Mechanisms of tendon injury and repair

Reliability and validity assessment of the Brazilian Version of the foot and ankle ability measure for individuals with Achilles tendinopathy

BACKGROUND

The Brazilian-Portuguese adaptation of the Foot and Ankle Ability Measure (FAAM-Brazil) remains untested and unvalidated in the context of Achilles Tendinopathy (AT).

OBJECTIVE

This study aims to validate the FAAM-Brazil specifically for individuals grappling with AT, examining its clinimetric properties: internal consistency, test-retest reliability, and construct validity.

METHODS

A cohort of 101 volunteers diagnosed with AT completed assessments including the FAAM-Brazil, Lower Extremity Functional Scale (LEFS-Brazil), and Victorian Institute of Sport Assessment (VISA-A Brazil) on two occasions with an interval of 2-3 days.

RESULTS

The FAAM-ADL and FAAM-Sport subscales demonstrated strong internal consistency (Cronbach's α = 0.84 and 0.89, respectively) and robust test-retest reliability (ICC2.1 reliability for FAAM-ADL: 0.81, 95%CI = 0.7 to 0.87; FAAM-Sport: 0.85, 95%CI = 0.78 to 0.90). The standard error of measurement (SEM) and Minimal Detectable Change (MDC) were 7.68 and 21.30 for the FAAM-ADL subscale and 6.52 and 18.09 for the FAAM-Sport subscale, respectively. Construct validity was evidenced by a strong correlation (rho = 0.67 for FAAM-Sport vs. VISA-A and rho = 0.68 for FAAM-Sport vs. LEFS), with no observed ceiling or floor effects.

CONCLUSION

This study provides compelling evidence supporting the FAAM as a valid and reliable outcome measure, warranting its recommendation for application in both scientific research and clinical practice, particularly in individuals managing AT.

Ex vivo mechanical testing of double strand, braided and knitted polyethylene suture for acute transverse section of the Achilles tendon in a dog model

BACKGROUND

Acute tendon cut represents a great challenge both in human and veterinary medical practice. The current study aimed to compare the ultimate biomechanical properties (tensile strength, elongation, stress load, yield load and break load) of double strand, braided and knitted polyethylene suture in an ex vivo model of acute transverse section of the Achilles tendon in dog model using locking loop suture and three-loop pulley suture.

METHODS

A-thirty-six Achilles tendon was transected from 18 dog cadavers. Tendon samples were randomly allocated (6 tendons/group) to be sutured either by double strand, braided and novel knitted formation techniques from polyethylene suture using either three-loop pulley suture or locking loop suture patterns. Biomechanical testing of different yarn for tensile strength, elongation, stress, yield load, break load was performed.

RESULTS

Braided polyethylene sutures demonstrated superior biomechanical properties, showing the highest maximum tension, load, stress, and yield load, while knitted sutures exhibited the greatest strain and elongation due to their looped structure. Despite the knitted yarn's high elongation, its tensile strength and load-bearing capabilities were significantly lower. Overall, yarn formation had a greater influence on biomechanical performance in association with suturing technique. The three-loop pulley suturing demonstrated significantly improved suturing outcomes.

CONCLUSION

Both novel knitted, and braided suture structure demonstrated improved biomechanical properties of tendon suturing by increasing the number of strands within the tendon, simplifying the suturing process, reducing the needle passes, and minimizing tendon punctures that may interfere with healing and the overall strength. Suturing technique had a major influence on the biomechanical properties where the three-loop pulley suture demonstrated superior biomechanical properties compared to locking loop suturing.

The impact of aging on achilles tendon ossification in mice

BACKGROUND

Heterotopic ossification is a frequent complication of soft tissue injuries, particularly in tendons. Although ossification in tendon tissue has been reported in a range of aging and disease models, the underlying biomarkers and mechanisms remain unknown. And the characterisation and sensitivity of previous diagnostic biomarkers for tendon ectopic ossification do not meet the demands of clinical use. The aim of this study was to characterise the effects of aging on ossification in the mouse Achilles tendon and to identify characteristic genes and therapeutic targets for tendon ossification in mice by using a machine learning approach.

METHODS

We retrieved the transcriptome profile of GSE126118 from the Gene Expression Omnibus (GEO) database. Following background correction and normalization using the transcripts per million (TPM) method, differentially expressed genes (DEGs) were identified with the limma R package (p < 0.05, |log2FC| > 1). Subsequently, 468 senescence genes were downloaded from the Aging Atlas database, and senescence-associated DEGs (HO senescence genes) were identified. Gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment, and protein-protein interaction (PPI) network analyses were conducted on the identified DEGs. To further refine the HO aging signature, support vector machine (SVM) regression was employed. Additionally, we predicted transcription factors, miRNAs, and small molecule drugs potentially associated with the characterized genes.

RESULTS

Three characterised genes were identified as biomarkers associated with ectopic ossification and aging in the mouse Achilles tendon, Atp5o, Mmp2 and Mmp13. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses revealed significant enrichment in processes related to cartilage endochondral ossification, metalloendopeptidase activity, and mitochondrial proton transport ATP synthase complex. Additionally, HIF-1 and GnRH signaling pathways were prominently represented among the differentially expressed genes.

CONCLUSION

Atp5o, Mmp2 and Mmp13 were identified as relevant signature genes for the effects of aging on Achilles tendon ossification in mice. Atp5o, Mmp2, and Mmp13 may influence tendon ossification by affecting mitochondrial function as well as extracellular matrix degradation to regulate senescence. This finding suggests a potential link between these processes, opening new avenues for research into diagnostic markers and therapeutic targets. These genes hold promise for the development of novel treatments for tendon ossification, a debilitating condition currently lacking effective therapeutic options.

Adipose derived stem cell activation by macrophages and tendon fibroblasts

AIMS

Tendon injuries are common, and healing often fails due to an over-exuberant inflammatory response and a lack of regeneration. Inflammatory cells play key roles in these processes, with a balance between classically activated pro-inflammatory M1 macrophages and alternatively activated inflammatory resolving M2 macrophages. Adipose-derived mesenchymal stem cells (ASCs) can dampen the pro-inflammatory effectsof macrophages, promote a regenerative environment, and enhance healing. Therefore, the goal of the study was to understand how ASCs are activated by macrophages in vitro.

METHODS

In vitro co-culture experiments were carried out with ASCs, macrophages, and tendon fibroblasts. RNA-seq and qRT-PCR were performed to determine expression patterns of activated ASCs.

RESULTS

M1 macrophages prompted ASCs to upregulate pro-inflammatory signaling, matrix remodeling, and cytokine production pathways, while downregulating those related to cell adhesion and cell cycle. Conversely, TFs prompted ASCs to upregulate pathways involved in cell cycle and cytoskeleton remodeling, and to downregulate pathways associated with immune cell adhesion, inflammatory mediator production, and protein metabolism.

CONCLUSIONS

The cell-specific activation profiles indicate a possible switch in ASC paracrine signaling depending on the context, from a pro-inflammatory pattern in response to M1 macrophages to a proliferative pattern in response to TFs. Understanding crosstalk between ASCs, TFs, and macrophages is essential for developing stem cell-based therapeutic strategies.

Programmed Drug Delivering Janus Hydrogel Adapted to the Spatio-temporal Therapeutic Window for Achilles Tendon Repair

Peritendinous adhesion formation and tendon re-rupture are prevalent clinical complications following tendon repair surgery. The key to reducing adhesions and enhancing the biomechanical strength of injured tendons lies in suppressing inflammation and extrinsic fibroblast activation while promoting intrinsic tenocyte proliferation. However, as tenocytes are inherently a type of fibroblast, it remains challenging for a single drug to reduce adhesion and improve tendon strength simultaneously. To address this challenge, a Janus hydrogel was designed for spatiotemporal programmed drug delivery specifically tailored to Achilles tendon repair. The outer layer of the Janus hydrogel rapidly releases melatonin (MT) via poly(N-acryloyl alaninamide) (PNAAA), effectively suppressing inflammation and extrinsic fibroblast activation. The inner layer gel, formed by thiol-modified gelatin (GelSH) and norbornene-modified hyaluronic acid (HANB), incorporates protein-binding AAc-NHS and gradually releases platelet-derived growth factor-BB (PDGF-BB), thereby promoting tenocyte proliferation. In the rat Achilles tendon injury model, the spatiotemporal programmed drug delivery Janus hydrogel successfully reduced adhesion while enhancing tendon healing strength. This work promoted Achilles tendon repair by meeting the distinct spatiotemporal therapeutic needs. STATEMENT OF SIGNIFICANCE: Melatonin may inhibit fibroblast proliferation and differentiation via the PI3K/AKT pathway, whereas PDGF-BB promotes tenocyte proliferation and differentiation through the same pathway. Consequently, the effects of these two drugs on fibroblasts and tenocytes may be conflicting. In this study, the programmed drug delivery Janus hydrogel was designed to match the different stages of tendon repair and achieved staggered release of melatonin and PDGF-BB. Melatonin@PNAAA primarily targets the extrinsic healing pathway, focusing on inflammatory cells during the inflammatory phase and fibroblasts during the proliferative phase. PDGF-BB@SHNB mainly targets intrinsic healing pathway, focusing on tenocytes during the proliferative phase and collagen synthesis during the remodeling phase. This spatiotemporal delivery system alleviates adhesion while promoting tendon healing.

Advanced Biomimetic Materials in the Prevention of Tendon Adhesions: Design, Preparation, and Application of Hydrogel and Electrospun fiber Membranes

Tendon adhesion formation results from a fibrotic process between the tendon and surrounding tissues, typically occurring after tendon injury or surgery. This condition significantly impacts the quality of life and motor function. Currently, treating adhesions following the repair of injured tendons remains challenging and is a prominent clinical issue that needs to be addressed. This review compiles the existing pathophysiological mechanisms underlying tendon adhesion formation, with a particular focus on the critical roles of inflammation and inflammatory pathways, growth factors and their associated pathways, as well as peritendinous cellular behaviors in promoting adhesion formation. Furthermore, this paper is dedicated to summarizing the evaluation of hydrogels and electrospun fiber membranes as anti-adhesion materials, emphasizing their design, preparation, and application. Additionally, the success of composite patches created by combining these two materials in preventing tendon adhesions is reviewed, which demonstrates the broad applicability of the hydrogel and electrospun film combination. Finally, the review provides insights into future directions for preventing tendon adhesion formation, focusing on material structure and functional design.

