JBMR Plus

Teriparatide (PTH 1-34) is an anabolic agent used to treat osteoporosis, yet clinical response varies widely among patients. To investigate genetic and sex-specific determinants of skeletal response, we administered intermittent PTH to male and female mice from eight genetically diverse inbred strains. Mice were treated for four weeks, and bone phenotypes were assessed via DXA, microCT, and mechanical testing. Response to PTH was highly strain- and sex-dependent, with some strains responding at the femur but not the spine, and vice versa. Heritability estimates for PTH-induced changes in bone mineral density (BMD), cortical area, breaking strength, and trabecular bone volume fraction (BV/TV) ranged from moderate to high, with BV/TV showing the strongest genetic influence. Cortical bone response mechanisms differed by sex: males exhibited periosteal expansion, while females showed endosteal remodeling. These findings mirror clinical observations where hip non-response is more prevalent than spine non-response and suggest that genetic background and sex significantly influence therapeutic outcomes. Our data support the use of genetically diverse mouse models to elucidate the genetic architecture of PTH response and highlight the potential for personalized approaches in osteoporosis treatment. Future genome-wide association studies in outbred mice may identify specific loci mediating skeletal responsiveness to PTH, advancing precision medicine strategies for bone anabolic therapies. LAY SUMMARYTeriparatide, a drug used to treat osteoporosis, consists of the active portion of parathyroid hormone (PTH). Information from clinical studies suggests that not all patients will respond to this medication. We used eight strains of inbred mice to study the impact of genetic background and sex on the response to PTH. We learned that response to PTH is driven by both genetics and sex. Some strains responded at the femur, but not the spine and vice versa. These results may explain why a failure to respond at the hip in humans is more common than at the spine.

Osteoblastic bone metastasis, in which disseminated tumor cells drive net bone formation, is a clinically distinct and mechanistically underexplored form of skeletal disease that is enriched in hormone receptor-positive breast cancers. Preclinical models of bone metastasis from breast cancer predominantly rely on immunodeficient hosts inoculated with osteolytic human breast cancer cell lines, limiting the study of immune-dependent mechanisms of bone remodeling. Here we describe the development and characterization of an immunocompetent, syngeneic osteoblastic bone metastasis model using intratibial injection of PyMT-CK(OB), a luciferase-expressing derivative of the MMTV-PyMT mammary carcinoma cell line, in FVB/N mice. PyMT-CK(OB) cells produced detectable bioluminescent signal after intratibial injection, enabling longitudinal monitoring of tumor progression. Micro-computed tomography (microCT) revealed significant increases in trabecular bone volume fraction and trabecular number at three and four weeks post-injection, consistent with osteoblastic remodeling. Histological analysis confirmed dense bone lesion formation in tumor-bearing bones. Critically, this osteoblastic phenotype was entirely absent in immunodeficient NOD SCID hosts, despite robust tumor growth, supporting a role for immune competence in tumor-induced bone formation. Loss of bioluminescent signal in immunocompetent mice reflected either immune pressure on reporter gene expression or limited space for cancer cell expansion in the bone, rather than tumor regression or hypoxia, as confirmed by hypoxia imaging and histological endpoint analysis. In contrast, a second PyMT cell subline, PyMT-CF, maintained sustained bioluminescent signal and produced predominantly osteolytic lesions, providing a complementary syngeneic model of osteolytic disease from the same parental background. In vitro hydrogel coculture experiments and protein array analysis of conditioned media revealed that the PyMT sublines have differing impact on MC3T3 osteoblast mineralization, identifying candidate mediators of divergent bone remodeling phenotypes. R7 mammary carcinoma cells derived from MMTV-RON transgenic mouse mammary tumors did not induce measurable bone remodeling under equivalent experimental conditions. Together, these models provide a validated, immunologically intact framework for studying the mechanistic basis of osteoblastic bone metastasis and evaluating therapeutic interventions targeting the tumor-bone microenvironment.

Purpose: The Fracture Risk Assessment Tool (FRAX) excludes objective skeletal muscle health and genetic variables. We evaluated the prognostic associations of handgrip-defined probable/possible sarcopenia and genome-wide polygenic scores (GPS) with 10-year fracture risk, and their incremental predictive value beyond FRAX across racial/ethnic groups and GPS strata. Methods: We analyzed 2,051 postmenopausal women from the Women's Health Initiative. Race-specific analyses focused on Black, Hispanic, and White participants (n=2,009), excluding American Indian/Alaska Native and Asian/Pacific Islander individuals due to sparse fracture events. Sarcopenia status was operationalized by low handgrip strength alone via EWGSOP2 (<16.0 kg) and AWGS 2025 (<18.0-20.0 kg) criteria. Fine-Gray models estimated subdistribution hazard ratios (sHR), treating death as a competing risk. Predictive performance at 10 years was assessed using time-dependent AUC, Brier scores, and decision curve analysis (DCA). Results: Handgrip-defined probable or possible sarcopenia prevalence was 4.4% (EWGSOP2) and 6.4% (AWGS 2025). Black women demonstrated lower risk for major osteoporotic fractures (MOF) (adjusted sHR=0.19, 95% CI: 0.08-0.48) and hip fractures (adjusted sHR=0.07, 95% CI: 0.01-0.52) compared to White women. Neither sarcopenia status nor high GPS showed statistically significant independent associations with fractures after FRAX adjustment. Adding sarcopenia status to baseline FRAX (AUC: 0.71 for MOF; 0.69 for hip) yielded near-identical AUCs, Brier scores, and within-sample net benefit. Conclusion: Handgrip-defined probable/possible sarcopenia and current GPS do not provide independent or incremental predictive value beyond the clinical FRAX framework within this genomic sub-sample of older women.

