Critical review on the socio-economic impact of tendinopathy

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.

Physiotherapy practices in the clinical assessment of lateral elbow tendinopathy: An international survey

BACKGROUND AND PURPOSE

Understanding physiotherapy practices is important to identify variations from empirical evidence and highlight requirements for training. This survey explored international physiotherapy practices for assessment of lateral elbow tendinopathy (LET).

METHODS

Two hundred ninety-nine surveyed physiotherapists from eight member countries of the International Federation of Manual and Orthopaedic Physical Therapists completed the survey. Respondents rated their frequency of use (never, rarely, sometimes, often, and always) for items related to: patient history; diagnostic tests; grip and upper limb strength; cervical and neurological assessment; and medical imaging. To establish practices, the five response categories were dichotomised into routine practice (often, always) and not-routine practice (sometimes, rarely, never). A response rate of ≥70% for each dichotomy was used to determine whether an assessment item was deemed routine practice or not, with items not meeting either criterion considered neither routine nor not-routine practice.

RESULTS

Most respondents were from United States (63%). The 'chair pick up test', 'cervical special tests', and 'plain radiograph' met our criteria for not routine practice (i.e., 70%, 72%, and 71%, respectively). All other assessment items did not meet the criteria to be considered routine or not-routine practice.

CONCLUSION

The chair pick-up test, cervical spine special tests (e.g., Spurling's test), and plain radiography appear to not be routinely used in the assessment of LET. The finding that no assessment technique met the criteria for routine use may imply that physiotherapists adopt a nuanced approach to selecting clinical assessment items as opposed to routinely applying tests.

Rehabilitation Approaches for Proximal Peroneal Tendinopathy With Concurrent Anterior Cruciate Ligament (ACL) Sprain: A Case Report

Proximal peroneal tendinopathy is a relatively rare condition and can cause severe pain, discomfort, and often disability, especially if it coexists with other pathologies of the lower limbs. This case report discusses a 32-year-old male surgeon with the condition of chronic lateral ankle pain due to proximal peroneal tendinopathy, complicated by an anterior cruciate ligament sprain, a posterior cruciate ligament ganglion cyst, and early medial meniscus degeneration. His ability to perform surgeries has been compromised due to the need to stand for prolonged periods. A multi-factorial rehabilitation approach was designed to address the tendon pathology and the knee dysfunctions associated with it. The treatment program included patient education, therapeutic exercise, and pain management. There were considerable improvements in terms of pain, range of motion, muscle strength, and function from the previous stage of six weeks. This case indicates the clinical necessity of kinetic-chain-oriented, very individualized approaches to rehabilitation for complex musculoskeletal conditions such as this, especially in active professionals. The success of the rehabilitation lies in the potential for recovery even with some tough conditions if the treatment modality is appropriately designed to address the interactive aspects of the patient's condition. This case highlights the importance of an integrated approach in managing complex peroneal tendonitis, especially when associated with upstream joint pathology. The positive outcome underscores the value of early recognition and individualized management to restore function and avoid permanent complications. Additionally, the report serves as a guide for future research into the potential long-term benefits of holistic, patient-specific approaches for similar cases.

Effectiveness of Percutaneous Needle Electrolysis to Reduce Pain in Tendinopathies: A Systematic Review With Meta-Analysis

CONTEXT

Tendon injuries are common disorders in both workers and athletes, potentially impacting performance in both conditions. This is why the search for effective treatments is continuing.

OBJECTIVE(S)

The objective of this study was to analyze whether the ultrasound-guided percutaneous needle electrolysis technique may be considered a procedure to reduce pain caused by tendinosis.

EVIDENCE ACQUISITION

The search strategy included the PubMed, SCOPUS, CINAHL, Physiotherapy Evidence Database, SciELO, and ScienceDirect up to the date of February 25, 2024. Randomized clinical trials that assessed pain caused by tendinosis using the Visual Analog Scale and Numeric Rating Scale were included. The studies were evaluated for quality using the Cochrane Risk of Bias 2, and the evidence strength was assessed by the GRADEpro GDT.

EVIDENCE SYNTHESIS

Out of the 534 studies found, 8 were included in the review. A random-effects meta-analysis and standardized mean differences (SMD) were conducted. The ultrasound-guided percutaneous needle electrolysis proved to be effective in reducing pain caused by tendinosis in the overall outcome (SMD = -0.97; 95% CI, -1.26 to -0.68; I2 = 58%; low certainty of evidence) and in the short-term (SMD = -0.83, 95% CI, -1.29 to -0.38; I2 = 65%; low certainty of evidence), midterm (SMD = -1.28; 95% CI, -1.65 to -0.91; I2 = 0%; moderate certainty of evidence), and long-term (SMD = -0.94; 95% CI, -1.62 to -0.26; I2 = 71%; low certainty of evidence) subgroups.

CONCLUSION(S)

The application of the ultrasound-guided percutaneous needle electrolysis technique for reducing pain caused by tendinosis appears to be effective. However, due to the heterogeneity found (partially explained), more studies are needed to define the appropriate dosimetry, specific populations that may benefit more from the technique, and possible adverse events.

Defining tennis elbow characteristics - The assessment of magnetic resonance imaging defined tendon pathology in an asymptomatic population

Background

This radiological study aims to assess the prevalence of lateral elbow pathology in an asymptomatic population using 3.0T magnetic resonance imaging (MRI).

Methods

Bilateral elbow MRI was undertaken in 30 asymptomatic volunteers. Exclusion criteria included elbow pain within 3 months, elbow trauma or previous diagnosis of lateral epicondylar tendinopathy. Baseline patient-reported outcome measures were recorded along with age and body mass index (BMI). Two musculoskeletal radiologists independently graded the degree of abnormality at the common extensor tendon.

Results

Thirty volunteers were categorised according to age; 35-44 (n = 10), 45-54 (n = 11), and 55-65 (n = 9) with a 1:1 male-to-female ratio. Radiological evidence of tendon abnormality was found in 37% of volunteers. The proportion with abnormal findings increased with age; 35-44 (10%), 45-54 (36%), 55-65 (67%) and BMI; 18-24.9 (23%), 25-29.9 (43%), > 30 (67%). Changes were generally 'mild' or 'moderate', with a single volunteer showing 'severe' pathology. Kappa for the radiographic agreement was 0.91 (0.83-0.98).

Discussion

This study has demonstrated MRI findings suggestive of pathology at the common extensor tendon to be prevalent in an asymptomatic population, increasing with age and BMI. This draws into question the diagnostic and prognostic value of MRI imaging in lateral epicondylar tendinopathy, especially in older patients.

Challenges and opportunities of medicines for treating tendon inflammation and fibrosis: A comprehensive and mechanistic review

BACKGROUND

Tendinopathy refers to conditions characterized by collagen degeneration within tendon tissue, accompanied by the proliferation of capillaries and arteries, resulting in reduced mechanical function, pain, and swelling. While inflammation in tendinopathy can play a role in preventing infection, uncontrolled inflammation can hinder tissue regeneration and lead to fibrosis and impaired movement.

OBJECTIVES

The inability to regulate inflammation poses a significant limitation in tendinopathy treatment. Therefore, an ideal treatment strategy should involve modulation of the inflammatory process while promoting tissue regeneration.

METHODS

The current review article was prepared by searching PubMed, Scopus, Web of Science, and Google Scholar databases. Several treatment approaches based on biomaterials have been developed.

RESULTS

This review examines various treatment methods utilizing small molecules, biological compounds, herbal medicine-inspired approaches, immunotherapy, gene therapy, cell-based therapy, tissue engineering, nanotechnology, and phototherapy.

CONCLUSION

These treatments work through mechanisms of action involving signaling pathways such as transforming growth factor-beta (TGF-β), mitogen-activated protein kinases (MAPKs), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), all of which contribute to the repair of injured tendons.

Pathophysiology of sex difference in refractoriness in lateral epicondylitis: Biomechanical study of wrist torque

Eccentric contractions of the wrist extensors worsen lateral epicondylitis (LE), whose pathophysiology may involve sex differences in wrist torque. This study aimed to investigate sex differences in wrist torque in patients with LE. The wrist extension and flexion torques of 22 patients with LE (11 males and 11 females) were measured. Maximum muscle output over time was measured for 20 s, initial torque was defined as muscle strength, and the degree of eccentric contraction was quantified and defined as the eccentric contraction index (ECI). The affected/unaffected side ratio of the wrist extensor, extensor/flexor ratio of muscle strength, and affected/unaffected side difference of ECI between sexes were statistically analyzed. Furthermore, correlations between wrist extensor torque, ECI, and Visual Analog Scale of pain during the examination were evaluated. Females were found to display lower affected/unaffected side ratios of the wrist extensor and wrist extension/flexion ratios for the affected side, compared with males; however, no differences were found in the wrist extension/flexion ratios for the unaffected side in both sexes. Additionally, females presented with larger differences between the affected and unaffected sides in the ECI. Based on correlations between wrist torques, ECI, and pain, females tended to suppress muscle output to prevent pain from eccentric contraction of wrist extensors more than males, which would induce an imbalance in muscle strength of the wrist extensors and flexors. This imbalance may result in chronic eccentric contraction of the wrist extensors with gripping, exacerbating LE.

Shear-wave elastography for the evaluation of tendinopathies: a systematic review and meta-analysis

PURPOSE

To compare pathologic and healthy tendons using shear-wave elastography (SWE).

