Tendon’s ultrastructure

Rotator cuff tears

Rotator cuff tears are the most common upper extremity condition seen by primary care and orthopaedic surgeons, with a spectrum ranging from tendinopathy to full-thickness tears with arthritic change. Some tears are traumatic, but most rotator cuff problems are degenerative. Not all tears are symptomatic and not all progress, and many patients in whom tears become more extensive do not experience symptom worsening. Hence, a standard algorithm for managing patients is challenging. The pathophysiology of rotator cuff tears is complex and encompasses an interplay between the tendon, bone and muscle. Rotator cuff tears begin as degenerative changes within the tendon, with matrix disorganization and inflammatory changes. Subsequently, tears progress to partial-thickness and then full-thickness tears. Muscle quality, as evidenced by the overall size of the muscle and intramuscular fatty infiltration, also influences symptoms, tear progression and the outcomes of surgery. Treatment depends primarily on symptoms, with non-operative management sufficient for most patients with rotator cuff problems. Modern arthroscopic repair techniques have improved recovery, but outcomes are still limited by a lack of understanding of how to improve tendon to bone healing in many patients.

Effects of adipose-derived mesenchymal stem cell conditioned medium on human tenocytes exposed to high glucose

Introduction

Diabetic tendinopathy is a common invalidating and challenging disease that may be treated using stem cells. However, the effects of adipose-derived mesenchymal stem cell conditioned medium (ASC-CM) in diabetic tendinopathy have never been explored.

Objectives

The present study evaluated the effects of ASC-CM on morphology, cell viability, structure, and scratch wound closure of human tenocytes (HTNC) exposed to high glucose (HG).

Design

Experimental study.

Methods

HTNC were exposed to HG (25 mM) for 7, 14 and 21 days with or without ASC-CM for the last 24 h. CM was collected from 4 × 105 ASCs, centrifuged for 10 min at 200 g and sterilized with 0.22 μm syringe filter.

Results

At 7 days, HG-HTNC had decreased cell viability [72 ± 2%, p < 0.01 versus normal glucose (NG)] compared to NG-HTNC (90 ± 5%). A further decrement was detected after 14 and 21 days (60 ± 4% and 60 ± 5%, both, p < 0.01 versus NG and p < 0.01 versus HG7). While NG-HTNC evidenced a normal fibroblast cell-like elongated morphology, HG-HTNC showed increased cell roundness. In contrast, HG-HTNC exposed to ASC-CM showed a significant increase in cell viability, an improved cell morphology and higher scratch wound closure at all HG time points. Moreover, the exposure to ASC-CM significantly increased thrombospondin 1 and transforming growth factor beta 1 (TGF-β1) content in HG-HTNC. The TGF-β1 elevation was paralleled by higher Collagen I and Vascular Endothelial Growth Factor in HG-HTNC.

Conclusion

ASC-CM may restore the natural morphology, cell viability and structure of HTNC, promoting their scratch wound closure through TGF-β1 increase.

Effect of Aging on Tendon Biology, Biomechanics and Implications for Treatment Approaches

Tendon aging is associated with an increasing prevalence of tendon injuries and/or chronic tendon diseases, such as tendinopathy, which affects approximately 25% of the adult population. Aged tendons are often characterized by a reduction in the number and functionality of tendon stem/progenitor cells (TSPCs), fragmented or disorganized collagen bundles, and an increased deposition of glycosaminoglycans (GAGs), leading to pain, inflammation, and impaired mobility. Although the exact pathology is unknown, overuse and microtrauma from aging are thought to be major causative factors. Due to the hypovascular and hypocellular nature of the tendon microenvironment, healing of aged tendons and related injuries is difficult using current pain/inflammation and surgical management techniques. Therefore, there is a need for novel therapies, specifically cellular therapy such as cell rejuvenation, due to the decreased regenerative capacity during aging. To augment the therapeutic strategies for treating tendon-aging-associated diseases and injuries, a comprehensive understanding of tendon aging pathology is needed. This review summarizes age-related tendon changes, including cell behaviors, extracellular matrix (ECM) composition, biomechanical properties and healing capacity. Additionally, the impact of conventional treatments (diet, exercise, and surgery) is discussed, and recent advanced strategies (cell rejuvenation) are highlighted to address aged tendon healing. This review underscores the molecular and cellular linkages between aged tendon biomechanical properties and the healing response, and provides an overview of current and novel strategies for treating aged tendons. Understanding the underlying rationale for future basic and translational studies of tendon aging is crucial to the development of advanced therapeutics for tendon regeneration.

