recent fragility fracture were randomized 1:1:1:1 to receive 2, 8, or 20 mg/kg setrusumab doses or placebo by monthly intravenous infusion during a 12-month treatment period. Participants initially randomized to the placebo group were subsequently reassigned to receive setrusumab 20 mg/kg open label. Therefore, only results from the 2, 8, and 20 mg/kg double-blind groups are presented herein. The primary endpoint of Asteroid was change in distal radial trabecular vBMD from baseline at Month 12, supported by changes in high-resolution peripheral quantitative computed tomography micro finite element-derived bone strength. A total of 110 adults were enrolled with similar baseline characteristics across treatment groups. At 12 months, there was a significant increase in mean (SE) failure load in the 20 mg/kg group (3.17% [1.26%]) and stiffness in the 8 (3.06% [1.70%]) and 20 mg/kg (3.19% [1.29%]) groups from baseline. There were no changes in radial trabecula vBMD (p > 0.05). Gains in failure load and stiffness were similar across OI types. There were no significant differences in annualized fracture rates between doses. Two adults in the 20 mg/kg group experienced related serious adverse reactions. Asteroid demonstrated a beneficial effect of setrusumab on estimates of bone strength across the different types of OI and provides the basis for additional phase 3 evaluation.

Osteogenesis imperfecta, or OI, is a rare disorder affecting patients' bones causing pain and an increased chance of the bone breaking. Setrusumab is a possible treatment for OI being studied in a clinical trial called Asteroid. The goal of Asteroid was to determine which dose of setrusumab helped adults with OI the most: 2, 8, or 20 mg/kg. Researchers looked at the density of patients' bones and estimated how strong their bones were before setrusumab and again after 12 months of treatment to see how they improved with treatment. Researchers could compare these improvements to see which dose of setrusumab helped patients the most. Patients on the highest dose of setrusumab (20 mg/kg) experienced improvements in the density of their arm bones (radius) and leg bones (tibia) after 12 months. The strength of these bones also improved. The density of other bones including the spine, hip, and the overall skeleton (total body) also improved with treatment. Of patients who had side effects after receiving setrusumab, most were mild or moderate intensity. Overall, setrusumab improved the bones of patients with OI with no serious safety concerns. More studies will include even more patients to see how setrusumab can improve their bones.

Bone matrix properties in adults with osteogenesis imperfecta are not adversely affected by Setrusumab - a sclerostin neutralizing antibody.

Osteogenesis imperfecta (OI) is a skeletal dysplasia characterized by low bone mass and frequent fractures. Children with OI are commonly treated with bisphosphonates to reduce fracture rate, but treatment options for adults are limited. In the Phase 2b ASTEROID trial, setrusumab (a sclerostin neutralizing antibody, SclAb) improved bone density and strength in adults with type I, III and IV OI. Here, we investigate bone matrix material properties in tetracycline-labeled trans-iliac biopsies from three groups: i) control: individuals with no metabolic bone disease, ii) OI: individuals with OI, iii) SclAb-OI: individuals with OI after six months of setrusumab treatment (as part of the ASTEROID trial). In addition to bone histomorphometry, bone mineral and matrix properties were evaluated with nanoindentation, Raman spectroscopy, second harmonic generation imaging, quantitative backscatter electron imaging, and small-angle x-ray scattering. Spatial locations of fluorochrome labels were identified to differentiate inter-label bone of the same tissue age and intra-cortical bone. No difference in collagen orientation was found between the groups. The bone mineral density distribution and analysis of Raman spectra indicate that OI groups have greater mean mineralization, greater relative mineral content, and lower crystallinity than the control group, which was not altered by SclAb treatment. Finally, a lower modulus and hardness were measured in the inter-label bone of the OI-SclAb group compared to the OI group. Previous studies suggest that even though bone from OI has a higher mineral content, the ECM has comparable mechanical properties. Therefore, fragility in OI may stem from contributions from other yet unexplored aspects of bone organization at higher length scales. We conclude that SclAb treatment leads to increased bone mass while not adversely affecting bone matrix properties in individuals with OI.