METHODS

A systematic review with meta-analysis was done searching Pubmed and EMBASE up to September 2022. Prospective, retrospective and cross-sectional studies that used SWE in the assessment of pathologic tendons versus control were included. Our primary outcome were SWE velocity (m/s) and stiffness (kPa). Methodological quality was assessed by the methodological index for non-randomized studies (MINORS). We used the mean difference (MD) with corresponding 95% confidence intervals (CIs) to quantify effects between groups. We performed sensitivity analysis in case of high heterogeneity, after excluding poor quality studies according to MINORS assessment. We used Grades of Recommendation, Assessment, Development and Evaluation to evaluate the certainty of evidence (CoE).

RESULTS

Overall, 16 studies with 676 pathologic tendons (188 Achilles, 142 patellar, 96 supraspinatus, 250 mixed) and 723 control tendons (484 healthy; 239 contralateral tendon) were included. Five studies (31.3%) were judged as poor methodological quality. Shear-wave velocity and stiffness meta-analyses showed high heterogeneity. According to a sensitivity analysis, pathologic tendons had a lower shear wave velocity (MD of - 1.69 m/s; 95% CI 1.85; - 1.52; n = 274; I2 50%) compared to healthy tendons with very low CoE. Sensitivity analysis on stiffness still showed high heterogeneity.

CONCLUSION

Pathological tendons may have reduced SWE velocity compared to controls, but the evidence is very uncertain. Future robust high-quality longitudinal studies and clear technical indications on the use of this tool are needed.

PROTOCOL

PROSPERO identifier: CRD42023405410 CLINICAL RELEVANCE STATEMENT: SWE is a relatively recent modality that may increase sensitivity and diagnostic accuracy of conventional ultrasound imaging promoting early detection of tendinopathy. Non-negligible heterogeneity has been observed in included studies, so our findings may encourage the conduct of future high-quality longitudinal studies which can provide clear technical indications on the use of this promising tool in tendon imaging.

Socioeconomic Status and Race Are Rarely Reported in Randomized Controlled Trials for Achilles Tendon Pathology in the Top 10 Orthopaedic Journals: A Systematic Review

Background

Randomized controlled trials (RCTs) are crucial in comparative research, and a careful approach to randomization methodology helps minimize bias. However, confounding variables like socioeconomic status (SES) and race are often underreported in orthopaedic RCTs, potentially affecting the generalizability of results. This study aimed to analyze the reporting trends of SES and race in RCTs pertaining to Achilles tendon pathology, considering 4 decades of data from top-tier orthopaedic journals.

Methods

This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and used PubMed to search 10 high-impact factor orthopaedic journals for RCTs related to the management of Achilles tendon pathology. The search encompassed all articles from the inception of each journal until July 11, 2023. Data extraction included year of publication, study type, reporting of SES and race, primary study location, and intervention details.

Results

Of the 88 RCTs identified, 68 met the inclusion criteria. Based on decade of publication, 6 articles (8.8%) reported on SES, whereas only 2 articles (2.9%) reported on race. No RCTs reported SES in the pre-1999 period, but the frequency of reporting increased in subsequent decades. Meanwhile, all RCTs reporting race were published in the current decade (2020-2030), with a frequency of 20%. When considering the study location, RCTs conducted outside the United States were more likely to report SES compared with those within the USA.

Conclusion

This review revealed a concerning underreporting of SES and race in Achilles tendon pathology RCTs. The reporting percentage remains low for both SES and race, indicating a need for comprehensive reporting practices in orthopaedic research. Understanding the impact of SES and race on treatment outcomes is critical for informed clinical decision making and ensuring equitable patient care. Future studies should prioritize the inclusion of these variables to enhance the generalizability and validity of RCT results.

Low-Intensity Pulsed Ultrasound Promotes the Repair of Achilles Tendinopathy by Downregulating the JAK/STAT Signaling Pathway in Rabbits

Tendinopathy is a complex tendon injury or pathology outcome, potentially leading to permanent impairment. Low-intensity pulsed ultrasound (LIPUS) is emerging as a treatment modality for tendon disorders. However, the optimal treatment duration and its effect on tendons remain unclear. This study aims to investigate the efficacy of LIPUS in treating injured tendons, delineate the appropriate treatment duration, and elucidate the underlying treatment mechanisms through animal experiments. Ninety-six three-month-old New Zealand white rabbits were divided into normal control (NC) and model groups. The model group received Prostaglandin E2 (PGE2) injections to induce Achilles tendinopathy. They were then divided into model control (MC) and LIPUS treatment (LT) groups. LT received LIPUS intervention with a 1-MHz frequency, a pulse repetition frequency (PRF) of 1 kHz, and spatial average temporal average sound intensity ( [Formula: see text]) of 100 mW/cm2. MC underwent a sham ultrasound, and NC received no treatment. Assessments on 1, 4, 7, 14, and 28 days after LT included shear wave elastography (SWE), mechanical testing, histologic evaluation, ribonucleic acid sequencing (RNA-seq), polymerase chain reaction (PCR), and western blot (WB) analysis. SWE results showed that the shear modulus in the LT group was significantly higher than that in the MC group after LT for seven days. Histological results demonstrated improved tendon tissue alignment and fibroblast distribution after LT. Molecular analyses suggested that LIPUS may downregulate the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway and regulate inflammatory and matrix-related factors. We concluded that LT enhanced injured tendon elasticity and accelerated Achilles tendon healing. The study highlighted the JAK/STAT signaling pathway as a potential therapeutic target for LT of Achilles tendinopathy, guiding future research.

Unraveling the link: locomotor activity exerts a dual role in predicting Achilles tendon healing and boosting regeneration in mice

Introduction

Tendon disorders present significant challenges in the realm of musculoskeletal diseases, affecting locomotor activity and causing pain. Current treatments often fall short of achieving complete functional recovery of the tendon. It is crucial to explore, in preclinical research, the pathways governing the loss of tissue homeostasis and its regeneration. In this context, this study aimed to establish a correlation between the unbiased locomotor activity pattern of CRL:CD1 (ICR) mice exposed to uni- or bilateral Achilles tendon (AT) experimental injuries and the key histomorphometric parameters that influence tissue microarchitecture recovery.

Methods

The study involved the phenotyping of spontaneous and voluntary locomotor activity patterns in male mice using digital ventilated cages (DVC®) with access to running wheels either granted or blocked. The mice underwent non-intrusive 24/7 long-term activity monitoring for the entire study period. This period included 7 days of pre-injury habituation followed by 28 days post-injury.

Results and discussion

The results revealed significant variations in activity levels based on the type of tendon injury and access to running wheels. Notably, mice with bilateral lesions and unrestricted wheel access exhibited significantly higher activity after surgery. Extracellular matrix (ECM) remodeling, including COL1 deposition and organization, blood vessel remodeling, and metaplasia, as well as cytological tendon parameters, such as cell alignment and angle deviation were enhanced in surgical (bilateral lesion) and husbandry (free access to wheels) groups. Interestingly, correlation matrix analysis uncovered a strong relationship between locomotion and microarchitecture recovery (cell alignment and angle deviation) during tendon healing. Overall, this study highlights the potential of using mice activity metrics obtained from a home-cage monitoring system to predict tendon microarchitecture recovery at both cellular and ECM levels. This provides a scalable experimental setup to address the challenging topic of tendon regeneration using innovative and animal welfare-compliant strategies.

A roadmap for delivering a human musculoskeletal cell atlas

Advances in single-cell technologies have transformed the ability to identify the individual cell types present within tissues and organs. The musculoskeletal bionetwork, part of the wider Human Cell Atlas project, aims to create a detailed map of the healthy musculoskeletal system at a single-cell resolution throughout tissue development and across the human lifespan, with complementary generation of data from diseased tissues. Given the prevalence of musculoskeletal disorders, this detailed reference dataset will be critical to understanding normal musculoskeletal function in growth, homeostasis and ageing. The endeavour will also help to identify the cellular basis for disease and lay the foundations for novel therapeutic approaches to treating diseases of the joints, soft tissues and bone. Here, we present a Roadmap delineating the critical steps required to construct the first draft of a human musculoskeletal cell atlas. We describe the key challenges involved in mapping the extracellular matrix-rich, but cell-poor, tissues of the musculoskeletal system, outline early milestones that have been achieved and describe the vision and directions for a comprehensive musculoskeletal cell atlas. By embracing cutting-edge technologies, integrating diverse datasets and fostering international collaborations, this endeavour has the potential to drive transformative changes in musculoskeletal medicine.

The superior healing capacity of MRL tendons is minimally influenced by the systemic environment of the MRL mouse

Murphy Roths Large mice (MRL) exhibit improved tendon healing and are often described as a "super-healer" strain. The underlying mechanisms that drive the superior healing response of MRL remain a controversial subject. We utilized a tendon transplantation model between MRL and "normal-healer" B6-mice to differentiate between the contribution of MRL's innate tendon and systemic environment to its improved healing capacity. Patellar tendons with a midsubstance punch injury were transplanted back into the same animal (autograft) or into an animal of the other strain (allograft). Findings at 4 weeks showed that the innate MRL tendon environment drives its improved healing capacity as demonstrated by improved stiffness and maximum load in MRL-grafts-in-B6-host-allografts compared to B6-autografts, and higher modulus in MRL-autografts compared to B6-graft-in-MRL-host-allografts. Groups with an MRL component showed an increase in pro-inflammatory cytokines in the 3 days after injury, suggesting an early enhanced inflammatory profile in MRL that ultimately resolves. A preserved range of motion of the knee joint in all MRL animals suggests a systemic "shielding effect" of MRL in regard to joint adhesiveness. Our findings 4-weeks post injury are consistent with previous studies showing tissue-driven improved healing and suggest that the systemic environment contributes to the overall healing process.