Association Between COL5a1, COL11a1, and COL11a2 Gene Variations and Rotator Cuff Tendinopathy in Young Athletes

OBJECTIVE

Tendinopathy is a prevalent condition in young athletes and in older nonathletic people. Recent tendinopathy research has shown a growing interest in the role played by genetic factors, basically genes involved in collagen synthesis and regulation, in view of collagen disorganization typically present in tendon pathologies.

DESIGN

A case-control, genotype-phenotype association study.

SETTING

La Ribera Hospital, Valencia, Spain.

PARTICIPANTS

A group of 137 young athletes (49 with rotator cuff tendon pathology and 88 healthy counterparts) who played upper-limb-loading sports were clinically and ultrasound (US) assessed for rotator cuff tendinopathy were included.

INTERVENTION

Genetic analysis was performed to determine whether there was a relationship between rotator cuff pathology and the genotype.

MAIN OUTCOME MEASURES

We hypothesized that the following single nucleotide polymorphisms: COL5a1 rs12722, COL11a1 rs3753841, COL11a1 rs1676486, and COL11a2 rs1799907 would be associated with rotator cuff tendinopathy.

RESULTS

A direct relationship between CC genotype and bilateral US pathological images was statistically significant (χ 2 = 0.0051) and confirmed by the Fisher test, with a correlation coefficient of 0.345 and a Cramer's v of 0.26.

CONCLUSION

A significant association was found between COL5a1 rs12722 genotype and rotator cuff pathology, with the CC genotype conferring increased risk of tendon abnormalities and being associated with rotator cuff pathology.

Sustainable Approach of Functional Biomaterials-Tissue Engineering for Skin Burn Treatment: A Comprehensive Review

Burns are a widespread global public health traumatic injury affecting many people worldwide. Non-fatal burn injuries are a leading cause of morbidity, resulting in prolonged hospitalization, disfigurement, and disability, often with resulting stigma and rejection. The treatment of burns is aimed at controlling pain, removing dead tissue, preventing infection, reducing scarring risk, and tissue regeneration. Traditional burn wound treatment methods include the use of synthetic materials such as petroleum-based ointments and plastic films. However, these materials can be associated with negative environmental impacts and may not be biocompatible with the human body. Tissue engineering has emerged as a promising approach to treating burns, and sustainable biomaterials have been developed as an alternative treatment option. Green biomaterials such as collagen, cellulose, chitosan, and others are biocompatible, biodegradable, environment-friendly, and cost-effective, which reduces the environmental impact of their production and disposal. They are effective in promoting wound healing and reducing the risk of infection and have other benefits such as reducing inflammation and promoting angiogenesis. This comprehensive review focuses on the use of multifunctional green biomaterials that have the potential to revolutionize the way we treat skin burns, promoting faster and more efficient healing while minimizing scarring and tissue damage.

Imaging Tendon Disorders in Athletes

Imaging plays a critical role in evaluating pathology affecting athletes from various fields. Tendon pathology manifests in terms of mechanical, degenerative, enthesitis, neoplastic, and overuse diseases. Tendon pathologies in athletes usually involve injuries to commonly injured tendons such as the tendons involving the ankle, elbow, rotator cuff, hip abductors, patellar tendon, and Achilles tendon. For the purposes of this article, the focus will be on the tendons involving the ankle such as the tibialis posterior and peroneal tendons. The 2 most common imaging modalities used for the evaluation of tendons are ultrasound (US) and magnetic resonance imaging (MRI). There are several emerging imaging techniques such as T2 mapping, ultra-short echo time MRI, and sonoelastography. These novel imaging techniques are all in research phase and have not been adapted to routine clinical practice.