The clinical utility of musculoskeletal ultrasonography in hemiplegic shoulder rehabilitation poststroke

Objective

This study aimed to assess the utility of musculoskeletal ultrasound (MSUS) in the rehabilitation of stroke patients with hemiplegic shoulder pain.

Methods

We conducted a study involving 80 stroke patients with hemiplegia and concomitant shoulder pain on the affected side, admitted to our hospital between April 2020 and March 2021. MSUS was used to evaluate shoulder structures, including the long head of the biceps brachii tendon (BICT) and its sheath, rotator cuff, subacromial-subdeltoid (SA-SD) bursa, labrum, acromioclavicular ligament, acromiocoracoid ligament, and acromion-greater tuberosity (AGT) distance. We compared pre- and post-rehabilitation measurements of supraspinatus tendon (SST) thickness, BICT sheath effusion thickness, SA-SD bursa effusion thickness, AGT distance, and visual analog scale (VAS) scores. Statistical significance was set at P < 0.05.

Results

Post-rehabilitation, the SST thickness on the hemiplegic side showed a statistically significant reduction (P = 0.023). No significant difference was observed in the mean maximum rupture diameter (P = 0.796). Both BICT sheath effusion (P < 0.001) and SA-SD bursa effusion (P < 0.001) exhibited significant decreases. The AGT distance on the hemiplegic side also demonstrated a statistically significant change (P < 0.001). Additionally, the VAS score significantly improved post-rehabilitation (P < 0.001).

Conclusion

MSUS is a feasible and reproducible tool for monitoring rehabilitation progress in stroke patients with hemiplegic shoulder pain.

Platelet-Rich Plasma in Arthroscopic Repair of Full-Thickness Rotator Cuff Tears: A Cross-sectional Analysis of Overlapping Meta-analyses

Background

Platelet-rich plasma (PRP) has been utilized as adjunctive therapy in arthroscopic rotator cuff repair. However, there is currently limited research available on the efficacy of PRP in arthroscopic repair of full-thickness rotator cuff tears.

Purpose

This study aimed to perform a cross-sectional analysis of overlapping meta-analyses comparing the clinical efficacy of arthroscopic repair of full-thickness rotator cuff tears with and without PRP to assist clinicians in assessing the most reliable evidence and formulating treatment recommendations accordingly.

Study Design

Systematic review; Level of evidence, 2.

Methods

Under PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, comprehensive searches of meta-analyses were performed in the PubMed, Embase, and Cochrane Library databases until June 1, 2024, and found 63 studies. The methodological quality of the included studies was evaluated using the Assessment of Multiple Systematic Reviews (AMSTAR) and Oxford Centre for Evidence-Based Medicine Levels of Evidence instruments. Data extraction from the included meta-analyses was independently performed by 2 reviewers. The Jadad decision algorithm was employed to identify meta-analyses with the most robust evidence.

Results

This study included 5 meta-analyses. These meta-analyses had AMSTAR scores ranging from 7 to 9, with a mean of 8. The most reliable evidence, assessed by the Jadad algorithm, included 8 randomized controlled trials and involved 566 patients. It showed that the short-term (≤12 months after surgery) retear rate and visual analog scale score were significantly lower in those with PRP than in those without PRP. The short-term Constant score, short-term University of California, Los Angeles (UCLA) activity score, and long-term (>12 months after surgery) UCLA score were significantly higher in the PRP group, especially in single-row fixation.

Conclusion

Our study demonstrates that the most reliable evidence suggests that PRP injections can be recommended as adjunctive therapy in single-row repair for enhanced short-term outcomes. Further high-quality randomized controlled trials are imperative to increase the strength of evidence.

Polylactic acid electrospun membranes coated with chiral hierarchical-structured hydroxyapatite nanoplates promote tendon healing based on a macrophage-homeostatic modulation strategy

Tendon injury is a common and challenging problem in the motor system that lacks an effective treatment, affecting daily activities and lowering the quality of life. Limited tendon regenerative capability and immune microenvironment dyshomeostasis are considered the leading causes hindering tendon repair. The chirality of biomaterials was proved to dictate immune microenvironment and dramatically affect tissue repair. Herein, chiral hierarchical structure hydroxylapatite (CHAP) nanoplates are innovatively synthesized for immunomodulatory purposes and further coated onto polylactic acid electrospinning membranes to achieve long-term release for tendon regeneration adaption. Notably, levorotatory-chiral HAP (L-CHAP) nanoplates rather than dextral-chiral or racemic-chiral exhibit good biocompatibility and bioactivity. In vitro experiments demonstrate that L-CHAP induces macrophage M2 polarization by enhancing macrophage efferocytosis, which alleviates inflammatory damage to tendon stem cells (TDSCs) through downregulated IL-17-NF-κB signaling. Meanwhile, L-CHAP-mediated macrophage efferocytosis also promotes TDSCs proliferation and tenogenic differentiation. By establishing a rat model of Achilles tendon injury, L-CHAP was demonstrated to comprehensively promoting tendon repair by enhancing macrophage efferocytosis and M2 polarization in vivo, finally leading to improvement of tendon ultrastructural and mechanical properties and motor function. This novel strategy highlights the role of L-CHAP in tendon repair and thus provides a promising therapeutic strategy for tendon injury.

Systematic Review of Relevant Biomarkers for Human Connective Tissue Repair and Healing Outcome: Implications for Understanding Healing Processes and Design of Healing Interventions

Objective: The healing process following connective tissue (CT) injuries is complex, resulting in variable and often suboptimal outcomes. Patients undergoing CT repair frequently experience healing failures, compromised function, and chronic degenerative diseases. The identification of biomarkers to guide improved clinical outcomes after CT injuries remains an emerging but promising field. [Figure: see text] [Figure: see text] Design: Systematic review. Data sources: Databases, including PubMed, MEDLINE Ovid, Web of Science, and Google Scholar, were searched up to August 2024. Eligibility criteria: To achieve the research objective, randomized control trials, cohort studies, and case-control studies on biomarkers associated with CT repair and healing outcomes were selected. The present analysis was confined to clinical and preclinical models, excluding imaging studies. The entire process of this systematic review adhered strictly to the guidelines outlined in the Preferred Reporting Items for Systematic Review and Meta-Analyses protocol checklist. Results: A total of 1,815 studies on biomarkers of CT repair were initially identified, with 75 studies meeting eligibility criteria and 55 passing quality assessments. For biomarkers associated with CT healing outcomes, 281 studies were considered, with 30 studies meeting eligibility criteria and 24 passing quality assessments. Twenty-one overlapping studies investigated the effects of biomarkers on both CT repair and healing outcomes. Specific biomarkers identified, and ranked from highest to lowest quality, include complement factor D, eukaryotic elongation factor-2, procollagen type I N-terminal propetide, procollagen type III N-terminal propetide, lactate, pyruvate, platelet-derived growth factor-BB, tissue inhibitor of metalloproteinase-3 (TIMP-3), cysteine-rich protein-1, plastin-3, periostin, protein S100-A11, vimentin, matrix metalloproteinases (MMP-2, MMP-7, and MMP-9), hepatocyte growth factor, interferon-γ, interleukins (IL-6, IL-8, and IL-10), MMP-1, MMP-3, tumor necrosis factor-α, fibroblast growth factor-2, IL-1α, chondroitin-6-sulfate, inter-alpha-trypsin inhibitor heavy chain-4, transforming growth factor-beta 1, vascular endothelial growth factor, C-C chemokine receptor 7, C-C chemokine ligand 19, IL-1β, IL-1Ra, IL-12p40, granulocyte-macrophage colony-stimulating factor (GM-CSF), and TIMP-1. Conclusions: All of the 37 identified potential biomarkers demonstrated regulatory effects on CT repair and mediated healing outcomes. Notably, the identified biomarkers from human studies can potentially play an essential role in the development of targeted treatment protocols to counteract compromised healing and can also serve as predictors for detecting CT healing processes and long-term outcomes.

Exploring cellular changes in ruptured human quadriceps tendons at single-cell resolution

Tendon ruptures in humans have often been studied during the chronic phase of injury, particularly in the context of rotator cuff disease. However, the early response to acute tendon ruptures remains less investigated. Quadriceps tendons, which require prompt surgical treatment, offer a model to investigate this early response. Therefore, this study aimed to explore the early cellular changes in ruptured compared to healthy human quadriceps tendons. Quadriceps tendon samples were collected from patients undergoing fracture repair (healthy) or tendon repair surgery (collected 7-8 days post-injury). Nuclei were isolated for single-nucleus RNA sequencing, and comprehensive transcriptomic analysis was conducted. The transcriptomes of 12,808 nuclei (7268 from healthy and 5540 from ruptured quadriceps tendons) were profiled, revealing 12 major cell types and several cell subtypes and states. Rupture samples showed increased expression of genes related to extracellular matrix organisation and cell cycle signalling, and a decrease in expression of genes in lipid metabolism pathways. These changes were predominantly driven by gene expression changes in the fibroblast, vascular endothelial cell (VEC), mural cell, and macrophage populations: fibroblasts shift to an activated phenotype upon rupture and there is an increase in the proportion of capillary and dividing VECs. A diverse immune environment was observed, with a shift from homeostatic to activated macrophages following rupture. Cell-cell interactions increased in number and diversity in rupture, and primarily involved fibroblast and VEC populations. Collectively, this transcriptomic analysis suggests that fibroblasts and endothelial cells are key orchestrators of the early injury response within ruptured quadriceps tendon. KEY POINTS: Tendon ruptures in humans have regularly been studied during the chronic phase of injury, but less is known about the early injury response after acute tendon ruptures. This study explored the early cellular changes in ruptured compared to healthy human quadriceps tendons at single-cell resolution. Fibroblasts and endothelial cells seem to be the key orchestrators of the early injury response within ruptured quadriceps tendon. Therefore, these cell types are obvious targets for interventions to enhance tendon healing. Overall, this study highlights that the development of more effective therapeutic options for tendon injury requires better understanding of the cellular, extracellular, and mechanical landscape of tendon tissue.