Background Vitamin D may influence bone healing and recovery after spine surgery, but its clinical effects remain uncertain. Objective To evaluate clinical, functional, and bone-related outcomes associated with vitamin D status and supplementation in patients undergoing spine surgery. Methods This systematic review and meta-analysis was registered in PROSPERO (CRD420261467482) and reported according to PRISMA 2020. PubMed/MEDLINE, Scopus, Web of Science, Embase, and the Cochrane Library were searched from inception through 1 June 2026. Random-effects meta-analyses used mean differences (MDs) for continuous outcomes and risk ratios (RRs) for dichotomous outcomes. Direct supplementation analyses were prioritized, while analyses combining supplementation, baseline vitamin D status, or co-interventions were considered exploratory. Risk of bias was assessed using design-specific Joanna Briggs Institute tools. Results Thirteen studies were included. Four supplementation studies involving 177 participants showed no significant reduction in postoperative pain (MD -0.82, 95% CI -2.50 to 0.86; I2 = 84.3%). Three studies involving 277 participants showed lower Oswestry Disability Index scores in an exploratory analysis (MD -6.40, 95% CI -10.41 to -2.39; I2 = 96.8%). Three supplementation studies involving 128 participants showed no significant improvement in fusion rate (RR 1.17, 95% CI 0.78 to 1.74; I2 = 31.5%). An exploratory four-study fusion analysis was also not statistically significant (RR 1.24, 95% CI 0.98 to 1.57; I2 = 45.5%). Conclusion Current evidence does not establish that vitamin D supplementation independently improves postoperative pain or fusion rates after spine surgery. Possible benefits for disability and other bone-related outcomes remain uncertain because of small study numbers, heterogeneity, co-interventions, and residual confounding. Larger randomized trials stratified by baseline vitamin D status are needed.

Implant-associated bone infection involves a complex interplay between pathogenic stimuli and host cell responses, yet analysis in preclinical models has typically relied on qualitative or semi-quantitative measures. We aimed to establish a quantified evaluation framework to define host-pathogen relationships in a preclinical implant infection model. Staphylococcus aureus-coated stainless-steel implants were inserted trans-cortically in mouse tibiae and bone changes recorded longitudinally by in vivo micro-CT. An automated segmentation task list was developed to independently isolate and quantify cortical, periosteal-reactive, and trabecular bone compartments. RGB trichrome histomorphometry was used to quantify bone matrix integrity, osteocyte lacunar geometry, and osteoclastic activity. Droplet digital PCR was used to determine absolute bacterial and host genome copy number. Infected implants produced marked reductions in trabecular bone volume fraction, number, and bone mineral density (BMD), together with decreased cortical bone volume fraction and increased cortical porosity, accompanied by significant elevations in periosteal bone volume fraction. Histologically, infected bone exhibited increased eroded surface indicative of osteoclastic resorption, extensive degraded bone matrix and pathological remodelling of osteocyte lacunae towards circularity, consistent with an osteocytic osteolysis response. Infection-induced changes to cortical bone structure correlated mostly with host cell rather than bacterial load; however, cortical BMD negatively correlated with the bacterial:host genome ratio. This multifaceted, quantified framework reveals distinct pathobiological effects of implant-associated infection on trabecular, cortical, and periosteal bone compartments, bone matrix and osteocyte and osteoclast populations, consistent with reports in human patients, suggesting that major pathological changes are driven by the host bone cell response to infection.

