Journal of Anatomy

Mammal tails have long been recognized for their diversity of morphological form and function, however, there remains a substantial gap between the motivation to understand and emulate the various performance functions of the tail and what is known about tail anatomy. In this study, we were motivated to discover the anatomical foundations of the fast, whipping motions of the tail of the lesser Egyptian jerboa (Jaculus jaculus), which may aid in the quick changes of direction as the animal escapes from predators using ricochetal bipedal hopping. We employed microCT scans, dissections, and museum data to describe the musculoskeletal anatomy of the jerboa in comparison with the laboratory mouse (Mus musculus) and rat (Rattus norvegicus). While many aspects of tail anatomy are conserved across these species, the jerboa does possess unique characteristics such as an extremely long tail arising from caudal vertebral elongation, development of extensive dorsal musculature differentiated into lateral and medial components to increase points of skeletal attachment, and a novel anatomical feature - the bi-lobed cranial transverse process - which serves as a supernumerary dorsal tendon attachment site and possible brace to protect the ventral tendons and intrinsic muscles for a section of caudal vertebrae which likely experiences high mechanical stress.

Abstract Introduction: Proximal humerus fractures account for approximately 5-6% of all adult fractures and are primarily managed nonoperatively. Healing is conventionally monitored with radiographs, with radiopaque callus formation indicating healing. Visible radiographic callus appears weeks after biological union begins. Ultrasound provides a dynamic, radiation-free, and cost-effective method that can detect early callus formation before x-ray visibility. Although ultrasound has demonstrated utility for fracture healing in the clavicle and humeral shaft, its role in proximal humerus fractures remains unclear. Methods: This single-centre prospective study will be conducted in two phases. The pilot phase will measure inter-rater reliability for ultrasound detection of early callus formation at 2 and 4 weeks post-injury. Ten patients with proximal humerus fractures treated nonoperatively will undergo standardized anterior and lateral scans. Each patient will generate four saved images (short- and long-axis views), producing forty anonymized images independently reviewed by two raters. The prospective cohort phase will recruit approximately thirty additional patients. Results: Reliability will be quantified using Cohens kappa. A power calculation will be performed after pilot analysis. Results from the prospective cohort phase will help determine the association and predictive value of early ultrasound-detected bridging callus for radiographic and clinical union at three and six months. Patient reported outcome measures will be assessed using the Quick Disabilities of Arm, Shoulder and Hand (QuickDASH) questionnaire. Discussion: This study will develop and validate a standardized ultrasound protocol for assessing early fracture healing in proximal humerus fractures. By establishing both inter-rater reliability and predictive value, the findings may support ultrasound as a reproducible, radiation-free adjunct to conventional imaging and enable earlier identification of union status.

Sharks exhibit extraordinary morphological diversity across a wide range of ecological niches, yet large-scale, high-resolution digital datasets of their internal anatomy remain limited. Here we present an open-access 3D shark anatomical repository derived from published X-ray computed tomography (CT) data, featuring manually segmented and systematically annotated models of the chondrocranium, visceral arches, axial skeleton, musculature, and viscera in standard STL format. The dataset comprises 117 individuals, representing 72 species across 25 families and all nine extant shark orders, with 115 full-body reconstructions and two head-only models. This open-access dataset offers a comprehensive resource for comparative anatomy, biomechanical simulations, evolutionary developmental biology and biomimetics research of extant sharks.

