Microarray analysis of the tendinopathic rat supraspinatus tendon: glutamate signaling and its potential role in tendon degeneration

Total rupture of Achilles tendon induces inflammatory response and glial activation on the spinal cord of mice

Rupture of Achilles tendon is a common accident affecting professional and recreational athletes. Acute and chronic pain are symptoms commonly observed in patients with rupture. However, few studies have investigated whether Achilles tendon rupture is able to promote disorders in the central nervous system (CNS). Therefore, the current study aimed to evaluate nociceptive alterations and inflammatory response in the L5 lumbar segment of Balb/c mice spinal cord after Achilles tendon rupture. We found increased algesia in the paw of the ruptured group on the 7th and 14th days post-tenotomy compared with the control group. This phenomenon was accompanied by overexpression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase-2 (NOS-2) as well as hyperactivation of astrocytes and microglia in nociceptive areas of L5 spinal cord as evidenced by intense GFAP and IBA-1 immunostaining, respectively. Biochemical studies also demonstrated increased levels of nitrite in the L5 spinal cord of tenotomized animals compared with the control group. Thus, we have demonstrated for the first time that total rupture of the Achilles tendon induced inflammatory response and nitrergic and glial activation in the CNS in the L5 spinal cord region.

Arthroscopic Repair Benefits Reparable Rotator Cuff Tear Patients Aged 65 Years or Older With a History of Traumatic Events

PURPOSE

To evaluate the clinical outcomes of arthroscopic rotator cuff repair at 2-year follow-up in patients aged 65 years or older with a history of traumatic events divided into groups based on symptom duration (<3 months, 3-6 months, and >6 months from injury to surgery) and to compared patient-reported outcomes among the 3 groups.

METHODS

Between 2015 and 2020, 110 patients who met the inclusion criteria were enrolled in this study; these patients were divided into 3 groups according to symptom duration: less than 3 months (group A), 3 to 6 months (group B) and more than 6 months (group C). Preoperative and 2-year postoperative clinical outcomes were compared, including American Shoulder and Elbow Surgeons, Constant-Murley, University of California, Los Angeles, Simple Shoulder Test, and visual analog scale scores; forward elevation; external rotation; and internal rotation. The minimal clinically important difference (MCID), patient acceptable symptom state, substantial clinical benefit, and maximum outcome improvement were also compared among the groups.

RESULTS

The American Shoulder and Elbow Surgeons score, as the primary outcome, improved significantly from 41.0 ± 18.5 to 85.4 ± 8.1 in group A, from 53.7 ± 14.3 to 86.3 ± 11.7 in group B, and from 49.7 ± 18.5 to 83.9 ± 11.9 in group C. All the other parameters showed statistically significant improvements at 2-year follow-up in each group (all P < .05). There was no significant difference in each parameter among the 3 groups except the visual analog scale score, which did not achieve the MCID. Overall, 86 patients (78.2%) exceeded the MCID, 87 patients (79.1%) achieved the patient acceptable symptom state, 77 patients (70.0%) achieved substantial clinical benefit, and 62 patients (56.4%) achieved maximum outcome improvement without significant differences among the 3 groups.

CONCLUSIONS

In rotator cuff tear patients aged 65 years or older with a history of traumatic events, arthroscopic rotator cuff repair significantly improves clinical outcomes at 2-year follow-up regardless of symptom duration if the tear is fully reparable.

LEVEL OF EVIDENCE

Level III, prognostic retrospective study.

Inflammatory mechanisms linking obesity and tendinopathy

Chronic tendinopathy is a debilitating tendon disorder with disappointing treatment outcomes. This review focuses on the potential roles of chronic low-grade inflammation in promoting tendinopathy in obesity. A systematic literature search was performed to identify all clinical studies supporting the actions of obesity-associated inflammatory mediators in the development of tendinopathy. The mechanisms of obesity-induced chronic inflammation in adipose tissue are firstly reviewed. Common inflammatory mediators potentially linking obesity and the development of tendinopathy, and their association with mechanical overuse, are discussed, along with pre-clinical evidences and a systematic literature search on clinical studies. The potential contribution of local adipose tissues in the promotion of inflammation, pain and tendon degeneration is then discussed. The future research directions are proposed.

Translational potential statement

Better understanding of the roles of obesity-associated inflammatory mediators on tendons will clarify the pathophysiological drivers of tendinopathy in patients with obesity and identify possible treatment targets. Further studies on the mechanisms of obesity-induced chronic inflammation on tendon are a promising direction for the treatment of tendinopathy.

Screening of key biomarkers of tendinopathy based on bioinformatics and machine learning algorithms

Tendinopathy is a complex multifaceted tendinopathy often associated with overuse and with its high prevalence resulting in significant health care costs. At present, the pathogenesis and effective treatment of tendinopathy are still not sufficiently elucidated. The purpose of this research is to intensely explore the genes, functional pathways, and immune infiltration characteristics of the occurrence and development of tendinopathy. The gene expression profile of GSE106292, GSE26051 and GSE167226 are downloaded from GEO (NCBI comprehensive gene expression database) and analyzed by WGCNA software bag using R software, GSE26051, GSE167226 data set is combined to screen the differential gene analysis. We subsequently performed gene enrichment analysis of Gene Ontology (GO) and "Kyoto Encyclopedia of Genes and Genomes" (KEGG), and immune cell infiltration analysis. By constructing the LASSO regression model, Support vector machine (SVM-REF) and Gaussian mixture model (GMMs) algorithms are used to screen, to identify early diagnostic genes. We have obtained a total of 171 DEGs through WGCNA analysis and differentially expressed genes (DEGs) screening. By GO and KEGG enrichment analysis, it is found that these dysregulated genes were related to mTOR, HIF-1, MAPK, NF-κB and VEGF signaling pathways. Immune infiltration analysis showed that M1 macrophages, activated mast cells and activated NK cells had infiltration significance. After analysis of THE LASSO SVM-REF and GMMs algorithms, we found that the gene MACROD1 may be a gene for early diagnosis. We identified the potential of tendon disease early diagnosis way and immune gene regulation MACROD1 key infiltration characteristics based on comprehensive bioinformatics analysis. These hub genes and functional pathways may as early biomarkers of tendon injuries and molecular therapy level target is used to guide drug and basic research.

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.