Transcatheter arterial embolisation for the relief of shoulder and elbow chronic joint pain refractory to conventional treatment: Systematic review

Angiogenesis and accompanying nerve fibres might cause unsettling joint pain. Studies have suggested that transcatheter arterial embolisation (TAE) of these abnormal neovessels could relieve pain and symptoms in patients with upper limb joint pain refractory to conventional treatment. This study aims to investigate the efficacy and safety of TAE in treating chronic pain of shoulder and elbow joints that have been resistant to other treatments. Using six databases, a systematic review was performed following Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. The primary outcome involved changes in the visual analogue scale (VAS) after TAE; while secondary outcomes involved comparing other parameters where relevant. Average VAS decreased from baseline, then at 1 day, 1 week, 1 month, 3 months, 4 months, 6 months, 1 year, 2 years and 44 months (7.5 at baseline vs. 4.7, 4.3, 3.4, 2.1, 2.5, 1.2, 0.7, 1.1 and 0.1, respectively). Average Quick-DASH scores decreased from baseline, then at 1, 3 and 6 months (61.3 at baseline vs. 30.6, 19.3 and 6.9, respectively). Minor adverse events were reported in 27/143 (18.9%) patients, where they resolved spontaneously or with oral analgesia. TAE is a possible treatment option for refractory shoulder and elbow joint pain; however, randomised controlled trials are still required.

Effect of resistance exercise dose components for tendinopathy management: a systematic review with meta-analysis

OBJECTIVE

To investigate potential moderating effects of resistance exercise dose components including intensity, volume and frequency, for the management of common tendinopathies.

DESIGN

Systematic review with meta-analysis and meta-regressions.

DATA SOURCES

Including but not limited to: MEDLINE, CINAHL, SPORTDiscus, ClinicalTrials.gov and ISRCTN Registry.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Randomised and non-randomised controlled trials investigating resistance exercise as the dominant treatment class, reporting sufficient information regarding ≥2 components of exercise dose.

RESULTS

A total of 110 studies were included in meta-analyses (148 treatment arms (TAs), 3953 participants), reporting on five tendinopathy locations (rotator cuff: 48 TAs; Achilles: 43 TAs; lateral elbow: 29 TAs; patellar: 24 TAs; gluteal: 4 TAs). Meta-regressions provided consistent evidence of greater pooled mean effect sizes for higher intensity therapies comprising additional external resistance compared with body mass only (large effect size domains: β BodyMass: External = 0.50 (95% credible interval (CrI): 0.15 to 0.84; p=0.998); small effect size domains (β BodyMass: External = 0.04 (95% CrI: -0.21 to 0.31; p=0.619)) when combined across tendinopathy locations or analysed separately. Greater pooled mean effect sizes were also identified for the lowest frequency (less than daily) compared with mid (daily) and high frequencies (more than once per day) for both effect size domains when combined or analysed separately (p≥0.976). Evidence for associations between training volume and pooled mean effect sizes was minimal and inconsistent.

SUMMARY/CONCLUSION

Resistance exercise dose is poorly reported within tendinopathy management literature. However, this large meta-analysis identified some consistent patterns indicating greater efficacy on average with therapies prescribing higher intensities (through inclusion of additional loads) and lower frequencies, potentially creating stronger stimuli and facilitating adequate recovery.

Cell-free fat extract-loaded microneedles attenuate inflammation-induced apoptosis and mitochondrial damage in tendinopathy

Existing clinical treatments for tendinopathy mainly focus on reducing pain, whereas inhibiting or reversing disease progression remains challenging. Local therapeutic drugs, such as glucocorticoids, cause adverse effects on the metabolism of tendon tissues and injection-related complications. Therefore, new administration modalities for tendinopathy need to be developed. In this study, we designed a hydrogel-based microneedle (MN) system for the long-term transdermal delivery of our novel biological cell-free fat extract (CEFFE) to treat tendinopathies. We found that CEFFE-loaded MNs (CEFFE-MNs) had good biosafety and inhibited lipopolysaccharide (LPS)-induced apoptosis and matrix degradation in Achilles tendon cells of rats. The Achilles tendons of rats returned to their maximum mechanical strength after applying CEFFE-MNs. The administration of CEFFE-MNs had better anti-apoptosis and tendon repair-promoting effects than CEFEF injections in vivo. Transcriptome sequencing indicated that the anti-apoptosis effect of CEFFE-MNs was highly related to tumor necrosis factor (TNF) signaling. CEFFE-MNs inhibited the expression of TNF, TNF receptor 1, and downstream nuclear factor-kappa B signaling. Additionally, CEFFE-MNs rescued LPS-induced mitochondrial dynamics in tendon cells via the TNF-Drp1 axis. Our study reports a novel CEFFE-MN system that exhibits long-term anti-inflammatory and anti-apoptotic effects, suggesting it as a new treatment route for tendinopathy with broad clinical translation prospects.

The Functions and Mechanisms of Tendon Stem/Progenitor Cells in Tendon Healing

Tendon injury is one of the prevalent disorders of the musculoskeletal system in orthopedics and is characterized by pain and limitation of joint function. Due to the difficulty of spontaneous tendon healing, and the scar tissue and low mechanical properties that usually develops after healing. Therefore, the healing of tendon injury remains a clinical challenge. Although there are a multitude of approaches to treating tendon injury, the therapeutic effects have not been satisfactory to date. Recent studies have shown that stem cell therapy has a facilitative effect on tendon healing. In particular, tendon stem/progenitor cells (TSPCs), a type of stem cell from tendon tissue, play an important role not only in tendon development and tendon homeostasis, but also in tendon healing. Compared to other stem cells, TSPCs have the potential to spontaneously differentiate into tenocytes and express higher levels of tendon-related genes. TSPCs promote tendon healing by three mechanisms: modulating the inflammatory response, promoting tenocyte proliferation, and accelerating collagen production and balancing extracellular matrix remodeling. However, current investigations have shown that TSPCs also have a negative effect on tendon healing. For example, misdifferentiation of TSPCs leads to a "failed healing response," which in turn leads to the development of chronic tendon injury (tendinopathy). The focus of this paper is to describe the characteristics of TSPCs and tenocytes, to demonstrate the roles of TSPCs in tendon healing, while discussing the approaches used to culture and differentiate TSPCs. In addition, the limitations of TSPCs in clinical application and their potential therapeutic strategies are elucidated.

Lived experience of people with lateral elbow tendinopathy: a qualitative study from the OPTimisE pilot and feasibility trial

OBJECTIVES

To explore the lived experience of people with lateral elbow tendinopathy (LET) and its impact on everyday life.

DESIGN

Qualitative semi-structured interviews, analysed using thematic analysis.

SETTING

Conducted as part of the mixed-methods OPTimisE pilot and feasibility randomised controlled trial of outpatient physiotherapy patients in the UK.

PARTICIPANTS

17 participants with LET, purposively sampled from the trial to provide representativeness based on age, sex, ethnicity, deprivation index and treatment allocation.

RESULTS

Four themes were identified from the participants' responses: (1) cause of onset-typically symptoms were attributed to: sudden changes in activity, repetitive work or compensating for other musculoskeletal conditions; (2) impact on everyday life-which included substantial impacts on quality-of-life, particularly due to pain disturbing sleep and difficulties performing daily tasks (related to work and hobbies) due to pain, although most reported being able to persevere with work; (3) self-help and understanding of the condition-with uncertainty about the appropriateness and potential harm of online advice and confusion from the diagnostic term 'Tennis Elbow' that non-sporting individuals struggled to relate to; (4) healthcare experiences-the treatments received were highly variable and often perceived as ineffectual.

CONCLUSIONS

For the first time, the lived experience of people from a range of backgrounds suffering from LET has been explored. Findings suggest that people frequently related the cause to a specific activity. They reported substantial impacts on daily tasks, sleep, work and hobbies. People also reported hesitancy to trust online information without formal healthcare advice, were confused by the common label of 'Tennis Elbow', and perceived the wide array of healthcare treatment options they had received to offer false hope and be largely ineffective. This study provides stimulus for clinicians to consider the advice and treatment provided, and whether the messages conveyed reflect the favourable natural history of the condition.

TRIAL REGISTRATION NUMBER

ISRCTN64444585.

The effectiveness of shockwave therapy on patellar tendinopathy, Achilles tendinopathy, and plantar fasciitis: a systematic review and meta-analysis

Background

Tendinopathy is a growing global concern affecting many people, like athletes, workers, and the elderly. Despite its commonality among the sporting population, there is no practical clinical guideline for patellar tendinopathy (PT). Furthermore, there is conflicting evidence between clinical guidelines on shockwave therapy's application and clinical utility for Achilles tendinopathy (AT) and plantar fasciitis (PF). Thus, our aim of this study is to evaluate the evidence for shockwave therapy; to provide a Grading of Recommendation, Assessment, Development and Evaluation (GRADE) level of the evidence and effectiveness of shockwave therapy for patellar tendinopathy, Achilles tendinopathy, and Plantar fasciitis.

