Microtrauma stimulates rat Achilles tendon healing via an early gene expression pattern similar to mechanical loading

Republication of "A Biomechanical Comparison of Limited Open Versus Krackow Repair for Achilles Tendon Rupture"

Background

Soft tissue complications after Achilles tendon repair has led to increased interest in less invasive techniques. Various limited open techniques have gained popularity as an alternative to open operative repair. The purpose of this study was to biomechanically compare an open Krackow and limited open repair for Achilles tendon rupture. We hypothesized that there would be no statistical difference in load to failure, work to failure, and initial linear stiffness.

Methods

A simulated Achilles tendon rupture was created 4 cm proximal to its insertion in 18 fresh-frozen cadaveric below-knee lower limbs. Specimens were randomized to open or limited open PARS Achilles Jig System repair. Repairs were loaded to failure at a rate of 25.4 mm/s to reflect loading during normal ankle range of motion. Load to failure, work to failure, and initial linear stiffness were compared between the 2 repair types.

Results

The average load to failure (353.8 ± 88.8 N vs 313.3 ± 99.9 N; P = .38) and work to failure (6.4 ± 2.3 J vs 6.3 ± 3.5 J; P = .904) were not statistically different for Krackow and PARS repair, respectively. Mean initial linear stiffness of the Krackow repair (17.8 ± 5.4 N/mm) was significantly greater than PARS repair (11.8 ± 2.5 N/mm) (P = .011).

Conclusion

No significant difference in repair strength was seen, but higher initial linear stiffness for Krackow repair suggests superior resistance to gap formation, which may occur during postoperative rehabilitation. With equal repair strength, but less soft tissue devitalization, the PARS may be a favorable option for patients with risk factors for soft tissue complications.

3D-printed hydrogel particles containing PRP laden with TDSCs promote tendon repair in a rat model of tendinopathy

Long-term chronic inflammation after Achilles tendon injury is critical for tendinopathy. Platelet-rich plasma (PRP) injection, which is a common method for treating tendinopathy, has positive effects on tendon repair. In addition, tendon-derived stem cells (TDSCs), which are stem cells located in tendons, play a major role in maintaining tissue homeostasis and postinjury repair. In this study, injectable gelatine methacryloyl (GelMA) microparticles containing PRP laden with TDSCs (PRP-TDSC-GM) were prepared by a projection-based 3D bioprinting technique. Our results showed that PRP-TDSC-GM could promote tendon differentiation in TDSCs and reduce the inflammatory response by downregulating the PI3K-AKT pathway, thus promoting the structural and functional repair of tendons in vivo.

Ultrasonography for Injecting (Around) the Lateral Epicondyle: EURO-MUSCULUS/USPRM Perspective

Lateral epicondylitis (LE) is a very common and painful condition seen in the daily practice of musculoskeletal physicians. Ultrasound-guided (USG) injections are commonly performed to manage the pain, promote the healing phase, and plan a tailored rehabilitation treatment. In this aspect, several techniques were described to target specific pain generators i the lateral elbow. Likewise, the aim of this manuscript was to extensively review those USG techniques together with the patients' pertinent clinical/sonographic features. The authors believe that this literature summary could also be refined as a practical, ready-to-use guide for planning the USG interventions of the lateral elbow in clinical practice.

Biological and Mechanical Factors and Epigenetic Regulation Involved in Tendon Healing

Tendons are an important part of the musculoskeletal system. Connecting muscles to bones, tendons convert force into movement. Tendon injury can be acute or chronic. Noticeably, tendon healing requires a long time span and includes inflammation, proliferation, and remodeling processes. The mismatch between endogenous and exogenous healing may lead to adhesion causing further negative effects. Management of tendon injuries and complications such as subsequent adhesion formation are still challenges for clinicians. Due to numerous factors, tendon healing is a complex process. This review introduces the role of various biological and mechanical factors and epigenetic regulation processes involved in tendon healing.

Gene expression profiling of the masticatory muscle tendons and Achilles tendons under tensile strain in the Japanese macaque Macaca fuscata

Both Achilles and masticatory muscle tendons are large load-bearing structures, and excessive mechanical loading leads to hypertrophic changes in these tendons. In the maxillofacial region, hyperplasia of the masticatory muscle tendons and aponeurosis affect muscle extensibility resulting in limited mouth opening. Although gene expression profiles of Achilles and patellar tendons under mechanical strain are well investigated in rodents, the gene expression profile of the masticatory muscle tendons remains unexplored. Herein, we examined the gene expression pattern of masticatory muscle tendons and compared it with that of Achilles tendons under tensile strain conditions in the Japanese macaque Macaca fuscata. Primary tenocytes isolated from the masticatory muscle tendons (temporal tendon and masseter aponeurosis) and Achilles tendons were mechanically loaded using the tensile force and gene expression was analyzed using the next-generation sequencing. In tendons exposed to tensile strain, we identified 1076 differentially expressed genes with a false discovery rate (FDR) < 10-10. To identify genes that are differentially expressed in temporal tendon and masseter aponeurosis, an FDR of < 10-10 was used, whereas the FDR for Achilles tendons was set at > 0.05. Results showed that 147 genes are differentially expressed between temporal tendons and masseter aponeurosis, out of which, 125 human orthologs were identified using the Ensemble database. Eight of these orthologs were related to tendons and among them the expression of the glycoprotein nmb and sphingosine kinase 1 was increased in temporal tendons and masseter aponeurosis following exposure to tensile strain. Moreover, the expression of tubulin beta 3 class III, which promotes cell cycle progression, and septin 9, which promotes cytoskeletal rearrangements, were decreased in stretched Achilles tendon cells and their expression was increased in stretched masseter aponeurosis and temporal tendon cells. In conclusion, cyclic strain differentially affects gene expression in Achilles tendons and tendons of the masticatory muscles.