N-acetylcysteine reduces glutamate-induced cytotoxicity to fibroblasts of rat supraspinatus tendons

Purpose: Neuronal theory regarding rotator cuff degeneration has developed from the findings that glutamate, an amino acid and an excitatory neurotransmitter, is present in increased concentrations in tendon tissues with tendinopathy and that glutamate induces cell death in fibroblasts of origin in rat supraspinatus tendon. The purpose of the current study was to determine whether N-acetylcysteine (NAC) has cytoprotective effects against glutamate-induced fibroblast death. Materials and Methods: Primary cultured fibroblasts were obtained from rat supraspinatus tendons. Varying concentrations of glutamate (0.5, 1, 5, and 10 mM) and of NAC (0.5, 1, 2, and 5 mM) were used for evaluation of cytotoxicity. Cell viability, cell cycles, types of cell death, intracellular ROS production, expressions of caspase-3/7, and Ca²⁺ influx were evaluated. Results: Glutamate significantly induced cell death, apoptosis, and Ca²⁺ influx and significantly increased caspase-3/7 activity and intracellular ROS production (p < 0.001). NAC significantly reduced the glutamate-induced cell death, apoptosis, Ca²⁺ influx, caspase-3/7 activity, and intracellular ROS production (p < 0.001). Conclusions: The glutamate-induced cytotoxic effects can be reduced by NAC, an antioxidant, through the reduction of intracellular oxidative stress and/or Ca²⁺ influx.

More tendon degeneration in patients with shoulder osteoarthritis

PURPOSE

Tendon disorders are a major problem in the general population. It is known that rotator cuff tendinopathy contributes to osteoarthritis (OA) of the shoulder. The aim of the study was to analyse the presence of tendinopathy in patients with shoulder OA and an intact rotator cuff, using a multimodal approach.

METHODS

Thirteen consecutive patients median age 67 (52-84) years, with OA of the shoulder, and 13 consecutive control patients, with a fracture of the proximal humerus, median age 70 (51-84) years, underwent an open biopsy procedure from the biceps and subscapularis tendon in conjunction with shoulder arthroplasty. In addition to a macroscopic evaluation, the samples underwent histologic, morphologic and ultrastructural analyses in light and transmission electron microscopy.

RESULTS

Macroscopic degeneration was found in 15 of 26 specimen in the OA group but in seven of 25 in the control group (p = 0.048). The histologic analysis revealed a non-significant difference for the total degeneration score (TDS) between the study groups. The morphologic evaluation of the samples revealed that the OA group had significantly more samples with non-homogeneous extracellular matrix (ECM), (p = 0.048). Ultrastructurally, the OA group revealed a significantly larger fibril diameter in the biceps tendon (p < 0.0001) but not in the subscapularis tendon compared with the control group.

CONCLUSION

A significantly worse macroscopic appearance and significantly more morphologically inhomogeneous ECM, indicating more tendon degeneration, were found in the OA group compared with the control group. This indicates that it could be beneficial to treat the tendinosis in an early stage to decrease symptoms from the OA.

STUDY DESIGN

Level of evidence, III.

A Systematic Summary of Systematic Reviews on the Topic of the Rotator Cuff

BACKGROUND

The number of systematic reviews and meta-analyses published on the rotator cuff (RC) has increased markedly.

PURPOSE

To quantify the number of systematic reviews and meta-analyses published on the RC and to provide a qualitative summary of the literature.

STUDY DESIGN

Systematic review; Level of evidence, 4.

METHODS

A systematic search for all systematic reviews and meta-analyses pertaining to the RC published between January 2007 and September 2017 was performed with PubMed, MEDLINE, and the Cochrane Database of Systematic Reviews. Narrative reviews and non-English language articles were excluded.

RESULTS

A total of 1078 articles were found, of which 196 met the inclusion criteria. Included articles were summarized and divided into 15 topics: anatomy and function, histology and genetics, diagnosis, epidemiology, athletes, nonoperative versus operative treatment, surgical repair methods, concomitant conditions and surgical procedures, RC tears after total shoulder arthroplasty, biological augmentation, postoperative rehabilitation, outcomes and complications, patient-reported outcome measures, cost-effectiveness of RC repair, and quality of randomized controlled trials.

CONCLUSION

A qualitative summary of the systematic reviews and meta-analyses published on the RC can provide surgeons with a single source of the most current literature.

Integrity of the Untorn Articular-Sided Tendon in Bursal-Sided Partial-Thickness Rotator Cuff Tear: A Comparative Study of Apoptotic Activity in Torn and Untorn Layers

BACKGROUND

Conversion to full-thickness tear in partial-thickness rotator cuff tears (PTRCTs) is based on the quality and thickness of the normal-looking untorn rotator cuff layer. However, whether the untorn tendon is a healthy tissue remains to be elucidated.

PURPOSE

To compare the apoptotic gene expression of the untorn articular layer with the torn bursal layer in PTRCTs.

STUDY DESIGN

Controlled laboratory study.

METHODS

Tendon tissues were harvested from 20 patients undergoing arthroscopic surgery for partial-thickness rotator cuff repair. As a control group, the tissues were harvested during intramedullary nail fixation in 10 proximal humeral fractures. In the experimental group, the samples were harvested from 2 sites: the torn bursal-sided tendon and the untorn articular-sided tendon. Hematoxylin and eosin (H&E) staining was conducted for basic histological evaluation, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining was used to detect apoptosis of tissue cells. The expression of caspase 3, 8, and 9 was confirmed immunohistochemically. Western blot analysis was used to assay the caspase activities.

RESULTS

In H&E staining, the direction of collagen bundles in untorn tendon was disoriented when compared with those of control tendon. However, the shape of the nuclei was not different, although the nuclei of the untorn tendon showed apoptosis in the TUNEL staining similar to those of the torn tendon. The immunohistochemical staining of caspase 3, 8, and 9 was increased concomitantly in untorn and torn tendons. All of the caspase activities in the untorn articular layer and torn bursal layer were significantly higher than in controls ( P < .05). However, no significant differences were found between the two layers ( P > .05).

CONCLUSION

The study demonstrates that apoptotic gene expression is increased not only in the torn bursal layer but also in the untorn articular layer of PTRCTs.

CLINICAL RELEVANCE

The untorn articular layer of PTRCTs is abnormal, which triggers postoperative pain and further rotator cuff tears. Therefore, treatment of the abnormal untorn articular layer is essential in bursal-sided PTRCTs.

Longer duration of operative time enhances healing metabolites and improves patient outcome after Achilles tendon rupture surgery

PURPOSE

The relationship between the duration of operative time (DOT), healing response and patient outcome has not been previously investigated. An enhanced healing response related to DOT may potentiate repair processes, especially in hypovascular and sparsely metabolized musculoskeletal tissues such as tendons. This study aimed to investigate the association between DOT and the metabolic healing response, patient-reported outcome and the rate of post-operative complications after acute Achilles tendon injury.

METHODS

Observational cohort, cross-sectional study with observers blinded to patient grouping. A total of two-hundred and fifty-six prospectively randomized patients (210 men, 46 women; mean age 41 years) with an acute total Achilles tendon rupture all operated on with uniform anaesthetic and surgical technique were retrospectively assessed. At 2 weeks post-operatively, six metabolites were quantified using microdialysis. At 3, 6 and 12 months, patient-reported pain, walking ability and physical activity were examined using self-reported questionnaires, Achilles tendon total rupture score, foot and ankle outcome score and physical activity scale. At 12 months, functional outcome was assessed using the heel-rise test. Complications, such as deep venous thrombosis, infections and re-operations, were recorded throughout the study.

