Tendinopathy: a review of the pathophysiology and evidence for treatment

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

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

The effectiveness of percutaneous ultrasound-guided needle tenotomy compared to alternative treatments for chronic tendinopathy: a systematic review

OBJECTIVES

To compare percutaneous ultrasound-guided needle tenotomy (PUNT) to alternative treatments for chronic tendinopathy.

MATERIALS AND METHODS

A systematic literature search was performed with the following combination of keywords: ultrasound-guided, percutaneous, needling, tenotomy, Tenex, tendinopathy, and fasciotomy. Original studies comparing PUNT to alternative treatments for chronic tendinopathy were included in this systematic review.

RESULTS

Twelve (n = 12) studies with 481 subjects were included. Two (2/12) articles compared PUNT to surgical tenotomy and concluded that PUNT provides the same outcomes as surgical tenotomy. Six (6/12) studies compared PUNT to platelet-rich plasma (PRP) injections, and two of them found both treatment modalities effective with no significant between-group differences. Three trials claimed that PUNT followed by PRP injections showed superior clinical outcomes compared to PUNT alone. However, the difference at long-term follow-up was statistically significant only in one of them. One study found PUNT superior to PUNT + PRP injection at short-term follow-up, although there were no between-group differences at long-term follow-up. Four (4/12) studies compared PUNT to steroid injection (SI) and showed that SI causes fast (2 weeks) but temporary pain relief, PUNT results in persistent but relatively slower improvement to SI, and the combined procedure has a more rapid and steady reduction in symptoms.

CONCLUSION

PUNT is an effective treatment technique for chronic tendinopathy and should be considered when non-invasive treatments have failed. Effects of PRP and SI are transient and dissipate over time and do not contribute to long-term outcome.

Regional differences in turnover, composition, and mechanics of the porcine flexor tendon

PURPOSE

Recent data suggest that there is a lack of turnover in the core of human tendon, but it remains unknown whether there are regional differences between core and periphery of the cross section. The purpose of this project was to investigate regional differences in turnover as estimated by the accumulation of fluorescent Advanced Glycation End-products (AGEs) and regional differences in mechanical properties.

MATERIALS AND METHODS

Tendons were obtained from lean control (n = 4) and diabetic Göttingen minipigs (streptozotocin-induced, n = 6). The deep digital flexor tendon of one hind limb was separated into a proximal, central and distal part. Autofluorescence was measured in the core and periphery of the proximal and distal parts of the tendon, and mechanical properties were tested on fascicles taken from the core and periphery of the central tendon (only diabetic animals).

RESULTS

Autofluorescence was greater in the proximal than the distal part. In the distal part of the lean control animals, autofluorescent AGE accumulation was also greater in the core than the periphery. Peak modulus in the core region (704 ± 79 MPa) was higher than the periphery (466 ± 53 MPa, p < 0.05) in diabetic tendons.

CONCLUSION

Taken together, autofluorescence varied both along the length and across the tendon cross section, indicating higher turnover in the distal and peripheral regions. In addition, mechanical properties differed across the tendon cross-section.

The transcription factor scleraxis differentially regulates gene expression in tenocytes isolated at different developmental stages

The transcription factor scleraxis (SCX) is expressed throughout tendon development and plays a key role in directing tendon wound healing. However, little is known regarding its role in fetal or young postnatal tendons, stages in development that are known for their enhanced regenerative capabilities. Here we used RNA-sequencing to compare the transcriptome of adult and fetal tenocytes following SCX knockdown. SCX knockdown had a larger effect on gene expression in fetal tenocytes, affecting 477 genes in comparison to the 183 genes affected in adult tenocytes, indicating that scleraxis-dependent processes may differ in these two developmental stages. Gene ontology, network and pathway analysis revealed an overrepresentation of extracellular matrix (ECM) remodelling processes within both comparisons. These included several matrix metalloproteinases, proteoglycans and collagens, some of which were also investigated in SCX knockdown tenocytes from young postnatal foals. Using chromatin immunoprecipitation, we also identified novel genes that SCX differentially interacts with in adult and fetal tenocytes. These results indicate a role for SCX in modulating ECM synthesis and breakdown and provide a useful dataset for further study into SCX gene regulation.

Dry Needling as a Treatment Modality for Tendinopathy: a Narrative Review

PURPOSE OF REVIEW

Tendinopathy describes a combination of pain, swelling, and impaired performance of the tendon and around structures. There are various treatment options for tendinopathy with unclear efficacy. Dry needling involves inserting needles into the affected tendon, and it is thought to disrupt the chronic degenerative process and encourage localized bleeding and fibroblastic proliferation. The purpose of this review is to review the use of dry needling as a treatment modality for tendinopathy.