Heterotopic mineral deposits in intact rat Achilles tendons are characterized by a unique fiber-like structure

Heterotopic mineralization entails pathological mineral formation inside soft tissues. In human tendons mineralization is often associated with tendinopathies, tendon weakness and pain. In Achilles tendons, mineralization is considered to occur through heterotopic ossification (HO) primarily in response to tendon pathologies. However, refined details regarding HO deposition and microstructure are unknown. In this study, we characterize HO in intact rat Achilles tendons through high-resolution phase contrast enhanced synchrotron X-ray tomography. Furthermore, we test the potential of studying local tissue injury by needling intact Achilles tendons and the relation between tissue microdamage and HO. The results show that HO occurs in all intact Achilles tendons at 16 weeks of age. HO deposits are characterized by an elongated ellipsoidal shape and by a fiber-like internal structure which suggests that some collagen fibers have mineralized. The data indicates that deposition along fibers initiates in the pericellular area, and propagates into the intercellular area. Within HO deposits cells are larger and more rounded compared to tenocytes between unmineralized fibers, which are fewer and elongated. The results also indicate that multiple HO deposits may merge into bigger structures with time by accession along unmineralized fibers. Furthermore, the presence of unmineralized regions within the deposits may indicate that HOs are not only growing, but mineral resorption may also occur. Additionally, phase contrast synchrotron X-ray tomography allowed to distinguish microdamage at the fiber level in response to needling. The needle injury protocol could in the future enable to elucidate the relation between local inflammation, microdamage, and HO deposition.

Early Tensile Loading in Nonsurgically Treated Achilles Tendon Ruptures Leads to a Larger Tendon Callus and a Lower Elastic Modulus: A Randomized Controlled Trial

BACKGROUND

Early tensile loading improves material properties of healing Achilles tendon ruptures in animal models and in surgically treated human ruptures. However, the effect of such rehabilitation in patients who are nonsurgically treated remains unknown.

HYPOTHESIS

In nonsurgically treated Achilles tendon ruptures, early tensile loading would lead to higher elastic modulus 19 weeks after the injury compared with controls.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 2.

METHODS

Between October 2015 and November 2018, a total of 40 nonsurgically treated patients with acute Achilles tendon rupture were randomized to an early tensile loading (loaded group) or control group. Tantalum bead markers were inserted percutaneously into the tendon stumps 2 weeks after the injury to allow high-precision measurements of callus deformation under mechanical testing. The loaded group used a training pedal twice daily to produce a gradual increase in tensile load during the following 5 weeks. Both groups were allowed full weightbearing in an ankle orthosis and unloaded range of motion exercises. Patients were followed clinically and via roentgen stereophotogrammetric analysis and computed tomography at 7, 19, and 52 weeks after the injury.

RESULTS

The mean ± standard deviation elastic modulus at 19 weeks was 95.6 ± 38.2 MPa in the loaded group and 108 ± 45.2 MPa in controls (P = .37). The elastic modulus increased in both groups, although it was lower in the loaded group at all time points. Tendon cross-sectional area increased from 7 weeks to 19 weeks, from 231 ± 99.5 to 388 ± 142 mm² in the loaded group and from 188 ± 65.4 to 335 ± 87.2 mm² in controls (P < .001 for the effect of time). Cross-sectional area for the loaded group versus controls at 52 weeks was 302 ± 62.4 mm² versus 252 ± 49.2 mm², respectively (P = .03). Gap elongation was 7.35 ± 13.9 mm in the loaded group versus 2.86 ± 5.52 mm in controls (P = .27).

CONCLUSION

Early tensile loading in nonsurgically treated Achilles tendon ruptures did not lead to higher elastic modulus in the healing tendon but altered the structural properties of the tendon via an increased tendon thickness.

REGISTRATION

NCT0280575 (ClinicalTrials.gov identifier).

No differences in histopathological degenerative changes found in acute, trauma-related rotator cuff tears compared with chronic, nontraumatic tears

PURPOSE

Acute trauma-related rotator cuff tears are believed to have better healing potential than chronic tears due to less degenerative changes of the tendons. However, the histopathological condition of tendons from trauma-related tears is not well investigated. The purpose of this study was to explore specific histopathological features in tendons from acute trauma-related full-thickness rotator cuff tears and to compare them to findings in tendons from nontraumatic, chronic tears.