Individuals with osteogenesis imperfecta (OI), also known as "brittle bone disease," have low bone mass and frequent fractures. Low bone mass occurs due to an imbalance between cells that remove bone and cells that form bone. Pharmaceutical treatments that block removal of bone lead to reduced fracture rates in children with OI. Effective treatment options for adults are limited. Setrusumab is a drug that leads to increased bone mass and strength in adults with OI. Here, we investigate whether Setrusumab alters the bone material in addition to improving bone mass. Three groups are compared: individuals with OI treated with Setrusumab, individuals with OI not treated with Setrusumab, and individuals without OI. A lower modulus and hardness were measured with nanoindentation in the Setrusumab-treated group. However, we did not find any changes in the bone's multi-scale structure. Fragility in OI may stem from other yet unexplored aspects of bone organization. We conclude that Setrusumab treatment leads to increased bone mass while not adversely affecting bone material properties in individuals with OI.

Resonance Frequency Analysis Identifies Implant- and Host-Related Factors Associated With Bone-Anchored Hearing Implant Stability.

HYPOTHESIS: Resonance frequency analysis (RFA) is a reliable, noninvasive method to assess the stability of bone-anchored hearing implants (BAHIs), although surgical-, implant-, and host-related factors can affect its outcome. BACKGROUND: BAHI plays an important role in restoring hearing function. However, implant- and host-related factors contribute to premature implant extrusion. To mitigate this, noninvasive methods to assess implant stability, along with a better understanding of factors contributing to BAHI failure, are needed. METHODS: We evaluated the utility of RFA to quantify implant stability in sawbone (bone mimicking material), 29 human cadaveric samples, and a prospective cohort of 29 pediatric and 27 adult participants, and identified factors associated with implant stability. To validate the use of RFA in BAHI, we compared RFA-derived implant stability quotient (ISQ) estimates to peak loads obtained from mechanical push-out testing. RESULTS: ISQ and peak loads were significantly correlated (Spearman rho = 0.48, p = 0.0088), and ISQ reliably predicted peak load up to 1 kN. We then showed that in cadaveric samples, abutment length, internal table bone volume, and donor age were significantly associated with implant stability. We validated findings in our prospective patient cohort and showed that minimally invasive Ponto surgery (MIPS; versus linear incision), longer implantation durations (>16 wk), older age (>25 yr), and shorter abutment lengths (≤10 mm) were associated with better implant stability. Finally, we characterized the short-term reproducibility of ISQ measurements in sawbone and patient implants. CONCLUSIONS: Together, our findings support the use of ISQ as a measure of implant stability and emphasize important considerations that impact implant stability, including surgical method, implant duration, age, and abutment lengths.

Swim training induces distinct osseous gene expression patterns in anosteocytic and osteocytic teleost fish.

The traditional understanding of bone mechanosensation implicates osteocytes, canaliculi, and the lacunocanalicular network in biomechanical adaptation. However, recent findings challenge this notion, as shown in advanced teleost fish where anosteocytic bone lacking osteocytes are nevertheless responsive to mechanical load. To investigate specific molecular mechanisms involved in bone mechanoadaptation in osteocytic and anosteocytic fish bone, we conducted a 5-min single swim-training experiment with zebrafish and ricefish, respectively. Through RNASeq analysis of fish spines, analyzed at various time points following swim training, we uncovered distinct gene expression patterns in osteocytic and anosteocytic fish bones. Notably, osteocytic fish bone exhibited an early response to mechanical load, contrasting to a delayed response observed in anosteocytic fish bones, both within 8 h following stimulation. We identified an increase in osteoblast differentiation in anosteocytic bone following training, while chordoblast activity was delayed. This temporal response suggests a time-dependent adaptation in anosteocytic bone, indicating the presence of intricate feedback networks within bone that lacks osteocytes.

Spatial variations in the osteocyte lacuno-canalicular network density and analysis of the connectomic parameters.

