Effects of nonsteroidal anti-inflammatory drugs on flexor tendon adhesion

Peritendinous adhesion: Therapeutic targets and progress of drug therapy

Peritendinous adhesion (PA) is one of the most common complications following hand surgery and characterized with abnormal hyperplasia of connective tissue and excessive deposition of extracellular matrix. Subsequently, various clinical symptoms such as chronic pain, limb dyskinesia and even joint stiffness occur and patients are always involved in the vicious cycle of "adhesion - release - re-adhesion", which seriously compromise the quality of life. Until present, the underlying mechanism remains controversial and lack of specific treatment, with symptomatic treatment being the only option to relieve symptoms, but not contributing no more to the fundamentally rehabilitation of basic structure and function. Recently, novel strategies have been proposed to inhibit the formation of adhesion tissues including implantation of anti-adhesion barriers, anti-inflammation, restraint of myofibroblast transformation and regulation of collagen overproduction. Furthermore, gene therapy has also been considered as a promising anti-adhesion treatment. In this review, we provide an overview of anti-adhesion targets and relevant drugs to summarize the potential pharmacological roles and present subsequent challenges and prospects of anti-adhesion drugs.

Current trends in the prevention of adhesions after zone 2 flexor tendon repair

Treating flexor tendon injuries within the digital flexor sheath (commonly referred to as palmar hand zone 2) presents both technical and logistical challenges. Success hinges on striking a delicate balance between safeguarding the surgical repair for tendon healing and initiating early rehabilitation to mitigate the formation of tendon adhesions. Adhesions between tendon slips and between tendons and the flexor sheath impede tendon movement, leading to postoperative stiffness and functional impairment. While current approaches to flexor tendon repair prioritize maximizing tendon strength for early mobilization and adhesion prevention, factors such as pain, swelling, and patient compliance may impede postoperative rehabilitation efforts. Moreover, premature mobilization could risk repair failure, necessitating additional surgical interventions. Pharmacological agents offer a potential avenue for minimizing inflammation and reducing adhesion formation while still promoting normal tendon healing. Although some systemic and local agents have shown promising results in animal studies, their clinical efficacy remains uncertain. Limitations in these studies include the relevance of chosen animal models to human populations and the adequacy of tools and measurement techniques in accurately assessing the impact of adhesions. This article provides an overview of the clinical challenges associated with flexor tendon injuries, discusses current on- and off-label agents aimed at minimizing adhesion formation, and examines investigational models designed to study adhesion reduction after intra-synovial flexor tendon repair. Understanding the clinical problem and experimental models may serve as a catalyst for future research aimed at addressing intra-synovial tendon adhesions following zone 2 flexor tendon repair.

Myeloid Cells and Sensory Nerves Mediate Peritendinous Adhesion Formation via Prostaglandin E2

Peritendinous adhesion that forms after tendon injury substantially limits daily life. The pathology of adhesion involves inflammation and the associated proliferation. However, the current studies on this condition are lacking, previous studies reveal that cyclooxygenase-2 (COX2) gene inhibitors have anti-adhesion effects through reducing prostaglandin E2 (PGE2) and the proliferation of fibroblasts, are contrary to the failure in anti-adhesion through deletion of EP4 (prostaglandin E receptor 4) gene in fibroblasts in mice of another study. In this study, single-cell RNA sequencing analysis of human and mouse specimens are combined with eight types of conditional knockout mice and further reveal that deletion of COX2 in myeloid cells and deletion of EP4 gene in sensory nerves decrease adhesion and impair the biomechanical properties of repaired tendons. Furthermore, the COX2 inhibitor parecoxib reduces PGE2 but impairs the biomechanical properties of repaired tendons. Interestingly, PGE2 local treatment improves the biomechanical properties of the repaired tendons. These findings clarify the complex role of PGE2 in peritendinous adhesion formation (PAF) and tendon repair.

Antioxidant Carbon Dots and Ursolic Acid Co-Encapsulated Liposomes Composite Hydrogel for Alleviating Adhesion Formation and Enhancing Tendon Healing in Tendon Injury

Background

The formation of adhesion after tendon injury represents a major obstacle to tendon repair, and currently there is no effective anti-adhesion method in clinical practice. Oxidative stress, inflammation, and fibrosis can occur in tendon injury and these factors can lead to tendon adhesion. Antioxidant carbon dots and ursolic acid (UA) both possess antioxidant and anti-inflammatory properties. In this experiment, we have for the first time created RCDs/UA@Lipo-HAMA using red fluorescent carbon dots and UA co-encapsulated liposomes composite hyaluronic acid methacryloyl hydrogel. We found that RCDs/UA@Lipo-HAMA could better attenuate adhesion formation and enhance tendon healing in tendon injury.