METHODS

In a prospective cohort study, 62 previously asymptomatic patients [14 women, median age 61 years (range 42-75)] with trauma-related full-thickness rotator cuff tears were consecutively included. Arthroscopic repair was performed within 30 (median, IQR 25-37) days after the injury. During surgery, tissue biopsies were harvested from the supraspinatus tendons in 53 (86%) of the patients. In addition, similar biopsies were harvested from 10 patients undergoing surgery for chronic tears without history of trauma. All tissue samples were examined by a well-experienced pathologist under light microscope. Tendon degeneration was determined using the Bonar score whereas immunostaining was used for proliferation (Ki67), inflammation (CD45), apoptosis (p53) and haemosiderin staining to study traces of bleeding.

RESULTS

The median (IQR) Bonar score for the acute trauma-related biopsies was 10.5 (7.5-14.5) compared to 11 (5-12.8) for the control group with no statistically significant difference between the groups. No statistically significant between-group difference was found for the inflammatory index whereas tendons from patients with trauma-related full-thickness rotator cuff tears had statistically significantly higher apoptosis [3.1 (0.5-8.9) vs. 0.1 (0-1.5), p = 0.003] and proliferation [4.0 (1.8-6.9) vs. 0.4 (0-2.0), p = 0.001) indices than those undergoing surgery for chronic tears. Positive haemosiderin staining was found in 34% of tissue samples from patients with trauma-related tears compared to 10% in the control group (n.s).

CONCLUSION

This study suggests that there is no difference with regard to degenerative changes between supraspinatus tendons harvested from patients with acute, trauma-related rotator cuff tears and patients with nontraumatic, chronic tears.

LEVEL OF EVIDENCE

II.

Secretome from In Vitro Mechanically Loaded Myoblasts Induces Tenocyte Migration, Transition to a Fibroblastic Phenotype and Suppression of Collagen Production

It is known that mechanical loading of muscles increases the strength of healing tendon tissue, but the mechanism involved remains elusive. We hypothesized that the secretome from myoblasts in co-culture with tenocytes affects tenocyte migration, cell phenotype, and collagen (Col) production and that the effect is dependent on different types of mechanical loading of myoblasts. To test this, we used an in vitro indirect transwell co-culture system. Myoblasts were mechanically loaded using the FlexCell^® Tension system. Tenocyte cell migration, proliferation, apoptosis, collagen production, and several tenocyte markers were measured. The secretome from myoblasts decreased the Col I/III ratio and increased the expression of tenocyte specific markers as compared with tenocytes cultured alone. The secretome from statically loaded myoblasts significantly enhanced tenocyte migration and Col I/III ratio as compared with dynamic loading and controls. In addition, the secretome from statically loaded myoblasts induced tenocytes towards a myofibroblast-like phenotype. Taken together, these results demonstrate that the secretome from statically loaded myoblasts has a profound influence on tenocytes, affecting parameters that are related to the tendon healing process.

A numerical framework for mechano-regulated tendon healing-Simulation of early regeneration of the Achilles tendon

Mechano-regulation during tendon healing, i.e. the relationship between mechanical stimuli and cellular response, has received more attention recently. However, the basic mechanobiological mechanisms governing tendon healing after a rupture are still not well-understood. Literature has reported spatial and temporal variations in the healing of ruptured tendon tissue. In this study, we explored a computational modeling approach to describe tendon healing. In particular, a novel 3D mechano-regulatory framework was developed to investigate spatio-temporal evolution of collagen content and orientation, and temporal evolution of tendon stiffness during early tendon healing. Based on an extensive literature search, two possible relationships were proposed to connect levels of mechanical stimuli to collagen production. Since literature remains unclear on strain-dependent collagen production at high levels of strain, the two investigated production laws explored the presence or absence of collagen production upon non-physiologically high levels of strain (>15%). Implementation in a finite element framework, pointed to large spatial variations in strain magnitudes within the callus tissue, which resulted in predictions of distinct spatial distributions of collagen over time. The simulations showed that the magnitude of strain was highest in the tendon core along the central axis, and decreased towards the outer periphery. Consequently, decreased levels of collagen production for high levels of tensile strain were shown to accurately predict the experimentally observed delayed collagen production in the tendon core. In addition, our healing framework predicted evolution of collagen orientation towards alignment with the tendon axis and the overall predicted tendon stiffness agreed well with experimental data. In this study, we explored the capability of a numerical model to describe spatial and temporal variations in tendon healing and we identified that understanding mechano-regulated collagen production can play a key role in explaining heterogeneities observed during tendon healing.

Molecular and Structural Effects of Percutaneous Interventions in Chronic Achilles Tendinopathy

Achilles tendinopathy (AT) is a common problem, especially in people of working age, as well as in the elderly. Although the pathogenesis of tendinopathy is better known, therapeutic management of AT remains challenging. Various percutaneous treatments have been applied to tendon lesions: e.g., injectable treatments, platelet-rich plasma (PRP), corticosteroids, stem cells, MMP inhibitors, and anti-angiogenic agents), as well as percutaneous procedures without any injection (percutaneous soft tissue release and dry needling). In this review, we will describe and comment on data about the molecular and structural effects of these treatments obtained in vitro and in vivo and report their efficacy in clinical trials. Local treatments have some impact on neovascularization, inflammation or tissue remodeling in animal models, but evidence from clinical trials remains too weak to establish an accurate management plan, and further studies will be necessary to evaluate their value.

