The "Race for the Surface" hypothesis remains the dogma for explaining the competition between host proteins, cells, and bacteria for implant colonization immediately post-op. Recently, we used intravital microscopy to provide direct evidence supporting this hypothesis by demonstrating that the race for the surface in a murine implant-associated infection (IAI) model is complete within 3 h. However, this intravital imaging is impractical for early-stage drug development research, thus warranting a cost-effective screening platform to mechanistically assess neutrophil-S. aureus interaction dynamics during the early infection period. To address this, we developed an in vitro IAI model using longitudinal confocal fluorescence microscopy (LCFM) of etched titanium implants contaminated with GFP[+]USA300 and cultured with tdTomato[+] neutrophils. This model enabled reproducible quantification of neutrophil swarming, phagocytosis, and nidus formation, which were validated with scanning electron microscopy, colony-forming unit assays, and imaging cytometry. To demonstrate the utility of these novel platforms, we evaluated an anti-glucosaminidase (Gmd) mAb known to mediate opsonophagocytosis of aggregated S. aureus and assessed its ability to increase total neutrophil volume and S. aureus internalization by neutrophils and cytoplasts. Collectively, these results demonstrate the utility of the LCFM and imaging cytometry platforms for defining mAb functions that enhance neutrophil and cytoplast activity to prevent IAI.

The study aimed to examine the association between knee surgery and infrapatellar fat pad volume in female and male runners, and the association between fat pad volume and patellofemoral-related symptoms among runners with knee surgery. This study presents a secondary exploratory analysis of a prospective cohort study. Data from female and male runners with (n = 104, 49% female) or without (n = 99, 52% female) knee surgery were included. Fat pad volumes were measured from knee magnetic resonance images. Patellofemoral-related symptoms were evaluated using the patellofemoral pain and osteoarthritis subscale of the Knee injury and Osteoarthritis Outcome Score. Linear regression models were used to assess the associations between prior knee surgery and fat pad volume in females and males, and zero-inflated beta regression models were used to evaluate the associations between fat pad volume and patellofemoral-related symptoms in the knee surgery group. All models were adjusted for age, body mass, and height. Females with prior knee surgery had a smaller fat pad volume (mean difference [95% CI]: -1.80 cm[3] [-3.02, -0.57], p = 0.004) than controls. However, this was not observed in males (0.30 cm[3] [-1.39, 2.00], p = 0.723). Among runners with prior knee surgery, fat pad volume was not associated with symptoms in either females (average marginal effects [95% CI]: -0.035 [-0.831, 83.10], p = 0.931) or males (0.255 [-0.233, 23.30], p = 0.306). Females, but not males, exhibit a smaller fat pad volume after knee surgery compared with no surgery controls. Among runners with a history of knee surgery, fat pad volume does not appear to be associated with patellofemoral-related symptoms.

Meniscal extrusion is a marker of meniscal dysfunction and has been associated with osteoarthritis progression. Assessment is typically performed on a single coronal magnetic resonance imaging (MRI) slice, but this method may miss the location of maximal circumferential displacement. We developed an extrusion mapping technique using radially oriented multiplanar reconstruction (rMPR) images from high-resolution 3D MRI to enable circumferential meniscal position measurements perpendicular to the tibial margin. Extrusion was measured by three independent readers on rMPR images generated from non-fat-saturated 3D fast spin-echo MRI in 20 patients stratified by meniscal tear and extrusion status. Intrareader and interreader measurement variabilities were assessed using intraclass correlation coefficient (ICC), 95% repeatability coefficient (RC; intrareader), and 95% reproducibility coefficient (RDC; interreader). Corresponding rMPR and standard 2D coronal midbody extrusion measurements were compared. Intrareader variability was low, with a mean within-meniscus within-angle standard deviation (SD) of 0.2 mm and mean RC of 0.6 mm. Interreader variability was also low, with a mean within-meniscus within-angle SD of 0.5 mm and mean RDC of 1.4 mm. At the midbody, there was 98% concordance for extrusion classification between rMPR and 2D coronal measurements within the interreader RDC (1.4 mm). Exploratory regional analysis suggested different extrusion patterns between medial and lateral menisci and between torn and intact menisci. These findings suggest that circumferential meniscal extrusion mapping using rMPR images from 3D knee MRI is feasible, with low intrareader and interreader measurement variabilities. This framework enables regional characterization of meniscal displacement and should support future investigations of meniscus-osteoarthritis relationships. STATEMENT OF CLINICAL SIGNIFICANCE: Meniscus extrusion circumferential mapping using radially oriented multiplanar reconstruction images is feasible and consistent across readers and allows a more complete assessment of meniscal position, which may be valuable for further investigation of meniscal injury and osteoarthritis.