RECENT FINDINGS

The effectiveness of dry needling for treatment of tendinopathy has been evaluated in 3 systematic reviews, 7 randomized controlled trials, and 6 cohort studies. The following sites were studied: wrist common extensor origin, patellar tendon, rotator cuff, and tendons around the greater trochanter. There is considerable heterogeneity of the needling techniques, and the studies were inconsistent about the therapy used after the procedure. Most systematic reviews and randomized controlled trials support the effectiveness of tendon needling. There was a statistically significant improvement in the patient-reported symptoms in most studies. Some studies reported an objective improvement assessed by ultrasound. Two studies reported complications. Current research provides initial support for the efficacy of dry needling for tendinopathy treatment. It seems that tendon needling is minimally invasive, safe, and inexpensive, carries a low risk, and represents a promising area of future research. In further high-quality studies, tendon dry needling should be used as an active intervention and compared with appropriate sham interventions. Studies that compare the different protocols of tendon dry needling are also needed.

Amnion Applications in the Foot and Ankle

Amnion and chorion products show great promise and have real potential to be mainstays of treatment for chronic, nonhealing wounds. Although amniotic products do carry a cost, the decrease in time to healing, with the assumed subsequent decrease in complication and infection rates, should also be taken into consideration. These products, with their unique biologic potential and availability in the clinical setting, may prove to be beneficial in a vast array of podiatric surgical applications.

Prevalence and incidence rate of lower-extremity tendinopathies in a Danish general practice: a registry-based study

Background

Tendinopathies of the lower extremity (e.g. Achilles, patellar, and plantar heel pain) are common in both general and sporting populations. However, the prevalence and incidence in Danish general practice is unknown. The aim was to determine the prevalence and incidence rate of lower-extremity tendinopathies in a Danish general practice.

Methods

In this registry-based study, we extracted data from the electronic patient files of all patients in a single Danish general practice. The practice included 8836 patients. We searched ICPC-2 codes to identify patients with either of the following lower-extremity tendinopathies: plantar heel pain; Achilles tendinopathy; patellar tendinopathy; greater trochanteric pain syndrome or adductor tendinopathy. We defined an incident and prevalent case as a patient with a consultation because of tendinopathy in 2016 only. A prevalent, but not incident case was a patient with consultations in both 2015 and 2016. Incidence and prevalence were expressed as the number of patients with a tendinopathy per 1000 registered patients.

Results

The prevalence and incidence rate were 16.6 and 7.9 per 1000 registered patients, respectively. Plantar heel pain was the most prevalent tendinopathy and accounted for 39% of lower-extremity tendinopathies. Patients with tendinopathies were significantly older than all registered patients (46.0 years (95%CI: 43.3;48.7) versus 38.8 years (95%CI: 38.4;39.3), respectively).

Conclusions

Lower-extremity tendinopathies, especially plantar heel pain, had a high prevalence and incidence rate in a Danish general practice. In a typical general practice with 5000 patients, general practitioners should expect to see more than 80 patients with a lower-extremity tendinopathy every year.

Quadriceps tendinopathy: a review, part 2-classification, prognosis, and treatment

Overuse injuries of the extensor mechanism of the knee are common in both athletes and non-athletes and usually occur during activities associated with repetitive loading, stress, and knee extension. Numerous reports have been published describing extensor mechanism injuries in athletes, but there is a paucity of studies that focus on quadriceps tendinopathy in the non-athlete population. In addition, there is no universally accepted classification system for tendon pathology. Therefore, we performed a comprehensive literature review of these studies. This review consists of 2 parts. In the previous part we reviewed: (I) epidemiology and (II) diagnosis of quadriceps tendinopathy in the athlete as well as the general population. In this part we discuss: (I) classification; (II) prognosis; and (III) treatment results.

Randomized Controlled Trial of Micronized Dehydrated Human Amnion/Chorion Membrane (dHACM) Injection Compared to Placebo for the Treatment of Plantar Fasciitis

BACKGROUND

Failure of conservative management to reduce/eliminate symptoms of plantar fasciitis (PF) may indicate need for advanced treatments. This study reports Level 1 evidence supporting 3-month safety and efficacy of micronized dehydrated human amnion/chorion membrane (dHACM) injection as a treatment for PF.