Investigation on the role of Icariin in tendon injury repair: focusing on tendon stem cell differentiation

OBJECTIVE

Tendon injury is a common and frequent disease in the field of sports medicine, and tendon repair after injury is a common clinical difficulty. Repair strategy based on tendon stem cells (TDSCs) therapy is considered a promising therapeutic option for the treatment of tendon injuries. Icariin (ICA) has been shown to be an effective herbal monomer for the treatment of tendon-bone healing and may be effective in the repair of tendon injuries.

METHODS

In vitro, TDSCs isolated from C57 mice were treated with ICA (0.01-100 µM) to assess proliferation (CCK-8 assay) and tendonogenic differentiation (qRT-PCR). In vivo, 42 C57 mice with surgically induced patellar tendon defects were randomized into three groups (n = 14/group): (1) 20 mg/kg ICA, (2) 40 mg/kg ICA, and (3) control group (DMSO), administered intraperitoneally for 14 days. Half of each group (n = 7) underwent histopathological (hematoxylin-eosin staining, Masson staining) and molecular (qRT-PCR) analyses at 2 and 4 weeks post-surgery.

RESULTS

In vitro, after 7 days of ICA intervention in TDSC, the expression of Mohawk (MKX), Scleraxis (SCX), fibromodulin (FMOD), and Tenomodulin (TNC) were higher in the ICA group than in the control group. In vivo, the expression of MKX, SCX, FMOD, and TNC was higher in the 20 mg/kg ICA group and 40 mg/kg ICA group than in the control group at 2 and 4 weeks after surgery. Histological evaluation revealed superior tendon repair in both ICA-treated groups compared to controls at both 2 and 4 weeks postoperative intervals. The 20 mg/kg ICA group demonstrated a significant enhancement in tissue continuity and collagen fiber organization, exhibiting greater defect filling, fewer interstitial gaps, and reduced vascular infiltration. In contrast, control specimens exhibited disorganized collagen architecture with prominent interstitial gaps. The 40 mg/kg ICA group showed intermediate repair outcomes between the 20 mg/kg ICA and control groups.

CONCLUSION

ICA can improve tendon injury repair by enhancing tendonogenic differentiation of TDSC.

An implantable hydrogel-based phononic crystal for continuous and wireless monitoring of internal tissue strains

Conventional implantable electronic sensors for continuous monitoring of internal tissue strains are yet to match the biomechanics of tissues while maintaining biodegradability, biocompatibility and wireless monitoring capability. Here we present a two-dimensional phononic crystal composed of periodic air columns in soft hydrogel, which was named ultrasonic metagel, and we demonstrate its use as implantable sensor for continuous and wireless monitoring of internal tissue strains. The metagel's deformation shifts its ultrasonic bandgap, which can be wirelessly detected by an external ultrasonic probe. We demonstrate ex vivo the ability of the metagel sensor for monitoring tissue strains on porcine tendon, wounded tissue and heart. In live pigs, we further demonstrate the ability of the metagel to monitor tendon stretching, respiration and heartbeat, working stably during 30 days of implantation, and we loaded the metagel with growth factors to achieve different healing rates in subcutaneous wounds. The metagel results almost completely degraded 12 weeks after implantation. Our finding highlights the clinical potential of the ultrasonic sensor for tendon rehabilitation monitoring and drug delivery efficacy evaluation.

Reactive oxygen species in tendon injury and repair

Reactive oxygen species (ROS) are chemical moieties that in physiological concentrations serve as fast-acting signaling molecules important for cellular homeostasis. However, their excess either due to overproduction or inability of the antioxidant system to inactivate them results in oxidative stress, contributing to cellular dysfunction and tissue damage. In tendons, which are hypovascular, hypocellular, and composed predominantly of extracellular matrix (ECM), particularly collagen I, ROS likely play a dual role: regulating cellular processes such as inflammation, proliferation, and ECM remodeling under physiological conditions, while contributing to tendinopathy and impaired healing when dysregulated. This review explores the sources of ROS in tendons, including NADPH oxidases and mitochondria, and their role in key processes such as tissue adaptation to mechanical load and injury repair, also in systemic conditions such as diabetes. In addition, we integrate the emerging perspective that calcium signaling-mediated by mechanically activated ion channels-plays a central role in tendon mechanotransduction under daily mechanical loads. We propose that mechanical overuse (overload) may lead to hyperactivation of calcium channels, resulting in chronically elevated intracellular calcium levels that amplify ROS production and oxidative stress. Although direct evidence linking calcium channel hyperactivity, intracellular calcium dysregulation, and ROS generation under overload conditions is currently circumstantial, this review aims to highlight these connections and identify them as critical avenues for future research. By framing ROS within the context of both adaptive and maladaptive responses to mechanical load, this review provides a comprehensive synthesis of redox biology in tendon injury and repair, paving the way for future work, including development of therapeutic strategies targeting ROS and calcium signaling to enhance tendon recovery and resilience.

Panda Rope Bridge Technique promoted Achilles tendon regeneration in a novel rat tendon defect model

PURPOSE

This study aimed to determine whether the Achilles tendon tissue can undergo the pathological process of Achilles tendon regeneration after the Panda Rope Bridge Technique (PRBT).

METHODS

Rats (n = 120) that operated with Achilles tendon rupture were divided into three treatment groups: Defect group (D group), PRBT group and Defect + Fix group (DF group). The D group represented natural healing with no treatment, the PRBT group represented healing receiving PRBT treatment and the DF group represented healing through conservative treatment by ankle fixation. The morphological, histological and biomechanical properties of the defective Achilles tendon were assessed at 7, 10, 12, 14, 28 and 56 days postoperatively.

RESULTS

Compared to that observed in the other two groups, defected rat Achilles tendons that underwent PRBT recruited more cells earlier, eventually forming mature tendons, as revealed by histological analysis. PRBT also enabled defected tendons to regain stronger mechanical properties, thereby improving the prognosis. This improvement may be related to the earlier polarization of macrophages.

CONCLUSION

By establishing and using a novel surgical model of Achilles tendon rupture in rats, most injured Achilles tendons can regenerate and regain normal histological properties, whereas tendons with other interventions formed fibrotic scar tissue. The strong regenerative capacity of tendon tissue enabled us to describe the pathological process of tendon regeneration after PRBT surgery in detail, which would aid in the treatment of tendon injuries. PRBT promotes Achilles tendon regeneration and has the potential to become a standard treatment.

LEVEL OF EVIDENCE

Not applicable.

Biomechanical comparison of tendon repair techniques: Bunnell suture leads in mode of failure and minimally invasive configuration in elongation

Purpose

In this experimental study, the Minimally Invasive Configuration (MIC), the Bunnell, Kessler and modified Bunnell-Kessler techniques for tendon rupture repair were compared in terms of the following biomechanical parameters: maximum load, mode of failure, failure elongation, tension/construct elongation and stiffness (Young's modulus). The scope of comparison involves understanding the properties of each suture technique in hopes of eventually contributing to surgical decision-making.

Methods

Thirty-two frozen ovine specimens were obtained, and transverse tenotomy was performed on each. Eight tendons were randomly allocated to each technique. Specimens were tested performing a unidirectional tensile load to failure using a servo-hydraulic testing device. The tendons were also loaded to failure at a rate of 10 mm/s. The total length of the construct was defined as the distance from the two clamps. Stiffness was calculated by determining the slope of the force-displacement curve in the linear region. Total failure was defined as a drop of measured force or rupture of the tendon-suture complex.

Results

In the mode of failure, Tukey's post hoc test showed a statistically significant difference between the Bunnell group and the other three groups (p < 0.05). For Tension/construct elongation at 5 and 10 mm, Tukey's post hoc test showed a statistically significant difference between the MIC group and the other three groups (p < 0.05). At 15 mm Tukey's post hoc test showed a statistically significant difference between the MIC group and the Kessler group (p < 0.05).

Conclusion

The Bunnell suture performed best in terms of mode of failure, while the MIC suture technique outperformed the rest in terms of tension/construct elongation. Findings show sufficient biomechanical evidence to support the ongoing clinical application of all techniques.

Level of Evidence

Level V.

Sustained slow-release TGF-β3 in a three-dimensional-printed titanium microporous scaffold composite system promotes ligament-to-bone healing

The treatment of tendon/ligament-to-bone injury is a long-standing research challenge in orthopedics and bone tissue engineering. Orderly healing of the fibrocartilage layer and mineralized bone layer is crucial for treating tendon-bone interface injuries. We designed a three-dimensional printed porous titanium scaffold composite system with thermosensitive collagen hydrogel loaded with transforming growth factor β3 (TGF-β3), formulated for the sustained slow release of TGF-β3 at a constant rate. In vitro, the composite system exhibited good biocompatibility and was beneficial for the adhesion and proliferation of bone marrow mesenchymal stem cells (BMSCs), which showed high growth activity. Moreover, the composite system promoted the differentiation of BMSCs via osteogenesis and chondrogenesis. In vivo, the composite system provided active substances at the injured site, promoting the repair of the fibrocartilage layer and of the mineralized bone layer at the interface between the ligament and bone. Micro-CT results demonstrated that the complex promotes the osseointegration of titanium scaffolds in bone defects. Hard tissue sections showed that the new bone, ligament, and the titanium alloy scaffold system formed a closely integrated whole; the composite system provided suitable attachment points for ligament growth. Additionally, the biomechanical strength of the tendon interface improved to some extent. Our results indicate that the composite system has potential as a bioactive implant interface for repairing ligament and bone injuries.

