Journal of Orthopaedic Research

To correct lower limb length discrepancies, orthopedic surgeons often perform limb lengthening procedures. These procedures involve directly lengthening a primary bone (e.g., femur), which also stretches the muscles and tendons spanning the elongation site. Limb lengthening procedures improve lower-limb length symmetry, often at the expense of chronic joint-level decrements. For example, knee joint range of motion and strength does not always return to pre-surgery values following femur lengthening. These joint-level decrements governed by altered muscle force-length characteristics, but it is unestablished how human muscles remodel during surgical limb lengthening. Here, we characterized bilateral human vastus lateralis fascicle force-length profiles following femur lengthening. At 2.2 {+/-} 1.7 years (Avg {+/-} SE) post-initial surgery, the lengthened limb's vastus lateralis fascicles were longer, effectively stiffer, and weaker than the contralateral limb. The lengthened limb's vastus lateralis fascicles were 38 mm longer (Avg) than that of the contralateral limb, even though the lengthened limb's femur was only 31 mm longer (Avg). The onset of vastus lateralis fascicle passive force production began at 22% shorter (Avg) operating lengths in lengthened versus contralateral limb muscles. Additionally, vastus lateralis peak active force production was 34% less (Avg) in the lengthened versus contralateral limbs, and in-series quadriceps tendon stiffness was not stiffer in lengthened limbs. These data suggest that active muscle tissues lengthen more than passive muscle tissues following limb lengthening, effectively creating stiffer muscles. Years after limb lengthening, patient muscles exhibit numerous differences in their force-length properties versus that of natural growth, likely contributing to impaired joint-function.

Osteoarthritis is characterized by inflammation, chondrocyte dysfunction, and progressive cartilage degradation. Boric acid (BA), a physiologically relevant boron compound, has shown anti-inflammatory properties, but its effects on human articular chondrocytes remain unclear. This study investigated whether BA could protect primary human chondrocytes against lipopolysaccharide-induced inflammatory injury. Cell survival, membrane damage, apoptosis, inflammatory mediator production, and expression of genes related to inflammation and extracellular matrix degradation were assessed. BA improved chondrocyte survival and reduced membrane damage and apoptosis following inflammatory stimulation. It also suppressed inflammatory and matrix-degrading gene expression, nitrite production, and the release of proinflammatory mediators. These protective effects were generally more pronounced with the higher treatment dose. Analysis of publicly available human chondrocyte RNA-sequencing datasets provided complementary support for the relevance of several investigated inflammatory and catabolic targets. Overall, these findings demonstrate that BA protects primary human chondrocytes against inflammatory and catabolic injury and support its further investigation as a potential chondroprotective approach in osteoarthritis.

Introduction: Osteoarthritis (OA) is a degenerative joint condition characterized by chronic pain and the need for pain management. Locally targeting the endocytotic AP2 complex in nociceptors presents a potential strategy for providing sustained pain relief in individuals with OA. Objective: We investigated whether pain behavior associated with OA can be mitigated by genetically silencing the AP2alpha2 subunit of the AP2 complex in nociceptors and by pharmacologically inhibiting the AP2 complex through the intraarticular administration of a small lipidated decoy peptide. Method: Monoiodoacetate (MIA) was employed to induce knee joint OA in mice and rats. Pain behavior was assessed using dynamic weight-bearing and von Frey filaments. Upon confirmation of established OA pain behavior, in vivo AP2alpha2 genetic knockdown in mice was achieved through sciatic nerve transfection of a targeting AP2alpha2 short hairpin RNA (shRNA). To pharmacologically target endocytosis, a single intraarticular injection of peptide was administered into the arthritic knee of rats. The injection contained either the AP2 inhibitor peptide or a scrambled peptide control. Results: Pain behavior was significantly reduced after both genetic and pharmacological disruption of AP2-driven endocytosis. Animals treated with the Ap2 inhibitor peptide exhibited reduced pain behavior throughout the 28-day assay period. Following the completion of behavioral testing, arthritic knee joints and contralateral healthy knee joints were subsequently collected to assess the impact of the treatment on disease progression. Micro-computed tomography analysis revealed a preservation of bone volume in the arthritic joints that received the AP2 inhibitor peptide treatment, in contrast to the scrambled peptide group. Conclusion: These findings demonstrate that the inhibition of nociceptor endocytosis by a small lipidated peptide presents a promising approach to provide sustained relief from joint pain in individuals with arthritis.