Materials and Methods

RCDs/UA@Lipo-HAMA were prepared and characterized. In vitro experiments on cellular oxidative stress and fibrosis were performed. Reactive oxygen species (ROS), and immunofluorescent staining of collagens type I (COL I), collagens type III (COL III), and α-smooth muscle actin (α-SMA) were used to evaluate anti-oxidative and anti-fibrotic abilities. In vivo models of Achilles tendon injury repair (ATI) and flexor digitorum profundus tendon injury repair (FDPI) were established. The major organs and blood biochemical indicators of rats were tested to determine the toxicity of RCDs/UA@Lipo-HAMA. Biomechanical testing, motor function analysis, immunofluorescence, and immunohistochemical staining were performed to assess the tendon adhesion and repair after tendon injury.

Results

In vitro, the RCDs/UA@Lipo group scavenged excessive ROS, stabilized the mitochondrial membrane potential (ΔΨm), and reduced the expression of COL I, COL III, and α-SMA. In vivo, assessment results showed that the RCDs/UA@Lipo-HAMA group improved collagen arrangement and biomechanical properties, reduced tendon adhesion, and promoted motor function after tendon injury. Additionally, the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) in the RCDs/UA@Lipo-HAMA group increased; the levels of cluster of differentiation 68 (CD68), inducible Nitric Oxide Synthase (iNOS), COL III, α-SMA, Vimentin, and matrix metallopeptidase 2 (MMP2) decreased.

Conclusion

In this study, the RCDs/UA@Lipo-HAMA alleviated tendon adhesion formation and enhanced tendon healing by attenuating oxidative stress, inflammation, and fibrosis. This study provided a novel therapeutic approach for the clinical treatment of tendon injury.

Uni-directional release of ibuprofen from an asymmetric fibrous membrane enables effective peritendinous anti-adhesion

Drug-loaded porous membranes have been deemed to be effective physicochemical barriers to separate postoperative adhesion-prone tissues in tendon healing. However, cell viability and subsequent tissue regeneration might be severely interfered with the unrestricted release and the locally excessive concentration of anti-inflammatory drugs. Herein, we report a double-layered membrane with sustained and uni-directional drug delivery features to prevent peritendinous adhesion without hampering the healing outcome. A vortex-assisted electrospinning system in combination with ibuprofen (IBU)-in-water emulsion was utilized to fabricate IBU-loaded poly-ʟ-lactic-acid (PLLA) fiber bundle membrane (PFB-IBU) as the anti-adhesion layer. The resultant highly porous structure, oleophilic and hydrophobic nature of PLLA fibers enabled in situ loading of IBU with a concentration gradient across the membrane thickness. Aligned collagen nanofibers were further deposited at the low IBU concentration side of the membrane for regulating cell growth and achieving uni-directional release of IBU. Drug release kinetics showed that the release amount of IBU from the high concentration side reached 79.32% at 14 d, while it was only 0.35% at the collagen side. Therefore, fibroblast proliferation at the high concentration side was successfully inhibited without affecting the oriented growth of tendon-derived stem cells at the other side. In vivo evaluation of the rat Achilles adhesion model confirmed the successful peritendinous anti-adhesion of our double-layered membrane, in that the macrophage recruitment, the inflammatory factor secretion and the deposition of pathological adhesion markers such as α-SMA and COL-III were all inhibited, which greatly improved the peritendinous fibrosis and restored the motor function of tendon.

Quantitative evaluation of adhesion severity around subscapularis and its relationship with shoulder range of motion in frozen shoulder and rotator cuff disorder: an observational study using dynamic ultrasonography

Background

This study aimed to evaluate the severity of adhesion between muscles in the shoulder joint using dynamic ultrasonography and to confirm whether adhesions cause range of motion (ROM) restrictions.

Methods

Twenty-four shoulders from 15 frozen shoulder patients and 24 shoulders from 18 rotator cuff disorder patients were enrolled. We obtained ultrasound video sequences of the subscapularis (SSC) and deltoid muscles during shoulder external rotation. The mean stretching velocities of the deltoid and SSC were subsequently analyzed using a personal computer. If adhesions occurred between both muscles, the deltoid was stretched more vigorously, and we calculated mean stretching velocity of the deltoid / SSC as adhesion severity. The coracohumeral ligament thickness was measured using the same images. Shoulder ROM was measured by using a universal goniometer.

Results

The intraclass correlation coefficients (1.1) and (2.1) of the adhesion severity measurements were 0.85 and 0.91, respectively. Multiple linear regression analysis revealed that the adhesion severity is a significant predictor for external rotation ROM in the rotator cuff disorder group (R2 = 0.44, F = 10.1, P < .01, t = -2.9), while coracohumeral ligament thickness predicts ROM in the frozen shoulder group (R2 = 0.28, F = 5.5, P = .01, t = -3.0).