In anatomic total shoulder arthroplasty (aTSA) research, postoperative anatomical measurements are often referenced to the reamed glenoid bone surface because the glenoid component is not fully visible on CT. However, the reliability of measurements based directly on the implant (implant-based method) and their agreement with the commonly used bone-based method remain unclear. In this study, CT scans from 29 patients undergoing primary aTSA were used to calculate postoperative glenoid positioning (translations, version, inclination) and HHS in the anterior-posterior (HHSAP) and superior-inferior (HHSSI) directions using both methods. The bone-based method referenced measurements to 3D postoperative scapular bone reconstructions, whereas the implant-based method used CT-registered digital glenoid component models. Inter- and intra-rater reliability of implant-based measurements were assessed using intraclass correlation coefficients (ICCs), and agreement between methods was evaluated using ICCs and Bland-Altman analyses. The implant-based approach demonstrated high inter- and intra-rater reliability (ICCs > 0.88), with minimal detectable changes below commonly cited clinical thresholds. The agreement between implant- and bone-based methods was moderate-to-excellent overall (ICC > 0.52), although significant bias and/or wide limits of agreement were observed for version, inclination, superior-inferior implant positioning, and HHSSI. Compared to implant-based measures, bone-based estimates showed a bias toward more superior implant positioning and superior HHSSI, greater retroversion, and more medialized implant positioning. In conclusion, direct implant-to-CT registration is a reliable method for 3D postoperative measurements after aTSA. Implant- and bone-based measurements can be used interchangeably for anterior-posterior implant positioning and HHSAP, but not for other measures when high precision is required. LEVEL OF EVIDENCE: Basic science study.

Carpal tunnel pressure (CTP) is affected by flexion/extension and radioulnar deviation of the wrist. The purpose of this study was to investigate the elevations in CTP as a function of dynamic wrist motion in cadaveric hands. A goniometer was attached on hand dorsal side of cadaveric hands (n = 5). A micro-tip catheter pressure transducer was placed inside the carpal tunnel. With a baseline pressure set around 30 mmHg, the wrist was dynamically and randomly moved in its flexion/extension and radioulnar workspace while position and CTP were simultaneously recorded. CTP as a function of flexion/extension and radioulnar wrist angle was fitted with a third-degree polynomial. A two-way repeated measures ANOVA was used to determine the effect of flexion/extension and radioulnar deviation on CTP (α = 0.05). Flexion-extension or radioulnar deviation significantly affected CTP (p < 0.05). CTP increased beyond 20° of flexion/extension or radioulnar deviation. The polynomial function captured the relationship of CTP with flexion/extension and radioulnar deviation with a coefficient of determination of R[2] = 0.90 ± 0.06. At 50° of flexion and 50° of extension, the CTP, on average, was 160.7 and 172.0 mmHg, respectively, more than 5 times greater than baseline CTP. CTP was dependent on the direction of the deviation. For the same ulnar deviation at 10°, the CTP at 50° of extension was 46% greater than that at 50° of flexion. CTP remains near baseline for small degrees of flexion/extension and radioulnar deviation and becomes increasingly elevated for greater deviations.