Current treatment of orthopedic ligament injury relies principally on non-regenerative materials and surgical repair rather than strategies that promote intrinsic tissue regeneration. This study evaluated whether biologic augmentation with XWRAP, a human amniotic membrane allograft, combined with a cryopreserved amniotic-fluid-derived biologic containing micronized human amnion membrane, promotes regeneration of ligament architecture in a rabbit medial collateral ligament (MCL) gap-defect model. Standardized 4-mm mid-substance MCL gap defects were created in New Zealand White rabbits (n=3) and either treated with the amniotic membrane/amniotic-fluid biologic combination or left untreated, with intact contralateral or adjacent MCL serving as native controls; ligaments were evaluated by transmission electron microscopy at 2 and 6 weeks post-procedure, with collagen fibril diameter quantified from calibrated high-magnification micrographs. Treated defects developed significantly larger mean collagen fibril diameters than untreated defects at both time points (75 vs. 50 nm at 2 weeks and 88 vs. 62 nm at 6 weeks; p<0.0001 for each comparison), reaching approximately 90% of native, uninjured ligament fibril diameter (98 nm) by 6 weeks. Treated defects also developed a broader, bimodal fibril-diameter distribution resembling native ligament architecture, whereas untreated defects remained characterized by a narrow, unimodal population of small-diameter fibrils typical of scar-associated repair. These findings indicate that biologic augmentation with XWRAP combined with an amniotic-fluid-derived biologic promotes a regenerative, rather than purely reparative, healing response following ligament injury, progressively restoring collagen fibril architecture toward that of native tissue in this preclinical model.

The primary source of strength in ligaments and tendons are hierarchically organized collagen fibers. These fibers largely do not regenerate after injury, with repair, nor in engineered replacements, limiting treatment options. Previously, we developed a culture system which guides ACL fibroblasts in high-density collagen gels to form native-size hierarchical fibers over 6 weeks, and demonstrated that intermittent cyclic stretch further improves maturation. However, additional maturation is needed for clinical relevance. Interestingly, we found cyclic load affected cells differentially depending on the degree of organization, with 10% cyclic strain driving early improvements in unorganized gels and 5% strain being more beneficial later in culture once cells were on aligned fibers. Here, we explored whether a stepped cyclic load, that increased or decreased in strain magnitude as collagen fibers developed, further improved maturation. We hypothesized that progressively decreasing cyclic strain as organization increases would drive cells to produce more mature hierarchical fibers, resulting in stronger replacements. Controls had intermittent cyclic stretch at 0, 5, 7, or 10% strain throughout culture, while stepped load constructs were cyclically loaded with a strain that increased or decreased by 2-3% every 2 weeks as constructs matured. Contrary to our hypothesis, neither decreasing nor increasing load led to further tissue maturation. We hypothesize stepped cyclic load may disrupt cellular tensional homeostasis, leading to repeated remodeling of collagen and shifted proteoglycan accumulation. This study provides insight into how stepped cyclic loading affects hierarchical fiber formation and maturation, which will help to engineer stronger replacements and better rehabilitation protocols.

Abstract Introduction The optimal autograft choice for anterior cruciate ligament (ACL) reconstruction remains a subject of debate in orthopedic surgery. This meta-analysis evaluates long-term structural outcomes and donor-site complications by pooling data exclusively from high-quality randomized controlled trials (RCTs) directly comparing patellar tendon (PT) and hamstring tendon (HT) autografts. Methods A systematic literature search was conducted to identify randomized clinical trials comparing primary PT and HT autografts. Revision surgeries and allografts were excluded. The primary endpoints analyzed were graft failure, objective rotational stability, and post-operative anterior knee pain (AKP). Results Data were pooled from 5 core RCTs encompassing 713 patients. A random-effects meta-analysis showed that the trend toward lower structural graft failure with PT autografts did not reach statistical significance [RR = 1.55, 95% CI: 0.82 to 2.93, $p = 0.174$]. However, PT autografts demonstrated statistically superior objective knee rotational stability [RR = 0.89, 95% CI: 0.84 to 0.95, $p < 0.001$]. Conversely, HT autografts were associated with a significant reduction in donor-site morbidity, demonstrating a 63% relative reduction in chronic post-operative anterior knee pain [RR = 0.37, 95% CI: 0.28 to 0.49, $p < 0.001$]. Conclusions Patellar tendon autografts provide superior objective rotational stability, though the observed reduction in structural graft failure rates was not statistically significant. Hamstring tendon autografts significantly reduce post-operative donor-site morbidity and chronic kneeling pain. Graft selection should be tailored to patient-specific athletic demands and occupational requirements. Clinical consensus regarding the optimal autograft selection for primary anterior cruciate ligament (ACL) reconstruction remains divided. While bone-patellar tendon-bone (PT) autografts have historically been associated with excellent mechanical stability, quadrupled hamstring tendon (HT) autografts are widely utilized to mitigate donor-site morbidity. However, individual randomized controlled trials often present variable data regarding the precise magnitude of differences in rotational laxity and long-term anterior knee pain. This meta-analysis pools recent high-quality prospective randomized controlled trials to provide a precise, consolidated quantitative matrix of clinical outcomes. It confirms that while the PT configuration offers statistically superior objective rotational joint stability (p < 0.001), the HT configuration yields a profound 63% relative risk reduction (p < 0.001) in chronic post-operative anterior knee pain and kneeling distress. This defines a clear trade-off matrix to guide patient-specific graft selection based on occupational and physical demands.