The role of the immune system in tendon healing: a systematic review

INTRODUCTION

The role of the immune system in tendon healing relies on polymorphonucleocytes, mast cells, macrophages and lymphocytes, the 'immune cells' and their cytokine production. This systematic review reports how the immune system affects tendon healing.

SOURCES OF DATA

We registered our protocol (registration number: CRD42019141838). After searching PubMed, Embase and Cochrane Library databases, we included studies of any level of evidence published in peer-reviewed journals reporting clinical or preclinical results. The PRISMA guidelines were applied, and risk of bias and the methodological quality of the included studies were assessed. We excluded all the articles with high risk of bias and/or low quality after the assessment. We included 62 articles assessed as medium or high quality.

AREAS OF AGREEMENT

Macrophages are major actors in the promotion of proper wound healing as well as the resolution of inflammation in response to pathogenic challenge or tissue damage. The immune cells secrete cytokines involving both pro-inflammatory and anti-inflammatory factors which could affect both healing and macrophage polarization.

AREAS OF CONTROVERSY

The role of lymphocytes, mast cells and polymorphonucleocytes is still inconclusive.

GROWING POINTS

The immune system is a major actor in the complex mechanism behind the healing response occurring in tendons after an injury. A dysregulation of the immune response can ultimately lead to a failed healing response.

AREAS TIMELY FOR DEVELOPING RESEARCH

Further studies are needed to shed light on therapeutic targets to improve tendon healing and in managing new way to balance immune response.

EGR1 Transcription Factor is a Multifaceted Regulator of Matrix Production in Tendons and Other Connective Tissues

Although the transcription factor EGR1 is known as NGF1-A, TIS8, Krox24, zif/268, and ZENK, it still has many fewer names than biological functions. A broad range of signals induce Egr1 gene expression via numerous regulatory elements identified in the Egr1 promoter. EGR1 is also the target of multiple post-translational modifications, which modulate EGR1 transcriptional activity. Despite the myriad regulators of Egr1 transcription and translation, and the numerous biological functions identified for EGR1, the literature reveals a recurring theme of EGR1 transcriptional activity in connective tissues, regulating genes related to the extracellular matrix. Egr1 is expressed in different connective tissues, such as tendon (a dense connective tissue), cartilage and bone (supportive connective tissues), and adipose tissue (a loose connective tissue). Egr1 is involved in the development, homeostasis, and healing processes of these tissues, mainly via the regulation of extracellular matrix. In addition, Egr1 is often involved in the abnormal production of extracellular matrix in fibrotic conditions, and Egr1 deletion is seen as a target for therapeutic strategies to fight fibrotic conditions. This generic EGR1 function in matrix regulation has little-explored implications but is potentially important for tendon repair.

Early Growth Response Genes Increases Rapidly After Mechanical Overloading and Unloading in Tendon Constructs

Tendon cells exist in a dense extracellular matrix and mechanical loading is important for the strength development of this matrix. We therefore use a three-dimensional (3D) culture system for tendon formation in vitro. The objectives of this study were to elucidate the temporal expression of tendon-related genes during the formation of artificial tendons in vitro and to investigate if early growth response-1 (EGR1), EGR2, FOS, and cyclooxygenase-1 and -2 (PTGS1 and PTGS2) are sensitive to mechanical loading. First, we studied messenger RNA (mRNA) levels of several tendon-related genes during formation of tendon constructs. Second, we studied the mRNA levels of, for example, EGR1 and EGR2 after different degrees of loading; dynamic physiologic-range loading (2.5% strain), dynamic overloading (approximately 10% strain), or tension release. The gene expression for tendon-related genes (i.e., EGR2, MKX, TNMD, COL3A1) increased with time after seeding into this 3D model. EGR1, EGR2, FOS, PTGS1, and PTGS2 did not respond to physiologic-range loading. But overloading (and tension release) lead to elevated levels of EGR1 and EGR2 (p ≤ 0.006). FOS and PTGS2 were increased after overloading (both p < 0.007) but not after tension release (p = 0.06 and 0.08). In conclusion, the expression of tendon-related genes increases during the formation of artificial tendons in vitro, including EGR2. Furthermore, the gene expression of EGR1 and EGR2 in human tendon cells appear to be sensitive to overloading and unloading but did not respond to the single episode of physiologic-range loading. These findings could be helpful for the understanding of tendon tensional homeostasis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:173-181, 2020.

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

BACKGROUND

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

SOURCES OF DATA

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

AREAS OF AGREEMENT

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

AREAS OF CONTROVERSY

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

GROWING POINTS

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

AREAS TIMELY FOR DEVELOPING RESEARCH

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

Minimally Invasive Treatments of Acute Achilles Tendon Ruptures

Achilles tendon rupture is a common injury to the lower extremity that requires appropriate treatment to minimize functional deficit. Available treatments of Achilles tendon ruptures include nonoperative, open surgical repair, percutaneous repair, and minimally invasive repair. Open surgical repair obtains favorable functional outcomes with significant potential for deep soft tissue complications, calling into question the value of open repair. Percutaneous repair is an alternative option with comparable functional results and minimal soft tissue complications; however, sural nerve injury is a complication. Minimally invasive Achilles repair offers optimal results with superior functional outcomes with minimal soft tissue complications and sural nerve injury.