Conclusion

The proposed method is reliable. Muscle adhesion causes ROM restriction of the shoulder joint. The primary cause of shoulder ROM restriction differed between the diagnostic groups.

Hyaluronic acid/PEO electrospun tube reduces tendon adhesion to levels comparable to native tendons - An in vitro and in vivo study

A major problem after tendon injury is adhesion formation to the surrounding tissue leading to a limited range of motion. A viable strategy to reduce adhesion extent is the use of physical barriers that limit the contact between the tendon and the adjacent tissue. The purpose of this study was to fabricate an electrospun bilayered tube of hyaluronic acid/polyethylene oxide (HA/PEO) and biodegradable DegraPol® (DP) to improve the anti-adhesive effect of the implant in a rabbit Achilles tendon full laceration model compared to a pure DP tube. Additionally, the attachment of rabbit tenocytes on pure DP and HA/PEO containing scaffolds was tested and Scanning Electron Microscopy, Fourier-transform Infrared Spectroscopy, Differential Scanning Calorimetry, Water Contact Angle measurements, and testing of mechanical properties were used to characterize the scaffolds. In vivo assessment after three weeks showed that the implant containing a second HA/PEO layer significantly reduced adhesion extent reaching levels comparable to native tendons, compared with a pure DP implant that reduced adhesion formation only by 20 %. Tenocytes were able to attach to and migrate into every scaffold, but cell number was reduced over two weeks. Implants containing HA/PEO showed better mechanical properties than pure DP tubes and with the ability to entirely reduce adhesion extent makes this implant a promising candidate for clinical application in tendon repair.

Evaluation of Anti-Nociceptive, Anti-Inflammatory, and Anti-Fibrotic effects of noscapine against a rat model of Achilles tendinopathy

During tendinopathy, prolonged inflammation results in fibrosis and the adherence of tendons to the adjacent tissues, causing discomfort and movement disorders. As a natural compound, noscapine has several anti-inflammatory and anti-fibrotic properties. Therefore, we aimed to investigate the effects of noscapine against a rat model of tendinopathy. We created a surgical rat model of Achilles tendon damage to emulate tendinopathy. Briefly, an incision was made on the Achilles tendon, and it was then sutured using an absorbable surgical thread. Immediately, the injured area was topically treated with the vehicle, noscapine (0.2, 0.6, and 1.8 mg/kg), or dexamethasone (0.1 mg/kg) as a positive control. During the 19-day follow-up period, animals were assessed for weight, behavior, pain, and motor coordination testing. On day 20th, the rats were sacrificed, and the tendon tissue was isolated for macroscopic scoring, microscopic (H&E, Masson's trichrome, Ki67, p53) analyses, and cytokine secretion levels. The levels of macroscopic parameters, including thermal hyperalgesia, mechanical and cold allodynia, deterioration of motor coordination, tendon adhesion score, and microscopic indices, namely histological adhesion, vascular prominence and angiogenesis, and Ki67 and p53 levels, as well as fibrotic and inflammatory biomarkers (IL-6, TNF-α, TGF-β, VEGF) were significantly increased in the vehicle group compared to the sham group (P < 0.05-0.001 for all cases). In contrast, the administration of noscapine (0.2, 0.6, and 1.8 mg/kg) attenuated the pain, fibrosis, and inflammatory indices in a dose-dependent manner compared to the vehicle group (P < 0.05-0.001). Histological research indicated that noscapine 0.6 and 1.8 mg/kg had the most remarkable healing effects. Interestingly, two higher doses of noscapine had impacts similar to those of the positive control group in both clinical and paraclinical assessments. Taken together, our findings suggested that noscapine could be a promising medicine for treating tendinopathies.

Advanced postoperative tissue antiadhesive membranes enabled with electrospun nanofibers

Tissue adhesion is one of the most common postoperative complications, which is frequently accompanied by inflammation, pain, and even dyskinesia, significantly reducing the quality of life of patients. Thus, to prevent the formation of tissue adhesions, various strategies have been explored. Among these methods, placing anti-adhesion membranes over the injured site to separate the wound from surrounding tissues is a simple and prominently favored method. Recently, electrospun nanofibers have been the most frequently investigated antiadhesive membranes due to their tunable porous structure and high porosities. They not only can act as an essential barrier and functional carrier system but also allow for high permeability and nutrient transport, showing great potential for preventing tissue adhesion. Herein, we provide a short review of the most recent applications of electrospun nanofibrous antiadhesive membranes in tendons, the abdominal cavity, dural sac, pericardium, and meninges. Firstly, each section highlights the most representative examples and they are sorted based on the latest progress of related research. Moreover, the design principles, preparation strategies, overall performances, and existing problems are highlighted and evaluated. Finally, the current challenges and several future ways to develop electrospun nanofibrous antiadhesive membranes are proposed. The systematic discussion and proposed directions can shed light on ideas and guide the reasonable design of electrospun nanofibrous membranes, contributing to the development of exceptional tissue anti-adhesive materials in the foreseeable future.