Objective: To determine how fibronectin fragment (Fn-f), a matrikine that induces an osteoarthritis (OA)-like phenotype, reshapes chondrocyte states and transcriptional programs at single-cell resolution. Design: Primary human ankle chondrocytes from two cadaveric donors without OA were treated with PBS or purified recombinant Fn-f for 18 hours and profiled by single-cell RNA sequencing. Transcriptional states were characterized by marker genes and functional enrichment, compared with classifications used for OA chondrocytes, and evaluated for Fn-f-dependent changes in abundance and transcriptional programs. Results: Five transcriptionally distinct populations were identified with features that matched previous classifications of effector, inflammatory, pre-hypertrophic/fibrochondrocyte, reparative, and homeostatic chondrocytes. Fn-f markedly redistributed cells among these states, enriching inflammatory chondrocytes while reducing effector and reparative populations. Within transcriptional states, Fn-f differentially altered matrix/cartilage, inflammatory, and stress/immediate-early programs. These responses did not uniformly correspond to assigned subtype identities, demonstrating that transcriptional programs can be dynamically deployed across chondrocyte states. Conclusions: Controlled perturbations of healthy chondrocytes complement observational OA atlases by resolving stimulus-dependent changes in chondrocyte state abundance and transcriptional programs. Discordance between subtype annotations and dynamic functional programs further highlights the need for harmonized definitions of chondrocytes across phenotypic states.

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.

Ultrasound is commonly used to assess structural changes in symptomatic Achilles tendons, but quantitative biomechanical metrics for progressive tendon deterioration remain limited. The goal of this study was to develop and validate an automated ultrasound tracking algorithm for regional tendon deformation and evaluate strain progression in survived and ruptured tendons during fatigue loading. We hypothesized that maximum strain, average strain, and strain heterogeneity would exhibit different trajectories between groups. Ten cadaveric Achilles tendons underwent cyclic loading with stress tests every 500 cycles until rupture or 150,000 cycles. Ultrasound images acquired during stress tests were analyzed using an automated tracking algorithm to generate spatially resolved regional strain fields. Ultrasound-derived bulk strain was highly correlated with actuator-derived strain in survived (R^2 = 0.968 +/- 0.017) and ruptured tendons (R^2 = 0.972 +/- 0.014). Maximum and average longitudinal strains progressively diverged between groups across fatigue life (Group x FatigueLife: p = 0.003 and p < 0.0001, respectively). During the first 10,000 cycles, average strain decreased in survived tendons ({beta} = -0.0268%, p = 0.0215) but not ruptured tendons ({beta} = 0.0147%, p = 0.1197), with a significant Group x Cycle interaction (p = 0.0061). This study demonstrates that the algorithm quantified Achilles tendon deformation with high fidelity and enabled spatially resolved strain assessment throughout fatigue loading. Maximum and average strain followed different trajectories between groups, whereas strain heterogeneity did not. Early differences in tendon biomechanics suggest that regional strain behavior may change before pronounced differences in absolute magnitude develop.