Purpose: Psychosocial factors are underexplored in relation to osteoporosis. This study examined whether depressive symptoms are associated with incident osteoporosis in middle aged and older adults, and whether this association is modified by age or sex. Methods: Prospective cohort study of 8,577 adults aged [&ge;]50 years from the English Longitudinal Study of Ageing. The sample were free of osteoporosis at baseline (2002-2003) and were followed up for incident osteoporosis until wave 11 (2023-2024). Depressive symptoms were measured at baseline (2002-03) using the 8-item Center for Epidemiologic Studies-Depression Scale (CES-D). Cox proportional hazards regressions were used to estimate associations, adjusting for age, sex and wealth. Results: Over 20 years of follow-up, 948 (11.1%) participants reported incident osteoporosis. Each one-point increase in baseline CES-D was associated with a higher hazard of incident osteoporosis adjusted for age, sex, and wealth (hazard ratio (HR) 1.07, 95% CI 1.04-1.11, p<0.001). The association was modified by age (interaction p=0.008) and concentrated in participants aged 50-64 years at baseline (HR 1.10, 95% CI 1.06-1.14), with no significant association in older age strata. Osteoporosis incidence was higher in women, but this was not modified by depressive symptoms. Findings were robust to sequential adjustment (informed by a directed acyclic graph) for education, wealth, inflammatory conditions and health behaviours (HR 1.04, 95% CI 1.01-1.08) Conclusion: Depressive symptoms are associated with incident osteoporosis over two decades of follow-up, particularly among adults aged 50-64. Mid-life may represent a target for psychosocial intervention to support bone health.

Abstract Fractures in older adults cause high morbidity and mortality. This study aims to identify fracture incidence and risk factors, and to develop the Fracture Risk Model-Abu Dhabi (FRM-AD). Method This retrospective cohort study of 1757 males and females aged 40+ from Abu Dhabi, United Arab Emirates, who participated in a screening program from 2016 to 2020, followed until 2024 for 4.7 years, SD =1.8. It utilized Electronic Medical Records (EMRs) data and telephone interviews. The outcome assessed was the occurrence of fractures. Results There were 58 out of the 1149 females (5.0%) and 26 out of the 608 males (4.3%) who had at least one incident fracture. Hip and vertebral fractures accounted for 12.1% and 11.5%, respectively. There was an annual incidence of 10.5 fractures per 1,000 person-years, 10.7 cases among females and 9.9 among males, rising after age 80 to 39.1 among females and 25.3 among males. Fracture Predictors identified using Poisson regression analysis were older age, smoking, history of previous fracture(s), interaction of history of fracture in a parent with a family history of osteoporosis, positive history of hip fracture in a parent after the age of 40, lack of dyslipidemia diagnosis and the interaction of diabetes mellitus diagnosis and family history of osteoporosis. A higher Body Mass Index (BMI) increased the risk of fractures in this cohort, especially in obese males. Logistic regression of variables at the end of follow-up showed that lower latest vitamin D levels were associated with increased fracture risk. FRM-AD, derived using Poisson regression, performed well in predicting fractures, with Receiver Operating Characteristic (ROC) curves of 0.736 (0.677-0.794) and 0.742 (0.684-0.800) without and with BMD, respectively. The FRAX AUC to predict MOF and hip fracture ranged between 0.624 and 0.683. Conclusion In this Emirati cohort, the locally derived FRM-AD showed moderate discrimination for incident fracture and outperformed FRAX-AD, suggesting that a locally derived model may improve fracture risk stratification. Several risk factors and predictors were identified that can be targeted for prevention.

Fracture nonunion remains a major cause of morbidity, yet patient-specific factors associated with impaired healing remain incompletely characterized. Anemia has been associated with adverse orthopaedic outcomes, but its relationship with fracture nonunion is poorly understood. We examined whether pre-fracture anemia, anemia burden, and clinically relevant anemia subtypes were associated with nonunion following tibial or femoral fractures. Using commercial and Medicare fee-for-service claims from 2016 through 2023, we identified adults aged 19 years or older with a tibial or femoral fracture, continuous enrollment during the preceding year and for at least six months after fracture, and no baseline cancer. Pre-fracture anemia was evaluated as any anemia, the number of distinct anemia diagnoses, and nutritional, hemolytic, aplastic, and other anemia subgroups. Nonunion occurring six to eighteen months after fracture was assessed using incidence rates and multivariable-adjusted hazard models. Among 326,673 adults, 149,704 had pre-fracture anemia and 176,969 did not. The crude incidence of nonunion was 42% higher among individuals with anemia than among those without anemia (incidence rate ratio, 1.42; 95% confidence interval, 1.32 to 1.53) and increased with greater anemia burden. After adjustment for demographic and clinical characteristics, including prior fractures at other anatomical sites, pre-fracture anemia remained associated with nonunion following tibial and femoral fractures, with hazard ratios of 1.83 (95% confidence interval, 1.54 to 2.18) and 1.38 (95% confidence interval, 1.26 to 1.50), respectively. Associations were also observed for nutritional and other anemias, whereas estimates for hemolytic and aplastic anemias were limited by few nonunion events. Within the femur, the association was strongest for distal fractures. These findings demonstrate that pre-fracture anemia is independently associated with nonunion. The increase in risk with greater anemia burden and findings across evaluable subgroups suggest that pre-fracture anemia may help identify patients at increased risk of impaired fracture healing.