Method

Medical Literature Analysis and Retrieval System Online (Medline), Embase, The Cumulative Index to Nursing and Allied Health Literature (CINAHL), Physiotherapy Evidence Database (PEDro) and China National Knowledge Infrastructure database (CNKI) were searched to find relevant studies published before December 14th, 2022.

Results

Our study showed that for PT in the short term, extracorporeal shockwave therapy (ESWT) or ESWT + eccentric exercise (EE) has a negligible effect on pain and function compared to a placebo or placebo + EE. On the contrary, ESWT significantly affects pain compared to conservative treatment (CT). For AT, ESWT has a small inconclusive effect on pain and function in the short term compared to EE. On the other hand, a placebo outperformed ESWT in improving function for AT but not pain outcomes. PF showed that ESWT significantly affects short- and long-term pain and function. When ESWT was compared to other interventions such as low laser therapy (LLLT), corticosteroid injection (CSI), or CT, there was a small inconclusive effect on pain and function in the short term.

Conclusion

There is low-moderate evidence that ESWT has a negligible effect on pain and function for PT and AT. However, high-quality evidence suggests ESWT has a large effect on pain and function for PF.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42023396835, identifier CRD42023396835.

Moderate evidence exists for four microRNAs as potential biomarkers for tendinopathies and degenerative tendon ruptures at the upper extremity in elderly patients: conclusion of a systematic review with best-evidence synthesis

PURPOSE

The aim of this systematic review was to investigate tendon-specific microRNAs (miRNAs) as biomarkers for the detection of tendinopathies or degenerative tendon ruptures. Also, their regulatory mechanisms within the tendon pathophysiology were summarized.

METHODS

A systematic literature research was performed using the PRISMA guidelines. The search was conducted in the Pubmed database. The SIGN checklist was used to assess the study quality of the included original studies. To determine the evidence and direction of the miRNA expression rates, a best-evidence synthesis was carried out, whereby only studies with at least a borderline methodological quality were considered for validity purposes.

RESULTS

Three thousand three hundred seventy studies were reviewed from which 22 fulfilled the inclusion criteria. Moderate evidence was found for miR-140-3p and miR-425-5p as potential biomarkers for tendinopathies as well as for miR-25-3p, miR-29a-3p, miR-140-3p, and miR-425-5p for the detection of degenerative tendon ruptures. This evidence applies to tendons at the upper extremity in elderly patients. All miRNAs were associated with inflammatory cytokines as interleukin-6 or interleukin-1ß and tumor necrosis factor alpha.

CONCLUSIONS

Moderate evidence exists for four miRNAs as potential biomarkers for tendinopathies and degenerative tendon ruptures at the upper extremity in elderly patients. The identified miRNAs are associated with inflammatory processes.

Effectiveness of Exercise Treatments with or without Adjuncts for Common Lower Limb Tendinopathies: A Living Systematic Review and Network Meta-analysis

INTRODUCTION

Exercise therapy is usually prescribed as first-line treatment for lower limb tendinopathies. The multitude of exercise- and non-exercise-based management options can be overwhelming for the treating sports professional and patient alike. We chose to investigate the comparative effectiveness of exercise therapy with or without adjuncts for managing the commonest lower limb tendinopathies.

METHODS

Through an extensive systematic literature search using multiple databases, we aimed to identify eligible randomised controlled trials (RCTs) on Achilles tendinopathy, patellar tendinopathy or greater trochanteric pain syndrome (GTPS) that included at least one exercise intervention in their treatment arms. Our primary outcomes were patient-reported pain and function (Victorian Institute of Sport Assessment; VISA). Follow-up was defined as short-term (≤ 12 weeks), mid-term (> 12 weeks to < 12 months) and long-term (≥ 12 months). The risk of bias and strength of evidence were assessed with the Cochrane Collaboration and GRADE-NMA tools, respectively. Analyses were performed separately for each one of the three tendinopathies.

RESULTS

A total of 68 RCTs were included in the systematic review. All pairwise comparisons that demonstrated statistically and clinically significant differences between interventions were based on low or very low strength of evidence. Based on evidence of moderate strength, the addition of extracorporeal shockwave therapy to eccentric exercise in patellar tendinopathy was associated with no short-term benefit in pain or VISA-P. From the network meta-analyses, promising interventions such as slow resistance exercise and therapies administered alongside eccentric exercise, such as topical glyceryl trinitrate for patellar tendinopathy and high-volume injection with corticosteroid for Achilles tendinopathy were based on low/very low strength of evidence.

CONCLUSION

In this network meta-analysis, we found no convincing evidence that any adjuncts administered on their own or alongside exercise are more effective than exercise alone. Therefore, we recommend that exercise monotherapy continues to be offered as first-line treatment for patients with Achilles and patellar tendinopathies and GTPS for at least 3 months before an adjunct is considered. We provide treatment recommendations for each tendinopathy. PROSPERO registration number CRD42021289534.

Pharmacological Therapies for Connective Tissue Fibrosis in Orthopaedics

Fibrosis is a common and debilitating pathological process that affects many organ systems and contributes to connective tissue disorders in orthopaedics. Tendons heal after acute and chronic injury through a process of fibrovascular scar tissue formation, and soft tissue joint capsules can be affected after traumatic joint injury, leading to arthrofibrosis. Although the precise underlying mechanisms are still being elucidated, fibrosis is thought to be a consequence of dysregulated immune and cytokine signaling that leads to myofibroblast activation and proliferation and subsequent excessive collagen deposition. Current treatments for connective tissue fibrosis include physical therapy and surgery, but there are no therapies that directly target the underlying cellular and molecular mechanisms of fibrosis. Many pharmacological agents have been used to successfully target fibrosis in other tissues and organ systems and thus are a promising treatment option to fill this gap. However, limited evidence is available to guide the use of these agents in musculoskeletal connective tissues. This article provides an overview of pharmacological therapies that have potential to treat connective tissue fibrosis in patients with musculoskeletal conditions, along with the current supporting evidence and future uses of each therapy.

Programmable DNA Hydrogel Provides Suitable Microenvironment for Enhancing TSPCS Therapy in Healing of Tendinopathy

Tendon stem/progenitor cells (TSPCs) therapy is a promising strategy for enhancing cell matrix and collagen synthesis, and regulating the metabolism of the tendon microenvironment during tendon injury repair. Nevertheless, the barren microenvironment and gliding shear of tendon cause insufficient nutrition supply, damage, and aggregation of injected TSPCs around tendon tissues, which severely hinders their clinical application in tendinopathy. In this study, a TSPCs delivery system is developed by encapsulating TSPCs within a DNA hydrogel (TSPCs-Gel) as the DNA hydrogel offers an excellent artificial extracellular matrix (ECM) microenvironment by providing nutrition for proliferation and protection against shear forces. This delivery method restricts TSPCs to the tendons, significantly extending their retention time. It is also found that TSPCs-Gel injections can promote the healing of rat tendinopathy in vivo, where cross-sectional area and load to failure of injured tendons in rats are significantly improved compared to the free TSPCs treatment group at 8 weeks. Furthermore, the potential healing mechanism of TSPCs-Gel is investigated by RNA-sequencing to identify a series of potential gene and signaling pathway targets for further clinical treatment strategies. These findings suggest the potential pathways of using DNA hydrogels as artificial ECMs to promote cell proliferation and protect TSPCs in TSPC therapy.

HMGB1: a potential new target for tendinopathy treatment

Tendinopathy describes a complex pathology of the tendon characterized by abnormalities in the microstructure, composition, and cellularity of the tendon, leading to pain, limitation of activity and reduced function. Nevertheless, the mechanism of tendinopathy has not been fully elucidated, and the treatment of tendinopathy remains a challenge. High mobility group box 1 (HMGB1), a highly conserved and multifaceted nuclear protein, exerts multiple roles and high functional variability and is involved in many biological and pathological processes. In recent years, several studies have suggested that HMGB1 is associated with tendinopathy and may play a key role in the pathogenesis of tendinopathy. Therefore, this review summarizes the expression and distribution of HMGB1 in tendinopathy, focuses on the roles of HMGB1 and HMGB1-based potential mechanisms involved in tendinopathy, and finally summarizes the findings on HMGB1-based therapeutic approaches in tendinopathy, probably providing new insight into the mechanism and further potential therapeutic targets of tendinopathy.

Single-cell and spatial transcriptomics reveal changes in cell heterogeneity during progression of human tendinopathy

BACKGROUND

Musculoskeletal tissue degeneration impairs the life quality and motor function of many people, especially seniors and athletes. Tendinopathy is one of the most common diseases associated with musculoskeletal tissue degeneration, representing a major global healthcare burden that affects both athletes and the general population, with the clinical presentation of long-term recurring chronic pain and decreased tolerance to activity. The cellular and molecular mechanisms at the basis of the disease process remain elusive. Here, we use a single-cell and spatial RNA sequencing approach to provide a further understanding of cellular heterogeneity and molecular mechanisms underlying tendinopathy progression.