Osteocyte lacuno-canalicular network (LCN) is comprised of micrometre-sized pores and submicrometric wide channels in bone. Accumulating evidence suggests multiple functions of this network in material transportation, mechanobiological signalling, mineral homeostasis and bone remodelling. Combining rhodamine staining and confocal laser scanning microscopy, the longitudinal cross-sections of six mouse tibiae were imaged, and the connectome of the network was quantified with a focus on the spatial heterogeneities of network density, connectivity and length of canaliculi. In-vivo loading and double calcein labelling on these tibiae allowed differentiating the newly formed bone from the pre-existing regions. The canalicular density of the murine cortical bone varied between 0.174 and 0.243 µm/µm3, and therefore is three times larger than the corresponding value for human femoral midshaft osteons. The spatial heterogeneity of the network was found distinctly more pronounced across the cortex than along the cortex. We found that in regions with a dense network, the LCN conserves its largely tree-like character, but increases the density by including shorter canaliculi. The current study on healthy mice should serve as a motivating starting point to study the connectome of genetically modified mice, including models of bone diseases and of reduced mechanoresponse.

CHD7 regulates craniofacial cartilage development via controlling HTR2B expression.

Mutations in the Chromodomain helicase DNA-binding protein 7 - coding gene (CHD7) cause CHARGE syndrome (CS). Although craniofacial and skeletal abnormalities are major features of CS patients, the role of CHD7 in bone and cartilage development remain largely unexplored. Here, using a zebrafish (Danio rerio) CS model, we show that chd7-/- larvae display abnormal craniofacial cartilage development and spinal deformities. The craniofacial and spine defects are accompanied by a marked reduction of bone mineralization. At the molecular level, we show that these phenotypes are associated with significant reduction in the expression levels of osteoblast differentiation markers. Additionally, we detected a marked depletion of collagen 2α1 in the cartilage of craniofacial regions and vertebrae, along with significantly reduced number of chondrocytes. Chondrogenesis defects are at least in part due to downregulation of htr2b, which we found to be also dysregulated in human cells derived from an individual with CHD7 mutation-positive CS. Overall, this study thus unveils an essential role for CHD7 in cartilage and bone development, with potential clinical relevance for the craniofacial defects associated with CS.

Patients with CHARGE syndrome exhibit skeletal defects. CHARGE syndrome is primarily caused by mutations in the chromatin remodeler-coding gene CHD7. To investigate the poorly characterized role of CHD7 in cartilage and bone development, here, we examine the craniofacial and bone anomalies in a zebrafish chd7-/- mutant model. We find that zebrafish mutant larvae exhibit striking dysmorphism of craniofacial structures and spinal deformities. Notably, we find a significant reduction in osteoblast, chondrocyte, and collagen matrix markers. This work provides important insights to improve our understanding of the role of chd7 in skeletal development.

From breast cancer cell homing to the onset of early bone metastasis: The role of bone (re)modeling in early lesion formation.

Breast cancer often metastasizes to bone, causing osteolytic lesions. Structural and biophysical changes are rarely studied yet are hypothesized to influence metastasis. We developed a mouse model of early bone metastasis and multimodal imaging to quantify cancer cell homing, bone (re)modeling, and onset of metastasis. Using tissue clearing and three-dimensional (3D) light sheet fluorescence microscopy, we located enhanced green fluorescent protein-positive cancer cells and small clusters in intact bones and quantified their size and spatial distribution. We detected early bone lesions using in vivo microcomputed tomography (microCT)-based time-lapse morphometry and revealed altered bone (re)modeling in the absence of detectable lesions. With a new microCT image analysis tool, we tracked the growth of early lesions over time. We showed that cancer cells home in all bone compartments, while osteolytic lesions are only detected in the metaphysis, a region of high (re)modeling. Our study suggests that higher rates of (re)modeling act as a driver of lesion formation during early metastasis.

Does tissue fixation change the mechanical properties of dry ovine bone extracellular matrix?