Objective To characterize regional subchondral bone metabolism before and after acute mechanical loading in individuals with unilateral knee pain using dynamic [18F]sodium fluoride ([18F]NaF) positron emission tomography (PET)/magnetic resonance imaging (MRI), and to investigate relationships with cartilage composition and pain severity. Design Twenty-two individuals with unilateral knee pain and 22 age- and sex-matched healthy controls underwent bilateral dynamic [18F]NaF PET/MRI before and after a standardized stair-climbing protocol in this prospective feasibility study. Automated MRI-based segmentations were used to quantify regional PET standardized uptake values (SUVmean, SUVmax) and pharmacokinetic parameters (K1: bone perfusion, Ki: bone mineralization, extraction fraction) across subchondral bone regions. Quantitative cartilage T2 mapping was performed using qDESS MRI. Painful knees were compared with contralateral asymptomatic knees and healthy control knees using regional effect sizes and regression analyses. Exploratory analyses evaluated associations between PET metrics, cartilage T2, and pain severity. Results Painful knees demonstrated consistently higher baseline subchondral bone metabolic activity than healthy controls, with the largest differences in the medial tibial and medial femoral subchondral bone (Cohen's d=0.51-0.90). Following mechanical loading, exercise-induced increases in bone metabolism were more widespread and demonstrated predominantly moderate-to-large effect sizes (d=0.62-1.15), particularly within the medial and lateral femoral and medial tibial subchondral bone. In contrast, comparisons between painful and contralateral knees showed only localized metabolic differences with predominantly negligible-to-small effect sizes (d=0.16-0.55). Sensitivity analyses adjusting for age and BMI produced similar regional patterns. Exploratory analyses demonstrated generally weak associations between PET-derived metabolic measures, cartilage T2, and pain severity, with only isolated moderate regional correlations. Conclusions Dynamic [18F]NaF PET/MRI demonstrates increased baseline subchondral bone metabolic activity and an exaggerated metabolic response to mechanical loading in symptomatic knees compared with healthy controls. The modest differences between painful and contralateral knees suggest that the asymptomatic limb may not represent a truly unaffected reference. Dynamic [18F]NaF PET provides complementary information beyond cartilage MRI and patient-reported pain and shows promise for investigating subchondral bone metabolism in knee pain, early joint degeneration, and treatment response.

Background and rationale: Knee osteoarthritis (KOA) is a leading cause of lower limb disability worldwide, characterized by functional limitations, stiffness and pain. The incidence of KOA is especially tied to age and obesity. It is a disabling disease that often makes patients less physically active, thus increasing the risk of other diseases and mortality1. The clinical diagnosis of KOA is based on the symptoms and functional limitations of the joint. The diagnosis is usually supported with a radiograph (X-ray) of the weight-bearing knee. Radiographic features, such as Kellgren-Lawrence grade, are used as eligibility criteria for clinical studies while other features, such as joint space width (JSW), are used as endpoints for structural KOA progression2,3. While the use of these radiographic features is standard in academia, the use of JSW as a structural biomarker has received criticism. Critics point out that JSW is an indirect and projection dependent measure of cartilage deterioration which is sensitive to technical factors such as the angulation of the X-ray beam and the positioning of the knee. Small differences in these factors can alter the measured joint space and may not reflect true disease progression4,5. Despite limitations, minimum joint space width (mJSW) remains as one of the most widely used structural biomarkers in KOA trials and is currently one of the only structural imaging accepted in regulatory guidance as evidence of disease modification in OA drug development3. For JSW to be reliable and consistent in determining the advancement of KOA, the use of fixed-flexion devices is crucial to reduce the risk of unwanted narrowing or widening of the radiographic joint space width6,7. The LOSEIT trial, which the present study is based on, acknowledges the angulation problem and uses a standard clinical fixed-flexion device in weight-bearing PA views to get reliable JSW results8. Historically, a radiologist would draw on and grade radiographs of the knee-joint to extract the features. However, manual reading and annotation is time consuming with notable interobserver variance9. With increasing computational power and the use of deep neural networks, off-the-shelf artificial intelligence (AI) tools have become available for automatic extraction of radiograph features. Automation would free up time from radiologists and provide more consistent measurements due to the reproducible nature of the models10. These tools have received regulatory approval for commercial use, however, regulatory approval does not guarantee uniform or bias free performance when used on real-world data11. Furthermore, in a large multi-hospital chest X-ray study, Zech et al., showed that convolutional neural networks achieved worse results on data from other hospitals than on the original hospitals in which it was tested12. This highlights the risk of overestimating the accuracy of AI tools when only internally validated. It is therefore apparent that external validation is required when testing these AI models. Objectives: The aim of this analysis is to evaluate the agreement of a commercially available AI tool for measuring JSW with the best practice radiologist annotation in the tibiofemoral joint of the knee in radiographs stabilized with a fixed-flexion device and acquired as part of a clinical trial. Methods: This study is a secondary analysis of the data from the LOSEIT trial, a randomized, double-blind, placebo-controlled, single-center trial, where patients were randomized to either liraglutide or identically appearing placebo after an initial weight-loss period to investigate the effects on KOA. Radiographs of the tibiofemoral joint were acquired at enrollment (week -8) and at end-of-trial (week 52) for a total acquisition-to-acquisition time of 60 weeks13. The primary analysis will assess agreement between AI-derived and reference-derived change in JSW from enrolment to follow-up. Change will be calculated as follow-up minus enrolment separately for the AI tool and the reference measurement. The main measure of interest will be the change in medial minimal JSW (mmJSW), with change in lateral minimal JSW (lmJSW), medial fixed JSW (mfJSW) and lateral fixed JSW (lfJSW) as secondary measures. This study will follow an equivalence framework using the two one-sided tests (TOST) approach with a Bland-Altman analysis as the main outcome. The equivalence margin will be set at {delta} = 0.5 mm. Agreement consistent with equivalence will be considered established if the upper limit of the 95% confidence interval (95% CI) for the upper limit of agreement (LoA) and the lower limit of the 95% CI for the lower LoA are within the established margins. The reference JSW will be the average measurement of two independent resident radiologists. If there is a mismatch in the measurements of more than 0.40 mm between the two radiologists, the radiologists will re-annotate the case independently. If the difference remains greater than 0.40 mm, a musculoskeletal radiology consultant will review the radiograph and establish the reference JSW. The index test will be the measurements output by the AI tool. Populations: Patients aged 18 to 74 with symptomatic knee osteoarthritis, radiographically confirmed KL grade 1-3, with a BMI [&ge;]27, motivated for weight loss and in accordance with the LOSEIT trial inclusion criteria Further statistical details Sample size: Not applicable as this is a secondary analysis. Framework: This is an agreement study assessing the equivalence of a commercially available AI tool for radiographic evaluation of knee osteoarthritis with best practice radiologist measurements. Confidence intervals and P values: All 95% confidence intervals and P-values will be two-sided. Statistical software: SAS Studio and/or R version 4.2.2 (or newer).