Successful cartilage repair remains one of the most significant challenges in the musculoskeletal field. Microfracture (MFx), a form of marrow stimulation, remains the predominant repair technique, but it exhibits routine failure due to inadequate defect fill and inferior fibrotic tissue formation. Whereas current strategies focus on augmenting MFx with scaffolds and bioactive factors, the potential to target the MFx clot itself and use the capabilities of this dynamic environment to guide MFx repair remains largely unexplored. We verified that MFx contraction and fibrosis hinder repair success in minipigs and become evident as early as one week in multiple animal models. Therefore, our objective was to investigate and direct microenvironmental interactions in the MFx clot to promote volumetric maintenance and reprogram cells from a fibrotic to more chondrogenic phenotype. Extracellular control of cell-environment interactions, through fibrinogen augmentation or anti-fibrinolytic treatment, limited contraction but had no effect on or even exacerbated the fibrotic susceptibility of marrow-derived cells (MDCs). Intracellular control of microenvironmental interactions, through modulation of the Rho-ROCK pathway, drove TGF-{beta}3 activity of MDCs along a "chondro-fibro axis". In particular, treatment with the ROCK inhibitor Fasudil drove TGF-{beta}3-treated cells away from a myofibroblast phenotype and towards chondrogenesis. Short-term Fasudil treatment prevented TGF-{beta}3-driven macroscale clot contraction and enhanced cartilage-specific matrix deposition in vitro. In a pilot rat study, this combination treatment improved GAG deposition and better protected surrounding cartilage. These findings suggest that Rho-ROCK modulates TGF-{beta} signaling along this chondro-fibro axis and its precise control could be the key to promoting precise and volumetric cartilage repair through microenvironmental interactions.

Seroma is a common complication following abdominoplasty and other procedures involving extensive soft tissue dissection. Although animal seroma models have been reported, the stromal pathology underlying post-abdominoplasty seroma, particularly the role of oxidative stress, remains poorly characterized. Here, we developed a rat abdominal seroma model by surgically separating the subcutaneous tissue from the underlying muscle fascia and investigated the temporal evolution of the associated stromal response. Seroma developed in 9 of 20 operated rats, corresponding to a formation rate of 45.0%. Longitudinal ultrasound demonstrated that fluid accumulation peaked around postoperative day (POD) 7 and largely resolved by POD30. Despite macroscopic fluid resolution, substantial stromal remodeling persisted. Compared with normal abdominal tissue, seroma-associated tissues at POD14 and POD35 exhibited increased collagen deposition, macrophage accumulation, oxidative injury, and vascular remodeling. Additionally, at POD35, macrophage accumulation and 4-hydroxynonenal staining were greater than at POD14, whereas collagen deposition and vascular density remained elevated with no significant differences between postoperative time points. To our knowledge, this study presents the first rat model specifically designed to reproduce post-abdominoplasty seroma and the first temporal characterization of oxidative stress within seroma-associated tissue. These findings reveal that seroma fluid resolution does not coincide with stromal recovery and identify persistent oxidative stress, inflammation, fibrosis, and vascular remodeling as important features of seroma pathology.

Purpose: To determine whether a cobalt-chrome genetic reactivity (CoGR) score - originally developed to identify patients at greater risk of developing adverse reaction to metal-on-metal hips - is associated with poorer patient-reported outcomes after knee arthroplasty (KA). Methods: In a prospective multicentre study, patients at a minimum two years post all cobalt-chrome KA were invited to research clinics. Participants provided samples for blood metal ion measurements and DNA sequencing and completed Forgotten Joint Scores (FJS). Component alignment was assessed on AP and lateral plain radiographs. The association between CoGR and FJS was assessed using regression adjusted for time since surgery, age, gender, BMI and tested for modification by blood cobalt. In a case-control analysis, CoGR scores of revised patients with histologically confirmed adverse reactions to metal debris (and specifically aseptic lymphocyte-dominated vasculitis-associated lesions (ALVAL)) were compared with controls (revised patients with no signs of ARMD and unrevised patients with FJS of 75 or more) using Firth logistic regression. Results: 376 patients were included: 312 unrevised patients and 64 patients who underwent revision. Each one-unit increase in CoGR score was associated with a 9.8 point lower FJS (95% confidence interval (CI) 4.2 to 15.4 points; p < 0.001). This increased to a 17.5 (9.4 to 25.5) point reduction per CoGR score unit in patients with blood cobalt above the median level. Comparing 28 ARMD cases (12 with ALVAL) with 177 controls, each one-unit CoGR increase was associated with odds ratios of 1.90 (CI 1.34 to 2.75) for ARMD and 3.05 (CI 1.89 to 5.34) for ALVAL. Conclusions: A higher CoGR score was associated with worse patient-reported outcome and higher odds of histologically confirmed adverse reaction to metal debris at revision. Adverse immune responses may be a more significant factor in unexplained pain after KA than is generally recognised.

