Increased serum and musculotendinous fibrogenic proteins following persistent low-grade inflammation in a rat model of long-term upper extremity overuse

Pathogenesis of Musculotendinous and Fascial Injuries After Physical Exercise - Short Review

Purpose

The identification of sports and physical exercises with injury risk is necessary to preserve the capacity of athletes and people who perform physical education and also to prevent the installation of functional deficiencies.

Methods

We have selected the articles related to the pathogenic mechanisms involved in musculotendinous and fascial injuries produced as a result of physical exercise.

Results and Discussions

The lesional pathogenesis is complex and incompletely clarified. Recent theories put in a new light the mechanisms of muscle pain and tendinopathy production. The accumulation of lactate anion, known to be a residue that induces fatigue and muscle pain, has been reconsidered by some authors. It appears that lactate anion is an excellent fuel for the myocardial fiber. Moreover, the accumulation of lactic acid after intense physical exercise could prevent the inexcitability of the sarcolemma induced by the increased concentration of interstitial K+. Most of the time, overuse injuries are not limited to muscles. They can cause myofascial, myotendinous or purely muscular injuries. The muscular fascia is more susceptible to injuries produced under the action of large external forces. Also, fascia is more sensitive to pain compared to muscle when external forces act eccentrically. Overloading the tendon and putting it under tension repeatedly is followed by ruptures of the tendon fibers. The regeneration of the degenerated tendon is defective in the context of the inflammation produced by the injury. Tendon fibers undergo a process of fibrosis, scarring, adhesion and heterogeneous calcification. Oxidative stress is responsible for inflammation, degeneration and apoptosis of tenocytes.

Conclusion

The benefits brought by physical education and sports are indisputable, but their practice requires a coordinated program to prevent possible traumatic and overuse injuries.

Possible relationship between the gut leaky syndrome and musculoskeletal injuries: the important role of gut microbiota as indirect modulator

This article aims to examine the evidence on the relationship between gut microbiota (GM), leaky gut syndrome and musculoskeletal injuries. Musculoskeletal injuries can significantly impair athletic performance, overall health, and quality of life. Emerging evidence suggests that the state of the gut microbiota and the functional intestinal permeability may contribute to injury recovery. Since 2007, a growing field of research has supported the idea that GM exerts an essential role maintaining intestinal homeostasis and organic and systemic health. Leaky gut syndrome is an acquired condition where the intestinal permeability is impaired, and different bacteria and/or toxins enter in the bloodstream, thereby promoting systemic endotoxemia and chronic low-grade inflammation. This systemic condition could indirectly contribute to increased local musculoskeletal inflammation and chronificate injuries and pain, thereby reducing recovery-time and limiting sport performance. Different strategies, including a healthy diet and the intake of pre/probiotics, may contribute to improving and/or restoring gut health, thereby modulating both systemically as local inflammation and pain. Here, we sought to identify critical factors and potential strategies that could positively improve gut microbiota and intestinal health, and reduce the risk of musculoskeletal injuries and its recovery-time and pain. In conclusion, recent evidences indicate that improving gut health has indirect consequences on the musculoskeletal tissue homeostasis and recovery through the direct modulation of systemic inflammation, the immune response and the nociceptive pain.

Response to Mechanical Properties and Physiological Challenges of Fascia: Diagnosis and Rehabilitative Therapeutic Intervention for Myofascial System Disorders

Damage to the fascia can cause significant performance deficits in high-performance sports and recreational exercise and may contribute to the development of musculoskeletal disorders and persistent potential pain. The fascia is widely distributed from head to toe, encompassing muscles, bones, blood vessels, nerves, and internal organs and comprising various layers of different depths, indicating the complexity of its pathogenesis. It is a connective tissue composed of irregularly arranged collagen fibers, distinctly different from the regularly arranged collagen fibers found in tendons, ligaments, or periosteum, and mechanical changes in the fascia (stiffness or tension) can produce changes in its connective tissue that can cause pain. While these mechanical changes induce inflammation associated with mechanical loading, they are also affected by biochemical influences such as aging, sex hormones, and obesity. Therefore, this paper will review the current state of knowledge on the molecular level response to the mechanical properties of the fascia and its response to other physiological challenges, including mechanical changes, innervation, injury, and aging; imaging techniques available to study the fascial system; and therapeutic interventions targeting fascial tissue in sports medicine. This article aims to summarize contemporary views.

Association between long-term static postures exposure and musculoskeletal disorders among university employees: A viewpoint of inflammatory pathways

Background

Musculoskeletal disorders (MSDs) are critical occupational and social problems. With the improvement of production mechanization and automation, and the widespread application of computers, more occupations are exposed to static postures and load. This study explored the role of inflammation in the association between static postures exposure and MSDs.

Methods

This study adopted a prospective nested case-control design in which 66 lower back MSDs cases and 66 healthy controls were selected from a cohort study of university employees. The personal information, postural load, musculoskeletal symptoms, pressure pain thresholds (PPTs), and inflammatory cytokines were collected. Logistic and linear regressions were used to investigate the association among postural load, inflammatory cytokines, and lower back MSDs. Mediation analysis was used to calculate the mediation effect.

Results

The results of logistic and linear regressions showed that postural load and inflammatory cytokines were positively associated with lower back MSDs (P < 0.05), and postural load was positively associated with inflammatory cytokines (P < 0.05). Further, mediation analysis showed that the mediation effect of postural load on the lower back MSDs through TNF-α was 0.073 (95%CI: 0.025-0.128), and the mediation effect of posture load on the lower back MSDs through IL-6 was 0.098 (95%CI: 0.041-0.179), respectively.

Conclusion

Static postures were associated with the occurrence of MSDs through inflammatory cytokines, and low-level inflammation may be a critical early event in the generation of MSDs. This study may help bridge the gap of potential mechanisms linking static postures to increased risks of MSDs, and provide new evidence for targeted protection against the global increasing MSDs.

Advances toward transformative therapies for tendon diseases

Approved therapies for tendon diseases have not yet changed the clinical practice of symptomatic pain treatment and physiotherapy. This review article summarizes advances in the development of novel drugs, biologic products, and biomaterial therapies for tendon diseases with perspectives for translation of integrated therapies. Shifting from targeting symptom relief toward disease modification and prevention of disease progression may open new avenues for therapies. Deep evidence-based clinical, cellular, and molecular characterization of the underlying pathology of tendon diseases, as well as therapeutic delivery optimization and establishment of multidiscipline interorganizational collaboration platforms, may accelerate the discovery and translation of transformative therapies for tendon diseases.

Aberrant Neuronal Activity in a Model of Work-Related Upper Limb Pain and Dysfunction

Work-related musculoskeletal disorders associated with intense repetitive tasks are highly prevalent. Painful symptoms associated with such disorders can be attributed to neuropathy. In this study, we characterized the neuronal discharge from the median nerve in rats trained to perform an operant repetitive task. After 3-weeks of the task, rats developed pain behaviors and a decline in grip strength. Ongoing activity developed in 17.7% of slowly conducting neurons at 3-weeks, similar to neuritis. At 12-weeks, an irregular high frequency neuronal discharge was prevalent in >88.4% of slow and fast conducting neurons. At this time point, 8.3% of slow and 21.2% of fast conducting neurons developed a bursting discharge, which, combined with a reduction in fast-conducting neurons with receptive fields (38.4%), is consistent with marked neuropathology. Taken together, we have shown that an operant repetitive task leads to an active and progressive neuropathy that is characterized by marked neuropathology following 12-weeks task that mainly affects fast conducting neurons. Such aberrant neuronal activity may underlie painful symptoms in patients with work-related musculoskeletal disorders. PERSPECTIVE: Aberrant neuronal activity, similar to that reported in this study, may contribute to upper limb pain and dysfunction in patients with work-related musculoskeletal disorders. In addition, profiles of instantaneous frequencies may provide an effective way of stratifying patients with painful neuropathies.