Low-intensity vibration (LIV) is a non-invasive mechanical stimulus capable of regulating skeletal adaptation and cellular signaling pathways involved in bone remodeling. Despite growing interest in LIV, substantial methodological heterogeneity persists in the selection of experimental vibration parameters such as frequency, expressed in Hertz (Hz) and intensity, defined as earth's gravitational field (g) (9.81 m/s2). Focusing on micro-computed tomography (CT) derived trabecular bone volume fraction (BV/TV) as the main outcome measure, this study sought to synthesize the effects of different LIV frequency and intensity on BV/TV in small rodents (mice and rats) as they remain as the most studied pre-clinical model. To accomplish this, we performed a systematic review searching for publications in English on PubMed, Web of Science, CINAHL, and Embase databases. Two independent investigators followed inclusion criteria to select only peer-reviewed studies with mature mice, using whole-body vibration experiments without other co-variables. We further restricted to include studies that analyzed non-fractured bones and compared pre- and post-intervention or control values. In addition to these core criteria, a detailed hierarchical screening framework was applied during full-text review. The two independent investigators extracted data independently and considered the characteristics of the study, animals' characteristics, intervention characteristics, and results. For this study we considered load-bearing hindlimbs, femur and tibia, separately but did not include vertebrae in the analysis. A Bayesian network meta-analysis and a revised SYRCLE risk of bias (RoB) tool were used to evaluate the risk of bias across included studies. Seven studies met the inclusion criteria. Results showed that an LIV regime applied at 45Hz at 2g presented higher chances to increase trabecular BV/TV of the mouse tibia (estimated effect 3.22 [CrI 1.98, 4.45]), while LIV regimes applied to the femur at 90Hz and 1.4g (estimated effect 3.08 [CrI -1.99, 7.97]) present better chances to increase trabecular BV/TV results compared to other interventions but with no significant differences. Finally, we applied 45Hz at 0.2g LIV to 5 month old male C57BL/6 for 5 weeks (n=10/group) which showed significantly increased Trabecular Thickness (Tb.Th) for both the tibia (10%, p<0.01) and femur (17%, p<0.001), with the femur showing further increases in trabecular BV/TV (32%, p<0.05) compared to non-LIV controls. We conclude that changes in the microarchitectures of the tibia and femur respond differently to the same application of LIV (45Hz, 0.2g) in mice and rats.