Relapse of aligned mandibular anterior teeth and the progressive collapse of the mandibular anterior arch are historically striking problems for orthodontists. The etiology of this collapse, and the cause of mesial molar drift, are unknown. However, light continuous (quasi-continuous) intra-oral pressures and forces applied to the mandibular dentition have been implicated. To explore this further, we use three-dimensional finite element analysis to investigate the influence of these intra-oral loads (tongue pressure, lip-cheek pressure, and interdental force) on mandibular arch collapse and mesial molar drift. Dentitions of three-dimensional finite element mandibular models were subjected to a wide range of simulated tongue pressures, lip-cheek pressures, and transseptal fiber-mediated interdental forces reported in the literature. Resulting crown displacement measurements from these isolated loads were made along with measurements resulting from simultaneous combined application of literature-defined mean tongue pressure, lip-cheek pressure, and interdental force. Our results indicate that tongue pressure alone results in generalized arch expansion and tooth spacing while lip-cheek pressure and interdental force result in generalized arch collapse, anterior crowding, and mesial molar displacement. Simultaneous application of tongue pressure, lip-cheek pressure, and interdental force mean values, as would occur in vivo, results in incisor crowding, intercanine width reduction, and mesial molar displacement. Our results suggest mandibular anterior arch collapse (incisor crowding / intercanine width reduction), and mesial molar displacement result from simultaneous application of tongue pressure, lip-cheek pressure, and interdental force.

The morphogenesis of the optic cup provides a robust system for studying how two apposed epithelial monolayers with distinct properties fold and stretch in a coordinated manner to form the primordial eye. While much research has been conducted on the temporal dynamics of retinal neuroepithelium invagination, the spatial organization and stretching of the retinal pigment epithelium has received less attention. The fish species Astyanax mexicanus offers a unique model to examine the mechanisms of optic tissue morphogenesis through a comparative lens, as it exhibits natural variation in eye development between its river-dwelling and cave-adapted morphs. Using quantitative 3D imaging of optic cups from both morphs, we found that RPE morphogenesis involves transient, graded, and anisotropic cell stretching that patterns the epithelium during optic cup shaping. Analyses of RPE nuclear spacing and cell morphology showed that tissue stretching gradually increases along the proximo-distal axis, suggesting maximal tension in the elongated distal RPE cells aligned along the optic cup meridians. Furthermore, nuclear volumes and apical surface areas of RPE cells scaled spatially along the same axis, independently of endoreplication. In the cavefish natural mutant, RPE expansion was delayed by over six hours and proximal stretching exhibited altered isotropy, indicative of disrupted temporal coordination and suggesting modified mechanical constraints. These results demonstrate that RPE morphogenesis is a highly heterogeneous process from a spatiotemporal perspective, offering new insights into the study of the biomechanical principles of eye development in vertebrates. Summary statementThis study reveals the emergence of cell morphology gradients within the retinal pigment epithelium during morphogenesis of the eye in two distinct populations of the same species of fish.

Extremely elongate necks have convergently evolved in several amniote lineages, including both aquatic and terrestrial forms (Fig. 1). The development of such a feature brings with it advantages in obtaining food items, but also biomechanical challenges, such as flexibility, stability, lift, and inertia. In Tanystropheus, a particularly long-necked Triassic archosauromorph, the neck is composed of only 13, mostly extraordinarily elongated and slender cervical vertebrae and accompanying rod-like, overlapping ribs, making it arguably the most extreme example of neck elongation in tetrapod evolution (Fig. 1;1-6). Understanding the function of this remarkable neck provides insights into the limits of neck elongation in amniotes and the evolution of morphological novelties in Triassic reptiles. Here we present the first quantitative biomechanical analysis of the Tanystropheus neck using a digital model based on three-dimensionally preserved bones. We assessed its range of motion (ROM) and performed finite element analysis (FEA) on the individual cervical ribs and the neck model in different configurations. Our results indicate that the neck of Tanystropheus was not extremely stiff, as previously postulated, and the ribs likely did not impair its movements. They transferred tensile forces towards the base of the neck, similar to what hypothesized for sauropods7. This study elucidates the bauplan of an extremely specialized animal and brings us closer to understanding the patterns of achieving neck elongation in vertebrates.