Tissue fixation is a prevalent method for bone conservation. Bone biopsies are typically fixed in formalin, dehydrated in ethanol, and infiltrated with polymethyl methacrylate (PMMA) Since some experiments can only be performed on fixed bone samples, it is essential to understand how fixation affects the measured material properties. The aim of this study was to quantify the influence of tissue fixation on the mechanical properties of cortical ovine bone at the extracellular matrix (ECM) level with state-of-the-art micromechanical techniques. A small section from the middle of the diaphysis of two ovine tibias (3.5 and 5.5 years old) was cut in the middle and polished on each side, resulting in a pair of mirrored surfaces. For each pair, one specimen underwent a fixation protocol involving immersion in formalin, dehydration with ethanol, and infiltration with PMMA. The other specimen (mirrored) was air-dried. Six osteons were selected in both pairs, which could be identified in both specimens. The influence of fixation on the mechanical properties was first analyzed using micropillar compression tests and nanoindentation in dry condition. Additionally, changes in the degree of mineralization were evaluated with Raman spectroscopy in both fixed and native bone ECM. Finally, micro tensile experiments were conducted in the 3.5-year fixed ovine bone ECM and compared to reported properties of unfixed dry ovine bone ECM. Interestingly, we found that tissue fixation does not alter the mechanical properties of ovine cortical bone ECM compared to experiments in dry state. However, animal age increases the degree of mineralization (p = 0.0159) and compressive yield stress (p = 0.041). Tissue fixation appears therefore as a valid conservation technique for investigating the mechanical properties of dehydrated bone ECM.

Tensile Mechanical Properties of Dry Cortical Bone Extracellular Matrix: A Comparison Among Two Osteogenesis Imperfecta and One Healthy Control Iliac Crest Biopsies.

Osteogenesis imperfecta (OI) is a genetic, collagen-related bone disease that increases the incidence of bone fractures. Still, the origin of this brittle mechanical behavior remains unclear. The extracellular matrix (ECM) of OI bone exhibits a higher degree of bone mineralization (DBM), whereas compressive mechanical properties at the ECM level do not appear to be inferior to healthy bone. However, it is unknown if collagen defects alter ECM tensile properties. This study aims to quantify the tensile properties of healthy and OI bone ECM. In three transiliac biopsies (healthy n = 1, OI type I n = 1, OI type III n = 1), 23 microtensile specimens (gauge dimensions 10 × 5 × 2 µm3) were manufactured and loaded quasi-statically under tension in vacuum condition. The resulting loading modulus and ultimate strength were extracted. Interestingly, tensile properties in OI bone ECM were not inferior compared to controls. All specimens revealed a brittle failure behavior. Fracture surfaces were graded according to their mineralized collagen fibers (MCF) orientation into axial, mixed, and transversal fracture surface types (FST). Furthermore, tissue mineral density (TMD) of the biopsy cortices was extracted from micro-computed tomogra[hy (µCT) images. Both FST and TMD are significant factors to predict loading modulus and ultimate strength with an adjusted R 2 of 0.556 (p = 2.65e-05) and 0.46 (p = 2.2e-04), respectively. The influence of MCF orientation and DBM on the mechanical properties of the neighboring ECM was further verified with quantitative polarized Raman spectroscopy (qPRS) and site-matched nanoindentation. MCF orientation and DBM were extracted from the qPRS spectrum, and a second mechanical model was developed to predict the indentation modulus with MCF orientation and DBM (R 2 = 67.4%, p = 7.73e-07). The tensile mechanical properties of the cortical bone ECM of two OI iliac crest biopsies are not lower than the one from a healthy and are primarily dependent on MCF orientation and DBM. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Effects of dynamization timing and degree on bone healing of different fracture types.