RESULTS

To explore the changes in tendon homeostasis during the tendinopathy process, we built a cell atlas of healthy and diseased human tendons using single-cell RNA sequencing of approximately 35,000 cells and explored the variations of cell subtypes' spatial distributions using spatial RNA sequencing. We identified and localized different tenocyte subpopulations in normal and lesioned tendons, found different differentiation trajectories of tendon stem/progenitor cells in normal/diseased tendons, and revealed the spatial location relationship between stromal cells and diseased tenocytes. We deciphered the progression of tendinopathy at a single-cell level, which is characterized by inflammatory infiltration, followed by chondrogenesis and finally endochondral ossification. We found diseased tissue-specific endothelial cell subsets and macrophages as potential therapeutic targets.

CONCLUSIONS

This cell atlas provides the molecular foundation for investigating how tendon cell identities, biochemical functions, and interactions contributed to the tendinopathy process. The discoveries revealed the pathogenesis of tendinopathy at single-cell and spatial levels, which is characterized by inflammatory infiltration, followed by chondrogenesis, and finally endochondral ossification. Our results provide new insights into the control of tendinopathy and potential clues to developing novel diagnostic and therapeutic strategies.

Computational Analysis of miR-140 and miR-135 as Potential Targets to Develop Combinatorial Therapeutics for Degenerative Tendinopathy

Background

Degenerative tendinopathy, a condition causing movement restriction due to high pain, highly impacts productivity and quality of life. The healing process is a complex phenomenon and involves a series of intra-cellular and inter-cellular processes. Proliferation and differentiation of the tenocyte is a major and essential process to heal degenerative tendinopathy. The recent development in microRNA (miRNA)-mediated reprogramming of the cellular function through specific pathways opened door for the development of new regenerative therapeutics. Based on information about gene expression and regulation of tendon injury and healing, we attempted to evaluate the combinatorial effect of selected miRNAs for better healing of degenerative tendinopathy.

Methods

The present study was designed to evaluate the combinatorial effect of two miRNAs (has-miR-140 and has-miR-135) in the healing process of the tendon. Publicly available information/data were retrieved from appropriate platforms such as PubMed. Only molecular data, directly associated with tendinopathies, including genes/proteins and miRNAs, were used in this study. The miRNAs involved in tendinopathy were analyzed by a Bioinformatics tools (e.g., TargetScan, miRDB, and the RNA22v2). Interactive involvement of the miRNAs with key proteins involved in tendinopathy was predicted by the Insilco approach.

Results

Based on information available in the public domain, tendon healing-associated miRNAs were predicted to explore their therapeutic potentials. Based on computation analysis, focusing on the potential regulatory effect on tendon healing, the miR-135 and miR-140 were selected for this study. These miRNAs were found as key players in tendon healing through Rho-associated coiled-coil containing protein kinase 1 (ROCK1), IGF-1/PI3K/Akt, PIN, and Wnt signaling pathways. It was also predicted that these miRNAs may reprogram the cells to induce proliferation and differentiation activity. Many miRNAs are likely to regulate genes important for the tendinopathy healing process, and the result of this study allows an approach for miRNA-mediated regeneration of the tenocyte for tendon healing. Based on computational analysis, the role of these miRNAs in different pathways was established, and the results provided insights into the combinatorial approach of miRNA-mediated cell reprogramming.

Conclusions

In this study, the association between miRNAs and the disease was evaluated to correlate the tendinopathy genes and the relevant role of different miRNAs in their regulation. Through this study, it was established that the synergistic effect of more than one miRNA on directed reprogramming of the cell could be helpful in the regeneration of damaged tissue. It is anticipated that this study will be helpful for the design of miRNA cocktails for the orchestration of cellular reprogramming events.

Nutritional Supplements in the Clinical Management of Tendinopathy: A Scoping Review

INTRODUCTION

Tendinopathy has a high prevalence and incidence in the general population and among athletes, with a lack of consensus among medical practitioners on optimal management strategies. The objective of this scoping review was to evaluate current research on the use of nutritional supplements for treating tendinopathies, including what supplements have been used and what outcomes, outcome measures, and intervention parameters have been reported.

METHODS

Databases searched included Embase, SPORTDiscus, the Cochrane Library, MEDLINE, CINAHL, and AMED. This scoping review considered primary studies investigating nutritional supplements for tendinopathies and was reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Extension for Scoping Reviews.

RESULTS

A total of 1527 articles were identified with 16 included in the review. Studies investigated a range of nutritional supplements in the clinical management of various tendinopathies, including several commercially available proprietary blends of several ingredients. TendoActive (mucopolysaccharides, type I collagen, and vitamin C) was used in 2 studies, TENDISULFUR (methylsulfonylmethane, hydrolyzed collagen, L-arginine, L-lysine, vitamin C, bromelain, chondroitin, glucosamine, Boswellia, and myrrh) was used in 3 studies, and Tenosan (arginine-L-alpha ketoglutarate, hydrolyzed collagen type I, methylsulfonylmethane, vitamin C, bromelain, and vinitrox) was used in 2 studies. Collagen peptides were used in 2 studies, with omega-3 fatty acids, combined fatty acids and antioxidants, turmeric rhizome combined with Boswellia, β-hydroxy β-methylbutyric, vitamin C in isolation and combined with gelatin, and creatine investigated in one study each.

CONCLUSION

Despite a paucity of studies to date, findings from this review suggest that several nutritional compounds may be beneficial in the clinical management of tendinopathies, by exerting anti-inflammatory effects and improving tendon healing. Nutritional supplements may have potential as an adjunctive method to standard treatment methods such as exercise, where their pain-relieving, anti-inflammatory, and structural tendon effects may augment the positive functional outcomes gained from progressive exercise rehabilitation.

Impact of elevated serum advanced glycation end products and exercise on intact and injured murine tendons

OVERVIEW

Delayed tendon healing is a significant clinical challenge for those with diabetes. We explored the role of advanced glycation end-products (AGEs), a protein modification present at elevated levels in serum of individuals with diabetes, on injured and intact tendons using a mouse model. Cell proliferation following tissue injury is a vital component of healing. Based on our previous work demonstrating that AGEs limit cell proliferation, we proposed that AGEs are responsible for the delayed healing process commonly observed in diabetic patients. Further, in pursuit of interventional strategies, we suggested that moderate treadmill exercise may support a healing environment in the presence of AGEs as exercise has been shown to stimulate cell proliferation in tendon tissue.

MATERIALS AND METHODS

Mice began receiving daily intraperitoneal injections of bovine serum albumin (BSA)-Control or AGE-BSA injections (200μg/ml) at 16-weeks of age. A tendon injury was created in the central third of both patellar tendons. Animals assigned to an exercise group began a moderate treadmill protocol one week following injury. The intact Achilles tendon and soleus muscle were also evaluated to assess the effect of BSA and AGE-BSA on un-injured muscle and tendon.

RESULTS

We demonstrate that our injection dosing and schedule lead to an increase in serum AGEs. Our findings imply that AGEs indeed modulate gene expression following a patellar tendon injury and have modest effects on gene expression in intact muscle and tendon.

CONCLUSIONS

While additional biomechanical analysis is warranted, these data suggest that elevated serum AGEs in persons with diabetes may impact tendon health.

What are small, medium and large effect sizes for exercise treatments of tendinopathy? A systematic review and meta-analysis

Objective

To quantify and describe effect size distributions from exercise therapies across a range of tendinopathies and outcome domains to inform future research and clinical practice through conducting a systematic review with meta-analysis.

Design

Systematic review with meta-analysis exploring moderating effects and context-specific small, medium and large thresholds.

Eligibility criteria

Randomised and quasi-randomised controlled trials involving any persons with a diagnosis of rotator cuff, lateral elbow, patellar, Achilles or gluteal tendinopathy of any severity or duration.

Methods

Common databases, six trial registries and six grey literature databases were searched on 18 January 2021 (PROSPERO: CRD42020168187). Standardised mean difference (SMD_pre) effect sizes were used with Bayesian hierarchical meta-analysis models to calculate the 0.25 (small), 0.5 (medium) and 0.75 quantiles (large) and compare pooled means across potential moderators. Risk of bias was assessed with Cochrane's Risk of Bias tool.

Results

Data were obtained from 114 studies comprising 171 treatment arms 4104 participants. SMD_pre effect sizes were similar across tendinopathies but varied across outcome domains. Greater threshold values were obtained for self-reported measures of pain (small=0.5, medium=0.9 and large=1.4), disability (small=0.6, medium=1.0 and large=1.5) and function (small=0.6, medium=1.1 and large=1.8) and lower threshold values obtained for quality of life (small=-0.2, medium=0.3 and large=0.7) and objective measures of physical function (small=0.2, medium=0.4 and large=0.7). Potential moderating effects of assessment duration, exercise supervision and symptom duration were also identified, with greater pooled mean effect sizes estimated for longer assessment durations, supervised therapies and studies comprising patients with shorter symptom durations.

Conclusion

The effect size of exercise on tendinopathy is dependent on the type of outcome measure assessed. Threshold values presented here can be used to guide interpretation and assist with further research better establishing minimal important change.

The effectiveness of intratissue percutaneous electrolysis for the treatment of tendinopathy: a systematic review

Background

Tendinopathy is highly prevalent in the general public and common in athletes. It makes up nearly 50% of all sport injuries. A number of treatment techniques with varying evidence of effectiveness are currently available. Intratissue percutaneous electrolysis (EPI) is one such modality, however little consensus exists for EPI's efficacy or the most effective treatment parameters.