The effects of NF-κB suppression on the early healing response following intrasynovial tendon repair in a canine model

The highly variable clinical outcomes noted after intrasynovial tendon repair have been associated with an early inflammatory response leading to the development of fibrovascular adhesions. Prior efforts to broadly suppress this inflammatory response have been largely unsuccessful. Recent studies have shown that selective inhibition of IkappaB kinase beta (IKK-β), an upstream activator of nuclear factor kappa-light chain enhancer of activated B cells (NF-κB) signaling, mitigates the early inflammatory response and leads to improved tendon healing outcomes. In the current study, we test the hypothesis that oral treatment with the IKK-β inhibitor ACHP (2-amino-6-[2-(cyclopropylmethoxy)-6-hydroxyphenyl]-4-piperidin-4-yl nicotinenitrile an inhibitor) will modulate the postoperative inflammatory response and improve intrasynovial flexor tendon healing. To test this hypothesis, the flexor digitorum profundus tendon of 21 canines was transected and repaired within the intrasynovial region and assessed after 3 and 14 days. Histomorphometry, gene expression analyses, immunohistochemistry, and quantitative polarized light imaging were used to examine ACHP-mediated changes. ACHP led to reduction in phosphorylated p-65, indicating that NF-κB activity was suppressed. ACHP enhanced expression of inflammation-related genes at 3 days and suppressed expression of these genes at 14 days. Histomorphometry revealed enhanced cellular proliferation and neovascularization in ACHP-treated tendons compared with time-matched controls. These findings demonstrate that ACHP effectively suppressed NF-κB signaling and modulated early inflammation, leading to increased cellular proliferation and neovascularization without stimulating the formation of fibrovascular adhesions. Together, these data suggest that ACHP treatment accelerated the inflammatory and proliferative phases of tendon healing following intrasynovial flexor tendon repair. Clinical Significance: Using a clinically relevant large-animal model, this study revealed that targeted inhibition of nuclear factor kappa-light chain enhancer of activated B cells signaling with ACHP provides a new therapeutic strategy for enhancing the repair of sutured intrasynovial tendons.

M2 Macrophage Membrane-Mediated Biomimetic-Nanoparticle Carrying COX-siRNA Targeted Delivery for Prevention of Tendon Adhesions by Inhibiting Inflammation

Tendon adhesion is the most common outcome of tendon or tendon-to-bone healing after injury. Our group developed a hydrogel-nanoparticle sustained-release system previously to inhibit cyclooxygenases (COXs) expression and consequently prevent tendon adhesion and achieved satisfactory results. However, effective treatment of multiple tendon adhesions is always a challenge in research on the prevention of tendon adhesion. In the present study, an M2M@PLGA/COX-siRNA delivery system is successfully constructed using the cell membranes of M2 macrophages and poly (lactic-co-glycolic acid) (PLGA) nanoparticles. Targeting properties and therapeutic effects are observed in mice or rat models of flexor digitorum longus (FDL) tendon injury combined with rotator cuff injury. The results showed that the M2M@PLGA/COX-siRNA delivery system has low toxicity and remarkable targeting properties to the injured areas. Treatment with the M2M@PLGA/COX-siRNA delivery system reduced the inflammatory reaction and significantly improved tendon adhesion in both the FDL tendon and rotator cuff tissues. These findings indicate that the M2M@PLGA delivery system can provide an effective biological strategy for preventing multiple tendon adhesions.

Flexor Tendon Adhesion Formation: Current Concepts

Over the years, various physical and chemical/biological methods of inhibiting adhesion formation have been developed, focusing on how to suppress healing around the tendon and not inhibit healing within the tendon. Unfortunately, however, these methods are accompanied by drawbacks, both large and small, and no absolute antiadhesion method capable of maintaining tendon repair strength has yet been developed. Recent innovations in biomaterials science and tissue engineering have produced new antiadhesion technologies, such as barriers combined with cytokines and cells, which have improved outcomes in animal models, and which may find clinical relevance in the future.