Dynamization, that is, increasing interfragmentary movement (IFM) by reducing fixation stiffness from a rigid to a more flexible state, has been successfully used in clinical practice to promote fracture healing. However, it remains unclear how dynamization timing and degree affect bone healing of different fracture types. Finite element models of tibial fractures based on the OTA/AO classification (Simple: A1-Spiral, A2-Oblique, A3-Transverse; Wedge: B2-Spiral, B3-Fragmented; Complex: C2-Segment, C3-Irregular), in combination with fuzzy logic-based mechano-regulatory tissue differentiation algorithms, were used to simulate the healing process when dynamization of varied degrees (dynamization coefficient or DC = 0-0.9; 0.9 represents 90% reduction in the fixation stiffness relative to a rigid fixation) were applied at different time points after fracture. The fuzzy logic-based algorithms have been validated with a preclinical animal model. The results showed that the healing responses of type A fractures were more sensitive to the changes in dynamization degree and timing comparing with type B or C fractures. Additionally, the optimal dynamization regime for each fracture type was different. For type A fractures, a moderate dynamization degree (e.g., DC = 0.5) applied after Week 1 promoted the recovery of biomechanical integrity. For type B and C fractures, the effective dynamization included a greater dynamization degree (DC = 0.7) applied after Week 2. Our results further demonstrated that the fracture morphology affected interfragmentary strain environments within the callus, leading to varied healing results for different fracture types. These results suggest that the effects of dynamization are highly dependent of the fracture types. Therefore, specific dynamization strategies should be chosen for different fracture types to achieve optimal healing outcomes.

Breed and loading history influence in vivo skeletal strain patterns in pre-pubertal female chickens.

The influence of loading history on in vivo strains within a given specie remains poorly understood, and although in vivo strains have been measured at the hindlimb bones of various species, strains engendered during modes of activity other than locomotion are lacking, particularly in non-human species. For commercial egg-laying chickens specifically, there is an interest in understanding their bones' mechanical behaviour, particularly during youth, to develop early interventions to prevent the high incidence of osteoporosis in this population. We measured in vivo mechanical strains at the tibiotarsus midshaft during steady activities (ground, uphill, downhill locomotion) and non-steady activities (perching, jumping, aerial transition landing) in 48 pre-pubescent female (egg-laying) chickens from two breeds that were reared in three different housing systems, allowing varying amounts and types of physical activity. Mechanical strain patterns differed between breeds, and were dependent on the activity performed. Mechanical strains were also affected by rearing environment: chickens that were restricted from performing dynamic load bearing activity due to caged-housing generally exhibited higher mechanical strain levels during steady, but not non-steady activities, compared to chickens with prior dynamic load-bearing activity experience. Among chickens with prior experience of dynamic load bearing activity, those reared in housing systems that allowed more frequent physical activity did not exhibit lower mechanical strains. In all groups, the tibiotarsus was subjected to a loading environment consisting of a combination of axial compression, bending, and torsion, with torsion being the predominant source of strain. Aerial transition landing produced the highest strain levels with unusual strain patterns compared to other activities, suggesting it may produce the strongest anabolic response. These results exemplify how different breeds within a given specie adapt to maintain different patterns of mechanical strains, and how benefits of physical activity in terms of resistance to strain are activity-type dependent and do not necessarily increase with increased physical activity. These findings directly inform controlled loading experiments aimed at studying the bone mechanoresponse in young female chickens and can also be associated to measures of bone morphology and material properties to understand how these features influence bone mechanical properties in vivo.

A 6-bromoindirubin-3'-oxime incorporated chitosan-based hydrogel scaffold for potential osteogenic differentiation: Investigation of material properties in vitro.

Effective treatments for critical size bone defects remain challenging. 6-Bromoindirubin-3'-Oxime (BIO), a glycogen synthase kinase 3ß inhibitor, is a promising alternative for treatment of these defects since it aids in promoting osteogenic differentiation. In this study, BIO is incorporated into a new formulation of the guanosine diphosphate cross-linked chitosan scaffold to promote osteogenic differentiation. BIO incorporation was confirmed with 13C NMR through a novel concentration dependent peak around 41 ppm. The rapid gelation rate was maintained along with the internal structure's stability. The 10 µM BIO dose supported the control scaffold's microstructure demonstrating a suitable porosity and a low closed pore percentage. While pore sizes of BIO incorporated scaffolds were slightly smaller, pore heterogeneity was maintained. A proof-of-concept study with C2C12 cells suggested a dose-dependent response of BIO on early stages of osteogenic differentiation within the scaffold. These results support future work to examine BIO's role on osteogenic differentiation and biomineralization of encapsulated cells in the scaffold for bone regeneration.