Platelet-rich plasma versus lidocaine as tenotomy adjuvants in people with elbow epicondylopathy: a randomized controlled trial

OBJECTIVES

To determine the efficacy of platelet-rich plasma (PRP) compared to lidocaine as a tenotomy adjuvant for people with elbow tendinopathy.

METHODS

Our study was a parallel-group, double-blind, randomized trial involving 71 patients with recalcitrant elbow tendinopathy who received two sessions of ultrasound-guided tenotomy with either PRP or lidocaine in a tertiary public hospital. The primary end point was the percentage of patients with an improvement exceeding 25% reduction in disability (Spanish version of the Disabilities of the Arm, Shoulder and Hand questionnaires-DASH-E) at 6 and 12 months; the secondary outcome was the percentage of patients exceeding 25% reduction in pain (VAS-P).

RESULTS

There was no evidence of significant differences in the proportion of patients who experienced clinically relevant improvements. After 6 months, 18 patients (78.59%) in the lidocaine group and 19 patients (73.08%) in the PRP group showed improved function above 25% (unadjusted odds ratio, 0.90; 95% confidence interval [CI], 0.90 (0.17 to 4.60)); 21 patients (72.21%) in the lidocaine group versus 22 patients (84.62%) in the PRP group achieved more than 25% pain reduction (unadjusted odds ratio, 0.48; 95% CI, 0.10 to 2.37). After 12 months, 17 patients (70.83%) in the lidocaine group versus 19 patients (76%) in the PRP group had improved function (unadjusted odds ratio, 0.71; 95% CI, 0.13 to 3.84), and 19 patients (76%) in the lidocaine group versus 20 patients (90.91%) in the PRP group had improved pain above 25% (unadjusted odds ratio, 0.35; 95% CI, 0.06 to 2.51). Hypercholesterolemia and baseline vascularization influenced outcomes. There were no differences between groups in the adjusted odds ratios.

CONCLUSION

PRP results in similar improvements to those obtained with lidocaine. Selecting patients according to their pretreatment status can improve treatment efficacy.

TRIAL REGISTRATION

NCT01945528 , EudraCT 2013-000478-32. Registered 18 August 2013, enrolment of the first participant 10 March 2014.

Electrical dry needling as an adjunct to exercise, manual therapy and ultrasound for plantar fasciitis: A multi-center randomized clinical trial

Study Design

Randomized, single-blinded, multi-center, parallel-group trial.

Objectives

To compare the effects of adding electrical dry needling into a program of manual therapy, exercise and ultrasound on pain, function and related-disability in individuals with plantar fasciitis (PF).

Background

The isolated application of electrical dry needling, manual therapy, exercise, and ultrasound has been found to be effective for PF. However, no previous study has investigated the combined effect of these interventions in this population.

Methods

One hundred and eleven participants (n = 111) with plantar fasciitis were randomized to receive electrical dry needling, manual therapy, exercise and ultrasound (n = 58) or manual therapy, exercise and ultrasound (n = 53). The primary outcome was first-step pain in the morning as measured by the Numeric Pain Rating Scale (NPRS). Secondary outcomes included resting foot pain (NPRS), pain during activity (NPRS), the Lower Extremity Functional Scale (LEFS), the Foot Functional Index (FFI), medication intake, and the Global Rating of Change (GROC). The treatment period was 4 weeks with follow-up assessments at 1 week, 4 weeks, and 3 months after the first treatment session. Both groups received 6 sessions of impairment-based manual therapy directed to the lower limb, self-stretching of the plantar fascia and the Achilles tendon, strengthening exercises for the intrinsic muscles of the foot, and therapeutic ultrasound. In addition, the dry needling group also received 6 sessions of electrical dry needling using a standardized 8-point protocol for 20 minutes. The primary aim was examined with a 2-way mixed-model analysis of covariance (ANCOVA) with treatment group as the between-subjects variable and time as the within-subjects variable after adjusting for baseline outcomes.

Results

The 2X4 ANCOVA revealed that individuals with PF who received electrical dry needling, manual therapy, exercise and ultrasound experienced significantly greater improvements in first-step morning pain (F = 22.021; P<0.001), resting foot pain (F = 23.931; P<0.001), pain during activity (F = 7.629; P = 0.007), LEFS (F = 13.081; P<0.001), FFI Pain Subscale (F = 13.547; P<0.001), FFI Disability Subscale (F = 8.746; P = 0.004), and FFI Total Score (F = 10.65; P<0.001) than those who received manual therapy, exercise and ultrasound at 3 months. No differences in FFI Activity Limitation Subscale (F = 2.687; P = 0.104) were observed. Significantly (X² = 9.512; P = 0.023) more patients in the electrical dry needling group completely stopped taking medication for their pain compared to the manual therapy, exercise and ultrasound group at 3 months. Based on the cutoff score of ≥+5 on the GROC, significantly (X² = 45.582; P<0.001) more patients within the electrical dry needling group (n = 45, 78%) achieved a successful outcome compared to the manual therapy, exercise and ultrasound group (n = 11, 21%). Effect sizes ranged from medium to large (0.53<SMD<0.85) at 3 months in favor of the electrical dry needling group.