Tendon healing is adversely affected by low-grade inflammation

BACKGROUND

Tendinopathy is common, presents with pain and activity limitation, and is associated with a high risk of recurrence of the injury. Tendinopathy usually occurs as a results of a disrupted healing response to a primary injury where cellular and molecular pathways lead to low grade chronic inflammation.

MAIN FINDINGS

There has been a renewed interest in investigating the role of Inflammation in the pathogenesis of tendinopathy, in particular during the initial phases of the condition where it may not be clinically evident. Understanding the early and late stages of tendon injury pathogenesis would help develop new and effective treatments addressed at targeting the inflammatory pathways.

CONCLUSION

This review outlines the role of low-grade Inflammation in the pathogenesis of tendinopathy, stressing the role of proinflammatory cytokines, proteolytic enzymes and growth factors, and explores how Inflammation exerts a negative influence on the process of tendon healing.

Tendinopathy and tendon material response to load: What we can learn from small animal studies

Tendinopathy is a debilitating disease that causes as much as 30% of all musculoskeletal consultations. Existing treatments for tendinopathy have variable efficacy, possibly due to incomplete characterization of the underlying pathophysiology. Mechanical load can have both beneficial and detrimental effects on tendon, as the overall tendon response depends on the degree, frequency, timing, and magnitude of the load. The clinical continuum model of tendinopathy offers insight into the late stages of tendinopathy, but it does not capture the subclinical tendinopathic changes that begin before pain or loss of function. Small animal models that use high tendon loading to mimic human tendinopathy may be able to fill this knowledge gap. The goal of this review is to summarize the insights from in-vivo animal studies of mechanically-induced tendinopathy and higher loading regimens into the mechanical, microstructural, and biological features that help characterize the continuum between normal tendon and tendinopathy. STATEMENT OF SIGNIFICANCE: This review summarizes the insights gained from in-vivo animal studies of mechanically-induced tendinopathy by evaluating the effect high loading regimens have on the mechanical, structural, and biological features of tendinopathy. A better understanding of the interplay between these realms could lead to improved patient management, especially in the presence of painful tendon.

Does the Interaction between Local and Systemic Inflammation Provide a Link from Psychology and Lifestyle to Tissue Health in Musculoskeletal Conditions?

Musculoskeletal conditions are known to involve biological, psychological, social and, often, lifestyle elements. However, these domains are generally considered in isolation from each other. This siloed approach is unlikely to be adequate to understand the complexity of these conditions and likely explains a major component of the disappointing effects of treatment. This paper presents a hypothesis that aims to provide a foundation to understand the interaction and integration between these domains. We propose a hypothesis that provides a plausible link between psychology and lifestyle factors with tissue level effects (such as connective tissue dysregulation/accumulation) in musculoskeletal conditions that is founded on understanding the molecular basis for interaction between systemic and local inflammation. The hypothesis provides plausible and testable links between mind and body, for which empirical evidence can be found for many aspects. We present this hypothesis from the perspective of connective tissue biology and pathology (fibrosis), the role of inflammation locally (tissue level), and how this inflammation is shaped by systemic inflammation through bidirectional pathways, and various psychological and lifestyle factors via their influence on systemic inflammation. This hypothesis provides a foundation for new consideration of the development and refinement of personalized multidimensional treatments for individuals with musculoskeletal conditions.

Infliximab prevents systemic bone loss and suppresses tendon inflammation in a collagen-induced arthritis rat model

Reduced Bone Mineral Density (BMD) and tendon abnormalities, such as tenosynovitis and enthesitis, are prevalent comorbidities in patients with rheumatoid arthritis (RA). The aim of the present study was to investigate the effect of chronic treatment with infliximab on BMD and tendon inflammation in an animal model of inflammatory arthritis. Collagen-Induced Arthritis (CIA) was induced in rats, followed by long-term intraperitoneal administration of infliximab. Two additional groups of animals received methotrexate either as a monotherapy or as a co-treatment to infliximab. BMD was evaluated by Micro-Computed Tomography (Micro-CT) and bone histological examination. Tendon inflammation was assessed histologically and by quantitative ELISA analysis of pro-inflammatory cytokines in tendon tissues. Both methotrexate and infliximab treatment alleviated joint inflammation and reduced paw edema. Infliximab-treated animals exhibited an improved trabecular microarchitecture on micro-CT and histological analysis compared to both non-treated and methotrexate-treated animals. Infliximab almost reversed the pathological changes in tendons induced by CIA. Finally, we observed statistically significant declines in tendon TNF-a and IL-23 levels after infliximab treatment. Our study provides evidence that infliximab prevents arthritis-related osteoporosis and suppresses tendon inflammation in an animal model of inflammatory arthritis, in addition to controlling disease activity. These findings offer perspectives for the management of osteoporosis and enthesitis in RA.

Relationships and Mechanisms Between Occupational Risk Factors and Distal Upper Extremity Disorders

OBJECTIVE

The relationships between workplace risk factors and upper extremity injuries from epidemiological and laboratory studies were examined.

BACKGROUND

Epidemiological studies are associated with several limitations, affecting the strength of association between risk factors and the development of injuries.

METHOD

In this narrative review, we identified epidemiological and laboratory studies (published primarily since 1997) investigating exposure to workplace risk factors (force, repetition, posture, vibration) and risk of hand/wrist tendon-related disorders, epicondylitis, and carpal tunnel syndrome (CTS).

RESULTS

Forceful exertions are strongly associated with hand/wrist tendon-related disorders, epicondylitis, and CTS. Dose-response relationships were found for epicondylitis (repetition) and CTS (posture). Interactions demonstrate multiplicative effects of risk factors for injury risk. Laboratory studies display clear associations between task demands and biomechanical measures linked to mechanisms for upper extremity injuries with animal models providing further evidence of a dose-response between risk factors and injury.

CONCLUSION

Forceful, repetitive work requiring non-neutral postures are associated with increasing risk of hand/wrist tendon-related disorders, epicondylitis, and CTS as evidenced by epidemiology studies and laboratory-based investigations of humans and animals.

APPLICATION

Understanding the relationship between exposure levels of workplace risk factors and upper extremity disorders can improve injury prevention and rehabilitation strategies.

Force dependent effects of chronic overuse on fibrosis-related genes and proteins in skeletal muscles

AIM

To examine the chronic effect of force on mRNA and protein expression levels of fibrosis-related genes in flexor digitorum muscles in a rat model of repetitive overuse injury that induces muscle fibrosis at high force levels.

MATERIALS AND METHODS

Two groups of rats were trained to perform a voluntary repetitive lever-pulling task at either a high (HFHR) or a low force (LFHR) for 18 weeks, while a control group (FRC) performed no task. RNA and protein were prepared from forelimb flexor digitorum muscles. Fibrosis-related gene RNA transcripts were evaluated using quantitative PCR (qPCR) and analyzed using the geometric mean of three housekeeping genes or the mean of each individually as reference. Protein levels were quantified using ELISA, western blot, or immunohistofluorescence.