Microcomputed tomography (micro-CT) is a useful tool that can be utilised for 3D structural characterisation and volumetric quantification of small biological specimens. Its potential application is particularly valuable within the field of cardiac development, where phenotypic profiling at the whole organ, cell, and molecular level is often most informative within the same sample. Consequently, this study sought to develop a multimodal imaging protocol to enable 3D phenotypic characterisation of embryonic avian hearts (iodine-based contrast X-ray imaging) prior to immunohistochemistry-based cell and molecular analysis. Micro-CT parameters were tested to establish an optimal protocol for 3D analysis of embryonic cardiac specimens across multiple developmental timepoints. Optimised parameters provided reliable and reproducible 3D analysis of cardiac macrostructures. Sodium thiosulphate treatment of X-ray imaged hearts effectively reversed the iodine-based contrast stain whilst maintaining antigen availability of nuclear, membranous, and cytoplasmic targets in traditional downstream imaging studies. Together, this study demonstrates a robust and highly efficient multimodal imaging strategy to comprehensively characterise cardiac morphology in avian embryos and may serve as a versatile foundation for a broad range of bioimaging applications within the wider scientific community.

Background: The hydrodynamic model of hydrocephalus proposes that ventriculomegaly is driven by exaggerated intraventricular pulsations rather than impaired CSF circulation alone. Under this model, endoscopic third ventriculostomy with choroid plexus cauterization (ETV/CPC) treats hydrocephalus by creating a pulsation absorber and by reducing a primary source of intraventricular pulsation. However, direct intraoperative human evidence supporting this two-step mechanism is lacking. This study aimed to test the hypothesis that ETV followed by CPC would produce measurable, stepwise decreases in mean intraventricular pressure (ICP) and pulsation amplitude in infants with hydrocephalus. Methods: This single-institution proof-of-concept study included infants with symptomatic hydrocephalus undergoing ETV/CPC as the first definitive treatment. A fiber-optic ICP sensor was attached to the operative ventriculoscope and passively recorded mean and pulsatile ICP (pulsation amplitude) throughout the procedure. Longitudinal brain parenchymal volume (BPV) and cerebrospinal fluid volume (CSFV) were obtained through segmentation of clinically acquired T2-weighted MRI and converted to age- and sex-matched z-scores. All patients were followed for a minimum of 6 months postoperatively. Results: Five infants (median corrected age at ETV/CPC 8 months) were included. No surgical complications occurred, and no ETV/CPC failures were observed during follow-up. Overall, mean ICP decreased by 56-97% after the combined procedure in four patients. In three patients (Patients 1, 3, and 5), both mean ICP and pulsation amplitude decreased stepwise following ETV and then CPC, consistent with the hypothesized therapeutic mechanism. Patient 4 demonstrated a large reduction in mean ICP after ETV with minimal additional effect from CPC and no significant change in pulsation amplitude. Patient 2 demonstrated neither a reduction in mean ICP nor a meaningful change in pulsation amplitude after either procedure; this patient also had a delayed and atypical clinical response. Intracranial segmentation demonstrated BPV z-score stabilization within normal range and CSFV plateau in all patients after surgery. Conclusions: This proof-of-concept study provides the first direct intraoperative human evidence supporting the hydrodynamic mechanism of ETV/CPC in a subset of infant with hydrocephalus. Our findings suggest that determination of intraoperative ICP parameters is feasible, safe and might ultimately prove helpful in improving patient selection for ETV/CPC, warranting further investigation in larger cohorts.

Background: Children with structural heart disease (SHD), particularly congenital heart disease (CHD), are increasingly recognised as being at risk of adverse neurological outcomes. Although advances in cardiac surgery and perioperative care have markedly improved survival, epilepsy has emerged as an important long-term complication. Reported prevalence estimates vary considerably across studies, and the overall burden remains uncertain. This systematic review and meta-analysis aimed to estimate the pooled prevalence of epilepsy among children with SHD and explore differences according to geographic region, lesion characteristics, and surgical exposure. Methods: This systematic review and meta-analysis was conducted in accordance with PRISMA 2020 and MOOSE guidelines and registered in PROSPERO (CRD420261378572). PubMed/MEDLINE, Scopus, and ProQuest were searched for observational studies published between January 2000 and December 2025. Eligible studies included children aged 0-18 years with SHD or CHD reporting epilepsy prevalence or incidence. Two reviewers independently screened studies, extracted data, and assessed methodological quality using the Joanna Briggs Institute Critical Appraisal Checklist for Prevalence Studies. A random-effects meta-analysis was performed to estimate pooled prevalence with 95% confidence intervals (CI). Results: Eight cohort studies comprising 21,731 children were included. Studies were conducted across North America, Europe, and Asia and predominantly involved surgically managed CHD populations. The pooled prevalence of epilepsy was 3.0% (95% CI 1.3%-4.8%), substantially higher than estimates reported in the general paediatric population. Heterogeneity was considerable (I{superscript 2} = 98.0%; p < 0.001). The 95% prediction interval ranged from 0% to 8.1%, indicating substantial variability across populations. Narrative subgroup synthesis suggested higher epilepsy prevalence among children with cyanotic and complex lesions and among surgically managed cohorts, particularly those exposed to cardiopulmonary bypass and perioperative neurological complications. Most studies were rated as having low risk of bias, and sensitivity analyses demonstrated stable findings. Conclusions: Children with SHD have a substantially increased burden of epilepsy compared with the general paediatric population. Complex lesions, perioperative neurological injury, and cardiac surgical exposure may contribute to epileptogenesis. Long-term neurological surveillance and multidisciplinary neurodevelopmental follow-up should be integrated into routine care for children with SHD.