Conclusion

The inclusion of electrical dry needling into a program of manual therapy, exercise and ultrasound was more effective for improving pain, function and related-disability than the application of manual therapy, exercise and ultrasound alone in individuals with PF at mid-term (3 months).

Level of evidence

Therapy, Level 1b.

Different mechanisms activated by mild versus strong loading in rat Achilles tendon healing

Background

Mechanical loading stimulates Achilles tendon healing. However, various degrees of loading appear to have different effects on the mechanical properties of the healing tendon, and strong loading might create microdamage in the tissue. This suggests that different mechanisms might be activated depending on the magnitude of loading. The aim of this study was to investigate these mechanisms further.

Methods

Female rats had their right Achilles tendon cut transversely and divided into three groups: 1) unloading (calf muscle paralysis by Botox injections, combined with joint fixation by a steel-orthosis), 2) mild loading (Botox only), 3) strong loading (free cage activity). Gene expression was analyzed by PCR, 5 days post-injury, and mechanical testing 8 days post-injury. The occurrence of microdamage was analyzed 3, 5, or 14 days post-injury, by measuring leakage of injected fluorescence-labelled albumin in the healing tendon tissue.

Results

Peak force, peak stress, and elastic modulus of the healing tendons gradually improved with increased loading as well as the expression of extracellular matrix genes. In contrast, only strong loading increased transverse area and affected inflammation genes. Strong loading led to higher fluorescence (as a sign of microdamage) compared to mild loading at 3 and 5 days post-injury, but not at 14 days.

Discussion

Our results show that strong loading improves both the quality and quantity of the healing tendon, while mild loading only improves the quality. Strong loading also induces microdamage and alters the inflammatory response. This suggests that mild loading exert its effect via mechanotransduction mechanisms, while strong loading exert its effect both via mechanotransduction and the creation of microdamage.

Conclusion

In conclusion, mild loading is enough to increase the quality of the healing tendon without inducing microdamage and alter the inflammation in the tissue. This supports the general conception that early mobilization of a ruptured tendon in patients is advantageous.

A Biomechanical Comparison of Limited Open Versus Krackow Repair for Achilles Tendon Rupture

Background:

Soft tissue complications after Achilles tendon repair has led to increased interest in less invasive techniques. Various limited open techniques have gained popularity as an alternative to open operative repair. The purpose of this study was to biomechanically compare an open Krackow and limited open repair for Achilles tendon rupture. We hypothesized that there would be no statistical difference in load to failure, work to failure, and initial linear stiffness.

Methods:

A simulated Achilles tendon rupture was created 4 cm proximal to its insertion in 18 fresh-frozen cadaveric below-knee lower limbs. Specimens were randomized to open or limited open PARS Achilles Jig System repair. Repairs were loaded to failure at a rate of 25.4 mm/s to reflect loading during normal ankle range of motion. Load to failure, work to failure, and initial linear stiffness were compared between the 2 repair types.

Results:

The average load to failure (353.8 ± 88.8 N vs 313.3 ± 99.9 N; P = .38) and work to failure (6.4 ± 2.3 J vs 6.3 ± 3.5 J; P = .904) were not statistically different for Krackow and PARS repair, respectively. Mean initial linear stiffness of the Krackow repair (17.8 ± 5.4 N/mm) was significantly greater than PARS repair (11.8 ± 2.5 N/mm) ( P = .011).

Conclusion:

No significant difference in repair strength was seen, but higher initial linear stiffness for Krackow repair suggests superior resistance to gap formation, which may occur during postoperative rehabilitation. With equal repair strength, but less soft tissue devitalization, the PARS may be a favorable option for patients with risk factors for soft tissue complications.

Effect of platelet-rich plasma on rat Achilles tendon healing is related to microbiota

Background and purpose - In 3 papers in Acta Orthopaedica 10 years ago, we described that platelet-rich plasma (PRP) improves tendon healing in a rat Achilles transection model. Later, we found that microtrauma has similar effects, probably acting via inflammation. This raised the suspicion that the effect ascribed to growth factors within PRP could instead be due to unspecific influences on inflammation. While testing this hypothesis, we noted that the effect seemed to be related to the microbiota. Material and methods - We tried to reproduce our old findings with local injection of PRP 6 h after tendon transection, followed by mechanical testing after 11 days. This failed. After fruitless variations in PRP production protocols, leukocyte concentration, and physical activity, we finally tried rats carrying potentially pathogenic bacteria. In all, 242 rats were used. Results - In 4 consecutive experiments on pathogen-free rats, no effect of PRP on healing was found. In contrast, apparently healthy rats carrying Staphylococcus aureus showed increased strength of the healing tendon after PRP treatment. These rats had lower [corrected] levels of cytotoxic T-cells in their spleens. Interpretation - The failure to reproduce older experiments in clean rats was striking, and the difference in response between these and Staphylococcus-carrying rats suggests that the PRP effect is dependent on the immune status. PRP functions may be more complex than just the release of growth factors. Extrapolation from our previous findings with PRP to the situation in humans therefore becomes even more uncertain.

