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Background Peritendinous adhesion is among the common complications after tendon injury. Numerous studies have been carried out to prevent its formation, including modifications of surgical procedures, postoperative cares, application of medicines, etc. This study dynamically monitored fluctuations of inflammation, state of oxidative stress, and histopathologic changes around injured tendon to provide theoretical basis for further exploration in mechanisms of peritendinous adhesion formation. Methods Eighteen mature Sprague-Dawley male rats were randomly allocated into 6 equal groups. Compared with control and sham group, every rat’s right hind Achilles tendon in experimental groups was cut and repaired by the modified Kessler technique. Besides control and sham group, samples of tendon margin and serum were collected at different time points after the surgery. Content of TNF-α, IL-1β, and TGF-β were assayed in harvested serum. Reactive oxygen species (ROS) were detected, expression levels of related genes (IL-1β, IL-6, SOD1, SOD2, COL1, HIF1A) were quantified by qPCR, and various histopathological evaluations were performed. Results Indicators (TNF-α, IL-1β, TGF-β1, ROS) were noticed to have a similar trend of significant rising 24 h after the surgery except TGF-β which was rising 72 h later. So were the expression trends of IL-1β, IL-6, SOD1, SOD2, and COL1. HIF1A, inversely correlated with SOD2, showed the progressive relief of regional tissue hypoxia. Histological evaluation showed the same tendency that fibrosis and inflammation were getting serious 48 h later after the surgery. Conclusions Inflammation, oxidative stress in injured tendon resulted from acute trauma, would be getting intense in 24 h. Peritendinous adhesion emerges and aggravates after 48 h. Thus, prompt efficient measures are advised to be taken after the injury as soon as possible.

Background Rupture of extensor pollicis longus tendon (EPL) is a known complication following a distal radius fracture (DRF). Although the precise mechanisms behind these ruptures remain unclear, vascular impairment is thought to play a significant role. Additionally, the impact of an EPL rupture on microstructure of the tendon and muscle is not well understood, but such information could be important in guiding treatment strategies. This study aims to explore the histopathological changes in the EPL tendon and muscle in patients who have experienced an EPL rupture following a DRF. Methods Consecutive patients with an EPL rupture following a DRF were included and treated with an Extensor Indicis Proprius to EPL tendon transfer. Samples were taken from the distal part of EPL muscle and the proximal tendon from the musculotendinous junction to the rupture site as well as from the tendon distal to the rupture. The tendon specimens were analysed by standard histopathological techniques including immunohistochemistry. In cases of sufficient amount of muscle, fresh frozen specimens were analysed by enzyme- and immuno-histochemistry on cryostat sections. Results Thirteen patients (12 females, 1 male; median age 61, range 18–72 years) were included in the study. The EPL muscle in all participants showed extensive inflammatory changes, muscle fiber necrosis and regeneration, structural changes in the muscle fibers and slight interstitial fibrosis. The EPL tendon showed profound degenerative changes mainly in the central part of the tendon whereas there were regenerative changes in the periphery of the tendon. The pathological changes were present in all samples regardless of time between the DRF and the EPL rupture or the time between the diagnosis of the rupture and surgery. Conclusions The extensive inflammatory changes in the EPL muscle indicate that immune mediated mechanisms are involved in muscle degeneration following tendon rupture. The EPL tendon showed characteristic degenerative changes at the myotendinous junction, as well as proximally and distally to the rupture site. The reversibility and the clinical significance of the severe pathological changes seen in the EPL muscle alongside the healing potential of the tendon need further investigation. Trial registration Retrospectively registered the 2024–03-15 at Clinicaltrials.gov, ID: NCT06313489.