The hallmark of sessile adult ascidians is a vase-like shape with a single oral and atrial siphon. Ciona, however, develops two atrial siphons after metamorphosis, which subsequently fuse into one. The mechanisms underlying this fusion are unknown. This study suggests that Hox2 controls this process. Hox2-knockout animals using Transcription-Activator-Like Effector Nuclease (TALEN) retain two atrial siphons throughout their lives. During normal fusion, epidermal cells between the siphons flatten along the anterior-posterior axis. This cellular flattening does not occur in Hox2-knockout animals, suggesting that the shape change in the epidermal cells produces tension, allowing the atrial siphon openings to converge at the midline for fusion. Hox2-knockout animals lack cupular organs, which are suspected hydrodynamic sensors in the internal epithelium of the fused atrial siphon and on the sperm duct. Among several knockout attempts, atrial siphon fusion was reproduced by only one TALEN pair, suggesting that this phenotype is driven by a mutation having a broader effect than those abolishing protein function. Many ascidians, unlike Ciona, develop a single atrial siphon shortly after metamorphosis. Our findings suggest that a phylogenetically conserved gene, Hox2, establishes this group-specific atrial siphon formation mechanism in Ciona.

Objectives: To develop and validate a disease-specific patient-reported outcome (PRO) measure for spinal and bulbar muscular atrophy (SBMA). Methods: A three-stage sequential design was adopted. Items were generated through qualitative interviews with patients with SBMA and expert review, refined using quantitative analyses, and evaluated for reliability and validity in independent cohorts from Japan and the United States. Results: Interviews with 12 patients generated 234 candidate items, which were refined into a final 31-item SBMAPRO comprising five domains based on an online survey of 106 patients. Internal consistency across domains ranged from Cronbach's alpha values of 0.651 to 0.901. In the Japanese cohort, test-retest reliability yielded intraclass correlation coefficients of 0.941 for physical function, 0.877 for mental health, and 0.858 for social function. Construct validity was examined through correlations with disease-specific functional measurements and the 36-Item Short Form Survey (SF-36). The SBMAPRO correlated with the SBMA Functional Rating Scale (r = -0.826, p <0.001) and with the SF-36 mental health (r = -0.693, p <0.001) and social functioning (r = -0.617, p <0.001) domains. In subscale analyses, the SBMAPRO social domain was associated with trunk-lower limb-related functional impairment (r = -0.587, p < 0.001). Similar patterns were observed in the American cohort. Conclusion: The SBMAPRO demonstrated reliability and validity in Japanese and American cohorts. Associations between mental and social domains and trunk-lower limb dysfunction suggest that mobility impairment may contribute to psychological burden and restricted social participation in SBMA, indicating that this disease-specific PRO may complement clinician-rated measures.