Accurate and reproducible Kellgren-Lawrence grading of radiographic knee osteoarthritis remains challenging, particularly for intermediate grades and anatomically heterogeneous compartments. We present X-VIG, an interpretable deep learning framework integrating paired anteroposterior and lateral knee radiographs via view-specific backbones with deformable convolutions, attention-based feature fusion, and dual classification-regression optimization aligned with five-grade clinical practice. Grad-CAM++ visualizations enhance model transparency and support clinical interpretation. In a retrospective cohort (n = 229) with consensus reference-standard KL labels established by double-blinded expert review and patient-level splitting (70%/30%), X-VIG achieved AUCs of 0.9646-0.9945 across five anatomical subregions. Multimodal fusion yielded a mean AUC gain of 5.6 percentage points over single-view models. In a reader study of 50 held-out patients comprising 100 individual radiographs, X-VIG outperformed junior radiologists, matched or surpassed senior performance in most subregions, and reduced reading time by 82% (27 s per case). These results position X-VIG as a credible second reader for standardizing the reporting of knee osteoarthritis in routine clinical workflows.

Recovery following anterior cruciate ligament reconstruction (ACLR) is multifaceted, encompassing strength, functional, and patient-reported outcome measures (PROMs). Determining which factors are most important for characterizing recovery and informing return-to-activity (RTA) decisions remains a clinical challenge. This study aimed to develop and externally validate a supervised machine learning model to classify individuals post-ACLR from healthy controls using comprehensive lower-extremity musculoskeletal assessments. Data from 863 participants (659 post-ACLR, 204 controls) at Site 1 were used to train and internally test Random Forest, Gradient Boosting Machine, and Extreme Gradient Boosting (XGBoost) models, with an 80/20 training-testing split and inner fivefold cross-validation for hyperparameter optimization. Model performance was evaluated using accuracy and area under the receiver operating characteristic curve (AUC), and external validation was performed on an independent Site 2 cohort (N = 174; 133 post-ACLR, 41 controls). The XGBoost model was selected for further analysis (internal test AUC = 0.98, Accuracy = 0.95), and maintained good discrimination on external validation (AUC = 0.83, Accuracy = 0.82). The most informative features included the Knee Osteoarthritis Outcome Score quality-of-life subscale, limb symmetry index for peak knee extension torque at 90°/s, and the International Knee Documentation Committee score, which were consistent across age and sex subgroups. These findings demonstrate that machine learning can effectively integrate strength, function, and PROM data to identify key indicators of ACLR status and support development of streamlined, data-driven protocols for post-ACLR recovery monitoring and RTA decision-making. STATEMENT OF CLINICAL SIGNIFICANCE: The Knee Osteoarthritis Outcome Score quality-of-life subscale, limb symmetry index for peak knee extension torque at 90°/s, and the International Knee Documentation Committee score most effectively distinguish individuals following ACLR from healthy controls. Clinicians may focus on these tests to determine ACLR recovery status as a feasible streamlined assessment battery or when results from a comprehensive testing battery are conflicting or inconclusive.

Tendinopathies comprise half of musculoskeletal injuries, yet medical treatments are lacking. Orthobiologics are novel therapeutics developed to address this gap, with extracellular vesicles (EVs) being a promising prospect. However, we lack a complete understanding of how EVs affect regeneration, both endogenously and as a tool for augmenting tendon healing. Therefore, the purpose of this review was to compile the literature focused on understanding the impact of EV treatment on tendon healing using animal models. We performed a literature search in accordance with PRISMA reporting guidelines. Title, abstract, and full-text screening were performed by two authors. We assessed transparency and risk-of-bias using the ARRIVE, MISEV, and SYRCLE Guidelines, and meta-analyses were performed on overlapping outcome variables. After screening, 46 articles were included. Most studies utilized young male Achilles tendons, with a diversity of EV cell sources, injury types, dosage schemes, and biomaterials. Several ARRIVE (e.g., blinding) and MISEV (e.g., seeding density) recommendations remain poorly reported in this literature, and the risk of bias per SYRCLE guidelines is relatively high. Despite high heterogeneity, EV treatment was associated with improved histological tendon healing scores and increased load to failure, tendon stiffness, and Young's modulus. Further meta-analyses revealed EV treatment was associated with increased type I collagen protein and type III collagen transcript expression, and decreased protein expression of IL-6 and markers of senescence. We recommend that future studies include different ages, sexes, and more systematically protocolized EV delivery scheme. Statement of Clinical Significance: This systematic review identifies gaps in the tendon and EV literature while also unveiling unexplored mechanisms by which EVs may promote tendon healing. This improved understanding and call for rigor in studies enhances the translational potential of EVs as a future treatment for tendon injuries.