BackgroundPalliative radiation therapy (RT) for metastatic spine disease significantly increases the risk of vertebral fractures. However, the temporal mechanisms underlying radiation-induced vertebral bone fragility remain poorly understood. ObjectiveTo evaluate the longitudinal effects of a single high-dose irradiation, simulating palliative RT, on vertebral bone mechanical, architectural, and compositional properties in a healthy, skeletally mature rat model. MethodsThirty-one male Sprague Dawley rats received a single 15 Gy lumbar spine irradiation (IR). L4 vertebrae were assessed across all groups (irradiation: 7, 14, and 28 days post-IR, controls: at 0 and 28 days post-IR) for compressive strength and stiffness, micro-CT-derived bone composition and trabecular indices, serum bone turnover markers (NTX and BAP) and advanced glycation endproducts (AGEs). ResultsIrradiation induced progressive deterioration of vertebral bone mechanical properties, with strength decreasing up to 44% and stiffness up to 38% by 28 days post-IR, compared to 0- day controls. Trabecular bone exhibited reduced BMD, BV/TV, and Tb.N with increased Tb.Sp, a shift toward a more rod-like structure. Early post-IR changes suggested disrupted bone remodeling, characterized by elevated NTX and AGEs, but decreased BAP. Multivariable regression demonstrated that Tb.Th and AGEs were independent predictors of stiffness, collectively explaining 61% of its variance. DiscussionHigh-dose irradiation induces sustained temporal degradation of vertebral mechanical properties driven by both trabecular architectural deterioration and alterations in bone matrix quality. Measures of bone composition and non-enzymatic bone turnover suggest this early damage was driven by disruption of bone cellular homeostasis, favoring increased resorption over formation. These findings support that radiation impairs both structural integrity and pre-yield mechanical behavior, providing mechanistic insight into the elevated fracture risk observed clinically after irradiation for metastatic spine disease. Lay summaryThis study used a rat model to mimic palliative radiation therapy for cancer that has spread to the spine and evaluated the changes in bone quality up to 28 days post-therapy. We found that irradiation progressively weakened the structural integrity and composition of the bones in the spine and disrupted the normal balance of bone breakdown and repair, leading to greater bone loss and fragility. Our findings provide insight into the increased risk of fractures observed in patients receiving radiation therapy to the spine and may support efforts to better protect bone health during treatment.

Geroprotectors extend lifespan and improve several aspects of healthspan, yet their effects on skeletal ageing remain poorly understood. They hold potential advantages over current bone-targeted osteoporosis therapies, as they may simultaneously improve bone, neuromuscular function, and vision, thereby reducing the risk of falls, the major cause of fractures. Here we examined, for the first time, the long-term effects of rapamycin, acarbose, and 17-estradiol, administered at lifespan-extending doses on trabecular and cortical bone architecture in male and female UM-HET3 mice measured with micro-computed tomography at 12 and 22 months of age. Bayesian modelling analysis reveals that all interventions produced responses in trabecular bone in females at 22 months. These effects were driven mainly by increases in trabecular number, with little evidence for changes in trabecular thickness. In contrast, treatment effects in males were generally negligible. Cortical responses were modest. Moderate increases in cortical area fraction were observed in females treated with rapamycin or 17-estradiol at 22 months, whereas cortical thickness remained largely unchanged, suggesting a geometrical rather than anabolic effect. Interestingly, geroprotectors strongest skeletal responses in females contrasts with the predominantly male-biased lifespan extension reported for acarbose and 17-estradiol, suggesting differential mechanisms mediating lifespan extension and bone structure preservation.

Micro-computed tomography ({micro}CT) is widely used to assess trabecular bone microarchitecture, with trabecular separation (Tb.Sp) among the core parameters recommended for reporting. Tb.Sp is typically expressed as a single volume-weighted mean derived from maximal sphere fitting, although the underlying distribution of local separation values is rarely examined. Here, we show that Tb.Sp distributions in metaphyseal trabecular bone are frequently non-Gaussian and bimodal or multimodal. Using {micro}CT datasets from three established models of osteoporosis, spinal cord injury (SCI), ovariectomy (OVX), and ageing, we demonstrate that this behaviour is most evident in metaphyseal trabecular bone and is less apparent in epiphyseal trabecular bone or trabecular thickness distributions. We further show that multimodal metaphyseal Tb.Sp distributions correspond to two spatially distinct contributions within the marrow space: lower-diameter local separation within the residual trabecular network, and higher-diameter regions associated with larger contiguous marrow cavities. Based on this observation, we introduce a simple extension to standard morphometric analysis in which Tb.Sp is decomposed into local trabecular separation (Tb.SpL) and marrow cavity separation (Tb.SpM). Tb.Sp decomposition revealed model-specific patterns of trabecular deterioration. SCI was characterised predominantly by increased Tb.SpM, consistent with expansion of larger marrow cavities, whereas OVX showed a more subtle or distributed alteration. Ageing showed changes in both Tb.SpL and Tb.SpM, with the higher-diameter component becoming most prominent in older animals. Together, these findings demonstrate that mean Tb.Sp can mask structurally distinct forms of metaphyseal marrow-space organisation and support reporting distributional descriptors, and where appropriate Tb.SpL and Tb.SpM, alongside conventional Tb.Sp.