Introduction Autologous and allogeneic chondrocyte cell sheet transplantation has shown safety and potential efficacy for cartilage defects associated with knee osteoarthritis. Although polydactyly-derived chondrocyte (PDC) cell sheets have been used clinically for allogeneic transplantation, a scalable and reliable alternative cell source is needed. This study aimed to establish a proof-of-concept protocol for generating chondrocyte cell sheets from clinical-grade human induced pluripotent stem cells (iPS cells). Methods Cartilaginous tissue was generated from human iPS cells, and isolated chondrocytes were used to fabricate iPS cell-derived chondrocyte sheets. In Phase 1, sheets were produced in high-serum medium under normoxic, hypoxic, or hypoxic/high-seeding-density conditions and compared with PDC sheets using a three-dimensional in vitro model and xenogeneic orthotopic transplantation in an immunodeficient rat model. In Phase 2, sheets were produced in low-serum medium under hypoxic/high-seeding-density conditions and evaluated for cartilage-related gene expression, secreted factors, cell surface marker expression, and in vivo cartilage repair. Results In Phase 1, hypoxic/high-seeding-density culture enhanced in vitro chondrogenic properties. However, after transplantation, iPS cell-derived chondrocyte sheets formed fibrotic repair tissue, whereas PDC sheets generated hyaline-like cartilage. In Phase 2, low-serum culture increased expression of cartilage-related genes, including collagen type II alpha 1 (COL2A1) and SRY-box transcription factor 9 (SOX9), enhanced secretion of transforming growth factor beta 1 and melanoma inhibitory activity, and upregulated CD9, CD26, CD56, CD201, CD227, and GD2. Low-serum iPS cell-derived chondrocyte sheets regenerated hyaline cartilage at 4 weeks, and the repair tissue was maintained at 12 weeks without bone formation. Conclusions A robust fabrication protocol enabled human iPS cell-derived chondrocyte sheets to regenerate hyaline-like cartilage in vivo. These findings support their potential as a scalable cell source for clinical cartilage repair.

Objective: Rotator cuff tears involving the supraspinatus tendon are a common cause of shoulder pain. Ultrasound (US) is accessible, dynamic, and lower cost than MRI, but diagnostic performance may vary by tear severity, operator expertise. This systematic review and meta-analysis compared the US with MRI for supraspinatus tear detection. Methods: MEDLINE, Embase, Scopus, and CINAHL Plus were searched for studies published from January 2015 to June 2026. Study quality was assessed using QUADAS-2. Diagnostic outcomes included sensitivity, specificity, accuracy, PPV, NPV. Meta-analyses were performed separately for any, partial-thickness, and full-thickness tears when complete 2 x 2 data were available. Results: 23 studies comprising 1,452 participants were included. US demonstrated stronger and more consistent performance for full-thickness than partial-thickness tears. Mean sensitivity, specificity, and accuracy were 88.5%, 95.2%, and 93.4%, respectively, for full-thickness tears, compared with 71.5%, 91.5%, and 79.2% for partial-thickness tears. HSROC analysis showed pooled sensitivity and specificity of 96% and 76% for any tear, 94% and 80% for partial-thickness tears, and 96% and 98% for full-thickness tears. Agreement measures also generally favored full-thickness tears. Operator expertise, study quality varied, and only one study evaluated a handheld ultrasound system. Conclusion: Ultrasound demonstrates strong diagnostic performance for supraspinatus tears, particularly full-thickness tears, while partial-thickness tears remain more challenging. Given the high observed sensitivity, well-performed US may serve as a practical first-line modality to rule out full-thickness tears, with MRI remaining complementary for equivocal partial-thickness tears, associated pathology, and preoperative assessment.