Biomaterial Properties and Differentiation Strategies for Tenogenic Differentiation of Mesenchymal Stem Cells

Tendinopathy is a prevalent musculoskeletal condition that affects both aging populations and individuals involved in repetitive, high-intensity activities, such as athletes. Current treatment options primarily address symptom management or involve surgery, which carries a significant risk of complications and re-injury. This highlights the need for regenerative medicine approaches that combine stem cells, biomaterials, and growth factors. However, achieving effective tenogenic differentiation remains challenging due to the absence of standardized differentiation protocols. Consequently, a review of existing research has been conducted to identify optimal biomaterial properties and growth factor protocols. Findings suggest that the ideal biomaterial for tenogenic differentiation should feature a 3D structure to preserve tenogenic expression, incorporate a combination of aligned micro- and nanofibers to promote differentiation, and require further investigation into optimal stiffness. Additionally, growth factor protocols should include an induction phase to initiate tenogenic lineage commitment, followed by a maintenance phase to support matrix production and maturation.

Neural Markers Predict Tendon Healing Outcomes in an Ovine Achilles Tendon Injury Model: Spontaneous Repair Versus Amniotic Epithelial Cell-Induced Regeneration

Tendon injuries pose a clinical challenge due to tendons' limited recovery. Emerging evidence points to the nervous system's critical role in tendon healing, with neural markers NGF, NF-200, NPY, CGRP, and GAL modulating inflammation, cell proliferation, and extracellular matrix (ECM) remodeling. This study investigates the predictive role of selected neural markers in a validated ovine Achilles tendon injury model, comparing spatio-temporal expression patterns in regenerating tendons transplanted with amniotic epithelial stem cells (AECs) versus spontaneous healing (CTR) 14 and 28 days post-injury (p.i.). AEC-treated tissues showed a spatio-temporal modulation of NF-200, NGF, NPY, CGRP, GAL, and enhanced ECM remodeling, with greater cell alignment, lower angle deviation, and accelerated collagen maturation, with a favorable Collagen type 1 (COL1) to Collagen type 3 (COL3) ratio. Pearson's matrix analysis revealed significant positive correlations between NGF, CGRP, and GAL expression, along a positive correlation between the three neural markers and cell alignment and angle deviation. As opposed to CTR, in AEC-treated tendons, lower levels of NGF, CGRP, and GAL correlated positively with improved tissue organization, suggesting these markers may predict successful tendon regeneration. The findings highlight the neuro-mediated activity of AECs in tendon regeneration, with NGF, CGRP, and GAL emerging as key predictive biomarkers for tendon healing.

Anatomohistological study of the peroneus longus tendon in the cuboid bone tunnel: Correlation with tunnel dimensions and the presence of os peroneum

BACKGROUND

Peroneal tendon injuries, particularly of the peroneus longus, contribute to lateral ankle pain and instability. However, limited literature addresses the anatomical influence of the cuboid tunnel and the os peroneum on such injuries. This study investigates histological changes in the peroneus longus tendon and their relationship to cuboid tunnel dimensions, os peroneum presence, and age.

METHODS

This cross-sectional study examined 60 peroneus longus tendons from 30 cadavers (ages 15-71). Tendons were sectioned and histologically analyzed for cellularity and collagen composition. Cuboid tunnel dimensions were measured, and the presence of os peroneum, an accessory ossicle located within the peroneus longus tendon, was recorded. Statistical correlations were performed.

RESULTS

Increased type III collagen and cellularity were significantly associated with advanced age, reduced tunnel width, and increased tunnel height (p < 0.05). No significant association was found with tunnel length or os peroneum presence.

CONCLUSIONS

Age, reduced cuboid tunnel width, and increased tunnel height are associated with peroneus longus tendon degeneration, with collagen type I replacement by type III, predisposing factors for tendinosis.

LEVEL OF EVIDENCE

Level IV (Anatomical Study).

Does quercetin affect tendon healing? An experimental study in a rat model of Achilles tendon injury

Purpose

The objective of this study was to investigate the impact of quercetin, a potent antioxidant, on tendon healing utilizing a rat Achilles tendon injury model.

Materials and methods

The study involved 32 male Wistar-Albino rats, randomly split into experimental (quercetin) and control groups, each with 16 rats. A bilateral Achilles tenotomy model was applied, with the experimental group receiving quercetin and the control group receiving corn oil via oral gavage from surgery until sacrifice. One Achilles tendon per rat underwent histopathological and immunohistochemical evaluations, while the other underwent biomechanical analysis.

Results

Tendons were evaluated histopathologically in terms of tenocyte, ground substance, collagen, and vascularity, and quercetin was observed to significantly increase tendon healing in the experimental group (p-values = 0.0232, 0.0128, 0.0272, 0.0307, respectively). In the immunohistochemical analysis, type I collagen, type III collagen, alpha smooth muscle actin (SMA), and Galectin-3 were evaluated, and it was observed that quercetin increased tendon healing (p-values = 0.0166, 0.0036, 0.0323, 0.0295, respectively). In the biomechanical analysis, the rupture strength was evaluated with six parameters (failure load, maximum energy, displacement, stiffness, ultimate stress, and strain), and it was observed that quercetin significantly increased the rupture strength (p-values = 0.032, 0.014, 0.026, 0.025, 0.045, 0.012, respectively).

Conclusion

Quercetin significantly enhanced tendon healing both biomechanically and immunohistochemically. However, further clinical studies are needed to understand its effects on human tendon healing, as this is the first study of its kind.

Erroneous Differentiation of Tendon Stem/Progenitor Cells in the Pathogenesis of Tendinopathy: Current Evidence and Future Perspectives

Tendinopathy is a condition characterized by persistent tendon pain, structural damage, and compromised functionality. Presently, the treatment for tendinopathy remains a formidable challenge, partly because of its unclear pathogenesis. Tendon stem/progenitor cells (TSPCs) are essential for tendon homeostasis, regeneration, remodeling, and repair. An innovative theory has been previously proposed, with insufficient evidence, that the erroneous differentiation of TSPCs may constitute one of the fundamental mechanisms underpinning tendinopathy. Over the past few years, there has been accumulating evidence for plausibility of this theory. In this review, we delve into alterations in the differentiation potential of TSPCs and the underlying mechanisms in the context of injury-induced tendinopathy, diabetic tendinopathy, and age-related tendinopathy to provide updated evidence on the erroneous differentiation theory. Despite certain limitations inherent in the existing body of evidence, the erroneous differentiation theory emerges as a promising and highly pertinent avenue for understanding tendinopathy. In the future, advanced methodologies will be harnessed to further deepen comprehension of this theory, paving the way for prospective developments in clinical therapies targeting TSPCs for the management of tendinopathy.

Tackling the Problem of Tendon Adhesions: Physical Barriers Prepared from α-Amino Acid-Based Poly(ester amide)s

In this work, electrospun membranes of α-amino acid based poly(ester amide)s (AAA-PEAs) from L-alanine (PEA_ala) or L-phenylalanine (PEA_phe) were successfully prepared to be used as physical barriers in the orthopedic field. Also, blends of these two polymers were used in different weight ratios (25:75, 50:50 and 75:25) to obtain physical barriers with different properties. All membranes had a suitable pore size to prevent fibroblast infiltration, and their porosity and permeability values were in a range that allowed the passage of nutrients. The membrane made from a blend of 25%wt of PEA_ala and 75% wt of PEA_phe showed the highest value of swelling capacity, suggesting a higher lubricant feature. The same membrane suffered a more pronounced degradation, as evidenced by the in vitro enzymatic degradation tests. All membranes showed suitable toughness values, a crucial property with regard to application. In vitro cytotoxicity tests performed with a NIH3T3 fibroblast cell line revealed decreased cell viability after 7 days, suggesting that these membranes are not ideal substrates to promote fibroblast adhesion and proliferation. These membranes as physical barriers represent a significant advance in the field given the limited literature on electrospun AAA-PEAs and their use to prevent tendon adhesion.

Response of a tenomodulin-positive subpopulation of human adipose-derived stem cells to decellularized tendon slices

The selection of appropriate cell sources is vital for the regeneration and repair of tendons using stem cell-based approaches. Human adipose-derived stem cells (hADSCs) have emerged as a promising therapeutic strategy for tendon injuries. However, the heterogeneity of hADSCs can lead to inconsistent or suboptimal therapeutic outcomes. In this study, we isolated and identified a tenomodulin (TNMD)-positive subpopulation from hADSCs (TNMD+hADSCs) using flow cytometry and then assessed the cellular response of this subpopulation to decellularized tendon slices (DTSs), including cell proliferation, migration, and tenogenic differentiation, using the CCK-8 assay, transwell migration assay, and quantitative real-time polymerase chain reaction. Our findings revealed that TNMD+hADSCs maintained the general characteristics of stem cells and exhibited significantly higher expressions of tendon-related markers compared to hADSCs. Importantly, DTSs significantly enhanced the proliferation, migration, and tenogenic differentiation of TNMD+hADSCs. This study provides preliminary experimental evidence for the translational application of ADSCs for tendon regeneration and repair.