The pathogenesis of trauma‐induced heterotopic ossification (HO) in the tendon remains unclear, posing a challenging hurdle in treatment. Recognizing inflammation as the root cause of HO, anti‐inflammatory agents hold promise for its management. Malvidin (MA), possessing anti‐inflammatory properties, emerges as a potential agent to impede HO progression. This study aimed to investigate the effect of MA in treating trauma‐induced HO and unravel its underlying mechanisms. Herein, the effectiveness of MA in preventing HO formation was assessed through local injection in a rat model. The potential mechanism underlying MA's treatment was investigated in the tendon‐resident progenitor cells of tendon‐derived stem cells (TDSCs), exploring its pathway in HO formation. The findings demonstrated that MA effectively hindered the osteogenic differentiation of TDSCs by inhibiting the mTORC1 signalling pathway, consequently impeding the progression of trauma‐induced HO of Achilles tendon in rats. Specifically, MA facilitated the degradation of Rheb through the K48‐linked ubiquitination‐proteasome pathway by modulating USP4 and intercepted the interaction between Rheb and the mTORC1 complex, thus inhibiting the mTORC1 signalling pathway. Hence, MA presents itself as a promising candidate for treating trauma‐induced HO in the Achilles tendon, acting by targeting Rheb for degradation through the ubiquitin‐proteasome pathway.

The interfascicular matrix (IFM) binds tendon fascicles and contains a population of morphologically distinct cells. However, the role of IFM-localised cell populations in tendon repair remains to be determined. The basement membrane protein laminin-α4 also localises to the IFM. Laminin-α4 is a ligand for several cell surface receptors, including CD146, a marker of pericyte and progenitor cells. We used a needle injury model in the rat Achilles tendon to test the hypothesis that the IFM is a niche for CD146+ cells that are mobilised in response to tendon damage. We also aimed to establish how expression patterns of circulating non-coding RNAs alter with tendon injury and identify potential RNA-based markers of tendon disease. The results demonstrate the formation of a focal lesion at the injury site, which increased in size and cellularity for up to 21 days post injury. In healthy tendon, CD146+ cells localised to the IFM, compared with injury, where CD146+ cells migrated towards the lesion at days 4 and 7, and populated the lesion 21 days post injury. This was accompanied by increased laminin-α4, suggesting that laminin-α4 facilitates CD146+ cell recruitment at injury sites. We also identified a panel of circulating microRNAs that are dysregulated with tendon injury. We propose that the IFM cell niche mediates the intrinsic response to injury, whereby an injury stimulus induces CD146+ cell migration. Further work is required to fully characterise CD146+ subpopulations within the IFM and establish their precise roles during tendon healing.

Background Skeletal muscle is a highly adaptive tissue, capable of responding to different physiological and functional demands, even in situations that may cause instability. Objectives: To evaluate how partial calcaneal tendon (CT) injuries affect the remodeling and plasticity of the gastrocnemius muscle over time. Methods and results The study was carried out with Wistar rats randomly divided into five groups. The control group comprised animals not subjected to partial CT damage. The remaining four groups were subjected to partial CT damage and were further categorized based on the time of euthanasia: 3, 14, 28, and 55 days after injury. The gastrocnemius muscle was collected and used for gene expression analysis, zymography, flow cytometry, and morphology. The calcaneal tendon was analyzed only to verify the presence of the partial injury. Results: The impact of partial CT injury on the gastrocnemius homeostasis, particularly on gene expression, was more pronounced in the 3-day group compared to the other groups, especially the control group. Cytokine profile and morphologic alterations occurred in the 55 days group when compared to the other groups. Conclusions The data reported here suggest that partial injury can negatively affect intracellular signaling and degradation pathways, disturbing the muscular extracellular matrix regulatory mechanisms and communication with the tendon. However, skeletal muscle seems to mitigate these harmful effects in comparison with lesions that affect muscle and tendon.