A persistent challenge in cartilage tissue engineering is identifying cell sources capable of regenerating cartilage with native-like properties. Variability in chondrogenic potential among human- and animal-derived cells complicates graft development and disease modeling. Here we benchmarked ten chondrogenic cell sources under standardized culture conditions using hyaluronan-alginate biomaterials and implementing a functionality index combining histological and mechanical metrics referenced to native tissue. Mesenchymal stem cells and fetal chondroprogenitors demonstrated superior regenerative capacity, achieving 103% and 95% of native cartilage functionality, respectively. In contrast, adult articular chondrocytes from healthy and osteoarthritic donors produced fibrocartilaginous tissue with functionality scores below 50%. These findings provide a quantitative framework to guide cell source selection and optimize cartilage graft standardization for clinical applications and physiologically relevant disease models, addressing regulatory demands for product characterization.

BackgroundIn mouse classic amputation model, second phalanx (P2) is incapable of regeneration. Extracellular matrix (ECM) solution has shown limited ability to induce digit regeneration in classical amputation model of the murine digit. However, the effect of solid ECM particles on bone regeneration is not well understood due to difficulties in treating solid particles in classical amputation model. MethodsWe examined the regenerative effects of ECM particles in mice digit by establishing a soft tissue preserved amputation (SPA) model on P2, through removing the amputated bone whilst preserving soft tissue. ECM particles implanted into the amputation site and wrapped in the preserved soft tissues. Bone regeneration was assessed by morphological examination and micro-CT scans. ResultsWe observed bone regeneration in the SPA model; specifically, new bone formed at the P2 distal end. Implantation of ECM particles exerted a pro-regenerative effect, characterized by increased bone volume and decreased bone density. Moreover, the ECM induced the formation of free-floating bone, further supporting its role in bone regeneration. Combined treatment with ECM particles and bone morphogenetic protein 2 (BMP2) resulted in a significant increase in bone volume. ConclusionsWe demonstrate that soft tissue preservation at the amputation site can overcome the intrinsic regenerative limitationsl. Using SPA model, we found that ECM particles have a proven ability to promote bone regeneration, and that the combination of ECM particles with BMP2 further enhances bone regeneration. These findings underscore the therapeutic promise of ECM-based strategies, for clinical translation in non-regenerative finger injuries. Summary statementSolid-state Extracellular matrix can induce mice digit regeneration and has the potential for clinical application. HighlightsThe SPA model we developed enables ECM particles to adhere to wounds, and our research has found that: O_LIDigit bone regeneration was shown in SPA model . C_LIO_LIECM particles treatment promoted bone regeneration and can generate free-floating bone in SPA model. C_LIO_LICombination of ECM + BMP2 treatment induced strong digit regeneration in SPA model. C_LI

The foreign body response (FBR) is an immune mediated event that occurs with every material implant. The extent of the fibrosis is dependent on many factors including the biomaterial design, tissue location, and host factors such as age, sex, ancestry, diet. There are known clinical outcomes of implants dependent on age and sex, including increased fibrosis and implant failure in aged and female patients. As the population ages, there is a growing need to understand how aging affects the FBR, and how preclinical models can capture this to guide biomaterial design. Here, we investigated how chronic fibrosis in a murine model of the FBR is altered by two biological factors: age and sex. We investigated changes in fibrosis using a volumetric muscle loss (VML) injury model coupled with polycaprolactone (PCL) or polyethylene (PE) microparticle implants. Fibrosis was quantified through gene expression, microscopic analysis of histologic sections, and the corresponding immune response measured via gene expression and flow cytometry data. We found gene expression differences with immune pathways enriched in female mice, and microscopy revealed collagen birefringence area increased in young male mice. Both the innate and adaptive immune response were altered by age and sex via T cell and macrophage phenotype, and the effects of aging differed between sexes. These results reveal both variables contribute to discrepant outcomes in both fibrosis and the local immune response to synthetic material implants. This demonstrates a clear need to understand and account for the influence of biological factors in biomaterial design.