Polydopamine Nanoparticles-Based Photothermal Effect Against Adhesion Formation in a Rat Model of Achilles Tendon Laceration Repair

Background

Adhesion formation after tendon surgery is a major obstacle to repair of tendon ruptures, and there is still no effective clinical anti-adhesion method. Myofibroblasts expressing α-smooth muscle actin (α-SMA) play a crucial role in adhered fibrous tissue. Heat shock protein (Hsp) 72 can selectively prevent the activation of c-Jun N-terminal kinase (JNK), which mediates the conversion from fibroblasts to myofibroblasts. The purpose of this study was to investigate for the first time whether polydopamine nanoparticles (PDA NPs)-based photothermal effect would attenuate adhesion formation in a rat model of Achilles tendon laceration repair.

Materials and Methods

Forty-five adult male Sprague-Dawley rats were randomly assigned to the photothermal group, the control group and the PDA NPs group (n = 15 per group). The primary outcome measure was the adhesion scores at two weeks after surgery according to the grading of Tang et al. The secondary outcomes included the expressions of Hsp 72, JNK, phosphorylated JNK and α-SMA, which were measured by immunohistochemistry or Western blot.

Results

The average adhesion score was significantly lower in the photothermal group (4.25 ± 0.21) than that in the control group (5.29 ± 0.12) (p = 0.005) and the PDA NPs group (5.29 ± 0.20) (p = 0.005). Relative to the control group and PDA NPs group, Hsp 72 in the photothermal group was significantly increased whereas α-SMA and p-JNK was significantly decreased, but JNK was not found to be different across the three groups.

Conclusion

The photothermal effect produced by PDA NPs could reduce tendon adhesion formation in rats by inhibiting myocyte fibrosis, which may have potential in developing endogenous heating for postsurgical tissue adhesions.

Combined Verapamil-Polydopamine Nanoformulation Inhibits Adhesion Formation in Achilles Tendon Injury Using Rat Model

Introduction

Topical verapamil has been demonstrated to reduce the fibroproliferative scar. Therefore, it was hypothesized that topical verapamil could reduce adhesion formation after tendon repair. The current study aimed to examine the effects of verapamil-loaded polydopamine nanoparticles (VP-PDA NPs) on the adhesion formation of Achilles tendon laceration and repair in a rat model.

Methods

We randomly assigned 72 male Sprague-Dawley rats to the control, the PDA NPs, and the VP-PDA NPs groups (n = 24 per group). The quality of tendon healing was evaluated by the maximal tensile strength four and six weeks after surgery. The degree of tendon adhesion was scored on days 4, 15, 29, and 43 after surgery. The expressions of transforming growth factor-beta 1 (TGF-β1), vimentin, α-smooth muscle actin (α-SMA), and collagens type I and III were detected through Western blotting or immunohistochemistry at four weeks after surgery.

Results

In vitro release tests revealed that 61.3% of verapamil was released from VP-PDA NPs in four weeks. There was a significant increase in average failure to load in the VP-PDA NPs group (89.27 ± 5.09 N) compared with the PDA NPs group (65.52 ± 2.04 N) (p = 0.003) and the control group (74.52 ± 4.24 N) (p = 0.029). Adhesion scores were significantly reduced in the VP-PDA NPs group at six weeks (3.175 ± 0.08) and four weeks (3.35 ± 0.25) compared with the other groups. Moreover, VP-PDA NPs significantly reduced the expression of vimentin, α-SMA, TGF-β1, and collagens type I and III.

Conclusion

These data suggest that VP-PDA NPs reduced adhesion formation and enhanced tendon healing during rat tendon injury. Since topical verapamil has been used in clinics without side effects, VP-PDA NPs would have direct translation implications. However, its anti-adhesive effects on intrasynovial tendon injury must be examined.

Prevention of peritoneal adhesions formation by core-shell electrospun ibuprofen-loaded PEG/silk fibrous membrane

Adhesion bands are pathological fibrous tissues that create in the middle of tissues and organs, often reasons of intestinal obstruction, and female infertility. Here, we explored the anti-adhesive and inflammatory capacities of PEG/silk and Ibuprofen-loaded PEG/Silk core-shell nanofibrous membranes, respectively. The ibuprofen-loaded Silk Fibroin-Poly ethylene Glycol (SF-PEG) core-shell membrane was fabricated by electrospinning and considered in terms of morphology, surface wettability, drug release, and degradation. To reveal the membrane capability for adhesion bands inhibition, the membrane was stitched among the abdominal partition and peritoneum and then evaluated using two scoring adhesion systems. According to results, the fibrous membrane hindered cell proliferation, and the scoring systems and pathology showed that in a rat model, Ibuprofen-loaded PEG/Silk core-shell membrane caused a lightening in post-operative adhesion bands and the low-grade inflammatory reaction in animal models. Collectively, we fabricated new ibuprofen-loaded PEG/SF membranes with anti-adhesion and anti-inflammation properties. Moreover, this core-shell electrospun fibrous membrane has not even now been used to prevent peritendinous adhesion generation.