Purpose: The primary objective of the Stanford Knee Osteoarthritis PET/MRI Evaluation (SKOPE) study is to develop and evaluate a multimodal, dynamic [18F]NaF PET-MRI framework for characterizing whole-joint physiology and its relationship to osteoarthritis (OA) risk, pain, and disease progression. Specifically, we aim to integrate dynamic PET with quantitative and anatomical MRI, to characterize structural, compositional, and metabolic features across the knee and surrounding musculoskeletal system, evaluate acute tissue responses to exercise, and identify imaging biomarkers associated with OA risk, pain, and disease progression. Methods: The SKOPE study includes multimodal PET-MRI of the knee and surrounding musculoskeletal tissues, with imaging of the knee, tibia, ankle, thigh, hip, pelvis, and lumbosacral spine. Dynamic [18F]NaF PET is combined with conventional anatomical MRI and quantitative MRI techniques, including quantitative double-echo steady-state (qDESS) T2 mapping of cartilage, Dixon fat-fraction imaging, ultrashort echo time (UTE) T2* mapping of short-T2 tissues, UTE imaging of tibial bone, and zero echo time (ZTE) imaging for bone morphology and pseudo-CT generation. Additional MRI sequences characterize muscle composition, bone and joint anatomy, intervertebral discs, and regional vascular anatomy. Selected scans are acquired before and after a standardized exercise protocol to assess the acute physiological response of the joint. Automated segmentation is used to generate subject-specific masks of muscles, bones, vertebrae, and intervertebral discs. A subset of the MRI protocol is repeated at 1- and 2-year follow-up to assess longitudinal changes. Expected Impact: By combining dynamic bone metabolic imaging with quantitative measures of cartilage, menisci, muscle, bone, fat, vascular structures, and the spine and hip, the SKOPE protocol provides a whole-joint and multijoint framework for studying the structural, metabolic, and physiological processes associated with OA and pain. Exercise and longitudinal imaging further enable assessment of acute tissue responses and changes over time, supporting the development of quantitative imaging biomarkers for OA risk, pain, and disease progression.

Critical sized defects (CSDs) are a serious challenge in orthopedics that require the development of more robust and effective treatments to improve quality of life for patients. Current CSD research is limited by the applicable and affordable animal models available. Mice would be the preferred species as they are cheaply housed and have many transgenic variations readily available; however, their small size makes CSD surgeries difficult and expensive. We propose the use of cerclage wires to achieve internal plate fixation. PEEK plates were secured to the right femur of 26 C57BL/6 mice using four cerclage wires to achieve modified double-loop fixation implemented through bicortical holes and defects were created. 10 received 3mm defects and 6 received 4mm defects that were left empty and were taken out to 20 weeks (Group E3, E4). Another 10 received 3mm defects that were filled with a morselized bone graft and were taken out to 8 weeks (Group G3). Blinded longitudinal x-ray grading by orthopedic surgeons was conducted on the empty defects for plate stability and wire fixation. All samples received microCT analysis at their endpoints. There were no significant differences in plate or wire stability between the empty groups and wire scores worsened negligibly over time. MicroCT analysis further supported wire integration as bone growth directly upon the wires was observed in all samples. The efficacy of this model in achieving non-union when left untreated was also confirmed via microCT. Further, only three mice in group G3 achieved union and two of these unions were not optimal. Our study is the first to successfully show that cerclage wire can be used in a murine CSD model to achieve affordability and clinical relevancy.

Spinal cord injury (SCI) causes rapid and severe bone loss in the paralysed lower limbs, particularly at the distal femur and proximal tibia, where fragility fracture risk is high. In vitro nanoscale vibration at 1 kHz has been shown to promote osteogenic differentiation and inhibit osteoclastogenesis, suggesting potential as a targeted mechanical intervention. This study aimed to develop and evaluate a wearable device for delivering and monitoring localised nanovibration at the distal femur in individuals with SCI. The device delivered continuous sinusoidal nanoscale stimulation at 1 kHz via a bone-conduction transducer, with an opposing accelerometer used to monitor transmitted vibration in real time. Design and target-site selection were refined through two healthy-volunteer investigations comparing the distal femur, proximal tibia, and distal tibia. Bovine femur experiments characterised vibration transmission under controlled benchtop conditions. Preliminary repeated-use feasibility was assessed in one individual with motor-complete SCI. Healthy volunteer testing showed that although the ankle initially produced the highest transmitted amplitudes, these were highly variable, and positioning was inconsistent. Within the knee region, the distal femur provided the most practical and repeatable site for a wearable application. In bovine femur experiments, scanning laser vibrometry demonstrated measurable vibration on the condylar surface opposite the transducer, and depth-resolved measurements confirmed that nanoscale vibration remained detectable within bone. A gel interface layer reduced the transmitted amplitude. In the feasibility evaluation, 61 sessions were completed over 14 weeks, with logged accelerometry confirming repeated nanoscale vibration transmission. These findings establish feasibility and support further device optimisation and translational studies.