METHODS

A prospective, single-blind, randomized controlled trial was conducted at 14 sites in the United States. Subjects were randomized to receive 1 injection, in the affected area, of micronized dHACM (n=73) or 0.9% sodium chloride placebo (n=72). Safety/efficacy assessments were conducted at 4 weeks, 8 weeks, 3 months, 6 months, and 12 months postinjection, using visual analog scale (VAS) for pain, Foot Function Index-Revised (FFI-R) score, and presence/absence of adverse events. Primary outcome was mean change in VAS score between baseline and 3 months expressed as difference in means for treatment versus control subjects. Secondary outcome was mean change in FFI-R score between baseline and 3 months expressed as difference in means for treatment versus control subjects.

RESULTS

Baseline VAS scores were similar between groups. At the 3-month follow-up, mean VAS scores in the treatment group were 76% lower compared with a 45% reduction for controls ( P < .0001), FFI-R scores for treatment subjects had mean reduction of 60% versus baseline, whereas control subjects had mean reduction of 40% versus baseline ( P = .0004). Of 4 serious adverse events, none were related to study procedures.

CONCLUSION

Pain reduction and functional improvement outcomes were statistically significant and clinically relevant, supporting use of micronized dHACM injection as a safe and effective treatment for PF.

LEVEL OF EVIDENCE

Level I, prospective randomized trial.

Novel roles for scleraxis in regulating adult tenocyte function

Background

Tendinopathies are common and difficult to resolve due to the formation of scar tissue that reduces the mechanical integrity of the tissue, leading to frequent reinjury. Tenocytes respond to both excessive loading and unloading by producing pro-inflammatory mediators, suggesting that these cells are actively involved in the development of tendon degeneration. The transcription factor scleraxis (Scx) is required for the development of force-transmitting tendon during development and for mechanically stimulated tenogenesis of stem cells, but its function in adult tenocytes is less well-defined. The aim of this study was to further define the role of Scx in mediating the adult tenocyte mechanoresponse.

Results

Equine tenocytes exposed to siRNA targeting Scx or a control siRNA were maintained under cyclic mechanical strain before being submitted for RNA-seq analysis. Focal adhesions and extracellular matrix-receptor interaction were among the top gene networks downregulated in Scx knockdown tenocytes. Correspondingly, tenocytes exposed to Scx siRNA were significantly softer, with longer vinculin-containing focal adhesions, and an impaired ability to migrate on soft surfaces. Other pathways affected by Scx knockdown included increased oxidative phosphorylation and diseases caused by endoplasmic reticular stress, pointing to a larger role for Scx in maintaining tenocyte homeostasis.

Conclusions

Our study identifies several novel roles for Scx in adult tenocytes, which suggest that Scx facilitates mechanosensing by regulating the expression of several mechanosensitive focal adhesion proteins. Furthermore, we identified a number of other pathways and targets affected by Scx knockdown that have the potential to elucidate the role that tenocytes may play in the development of degenerative tendinopathy.

Electronic supplementary material

The online version of this article (10.1186/s12860-018-0166-z) contains supplementary material, which is available to authorized users.

A comparison of the stem cell characteristics of murine tenocytes and tendon-derived stem cells

Tendon is a commonly injured soft musculoskeletal tissue, however, poor healing potential and ineffective treatment strategies result in persistent injuries and tissue that is unable to perform its normal physiological function. The identification of a stem cell population within tendon tissue holds therapeutic potential for treatment of tendon injuries. This study aimed, for the first time, to characterise and compare tenocyte and tendon-derived stem cell (TDSC) populations in murine tendon. Tenocytes and TDSCs were isolated from murine tail tendon. The cells were characterised for morphology, clonogenicity, proliferation, stem cell and tenogenic marker expression and multipotency. TDSCs demonstrated a rounded morphology, compared with a more fibroblastic morphology for tenocytes. Tenocytes had greater clonogenic potential and a smaller population doubling time compared with TDSCs. Stem cell and early tenogenic markers were more highly expressed in TDSCs, whereas late tenogenic markers were more highly expressed in tenocytes. Multipotency was increased in TDSCs with the presence of adipogenic differentiation which was absent in tenocytes. The differences in morphology, clonogenicity, stem cell marker expression and multipotency observed between tenocytes and TDSCs indicate that at least two cell populations are present in murine tail tendon. Determination of the most effective cell population for tendon repair is required in future studies, which in turn may aid in tendon repair strategies.