The influence of a nanoparticle gel loaded with siRNA-cyclooxygenase on flexor tendon healing: an in vivo animal study

We investigated the influence of cyclooxygenase (COX)-1 and COX-2 siRNAs delivered through a nanoparticle-gel system on the strength of flexor tendon repairs. Sixteen flexor digitorum profundus (FDP) tendons of chicken toes were transected, repaired and wrapped with gels to evaluate gel adherence. We found that the gel adhered to the tendon surface firmly. Next, 56 tendons were used in a first set of in vivo experiments to compare the therapeutic effects of different doses of COX siRNAs. Another 15 tendons were added in a second set to further assess the effects of a dosage of 12 μg. After 4 weeks, the mean strength of the repaired tendons increased most notably in the toes treated with 12 μg COX siRNAs, and the number of samples with low strength (<35 N) was significantly smaller than in the group without molecular treatment. We conclude that COX-1 and COX-2 siRNAs delivered through a nanoparticle-gel system increased the healing strength of the repaired tendons.

Practice Patterns in Operative Flexor Tendon Laceration Repair: A 15-Year Analysis of Continuous Certification Data from the American Board of Plastic Surgery

The American Board of Plastic Surgery has been collecting practice data on operative repair of flexor tendon lacerations since 2006, as part of its Continuous Certification program.

Morphological Changes in Flexor Tendon Adhesion Following Early Exercise After Tendon Repair

Adhesion is a common complication following surgical repair of flexor tendons, resulting in the restriction of tendon gliding. We investigated the effect of early exercise on adhesion formation. To create an adhesion model, the proximal region of the second phalanx of the third toe in 4-month-old White Leghorn chickens was cut. The gliding side of the flexor digitorum profundus was hemiresected and the bony floor was crushed to enhance adhesion formation. The resected area was fixed in an extended position for 1, 2, or 3 weeks. Following 1, 2, or 3 weeks of active exercise, the chickens were sacrificed and morphological changes in the adhesions were assessed. In the 1- and 2-week fixed groups, 1, 2, or 3 weeks of active exercise resulted in mesotenon-like adhesion that was elastic and had no effect on tendon gliding. However, in the 3-week fixed group, a mature adhesion remained with limited change and tendon gliding was inhibited even after 3 weeks of active exercise. Thus, we concluded that adhesions become more elastic with early exercise within 2 weeks after tendon repair, but that adhesions following tendon repair tend not to show any further elastic changes when exercise is started 3 weeks after the repair.

Intrinsic Tendon Regeneration After Application of Purified Exosome Product: An In Vivo Study

Background:

Tendons are primarily acellular, limiting their intrinsic regenerative capabilities. This limited regenerative potential contributes to delayed healing, rupture, and adhesion formation after tendon injury.

Purpose:

To determine if a tendon’s intrinsic regenerative potential could be improved after the application of a purified exosome product (PEP) when loaded onto a collagen scaffold.

Study Design:

Controlled laboratory study.

Methods:

An in vivo rabbit Achilles tendon model was used and consisted of 3 groups: (1) Achilles tenotomy with suture repair, (2) Achilles tenotomy with suture repair and collagen scaffold, and (3) Achilles tenotomy with suture repair and collagen scaffold loaded with PEP at 1 × 10¹² exosomes/mL. Each group consisted of 15 rabbits for a total of 45 specimens. Mechanical and histologic analyses were performed at both 3 and 6 weeks.

Results:

The load to failure and ultimate tensile stress were found to be similar across all groups (P ≥ .15). The tendon cross-sectional area was significantly smaller for tendons treated with PEP compared with the control groups at 6 weeks, which was primarily related to an absence of external adhesions (P = .04). Histologic analysis confirmed these findings, demonstrating significantly lower adhesion grade both macroscopically (P = .0006) and microscopically (P = .0062) when tendons were treated with PEP. Immunohistochemical staining showed a greater intensity for type 1 collagen for PEP-treated tendons compared with collagen-only or control tendons.

Conclusion:

Mechanical and histologic results suggested that healing in the PEP-treated group favored intrinsic healing (absence of adhesions) while control animals and animals treated with collagen only healed primarily via extrinsic scar formation. Despite a smaller cross-sectional area, treated tendons had the same ultimate tensile stress. This pilot investigation shows promise for PEP as a means of effectively treating tendon injuries and enhancing intrinsic healing.

Clinical Relevance:

The production of a cell-free, off-the-shelf product that can promote tendon regeneration would provide a viable solution for physicians and patients to enhance tendon healing and decrease adhesions as well as shorten the time required to return to work or sports.