Effect of the accordion technique on bone regeneration during distraction osteogenesis: A computational study.

BACKGROUND AND OBJECTIVE: Distraction osteogenesis (DO), a bone lengthening technique, is widely employed to treat congenital and acquired limb length discrepancies and large segmental bone defects. However, a major issue of DO is the prolonged consolidation phase (10-36 months) during which patients must wear a cumbersome external fixator. Attempts have been made to accelerate the healing process of DO by an alternating distraction and compression mode (so-called "accordion" technique or AT). However, it remains unclear how varied AT parameters affect DO outcomes and what the most effective AT mode is. METHODS: Based on an experimentally-verified mechanobiological model, we performed a parametric analysis via in silico simulation of the bone regeneration process of DO under different AT modes, including combinations of varied application times (AT began at week 1-8 of the consolidation phase), durations (AT was used continuously for 1 week, 2 weeks or 4 weeks) and rates (distraction or compression at 0.25, 0.5, 0.75, and 1 mm/12 h). The control group had no AT applied during the consolidation phase. RESULTS: Compared with the control group (no AT), AT applied at an early consolidation stage (e.g. week 1 of the consolidation phase) significantly enhanced bone formation and reduced the overall healing time. However, the effect of AT on bone healing was dependent on its duration and rate. Specifically, a moderate rate of AT (e.g. 0.5 mm/12 h) lasting for two weeks promoted blood perfusion recovery and bone regeneration, ultimately shortening the healing time. Conversely, over-high rates (e.g. 1 mm/12 h) and longer durations (e.g. 4 weeks) of AT adversely affected bone regeneration and blood perfusion recovery, thereby delaying bone bridging. CONCLUSIONS: These results suggest that the therapeutic effects of AT on DO are highly dependent of the AT parameters of choice. Under appropriate durations and rates, the AT applied at an early consolidation phase is beneficial for blood recovery and bone regeneration. These results may provide a basis for selecting effective AT modes to accelerate consolidation and reduce the overall treatment period of DO.

In vivo microCT-based time-lapse morphometry reveals anatomical site-specific differences in bone (re)modeling serving as baseline parameters to detect early pathological events.

The bone structure is very dynamic and continuously adapts its geometry to external stimuli by modeling and remodeling the mineralized tissue. In vivo microCT-based time-lapse morphometry is a powerful tool to study the temporal and spatial dynamics of bone (re)modeling. Here an advancement in the methodology to detect and quantify site-specific differences in bone (re)modeling of 12-week-old BALB/c nude mice is presented. We describe our method of quantifying new bone surface interface readouts and how these are influenced by bone curvature. This method is then used to compare bone surface (re)modeling in mice across different anatomical regions to demonstrate variations in the rate of change and spatial gradients thereof. Significant differences in bone (re)modeling baseline parameters between the metaphyseal and epiphyseal, as well as cortical and trabecular bone of the distal femur and proximal tibia are shown. These results are validated using conventional static in vivo microCT analysis. Finally, the insights from these new baseline values of physiological bone (re)modeling were used to evaluate pathological bone (re)modeling in a pilot breast cancer bone metastasis model. The method shows the potential to be suitable to detect early pathological events and track their spatio-temporal development in both cortical and trabecular bone. This advancement in (re)modeling surface analysis and defined baseline parameters according to distinct anatomical regions will be valuable to others investigating various disease models with site-distinct local alterations in bone (re)modeling.

Bone strength and composition in spacefaring rodents: systematic review and meta-analysis.