RESULTS

Of eight fibrosis-related mRNAs examined, only FGF2 demonstrated a consistent significant increase in the HFHR group, compared to the FRC group. However, protein amounts of collagen type 1, collagen type 3, and TGFβ1 were significantly higher in the HFHR, compared to the FRC and LFHR groups, while CCN2 and FGF2 were higher in both HFHR and LFHR, compared to the FRC group.

CONCLUSIONS

Our results suggest that there is steady-state transcription of fibrogenic genes in muscles with established fibrosis, implying that post-transcriptional processes are responsible for the increased protein levels of fibrotic factors during muscle overuse conditions. We hypothesize that targeting such pathways represents a valid approach to treat overuse injury. Alternatively, FGF2 gene expression may represent a valid target for therapy.

Tendon Extracellular Matrix Assembly, Maintenance and Dysregulation Throughout Life

In his Lissner Award medal lecture in 2000, Stephen Cowin asked the question: "How is a tissue built?" It is not a new question, but it remains as relevant today as it did when it was asked 20 years ago. In fact, research on the organization and development of tissue structure has been a primary focus of tendon and ligament research for over two centuries. The tendon extracellular matrix (ECM) is critical to overall tissue function; it gives the tissue its unique mechanical properties, exhibiting complex non-linear responses, viscoelasticity and flow mechanisms, excellent energy storage and fatigue resistance. This matrix also creates a unique microenvironment for resident cells, allowing cells to maintain their phenotype and translate mechanical and chemical signals into biological responses. Importantly, this architecture is constantly remodeled by local cell populations in response to changing biochemical (systemic and local disease or injury) and mechanical (exercise, disuse, and overuse) stimuli. Here, we review the current understanding of matrix remodeling throughout life, focusing on formation and assembly during the postnatal period, maintenance and homeostasis during adulthood, and changes to homeostasis in natural aging. We also discuss advances in model systems and novel tools for studying collagen and non-collagenous matrix remodeling throughout life, and finally conclude by identifying key questions that have yet to be answered.

The Pelvic Girdle Pain deadlock: 2. Topics that, so far, have remained out of focus

INTRODUCTION

In our preceding paper, we concluded that Pelvic Girdle Pain (PGP) should be taken seriously. Still, we do not know its causes. Literature reviews on treatment fail to reveal a consistent pattern, and there are patients who do not respond well to treatment. We designated the lack of progress in research and in the clinic as 'deadlock', and proposed a 'deconstruction' of PGP, that is to say, taking PGP apart into its relevant dimensions.

PURPOSE

We examine the proposition that PGP may emerge as local inflammation. Inflammation would be a new dimension to be taken into account, between biomechanics and psychology. To explore the consequences of this idea, we present four different topics that, so far, have remained out of focus. One: The importance of microtrauma. Two: Ways to counteract chronification. Three: The importance of sickness behaviour when systemic inflammation turns into neuroinflammation of the brain. And Four: The mainly emotional and cognitive nature of chronic pain, and how aberrant neuroinflammation may render chronic pain intractable. For intractable pain, sleep and stress management are promising treatment options.

IMPLICATIONS

The authors hope that the present paper helps to stimulate the flexible creativity that is required to deal with the biological and psychological impact of PGP. Measuring inflammatory mediators in PGP should be a research priority. It should be understood that the boundaries between biology and psychology are becoming blurred. Clinicians must frequently monitor pain, disability, and mood, and be ready to switch treatment whenever the patient does not improve.

Common Musculoskeletal Disorders in the Elderly: The Star Triad

Musculoskeletal disorders are debilitating conditions that significantly impair the state of health, especially in elderly subjects. A pathological triad of inter-related disorders that are highly prevalent in the elderly consists of the following main “components”: sarcopenia, tendinopathies, and arthritis. The aim of this review is to critically appraise the literature relative to the different disorders of this triad, in order to highlight the pathophysiological common denominator and propose strategies for personalized clinical management of patients presenting with this combination of musculoskeletal disorders. Their pathophysiological common denominator is represented by progressive loss of (focal or generalized) neuromuscular performance with a risk of adverse outcomes such as pain, mobility disorders, increased risk of falls and fractures, and impaired ability or disability to perform activities of daily living. The precise management of these disorders requires not only the use of available tools and recently proposed operational definitions, but also the development of new tools and approaches for prediction, diagnosis, monitoring, and prognosis of the three disorders and their combination.

Pathogenesis and Development of Patellar Tendon Fibrosis in a Rabbit Overuse Model

BACKGROUND

The pathogenesis of patellar tendon fibrosis caused by overuse remains unclear. In an effort to further investigate effective treatments for patellar tendon fibrosis attributed to overuse, it is necessary to construct a reliable animal model.

PURPOSE

A rabbit patellar tendon fibrosis model was developed with the use of electrical stimulation to induce jumping. The pathogenesis and development of patellar tendon fibrosis were subsequently investigated with this model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 32 New Zealand White rabbits were randomly divided into a jumping group and a control group. Rabbits in the control group did not receive any treatment, while those in the jumping group jumped 150 times daily, 5 days per week. At 2, 4, 6, and 8 weeks after the initiation of treatment, the patellar tendons of 4 rabbits from each group were harvested and subjected to hematoxylin and eosin staining, immunohistochemical staining, and real-time polymerase chain reaction. The influence of jumping training on the expressions of histology- and fibrosis-related factors in the patellar tendon was assessed.

RESULTS

The histological changes of patellar tendon fibrosis in the jumping group were most pronounced at 4 weeks. When compared with the control group at corresponding time points, the mRNA and protein expressions of TGF-β1, CTGF, COL-I, and COL-III were upregulated significantly in the patellar tendon after jumping training for 4 weeks (P < .05). Intragroup comparison at different time points indicated that the mRNA and protein expressions of TGF-β1, COL-I, and COL-III were the highest at 4 weeks in the jumping group (P < .01).

CONCLUSION

It was found that patellar tendon fibrosis occurred because of overuse and the peak changes occurred at 4 weeks. Jumping load increased the secretions of TGF-β1 and Smad3 in the patellar tendon, with CTGF upregulation and higher synthesis of COL-I and COL-III, which were considered the pathogenesis of fibrosis.

CLINICAL RELEVANCE

This study simulated the effects of jumping load on tendon fibrosis at different time points. Moreover, the time course relationship between jumping training and patellar tendon fibrosis in the rabbit model was determined, which provided a new animal model for the study of patellar tendon fibrosis.

Forced treadmill running reduces systemic inflammation yet worsens upper limb discomfort in a rat model of work-related musculoskeletal disorders

BACKGROUND

Musculoskeletal disorders can result from prolonged repetitive and/or forceful movements. Performance of an upper extremity high repetition high force task increases serum pro-inflammatory cytokines and upper extremity sensorimotor declines in a rat model of work-related musculoskeletal disorders. Since one of the most efficacious treatments for musculoskeletal pain is exercise, this study investigated the effectiveness of treadmill running in preventing these responses.

METHODS

Twenty-nine young adult female Sprague-Dawley rats were used. Nineteen were trained for 5 weeks to pull a lever bar at high force (15 min/day). Thirteen went on to perform a high repetition high force reaching and lever-pulling task for 10 weeks (10-wk HRHF; 2 h/day, 3 days/wk). From this group, five were randomly selected to undergo forced treadmill running exercise (TM) during the last 6 weeks of task performance (10-wk HRHF+TM, 1 h/day, 5 days/wk). Results were compared to 10 control rats and 6 rats that underwent 6 weeks of treadmill running following training only (TR-then-TM). Voluntary task and reflexive sensorimotor behavioral outcomes were assessed. Serum was assayed for inflammatory cytokines and corticosterone, reach limb median nerves for CD68+ macrophages and extraneural thickening, and reach limb flexor digitorum muscles and tendons for pathological changes.