Therapeutic Mechanisms of Human Adipose-Derived Mesenchymal Stem Cells in a Rat Tendon Injury Model

BACKGROUND

Although survival of transplanted stem cells in vivo and differentiation of stem cells into tenocytes in vitro have been reported, there have been no in vivo studies demonstrating that mesenchymal stem cells (MSCs) could secrete their own proteins as differentiated tenogenic cells. Purpose/Hypothesis: Using a xenogeneic MSC transplantation model, we aimed to investigate whether MSCs could differentiate into the tenogenic lineage and secrete their own proteins. The hypothesis was that human MSCs would differentiate into the human tenogenic lineage and the cells would be able to secrete human-specific proteins in a rat tendon injury model.

STUDY DESIGN

Controlled laboratory study.

METHODS

The Achilles tendons of 57 Sprague Dawley rats received full-thickness rectangular defects. After the modeling, the defective tendons were randomly assigned to 3 groups: (1) cell group, implantation with human adipose-derived mesenchymal stem cells (hASCs) and fibrin glue (10⁶ cells in 60 μL); (2) fibrin group, implantation with fibrin glue and same volume of cell media; and (3) sham group, identical surgical procedure without any treatment. Gross observation and biomechanical, histopathological, immunohistochemistry, and Western blot analyses were performed at 2 and 4 weeks after modeling.

RESULTS

hASCs implanted into the defective rat tendons were viable for 4 weeks as detected by immunofluorescence staining. Tendons treated with hASCs showed better gross morphological and biomechanical recovery than those in the fibrin and sham groups. Furthermore, the expression of both human-specific collagen type I and tenascin-C was significantly higher in the cell group than in the other 2 groups.

CONCLUSION

Transplantation of hASCs enhanced rat tendon healing biomechanically. hASCs implanted into the rat tendon defect model survived for at least 4 weeks and secreted human-specific collagen type I and tenascin-C. These findings suggest that transplanted MSCs may be able to differentiate into the tenogenic lineage and contribute their own proteins to tendon healing.

CLINICAL RELEVANCE

In tendon injury, MSCs can enhance tendon healing by secreting their own protein and have potential as a therapeutic option in human tendinopathy.

Acute Achilles Tendon Ruptures: An Update on Treatment

Acute rupture of the Achilles tendon is common and seen most frequently in people who participate in recreational athletics into their thirties and forties. Although goals of treatment have not changed in the past 15 years, recent studies of nonsurgical management, specifically functional bracing with early range of motion, demonstrate rerupture rates similar to those of tendon repair and result in fewer wound and soft-tissue complications. Satisfactory outcomes may be obtained with nonsurgical or surgical treatment. Newer surgical techniques, including limited open and percutaneous repair, show rerupture rates similar to those of open repair but lower overall complication rates. Early research demonstrates no improvement in functional outcomes or tendon properties with the use of platelet-rich plasma, but promising results with the use of bone marrow-derived stem cells have been seen in animal models. Further investigation is necessary to warrant routine use of biologic adjuncts in the management of acute Achilles tendon ruptures.

EGR1 Regulates Transcription Downstream of Mechanical Signals during Tendon Formation and Healing

BACKGROUND

Tendon is a mechanical tissue that transmits forces generated by muscle to bone in order to allow body motion. The molecular pathways that sense mechanical forces during tendon formation, homeostasis and repair are not known. EGR1 is a mechanosensitive transcription factor involved in tendon formation, homeostasis and repair. We hypothesized that EGR1 senses mechanical signals to promote tendon gene expression.

METHODOLOGY/PRINCIPAL FINDINGS

Using in vitro and in vivo models, we show that the expression of Egr1 and tendon genes is downregulated in 3D-engineered tendons made of mesenchymal stem cells when tension is released as well as in tendon homeostasis and healing when mechanical signals are reduced. We further demonstrate that EGR1 overexpression prevents tendon gene downregulation in 3D-engineered tendons when tension is released. Lastly, ultrasound and microbubbles mediated EGR1 overexpression prevents the downregulation of tendon gene expression during tendon healing in reduced load conditions.

CONCLUSION/SIGNIFICANCE

These results show that Egr1 expression is sensitive to mechanical signals in tendon cells. Moreover, EGR1 overexpression prevents the downregulation of tendon gene expression in the absence of mechanical signals in 3D-engineered tendons and tendon healing. These results show that EGR1 induces a transcriptional response downstream of mechanical signals in tendon cells and open new avenues to use EGR1 to promote tendon healing in reduced load conditions.