Studying the effects of space travel on bone of experimental animals provides unique advantages, including the ability to perform post-mortem analysis and mechanical testing. To synthesize the available data to assess how much and how consistently bone strength and composition parameters are affected by spaceflight, we systematically identified studies reporting bone health in spacefaring animals from Medline, Embase, Web of Science, BIOSIS, and NASA Technical reports. Previously, we reported the effect of spaceflight on bone architecture and turnover in rodents and primates. For this study, we selected 28 articles reporting bone strength and composition in 60 rats and 60 mice from 17 space missions ranging from 7 to 33 days in duration. Whole bone mechanical indices were significantly decreased in spaceflight rodents, with the percent difference between spaceflight and ground control animals for maximum load of -15.24% [Confidence interval: -22.32, -8.17]. Bone mineral density and calcium content were significantly decreased in spaceflight rodents by -3.13% [-4.96, -1.29] and -1.75% [-2.97, -0.52] respectively. Thus, large deficits in bone architecture (6% loss in cortical area identified in a previous study) as well as changes in bone mass and tissue composition likely lead to bone strength reduction in spaceflight animals.

3D Image Registration Marginally Improves the Precision of HR-pQCT Measurements Compared to Cross-Sectional-Area Registration in Adults With Osteogenesis Imperfecta.

Repositioning error in longitudinal high-resolution peripheral-quantitative computed tomography (HR-pQCT) imaging can lead to different bone volumes being assessed over time. To identify the same bone volumes at each time point, image registration is used. While cross-sectional area image registration corrects axial misalignment, 3D registration additionally corrects rotations. Other registration methods involving matched angle analysis (MA) or boundary transformations (3D-TB) can be used to limit interpolation error in 3D-registering micro-finite-element data. We investigated the effect of different image registration methods on short-term in vivo precision in adults with osteogenesis imperfecta, a collagen-related genetic disorder resulting in low bone mass, impaired quality, and increased fragility. The radii and tibiae of 29 participants were imaged twice on the same day with full repositioning. We compared the precision error of different image registration methods for density, microstructural, and micro-finite-element outcomes with data stratified based on anatomical site, motion status, and scanner generation. Regardless of the stratification, we found that image registration improved precision for total and trabecular bone mineral densities, trabecular and cortical bone mineral contents, area measurements, trabecular bone volume fraction, separation, and heterogeneity, as well as cortical thickness and perimeter. 3D registration marginally outperformed cross-sectional area registration for some outcomes, such as trabecular bone volume fraction and separation. Similarly, precision of micro-finite-element outcomes was improved after image registration, with 3D-TB and MA methods providing greatest improvements. Our regression model confirmed the beneficial effect of image registration on HR-pQCT precision errors, whereas motion had a detrimental effect on precision even after image registration. Collectively, our results indicate that 3D registration is recommended for longitudinal HR-pQCT imaging in adults with osteogenesis imperfecta. Since our precision errors are similar to those of healthy adults, these results can likely be extended to other populations, although future studies are needed to confirm this. © 2022 American Society for Bone and Mineral Research (ASBMR).

In vivo and in silico monitoring bone regeneration during distraction osteogenesis of the mouse femur.

BACKGROUND AND OBJECTIVE: Distraction osteogenesis (DO) is a mechanobiological process of producing new bone by gradual and controlled distraction of the surgically separated bone segments. Mice have been increasingly used to study the role of relevant biological factors in regulating bone regeneration during DO. However, there remains a lack of in silico DO models and related mechano-regulatory tissue differentiation algorithms for mouse bone. This study sought to establish an in silico model based on in vivo experimental data to simulate the bone regeneration process during DO of the mouse femur. METHODS: In vivo micro-CT, including time-lapse morphometry was performed to monitor the bone regeneration in the distraction gap. A 2D axisymmetric finite element model, with a geometry originating from the experimental data, was created. Bone regeneration was simulated with a fuzzy logic-based two-stage (distraction and consolidation) mechano-regulatory tissue differentiation algorithm, which was adjusted from that used for fracture healing based on our in vivo experimental data. The predictive potential of the model was further tested with varied distraction frequencies and distraction rates. RESULTS: The computational simulations showed similar bone regeneration patterns to those observed in the micro-CT data from the experiment throughout the DO process. This consisted of rapid bone formation during the first 10 days of the consolidation phase, followed by callus reshaping via bone remodeling. In addition, the computational model predicted a faster and more robust bone healing response as the model's distraction frequency was increased, whereas higher or lower distraction rates were not conducive to healing. CONCLUSIONS: This in silico model could be used to investigate basic mechanobiological mechanisms involved in bone regeneration or to optimize DO strategies for potential clinical applications.