RESULTS

Patients who underwent longer DOT exhibited higher levels of glutamate (p = 0.026) and glycerol (p = 0.023) at 2 weeks. At the 1-year follow-up, longer DOT was associated with significantly less loss in physical activity (p = 0.003), less pain (p = 0.009), less walking limitations (p = 0.022) and better functional outcome (p = 0.014). DOT did not significantly correlate with the rate of adverse events, such as deep venous thrombosis, infections or re-ruptures. Higher glutamate levels were associated with less loss in physical activity (p = 0.017). All correlations were confirmed by multiple linear regressions taking confounding factors into consideration.

CONCLUSION

The results from this study suggest a previously unknown mechanism, increased metabolic response associated with longer DOT, which may improve patient outcome after Achilles tendon rupture surgery. Allowing for a higher amount of traumatized tissue, as reflected by up-regulation of glycerol in patients with longer DOT, may prove to be an important surgical tip for stimulation of repair of hypometabolic soft tissue injuries, such as Achilles tendon ruptures.

LEVEL OF EVIDENCE

II.

Differences of RNA Expression in the Tendon According to Anatomic Outcomes in Rotator Cuff Repair

BACKGROUND

Despite increased understanding of the pathophysiology of rotator cuff tears and the evolution of rotator cuff repair, healing failure remains a substantial problem. The critical roles played by biological factors have been emphasized, but little is known of the implications of gene expression profile differences at the time of repair.

PURPOSE

To document the relationship between the perioperative gene expression of healed and unhealed rotator cuffs by RNA microarray analysis.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

Superior (supraspinatus involvement) and posterosuperior (supraspinatus and infraspinatus involvement) tears were included in the study. Samples of rotator cuff tendons were prospectively collected during rotator cuff surgery. Three samples were harvested at the tendon ends of tears from the anterior, middle (apex), and posterior parts using an arthroscopic punch. Seven patients with an unhealed rotator cuff were matched one-to-one with patients with a healed rotator cuff by sex, age, tear size, and fatty degeneration of rotator cuff muscles. mRNA microarray analysis was used to identify genetic differences between healed and unhealed rotator cuff tendons. Gene ontology and gene association files were obtained from the Gene Ontology Consortium, and the Gene Ontology system in DAVID was used to identify enhanced biological processes.

RESULTS

Microarray analyses identified 262 genes that were differentially expressed by at least 1.5-fold between the healed and unhealed groups. Overall, in the healed group, 103 genes were significantly downregulated, and 159 were significantly upregulated. DAVID Functional Annotation Cluster analysis showed that in the healed group, the genes most upregulated were related to the G protein-coupled receptor protein signaling pathway and to the neurological system. On the other hand, the genes most downregulated were related to immune and inflammatory responses. BMP5 was the gene most upregulated in the healed group, and the majority of downregulated genes were involved in the immune/inflammatory response.

CONCLUSION

The downregulation of inflammatory response genes and the upregulation of cell differentiation genes in torn rotator cuffs at the time of surgery are related to rotator cuff healing. These results provide useful baseline information for future biological studies on rotator cuff healing.

Review: Emerging concepts in the pathogenesis of tendinopathy

Tendinopathy is a common clinical problem and has a significant disease burden attached, not only in terms of health care costs, but also for patients directly in terms of time off work and impact upon quality of life. Controversy surrounds the pathogenesis of tendinopathy, however the recent systematic analysis of the evidence has demonstrated that many of the claims of an absence of inflammation in tendinopathy were more based around belief than robust scientific data. This review is a summary of the emerging research in this topical area, with a particular focus on the role of neuronal regulation and inflammation in tendinopathy.

Mini-Review: Toxic Tendinopathy

Toxic tendinopathy is a rare but reproducible complication in humans, given agents of four drug classes: aromatase inhibitors, fluoroquinolone antibiotics, glucocorticoids (long-term regimens), and statins. Toxic tendinopathy in humans has been linked less consistently to treatment with anabolic steroids, antiretroviral agents (mainly protease inhibitors), metalloproteinase inhibitors (MMPI), and isotretinoin. Classic drug-induced tendinopathies appear as "tendinosis" (i.e., progressive tendon degeneration without inflammation), although cases associated with aromatase inhibitors exhibit mainly tenosynovitis. Any tendon may be affected, but fluoroquinolones, glucocorticoids, and statins most frequently affect large load-bearing tendons in the lower limb, especially the calcaneal ("Achilles") tendon-which ruptures in approximately 30 to 40% of cases. The time to symptom onset ranges from days (fluoroquinolones) to weeks, months, or even years. The pathogenesis is incompletely understood, but proposed mechanisms include apoptosis of tenoblasts and tenocytes, deficient tenocyte function (leading to abnormal extracellular matrix maintenance and repair as well as disrupted intercellular signaling), and structural disintegration (via a combination of increased expression of lytic enzymes, lessened cholesterol content in cell membranes, and neoangiogenesis within highly ordered tendon tissue). Nonclinical safety assessment of therapeutic candidates in these drug classes should incorporate tendon routinely as a protocol-specified tissue for pathology evaluation.

Glutamate signaling through the NMDA receptor reduces the expression of scleraxis in plantaris tendon derived cells

Background

A body of evidence demonstrating changes to the glutaminergic system in tendinopathy has recently emerged. This hypothesis was further tested by studying the effects of glutamate on the tenocyte phenotype, and the impact of loading and exposure to glucocorticoids on the glutamate signaling machinery.

Methods

Plantaris tendon tissue and cultured plantaris tendon derived cells were immunohisto-/cytochemically stained for glutamate, N-Methyl-D-Aspartate receptor 1 (NMDAR1) and vesicular glutamate transporter 2 (VGluT2). Primary cells were exposed to glutamate or receptor agonist NMDA. Cell death/viability was measured via LDH/MTS assays, and Western blot for cleaved caspase 3 (c-caspase 3) and cleaved poly (ADP-ribose) polymerase (c-PARP). Scleraxis mRNA (Scx)/protein(SCX) were analyzed by qPCR and Western blot, respectively. A FlexCell system was used to apply cyclic strain. The effect of glucocorticoids was studies by adding dexamethasone (Dex). The mRNA of the glutamate synthesizing enzymes Got1 and Gls, and NMDAR1 protein were measured. Levels of free glutamate were determined by a colorimetric assay.

Results

Immunoreactions for glutamate, VGluT2, and NMDAR1 were found in tenocytes and peritendinous cells in tissue sections and in cultured cells. Cell death was induced by high concentrations of glutamate but not by NMDA. Scleraxis mRNA/protein was down-regulated in response to NMDA/glutamate stimulation. Cyclic strain increased, and Dex decreased, Gls and Got1 mRNA expression. Free glutamate levels were lower after Dex exposure.