Electrospun tube reduces adhesion in rabbit Achilles tendon 12 weeks post-surgery without PAR-2 overexpression

One great challenge in surgical tendon repair is the minimization of peritendinous adhesions. An electrospun tube can serve as a physical barrier around a conventionally sutured tendon. Six New Zealand White rabbits had one Achilles tendon fully transsected and sutured by a 4-strand suture. Another six rabbits had the same treatment, but with the additional electrospun DegraPol tube set around the sutured tendon. The adhesion formation to the surrounding tissue was investigated 12 weeks post-operation. Moreover, inflammation-related protease-activated receptor-2 (PAR-2) protein expression was assessed. Finally, rabbit Achilles tenocyte cultures were exposed to platelet-derived growth factor-BB (PDGF-BB), which mimicks the tendon healing environment, where PAR-2 gene expression was assessed as well as immunofluorescent staining intensity for F-actin and α-tubulin, respectively. At 12 weeks post-operation, the partially degraded DegraPol tube exhibited significantly lower adhesion formation (- 20%). PAR-2 protein expression was similar for time points 3 and 6 weeks, but increased at 12 weeks post-operation. In vitro cell culture experiments showed a significantly higher PAR-2 gene expression on day 3 after exposure to PDGF-BB, but not on day 7. The cytoskeleton of the tenocytes changed upon PDGF-BB stimulation, with signs of reorganization, and significantly decreased F-actin intensity. An electrospun DegraPol tube significantly reduces adhesion up to twelve weeks post-operation. At this time point, the tube is partially degraded, and a slight PAR-2 increase was detected in the DP treated tendons, which might however arise from particles of degrading DegraPol that were stained dark brown. PAR-2 gene expression in rabbit tenocytes reveals sensitivity at around day 10 after injury.

The role of MicroRNAs in tendon injury, repair, and related tissue engineering

Tendon injuries are one of the most common musculoskeletal disorders that cause considerable morbidity and significantly compromise the patients' quality of life. The innate limited regenerative capacity of tendon poses a substantial treating challenge for clinicians. MicroRNAs (miRNAs) are a family of small non-coding RNAs that play a vital role in orchestrating many biological processes through post-transcriptional regulation. Increasing evidence reveals that miRNA-based therapeutics may serve as an innovative strategy for the treatment of tendon pathologies. In this review, we briefly present miRNA biogenesis, the role of miRNAs in tendon cell biology and their involvement in tendon injuries, followed by a summary of current miRNA-based approaches in tendon tissue engineering with a special focus on attenuating post-injury fibrosis. Next, we discuss the advantages of miRNA-functionalized scaffolds in achieving sustained and localized miRNA administration to minimize off-target effects, and thus hoping to inspire the development of effective miRNA delivery platforms specifically for tendon tissue engineering. We envision that advancement in miRNA-based therapeutics will herald a new era of tendon tissue engineering and pave a way for clinical translation for the treatments of tendon disorders.

Prevention of Post-Operative Adhesions: A Comprehensive Review of Present and Emerging Strategies

Post-operative adhesions affect patients undergoing all types of surgeries. They are associated with serious complications, including higher risk of morbidity and mortality. Given increased hospitalization, longer operative times, and longer length of hospital stay, post-surgical adhesions also pose a great financial burden. Although our knowledge of some of the underlying mechanisms driving adhesion formation has significantly improved over the past two decades, literature has yet to fully explain the pathogenesis and etiology of post-surgical adhesions. As a result, finding an ideal preventative strategy and leveraging appropriate tissue engineering strategies has proven to be difficult. Different products have been developed and enjoyed various levels of success along the translational tissue engineering research spectrum, but their clinical translation has been limited. Herein, we comprehensively review the agents and products that have been developed to mitigate post-operative adhesion formation. We also assess emerging strategies that aid in facilitating precision and personalized medicine to improve outcomes for patients and our healthcare system.

Dynamic exacerbation in inflammation and oxidative stress during the formation of peritendinous adhesion resulted from acute tendon injury

BACKGROUND

Peritendinous adhesion is among the common complications after tendon injury. Numerous studies have been carried out to prevent its formation, including modifications of surgical procedures, postoperative cares, application of medicines, etc. This study dynamically monitored fluctuations of inflammation, state of oxidative stress, and histopathologic changes around injured tendon to provide theoretical basis for further exploration in mechanisms of peritendinous adhesion formation.