RESULTS

10-wk HRHF rats had higher serum levels of IL-1α, IL-1β and TNFα, than control rats. In the 10-wk HRHF+TM group, IL-1β and TNFα were lower, whereas IL-10 and corticosterone were higher, compared to 10-wk HRHF only rats. Unexpectedly, several voluntary task performance outcomes (grasp force, reach success, and participation) worsened in rats that underwent treadmill running, compared to untreated 10-wk HRHF rats. Examination of forelimb tissues revealed lower cellularity within the flexor digitorum epitendon but higher numbers of CD68+ macrophages within and extraneural fibrosis around median nerves in 10-wk HRHF+TM than 10-wk HRHF rats.

CONCLUSIONS

Treadmill running was associated with lower systemic inflammation and moderate tendinosis, yet higher median nerve inflammation/fibrosis and worse task performance and sensorimotor behaviors. Continued loading of the injured tissues in addition to stress-related factors associated with forced running/exercise likely contributed to our findings.

Tendon healing in presence of chronic low-level inflammation: a systematic review

BACKGROUND

Tendinopathy is a common musculoskeletal condition affecting subjects regardless of their activity level. Multiple inflammatory molecules found in ex vivo samples of human tendons are related to the initiation or progression of tendinopathy. Their role in tendon healing is the subject of this review.

SOURCES OF DATA

An extensive review of current literature was conducted using PubMed, Embase and Cochrane Library using the term 'tendon', as well as some common terms of tendon conditions such as 'tendon injury OR (tendon damage) OR tendonitis OR tendinopathy OR (chronic tendonitis) OR tendinosis OR (chronic tendinopathy) OR enthesitis' AND 'healing' AND '(inflammation OR immune response)' as either key words or MeSH terms.

AREAS OF AGREEMENT

An environment characterized by a low level of chronic inflammation, together with increased expression of inflammatory cytokines and growth factors, may influence the physiological tendon healing response after treatment.

AREAS OF CONTROVERSY

Most studies on this topic exhibited limited scientific translational value because of their heterogeneity. The evidence associated with preclinical studies is limited.

GROWING POINTS

The role of inflammation in tendon healing is still unclear, though it seems to affect the overall outcome. A thorough understanding of the biochemical mediators of healing and their pathway of pain could be used to target tendinopathy and possibly guide its management.

AREAS TIMELY FOR DEVELOPING RESEARCH

We require further studies with improved designs to effectively evaluate the pathogenesis and progression of tendinopathy to identify cellular and molecular targets to improve outcomes.

Minocycline microspheres did not significantly improve outcomes after collagenase injection of tendon

BACKGROUND

Tetracycline antibiotics inhibit matrix metalloproteinases and pro-inflammatory cytokines implicated in the pathogenesis of tendinopathy, while microsphere formulations allow sustained release of drug contents. The purpose of this study was to evaluate the ability of a local minocycline microsphere injection to restore normal tendon properties in a rat model of collagenase-induced patellar tendinopathy.

METHODS

A total of 22 rats were randomly assigned to the control (n = 11) or minocycline (n = 11) group and received bilateral patellar tendon injections of collagenase. After 7 days, the minocycline group received the minocycline microsphere treatment and the control group received phosphate buffered solution. Pain was assessed via activity monitors and Von Frey filament testing. At 4 weeks post-collagenase injections, animals were euthanized.

RESULTS

Cage crossings significantly decreased among all rats 2-3 days following each injection period, however, tactile allodynia measures did not reflect this injury response. Biomechanical properties, interleukin-1 beta levels, and glycosaminoglycan content did not differ between groups. While not statistically significant, levels of leukotriene B4 were lower in the minocycline group compared to controls (p = 0.061), suggesting a trend.

CONCLUSIONS

Our study further characterizes the collagenase model of tendinopathy by demonstrating no evidence of central sensitization with collagenase-induced injury. We found no adverse effect of intratendinous injections of minocycline-loaded poly-lactic-co-glycolic acid microspheres, although no therapeutic effect was observed. Future studies involving a more substantial tendon injury with a greater inflammatory component may be necessary to more thoroughly evaluate the effects of minocycline on tendon pathology.

Functional Measures of Grip Strength and Gait Remain Altered Long-term in a Rat Model of Post-traumatic Elbow Contracture

Post-traumatic joint contracture (PTJC) is a debilitating condition, particularly in the elbow. Previously, we established an animal model of elbow PTJC quantifying passive post-mortem joint mechanics and histological changes temporally. These results showed persistent motion loss similar to what is experienced in humans. Functional assessment of PTJC in our model was not previously considered; however, these measures would provide a clinically relevant measure and would further validate our model by demonstrating persistently altered joint function. To this end, a custom bilateral grip strength device was developed, and a recently established open-source gait analysis system was used to quantify forelimb function in our unilateral injury model. In vivo joint function was shown to be altered long-term and never fully recover. Specifically, forelimb strength in the injured limbs showed persistent deficits at all time points; additionally, gait patterns remained imbalanced and asymmetric throughout the study (although a few gait parameters did return to near normal levels). A quantitative understanding of these longitudinal, functional disabilities further strengthens the clinical relevance of our rat PTJC model enabling assessment of the effectiveness of future interventions aimed at reducing or preventing PTJC.

Comparing effects of rest with or without a NK1RA on fibrosis and sensorimotor declines induced by a voluntary moderate demand task

OBJECTIVES

Fibrosis is one contributing factor in motor dysfunction and discomfort in patients with overuse musculoskeletal disorders. We pharmacologically targeted the primary receptor for Substance P, neurokinin-1, using a specific antagonist (NK1RA) in a rat model of overuse with the goal of improving tissue fibrosis and discomfort.

METHODS

Female rats performed a low repetition, high force (LRHF) grasping task for 12 weeks, or performed the task for 12 weeks before being placed on a four week rest break, with or without simultaneous NK1RA treatment. Results were compared to control rats (untreated, or treated 4 weeks with NK1RA or vehicle).

RESULTS

Rest improved LRHF-induced declines in grip strength, although rest plus NK1RA treatment (Rest/NK1RA) rescued it. Both treatments improved LRHF-induced increases in muscle TGFβ1 and collagen type 1 levels, forepaw mechanical hypersensitivity (Rest/NK1RA more effectively), macrophage influx into median nerves, and enhanced collagen deposition in forepaw dermis. Only Rest/NK1RA reduced muscle hypercellularity. However, LRHF+4wk Rest /NK1RA rats showed hyposensitivity to noxious hot temperatures.

CONCLUSIONS

While the NK1RA induced hot temperature hyposensitivity should be taken into consideration if this or related drug were used long-term, the NK1RA more effectively reduced muscle hypercellularity and improved grip strength and forepaw mechanical hypersensitivity.