Conclusions

In conclusion, NMDA receptor stimulation leads to a reduction of scleraxis expression that may be involved in a change of phenotype in tendon cells. Glutamate synthesis is increased in tendon cells in response to strain and decreased by glucocorticoid stimulation. This implies that locally produced glutamate could be involved in the tissue changes observed in tendinopathy.

Efficacy of platelet-rich plasma injections in pain associated with chronic tendinopathy: A systematic review

BACKGROUND

Chronic tendinopathy has often been a management dilemma for general practitioners. With our understanding of the pathophysiology of tendinopathy evolving, so has our management, with the advent of newer strategies such as topical glycerol trinitrate, extracorporeal shock-wave therapy, as well as platelet-rich plasma (PRP).

AIM

To systematically review the literature regarding PRP therapy in chronic tendinopathy.

DESIGN AND SETTING

The databases used in our search include the Elton B. Stephens Co. (EBSCO) database, Medline, the Cochrane library, Ovid, and Embase (the Excerpta Medica database). A total of 389 articles were reviewed from Feb 2010 to April 2014, for possible inclusion. Of these articles, a total of 9 randomized controlled trials (RCTs) met our inclusion criteria. Only 1 RCT was excluded due to previous surgery in both the trial and control groups.

METHODS

Each article was reviewed independently by 2 authors. Each article was analyzed using the Cochrane Criteria checklist. Where any discrepancy occurred in results, a third independent reviewer was consulted.

RESULTS

Our review found that PRP was most effective in patellar and lateral epicondylar tendinopathy, with both RCTs in the patellar section of our study supporting the use of PRP in pain reduction at 3 and 12 months, whereas 2 of 4 studies in the lateral epicondylar section showed improvements in pain and disability at 6 and 12 months. There was a lack of evidence to support the use of PRP in Achilles and rotator cuff tendinopathy.

CONCLUSIONS

Although the results of this review show promise for the use of PRP in chronic tendinopathy, the analysis highlighted the need for more controlled clinical trials comparing PRP with placebo.

Transcriptome analysis of ageing in uninjured human Achilles tendon

INTRODUCTION

The risk of tendon injury and disease increases significantly with increasing age. The aim of the study was to characterise transcriptional changes in human Achilles tendon during the ageing process in order to identify molecular signatures that might contribute to age-related degeneration.

METHODS

RNA for gene expression analysis using RNA-Seq and quantitative real-time polymerase chain reaction analysis was isolated from young and old macroscopically normal human Achilles tendon. RNA sequence libraries were prepared following ribosomal RNA depletion, and sequencing was undertaken by using the Illumina HiSeq 2000 platform. Expression levels among genes were compared by using fragments per kilobase of exon per million fragments mapped. Differentially expressed genes were defined by using Benjamini-Hochberg false discovery rate approach (P<0.05, expression ratios 1.4 log2 fold change). Alternative splicing of exon variants were also examined by using Cufflinks. The functional significance of genes that showed differential expression between young and old tendon was determined by using ingenuity pathway analysis.

RESULTS

In total, the expression of 325 transcribed elements, including protein-coding transcripts and non-coding transcripts (small non-coding RNAs, pseudogenes, long non-coding RNAs and a single microRNA), was significantly different in old compared with young tendon (±1.4 log2 fold change, P<0.05). Of these, 191 were at higher levels in older tendon and 134 were at lower levels in older tendon. The top networks for genes differentially expressed with tendon age were from cellular function, cellular growth, and cellular cycling pathways. Notable differential transcriptome changes were also observed in alternative splicing patterns. Several of the top gene ontology terms identified in downregulated isoforms in old tendon related to collagen and post-translational modification of collagen.

CONCLUSIONS

This study demonstrates dynamic alterations in RNA with age at numerous genomic levels, indicating changes in the regulation of transcriptional networks. The results suggest that ageing is not primarily associated with loss of ability to synthesise matrix proteins and matrix-degrading enzymes. In addition, we have identified non-coding RNA genes and differentially expressed transcript isoforms of known matrix components with ageing which require further investigation.

Up-regulation of Glutamate in Painful Human Supraspinatus Tendon Tears

BACKGROUND

Pain related to rotator cuff tendinopathy is a common problem, but little is known regarding the origin and cause of pain from the tendon substance. No study to date has looked at the association between tissue changes and patient outcomes.

PURPOSE

To describe the peripheral neuronal phenotype in painful rotator cuff tears and to determine correlations between tissue changes and clinical outcome measures.

STUDY DESIGN

Controlled laboratory study.

METHODS

Tissue samples of the supraspinatus were taken from patients undergoing surgery to repair a rotator cuff tendon tear. Patients were classified as having small/medium or large/massive tears. Control tissue was obtained from patients undergoing surgery for posttraumatic shoulder instability. Immunohistochemical techniques were performed using antibodies to known nociceptive and neuronal markers as well as general tissue structural markers.

RESULTS

There was no correlation between tissue changes and patient-reported outcomes. A significant increase in the expression of glutamate was seen in tendon tears. There were differences in the expression of metabotropic and ionotropic glutamate receptors. Expression changes were also observed for markers of the sensory and autonomic systems; however, no differences were found in neurotrophins.

CONCLUSION

Glutamate and the glutaminergic system play a key role in painful human tendon tears; however, the exact role is still uncertain, as glutamate is highly involved in both pain and metabolic pathways.

CLINICAL RELEVANCE

This study has identified a number of markers that could be potential therapeutic targets.

Clinical outcome and repair integrity after rotator cuff repair in patients older than 70 years versus patients younger than 70 years

PURPOSE

The purpose of this study was to evaluate and compare the clinical and structural outcomes of rotator cuff repairs in patients older than 70 years and those younger than 70 years and to analyze a correlation between patient factors and retear rate.

METHODS

Two hundred thirty-eight patients between the ages of 60 and 79 who underwent rotator cuff repair between 2006 and 2011 and were available for postoperative magnetic resonance imaging (MRI) evaluation at least 6 months after surgery were enrolled in this study. They were divided into 2 groups, one group (n = 191) included patients aged between 60 and 69 years, and the other group (n = 47) included patients aged between 70 and 79 years. The mean follow-up period was 14.6 months (range, 12-63 months) and 13.2 months (range, 12-62 months) for patients in their 60s and 70s, respectively.