Medial meniscus posterior root tear (MMPRT) repairs stabilize root attachment and yield improved clinical outcomes, yet many patients develop persistent meniscal extrusion and osteoarthritis. This study evaluates menisci in MMPRT patients using 3D T2* mapping and assesses T2* correlation with medial meniscal extrusion. Patients underwent 7 T knee MRI before root tear repair and again at 6-month postoperative follow-up. Age- and gender-matched controls were scanned once. The protocol included clinical turbo-spin-echo sequences and a quantitative 3D GRE sequence, used to calculate T2* mapping of the menisci. Pre- and postrepair meniscal extrusion was measured on coronal T2-weighted images by two independent radiologists. Twenty-five patients (mean age 53 ± 8 years) and nine controls (51 ± 11 years) were included. Repairs were intact on follow-up MRI in all patients. T2* values were significantly elevated in patients both pre- and postrepair compared with controls across medial and lateral meniscal subregions. Medial meniscal extrusion increased from 3.7 ± 1.1 mm at baseline to 4.9 ± 1.5 mm (p = 0.002), postoperatively. Prerepair meniscal T2* strongly correlated with postrepair extrusion (ρ = 0.765; p < 0.001). High-resolution 3D T2* mapping at 7 T revealed persistently elevated T2* values after MMPRT repair, consistent with ongoing collagen fiber disorganization. Prerepair T2* values were strongly correlated with early postrepair meniscal extrusion despite MRI-intact repairs, indicating that preoperative tissue quality is associated with postoperative outcomes. These findings support quantitative T2* mapping as a prognostic imaging biomarker that complements conventional morphologic MRI in the evaluation of MMPRTs.

Meniscal calcification is increasingly recognized as a pathological feature associated with the progression of osteoarthritis (OA). However, the molecular mechanisms underlying this process remain poorly understood. This study aimed to investigate the involvement of Wnt/β-catenin signaling and its extracellular antagonist frizzled-related protein B (FRZB) in pathological calcification of degenerative human menisci. Human meniscal specimens were obtained from patients with knee OA and non-OA controls and analyzed histologically and immunohistochemically for calcification and expression of hypertrophic/calcification-associated markers, β-catenin, and FRZB. An in vitro calcification model using primary human meniscal cells was established, and the role of FRZB was examined by supplementation with recombinant FRZB or shRNA-mediated FRZB knockdown. Calcification was assessed with Alizarin Red S staining, and expression of Wnt/β-catenin signaling-related and hypertrophic/calcification-associated genes was analyzed using quantitative PCR and western blotting. Degenerative menisci exhibited prominent calcium deposition accompanied by increased expressions of RUNX2, collagen type X, and MMP-13. Calcified menisci showed enhanced β-catenin expression and reduced FRZB expression compared with non-calcified menisci. In an in vitro model, meniscal cell calcification was accompanied by downregulation of FRZB and activation of Wnt/β-catenin signaling, along with upregulation of RUNX2, collagen type X, and MMP-13. Recombinant FRZB attenuated Wnt/β-catenin signaling activity and reduced calcification, whereas FRZB knockdown enhanced Wnt/β-catenin signaling and increased calcium deposition. Reduced FRZB expression was associated with enhanced Wnt/β-catenin signaling activity and increased calcification in degenerative menisci. The findings suggest a potential inhibitory role for FRZB in the context of Wnt/β-catenin signaling associated meniscal calcification.