Advancements in biomaterials and scaffold design for tendon repair and regeneration

Tendon injuries present a significant clinical challenge due to their limited natural healing capacity and the mechanical demands placed on these tissues. This review provides a comprehensive evaluation of the current strategies and advancements in tendon repair and regeneration, focusing on biomaterial innovations and scaffold design. Through a systematic literature search of databases such as PubMed, Scopus, and Web of Science, key studies were analyzed to assess the efficacy of biocompatible materials like hydrogels, synthetic polymers, and fiber-reinforced scaffolds in promoting tendon healing. Emphasis is placed on the role of collagen fiber architecture, including fiber diameter, alignment, and crimping, in restoring the mechanical strength and functional properties of tendons. Additionally, the review highlights emerging techniques such as electrospinning, melt electrowriting, and hybrid textile methods that allow for precise scaffold designs mimicking native tendon structures. Cutting-edge approaches in regenerative medicine, including stem cell therapies, bioelectronic devices, and bioactive molecules, are also explored for their potential to enhance tendon repair. The findings underscore the transformative impact of these technologies on improving tendon biomechanics and functional recovery. Future research directions are outlined, aiming to overcome the current limitations in scaffold mechanical properties and integration at tendon-bone and tendon-muscle junctions. This review contributes to the development of more effective strategies for tendon regeneration, advancing both clinical outcomes and the field of orthopedic tissue engineering.

Biologic Adjuvants to Rotator Cuff Repairs Induce Anti-inflammatory Macrophage 2 Polarization and Reduce Inflammatory Macrophage 1 Polarization In Vitro

PURPOSE

To examine the effect of various biologic adjuvants on the polarization of macrophages in an in vitro model for rotator cuff tears.

METHODS

Tissue was harvested from 6 patients undergoing arthroscopic rotator cuff repair. An in vitro model of the supraspinatus and subacromial bursa was created and treated with control, platelet-rich plasma (PRP), autologous activated serum (AAS), or a combination of PRP+AAS. The effect of treatment on macrophage polarization between M1 proinflammatory macrophages or M2 anti-inflammatory macrophages was measured using gene expression, protein expression, flow cytometry, and nitric oxide production.

RESULTS

Tendon and bursa treated with PRP, AAS, and PRP+AAS significantly decreased the gene expression of M1 markers interleukin (IL)-12 and tumor necrosis factor-alpha while significantly increasing the expression of M2 markers arginase, IL-10, and transforming growth factor-β (P < .05) compared with treatment with control. Enzyme-linked immunosorbent assay analysis of protein production demonstrated that, compared with control, coculture treated with PRP, AAS, and PRP+AAS significantly decreased markers of M1-macrophages (IL-6, IL-12, and tumor necrosis factor-alpha) while significantly increasing the expression of markers of M2-macrophages (arginase, IL-10, and transforming growth factor-beta) (P < .05). Flow cytometry analysis of surface markers demonstrated that compared with control, tendon and bursa treated with PRP, AAS, and PRP+AAS significantly decreased markers of M1-macrophages (CD80, CD86, CD64, CD16) while significantly increasing the expression of markers of M2-macrophages (CD163 and CD206) (P < .05). Treatment of the coculture with PRP, AAS, and PRP+AAS consistently demonstrated a decrease in nitric oxide production (P < .05) compared with control. AAS and PRP+AAS demonstrated an increased macrophage shift to M2 compared with PRP alone, whereas there was not as uniform of a shift when comparing PRP+AAS with AAS alone.

CONCLUSIONS

In an in vitro model of rotator cuff tears, the treatment of supraspinatus tendon and subacromial bursa with PRP, AAS, and PRP+AAS demonstrated an increase in markers of anti-inflammatory M2-macrophages and a concomitant decrease in markers of proinflammatory M1-macrophages. AAS and PRP+AAS contributed to a large shift to macrophage polarization to the anti-inflammatory M2 compared with PRP.

CLINICAL RELEVANCE

The mechanism of biologic adjuvant effects on the rotator cuff remains poorly understood. This study suggests that they may contribute to polarization of macrophages for their proinflammatory (M1) state to the anti-inflammatory (M2) state.

Clinical Outcomes of Hip Abductor Repair Using Transosseous Sutures Versus Suture Anchors: A Systematic Review and Meta-analysis

Background

Hip abductor tendon tears have been identified as a common cause of greater trochanteric pain syndrome. While abductor tendon tears are often managed surgically, the optimal tendon attachment technique remains controversial.

Purpose

To compare the outcomes of hip abductor tendon repair between the suture anchor (SA) and transosseous suture (TS) techniques.

Study Design

Systematic review; Level of evidence, 4.

Methods

A literature search was performed in June 2023 in Embase, PubMed, and Web of Science databases. Studies reporting pre- and postoperative clinical outcomes of hip abductor repairs using SA or TS fixation with a minimum follow-up of 12 months were included in our analysis. From 608 studies initially identified, 21 studies (14 SA and 7 TS) with a total of 680 patients met the inclusion criteria. The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) checklist guided the reporting and data abstraction, and the quality of the studies was assessed using the methodological index for non-randomized studies checklist. The results were presented as a narrative summary using descriptive statistics such as ranges and agreement statistics.

Results

Significant pre- to postoperative improvement in pain scores and functional outcomes were reported on all included studies. The mean improvement on the Harris Hip Score/modified Harris Hip Score was 32.5 (95% CI, 28.4-36.7) for the SA technique versus 21.9 (95% CI, 6.7-37.0) for the TS technique, while mean improvement in pain according to the visual analog scale was 5.1 ± 2.3 for SA and 4.8 ± 2.2 for TS (P = .9). There was a trend toward statistical significance regarding retear rates, with higher rates for SA (6.7% ± 7.6%) versus TS (1.3% ± 4.7%) (t[13.9] = 2.0; P = .06).

Conclusion

We observed no significant difference between SA and TS regarding improvements in patient-reported hip outcome and pain scores. However, SA trended toward a higher retear rate. Future research should propose a classification scheme that considers tear size and morphology, the extent of associated muscle degeneration, and the distance of tendon retraction to provide more context for the understanding of expected functional outcomes.

A dual-phase biologic augmentation of rotator cuff healing in a preclinical rat model using interleukin-17F and low-dose lithium

Background

Rotator cuff tendon tears are a common cause of shoulder dysfunction in adults. Yet, impaired healing continues to result in higher failure rates after surgical repair resulting in patient dysfunction and prolonged recovery. This has spurred increased investigation of biologic augmentation to improve tendon healing. This study examines the outcome of peritendinous interleukin-17F (IL-17F) administration and oral low-dose lithium carbonate (Li) on rotator cuff healing following acute surgical repair in a rat model.

Methods

Treatment group included an open supraspinatus peel and repair followed by a local injection of IL-17F at the bone-tendon interface and a 7-day course of oral Li. Control rats received no additional intervention before surgical closure. Evaluation of healing was then preformed using MRI imaging, biomechanical testing, and histological analysis at the bone-tendon interface.

Results

Eighteen rats (9 control, 9 experimental) underwent complete testing. Combined treatment of peritendinous IL-17F and oral low-dose Li after rotator cuff repair improved rotator cuff healing in all outcomes when compared to controls. MRI imaging in the treatment group showed complete healing of all supraspinatus tendons across the anatomic footprint after repair. We also found significant increases in biomechanical stiffness compared to controls (P < .01). At the histological level, treatment groups also had decreased osteoclasts (P < .001), and increased histologic organization of fibroblasts compared to controls. These findings are consistent with an increase in biomechanical stiffness.

Conclusion

We demonstrated that the combined treatment of IL-17F and oral low-dose lithium improved rotator cuff tendon healing quality following acute surgical repair in a rat model.

Harnessing the potential of hyaluronic acid methacrylate (HAMA) hydrogel for clinical applications in orthopaedic diseases

The treatment of orthopaedic diseases, such as fractures and osteoarthritis, remains a significant challenge due to the complex requirements for mechanical strength and tissue repair. Hydrogels based on hyaluronic acid methacrylate (HAMA) show promise as tissue engineering materials for these conditions. Hyaluronic acid (HA) is a natural component of the extracellular matrix, known for its good compatibility. The mechanical strength of HAMA-based hydrogels can be adjusted through crosslinking and by combining them with other materials. This review provides an overview of recent research on HAMA-based hydrogels for tissue engineering applications in orthopaedic diseases. First, we summarize the techniques for the preparation and characterization of HAMA hydrogels. Next, we offer a detailed review of the use of HAMA-based hydrogels in treating conditions such as cartilage injuries, bone defects, and meniscus injuries. Additionally, we discuss the applications of HAMA-based hydrogels in other diseases related to orthopaedics. Finally, we point out the challenges and propose future directions for the clinical translation of HAMA-based hydrogels.

Translational potential statement

HAMA-based hydrogels show strong translational potential in orthopaedics due to their biocompatibility, adjustable mechanical properties, and regenerative capabilities. With ongoing research, these hydrogels are well-positioned for clinical applications, particularly in cartilage repair, meniscus injuries, and osteoarthritis treatment.

Distal Triceps Tendon Rupture-First Retrospective Study in Central Europe

Background: This retrospective study is the only one in the last 10 years from central Europe and provides a current picture of prevalence, new diagnostic modalities, new methods of surgical treatment, and also offers new insights into post-operative care. Triceps tendon rupture is the least reported among all the tendon injuries in the literature. In general, effective treatments for tendon injuries are lacking because the understanding of tendon biology lags behind that of the other components of the musculoskeletal system. Tendon tissue has a low number of cells and growth hormones and thus a lack of natural healing ability. Understanding the links between the mechanical and biological parameters involved in tendon development, homeostasis, and repair is a prerequisite for the identification of effective treatments for chronic and acute tendon injuries. Methods: The authors statistically evaluated the set of patients with this diagnosis in the largest University Hospital in Slovakia over the last 10 years. Results: Between 2014 and 2023, 23 patients with distal triceps tendon ruptures (DTTR) were treated at University Hospital. In some years not a single patient with this diagnosis underwent surgery, reinforcing the idea that DTTR may be either rare or underdiagnosed. The incidence in our region is 0.46 cases per 100,000 inhabitants. The average age of patients was 57.7 years, with a male predominance of 90%. Less than half of the patients (43.5%) underwent surgical intervention, and the median time from injury to surgery was less than 10 days. This rapid timeline indicates a high standard of medical care, given the semi-elective nature of the surgery and the need for MRI (Magnetic Resonance Imaging) confirmation of tendon rupture exceeding 50% of the fibers before proceeding with surgery. The three standard surgical techniques were employed in approximately equal proportions. Conclusions: This study suggests that none of the methods is currently preferred, and that the choice of the technique was largely determined by perioperative findings and the surgeon's discretion. Post-operative complications were minimal, with only one patient experiencing any issues after surgery.