RESULTS

The mean visual analog scale (VAS), University of California Los Angeles (UCLA), and Constant scores significantly improved from 5.4, 18.1, and 57.4 preoperatively to 1.0, 31.2, and 75.0 at the final follow-up, respectively (P < .001), in the 60s group and from 5.9, 17.0, and 53.6 to 1.3, 30.1, and 72.7, respectively (P < .001), in the 70s group. There were no significant differences between the 2 groups (P > .05). Instead, intraoperative tear size was correlated with the clinical scores with Pearson correlation coefficients of -0.161 and -0.211 for patients in their 60s and 70s, respectively. There were 76 (39.8%) retears among patients in their 60s and 24 (51.1%) retears among patients in their 70s, with no significant difference between the 2 groups (P = .161). The retear rate increased significantly with increasing preoperative tear size (P < .001; odds ratio [OR], 7.1 in large tears; P < .0001; OR, 17.2 in massive tears). Age and sex were not significantly correlated with the retear rate.

CONCLUSIONS

Both patients in their 60s and 70s showed significant improvement in clinical outcomes after rotator cuff repair, without a significant difference between the 2 populations. The retear rate increased significantly with increasing intraoperative tear size but not with increasing age.

LEVEL OF EVIDENCE

Level III, case-control study.

Glucocorticoids induce specific ion-channel-mediated toxicity in human rotator cuff tendon: a mechanism underpinning the ultimately deleterious effect of steroid injection in tendinopathy?

BACKGROUND

Glucocorticoid injection (GCI) and surgical rotator cuff repair are two widely used treatments for rotator cuff tendinopathy. Little is known about the way in which medical and surgical treatments affect the human rotator cuff tendon in vivo. We assessed the histological and immunohistochemical effects of these common treatments on the rotator cuff tendon.

STUDY DESIGN

Controlled laboratory study.

METHODS

Supraspinatus tendon biopsies were taken before and after treatment from 12 patients undergoing GCI and 8 patients undergoing surgical rotator cuff repair. All patients were symptomatic and none of the patients undergoing local GCI had full thickness tears of the rotator cuff. The tendon tissue was then analysed using histological techniques and immunohistochemistry.

RESULTS

There was a significant increase in nuclei count and vascularity after rotator cuff repair and not after GCI (both p=0.008). Hypoxia inducible factor 1α (HIF-1α) and cell proliferation were only increased after rotator cuff repair (both p=0.03) and not GCI. The ionotropic N-methyl-d-aspartate receptor 1 (NMDAR1) glutamate receptor was only increased after GCI and not rotator cuff repair (p=0.016). An increase in glutamate was seen in both groups following treatment (both p=0.04), while an increase in the receptor metabotropic glutamate receptor 7 (mGluR7) was only seen after rotator cuff repair (p=0.016).

CONCLUSIONS

The increases in cell proliferation, vascularity and HIF-1α after surgical rotator cuff repair appear consistent with a proliferative healing response, and these features are not seen after GCI. The increase in the glutamate receptor NMDAR1 after GCI raises concerns about the potential excitotoxic tendon damage that may result from this common treatment.

IL-21 receptor expression in human tendinopathy

The pathogenetic mechanisms underlying tendinopathy remain unclear, with much debate as to whether inflammation or degradation has the prominent role. Increasing evidence points toward an early inflammatory infiltrate and associated inflammatory cytokine production in human and animal models of tendon disease. The IL-21/IL-21R axis is a proinflammatory cytokine complex that has been associated with chronic inflammatory diseases including rheumatoid arthritis and inflammatory bowel disease. This project aimed to investigate the role and expression of the cytokine/receptor pair IL-21/IL-21R in human tendinopathy. We found significantly elevated expression of IL-21 receptor message and protein in human tendon samples but found no convincing evidence of the presence of IL-21 at message or protein level. The level of expression of IL-21R message/protein in human tenocytes was significantly upregulated by proinflammatory cytokines (TNFα/IL-1β) in vitro. These findings demonstrate that IL-21R is present in early human tendinopathy mainly expressed by tenocytes and macrophages. Despite a lack of IL-21 expression, these data again suggest that early tendinopathy has an inflammatory/cytokine phenotype, which may provide novel translational targets in the treatment of tendinopathy.

Current concepts in examination and treatment of elbow tendon injury

Context:

Injuries to the tendons of the elbow occur frequently in the overhead athlete, creating a significant loss of function and dilemma to sports medicine professionals. A detailed review of the anatomy, etiology, and pathophysiology of tendon injury coupled with comprehensive evaluation and treatment information is needed for clinicians to optimally design treatment programs for rehabilitation and prevention.

Evidence Acquisitions:

The PubMed database was searched in January 2012 for English-language articles pertaining to elbow tendon injury.

Results:

Detailed information on tendon pathophysiology was found along with incidence of elbow injury in overhead athletes. Several evidence-based reviews were identified, providing a thorough review of the recommended rehabilitation for elbow tendon injury.

Conclusions:

Humeral epicondylitis is an extra-articular tendon injury that is common in athletes subjected to repetitive upper extremity loading. Research is limited on the identification of treatment modalities that can reduce pain and restore function to the elbow. Eccentric exercise has been studied in several investigations and, when coupled with a complete upper extremity strengthening program, can produce positive results in patients with elbow tendon injury. Further research is needed in high-level study to delineate optimal treatment methods.

Neuronal regulation of tendon homoeostasis

The regulation of tendon homoeostasis, including adaptation to loading, is still not fully understood. Accumulating data, however, demonstrates that in addition to afferent (sensory) functions, the nervous system, via efferent pathways which are associated with through specific neuronal mediators plays an active role in regulating pain, inflammation and tendon homeostasis. This neuronal regulation of intact-, healing- and tendinopathic tendons has been shown to be mediated by three major groups of molecules including opioid, autonomic and excitatory glutamatergic neuroregulators. In intact healthy tendons the neuromediators are found in the surrounding structures: paratenon, endotenon and epitenon, whereas the proper tendon itself is practically devoid of neurovascular supply. This neuroanatomy reflects that normal tendon homoeostasis is regulated from the tendon surroundings. After injury and during tendon repair, however, there is extensive nerve ingrowth into the tendon proper, followed by a time-dependent emergence of sensory, autonomic and glutamatergic mediators, which amplify and fine-tune inflammation and regulate tendon regeneration. In tendinopathic condition, excessive and protracted presence of sensory and glutamatergic neuromediators has been identified, suggesting involvement in inflammatory, nociceptive and hypertrophic (degenerative) tissue responses. Under experimental and clinical conditions of impaired (e.g. diabetes) as well as excessive (e.g. tendinopathy) neuromediator release, dysfunctional tendon homoeostasis develops resulting in chronic pain and gradual degeneration. Thus there is a prospect that in the future pharmacotherapy and tissue engineering approaches targeting neuronal mediators and their receptors may prove to be effective therapies for painful, degenerative and traumatic tendon disorders.