Histoarchitecture of the fibrillary matrix of human fetal posterior tibial tendons

Adult tendons are highly differentiated. In mature individuals, tendon healing after an injury occurs through fibrotic tissue formation. Understanding the intrinsic reparative properties of fetal tendons would help to understand the maturation tissue process and tendon tissue repair. The present study evaluated the evolution of histoarchitecture, cellularity and the distribution of collagens I, III and V in the posterior tibial tendon in human fetuses at different gestational ages. Morphological profiles were assessed in nine fresh spontaneously aborted fetuses (Group I: five fetuses aged between 22 and 28 weeks of gestation; Group II: four fetuses aged between 32 and 38 weeks of gestation), characterized by a combination of histology, fluorescence and immunohistochemistry. In Group I, the posterior tibial tendon showed statistically significant greater cellularity and presence of collagen III and V than in Group II tendon, which showed a predominance of collagenous I and a better organization of the extracellular matrix compared with Group I tendons. In addition, a statistically significant higher rate of CD90, a marker of mesenchymal cells, was found in Group I tendons. In fetuses with gestational age between 22 and 28 weeks, the posterior tibialis tendons showed a thin and disorganized fibrillar structure, with an increase in collagen III and V fibers and mesenchymal cells. In the posterior tibialis tendons of fetuses with gestational age between 32 and 38 weeks, the fibrillar structure was thicker with a statistically significant increase in type I collagen and decreased cellularity.

A Comprehensive Review on Collagen Type I Development of Biomaterials for Tissue Engineering: From Biosynthesis to Bioscaffold

Collagen is the most abundant structural protein found in humans and mammals, particularly in the extracellular matrix (ECM). Its primary function is to hold the body together. The collagen superfamily of proteins includes over 20 types that have been identified. Yet, collagen type I is the major component in many tissues and can be extracted as a natural biomaterial for various medical and biological purposes. Collagen has multiple advantageous characteristics, including varied sources, biocompatibility, sustainability, low immunogenicity, porosity, and biodegradability. As such, collagen-type-I-based bioscaffolds have been widely used in tissue engineering. Biomaterials based on collagen type I can also be modified to improve their functions, such as by crosslinking to strengthen the mechanical property or adding biochemical factors to enhance their biological activity. This review discusses the complexities of collagen type I structure, biosynthesis, sources for collagen derivatives, methods of isolation and purification, physicochemical characteristics, and the current development of collagen-type-I-based scaffolds in tissue engineering applications. The advancement of additional novel tissue engineered bioproducts with refined techniques and continuous biomaterial augmentation is facilitated by understanding the conventional design and application of biomaterials based on collagen type I.

Abnormal spinal cord motion at the craniocervical junction in hypermobile Ehlers-Danlos patients

OBJECTIVE

The craniocervical junction (CCJ) is anatomically complex and comprises multiple joints that allow for wide head and neck movements. The thecal sac must adjust to such movements. Accordingly, the thecal sac is not rigidly attached to the bony spinal canal but instead tethered by fibrous suspension ligaments, including myodural bridges (MDBs). The authors hypothesized that pathological spinal cord motion is due to the laxity of such suspension bands in patients with connective tissue disorders, e.g., hypermobile Ehlers-Danlos syndrome (EDS).

METHODS

The ultrastructure of MDBs that were intraoperatively harvested from patients with Chiari malformation was investigated with transmission electron microscopy, and 8 patients with EDS were compared with 8 patients without EDS. MRI was used to exclude patients with EDS and craniocervical instability (CCI). Real-time ultrasound was used to compare the spinal cord at C1-2 of 20 patients with EDS with those of 18 healthy control participants.

RESULTS

The ultrastructural damage of the collagen fibrils of the MDBs was distinct in patients with EDS, indicating a pathological mechanical laxity. In patients with EDS, ultrasound revealed increased cardiac pulsatory motion and irregular displacement of the spinal cord during head movements.

CONCLUSIONS

Laxity of spinal cord suspension ligaments and the associated spinal cord motion disorder are possible pathogenic factors for chronic neck pain and headache in patients with EDS but without radiologically proven CCI.

Picrosirius-Polarization Method for Collagen Fiber Detection in Tendons: A Mini-Review

Although the structure and composition of collagen have been studied by polarized light microscopy since the early 19th century, many studies and reviews have paid little or no attention to the morphological problems of histopathological diagnosis. The morphology of collagen fibers is critical in guiding mechanical and biological properties in both normal and pathological tendons. Highlighting the organization and spatial distribution of tendon‐containing collagen fibers can be very useful for visualizing a tendon's ultrastructure, biochemical and indirect mechanical properties, which benefits other researchers and clinicians. Picrosirius red (PSR) staining, relying on the birefringence of collagen fibers, is one of the best understood histochemical methods that can highly and specifically underline fibers better than other common staining techniques when combined with polarized light microscopy (PLM). Polarized light microscopy provides complementary information about collagen fibers, such as orientation, type and spatial distribution, which is important for a comprehensive assessment of collagen alteration in a tendon. Here, this brief review serves as a simplistic and important primer to research developments in which differential staining of collagen types by the Picrosirius‐polarization method is increasing in diverse studies of the medical field, mainly in the assessment of the morphology, spatial distribution, and content of collagen in tendons.