A possible link between loading, inflammation and healing: Immune cell populations during tendon healing in the rat

Loading influences tendon healing, and so does inflammation. We hypothesized that the two are connected. 48 rats underwent Achilles tendon transection. Half of the rats received Botox injections into calf muscles to reduce mechanical loading. Cells from the regenerating tissue were analyzed by flow cytometry. In the loaded group, the regenerating tissue contained 83% leukocytes (CD45⁺) day 1, and 23% day 10. The M1/M2 macrophage ratio (CCR7/CD206) peaked at day 3, while T helper (CD3⁺CD4⁺) and T_reg cells (CD25⁺ Foxp3⁺) increased over time. With Botox, markers associated with down-regulation of inflammation were more common day 5 (CD163, CD206, CD25, Foxp3), and M1 or M2 macrophages and T_reg cells were virtually absent day 10, while still present with full loading. The primary variable, CCR7/CD206 ratio day 5, was higher with full loading (p = 0.001) and the T_reg cell fraction was lower (p < 0.001). Free cage activity loading is known to increase size and strength of the tendon in this model compared to Botox. Loading now appeared to delay the switch to an M2 type of inflammation with more T_reg cells. It seems a prolonged M1 phase due to loading might make the tendon regenerate bigger.

Tenogenic differentiation of mesenchymal stem cells and noncoding RNA: From bench to bedside

Tendon is a critical unit of musculoskeletal system that connects muscle to bone to control bone movement. More population participate in physical activities, tendon injuries, such as acute tendon rupture and tendinopathy due to overuse, are common causing unbearable pain and disability. However, the process of tendon development and the pathogenesis of tendinopathy are not well defined, limiting the development of clinical therapy for tendon injuries. Studying the tendon differentiation control pathways may help to develop novel therapeutic strategies. This review summarized the novel molecular and cellular events in tendon development and highlighted the clinical application potential of non-coding RNAs and tendon-derived stem cells in gene and cell therapy for tendon injuries, which may bring insights into research and new therapy for tendon disorders.

Three-Dimensional Platelet-Rich Plasma Hydrogel Model to Study Early Tendon Healing

Since the experimental conditions of cell cultures may bias results, it is critical to use suitable models. This is also true in the context of tendon cell biology and the study of platelet-rich plasma (PRP) therapies and PRP-augmented cell-based therapies. We compared the culture of human tendon cells in 2 dimensions (2D) with PRP-supplemented media to culture in matching 3-dimensional (3D) PRP hydrogels. Cell proliferation, cell shape, and the pattern of gene and protein expression were examined. Our data revealed modifications in cell shape and enhanced expression of tenomodulin and scleraxis in 3D hydrogels. Additionally, protein secretion analysis using glass-based arrays specific for angiogenesis revealed differences in interleukin (IL)-6 and IL-8 protein expression between 2D cultures and 3D hydrogels, while the secretion of other angiogenic or inflammatory cytokines was unaffected. Our study suggests that 3D hydrogels are physiologically more relevant than 2D cultures in the study of tendon cells, based on cell shape, support of tenocyte proliferation, phenotype, and the pattern of gene and protein expression.

COX-2 inhibition impairs mechanical stimulation of early tendon healing in rats by reducing the response to microdamage

Early tendon healing can be stimulated by mechanical loading and inhibited by cyclooxygenase (COX) inhibitors (nonsteroidal anti-inflammatory drugs). Therefore, we investigated if impairment of tendon healing by a COX-2 inhibitor (parecoxib) is related to loading. Because loading might infer microdamage, which also stimulates healing, we also investigated if this effect is inhibited by parecoxib. The Achilles tendon was transected in 114 rats. Three degrees of loading were used: full loading, partial unloading, and unloading (no unloading, Botox injections in the plantar flexor muscles, or Botox in combination with tail suspension). For each loading condition, the rats received either parecoxib or saline. In a second experiment, rats were unloaded with Botox, and the tendon was subjected to microdamage by needling combined with either saline or parecoxib. Mechanical testing day 7 showed that there was a significant interaction between loading and parecoxib for peak force at failure (P < 0.01). However, logarithmic values showed no significant interaction, meaning that we could not exclude that the inhibitory effect of parecoxib was proportionate to the degree of loading. Microbleeding was common in the healing tissue, suggesting that loading caused microdamage. Needling increased peak force at failure (P < 0.01), and this effect of microdamage was almost abolished by parecoxib (P < 0.01). Taken together, this suggests that COX-2 inhibition impairs the positive effects of mechanical loading during tendon healing, mainly by reducing the response to microdamage.

Tendon injury: from biology to tendon repair

Tendon is a crucial component of the musculoskeletal system. Tendons connect muscle to bone and transmit forces to produce motion. Chronic and acute tendon injuries are very common and result in considerable pain and disability. The management of tendon injuries remains a challenge for clinicians. Effective treatments for tendon injuries are lacking because the understanding of tendon biology lags behind that of the other components of the musculoskeletal system. Animal and cellular models have been developed to study tendon-cell differentiation and tendon repair following injury. These studies have highlighted specific growth factors and transcription factors involved in tenogenesis during developmental and repair processes. Mechanical factors also seem to be essential for tendon development, homeostasis and repair. Mechanical signals are transduced via molecular signalling pathways that trigger adaptive responses in the tendon. Understanding the links between the mechanical and biological parameters involved in tendon development, homeostasis and repair is prerequisite for the identification of effective treatments for chronic and acute tendon injuries.