Heat shock proteins in tendinopathy: novel molecular regulators

Tendon disorders—tendinopathies—are the primary reason for musculoskeletal consultation in primary care and account for up to 30% of rheumatological consultations. Whilst the molecular pathophysiology of tendinopathy remains difficult to interpret the disease process involving repetitive stress, and cellular load provides important mechanistic insight into the area of heat shock proteins which spans many disease processes in the autoimmune community. Heat shock proteins, also called damage-associated molecular patterns (DAMPs), are rapidly released following nonprogrammed cell death, are key effectors of the innate immune system, and critically restore homeostasis by promoting the reconstruction of the effected tissue. Our investigations have highlighted a key role for HSPs in tendion disease which may ultimately affect tissue rescue mechanisms in tendon pathology. This paper aims to provide an overview of the biology of heat shock proteins in soft tissue and how these mediators may be important regulators of inflammatory mediators and matrix regulation in tendinopathy.

Tendinopathy in sport

CONTEXT

Tendinopathy is increasing in prevalence and accounts for a substantial part of all sports injuries and occupational disorders. Despite the magnitude of the disorder, high-quality scientific data on etiology and available treatments have been limited.

EVIDENCE ACQUISITION

The authors conducted a MEDLINE search on tendinopathy, or "tendonitis" or "tendinosis" or "epicondylitis" or "jumpers knee" from 1980 to 2011. The emphasis was placed on updates on epidemiology, etiology, and recent patient-oriented Level 1 literature.

RESULTS

Repetitive exposure in combination with recently discovered intrinsic factors, such as genetic variants of matrix proteins, and metabolic disorders is a risk factor for the development of tendinopathy. Recent findings demonstrate that tendinosis is characterized by a fibrotic, failed healing response associated with pathological vessel and sensory nerve ingrowth. This aberrant sensory nerve sprouting may partly explain increased pain signaling and partly, by release of neuronal mediators, contribute to the fibrotic alterations observed in tendinopathy. The initial nonoperative treatment should involve eccentric exercise, which should be the cornerstone (basis) of treatment of tendinopathy. Eccentric training combined with extracorporeal shockwave treatment has in some reports shown higher success rates compared to any therapies alone. Injection therapies (cortisone, sclerosing agents, blood products including platelet-rich plasma) may have short-term effects but have no proven long-term treatment effects or meta-analyses to support them. For epicondylitis, cortisone injections have demonstrated poorer long-time results than conservative physiotherapy. Today surgery is less indicated because of successful conservative therapies. New minioperative procedures that, via the endoscope, remove pathologic tissue or abnormal neoinnervation demonstrate promising results but need confirmation by Level 1 studies.

CONCLUSIONS

Novel targeted therapies are emerging, but multicenter trials are needed to confirm the results of exercise and mini-invasive treatments.

A systematic review of the histological and molecular changes in rotator cuff disease

INTRODUCTION

The pathogenesis of rotator cuff disease (RCD) is complex and not fully understood. This systematic review set out to summarise the histological and molecular changes that occur throughout the spectrum of RCD.

METHODS

We conducted a systematic review of the scientific literature with specific inclusion and exclusion criteria.

RESULTS

A total of 101 studies met the inclusion criteria: 92 studies used human subjects exclusively, seven used animal overuse models, and the remaining two studies involved both humans and an animal overuse model. A total of 58 studies analysed supraspinatus tendon exclusively, 16 analysed subacromial bursal tissue exclusively, while the other studies analysed other tissue or varying combinations of tissue types including joint fluid and muscle. The molecular biomarkers that were altered in RCD included matrix substances, growth factors, enzymes and other proteins including certain neuropeptides.

CONCLUSIONS

The pathogenesis of RCD is being slowly unravelled as a result of the significant recent advances in molecular medicine. Future research aimed at further unlocking these key molecular processes will be pivotal in developing new surgical interventions both in terms of the diagnosis and treatment of RCD.

Cytokines in rotator cuff degeneration and repair

The pathogenesis of rotator cuff degeneration remains poorly defined, and the incidence of degenerative tears is increasing in the aging population. Rates of recurrent tear and incomplete tendon-to-bone healing after repair remain significant for large and massive tears. Previous studies have documented a disorganized, fibrous junction at the tendon-to-bone interface after rotator cuff healing that does not recapitulate the organization of the native enthesis. Many biologic factors have been implicated in coordinating tendon-to-bone healing and maintenance of the enthesis after rotator cuff repair, including the expression and activation of transforming growth factor-β, basic fibroblast growth factor, platelet-derived growth factor-β, matrix metalloproteinases, and tissue inhibitors of metalloproteinases. Future techniques to treat tendinopathy and enhance tendon-to-bone healing will be driven by our understanding of the biology of this healing process after rotator cuff repair surgery. The use of cytokines to provide important signals for tissue formation and differentiation, the use of gene therapy techniques to provide sustained cytokine delivery, the use of stem cells, and the use of transcription factors to modulate endogenous gene expression represent some of these possibilities.

Lessons we can learn from gene expression patterns in rotator cuff tears and tendinopathies

Persistently high failure rates that are reported after rotator cuff repairs have encouraged greater understanding of the pathophysiology that underlies rotator cuff tears. Biologic changes that contribute to the pathogenesis of rotator cuff tears and tendinopathies, as well as adaptation after these changes, have been well described. A subset of patients with a genetic predisposition to early onset of rotator cuff tears and earlier symptom and disease progression have been identified. Many biologic changes occurring at the gene level have been identified. Pathways that are believed to contribute to rotator cuff tendinopathies include extracellular matrix remodeling, angiogenesis, changes in metabolism, apoptosis, and stress-related genes. Metaplasia of rotator cuff cells is contributed to by changes in gene expression. Modification of these gene changes may be possible through mechanical loading, drugs, or cellular manipulation. Gene changes may offer greater insight into why certain tears fail to heal and help to identify therapeutic targets.

Alterations of overused supraspinatus tendon: a possible role of glycosaminoglycans and HARP/pleiotrophin in early tendon pathology

Supraspinatus tendon overuse injuries lead to significant pain and disability in athletes and workers. Despite the prevalence and high social cost of these injuries, the early pathological events are not well known. We analyzed the potential relation between glycosaminoglycan (GAG) composition and phenotypic cellular alteration using a rat model of rotator cuff overuse. Total sulfated GAGs increased after 4 weeks of overuse and remained elevated up to 16 weeks. GAG accumulation was preceded by up-regulation of decorin, versican, and aggrecan proteoglycans (PGs) mRNAs and proteins and biglycan PG mRNA after 2 weeks. At 2 weeks, collagen 1 transcript decreased whereas mRNAs for collagen 2, collagen 3, collagen 6, and the transcription factor Sox9 were increased. Protein levels of heparin affine regulatory peptide (HARP)/pleiotrophin, a cytokine known to regulate developmental chondrocyte formation, were enhanced especially at 4 weeks, without up-regulation of HARP/pleiotrophin mRNA. Further results suggest that the increased GAGs present in early lesions may sequester HARP/pleiotrophin, which could contribute to a loss of tenocyte's phenotype. All these modifications are characteristic of a shift towards the chondrocyte phenotype. Identification of these early changes in the extra-cellular matrix may help to prevent the progression of the pathology to more disabling, degenerative alterations.