Influence of genetic factors in elbow tendon pathology: a case-control study

Elbow tendinopathy is a common pathology of the upper extremity that impacts both athletes and workers. Some research has examined the genetic component as a risk factor for tendinopathy, mainly in the lower limbs. A case-control study was designed to test for a relationship between certain collagen gene single nucleotide polymorphisms (SNPs) and elbow tendon pathology. A sample of 137 young adult athletes whose sports participation involves loading of the upper limb were examined for the presence of structural abnormalities indicative of pathology in the tendons of the lateral and medial elbow using ultrasound imaging and genotyped for the following SNPs: COL5A1 rs12722, COL11A1 rs3753841, COL11A1 rs1676486, and COL11A2 rs1799907. Anthropometric measurements and data on participants’ elbow pain and dysfunction were collected using the Disabilities of the Arm, Shoulder and Hand and the Mayo Clinic Performance Index for the Elbow questionnaires. Results showed that participants in the structural abnormality group had significantly higher scores in pain and dysfunction. A significant relationship between COL11A1 rs3753841 genotype and elbow tendon pathology was found (p = 0.024), with the CT variant associated with increased risk of pathology.

Local treatment with ascorbic acid accelerates recovery of post-sutured Achilles tendon in male Wistar rats

Tendon rupture is a very frequent accident involving average people and high-performance athletes. Clinical studies describe tendon recovery as a painful and slow process involving different biochemical and histological events. Ascorbic acid (AA) is a potent antioxidant as well as an important cofactor for collagen synthesis. In the current study, we evaluated if local treatment with AA is able to promote tendon repair in tenotomized rats. Animals were submitted to Achilles tendon rupture followed by surgical suture. Control and AA groups received in loco injection of saline solution (0.9% NaCl) and 30 mM AA, respectively. Histological and functional recovery of Achilles tendon tissue was evaluated at 7, 14, and 21 days post-surgery. Hematoxylin/eosin staining and collagen fluorescence analysis showed intense disarrangement of tendon tissue in the saline group. Tenotomized animals also showed hypercellularity in tendon tissue compared with non-tenotomized animals. The Achilles functional index (AFI) showed a significant decrease of tendon functionality in tenotomized animals at 7, 14, and 21 days post-surgery. AA accelerated tissue organization and the recovery of function of the Achilles tendons. The beneficial effect of AA treatment was also observed in the organization of the collagen network. Data presented in the current work showed that in loco treatment with AA accelerated the recovery of injured Achilles tendon post-surgery.

Application of a Purified Protein From Natural Latex and the Influence of Suture Type on Achilles Tendon Repair in Rats

BACKGROUND

The prolonged tendon-healing process, the high costs associated with treatment, the increase in the number of injuries over the past decades, and the lack of consensus on the optimal treatment of tendon injuries are a global problem. Restoring the normal tendon anatomy and decreasing the healing time are key factors for treatment advancement.

HYPOTHESIS

Application of a purified protein from natural latex (PPNL) accelerates the healing process, increasing collagen synthesis and decreasing metalloproteinases. PPNL associated with a simpler suture technique should decrease the healing time.

STUDY DESIGN

Controlled laboratory study.

METHODS

Injury, surgery, and treatment with PPNL were conducted with male Sprague-Dawley rats. Two suture techniques were used: U-suture, a simpler and lesser traumatic technique, and Kessler-Tajima, to avoid strangulation of the microcirculation. Achilles tendons were completely sectioned, and 100 µL of 0.1% PPNL was applied on the tendon during surgery. Tendon morphology, distribution, and quantity of collagen types I and III, as well as expression of TIMP-1, TIMP-2, MMP-2, and MMP-9 and ultrastructural aspects of cells and collagen fibrils, were assessed after 2 and 4 weeks.