Purpose To assess the most common presenting symptoms, clinical outcomes, and patient satisfaction following treatment of either snapping medial pes anserinus hamstrings or snapping lateral biceps femoris tendons. Methods Consecutive patients with a minimum 2-year follow-up after isolated medial hamstring release for a diagnosis of medial snapping pes anserinus tendons or patients treated with primary biceps repair for lateral snapping biceps femoris tendons were evaluated. Clinical outcome scores of the following domains were collected: SF12, WOMAC score, Lysholm Knee Survey, and a simple numeric patient satisfaction score (0–10). Statistical analysis was performed with paired t-tests between preoperative and postoperative scores. Results At an average follow-up of 4.6 years (range 2.0–8.6 years) with two patients lost to follow-up, six consecutive patients (three male, three female) with seven knees were diagnosed with medial snapping pes anserinus tendons and treated with semitendinosus and gracilis tenotomies. Seven knees in seven patients (three male, four female) were diagnosed with lateral snapping biceps femoris tendons and were treated with an isolated biceps femoris repair. Nine of 13 patients were able to return to full desired activities/pre-operative level of sporting activities (4/6 medial, 5/7 lateral. Lysholm and SF-12 scores improved from preoperative to post-operative status for patients with snapping biceps femoris. Only patients undergoing primary biceps repair showed improvement across all WOMAC domains. Patients with medial hamstring tenotomy demonstrated improvement in Lysholm scores. Median postoperative satisfaction for both pathologies was 7 out of 10. Conclusion Medial hamstring release for snapping pes anserinus and isolated biceps repair for lateral snapping biceps femoris yields improvement in patient satisfaction and clinical outcomes at mid-term follow-up. Level of evidence IV

Objective To assess whether a platelet-rich plasma (PRP) injection leads to an enhanced tendon structure and neovascularisation, measured with ultrasonographic techniques, in chronic midportion Achilles tendinopathy. Design Double-blind, randomised, placebo-controlled clinical trial. Setting Sports medical department of The Hague medical centre. Patients 54 patients with chronic midportion Achilles tendinopathy were included. Interventions Patients were randomised to eccentric exercise therapy with either a PRP injection (PRP group) or a saline injection (placebo group). Main outcome measurements Tendon structure was evaluated by ultrasonographic tissue characterisation, a novel technique which quantifies tendon structure into four echo-types: echo-types I+II represent organised tendon bundles, whereas echo-types III+IV represent a disorganised tendon structure. Colour Doppler ultrasonography was used to measure the degree of neovascularisation. Follow-up was at 6, 12 and 24 weeks. Results A significant improvement in echo-types I+II was found after 24 weeks within both the PRP group (n=27) and the placebo group (n=27), but there was no significant between-group difference (95% CI −1.6 to 7.8, p=0.169). After 6 weeks, the neovascularisation score increased within the PRP group (p=0.001) and the placebo group (p=0.002), but there was no significant between-group difference in change in neovascularisation score at any point in time. Conclusion Injecting PRP for the treatment of chronic midportion Achilles tendinopathy does not contribute to an increased tendon structure or alter the degree of neovascularisation, compared with placebo. Funding Biomet Biologics LLC, Warsaw, Indiana.

IntroductionSystemic osteogenesis has been speculated to be involved in the pathogenesis of ossification of the posterior longitudinal ligament (OPLL). Our purpose was to compare the radiologic prevalence and severity of heterotopic ossification in foot tendons of Japanese patients with OPLL and to determine their association with systemic heterotopic ossification.Materials and methodsClinical and radiographic data of 114 patients with OPLL were collected from 2020 to 2022. Control data were extracted from a medical database of 362 patients with ankle radiographs. Achilles and plantar tendon ossification were classified as grades 0–4, and the presence of osteophytes at five sites in the foot/ankle joint was assessed by radiography. Factors associated with the presence and severity of each ossification were evaluated by multivariable logistic regression and linear regression analysis.ResultsThe prevalence of Achilles and plantar tendon ossification (grade ≥ 2) was 4.0–5.5 times higher in patients with OPLL (40–56%) than in the controls (10–11%). The presence of Achilles tendon ossification was associated with OPLL, age, and coexisting plantar tendon ossification, and was most strongly associated with OPLL (standardized regression coefficient, 0.79; 95% confidence interval, 1.34–2.38). The severity of Achilles and plantar tendon ossification was associated with the severity of ossification of the entire spinal ligament.ConclusionsThe strong association of foot tendon ossification with OPLL suggests that patients with OPLL have a systemic osteogenesis background. These findings will provide a basis for exploring new treatment strategies for OPLL, including control of metabolic abnormalities.