Fascial tissue research in sports medicine: from molecules to tissue adaptation, injury and diagnostics: consensus statement

The fascial system builds a three-dimensional continuum of soft, collagen-containing, loose and dense fibrous connective tissue that permeates the body and enables all body systems to operate in an integrated manner. Injuries to the fascial system cause a significant loss of performance in recreational exercise as well as high-performance sports, and could have a potential role in the development and perpetuation of musculoskeletal disorders, including lower back pain. Fascial tissues deserve more detailed attention in the field of sports medicine. A better understanding of their adaptation dynamics to mechanical loading as well as to biochemical conditions promises valuable improvements in terms of injury prevention, athletic performance and sports-related rehabilitation. This consensus statement reflects the state of knowledge regarding the role of fascial tissues in the discipline of sports medicine. It aims to (1) provide an overview of the contemporary state of knowledge regarding the fascial system from the microlevel (molecular and cellular responses) to the macrolevel (mechanical properties), (2) summarise the responses of the fascial system to altered loading (physical exercise), to injury and other physiological challenges including ageing, (3) outline the methods available to study the fascial system, and (4) highlight the contemporary view of interventions that target fascial tissue in sport and exercise medicine. Advancing this field will require a coordinated effort of researchers and clinicians combining mechanobiology, exercise physiology and improved assessment technologies.

Prolonged high force high repetition pulling induces osteocyte apoptosis and trabecular bone loss in distal radius, while low force high repetition pulling induces bone anabolism

We have an operant rat model of upper extremity reaching and grasping in which we examined the impact of performing a high force high repetition (High-ForceHR) versus a low force low repetition (Low-ForceHR) task for 18weeks on the radius and ulna, compared to age-matched controls. High-ForceHR rats performed at 4 reaches/min and 50% of their maximum voluntary pulling force for 2h/day, 3days/week. Low-ForceHR rats performed at 6% maximum voluntary pulling force. High-ForceHR rats showed decreased trabecular bone volume in the distal metaphyseal radius, decreased anabolic indices in this same bone region (e.g., decreased osteoblasts and bone formation rate), and increased catabolic indices (e.g., microcracks, increased osteocyte apoptosis, secreted sclerostin, RANKL, and osteoclast numbers), compared to controls. Distal metaphyseal trabeculae in the ulna of High-ForceHR rats showed a non-significant decrease in bone volume, some catabolic indices (e.g., decreased trabecular numbers) yet also some anabolic indices (e.g., increased osteoblasts and trabecular thickness). In contrast, the mid-diaphyseal region of High-ForceHR rats' radial and ulnar bones showed few to no microarchitecture differences and no changes in apoptosis, sclerostin or RANKL levels, compared to controls. In further contrast, Low-ForceHR rats showed increased trabecular bone volume in the radius in the distal metaphysis and increased cortical bone area its mid-diaphysis. These changes were accompanied by increased anabolic indices, no microcracks or osteocyte apoptosis, and decreased RANKL in each region, compared to controls. Ulnar bones of Low-ForceHR rats also showed increased anabolic indices, although fewer than in the adjacent radius. Thus, prolonged performance of an upper extremity reaching and grasping task is loading-, region-, and bone-dependent, with high force loads at high repetition rates inducing region-specific increases in bone degradative changes that were most prominent in distal radial trabeculae, while low force task loads at high repetition rates induced adaptive bone responses.

Cytokines in tendon disease: A Systematic Review

OBJECTIVES

Emerging evidence indicates that tendon disease is an active process with inflammation that is critical to disease onset and progression. However, the key cytokines responsible for driving and sustaining inflammation have not been identified.

METHODS

We performed a systematic review of the literature using MEDLINE (U.S. National Library of Medicine, Bethesda, Maryland) in March 2017. Studies reporting the expression of interleukins (ILs), tumour necrosis factor alpha (TNF-α) and interferon gamma in diseased human tendon tissues, and animal models of tendon injury or exercise in comparison with healthy control tissues were included.

RESULTS

IL-1β, IL-6, IL-10, and TNF-α are the cytokines that have been most frequently investigated. In clinical samples of tendinopathy and tendon tears, the expression of TNF-α tended not to change but IL-6 increased in tears. Healthy human tendons showed increased IL-6 expression after exercise; however, IL-10 remained unchanged. Animal tendon injury models showed that IL-1β, IL-6, and TNF-α tend to increase from the early phase of tendon healing. In animal exercise studies, IL-1β expression showed a tendency to increase at the early stage after exercise, but IL-10 expression remained unchanged with exercise.

CONCLUSIONS

This review highlights the roles of IL-1β, IL-6, IL-10, and TNF-α in the development of tendon disease, during tendon healing, and in response to exercise. However, there is evidence accumulating that suggests that other cytokines are also contributing to tendon inflammatory processes. Further work with hypothesis-free methods is warranted in order to identify the key cytokines, with subsequent mechanistic and interaction studies to elucidate their roles in tendon disease development.Cite this article: W. Morita, S. G. Dakin, S. J. B. Snelling, A. J. Carr. Cytokines in tendon disease: A Systematic Review. Bone Joint Res 2017;6:656-664. DOI: 10.1302/2046-3758.612.BJR-2017-0112.R1.

Decreased grip strength, muscle pain, and atrophy occur in rats following long-term exposure to excessive repetitive motion

Work‐related musculoskeletal disorders (WMSD) are caused by the overuse of muscles in the workplace. Performing repetitive tasks is a primary risk factor for the development of WMSD. Many workers in highly repetitive jobs exhibit muscle pain and decline in handgrip strength, yet the mechanisms underlying these dysfunctions are poorly understood. In our study, rats performed voluntary repetitive reaching and grasping tasks (Task group), while Control group rats did not perform these activities. In the Task group, grip strength and forearm flexor withdrawal threshold declined significantly from week 2 to week 6, compared with these values at week 0 (P < 0.05). Relative muscle weight and muscle fiber cross‐sectional area of flexor digitorum superficialis (FDS) muscles decreased significantly in the Task group, compared with the Control group, at 6 weeks (P < 0.05 and P < 0.01, respectively). Nerve growth factor, glial cell line‐derived neurotrophic factor, and tumor necrosis factor α‐expression in FDS muscles were not significantly different in Control and Task groups at 3 and 6 weeks. At 6 weeks, the Task group had elevated MuRF1 protein levels (P = 0.065) and significant overexpression of the autophagy‐related (Atg) proteins, Beclin1 and Atg5–Atg12, compared with in the Control group (both P < 0.05). These data suggested that long‐term exposure to excessive repetitive motion causes loss of grip strength, muscle pain, and skeletal muscle atrophy. Furthermore, this exposure may enhance protein degradation through both the ubiquitin‐proteasome and autophagy‐lysosome systems, thereby decreasing skeletal muscle mass.

Impact of Inflammation and Anti-inflammatory Modalities on Skeletal Muscle Healing: From Fundamental Research to the Clinic

Anti-inflammatory modalities are commonly used for the treatment of various musculoskeletal injuries. Although inflammation was originally believed to interfere with skeletal muscle regeneration, several recent studies have highlighted the beneficial effects of inflammatory cells on muscle healing. This discrepancy is attributable to an evolving understanding of the complex inflammatory process. To better appreciate the paradoxical roles of inflammation, clinicians must have a better comprehension of the fundamental mechanisms regulating the inflammatory response. In this perspective article, cellular, animal, and human studies were analyzed to summarize recent knowledge regarding the impact of inflammation on muscle regeneration in acute or chronic conditions. The effect of anti-inflammatory drugs on the treatment of various muscle injuries was also considered. Overall, this work aims to summarize the current state of the literature on the inflammatory process associated with muscle healing in order to give clinicians the necessary tools to have a more efficient and evidence-based approach to the treatment of muscle injuries and disorders.