Purpose To explore patient and caregiver perspectives on factors influencing mobility during hospitalization after hip fracture surgery, and how these are experienced and negotiated in everyday hospital practice. Materials and methods A qualitative interview study informed by a hermeneutic-phenomenological perspective was conducted in a hospital setting in Denmark. Using purposive sampling with maximum variation, ten patients and nine caregivers were interviewed during hospitalization. Data were analyzed using reflexive thematic analysis following Braun and Clarke. Results Five interrelated themes were identified; (1) Body and mind in transition; (2) Communication as a prerequisite for safety and mobility; (3) Structural barriers and ambiguities in responsibility; (4) The physical environment and ward culture; and (5) Mobility as preparation for life after discharge. Across themes, mobility emerged as a socially shaped and negotiated practice through everyday interactions, communication, organizational routines, and situational support during hospitalization. Conclusions Mobility during hospitalization after hip fracture surgery emerged as a context-dependent and socially shaped practice rather than a purely physical task. These findings suggest that rehabilitation during hospitalization may need to attend not only to mobility prescription, but also to relational, communicative, and contextual aspects of everyday ward routines that shape patients' confidence and participation.

Background The incidence of post-operative periprosthetic femoral fractures (POPFFs) is increasing. However, specific clinical guidance relating to patient management does not exist, resulting in variations in care and outcomes. This study aimed to elicit and synthesise expert knowledge in POPFF service delivery and explore views on variations in service provision and the factors influencing these. Methods Semi-structured interviews were undertaken with healthcare professionals with expertise in POPFF care from England and Wales to explore current practices, challenges, service variations and perceived future opportunities. Participants were identified through specialist research and clinical networks for POPFF and hip fracture care, authors of key publications on the subject, national leads for POPFF/hip fracture networks, and research team contacts. Interviews were analysed using thematic analysis. Results Ten interviews were undertaken with experts in POPFF services across a range of professional roles. Four themes were identified: conceptualisation of POPFF (by different professional groups and in different service settings) and understanding of POPFF patient needs; sources of variation in management and care of POPFF patients; service model rationales, advantages and disadvantages; and potential strategies to improve POPFF care. Conclusion When designing POPFF services, we suggest that four key areas need consideration: the extent to which POPFF patients are a distinct group with particular care needs; the necessity for and consequences of patient transfer between wards and hospitals; the resourcing of extensive multidisciplinary support for POPFF patients; and the need for national initiatives to encourage service developments. These findings should form the basis of future clinical guidance. Sensitivity to contextual factors driving variation in services is needed to ultimately improve care for POPFF patients.

Muscle force sharing during locomotion is influenced by the mechanical demands of movement and the contractile properties of synergistic muscles. In cats, plantarflexor muscles exhibit distinct functional specialization, with the slow-fibred soleus maintaining relatively constant force across conditions while faster muscles such as the plantaris and gastrocnemius increase force production with increasing locomotor demand. However, it remains unclear whether similar force-sharing patterns occur in larger animals with different musculoskeletal designs. Therefore, the purpose of this study was to examine force sharing between the superficial digital flexor (SDF) and medial gastrocnemius (MG) muscles during treadmill locomotion in sheep. Tendon buckle force transducers were surgically implanted on the SDF and MG tendons of seven sheep, and in vivo muscle forces were recorded during walking and trotting across different speeds and inclines. Both muscles increased force with increasing speed and incline; however, speed had a substantially greater effect than incline. The SDF consistently produced greater absolute force than the MG across all conditions, whereas the MG exhibited slightly larger relative increases in force with increasing speed. Time to peak force decreased with increasing speed in both muscles, although the SDF reached peak force later in stance than the MG across conditions. In contrast to the distinct specialization observed in cats, neither muscle displayed a relatively condition-independent, soleus-like force contribution. These findings suggest that force sharing in sheep is more distributed across synergistic muscles and may reflect the influence of musculoskeletal design, tendon compliance, and mixed fibre-type composition on muscle function in larger species.