RESULTS

PPNL treatment improved collagen type I synthesis and reduced MMP-2 expression. All groups showed a 6.8-times increase in tendon weight as compared with the control group after 2 weeks and a 5.2-times increase after 4 weeks. All groups showed an increase in diameter after 4 weeks, except for the ones treated with PPNL, which showed a slight reduction in diameter. The peak of concentration of collagen fibrils with a 80-nm diameter was 27.79% in the control group; all other experimental groups presented fibrils between 50 and 60 nm. However, the best results were observed with Kessler-Tajima suture associated with PPNL.

CONCLUSION/CLINICAL RELEVANCE

There are no known medicines or substances capable of aiding the tendon healing process besides surgery. The discovery of a substance able to improve this process and decrease its duration represents an important advancement in orthopaedic medicine.

Hormones and tendinopathies: the current evidence

BACKGROUND

Tendinopathies negatively affect the quality of life of millions of people, but we still do not know the factors involved in the development of tendon conditions.

SOURCES OF DATA

Published articles in English in PubMed and Google Scholar up to June 2015 about hormonal influence on tendinopathies onset. One hundred and two papers were included following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

AREAS OF AGREEMENT

In vitro and in vivo, tenocytes showed changes in their morphology and in their functional properties according to hormonal imbalances.

AREAS OF CONTROVERSY

Genetic pattern, sex, age and comorbidities can influence the hormonal effect on tendons.

GROWING POINTS

The increasing prevalence of metabolic disorders prompts to investigate the possible connection between metabolic problems and musculoskeletal diseases.

AREAS TIMELY FOR DEVELOPING RESEARCH

The influence of hormones on tendon structure and metabolism needs to be further investigated. If found to be significant, multidisciplinary preventive and therapeutic strategies should then be developed.

Influence of Thyroid Hormones on Tendon Homeostasis

Tendinopathies have a multifactorial etiology driven by extrinsic and intrinsic factors. Recent studies have elucidated the importance of thyroid hormones in the alteration of tendons homeostasis and in the failure of tendon healing after injury. The effects of thyroid hormones are mediated by receptors (TR)-α and -β that seem to be ubiquitous. In particular, T3 and T4 play an antiapoptotic role on tenocytes, causing an increase in vital tenocytes isolated from tendons in vitro and a reduction of apoptotic ones; they are also able to influence extra cellular matrix proteins secretion in vitro from tenocytes, enhancing collagen production. From a clinical point of view, disorders of thyroid function have been investigated only for rotator cuff calcific tendinopathy and tears. In this complex scenario, further research is needed to clarify the role of thyroid hormones on the onset of tendinopathies.

Human adipose-derived stem cells accelerate the restoration of tensile strength of tendon and alleviate the progression of rotator cuff injury in a rat model

Adult stem cell therapy for the treatment of tendon injuries is a growing area of research. This study is aimed to investigate the efficacy of human adipose-derived stem cell (hADSC) injection on the tendon during its healing process in a rat model of rotator cuff injury. hADSCs were injected 3 days after collagenase-induced rotator cuff injuries in experimental groups, while the control group received saline as a placebo. Histological and biomechanical analyses were performed 7, 14, 21, and 28 days after collagenase injection. Compared to the control group, it was found that inflammatory cells were significantly decreased in the hADSC-treated group after collagenase injection for 7 and 14 days. In the hADSC-injected group, the fiber arrangement and tendon organization had also been improved. On the seventh day after collagenase injection, the load to failure of the hADSC-injected group (15.87 ± 2.20 N) was notably higher than that of the saline-injected group (11.20 ± 1.35 N). It is suggested that the tensile strength of the supraspinatus tendon was significantly enhanced. Local administration of hADSCs might have the possibility to restore the tensile strength and attenuate the progression of tendinitis. Taken together, these findings demonstrate that the recovery processes in damaged tendons can be facilitated architecturally and functionally after hADSC injection.

Extracellular matrix assembly: a multiscale deconstruction

The biochemical and biophysical properties of the extracellular matrix (ECM) dictate tissue-specific cell behaviour. The molecules that are associated with the ECM of each tissue, including collagens, proteoglycans, laminins and fibronectin, and the manner in which they are assembled determine the structure and the organization of the resultant ECM. The product is a specific ECM signature that is comprised of unique compositional and topographical features that both reflect and facilitate the functional requirements of the tissue.