Objective

To review and appraise available evidence for Intratissue Percutaneous Electrolysis (EPI) in the treatment of tendinopathy, examining the effectiveness of EPI in conjunction with other modalities and identifying the strengths and limitations of the evidence base for EPI in order to make evidence-based recommendation for future studies of EPI.

Methods

PubMed, Embase and Scopus were searched with keywords related to EPI and tendinopathy. Grey literature searches were conducted with Embase, OpenGrey, and ProQuest. Extensive citation searching was undertaken. Randomised controlled trials (RCTs), uncontrolled and observational studies of the application of EPI in patients aged 18-65 years with Magnetic Resonance Imaging (MRI) or clinical Ultrasonography (US) confirmed diagnosis of tendinopathy were eligible.

Results

Eleven studies met inclusion criteria: six randomised control trials (RCTs) and five uncontrolled studies. Clinical trials of EPI as an adjunct modality with physical therapy reporting greater decreased pain and return to function than treatment with physical therapy alone. The evidence for EPI is limited and influenced by small sample sizes, varying treatment protocols, clinical heterogeneity and high risk of bias.

Conclusion

It is currently not possible to conclude that EPI is an effective modality for the treatment of tendinopathy. RCTs with clearly described EPI treatment protocols, larger sample sizes and intervention reporting sufficient to support reproducibility are needed to determine the effectiveness of EPI for the treatment of tendinopathy.

Tendon pain - what are the mechanisms behind it?

OBJECTIVES

Management of chronic tendon pain is difficult and controversial. This is due to poor knowledge of the underlying pathophysiology of chronic tendon pain, priorly known as tendinitis but now termed tendinopathy. The objective of this topical review was to synthesize evolving information of mechanisms in tendon pain, using a comprehensive search of the available literature on this topic.

CONTENT

This review found no correlations between tendon degeneration, collagen separation or neovascularization and chronic tendon pain. The synthesis demonstrated that chronic tendon pain, however, is characterized by excessive nerve sprouting with ingrowth in the tendon proper, which corresponds to alterations oberserved also in other connective tissues of chronic pain conditions. Healthy, painfree tendons are devoid of nerve fibers in the tendon proper, while innervation is confined to tendon surrounding structures, such as sheaths. Chronic painful tendons exhibit elevated amounts of pain neuromediators, such as glutamate and substance p as well as up-regulated expression and excitability of pain receptors, such as the glutamate receptor NMDAR1 and the SP receptor NK1, found on ingrown nerves and immune cells. Increasing evidence indicates that mast cells serve as an important link between the peripheral nervous system and the immune systems resulting in so called neurogenic inflammation.

SUMMARY

Chronic painful tendons exhibit (1) protracted ingrowth of sensory nerves (2) elevated pain mediator levels and (3) up-regulated expression and excitability of pain receptors, participating in (4) neuro-immune pathways involved in pain regulation. Current treatments that entail the highest scientific evidence to mitigate chronic tendon pain include eccentric exercises and extracorporeal shockwave, which both target peripheral neoinnervation aiming at nerve regeneration.

OUTLOOK

Potential mechanism-based pharmacological treatment approaches could be developed by blocking promotors of nerve ingrowth, such as NGF, and promoting inhibitors of nerve ingrowth, like semaphorins, as well as blocking glutamate-NMDA-receptor pathways, which are prominent in chronic tendon pain.

Tendon Aging

Tendons are mechanosensitive connective tissues responsible for the connection between muscles and bones by transmitting forces that allow the movement of the body, yet, with advancing age, tendons become more prone to degeneration followed by injuries. Tendon diseases are one of the main causes of incapacity worldwide, leading to changes in tendon composition, structure, and biomechanical properties, as well as a decline in regenerative potential. There is still a great lack of knowledge regarding tendon cellular and molecular biology, interplay between biochemistry and biomechanics, and the complex pathomechanisms involved in tendon diseases. Consequently, this reflects a huge need for basic and clinical research to better elucidate the nature of healthy tendon tissue and also tendon aging process and associated diseases. This chapter concisely describes the effects that the aging process has on tendons at the tissue, cellular, and molecular levels and briefly reviews potential biological predictors of tendon aging. Recent research findings that are herein reviewed and discussed might contribute to the development of precision tendon therapies targeting the elderly population.

Efficacy of percutaneous electrolysis for the treatment of tendinopathies: A systematic review and meta-analysis

OBJECTIVE

To evaluate the efficacy of percutaneous electrolysis for the treatment of patients with tendinopathies.

DATA SOURCES

A systematic search of publications was conducted in Pubmed, Cinahl, Medline, Scopus and Web of Science.

METHODS

The Oxford 2011 Levels of Evidence and the Jadad scale were used to assess the quality of studies. The mean and standard deviation were obtained for each study group and used to calculate the effect size. The DerSimonian and Laird method was used to develop a random-effects model.

RESULTS

Of the 14 articles, four applied percutaneous electrolysis to the knee, three to the shoulder, three to the elbow, two to the hip and two to the ankle and foot. A meta-analysis on intensity of pain (evaluated with algometer and the Visual Analogue Scale) was performed on studies comparing percutaneous electrolysis with a control group, indicating that the groups treated with percutaneous electrolysis had better results (p = 0.01). Although percutaneous electrolysis did not overcome the analgesic effect achieved by corticosteroid injections.

CONCLUSIONS

The percutaneous electrolysis is effective for the treatment of tendinopathies. The combination of this technique with eccentric training has proven to be one of the most effective treatments to date for improving pain. PROSPERO Registration: CRD42021230005.

Achilles Tendons Display Region-Specific Transcriptomic Signatures Associated With Distinct Mechanical Properties

BACKGROUND

Previous studies have examined the transcriptomes and mechanical properties of whole tendons in different regions of the body. However, less is known about these characteristics within a single tendon.

PURPOSE

To develop a regional transcriptomic atlas and evaluate the region-specific mechanical properties of Achilles tendons.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Achilles tendons from 2-month-old male Sprague Dawley rats were used. Tendons were isolated and divided into proximal, middle, and distal thirds for RNA sequencing (n = 5). For mechanical testing, the Achilles muscle-tendon-calcaneus unit was mounted in a custom-designed materials testing system with the unit clamped over the musculotendinous junction (MTJ) and the calcaneus secured at 90° of dorsiflexion (n = 9). Tendons were stretched to 20 N at a constant speed of 0.0167 mm/s. Cross-sectional area, strain, stress, and Young modulus were determined in each tendon region.

RESULTS

An open-access, interactive transcriptional atlas was generated that revealed distinct gene expression signatures in each tendon region. The proximal and distal regions had the largest differences in gene expression, with 2596 genes significantly differentially regulated at least 1.5-fold (q < .01). The proximal tendon displayed increased expression of genes resembling a tendon phenotype and increased expression of nerve cell markers. The distal region displayed increases in genes involved in extracellular matrix synthesis and remodeling, immune cell regulation, and a phenotype similar to cartilage and bone. There was a 3.72-fold increase in Young modulus from the proximal to middle region (P < .01) and an additional 1.34-fold increase from the middle to distal region (P = .027).

CONCLUSION

Within a single tendon, there are region-specific transcriptomic signatures and mechanical properties, and there is likely a gradient in the biological and functional phenotype from the proximal origin at the MTJ to the distal insertion at the enthesis.

CLINICAL RELEVANCE

These findings improve our understanding of the underlying biological heterogeneity of tendon tissue and will help inform the future targeted use of regenerative medicine and tissue engineering strategies for patients with tendon disorders.

MRI evaluation of shoulder pathologies in wheelchair users with spinal cord injury and the relation to shoulder pain

OBJECTIVE

To describe the number, specifics and co-occurrence of shoulder pathologies detected by MRI in manual wheelchair users with spinal cord injury and to evaluate the association between shoulder pathologies and presence of shoulder pain.

DESIGN

Cross-sectional observation study.

SETTING

Community.

PARTICIPANTS

Fifty-one wheelchair-dependent persons with spinal cord injury (44 males, 7 females, median age 50 years (IQR 14), median time since injury 24 years (IQR 16)) were allocated to pain or no-pain group based on the Wheelchair User Shoulder Pain Index.

INTERVENTIONS

Not applicable.

OUTCOME MEASURES

All persons underwent shoulder MRI. Pathologies were scored blinded by two experienced radiologists. Participant characteristics, number and severity of shoulder pathologies were analyzed descriptively. Logistic regression was performed to evaluate the association between MRI findings and shoulder pain.

RESULTS

The median number of co-occurring MRI findings per person ranged from 0 to 19 (out of 31 possible findings). The cluster of MRI findings occurring most often together were tendon tears of supraspinatus (present in 84%), subscapularis (69%) and biceps (67%) and osteoarthritis of acromioclavicular joint (80%). When correcting for age and time since injury, the logistic regression showed no statistically significant correlation between the individual pathologies and shoulder pain.

CONCLUSION

MRI findings of shoulder pathology are very frequent in persons with and without shoulder pain. Therefore, when diagnosing the cause of shoulder pain and planning interventions, health care professionals should keep this finding in mind and MRI should not be interpreted without careful consideration of clinical history and functional testing.

Treatment of chronic lateral epicondylosis: a randomized trial comparing the efficacy of ultrasound-guided tendon dry needling and open-release surgery

OBJECTIVE

Evaluate the efficacy of ultrasound-guided dry needling and open-release surgery in reducing pain and improving function in workers with lateral epicondylosis refractory to at least 6 months of nonsurgical management.