Profibrotic mediators in tendon disease: a systematic review

Background

Tendon disease is characterized by the development of fibrosis. Transforming growth factor beta (TGF-β), bone morphogenic proteins (BMPs) and connective tissue growth factor (CTGF) are key mediators in the pathogenesis of fibrotic disorders. The aim of this systematic review was to investigate the evidence for the expression of TGF-β, BMPs and CTGF along tendon disease progression and the response of tendon cells to these growth factors accordingly.

Method

We conducted a systematic screen of the scientific literature using the Medline database. The search terms used were “tendon AND TGF-β,” “tendon AND BMP” or “tendon AND CTGF.” Studies of human samples, animal tendon injury and overuse models were included.

Results

Thirty-three studies were included. In eight studies the expression of TGF-β, BMPs or CTGF was dysregulated in chronic tendinopathy and tendon tear patient tissues in comparison with healthy control tissues. The expression of TGF-β, BMPs and CTGF was increased and showed temporal changes in expression in tendon tissues from animal injury or overuse models compared with the healthy control (23 studies), but the pattern of upregulation was inconsistent between growth factors and also the type of animal model. No study investigated the differences in the effect of TGF-β, BMPs or CTGF treatment between patient-derived cells from healthy and diseased tendon tissues. Tendon cells derived from animal models of tendon injury showed increased expression of extracellular matrix protein genes and increased cell signaling response to TGF-β and BMP treatments compared with the control cells (two studies).

Conclusion

The expression of TGF-β, BMPs and CTGF in tendon tissues is altered temporally during healing in animal models of tendon injury or overuse, but the transition during the development of human tendon disease is currently unknown. Findings from this systematic review suggest a potential and compelling role for TGF-β, BMPs and CTGF in tendon disease; however, there is a paucity of studies analyzing their expression and stimulated cellular response in well-phenotyped human samples. Future work should investigate the dynamic expression of these fibrotic growth factors and their interaction with tendon cells using patient samples at different stages of human tendon disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1165-0) contains supplementary material, which is available to authorized users.

Influence of repetitive mechanical loading on MMP2 activity in tendon fibroblasts

Matrix metalloproteinase2 has been implicated in tendon pathology caused by repetitive movements. However, its activity in the early stages of the tendon's response to overuse, and its presence in the circulation as a possible indicator of tendon degradation, remain unknown. Human tendon cells were repetitively stretched for 5 days, and the rabbit Achilles tendon complex underwent repetitive motion 3× per week for 2 weeks. Quantitative polymer chain reaction analysis was performed to detect matrix metalloproteinase2/14 and tissue inhibitor of matrix metalloproteinase2 messenger ribonucleic acid of cells and rabbit tissue, and matrix metalloproteinase2 protein levels were determined with an enzyme linked immunoassay. Matrix metalloproteinase2 activity was examined using zymography of the conditioned media, tendon and serum. Immunohistochemistry was used to localize matrix metalloproteinase2 in tendon tissue, and the density of fibrillar collagen in tendons was examined using second harmonic generation microscopy. Tendon cells stretched with high strain or high frequency demonstrated increased matrix metalloproteinase2 messenger ribonucleic acid and protein levels. Matrix metalloproteinase2 activity was increased in the rabbit Achilles tendon tissue at weeks 1 and 2; however, serum activity was only increased at week 1. After 2 weeks of exercise, the collagen density was lower in specific regions of the exercised rabbit Achilles tendon complex. Matrix metalloproteinase2 expression in exercised rabbit Achilles tendons was detected surrounding tendon fibroblasts. Repetitive mechanical stimulation of tendon cells results in a small increase in matrix metalloproteinase2 levels, but it appears unlikely that serum matrix metalloproteinase2 will be a useful indicator of tendon overuse injury. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1991-2000, 2016.

Miniscalpel-Needle Treatment Is Effective for Work-Related Neck and Shoulder Musculoskeletal Disorders

Background. Work-related musculoskeletal disorders (MSDs) are a group of painful disorders of muscles, tendons, and nerves, such as neck and shoulder MSD. This study was designed to use miniscalpel-needle (MSN) technique as an intervention for work-related MSDs. Methods. Thirty-one patients with work-related MSDs and 28 healthy subjects were enrolled as controls in this study. The MSD symptoms of each patient were assessed by visual analog scale (VAS) and neck disability index (NDI). Blood samples were collected from control subjects and MSD patients before and after treatment. Serum levels of C-reactive protein (CRP) and tumor necrosis factor (TNF) were measured using ELISA. Results. Prior to MSN treatment, serum levels of CRP and TNF were significantly higher in the MSD patients than the healthy controls. Serum CRP levels correlated with VAS and NDI scores, and serum TNF levels correlated with NDI scores. Compared to pretreatment, VAS and NDI scores were significantly lower in MSD patients after MSN treatment, while serum CRP and TNF levels were significantly lower compared with the healthy control levels. Conclusions. Our results indicate that MSN may be an effective intervention for work-related MSDs and be associated with lower serum levels of inflammatory biomarkers.

Angiopoietin-like 4 promotes angiogenesis in the tendon and is increased in cyclically loaded tendon fibroblasts

KEY POINTS

Angiopoietin-like 4 (ANGPTL4) modulates tendon neovascularization. Cyclic loading stimulates the activity of transforming growth factor-β and hypoxia-inducible factor 1α and thereby increases the expression and release of ANGPTL4 from human tendon cells. Targeting ANGPTL4 and its regulatory pathways is a potential avenue for regulating tendon vascularization to improve tendon healing or adaptation.

ABSTRACT

The mechanisms that regulate angiogenic activity in injured or mechanically loaded tendons are poorly understood. The present study examined the potential role of angiopoietin-like 4 (ANGPTL4) in the angiogenic response of tendons subjected to repetitive mechanical loading or injury. Cyclic stretching of human tendon fibroblasts stimulated the expression and release of ANGPTL4 protein via transforming growth factor-β (TGF-β) and hypoxia-inducible factor 1α (HIF-1α) signalling, and the released ANGPTL4 was pro-angiogenic. Angiogenic activity was increased following ANGPTL4 injection into mouse patellar tendons, whereas the patellar tendons of ANGPTL4 knockout mice displayed reduced angiogenesis following injury. In human rotator cuff tendons, the expression of ANGPTL4 was correlated with the density of tendon endothelial cells. To our knowledge, this is the first study characterizing a role of ANGPTL4 in the tendon. ANGPTL4 may assist in the regulation of vascularity in the injured or mechanically loaded tendon. TGF-β and HIF-1α comprise two signalling pathways that modulate the expression of ANGPTL4 by mechanically stimulated tendon fibroblasts and, in the future, these could be manipulated to influence tendon healing or adaptation.

Midlife Occupational Physical Activity and Risk of Disability Later in Life: National Health and Aging Trends Study

OBJECTIVES

To determine whether midlife occupational physical activity (PA) is associated with disability in older adults and to test disease as a mediating variable.

DESIGN

Cross-sectional study.

SETTING

National Health and Aging Trends Study.

PARTICIPANTS

Individuals aged 65 and older (N = 7,307).

MEASUREMENTS

Participants were classified as to occupational PA levels by linking information from the Occupational Information Network database using standard occupation codes. Disability outcomes and covariates were obtained through in-person interviews. Logistic regression models were used to examine the association between occupational PA and disability. Structural equation modeling (SEM) was fitted to examine the mediating effect of disease.