ObjectiveThis study investigates knee joint biomechanics during lunges under varying tibial angles and external loads using musculoskeletal modeling and finite element analysis. The goal is to provide a biomechanical basis for understanding knee loading patterns and optimizing sports training and rehabilitation. MethodsTwenty-six healthy young men performed lunges under tibial inclination angles relative to the ground (60{degrees} and 90{degrees}) and two external load conditions (bodyweight and an additional 98 N external load). Kinematic and kinetic data were captured using motion capture and force plates. Musculoskeletal models were used to estimate joint moments, range of motion, and stiffness, with data analyzed using two-way repeated-measures ANOVA. Finite element analysis was performed at 90{degrees} tibial angle to evaluate tissue stress and displacement. ResultsThe joint moment at a 60{degrees} tibial angle was much higher than at a 90{degrees}. External load showed significant effects on knee stiffness, with lower rotational stiffness in the horizontal plane (P < 0.001) and lower coronal plane stiffness at 90{degrees} (P = 0.012) under the 98 N external-load condition, indicating reduced resistance to angular displacement in these planes. Under the 90{degrees} tibial-angle condition with external load, peak stress and displacement were concentrated in the posterior horn of the meniscus, with a maximum displacement of 3.12 mm. ConclusionThe anterior tilt of the tibia increased sagittal-plane knee loading, while external load mainly reduced joint stiffness in the coronal and horizontal planes. Under the 90{degrees} loaded condition, the concentration of stress and displacement in the posterior horn of the meniscus suggests a mechanically unfavorable loading pattern rather than direct evidence of injury risk. These findings may provide useful biomechanical information for load management during lunge-based training and rehabilitation.

Osteoarthritis (OA) disproportionately affects women, and estrogen has been implicated in cartilage and joint homeostasis, yet its effects on meniscal fibrochondrocytes (MFCs), and whether those effects differ by sex, remain poorly defined. We reanalyzed a publicly available RNA-sequencing dataset (Gene Expression Omnibus, GSE199087) comprising human MFCs from a male and a female donor treated with 17{beta}-estradiol (E2) or vehicle. Differential expression, Gene Set Enrichment Analysis, Enrichr, and iLINCS were integrated to identify the transcriptional programs modulated by E2 in each sex. In female MFCs, E2 upregulated pathways governing DNA replication, cell-cycle progression, and genomic maintenance (e.g., MCM8, BRCA1, RAD51), while downregulating inflammatory and extracellular matrix-degrading genes, including MMP1, IL12A, CXCL12, and MYD88. In male MFCs, E2 instead upregulated chromatin remodeling and developmental signaling programs, led by SRCAP, ERCC6, and NOTCH1, and downregulated antigen presentation and mitochondrial genes. These divergent responses indicate that E2 engages distinct, sex-specific transcriptional programs in MFCs, with the female profile favoring proliferation and matrix preservation. Although derived from a limited sample and therefore hypothesis-generating, these findings nominate candidate mechanisms underlying sex differences in meniscal biology and OA susceptibility, and warrant validation in larger, sex-balanced cohorts. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/740612v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@16026fforg.highwire.dtl.DTLVardef@1a048acorg.highwire.dtl.DTLVardef@3246corg.highwire.dtl.DTLVardef@4c598b_HPS_FORMAT_FIGEXP M_FIG C_FIG

Bone strain and remodeling are important factors for bone health. Improved characterization of relationships between these factors in response to acute loading will improve our understanding of bone maintenance, adaptation to load, and pathophysiology. The purpose of this study was to evaluate colocalization between finite-element-estimated bone strain and [18F]sodium fluoride positron emission tomography imaging-estimated subchondral bone remodeling in the tibial diaphysis in response to acute exercise. We hypothesized that the exercise-induced change in standardized uptake values would be greatest in regions of higher strain. 26 participants underwent bilateral positron emission tomography/magnetic resonance scans before and after a bout of stair ascent and descent exercise. Finite element analysis was performed to calculate principal strain distributions in the tibial diaphysis. [18F]sodium fluoride standardized uptake values were calculated from pre- and post-exercise positron emission tomography data and mapped to the tibial surface. Mean pre-exercise and exercise-induced change in standardized uptake values were calculated and compared between regions defined by strain percentile. Both normalized mean pre-exercise and exercise-induced change in standardized uptake values increased with maximum principal strain in a pattern suggesting an exponential relationship. Pre-exercise and exercise-induced change in standardized uptake value were notably much greater in the region of highest maximum principal strains (estimated marginal means = 76.9 and 71.0 percentile, respectively) when compared to all other regions of the tibial diaphysis ([&le;] 61.1 and [&le;] 57.0 percentile, respectively, p < 0.001). This study is the first to directly show a relationship between bone mechanical loads and acute [18F]sodium fluoride uptake in humans in vivo. Our results highlight the influence of tensile strain magnitude on bone metabolic activity in response to acute loading. Furthermore, we demonstrate the utility of a combined finite element analysis and positron emission tomography approach to interrogate relationships between bone loading and bone metabolic response to acute exercise.