Sutures are the primary sites of cranial bone growth, allowing the skull to accommodate the growing brain. External mechanical stimulus has been shown to delay suture fusion and induce tissue remodelling. Recent studies suggest that in vivo cyclic bone loading increased proliferation of mesenchymal stem cells (MSC) in the coronal suture. The overall aim of this study was to understand how many loading sessions (exposure-response) and how long after loading (time-course) did MSC proliferation increase in the coronal suture. In the exposure-response analysis, mice underwent 1, 3, or 5 loading sessions between Postnatal day 7 (P7) and P11, and in the time-course analysis, treated mice underwent 10 loading sessions between P7 and P21. Loading sessions were 10 minutes at a frequency of 1 Hz and a force of 10 g (0.1 N). The loading tip was positioned on the posterior aspect of the left frontal bone, dorsal to the coronal suture. The EdU marker shows a statistically significant increase in proliferation after one loading session and a decrease after three loading sessions. The PCNA marker shows a statistically significant increase after three and five loading sessions. The exposure-response analysis showed that when the results of both markers are combined, levels of proliferation cannot be interpreted until at least five loading sessions have been completed, after which a clear increase in proliferation was observed. In the time-course analysis, proliferation was highest immediately after the final treatment session and 24 hours after the final loading session the effects of mechanical bone loading gradually returned to baseline.

Introduction: Acute compartment syndrome (ACS) is a limb-threatening complication of extremity trauma that requires timely diagnosis to prevent irreversible muscle and nerve injury. Current diagnostic methods are invasive, intermittent, and operator-dependent. We evaluated the feasibility of a novel, Bluetooth-enabled electrical impedance myography (EIM) device (mAlert, Myolex, Inc., Brookline, MA, USA) for continuous, noninvasive detection of ACS-related tissue changes. Methods: Ten Yorkshire swine underwent anterior tibial compartment monitoring using three ACS models: albumin infusion (ALB, n=3), femoral artery and vein ligation (LIG, n=3), and combined albumin infusion plus ligation (ALB+LIG, n=4). Resistance (R), reactance (X), and phase (P) were measured every minute across 1 to 199 kHz alongside continuous intra-compartmental pressure (ICP) monitoring. Group differences in normalized impedance trends were evaluated using the Kruskal Wallis test with Dunn post hoc correction. As a proof-of-concept human study, nine healthy volunteers wore the device for up to five days to assess electrode durability and signal stability. Tissue ischemia was validated using pimonidazole immunohistochemistry. Results: ALB infusion produced progressive, frequency-dependent decreases in R, X, and P, whereas LIG produced consistent increases in R and X across frequencies. The ALB+LIG model generated mixed responses, reflecting the competing effects of edema and ischemia. Normalized phase slopes differed significantly among groups (H=6.14, p=0.046), with post hoc testing showing significant divergence between the ALB and LIG models (p=0.041). Control limbs remained stable throughout monitoring. Pimonidazole staining confirmed hypoxic injury in the intervention limb. In the human pilot study, three participants completed five days of monitoring, demonstrating sustained signal acquisition, while electrode degradation limited data collection in the remaining participants. Conclusions: This preliminary feasibility study demonstrates that wearable EIM can continuously detect model-specific physiological changes associated with ACS in a large-animal model. These findings support further development and clinical evaluation of wearable EIM as a non-invasive monitoring technology for early ACS detection in trauma patients.