RESULTS

Occupations with high physically demands were associated with greater decline in functional capacity later in life. Individuals with occupations with high and very high PA were less likely to be able to perform activities of daily living than those with occupations with low PA. SEM showed that occupational PA has a very strong direct effect on disability (P < .001) and has an indirect effect on disability through disease (P = .003). The population attributable fraction for high occupational PA was 11%.

CONCLUSION

Higher midlife occupational PA levels were significantly associated with poorer ability to perform activities of daily living in older age. Performing the optimal level of occupational PA may be instrumental in reducing disability later in life.

Manual therapy as an effective treatment for fibrosis in a rat model of upper extremity overuse injury

Key clinical features of carpal tunnel syndrome and other types of cumulative trauma disorders of the hand and wrist include pain and functional disabilities. Mechanistic details remain under investigation but may involve tissue inflammation and/or fibrosis. We examined the effectiveness of modeled manual therapy (MMT) as a treatment for sensorimotor behavior declines and increased fibrogenic processes occurring in forearm tissues of rats performing a high repetition high force (HRHF) reaching and grasping task for 12 weeks. Young adult, female rats were examined: food restricted control rats (FRC, n=12); rats that were trained for 6 weeks before performing the HRHF task for 12 weeks with no treatment (HRHF-CON, n=11); and HRHF task rats received modeled manual therapy (HRHF-MMT, n=5) for 5 days/week for the duration of the 12-week of task. Rats receiving the MMT expressed fewer discomfort-related behaviors, and performed progressively better in the HRHF task. Grip strength, while decreased after training, improved following MMT. Fibrotic nerve and connective tissue changes (increased collagen and TGF-β1 deposition) present in 12-week HRHF-CON rats were significantly decreased in 12-week HRHF-MMT rats. These observations support the investigation of manual therapy as a preventative for repetitive motion disorders.

Growth and repair factors, osteoactivin, matrix metalloproteinase and heat shock protein 72, increase with resolution of inflammation in musculotendinous tissues in a rat model of repetitive grasping

BACKGROUND

Expression of the growth factor osteoactivin (OA) increases during tissue degeneration and regeneration, fracture repair and after denervation-induced disuse atrophy, concomitant with increased matrix metalloproteinases (MMPs). However, OA's expression with repetitive overuse injuries is unknown. The aim of this study was to evaluate: 1) OA expression in an operant rat model of repetitive overuse; 2) expression of MMPs; 3) inflammatory cytokines indicative of injury or inflammation; and 4) the inducible form of heat shock protein 70 (HSPA1A/HSP72) as the latter is known to increase during metabolic stress and to be involved in cellular repair. Young adult female rats performed a high repetition negligible force (HRNF) food retrieval task for up to 6 weeks and were compared to control rats.

METHODS

Flexor digitorum muscles and tendons were collected from 22 young adult female rats performing a HRNF reaching task for 3 to 6 weeks, and 12 food restricted control (FRC) rats. OA mRNA levels were assessed by quantitative polymerase chain reaction (qPCR). OA, MMP-1, -2, -3, and -13 and HSP72 protein expression was assayed using Western blotting. Immunohistochemistry and image analysis was used to evaluate OA and HSP72 expression. ELISA was performed for HSP72 and inflammatory cytokines.

RESULTS

Flexor digitorum muscles and tendons from 6-week HRNF rats showed increased OA mRNA and protein expression compared to FRC rats. MMP-1, -2 and -3 progressively increased in muscles whereas MMP-1 and -3 increased in tendons with HRNF task performance. HSP72 increased in 6-week HRNF muscles and tendons, compared to controls, and co-localized with OA in the myofiber sarcolemma. IL-1alpha and beta increased transiently in tendons or muscles in HRNF week 3 before resolving in week 6.

CONCLUSION

The simultaneous increases of OA with factors involved in tissue repair (MMPs and HSP72) supports a role of OA in tissue regeneration after repetitive overuse.

Tendinopathy: Update on Pathophysiology

Synopsis Tendinopathy has become the accepted term to describe a spectrum of changes that occur in damaged and/or diseased tendons. Over the past 2 decades, there have been new insights into tendon pathophysiology of relevance to clinicians, including (1) better characterization of the overuse injury process and the resultant structural and functional disruption in chronically painful tendons, (2) improved understanding of the pathomechanics associated with chronic tendon injury, and (3) greater knowledge about the influence of lifestyle factors and drugs on tendon pathology. The implications of these new insights are discussed. J Orthop Sports Phys Ther 2015;45(11):833-841. Epub 21 Sep 2015. doi:10.2519/jospt.2015.5884.

Effects of Noxious Electrical Stimulation and Eccentric Exercise on Pain Sensitivity in Asymptomatic Individuals

BACKGROUND

Achilles tendinopathy is a common overuse injury in running and jumping athletes. Currently, we do not understand why some conservative interventions (eg, noxious electrical stimulation and eccentric training) may reduce the pain associated with tendinopathy.

OBJECTIVE

To determine whether noxious electrical stimulation (NES) or eccentric contractions would alter pain sensitivity around the asymptomatic Achilles tendon.

DESIGN

A double-blind trial with block-randomization by gender into 3 intervention arms: NES, eccentric contractions, or low-intensity cycling.

PARTICIPANTS

A total of 40 volunteers with no current pain conditions started the study, and 39 completed follow-up testing.

METHODS

Participants underwent 2 baseline sessions to assess pain sensitivity response stability of pressure pain threshold (PPT), heat pain threshold (HPT), and heat temporal summation (HTS) over the Achilles tendon. Immediately after the second baseline session, participants performed 1 session of an intervention and were tested immediately postintervention and the next morning. Eccentric-only plantarflexor exercise was performed (4 sets of 15 repetitions) using full bodyweight and slow, 5-second contractions. Noxious electrical stimulation was applied to the Achilles for 20 minutes and dosed to the subjects' pain tolerance. Low-intensity cycling was dosed (60-70 W for 20 minutes) to minimize occurrence of exercise-induced hypoalgesia. The PPT was the primary outcome measure.

RESULTS

For PPT, both NES (P < .001) and eccentric (P = .003) groups were less sensitive to pressure immediately posttreatment, and the eccentric group maintained this effect through the next morning (P = .043). No group differences were seen for HPT, but the NES (P = .031) and eccentric (P = .036) groups had less HTS the next morning.

CONCLUSIONS

A single session of eccentric exercise and NES can produce immediate and next-day reductions in pain sensitivity in asymptomatic adults. The immediacy of these effects points toward a neurophysiologic mechanism. Future research needs to be performed in clinical populations and to assess any cumulative effects to repetitive intervention.

IMPROVED PRESSURE PAIN THRESHOLDS AND FUNCTION FOLLOWING NOXIOUS ELECTRICAL STIMULATION ON A RUNNER WITH CHRONIC ACHILLES TENDINOPATHY: A CASE REPORT

BACKGROUND AND PURPOSE

Achilles tendinopathy is a common overuse injury sustained by athletes including runners. The use of noxious electrical stimulation for the treatment of chronic tendinopathies is a novel treatment intervention, which may alter pain perception and serve as adjunct technique in the recovery of painfree function. The purpose of this case report is to demonstrate the use of noxious electrical stimulation for the treatment of chronic, bilateral Achilles tendinopathy that was resistant to conservative treatment using plantarflexor eccentric exercise.