Objectives To investigate the ability of whole-body MRI (WBMRI) to detect axial and peripheral enthesitis in patients with psoriatic arthritis (PsA) and axial spondyloarthritis (axSpA), and in healthy subjects (HS). Furthermore, to develop MRI enthesitis indices based on WBMRI and validate these by use of clinical measures of disease activity. Methods Prospective cross-sectional study of patients with PsA (n=18) and axSpA (n=18) with moderate to high disease activity, and HS (n=12). Enthesitis at 35 individual sites located at upper and lower limbs, chest and pelvis were evaluated by WBMRI and clinical examination, and compared. Three new WBMRI enthesitis indices were developed. Results WBMRI allowed evaluation of 888 (53%) of 1680 sites investigated, and 19 (54%) of 35 entheses had a readability >70%. The percentage agreement between WBMRI and clinical enthesitis was 49–100%, when compared at the level of the individual entheses. Enthesitis on WBMRI was observed in 148 (17%) of the entheseal sites, and was frequently present at greater trochanters (55%) and Achilles (43%) and supraspinate (23%) tendon insertions in patients and HS. At the first mentioned two locations enthesitis often appeared without clinical signs of enthesitis. Patients and HS differed significantly in one of the new WBMRI enthesitis scores. Patients and HS differed significantly in one of the new WBMRI enthesitis scores, and this score correlated weakly with BASDAI question 4 (tenderness in relation to entheses), BASDAI and patient global (ρ=0.29–0.31, p<0.05). Conclusions WBMRI is a promising new imaging modality for evaluation of enthesitis in patients with PsA and axSpA, but requires further investigation before clinical use.

Objectives To quantify the muscle fat-content (MFC) in phantoms, volunteers and patients with achillodynia using two-point Dixon-based magnetic resonance imaging (2pt-MRI DIXON ) in comparison to MR spectroscopy (MRS) and visual assessment of MFC. Methods Two-point Dixon-based MRI was used to measure the MFC of 15 phantoms containing 0-100 % fat-content and calf muscles in 30 patients (13 women; 57 ± 15 years) with achillodynia and in 20 volunteers (10 women; 30 ± 14 years) at 1.5 T. The accuracy of 2pt-MRI DIXON in quantification of MFC was assessed in vitro using phantoms and in vivo using MRS as the standard of reference. Fat-fractions derived from 2pt-MRI DIXON (FF DIXON ) and MRS (FF MRS ) were related to visual assessment of MFC (Goutallier grades 0–4) and Achilles-tendon quality (grade 0-4). Results Excellent linear correlation was demonstrated for FF DIXON with phantoms and with FF MRS in patients ( p c  = 0.997/0.995; p  < 0.001). FF DIXON of the gastrocnemius muscle was significantly higher ( p  = 0.002) in patients (7.0 % ± 4.7 %) compared with volunteers (3.6 % ± 0.7 %), whereas visual-grading showed no difference between both groups ( p  > 0.05). FF MRS and FF DIXON were significantly higher in subjects with (>grade 1) structural damage of the Achilles-tendon ( p  = 0.01). Conclusions Two-point Dixon-based MRI allows for accurate quantification of MFC, outperforming visual assessment of calf muscle fat. Structural damage of the Achilles tendon is associated with a significantly higher MFC. Key points • Two-point Dixon-based MRI allows accurate quantification of muscular fat content (MFC). • Quantitative analysis outperforms visual analysis in the detection of elevated MFC. • Achillodynia results in an increased MFC of the gastrocnemius muscles. • Structural damage of the Achilles tendon further increases the MFC.