Evidence indicates that alpha angle (AA) is inadequate for describing cam morphology, contributing to poor patient selection and clinical outcomes for cam-type femoroacetabular impingement syndrome (FAI). While techniques such as statistical shape modeling (SSM) have advanced knowledge of 3D femoral morphology, many studies utilize computed tomography, which incurs ionizing radiation, or small sample sizes, limiting clinical implementation and generalization. Here, we conducted SSM using MRI-derived 3D femur models from a large cohort of FAI patients to explore: (1) What proximal femur features drive shape variability? (2) What variability exists within the area of the cam deformity? (3) Are shape modes correlated to AA, age, sex, and BMI? 103 FAI patients were enrolled (µ ± σ): Age (29.9 ± 12.1 Years), BMI (24.6 ± 4.8), AA (60.3° ± 9.8), Female/Male (75/28). Shape modes were determined through principal component analysis. Relationships between shape modes and AA, age, and BMI were evaluated through linear regression. Sex differences were analyzed using linear discriminant analysis. Thirteen modes explained 91.0% of femoral shape variance, with the first six modes explaining 82.2%, four of which were associated with the cam deformity region. No relationship was found between any mode versus AA, BMI, or age. Sex-based shape differences were primarily captured by the first mode. CLINICAL SIGNIFICANCE: The proximal femur in cam-type FAI patients demonstrated substantial regional shape variability, with cam-related morphology distributed across multiple independent modes rather than a single uniform deformity pattern. Sex was a major driver of proximal femoral shape variation. These findings may inform morphology-based classification, outcome analysis, and patient-specific surgical planning.

Cartilage is traditionally viewed as a metabolically quiescent tissue that relies primarily on exogenous lipid uptake to meet its energetic and structural demands. However, increasing evidence suggests that chondrocytes exhibit metabolically active behaviors, particularly under aging and pathological conditions. Here, we developed and applied an in vivo deuterium oxide (D2O)-based stable isotope labeling approach to directly quantify de novo fatty-acid synthesis in cartilage. Using gas chromatography-mass spectrometry (GC-MS), we tracked deuterium incorporation into palmitate in serum and articular cartilage from wild-type (WT) and cartilage-specific acetyl-CoA carboxylase 1 (ACC1) knockout mice. Progressive incorporation of deuterium into palmitate confirmed active fatty-acid synthesis in cartilage, with labeling kinetics distinct from those observed in serum, consistent with slower lipid turnover in the matrix-dense cartilage environment. Although fractional new synthesis of palmitate was comparable between genotypes during the labeling window, ACC1-deficient cartilage exhibited reduced palmitate abundance and decreased higher-order isotopomer enrichment at early labeling time points, indicating attenuated lipogenic flux. These findings provide direct in vivo evidence that chondrocytes possess intrinsic lipogenic capacity and that ACC1 contributes to the maintenance of the cartilage lipid pool. Together, this study establishes D2O-based isotope tracing as a robust and quantitative framework for assessing cartilage lipid metabolism in vivo and reveals de novo lipogenesis as an active metabolic process in cartilage. CLINICAL SIGNIFICANCE: This approach offers a valuable platform for investigating lipid dysregulation in osteoarthritis and other joint diseases.