Collagen scaffold-seeded iTenocytes accelerate the healing and functional recovery of Achilles tendon defects in a rat model

Introduction

Tendon injuries represent an ongoing challenge in clinical practice due to poor regenerative capacity, structure, and biomechanical function recovery of ruptured tendons. This study is focused on the assessment of a novel strategy to repair ruptured Achilles tendons in a Nude rat model using stem cell-seeded biomaterial.

Methods

Specifically, we have used induced pluripotent stem cell (iPSC)-derived mesenchymal stem cells (iMSCs) overexpressing the early tendon marker Scleraxis (SCX, iMSCSCX+, iTenocytes) in combination with an elastic collagen scaffold. Achilles tendon defects in Nude rat models were created by isolating the tendon and excising 3 mm of the midsection. The Achilles tendon defects were then repaired with iTenocyte-seeded scaffolds, unseeded scaffolds, or suture only and compared to native Nude rat tendon tissue using gait analyses, biomechanical testing, histology, and immunohistochemistry.

Results

The results show faster functional recovery of gait in iTenocyte-seeded scaffold group comparing to scaffold only and suture only groups. Both iTenocyte-seeded scaffold and scaffold only treatment groups had improved biomechanical properties when compared to suture only treatment group, however no statistically significant difference was found in comparing the cell seeding scaffold an scaffold only group in terms of biomechanical properties. Immunohistochemistry staining further demonstrated that iTenocytes successfully populated the collagen scaffolds and survived 9 weeks after implantation in vivo. Additionally, the repaired tissue of iTenocyte-treated injuries exhibited a more organized structure when compared to tendon defects that were repaired only with suturing or unseeded scaffolds.

Conclusion

We suggest that iTenocyte-seeded DuRepair™ collagen scaffold can be used as potential treatment to regenerate the tendon tissue biomechanically and functionally.

The current status of various preclinical therapeutic approaches for tendon repair

Tendons are fibroblastic structures that link muscle and bone. There are two kinds of tendon injuries, including acute and chronic. Each form of injury or deterioration can result in significant pain and loss of tendon function. The recovery of tendon damage is a complex and time-consuming recovery process. Depending on the anatomical location of the tendon tissue, the clinical outcomes are not the same. The healing of the wound process is divided into three stages that overlap: inflammation, proliferation, and tissue remodeling. Furthermore, the curing tendon has a high re-tear rate. Faced with the challenges, tendon injury management is still a clinical issue that must be resolved as soon as possible. Several newer directions and breakthroughs in tendon recovery have emerged in recent years. This article describes tendon injury and summarizes recent advances in tendon recovery, along with stem cell therapy, gene therapy, Platelet-rich plasma remedy, growth factors, drug treatment, and tissue engineering. Despite the recent fast-growing research in tendon recovery treatment, still, none of them translated to the clinical setting. This review provides a detailed overview of tendon injuries and potential preclinical approaches for treating tendon injuries.

Dendritic Cell-Derived Exosomes Promote Tendon Healing and Regulate Macrophage Polarization in Preventing Tendinopathy

Introduction

Tendon injuries present a significant challenge for independent repair, and can progress into tendinopathy over time, highlighting the importance of early intervention. Dendritic cell-derived exosomes (DEXs) has been shown to shift the polarization of M1 macrophages, the predominant inflammatory cells in the early stages of tendon injury. This study introduces a therapeutic approach that effectively manages inflammation while promoting regeneration in the treatment of tendinopathy.

Methods

The purification and characterization of DEXs were meticulously conducted. Experiments were carried out using an Achilles tendon rupture mouse model, with weekly DEXs treatment starting on postoperative day (POD) 4. In vitro, the function of DEXs was assessed by coculturing them with tendon stem/progenitor cells (TSPCs) in culture medium containing IL-1β. Tendon healing progress was evaluated using Sirius Red staining, Masson's trichrome staining, biomechanical testing, and immunofluorescence microscopy. The inflammatory microenvironment of injured tendons was evaluated using the Luminex procedure and flow cytometry analysis.

Results

DEXs treatment significantly enhanced tendon cell differentiation, promoted collagen type I synthesis, and inhibited collagen type III synthesis, thereby expediting tendon healing. Furthermore, DEXs treatment improved the inflammatory microenvironment by reducing multiple cytokines (IL-1β, IL-4, IL-6, TNF-α, and IFN-γ) and induced the conversion of M1 macrophages to M2 macrophages by activating the PI3K/AKT pathway.

Conclusion

DEXs demonstrated a potent ability to promote tendon healing while ameliorating the inflammatory microenvironment, suggesting their potential as a therapeutic approach to prevent the development of tendinopathy.

Decorin and/or biglycan knockdown in aged mouse patellar tendon impacts fibril morphology, scar area, and mechanical properties

Small leucine-rich proteoglycans, such as decorin and biglycan, play pivotal roles in collagen fibrillogenesis during development, healing, and aging in tendon. Previous work has shown that the absence of decorin and biglycan affects fibril shape and mechanical properties during tendon healing. However, the roles of decorin and biglycan in the healing process of aged tendons are unclear. Therefore the objective of this study was to evaluate the differential roles of decorin and biglycan during healing of patellar tendon injury in aged mice. Aged (300 days old) female Dcn+/+/Bgn+/+ control (WT, n = 52), Dcnflox/flox (I-Dcn-/-, n = 36), Bgnflox/flox (I-Bgn-/-, n = 36), and compound Dcnflox/flox/Bgnflox/flox (I-Dcn-/-/Bgn-/-, n = 36) mice with a tamoxifen-inducible Cre were utilized. Targeted gene expression, collagen fibril diameter distributions, mechanical properties, and histological assays were employed to assess the effects of knockdown of decorin and/or biglycan at the time of injury. Knockdown resulted in alterations in fibril diameter distribution and scar area, but surprisingly did not lead to many differences in mechanical properties. Biglycan played a larger role in early healing stages, while decorin is more significant in later stages, particularly in scar remodeling. This study highlights some of the differential roles of biglycan and decorin in the regulation of fibril structure and scar area, as well as influencing gene expression during healing in aged mice.

Epidemiology of Sports-Related Tendon Ruptures Presenting to Emergency Departments in the United States

BACKGROUND

Participation in recreational and competitive sports can predispose people to musculoskeletal injuries. Chronic overuse with insufficient recovery, overloading, and direct contact can result in acute primary tendon ruptures. There is scarce literature regarding the epidemiology of sports-related acute primary tendon ruptures in the United States (US).

PURPOSE

To identify the incidence rate (IR) of sports-related acute primary tendon ruptures presenting to US emergency departments using the National Electronic Injury Surveillance System (NEISS) database and describe the trends in the IR from 2001 to 2020.

STUDY DESIGN

Descriptive epidemiology study.

METHODS

The NEISS database was queried using injury case narratives; cases with a clear diagnosis of an acute primary tendon rupture were included in the final analysis. National estimates, estimated IRs (reported as per 1,000,000 person-years at risk), and temporal trends in the annual IR (reported as average annual percent change) of acute primary tendon ruptures were calculated using NEISS sample estimates and US Census Bureau population estimates.

RESULTS

An estimated total of 141,382 patients (95% confidence interval [CI], 107,478-175,286) presented to US emergency departments with a sports-related tendon rupture over the study period (IR, 22.9 person-years at risk [95% CI, 17.4-28.3]). The mean age was 37.7 years (95% CI, 37.0-38.5). Of all cases of a tendon rupture identified from 2001 to 2020, 60.1% were secondary to exercise/sports-related injury mechanisms. An Achilles tendon rupture was the most common injury, representing 55.9% of cases. Basketball was the most common sports-related injury mechanism, accounting for 36.6% of cases. The overall injury rate in male patients was 7.7 times that of female patients (IR ratio, 7.7 [95% CI, 4.4-13.5]; P < .05). The annual incidence of all sports-related tendon ruptures in the US increased significantly from 2001 to 2020 (average annual percent change, 1.9 [95% CI, 1.0-2.8]; P < .01).

CONCLUSION

Recreational/competitive sports participation accounted for a large proportion of acute primary tendon ruptures in the US during the study period.

Single-nucleus transcriptional and chromatin accessibility analyses of maturing mouse Achilles tendon uncover the molecular landscape of tendon stem/progenitor cells

Tendons and ligaments are crucial connective tissues linking bones and muscles, yet achieving full functional recovery after injury remains challenging. We investigated the characteristics of tendon stem/progenitor cells (TSPCs) by focusing on the declining tendon repair capacity with growth. Using single-cell RNA sequencing on Achilles tendon cells from 2- and 6-week-old mice, we identified Cd55 and Cd248 as novel surface antigen markers for TSPCs. Combining single-nucleus ATAC and RNA sequencing analyses revealed that Cd55 and Cd248 positive fractions in tendon tissue are TSPCs, with this population decreasing at 1 weeks. We also identified candidate upstream transcription factors regulating these fractions. Functional analyses of isolated CD55/CD248 positive cells demonstrated high clonogenic potential and tendon differentiation capacity, forming functional tendon-like tissue in vitro . This study establishes CD55 and CD248 as novel TSPC surface antigens, potentially advancing tendon regenerative medicine and contributing to the development of new treatment strategies for tendon and ligament injuries.