The combined effects of dynamization time and degree on bone healing.

Dynamization, increasing the interfragmentary movement (IFM) by reducing the fixation stiffness from a rigid to a more flexible condition, is widely used clinically to promote fracture healing. However, it remains unknown how dynamization degree (relative change in fixation stiffness/IFM from a rigid to a flexible fixation) affects bone healing at various stages. To address this issue, we used a fuzzy logic-based mechano-regulated tissue differentiation algorithm on published experimental data from a sheep osteotomy healing model. We applied a varied degree of dynamization, from 0 (fully rigid fixation) to 0.9 (90% reduction in stiffness relative to the rigid fixation) after 1, 2, 3, and 4 weeks of osteotomy (R1wF, R2wF, R3wF, and R4wF) and computationally evaluated bone regeneration and biomechanical integrity over the healing process of 8 weeks. Compared with the constant rigid fixation, early dynamization (R1wF and R2wF) led to delays in bone bridging and biomechanical recovery of the osteotomized bone. However, the effect of early dynamization on healing was dependent of the degree of dynamization. Specifically, a higher dynamization degree (e.g., 0.9 for R1wF) led to a prolonged delay in bone bridging and largely unrecovered bending stiffness (48% relative to the intact bone), whereas a moderate degree of dynamization (e.g., 0.5 or 0.7) significantly enhanced bone formation and biomechanical properties of the osteotomized bone. These results suggest that dynamization degree and timing interactively affect the healing process. A combination of early dynamization with a moderate degree could enhance the ultimate biomechanical recovery of the fractured bone.

Bone adaptation to mechanical loading in mice is affected by circadian rhythms.

Physical forces are critical for successful function of many organs including bone. Interestingly, the timing of exercise during the day alters physiology and gene expression in many organs due to circadian rhythms. Circadian clocks in tissues, such as bone, express circadian clock genes that target tissue-specific genes, resulting in tissue-specific rhythmic gene expression (clock-controlled genes). We hypothesized that the adaptive response of bone to mechanical loading is regulated by circadian rhythms. First, mice were sham loaded and sacrificed 8 h later, which amounted to tissues being collected at zeitgeber time (ZT)2, 6, 10, 14, 18, and 22. Cortical bone of the tibiae collected from these mice displayed diurnal expression of core clock genes and key osteocyte and osteoblast-related genes, such as the Wnt-signaling inhibitors Sost and Dkk1, indicating these are clock-controlled genes. Serum bone turnover markers did not display rhythmicity. Second, mice underwent a single bout of in vivo loading at either ZT2 or ZT14 and were sacrificed 1, 8, or 24 h after loading. Loading at ZT2 resulted in Sost upregulation, while loading at ZT14 led to Sost and Dkk1 downregulation. Third, mice underwent daily in vivo tibial loading over 2 weeks administered either in the morning, (ZT2, resting phase) or evening (ZT14, active phase). In vivo microCT was performed at days 0, 5, 10, and 15 and conventional histomorphometry was performed at day 15. All outcome measures indicated a robust response to loading, but only microCT-based time-lapse morphometry showed that loading at ZT14 resulted in a greater endocortical bone formation response compared to mice loaded at ZT2. The decreased Sost and Dkk1 expression coincident with the modest, but significant time-of-day specific increase in adaptive bone formation, suggests that circadian clocks influence bone mechanoresponse.