Abstract Importance Acute otitis media is the most common infection in children and a major reason for antibiotic prescriptions, up to one third of which may be unnecessary. Sector of care may influence AOM management through differences in access to care, specialist involvement, parental expectations and financial foundation. Objective The objective is to examine differences in antibiotic prescribing practices between healthcare sectors. Design This is a nationwide register-based study comparing data from different healthcare sectors. Setting Finnish primary and secondary healthcare, covering both public- and private-sector visits. Prescriptions and sociodemographic information were linked from nationwide registers. Participants We included children under 18 years old who received a diagnosis of acute otitis media, defined by ICD-10 codes H65-H67, between January 1, 2017 and December 31, 2022. Exposures The exposure is the sector of care (public sector vs. private sector). Main Outcomes and Measures Primary outcomes were antibiotic prescribing, guideline adherence of the prescribed antibiotics, and rates of management failure. Secondary outcomes included antibiotic selection and guideline-adherent eligibility for tympanostomy tube placement. Associations were estimated using adjusted odds ratios (aORs) with 95% confidence intervals (CIs). Results The study included 295 064 children with 596 634 acute otitis media index visits, of which 77.6% resulted in an antibiotic prescription. Private-sector visits were associated with higher odds of antibiotic being prescribed (adjusted odds ratio [aOR]: 1.45; 95% CI: 1.41-1.49). Overall, 87.3% of antibiotic prescriptions were guideline adherent, but private-sector care was associated with lower odds of guideline-adherent prescribing (aOR: 0.64; 95% CI: 0.60-0.69). Compared with amoxicillin, the private sector showed higher odds of prescribing amoxicillin-clavulanic acid (32.8% vs. 8.3%; aOR: 3.00; 95% CI: 2.91-3.10). Management failure occurred in 7.0% of episodes and was more common in the private sector (aOR:1.52; 95% CI: 1.48-1.56). Only 48.7% of all tympanostomy tube insertions met the eligibility criteria. Conclusions and Relevance In this study overall adherence to guideline-recommended antibiotic treatment for AOM was high in Finland. Nevertheless, observed clinically meaningful sectoral differences in antibiotic selection, treatment failure, and tympanostomy eligibility adherence indicate a need for targeted antimicrobial stewardship and quality-improvement efforts, especially in the private sector.

Purpose: Animal models of myopia typically induce monocular refractive shifts via form deprivation (FD) or lens-induced myopia (LIM), modeling susceptibility to myopia, but with potentially limited applicability to childhood myopia. Here we describe a novel, genetically diverse mouse model of naturally occurring refractive error (NORE) with three distinct refractive phenotypes: hyperopic, myopic, and intermediate. Methods: C57BL/6J mice were mated to 129S2/SvPasCrl mice to create F1 or F2 offspring. Refractive errors in male and female F1 (N=21) and F2 (N=101) mice were assessed on postnatal days (P) 28 and 42 using photorefractometry. In a subset of mice (N=30 - 40), corneal radius of curvature, axial ocular dimensions, retinal and visual function were assessed. Results: F2 mice were classified as NORE with either hyperopic (RE [&ge;] 0 diopters (D) at P28 and P42), myopic (RE<0D at P28 and P42) or intermediate (RE<0D at P28 and RE [&ge;] 0D at P42) refractions based on individual trajectories. All ocular parameters changed with age, with significantly slower growth in axial length and vitreous chamber depth in the intermediate versus myopic mice (p<0.05). Lens thickness was smaller in the myopic group at P28. Differences in refraction were not attributed to variances in retinal function or dopamine signaling. Conclusions: NORE mice represent a novel, genetically diverse wild-type mouse model that, unlike traditional models, does not require interventions such as FD or LIM to induce myopia. NORE mice provide a valuable tool for future investigations of genetic and environmental mechanisms and targeted therapeutic strategies for refractive errors.

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.

Neuromuscular contractures arising from neonatal brachial plexus injuries (NBPI) are highly disabling and currently incurable. We previously showed that contractures involve impaired longitudinal growth of denervated muscles, a defect mediated through myostatin (MSTN) signaling, a potent negative regulator of muscle size. However, MSTN-mediated contractures occur independent of canonical signaling pathways, including SMAD 2/3 and AKT/mTOR. Through a mouse model of NBPI, our present study extended these findings by revealing pharmacologic inhibition of JNK signaling, a noncanonical pathway downstream of MSTN, partially rescues contractures without restoring muscle length. Rather, JNK activation upregulates myofiber expression of the target gene Lmna, which encodes the nuclear envelope proteins Lamin A and Lamin C that are vital for nuclear stability, resulting in pervasive myonuclear displacement. These results suggest that other factors contribute to contracture pathology beyond deficits in longitudinal muscle growth. Further, while JNK inhibition does not restore length of denervated muscles, it impedes size and mass of normally innervated neonatal muscles, suggesting a requirement of JNK signaling for neonatal muscle growth. Our collective findings thereby establish new mechanistic insights into the molecular basis of aberrant muscle growth and neuromuscular contracture formation, potentially leading to novel targets for muscle restorative strategies and medical contracture prevention.