Biological factors in the pathogenesis of rotator cuff tears

Rotator cuff tears are common, and lead to shoulder pain and functional impairment. Despite their frequency and related disability, etiology and pathogenesis are still debated. Multiple factors contribute to tears of the rotator cuff. Extrinsic factors are anatomic variables, such as acromial morphologic characteristics, os acromiale, and acromial spurs that compress the rotator cuff by bony impingement or direct pressure from the surrounding soft tissue. Intrinsic factors arise from the tendon itself, because of tensile overload, aging, microvascular supply, traumatisms, or degeneration. Little information is available from a cellular and molecular point of view. We reviewed the biological factors involved in the pathogenesis of rotator cuff tears. Understanding the mechanism of rotator cuff pathology would facilitate the rationale for therapeutic interventions, by guiding the design, selection, and implementation of treatment strategies such as biologic modulation and preventive measures.

Gap junctions in IL-1β-mediated cell survival response to strain

Mechanical stimuli play important roles in proliferation and differentiation of connective tissue cells, and development and homeostatic maintenance of tissues. However, excessive mechanical loading to a tissue can injure cells and disrupt the matrix, as occurs in tendinopathy. Tendinopathy is a common clinical problem in athletes and in many occupational settings due to overuse of the tendon. Moreover, interleukin (IL)-1β is generally considered to be a "bad" cytokine, activating NF-κb and cell death and inducing matrix metalloproteinase (MMPs 1, 2, 3) expression and matrix destruction. However, activated NF-κB can also drive a cell survival pathway. We have reported that cyclic strain induced tenocyte death in three-dimensional (3D) cultures, and IL-1β could promote cell survival under strain. Therefore, it was hypothesized that 1) cyclic strain could induce cell death in tenocytes as observed in pathologic tendons in vivo; 2) a gene expression profile indicative of tendinopathy could be identified; and 3) low-dose IL-1β could protect cells from strain-induced, tendinopathy-like changes. Human tenocytes were cultured in 3D type I collagen hydrogels and subjected to 3.5% elongation at 1 Hz for 1 h/day for up to 5 days with or without IL-1β. Real-time RT-PCR data showed that cyclic strain regulated the expression of tendinopathy marker genes in a manner similar to that found in pathological tendons from patients and that addition of IL-1β reversed the gene expression changes to control levels. Results of further studies showed that IL-1β may modulate cell survival through upregulating the expression of connexin 43, which is involved in the modulation of cell death/survival in a variety of cells and tissues. The elucidation of the mechanisms underlying strain-induced cell death and recovery from strain injury will facilitate our understanding of the pathogenesis of tendinopathy and may lead to the discovery of new molecular targets for early diagnosis and treatment of tendinopathy.

Mid-portion Achilles tendinopathy: why painful? An evidence-based philosophy

Chronic mid-portion Achilles tendinopathy is generally difficult to treat as the background to the pain mechanisms has not yet been clarified. A wide range of conservative and surgical treatment options are available. Most address intratendinous degenerative changes when present, as it is believed that these changes are responsible for the symptoms. Since up to 34% of asymptomatic tendons show histopathological changes, we believe that the tendon proper is not the cause of pain in the majority of patients. Chronic painful tendons show the ingrowth of sensory and sympathetic nerves from the paratenon with release of nociceptive substances. Denervating the Achilles tendon by release of the paratenon is sufficient to cause pain relief in the majority of patients. This type of treatment has the additional advantage that it is associated with a shorter recovery time when compared with treatment options that address the tendon itself. An evidence-based philosophy on the cause of pain in chronic mid-portion Achilles tendinopathy is presented. Level of evidence V.

Retro-trochanteric sciatica-like pain: current concept

The aim of this manuscript is to review the current knowledge in terms of retro-trochanteric pain syndrome, make recommendations for diagnosis and differential diagnosis and offer suggestions for treatment options. The terminology in the literature is confusing and these symptoms can be referred to as 'greater trochanteric pain syndrome', 'trochanteric bursitis' and 'trochanteritis', among other denominations. The authors focus on a special type of sciatica, i.e. retro-trochanteric pain radiating down to the lower extremity. The impact of different radiographic assessments is discussed. The authors recommend excluding pathology in the spine and pelvic area before following their suggested treatment algorithm for sciatica-like retro-trochanteric pain.

[Tendinopathy of the tibialis anterior tendon : surgical management]

A tendinopathy of the tibialis anterior tendon is a rare clinical problem. MRI is the diagnostic tool of choice. The first-line therapy should be conservative. We report about five patients who underwent operative therapy after failed conservative treatment. The operation included débridement and augmentation of the tendon. The follow-up was at least 6 months. The mean preoperative Kitaoka score was 63 (50-68) points. After 3 months follow-up the mean Kitaoka score was up to 84 (80-90) points and at the 6-month follow-up up to 96 (94-100) points. The results showed a significant reduction of pain. Operative therapy should be considered in cases of failed conservative therapy.

Inflammation is present in early human tendinopathy

BACKGROUND

The cellular mechanisms of tendinopathy remain unclear particularly with respect to the role of inflammation in early disease. The authors previously identified increased levels of inflammatory cytokines in an early human model of tendinopathy and sought to extend these studies to the cellular analysis of tissue.

PURPOSE

To characterize inflammatory cell subtypes in early human tendinopathy, the authors explored the phenotype and quantification of inflammatory cells in torn and control tendon samples.

DESIGN

Controlled laboratory study.

METHODS

Torn supraspinatus tendon and matched intact subscapularis tendon samples were collected from 20 patients undergoing arthroscopic shoulder surgery. Control samples of subscapularis tendon were collected from 10 patients undergoing arthroscopic stabilization surgery. Tendon biopsy samples were evaluated immunohistochemically by quantifying the presence of macrophages (CD68 and CD206), T cells (CD3), mast cells (mast cell tryptase), and vascular endothelium (CD34).

RESULTS

Subscapularis tendon samples obtained from patients with a torn supraspinatus tendon exhibited significantly greater macrophage, mast cell, and T-cell expression compared with either torn supraspinatus samples or control subscapularis-derived tissue (P < .01). Inflammatory cell infiltrate correlated inversely (r = .5; P < .01) with rotator cuff tear size, with larger tears correlating with a marked reduction in all cell lineages. There was a modest but significant correlation between mast cells and CD34 expression (r = .4; P < .01) in matched subscapularis tendons from shoulders with supraspinatus ruptures.

CONCLUSION

This study provides evidence for an inflammatory cell infiltrate in early mild/moderate human tendinopathy. In particular, the authors demonstrate significant infiltration of mast cells and macrophages, suggesting a role for innate immune pathways in the events that mediate early tendinopathy. Clinical Relevance Further mechanistic studies to evaluate the net contribution and hence therapeutic utility of these cellular lineages and their downstream processes may reveal novel therapeutic approaches to the management of early tendinopathy.