METHODS

We randomly assigned participants in a 1:1 ratio to receive dry needling or surgery. The primary outcome was the Patient Rated Tennis Elbow Evaluation (PRTEE) score at 6 months. Secondary outcome measures examined the impact of these techniques on professional activity, grip strength, and Global Rating of Change and Satisfaction scales. Statistical analyses included mixed-effects models and Fisher's exact tests.

RESULTS

From October 2016 through June 2019, we enrolled 64 participants. Two participants were excluded, and data from 62 participants (48 ± 8 years, 33 men) with a mean duration of symptoms of 23 ± 21 months were analyzed. Baseline characteristics were similar in both groups. In the intention-to-treat analysis, no treatment-by-time interaction was observed (F_(4,201) = 0.72; p = .58). The least-squares mean difference from baseline in PRTEE scores at 6 months was 33.4 (CI 25.2 - 41.5) in the surgery group and 26.9 (CI 19.4 - 34.4) in the dry needling group (p = .25). The proportion of successful treatment was 83% (CI 63 - 95%) and 81% (CI 63 - 93%) in the surgery and dry needling groups, respectively (p = 1.00). Changes in secondary outcomes were in the same direction as those of the primary outcome. No adverse event occurred.

CONCLUSIONS

Ultrasound-guided dry needling resulted in comparable improvement in outcome scores on scales of pain, physical function, and global assessment of change and satisfaction than open-release surgery.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02710682 KEY POINTS: • In patients with chronic lateral epicondylosis, ultrasound-guided tendon dry needling provides comparable therapeutic efficacy to open-release surgery. • Ultrasound-guided tendon dry needling allows for an earlier return to work and may be less costly than open-release surgery. • Care management guidelines should recommend treatment by ultrasound-guided tendon dry needling before open-release surgery.

Association between Body Weight and Body Mass Index and Patellar Tendinopathy in Elite Basketball and Volleyball Players, a Systematic Review and Meta-Analysis

The features of Patellar-Tendinopathy are (1): pain localised to the inferior pole of the patellar; (2): the presence of load-related pain. Body-Weight and Body-Mass-Index, as two easily-measured variables, could potentially aid the prediction of PT. This review aims to establish relationships between Body-Weight and Body-Mass-Index and Patellar-Tendinopathy via synthesising the evidence from prospective-cohort and cross-sectional studies in elite basketball and volleyball players. Seven databases (PubMed, EMBASE, CINAHL, Google Scholar, Health-Management-Information-Consortium, National-Technical-Information-Service, ClinicalTrial.gov) and citation chasing were used to identify English peer-review articles from 2000 to 2022. An adapted version of the Newcastle-Ottawa scale was used for critical appraisal. Two reviewers were involved in literature searching, data extraction, and quality review. Two prospective cohort and five cross-sectional studies met the inclusion criteria, providing 849 subjects (male:female: 436:413). Five studies found BW is associated with PT. Three studies found a relationship between BMI and PT. Six out of seven studies were classified as very good studies. All studies were level IV evidence. The very low certainty evidence suggests an association between BW and PT. There is moderate certainty evidence that BMI is associated with PT. These preliminary findings should be treated cautiously due to the lack of strong evidence.

Advanced Robotics to Address the Translational Gap in Tendon Engineering

Tendon disease is a significant and growing burden to healthcare systems. One strategy to address this challenge is tissue engineering. A widely held view in this field is that mechanical stimulation provided to constructs should replicate the mechanical environment of native tissue as closely as possible. We review recent tendon tissue engineering studies in this article and highlight limitations of conventional uniaxial tensile bioreactors used in current literature. Advanced robotic platforms such as musculoskeletal humanoid robots and soft robotic actuators are promising technologies which may help address translational gaps in tendon tissue engineering. We suggest the proposed benefits of these technologies and identify recent studies which have worked to implement these technologies in tissue engineering. Lastly, key challenges to address in adapting these robotic technologies and proposed future research directions for tendon tissue engineering are discussed.

Challenges and perspectives of tendon-derived cell therapy for tendinopathy: from bench to bedside

Tendon is composed of dense fibrous connective tissues, connecting muscle at the myotendinous junction (MTJ) to bone at the enthesis and allowing mechanical force to transmit from muscle to bone. Tendon diseases occur at different zones of the tendon, including enthesis, MTJ and midsubstance of the tendon, due to a variety of environmental and genetic factors which consequently result in different frequencies and recovery rates. Self-healing properties of tendons are limited, and cell therapeutic approaches in which injured tendon tissues are renewed by cell replenishment are highly sought after. Homologous use of individual’s tendon-derived cells, predominantly differentiated tenocytes and tendon-derived stem cells, is emerging as a treatment for tendinopathy through achieving minimal cell manipulation for clinical use. This is the first review summarizing the progress of tendon-derived cell therapy in clinical use and its challenges due to the structural complexity of tendons, heterogeneous composition of extracellular cell matrix and cells and unsuitable cell sources. Further to that, novel future perspectives to improve therapeutic effect in tendon-derived cell therapy based on current basic knowledge are discussed.

Applicability of ARFI elastography in detecting elasticity changes of the equine superficial digital flexor tendon with induced injury

The objectives of this prospective, experimental study were to describe changes in the stiffness of the equine superficial digital flexor tendon (SDFT) after induced injury, deep digital flexor tendon (DDFT), accessory ligament (AL-DDFT), and suspensory ligament (SL) during 90 days of healing using acoustic radiation force impulse (ARFI) elastography. Eight healthy horses were selected. Preinjury B mode and ARFI evaluations were performed bilaterally in the palmar metacarpal region. Injury was induced only on the left forelimb (G2) by a single injection of collagenase in SDFT, 15 cm distal to the accessory carpal bone. The right forelimb was used as a control (G1). Evaluations were performed at eight timepoints: one before injury (T0) and seven (T1-T7) after injury (3, 15, 30, 40, 60, 75, and 90 days post-induction). Tendinopathies were visualized as hypoechoic areas with loss of parallel tendon fiber pattern. Injured SDFTs presented mainly cool colors (soft) from T1 to T3, and from T4, there was an increase in warm colors (hard), close to the appearance of tendons of G1. In the first four timepoints, there was a decrease in stiffness compared to G1 (P < 0.001). On T1 and T2, a cutoff value <6.21 m/s to determine tendinopathy of the SDFT was established (75.8% sensitivity and 92.03% specificity). Stiffness changes in the DDFT, AL-DDFT, and SL of injured limbs occurred at different timepoints. Tendinopathy significantly altered the stiffness of the injured tendon and the adjacent tissues. ARFI made it possible to detect these changes, helping to monitor the reparation of this injury.

Comparing an optimised physiotherapy treatment package with usual physiotherapy care for people with tennis elbow - protocol for the OPTimisE pilot and feasibility randomised controlled trial

BACKGROUND

Physiotherapy is recommended for people with tennis elbow, but whilst a wide array of treatments is available, the optimal approach remains uncertain. We have therefore recently developed an optimised physiotherapy treatment package for tennis elbow based on a synthesis of the evidence, patient input and clinical consensus. It consists of detailed advice and education, a structured progressive exercise programme and provision of a counter-force elbow brace. Here, we report the protocol for our multicentre pilot and feasibility randomised controlled trial (RCT) designed to (a) examine the feasibility of our optimised physiotherapy treatment package and (b) to pilot trial processes for a future fully powered RCT to test clinical and cost-effectiveness compared with usual physiotherapy treatment.

METHODS

A multicentre pilot and feasibility RCT will be conducted across three sites in England, recruiting up to 50 patients (or for a maximum of 12 months). Participants with tennis elbow, identified from physiotherapy clinic waiting lists and general practice surgeries, will be randomly allocated to receive the optimised physiotherapy treatment package or usual physiotherapy care. Analysis will focus on feasibility measures including consent rate, intervention fidelity, follow-up rate and outcome completion rate. A nested qualitative study will explore the acceptability of the study processes and patient and physiotherapist experiences of the new optimised intervention.

DISCUSSION

This study will determine the feasibility of a new optimised physiotherapy treatment package for people with tennis elbow and pilot the processes for a future fully powered RCT. In the longer term, this treatment package may provide superior clinical outcomes for patients, in terms of pain and quality of life, and be more cost-effective for the health service.

TRIAL REGISTRATION

Registered with the ISRCTN database 19/7/2021, https://www.isrctn.com/ISRCTN64444585.

Tendinopathy: sex bias starts from the preclinical development of tendon treatments. A systematic review

Tendinopathies are common overuse disorders that arise both in athletes and the general population. Available tendon treatments are used both for women and men without distinction. However, the existence of a sex-based difference in tendon biology is widely demonstrated. Since basic research represents the foundation for treatment development, an equal female–male representation should be pursued in preclinical studies. This systematic review quantified the current evidence by analyzing 150 studies on 8231 animals. Preclinical studies largely neglected the importance of sex, none analyzed sex-based differences, and only 4% of the studies reported disaggregated data suitable for the analysis of treatment results in males and females. There is an alarming female under-representation, in particular in the field of injective therapies. Despite the growing awareness on the importance of investigating treatments in both males and females, the investigated field proved resistant from properly designing studies including both sexes, and the lack of sex-representation remains critical.