PurposeEstrogen deficiency drives bone loss through interacting endocrine, oxidative, inflammatory and bone-remodeling disturbances. Ergothioneine (EGT) is a diet-derived thiol/thione antioxidant whose effects on the estrogen-deficient skeleton are unknown. We evaluated whether EGT, alone or combined with vitamin K2, vitamin D3 and magnesium L-threonate, attenuates the skeletal and systemic consequences of ovariectomy (OVX) in mice. MethodsForty-eight female C57BL/6J mice underwent sham surgery or OVX and received daily oral gavage for 12 weeks of vehicle, alendronate (1.53 mg/kg), EGT (30 mg/kg/day), EGT with vitamin K2 (40 {micro}g/kg/day) and vitamin D3 (500 IU/kg/day), or EGT with vitamin K2, magnesium L-threonate (350 mg/kg/day) and vitamin D3 (n = 5-6 analysed per group). Outcomes included the uterine index, tibial micro-computed tomography, distal-femoral histology, and serum bone turnover markers (CTX-I, PINP, osteocalcin), sex hormones, TNF-, IL-6, SOD and MDA. OVX lowered the uterine index and induced tibial trabecular deterioration, with increased CTX-I, decreased PINP and osteocalcin, elevated TNF- and IL-6, reduced SOD and increased MDA (all P < 0.01 vs sham). Alendronate restored tibial micro-CT bone-volume fraction (BV/TV) and trabecular number (P < 0.01 vs OVX). The EGT-based regimens did not significantly restore tibial micro-CT BV/TV, trabecular thickness or trabecular number (all P > 0.05 vs OVX), but significantly increased trabecular area on distal-femoral histology (OVX 7.6% vs 14.2-15.0% across regimens; P < 0.05 vs OVX) and lowered CTX-I, TNF-, IL-6 and MDA while raising SOD and partially restoring PINP and osteocalcin (P < 0.05-0.01 vs OVX). Because the histological and micro-CT endpoints were assessed at different skeletal sites, structural interpretation is cautious. Apparent increases in serum estradiol were assay-dependent and are regarded as exploratory. Ergothioneine-based nutritional regimens improved the systemic oxidative, inflammatory and bone-turnover environment of estrogen-deficient bone loss and preserved distal-femoral trabecular area on histology, although tibial three-dimensional microarchitecture by micro-CT was not restored. Because the histological and micro-CT endpoints were assessed at different skeletal sites, the structural interpretation is necessarily cautious. These findings support further evaluation of EGT as a dietary adjunct, with mechanistic and dose-optimization studies warranted.

Abstract Calcific deposits in the arterial media have been associated with a number of metabolic and genetic disorders including diabetes, chronic kidney disease and generalized arterial calcification of infancy. While medial calcification and physiologic hard tissue mineralization in the skeleton are both regulated by several common determinants, emerging data suggest that there might be fundamental differences in the mechanisms underlying these two processes. Objective: We previously demonstrated that elastin haploinsufficiency delays medial calcification in MGP-deficient mice. Here, using mice in which a human ELN transgene rescues mouse elastin deficiency, we investigated whether the origin and abundance of arterial elastin differentially affect the initiation and progression of medial calcification. Approach and Results: We pursued a transgenic approach to alter the arterial elastin scaffold in MGP-deficient mice. Our analyses of a humanized MGP-deficient model with 40% reduction of medial elastin content showed a complete absence of the early-stage vascular calcification. Additionally, we showed that mouse and human elastin orthologues affect vascular calcification in a comparable manner. Conclusion: Arterial elastin abundance, rather than orthologue origin, modulates the initiation and progression of medial calcification in MGP-deficient mice. A further reduction in arterial elastin beyond that achieved by elastin haploinsufficiency profoundly delays mineral deposition and maturation, whereas restoration of elastin abundance through transgenic human ELN expression restores arterial calcification.

Objective: To examine associations between volume and intensity of leisure time physical activity (LTPA) and fracture risk during midlife and determine whether adherence to World Health Organisation (WHO) physical activity recommendations was associated with fracture risk. Methods: Cross-sectional analysis of UK Biobank participants aged 40 to 65 years using self-reported physical activity and fracture data. LTPA volume (LTPAV) was derived from walking, moderate and vigorous activity. Participants were categorised into LTPAV quintiles and by adherence to WHO physical activity recommendations. Multivariable logistic regression examined associations with self-reported fracture within the previous five years, with sex stratified analyses. Results: Among 322,749 participants, 53% were female with a mean age of 47 years. Fracture risk increased with higher LTPAV, although the association was non-linear and varied by age and sex. The strongest associations were in the highest quintile among men and women aged 40 to 49 years (OR 1.81, 95% CI 1.64 to 1.99 and OR 1.42, 95% CI 1.28 to 1.58 respectively). In mutually adjusted models, vigorous activity demonstrated the strongest independent association with fracture risk. Meeting WHO physical activity recommendations, without exceeding them, was not associated with increased fracture risk. Conclusions: Higher fracture risk was observed in individuals undertaking higher volumes of leisure-time physical activity, with the association largely driven by vigorous-intensity activity. The association was strongest in adults aged 40 to 49 years and in men. Physical activity consistent with current WHO recommendations was not associated with increased fracture risk, supporting continued promotion of physical activity during midlife.