Pathogenesis of tendinopathies: inflammation or degeneration?

The intrinsic pathogenetic mechanisms of tendinopathies are largely unknown and whether inflammation or degeneration has the prominent role is still a matter of debate. Assuming that there is a continuum from physiology to pathology, overuse may be considered as the initial disease factor; in this context, microruptures of tendon fibers occur and several molecules are expressed, some of which promote the healing process, while others, including inflammatory cytokines, act as disease mediators. Neural in-growth that accompanies the neovessels explains the occurrence of pain and triggers neurogenic-mediated inflammation. It is conceivable that inflammation and degeneration are not mutually exclusive, but work together in the pathogenesis of tendinopathies.

Animal models of tendinopathy

PURPOSE

The term tendinopathy describes non-ruptured tendon injuries. While several important studies have evaluated the aetiology, pathogenesis, and treatment of this common condition, further study is needed. Several animal models, which allow for full tissue evaluation on different organizational levels and stages of disease, have been used to investigate tendinopathy.

METHOD

A literature review was conducted to identify and evaluate animal models that have been developed and used to study the aetiology and pathology of tendinopathy.

RESULTS

Animal models of tendinopathy fit into two general categories based on the mode of injury application: (i) models that induce tendinopathy through a change in the mechanical environment, and (ii) models that induce tendinopathy through a chemical agent. The cost, difficulty, invasiveness, reproducibility and time required to induce injury in these models varies. Mechanically-induced models are beneficial since they induce injury through repetitive mechanical loading, similar to how tendinopathy is believed to develop in the human condition. Chemically-induced models are beneficial by allowing for the study of the interplay among inflammatory cells, mechanical loading and tissue healing.

CONCLUSION

Further work is needed to fully characterize and understand tendinopathy. Appropriate animal models provide a greater understanding of human tendinopathy, leading to better prevention and treatment.

Neuropeptides in tendinopathy

Overuse tendinopathy remains a major clinical burden for sports medicine and general practitioners. Recent studies have highlighted the role of sensory and autonomic nerves in generating or perpetuating the symptoms and tissue abnormalities associated with tendinopathy. We outline the neuroanatomy and potential roles of nerves and associated neuropeptides in tendinopathy. In addition, intriguing new data is reviewed which suggests that there may be a substantial intrinsic source of neuropeptides within tendons - namely, the tenocytes themselves. The potential roles of Substance P and mast cells are highlighted in particular. We discuss the implications for conservative management including sclerosing injections and exercise training.

The basic science of tendinopathy

Tendinopathy is a common clinical problem with athletes and in many occupational settings. Tendinopathy can occur in any tendon, often near its insertion or enthesis where there is an area of stress concentration, and is directly related to the volume of repetitive load to which the tendon is exposed. Recent studies indicate tendinopathy is more likely to occur in situations that increase the "dose" of load to the tendon enthesis - including increased activity, weight, advancing age, and genetic factors. The cells in tendinopathic tendon are rounder, more numerous, and show evidence of oxidative damage and more apoptosis. These cells also produce a matrix that is thicker and weaker with more water, more immature and cartilage-like matrix proteins, and less organization. There is now evidence of a population of regenerating stem cells within tendon. These studies suggest prevention of tendinopathy should be directed at reducing the volume of repetitive loads to below that which induces oxidative-induced apoptosis and cartilage-like genes. The management strategies might involve agents or cells that induce tendon stem cell proliferation, repair and restoration of matrix integrity.

Gene expression in rat supraspinatus tendon recovers from overuse with rest

Rest is a common treatment for overuse injuries, but its effectiveness on gene expression has not been systematically evaluated under controlled experimental conditions. We asked whether genes regulated in the supraspinatus tendon as a result of overuse would return to normal levels after 2 or 4 weeks of rest. We used a rat model of tendon overuse that generates reproducible changes in the histology, geometry, gene expression, and mechanical properties consistent with an overuse injury. Animals were subjected to the overuse protocol for 2 or 4 weeks followed by either 2 or 4 weeks of rest. Microarray analysis was used to measure global changes in gene expression after the overuse plus rest protocol. Genes upregulated as a result of the overuse returned to near normal levels after rest in most animals. The biochemical composition of the tendon was similar to normal after the imposed rest period, except for slightly lower collagen content. These results suggest as little as 2 weeks of rest is often sufficient to recover from the molecular and biochemical effects of 2 and 4 weeks of overuse in this rat model.

Effects of low-level laser therapy and eccentric exercises in the treatment of recreational athletes with chronic achilles tendinopathy

BACKGROUND

Eccentric exercises (EEs) are recommended for the treatment of Achilles tendinopathy, but the clinical effect from EE has a slow onset.

HYPOTHESIS

The addition of low-level laser therapy (LLLT) to EE may cause more rapid clinical improvement.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

A total of 52 recreational athletes with chronic Achilles tendinopathy symptoms were randomized to groups receiving either EE + LLLT or EE + placebo LLLT over 8 weeks in a blinded manner. Low-level laser therapy (lambda = 820 nm) was administered in 12 sessions by irradiating 6 points along the Achilles tendon with a power density of 60 mW/cm(2) and a total dose of 5.4 J per session.

RESULTS

The results of the intention-to-treat analysis for the primary outcome, pain intensity during physical activity on the 100-mm visual analog scale, were significantly lower in the LLLT group than in the placebo LLLT group, with 53.6 mm versus 71.5 mm (P = .0003) at 4 weeks, 37.3 mm versus 62.8 mm (P = .0002) at 8 weeks, and 33.0 mm versus 53.0 mm (P = .007) at 12 weeks after randomization. Secondary outcomes of morning stiffness, active dorsiflexion, palpation tenderness, and crepitation showed the same pattern in favor of the LLLT group.

CONCLUSION

Low-level laser therapy, with the parameters used in this study, accelerates clinical recovery from chronic Achilles tendinopathy when added to an EE regimen. For the LLLT group, the results at 4 weeks were similar to the placebo LLLT group results after 12 weeks.

Rotator cuff degeneration: etiology and pathogenesis

By virtue of its anatomy and function, the rotator cuff is vulnerable to considerable morbidity, often necessitating surgical intervention. How we intervene is governed by our understanding of the pathological mechanisms in cuff disease. These factors can be divided into those extrinsic to the rotator cuff (impingement, demographic factors) and those intrinsic to the cuff (age-related degeneration, hypovascularity, inflammation, and oxidative stress, among others). In an era where biologic interventions are increasingly being investigated, our understanding of these mechanisms is likely to become more important in designing effective new interventions. Here we present a literature review summarizing our current understanding of the pathophysiological mechanisms underlying rotator cuff degeneration.