Tendinopathy has sex-specific features, with sex hormones affecting tendon metabolism, structure, biomechanical properties, and injury risk.

The preclinical research on tendinopathy treatments still neglects sex-based differences, leading to translation of male data to females which may affect clinical effectiveness in women.

None of the reviewed studies looked at differences between sexes, and only 4% of the studies reported disaggregated data. Besides, female animals are under-represented.

The lack of sex-representation in tendinopathy research remains critical.

Digital Rehabilitation for Elbow Pain Musculoskeletal Conditions: A Prospective Longitudinal Cohort Study

Elbow musculoskeletal pain (EP) is a major cause of disability. Telerehabilitation has shown great potential in mitigating musculoskeletal pain conditions, but EP is less explored. This single-arm interventional study investigates clinical outcomes and engagement levels of a completely remote multimodal digital care program (DCP) in patients with EP. The DCP consisted of exercise, education, and cognitive-behavioral therapy for 8 weeks. Primary outcome: disability change (through the Quick Disabilities of the Arm, Shoulder, and Hand questionnaire (QuickDASH), treatment response cut-offs: 12.0-point reduction and 30% change). Secondary outcomes: pain, analgesic intake, surgery intent, mental health, fear-avoidance beliefs, work productivity, and patient engagement. Of the 132 individuals that started the DCP, 112 (84.8%) completed the intervention. Significant improvements were observed in QuickDASH with an average reduction of 48.7% (11.9, 95% CI 9.8; 14.0), with 75.3% of participants reporting ≥30% change and 47.7% reporting ≥12.0 points. Disability change was accompanied by reductions in pain (53.1%), surgery intent (57.5%), anxiety (59.8%), depression (68.9%), fear-avoidance beliefs (34.2%), and productivity impairment (72.3%). Engagement (3.5 (SD 1.4) sessions per week) and satisfaction 8.5/10 (SD 1.6) were high. The significant improvement observed in clinical outcomes, alongside high engagement, and satisfaction suggests patient acceptance of this care delivery mode.

Why Use Adipose-Derived Mesenchymal Stem Cells in Tendinopathic Patients: A Systematic Review

The aim of the present systematic review was to provide a clear overview of the clinical current research progress in the use of adipose-derived mesenchymal stem cells (ASCs) as an effective therapeutic option for the management of tendinopathies, pathologies clinically characterized by persistent mechanical pain and structural alteration of the tendons. The review was carried out using three databases (Scopus, ISI Web of Science and PubMed) and analyzed records from 2013 to 2021. Only English-language papers describing the isolation and manipulation of adipose tissue as source of ASCs and presenting ASCs as treatment for clinical tendinopathies were included. Overall, seven clinical studies met the inclusion criteria and met the minimum quality inclusion threshold. Data extraction and quality assessment were performed by groups of three reviewers. The available evidence showed the efficacy and safety of ASCs treatment for tendinopathies, although it lacked a clear description of the biomolecular mechanisms underlying the beneficial properties of ASCs.

Effects of isometric loading intensity on patellar tendon microvascular response

Acute increases in tendon blood flow and oxygenation after stress (i.e., hyperemic response) can enhance tendon recovery. While loading intensity is a fundamental part of resistance training programs, its effects on tendon's hyperemic response are unknown. This study aimed to compare acute changes in total (total hemoglobin [THb]) and oxygenated hemoglobin (HbO₂ ) concentrations in the patellar tendon after isometric exercise at different intensities. Thirteen participants performed 8 (5 s) isometric knee extensions at 25%, 50%, and 75% maximal load (maximal voluntarily isometric contraction [MVIC]), separated by 20 min recovery, prescribed in randomized and counterbalanced order. Changes in patellar tendon THb, HbO₂ and deoxygenated hemoglobin (HHb) in response to exercise at each intensity were measured using near-infrared spectroscopy. Post-exercise, HbO₂ increased with 50% ( η p 2 $$ {\eta}_p^2 $$  = 0.305, f = 5.26, p < 0.01) and 75% ( η p 2 $$ {\eta}_p^2 $$  = 0.245, f = 4.56, p < 0.01) but not 25% ( η p 2 $$ {\eta}_p^2 $$  = 0.088, f = 1.16, p = 0.339) MVIC, while THb increased in 50% ( η p 2 $$ {\eta}_p^2 $$  = 0.305, f = 5.26, p = 0.01) but not 25% ( η p 2 $$ {\eta}_p^2 $$  = 0.067, f = 0.865, p = 0.51) or 75% ( η p 2 $$ {\eta}_p^2 $$  = 0.126, f = 1.729, p = 0.14) MVIC. Additionally, increasing load from 25% to 50% MVIC resulted in greater THb (f = 2.459, p = 0.43), HbO₂ (f = 3.389, p = 0.13) and HHb (f = 0.320, p = 0.01) post-exercise responses, but no differences were observed between 50% and 75% MVIC (THb: f = 0.748, p = 0.59; HbO₂ : f = 0.825, p = 0.54; HHb: f = 0.713, p = 0.62). Our results suggest there is a loading threshold at ~50% MVIC at which the tendon hyperemic response is fully achieved. Training above this intensity is not expected to provide any additional change to the tendon microvascular response. Therefore, moderate loading seems to be sufficient to fully elicit the patellar tendon hyperemic response that's believed to stimulate tendon healing.

Blood Flow Restriction Resistance Training in Tendon Rehabilitation: A Scoping Review on Intervention Parameters, Physiological Effects, and Outcomes

Objective

To identify current evidence on blood flow restriction training (BFRT) in tendon injuries and healthy tendons, evaluating physiological tendon effects, intervention parameters, and outcomes.

Methods

This scoping review was reported in accordance with the PRISMA Extension for Scoping Reviews (PRISMA-ScR). Databases searched included MEDLINE, CINAHL, AMED, EMBase, SPORTDiscus, Cochrane library (Controlled trials, Systematic reviews), and five trial registries. Two independent reviewers screened studies at title/abstract and full text. Following screening, data was extracted and charted, and presented as figures and tables alongside a narrative synthesis. Any study design conducted on adults, investigating the effects of BFRT on healthy tendons or tendon pathology were included. Data were extracted on physiological tendon effects, intervention parameters and outcomes with BFRT.

Results

Thirteen studies were included, three on tendinopathy, two on tendon ruptures, and eight on healthy Achilles, patellar, and supraspinatus tendons. A variety of outcomes were assessed, including pain, function, strength, and tendon morphological and mechanical properties, particularly changes in tendon thickness. BFRT intervention parameters were heterogeneously prescribed.

Conclusion

Despite a dearth of studies to date on the effects of BFRT on healthy tendons and in tendon pathologies, preliminary evidence for beneficial effects of BFRT on tendons and clinical outcomes is encouraging. As BFRT is a relatively novel method, definitive conclusions, and recommendations on BFRT in tendon rehabilitation cannot be made at present, which should be addressed in future research, due to the potential therapeutic benefits highlighted in this review.

Mechanical and strain behaviour of human Achilles tendon during in vitro testing to failure

The Achilles tendon is the strongest tendon in the human body but its mechanical behaviour during failure has been little studied and the basis of its high tensile strength has not been elucidated in detail. In the present study, healthy, human, Achilles tendons were loaded to failure in an anatomically authentic fashion while the local deformation and strains were studied in real time, with very high precision, using digital image correlation (DIC). The values determined for the strength of the Achilles tendon were at the high end of those reported in the literature, consistent with the absence of a pre-existing tendinopathy in the samples, as determined by careful gross inspection and histology. Early in the loading cycle, the proximal region of the tendon accumulated high lateral strains while longitudinal strains remained low. However, immediately before rupture, the mid-substance of the Achilles tendon, its weakest part, started to show high longitudinal strains. These new insights advance the understanding of the mechanical behaviour of tendons as they are stretched to failure.

The role of the tendon ECM in mechanotransduction: disruption and repair following overuse

Purpose: Tendon overuse injuries are prevalent conditions with limited therapeutic options to halt disease progression. The specialized extracellular matrix (ECM) both enables joint function and mediates mechanical signals to tendon cells, driving biological responses to exercise or injury. With overuse, tendon ECM composition and structure changes at multiple scales, disrupting mechanotransduction and resulting in inadequate repair and disease progression. This review highlights the multiscale ECM changes that occur with tendon overuse and corresponding effects on cell-matrix interactions and cellular response to load.Results: Different functional joint requirements and tendon types experience a wide range of loading profiles, creating varied downstream mechanical stimuli. Distinct ECM structure and mechanical properties within the fascicle matrix, interfascicle matrix, and enthesis and their varied disruption with overuse are considered. The pericellular matrix (PCM) comprising the microscale tendon cell environment has a unique composition that changes with overuse injury and exercise, suggesting an important role in mechanotransduction and promoting repair. Cell-matrix interactions are mediated by structures including cilia, integrins, connexins and cytoskeleton that signal downstream homeostasis, adaptation, or repair. ECM disruption with tendon overuse may cause altered mechanical loading and cell-matrix interactions, resulting in mechanobiological understimulation, apoptosis, and ineffective repair. Current interventions to promote repair of tendon overuse injuries including exercise, targeting cell signaling, and modulating inflammation are considered.Conclusion: Future therapeutics should be assessed with regard of their effects on multiscale mechanotransduction in addition to joint function, with consideration of the central role of ECM.