Deprivation of loading during rat Achilles tendon healing affects extracellular matrix composition and structure, and reduces cell density and alignment

Tendon healing involves mechanosensitive cells that adapt to mechanical stimuli through mechanotransduction, resulting in increased tissue strength. However, detailed insights into this process in response to different loads remain limited. We aimed to investigate how different loading regimes impact the spatial composition of elastin and collagens during Achilles tendon healing. Histological analysis was conducted on healing rat Achilles tendons exposed to (1) full loading, (2) reduced loading, or (3) minimal loading. Histological analysis included Hematoxylin & Eosin and immunohistochemical staining targeting elastin, Collagen 1, Collagen 3, and CD31. Our results showed that the impact of mechanical stimuli on healing tendons varied with the degree of loading. Unexpectedly, minimal loading led to higher staining intensity for collagens and elastin. However, tendons exposed to minimal loading appeared thinner and exhibited a less organized matrix structure, with fewer, less aligned, and more rounded cells. Additionally, our findings indicated an inverse correlation between angiogenesis and load level, with more blood vessels in tendons subjected to less loading. Tissue integrity improved by 12 weeks post-injury, but the healing process continued and did not regain the structure seen in intact tendons even after 20 weeks. This study reveals a load-dependent effect on matrix alignment, cell density, and cell alignment.

Collagen denaturation in post-run Achilles tendons and Achilles tendinopathy: In vivo mechanophysiology and magnetic resonance imaging

Achilles tendinopathy is often attributed to overuse, but its pathophysiology remains poorly understood. Disruption to the molecular structure of collagen is fundamental for the onset and progression of tendinopathy but has mostly been investigated in vitro. Here, we interrogated the in vivo molecular structure changes of collagen in rat Achilles tendons following treadmill running. Unexpectedly, the tendons' collagen molecules were not mechanically unfolded by running but denatured through proteolysis during physiological post-run remodeling. We further revealed that running induces inflammatory gene expressions in Achilles tendons and that long-term running causes prolonged, elevated collagen degradation, leading to the accumulation of denatured collagen and tendinopathy development. For applications, we demonstrated magnetic resonance imaging of collagenase-induced Achilles tendon injury in vivo using a denatured collagen targeting contrast agent. Our findings may help close the knowledge gaps in the mechanobiology and pathogenesis of Achilles tendinopathy and initiate new strategies for its imaging-based diagnosis.

The Correlation of Dynamic Magnetic Resonance Imaging Evaluation With Histological, Biochemical, and Biomechanical Properties in Healing Progress After Achilles Tendon Injury: A Review

Achilles tendon injury is a common sports injury, and an in-depth understanding of its healing process is essential for improving rehabilitation strategies. As a non-invasive imaging technology with excellent anatomical and functional information extraction abilities, magnetic resonance imaging (MRI) has been widely used in the evaluation and monitoring of Achilles tendon injury. MRI scans at different stages of Achilles tendon healing can provide information about the structure of the Achilles tendon tissue, blood supply, composition, and metabolism. The change pattern on dynamic MRI evaluation is closely related to the specific stage of Achilles tendon healing and tissue characteristics. For example, the signal strength of dynamic enhanced MRI sequences can reflect blood supply to the Achilles tendon, whereas some quantitative MRI techniques can provide information on the recovery of water and collagen contents in the Achilles tendon. This article discusses the pathophysiological changes after Achilles tendon injury and summarizes the clinical and research status of the MRI techniques used for monitoring Achilles tendon healing. The feasibility of various MRI techniques for monitoring Achilles tendon healing and their correlation with histology, biochemistry, and biomechanics are reviewed, along with the challenges, limitations, and potential opportunities for their application. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 2.

[Transverse small incision intrathecal "loop" minimally invasive suture for treatment of acute Achilles tendon rupture]

Objective

To evaluate the effectiveness and feasibility of a transverse small incision intrathecal "loop" minimally invasive suture for acute Achilles tendon rupture.

Methods

The clinical data of 30 patients with acute Achilles tendon rupture treated with transverse small incision intrathecal "loop" minimally invasive suture between January 2022 and October 2023 was retrospectively analyzed. The patients were all male, aged from 29 to 51 years, with an average of 39.8 years. The cause of injury was acute sports injury, and the time from injury to operation was 1-14 days, with an average of 3.4 days. The operation time, incision length, intraoperative blood loss, intraoperative complications, wound healing, and hospital stay were recorded. Postoperative appearance and function of ankle were evaluated by American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score, Vancouver Scar Scale (VSS) score, and Arner-Lindholm score.

Results

The operation time ranged from 30 to 90 minutes, with an average of 54.2 minutes; the incision length ranged from 1.3 to 3.5 cm, with an average of 2.2 cm; the intraoperative blood loss ranged from 5 to 70 mL, with an average of 22.3 mL; and the hospital stay ranged from 2 to 6 days, with an average of 3.7 days. All incisions healed by first intention, and there was no incision infection, poor healing, and deep venous thrombosis. All patients were followed up 5.3-22.0 months (mean, 14.7 months). During the follow-up, all the 30 patients had returned to exercise, and there was no complication such as Achilles tendon re-rupture, postoperative infection, and gastrocnemius muscle injury. At last follow-up, the AOFAS ankle-hindfoot score was 82-100, with an average of 95.1; the VSS score was 1-4, with an average of 2.1; according to the Arner-Lindholm score, 24 cases were rated as excellent and 6 cases as good.

Conclusion

Transverse small incision intrathecal "loop" minimally invasive suture for the treatment of acute Achilles tendon rupture has the advantages of simple instrument, convenient operation, small trauma, quick recovery, and satisfactory effectiveness.

Advanced glycation end products impair the repair of injured tendon: a study in rats

BACKGROUND

The AGEs levels in tissues of diabetics and elderly tend to be higher than in normal individuals. This study aims to determine the effects of AGEs on Achilles tendon repair.

MATERIALS AND METHODS

Thirty-six male eight-week-old Sprague Dawley rats were selected in this study. The rats were randomly divided into two experimental groups and a control group after the transection of the Achilles tendon. During the tendon repair, the experimental groups were injected around the Achilles tendon with 350mmol/L (low dose group) and 1000mmol/L (high dose group) D-ribose 0.2 ml respectively to increase the AGEs level, while in the control group were given the same amount of PBS. The injections were given twice a week for six weeks. Collagen-I, TNF-α, and IL-6 expression in the healed Achilles tendon was assessed. Additionally, macroscopic, pathological, and biomechanical evaluations of Achilles tendon repair were conducted.

RESULTS

The repaired Achilles tendons in the high dose group showed severe swelling and distinctive adhesions. The histological score went up with the increase of the AGEs in the Achilles tendon (p<0.001). TNF- α and IL-6 in the Achilles tendon increased (p<0.001, p<0.001), and the production of collagen-I decreased with the accumulation of AGEs in the repaired Achilles tendon (p<0.001). The tensile strength of Achilles tendon in the high dose group was impaired significantly.

CONCLUSION

In current study, the compromised tendon repair model induced by AGEs was successfully established in rat. The study demonstrated that AGEs significantly impair Achilles tendon repair.

Mesenchymal stem cell-derived extracellular vesicles in joint diseases: Therapeutic effects and underlying mechanisms

Joint diseases greatly impact the daily lives and occupational functioning of patients globally. However, conventional treatments for joint diseases have several limitations, such as unsatisfatory efficacy and side effects, necessitating the exploration of more efficacious therapeutic strategies. Mesenchymal stem cell (MSC)-derived EVs (MSC-EVs) have demonstrated high therapeutic efficacyin tissue repair and regeneration, with low immunogenicity and tumorigenicity. Recent studies have reported that EVs-based therapy has considerable therapeutic effects against joint diseases, including osteoarthritis, tendon and ligament injuries, femoral head osteonecrosis, and rheumatoid arthritis. Herein, we review the therapeutic potential of various types of MSC-EVs in the aforementioned joint diseases, summarise the mechanisms underlying specific biological effects of MSC-EVs, and discuss future prospects for basic research on MSC-EV-based therapeutic modalities and their clinical translation. In general, this review provides an in-depth understanding of the therapeutic effects of MSC-EVs in joint diseases, as well as the underlying mechanisms, which may be beneficial to the clinical translation of MSC-EV-based treatment. The translational potential of this article: MSC-EV-based cell-free therapy can effectively promote regeneration and tissue repair. When used to treat joint diseases, MSC-EVs have demonstrated desirable therapeutic effects in preclinical research. This review may supplement further research on MSC-EV-based treatment of joint diseases and its clinical translation.

Evaluation of suitable reference genes for qPCR normalisation of gene expression in a Achilles tendon injury model

Tendons are one of the major load-bearing tissues in the body; subjected to enormous peak stresses, and thus vulnerable to injury. Cellular responses to tendon injury are complex, involving inflammatory and repair components, with the latter employing both resident and recruited exogenous cell populations. Gene expression analyses are valuable tools for investigating tendon injury, allowing assessment of repair processes and pathological responses such as fibrosis, and permitting evaluation of therapeutic pharmacological interventions. Quantitative polymerase chain reaction (qPCR) is a commonly used approach for such studies, but data obtained by this method must be normalised to reference genes: genes known to be stably expressed between the experimental conditions investigated. Establishing suitable tendon injury reference genes is thus essential. Accordingly we investigated mRNA expression stability in a rat model of tendon injury, comparing both injured and uninjured tendons, and the effects of rapamycin treatment, at 1 and 3 weeks post injury. We used 11 candidate genes (18S, ACTB, AP3D1, B2M, CSNK2A2, GAPDH, HPRT1, PAK1IP1, RPL13a, SDHA, UBC) and assessed stability via four complementary algorithms (Bestkeeper, deltaCt, geNorm, Normfinder). Our results suggests that ACTB, CSNK2A2, HPRT1 and PAK1IP1 are all stably expressed in tendon, regardless of injury or drug treatment: any three of these would serve as universally suitable reference gene panel for normalizing qPCR expression data in the rat tendon injury model. We also reveal 18S, UBC, GAPDH, and SDHA as consistently poor scoring candidates (with the latter two exhibiting rapamycin- and injury-associated changes, respectively): these genes should be avoided.