Effect of platelet mediator concentrate (PMC) on Achilles tenocytes: an in vitro study

Background

Although there are many studies discussing the etiological and pathological factors leading to both, acute and chronic tendon injuries, the pathophysiology of tendon injuries is still not clearly understood. Although most lesions are uncomplicated, treatment is long and unsatisfactory due to the poor vascularity of tendon tissue. Platelet mediator concentrate (PMC) contains many growth factors derived from platelets, which can promote wound healing. In this study we investigate the effects of PMC on tenocyte proliferation and differentiation in order to provide an experimental basis for tissue regeneration strategies and to develop new treatment concepts.

Methods

Using enzyme linked immunosorbent assay (ELISA) we were able to quantify the several growth factors and cytokines found in PMC. Tenocytes were isolated both from human and from mouse Achilles tendons and stimulated with PMC. CyQuant® and Cell Titer Blue® assays were carried out to analyze tendon growth and viability at different concentrations of PMC. Real time RT-PCR was used to analyze tenocyte gene expression with or without PMC treatment. Immunohistochemistry was carried out to detect the tenocyte-specific antibody tenomodulin (TNMD) and scleraxis (SCX).

Results

We were able to detect numerous mediators such as platelet derived growth factor BB (PDGF-BB), interleukin 6 (IL-6), vascular endothelial growth factor (VEGF), tumor necrosis factor (TNF-α), transforming growth factor beta 1 (TGF-ß1), and bone morphogenetic proteins 2, 4 and 7 (BMP-4, BMP-2, BMP-7) in PMC. It was possible to show a positive effect of PMC on human tendon cell growth and viability in a dose-dependent manner. Furthermore, PMC treatment led to induction of gene expression of scleraxis (SCX), type I collagen A 1 (Col1A1) and TNMD by tenocytes.

Conclusions

We suggest that the use of autologous PMC may be a suitable addition to conventional tendon therapy that is capable of increasing and optimizing tendon healing and reducing the risk of recurrence.

Biology and mechano-response of tendon cells: Progress overview and perspectives

In this review, we summarize the group discussions on Cell Biology & Mechanics from the 2014 ORS/ISMMS New Frontiers in Tendon Research Conference. The major discussion topics included: (1) the biology of tendon stem/progenitor cells (TSPCs) and the potential of stem cell-based tendon therapy using TSPCs and other types of stem cells, namely, embryonic and/or induced pluripotent stem cells (iPSCs), (2) the biological concept and potential impact of cellular senescence on tendon aging, tendon injury repair and the development of degenerative disease, and (3) the effects of tendon cells' mechano-response on tendon cell fate and metabolism. For each topic, a brief overview is presented which summarizes the major points discussed by the group participants. The focus of the discussions ranged from current research progress, challenges and opportunities, to future directions on these topics. In the preparation of this manuscript, authors consulted relevant references as a part of their efforts to present an accurate view on the topics discussed.

Tendon needling for treatment of tendinopathy: A systematic review

OBJECTIVE

To summarize the best available evidence to determine if tendon needling is an effective treatment for tendinopathy. Data source. Medline and Cochrane Databases through November 2013.

REVIEW METHODS

Utilizing the search terms tendinopathy, needle, needling, tenotomy, dry needling, needling tendon, needle fenestration, and tendon fenestration, 17 articles were identified through our systematic literature search. Of these, 4 studies met the inclusion criteria. Four independent reviewers reviewed the articles. The study results and generated conclusions were agreed upon.

RESULTS

The studies that were included in this review suggest that tendon needling improves patient reported outcomes in patients with tendinopathy. In 2 studies evaluating tendon needling in lateral epicondylosis, one showed an improvement in a subjective visual analogue scale score of 34% (significant change > 25%) from baseline at 6 months. The other showed an improvement of 56.1% in a visual analogue scale score from baseline. In 1 study evaluating tendon needling in addition to eccentric therapy for Achilles tendinosis, the subjective Victorian Institute of Sport Assessment-Achilles (VISA-A) score improved by 19.9 (significant change > 10) (95% CI, 13.6-26.2) from baseline. In 1 study evaluating tendon needling in rotator cuff tendinosis, the subjective shoulder pain and disability index showed statistical significant improvement from baseline at 6 months (P < 0.05).

CONCLUSIONS

The evidence suggests that tendon needling improves patient-reported outcome measures in patients with tendinopathy. There is a trend that shows that the addition of autologous blood products may further improve theses outcomes.