This study aimed to elucidate the cellular and molecular mechanisms underlying knee osteoarthritis pathogenesis by analyzing chondrocyte populations and their spatial distribution using single-cell RNA sequencing (scRNA-seq). Knee cartilage cells underwent scRNA-seq. Cellular clusters were identified via gene expression profiles and annotated using gene ontology analyses. Correlations between cluster proportions and patient background characteristics were evaluated. Differentiation trajectories were evaluated using pseudotime analysis. Differentially expressed genes between osteoarthritis and non-osteoarthritis samples were identified, and their functional relevance was experimentally assessed. Cartilage stratification analysis was also performed. A total of 104,951 cells from 12 patients (9 osteoarthritis, 3 non-osteoarthritis) were analyzed. Initially, 11 clusters were identified; three non-chondrocytic clusters (mesenchymal stromal cell-like cells, blood cells, fibroblasts) were identified and excluded from chondrocyte analysis. Eight chondrocyte subpopulations were annotated, including a novel stress-responsive metabolic chondrocytes (MetabCs) associated with serum total cholesterol levels and linked to cholesterol metabolism and endoplasmic reticulum stress pathways. Correlation and trajectory analyses revealed two paths: one toward fibrocartilage chondrocytes (FCs) associated with aging and another toward MetabCs associated with osteoarthritis progression. Novel osteoarthritis-related genes identified included chondroprotective HILPDA and destructive AKR1C2. Stratification analysis indicated that worn cartilage chondrocytes exhibited a hybrid phenotype, shifting toward upper-zone features while retaining deep-zone characteristics. In conclusion, a novel chondrocyte cluster was identified as implicated in osteoarthritis pathogenesis, where elevated serum cholesterol levels potentially increase endoplasmic reticulum stress response, promoting MetabC formation. Chondrocytes altered their phenotype in response to spatial distribution changes caused by cartilage thinning.

Metatarsal bone stress injuries (BSI) are painful, overuse injuries commonly seen in athletes and military personnel. High strain magnitudes combined with repetitive loading cycles causes bone fatigue and microdamage accumulation. To protect against BSI, it is necessary to determine how to limit bone strain magnitude without sacrificing physical activity. This study examined maximum and minimum principal dorsal strains of metatarsals 2-4 during tibial dorsiflexion/plantarflexion, external/internal rotation, and varus/valgus alignment with four underfoot conditions. Five lower-limb cadaveric specimens were instrumented with strain gauges on metatarsals 2-4 and a robotic actuator applied 25% bodyweight and moved the ankle/foot through its envelope of passive motion. Dorsiflexion and varus tibial motion produced the greatest increase in strain magnitudes during all underfoot conditions. Adding half-inch blocks beneath the medial and lateral forefoot caused principal strain magnitudes to increase threefold within the metatarsals adjacent to the block across all motions. Passive engagement of the windlass mechanism during dorsiflexion caused approximately a threefold increase in maximum principal strain of metatarsals 2-3 coinciding with a significant decrease in metatarsal 4. The results emphasize the role that the arch and its supporting structures play in modulating metatarsal loading even within a passive model.

Increased femoral version is linked to patellofemoral instability, increased lateral loading of the patella and might be treated with femoral derotation osteotomy (FDO) in excessive cases. However, the effects of FDO on patellofemoral stability and loading while walking are not fully understood and not measurable in vivo. This study used personalized in-silico musculoskeletal modeling to investigate the impact of FDO on medio-lateral patellofemoral joint loading in individuals with patellofemoral instability. We analyzed retrospective data from 16 participants with recurrent patellofemoral instability and femoral version ≥ 30° using musculoskeletal simulations. We prepared two models per participant based on gait analysis and magnetic resonance data: (i) a model with personalized femoral version and tibial torsion and (ii) a post-surgery model with femoral version adjusted to 12° to simulate the derotation osteotomy. We assessed joint angles, joint moments, muscle moments, muscle forces, and patellofemoral joint contact forces. Simulated FDO significantly altered superior-inferior and anterior-posterior patellofemoral joint contact forces but did not significantly change medio-lateral patellofemoral joint loading at the group level. Six participants (37.5%) demonstrated a reduction in lateralizing patellofemoral joint contact forces, three (18.8%) showed no relevant change, and seven (43.7%) exhibited increased lateralizing forces. Changes in rectus femoris muscle force correlated with changes in medio-lateral patellofemoral joint loading. Participants with worsening patellofemoral loading had greater tibial torsion and exhibited distinct gait characteristics. These findings suggest that patient-specific functional and anatomical characteristics should be considered when selecting candidates for FDO and planning surgical treatment.