Uni-directional release of ibuprofen from an asymmetric fibrous membrane enables effective peritendinous anti-adhesion

Drug-loaded porous membranes have been deemed to be effective physicochemical barriers to separate postoperative adhesion-prone tissues in tendon healing. However, cell viability and subsequent tissue regeneration might be severely interfered with the unrestricted release and the locally excessive concentration of anti-inflammatory drugs. Herein, we report a double-layered membrane with sustained and uni-directional drug delivery features to prevent peritendinous adhesion without hampering the healing outcome. A vortex-assisted electrospinning system in combination with ibuprofen (IBU)-in-water emulsion was utilized to fabricate IBU-loaded poly-ʟ-lactic-acid (PLLA) fiber bundle membrane (PFB-IBU) as the anti-adhesion layer. The resultant highly porous structure, oleophilic and hydrophobic nature of PLLA fibers enabled in situ loading of IBU with a concentration gradient across the membrane thickness. Aligned collagen nanofibers were further deposited at the low IBU concentration side of the membrane for regulating cell growth and achieving uni-directional release of IBU. Drug release kinetics showed that the release amount of IBU from the high concentration side reached 79.32% at 14 d, while it was only 0.35% at the collagen side. Therefore, fibroblast proliferation at the high concentration side was successfully inhibited without affecting the oriented growth of tendon-derived stem cells at the other side. In vivo evaluation of the rat Achilles adhesion model confirmed the successful peritendinous anti-adhesion of our double-layered membrane, in that the macrophage recruitment, the inflammatory factor secretion and the deposition of pathological adhesion markers such as α-SMA and COL-III were all inhibited, which greatly improved the peritendinous fibrosis and restored the motor function of tendon.

The Categorization of Perinatal Derivatives for Orthopedic Applications

Musculoskeletal (MSK) pathology encompasses an array of conditions that can cause anything from mild discomfort to permanent injury. Their prevalence and impact on disability have sparked interest in more effective treatments, particularly within orthopedics. As a result, the human placenta has come into focus within regenerative medicine as a perinatal derivative (PnD). These biologics are sourced from components of the placenta, each possessing a unique composition of collagens, proteins, and factors believed to aid in healing and regeneration. This review aims to explore the current literature on PnD biologics and their potential benefits for treating various MSK pathologies. We delve into different types of PnDs and their healing effects on muscles, tendons, bones, cartilage, ligaments, and nerves. Our discussions highlight the crucial role of immune modulation in the healing process for each condition. PnDs have been observed to influence the balance between anti- and pro-inflammatory factors and, in some cases, act as biologic scaffolds for tissue growth. Additionally, we assess the range of PnDs available, while also addressing gaps in our understanding, particularly regarding biologic processing methods. Although certain PnD biologics have varying levels of support in orthopedic literature, further clinical investigations are necessary to fully evaluate their impact on human patients.

Dexamethasone treatment influences tendon healing through altered resolution and a direct effect on tendon cells

Inflammation, corticosteroids, and loading all affect tendon healing, with an interaction between them. However, underlying mechanisms behind the effect of corticosteroids and the interaction with loading remain unclear. The aim of this study was to investigate the role of dexamethasone during tendon healing, including specific effects on tendon cells. Rats (n = 36) were randomized to heavy loading or mild loading, the Achilles tendon was transected, and animals were treated with dexamethasone or saline. Gene and protein analyses of the healing tendon were performed for extracellular matrix-, inflammation-, and tendon cell markers. We further tested specific effects of dexamethasone on tendon cells in vitro. Dexamethasone increased mRNA levels of S100A4 and decreased levels of ACTA2/α-SMA, irrespective of load level. Heavy loading + dexamethasone reduced mRNA levels of FN1 and TenC (p < 0.05), while resolution-related genes were unaltered (p > 0.05). In contrast, mild loading + dexamethasone increased mRNA levels of resolution-related genes ANXA1, MRC1, PDPN, and PTGES (p < 0.03). Altered protein levels were confirmed in tendons with mild loading. Dexamethasone treatment in vitro prevented tendon construct formation, increased mRNA levels of S100A4 and decreased levels of SCX and collagens. Dexamethasone during tendon healing appears to act through immunomodulation by promoting resolution, but also through an effect on tendon cells.

Hyaluronic acid/PEO electrospun tube reduces tendon adhesion to levels comparable to native tendons - An in vitro and in vivo study

A major problem after tendon injury is adhesion formation to the surrounding tissue leading to a limited range of motion. A viable strategy to reduce adhesion extent is the use of physical barriers that limit the contact between the tendon and the adjacent tissue. The purpose of this study was to fabricate an electrospun bilayered tube of hyaluronic acid/polyethylene oxide (HA/PEO) and biodegradable DegraPol® (DP) to improve the anti-adhesive effect of the implant in a rabbit Achilles tendon full laceration model compared to a pure DP tube. Additionally, the attachment of rabbit tenocytes on pure DP and HA/PEO containing scaffolds was tested and Scanning Electron Microscopy, Fourier-transform Infrared Spectroscopy, Differential Scanning Calorimetry, Water Contact Angle measurements, and testing of mechanical properties were used to characterize the scaffolds. In vivo assessment after three weeks showed that the implant containing a second HA/PEO layer significantly reduced adhesion extent reaching levels comparable to native tendons, compared with a pure DP implant that reduced adhesion formation only by 20 %. Tenocytes were able to attach to and migrate into every scaffold, but cell number was reduced over two weeks. Implants containing HA/PEO showed better mechanical properties than pure DP tubes and with the ability to entirely reduce adhesion extent makes this implant a promising candidate for clinical application in tendon repair.

Reconstruction of proximal hamstring ruptures restores joint biomechanics during various walking conditions

PURPOSE

We aimed to examine the functional outcome in different walking conditions in elderly adults who underwent surgical repair after a non-contact hamstring injury. Our objective was to compare lower limb kinematics and kinetics over the entire gait cycle between the injured and contralateral leg in overground and level and uphill treadmill walking.

METHODS

12 patients (mean ± SD, age: 65 ± 9 years; body mass index: 30 ± 6 kg/m2) walked at self-selected speed in overground (0% slope) and treadmill conditions (0% and 10% slope). We measured spatiotemporal parameters, joint angles (normalised to gait cycle) and joint moments (normalised to stance phase) of the hip, knee and ankle. Data between sides were compared using paired sample t-tests (p < 0.05) and continuous 95% confidence intervals of the paired difference between trajectories.

RESULTS

Patients walked at an average speed of 1.31 ± 0.26 m/second overground and 0.92 ± 0.31 m/second on the treadmill. Spatiotemporal parameters were comparable between the injured and contralateral leg (p > 0.05). Joint kinematic and joint kinetic trajectories were comparable between sides for all walking conditions.

CONCLUSIONS

Refixation of the proximal hamstring tendons resulted in comparable ambulatory mechanics at least 1 year after surgery in the injured leg and the contralateral leg, which were all within the range of normative values reported in the literature. These results complement our previous findings on hamstring repair in terms of clinical outcomes and muscle strength and support that surgical repair achieves good functional outcomes in terms of ambulation in an elderly population.

TRIAL REGISTRATION

clinicaltrials.gov (NCT04867746).

Engineered Microenvironmental Cues from Fiber-Reinforced Hydrogel Composites Drive Tenogenesis and Aligned Collagen Deposition

Effective tendon regeneration following injury is contingent on appropriate differentiation of recruited cells and deposition of mature, aligned, collagenous extracellular matrix that can withstand the extreme mechanical demands placed on the tissue. As such, myriad biomaterial approaches have been explored to provide biochemical and physical cues that encourage tenogenesis and template aligned matrix deposition in lieu of dysfunctional scar tissue formation. Fiber-reinforced hydrogels present an ideal biomaterial system toward this end given their transdermal injectability, tunable stiffness over a range amenable to tenogenic differentiation of progenitors, and capacity for modular inclusion of biochemical cues. Here, tunable and modular, fiber-reinforced, synthetic hydrogels are employed to elucidate salient microenvironmental determinants of tenogenesis and aligned collagen deposition by tendon progenitor cells. Transforming growth factor β3 drives a cell fate switch toward pro-regenerative or pro-fibrotic phenotypes, which can be biased toward the former by culture in softer microenvironments or inhibition of the RhoA/ROCK activity. Furthermore, studies demonstrate that topographical anisotropy in fiber-reinforced hydrogels critically mediates the alignment of de novo collagen fibrils, reflecting native tendon architecture. These findings inform the design of cell-free, injectable, synthetic hydrogels for tendon tissue regeneration and, likely, that of a range of load-bearing connective tissues.

Stem Cell‐Based Therapies and Tissue Engineering Innovations for Tendinopathy: A Comprehensive Review of Current Strategies and Future Directions

Tendon diseases commonly lead to physical disability, exerting a profound impact on the routine of affected patients. These conditions respond poorly to existing treatments, presenting a substantial challenge for orthopedic scientists. Research into clinical translational therapy has yet to yield highly versatile interventions capable of effectively addressing tendon diseases, including tendinopathy. Stem cell‐based therapies have emerged as a promising avenue for modifying the biological milieu through the secretion of regenerative and immunomodulatory factors. The current review provides an overview of the intricate tendon microenvironment, encompassing various tendon stem progenitor cells within distinct tendon sublocations, gene regulation, and pathways pertinent to tendon development, and the pathology of tendon diseases. Subsequently, the advantages of stem cell‐based therapies are discussed that utilize distinct types of autologous and allogeneic stem cells for tendon regeneration at the translational level. Moreover, this review outlines the challenges, gaps, and future innovations to propose a consolidated stem cell‐based therapy to treat tendinopathy. Finally, regenerative soluble therapies, insoluble bio‐active therapies, along with insoluble bio‐active therapies, and implantable 3D scaffolds for tendon tissue engineering are discussed, thereby presenting a pathway toward enhanced tissue regeneration and engineering.