CASE DESCRIPTION

A 27-year old male runner was referred to physical therapy with a 7-year history of bilateral Achilles tendinopathy. He scored a 73/80 on the Lower Extremity Functional Scale (LEFS) and a 64% on the Victorian Institute of Sports Assessment-Achilles (VISA-A). Pain pressure threshold testing of the Achilles tendon was performed, followed by a single session of noxious electric stimulation to bilateral Achilles tendons, and the subject was instructed to continue with eccentric gastroc-soleus complex strengthening as previously performed.

OUTCOMES

Pain pressure threshold testing was performed to the mid-portion of the posterior Achilles tendon. The left Achilles tendon mean was 10.50kg and right Achilles tendon was 8.33kg prior to the noxious stimulation intervention. Twenty-four hours after the noxious stimulation treatment, improvements in mean pain threshold testing were found for both the left (16.31kg) and right (12.36kg) Achilles tendons. At one month after the physical therapy noxious stimulation session, the subject was able to progress his workouts to include sprints and interval training. His LEFS improved to 76/80 and his VISA-A improved to 96%.

DISCUSSION

The case illustrates the successful pain reduction and return to progressive sports activity in a runner with chronic Achilles tendinopathy. The utilization of noxious electric stimulation may have altered the pain perception of the nervous system as evidenced by the improvement in pain pressure threshold testing. Future studies on the application of noxious electric stimulation on chronic Achilles tendinopathy may help support the benefit of this intervention on pain and function.

LEVEL OF EVIDENCE

Therapy, Level 4.

Increased CCN2, substance P and tissue fibrosis are associated with sensorimotor declines in a rat model of repetitive overuse injury

Key clinical features of cumulative trauma disorders include pain, muscle weakness, and tissue fibrosis, although the etiology is still under investigation. Here, we characterized the temporal pattern of altered sensorimotor behaviors and inflammatory and fibrogenic processes occurring in forearm muscles and serum of young adult, female rats performing an operant, high repetition high force (HRHF) reaching and grasping task for 6, 12, or 18 weeks. Palmar mechanical sensitivity, cold temperature avoidance and spontaneous behavioral changes increased, while grip strength declined, in 18-week HRHF rats, compared to controls. Flexor digitorum muscles had increased MCP-1 levels after training and increased TNFalpha in 6-week HRHF rats. Serum had increased IL-1beta, IL-10 and IP-10 after training. Yet both muscle and serum inflammation resolved by week 18. In contrast, IFNγ increased at week 18 in both muscle and serum. Given the anti-fibrotic role of IFNγ, and to identify a mechanism for the continued grip strength losses and behavioral sensitivities, we evaluated the fibrogenic proteins CCN2, collagen type I and TGFB1, as well as the nociceptive/fibrogenic peptide substance P. Each increased in and around flexor digitorum muscles and extracellular matrix in the mid-forearm, and in nerves of the forepaw at 18 weeks. CCN2 was also increased in serum at week 18. At a time when inflammation had subsided, increases in fibrogenic proteins correlated with sensorimotor declines. Thus, muscle and nerve fibrosis may be critical components of chronic work-related musculoskeletal disorders. CCN2 and substance P may serve as potential targets for therapeutic intervention, and CCN2 as a serum biomarker of fibrosis progression.

Inflammatory biomarkers in serum in subjects with and without work related neck/shoulder complaints

Background

Although it has recently been recognised that inflammation is important in the development of work-related musculoskeletal disorders (MSDs), the exact pathophysiological pathways are unknown.

Methods

We investigated serum concentrations of inflammatory cytokines in 35 female supermarket cashiers with repetitive work tasks and work related neck/shoulder complaints, compared with those from 25 women without MSDs (6 supermarket cashiers and 19 middle-school teachers or faculty staff). None of the subjects were pregnant or lactating, and showed no signs of rheumatoid arthritis, systemic lupus erythematosus, cancer, diabetes, coronary artery disease or inadequately controlled hypertension. Serum levels of IL-1α, IL-1β, IL-6, IL-8, IL-10, IL-12, MCP-1, MIP-1α, MIP-1β, TNF-α, GM-CSF, CTGF and CRP were analysed.

Results

The women with pain related to MSD had higher serum concentrations of MIP-1β (median, 25th-75th percentile: 90.0 pg/mL, 62.5-110 vs. 73.1 pg/mL, 54.6-88.3; p = 0.018), IL-12 (0.26 pg/mL, 0.26-0.26 vs. 0.26 pg/mL, 0.26-0.26; p = 0.047) and CRP (0.5 mg/L, 0.5-1.6 vs. 0.5 mg/L, 0.5-0.5; p = 0.003), than control subjects. Levels of MIP-1α, MIP-1β and CRP were correlated with the reported intensity of neck/shoulder pain (r = 0.29, p = 0.03 for MIP-1α; r = 0.29, p = 0.02 for MIP-1β and r = 0.43, p = 0.001 for CRP). No statistically significant differences in serum levels were found for the remaining cytokines.

Conclusions

Otherwise healthy females with ongoing work-related neck/shoulder pain showed higher serum concentrations of MIP-1β, IL-12 and CRP than controls, and the levels of MIP-1α, MIP-1β and CRP were correlated to pain intensity. These results support previous findings that inflammatory processes play a part in work related MSDs.

The interaction of force and repetition on musculoskeletal and neural tissue responses and sensorimotor behavior in a rat model of work-related musculoskeletal disorders

Background

We examined the relationship of musculoskeletal risk factors underlying force and repetition on tissue responses in an operant rat model of repetitive reaching and pulling, and if force x repetition interactions were present, indicative of a fatigue failure process. We examined exposure-dependent changes in biochemical, morphological and sensorimotor responses occurring with repeated performance of a handle-pulling task for 12 weeks at one of four repetition and force levels: 1) low repetition with low force, 2) high repetition with low force, 3) low repetition with high force, and 4) high repetition with high force (HRHF).

Methods

Rats underwent initial training for 4–6 weeks, and then performed one of the tasks for 12 weeks, 2 hours/day, 3 days/week. Reflexive grip strength and sensitivity to touch were assayed as functional outcomes. Flexor digitorum muscles and tendons, forelimb bones, and serum were assayed using ELISA for indicators of inflammation, tissue stress and repair, and bone turnover. Histomorphometry was used to assay macrophage infiltration of tissues, spinal cord substance P changes, and tissue adaptative or degradative changes. MicroCT was used to assay bones for changes in bone quality.

Results

Several force x repetition interactions were observed for: muscle IL-1alpha and bone IL-1beta; serum TNFalpha, IL-1alpha, and IL-1beta; muscle HSP72, a tissue stress and repair protein; histomorphological evidence of tendon and cartilage degradation; serum biomarkers of bone degradation (CTXI) and bone formation (osteocalcin); and morphological evidence of bone adaptation versus resorption. In most cases, performance of the HRHF task induced the greatest tissue degenerative changes, while performance of moderate level tasks induced bone adaptation and a suggestion of muscle adaptation. Both high force tasks induced median nerve macrophage infiltration, spinal cord sensitization (increased substance P), grip strength declines and forepaw mechanical allodynia by task week 12.

Conclusions

Although not consistent in all tissues, we found several significant interactions between the critical musculoskeletal risk factors of force and repetition, consistent with a fatigue failure process in musculoskeletal tissues. Prolonged performance of HRHF tasks exhibited significantly increased risk for musculoskeletal disorders, while performance of moderate level tasks exhibited adaptation to task demands.