METHODS

Eighteen mature Sprague-Dawley male rats were randomly allocated into 6 equal groups. Compared with control and sham group, every rat's right hind Achilles tendon in experimental groups was cut and repaired by the modified Kessler technique. Besides control and sham group, samples of tendon margin and serum were collected at different time points after the surgery. Content of TNF-α, IL-1β, and TGF-β were assayed in harvested serum. Reactive oxygen species (ROS) were detected, expression levels of related genes (IL-1β, IL-6, SOD1, SOD2, COL1, HIF1A) were quantified by qPCR, and various histopathological evaluations were performed.

RESULTS

Indicators (TNF-α, IL-1β, TGF-β1, ROS) were noticed to have a similar trend of significant rising 24 h after the surgery except TGF-β which was rising 72 h later. So were the expression trends of IL-1β, IL-6, SOD1, SOD2, and COL1. HIF1A, inversely correlated with SOD2, showed the progressive relief of regional tissue hypoxia. Histological evaluation showed the same tendency that fibrosis and inflammation were getting serious 48 h later after the surgery.

CONCLUSIONS

Inflammation, oxidative stress in injured tendon resulted from acute trauma, would be getting intense in 24 h. Peritendinous adhesion emerges and aggravates after 48 h. Thus, prompt efficient measures are advised to be taken after the injury as soon as possible.

A review: progress in preventing tissue adhesions from a biomaterial perspective

Postoperative adhesions (POA) are one of the main problems suffered by patients and are a common complaint. It is considered to be closely associated with the healing mechanism of damaged tissues. Tissue adhesions accompany other symptoms such as inflammation, pain, and even dyskinesia under certain conditions, compromising the patients' quality of life. On the other hand, common treatments involve high costs, re-surgery or long-term hospital stays. Therefore, alternative approaches need to be formulated so that aforementioned problems can be resolved. To this end, a review of recent advances in this context is imperative. In this review, we have highlighted the mechanism of adhesion formation, advances in common therapeutic approaches, and prospective treatments in preventing tissue adhesions. Based on the literature, it can be determined that the disadvantages of available commercial products in the treatment of tissue adhesion have led researchers to utilize alternative methods for designing anti-adhesive products with different structures such as electrospun fibrous mats, hydrogels, and nanospheres. These studies are on the fast track in producing optimal anti-adhesion materials. We hope that this article can attract attention by showing various mechanisms and solutions involved in adhesion problems and inspire the further development of anti-adhesion biomaterials.

Localized delivery of ibuprofen via a bilayer delivery system (BiLDS) for supraspinatus tendon healing in a rat model

The high prevalence of tendon retear following rotator cuff repair motivates the development of new therapeutics to promote improved tendon healing. Controlled delivery of non-steroidal anti-inflammatory drugs to the repair site via an implanted scaffold is a promising option for modulating inflammation in the healing environment. Furthermore, biodegradable nanofibrous delivery systems offer an optimized architecture and surface area for cellular attachment, proliferation, and infiltration while releasing soluble factors to promote tendon regeneration. To this end, we developed a bilayer delivery system (BiLDS) for localized and controlled release of ibuprofen (IBP) to temporally mitigate inflammation and enhance tendon remodeling following surgical repair by promoting organized tissue formation. In vitro evaluation confirmed the delayed and sustained release of IBP from Labrafil-modified poly(lactic-co-glycolic) acid microspheres within sintered poly(ε-caprolactone) electrospun scaffolds. Biocompatibility of the BiLDS was demonstrated with primary Achilles tendon cells in vitro. Implantation of the IBP-releasing BiLDS at the repair site in a rat rotator cuff injury and repair model led to decreased expression of proinflammatory cytokine, tumor necrotic factor-α, and increased anti-inflammatory cytokine, transforming growth factor-β1. The BiLDS remained intact for mechanical reinforcement and recovered the tendon structural properties by 8 weeks. These results suggest the therapeutic potential of a novel biocompatible nanofibrous BiLDS for localized and tailored delivery of IBP to mitigate tendon inflammation and improve repair outcomes. Future studies are required to define the mechanical implications of an optimized BiLDS in a rat model beyond 8 weeks or in a larger animal model.

Ibuprofen-Loaded Hyaluronic Acid Nanofibrous Membranes for Prevention of Postoperative Tendon Adhesion through Reduction of Inflammation

A desirable multi-functional nanofibrous membrane (NFM) for prevention of postoperative tendon adhesion should be endowed with abilities to prevent fibroblast attachment and penetration and exert anti-inflammation effects. To meet this need, hyaluronic acid (HA)/ibuprofen (IBU) (HAI) NFMs were prepared by electrospinning, followed by dual ionic crosslinking with FeCl3 (HAIF NFMs) and covalent crosslinking with 1,4-butanediol diglycidyl ether (BDDE) to produce HAIFB NFMs. It is expected that the multi-functional NFMs will act as a physical barrier to prevent fibroblast penetration, HA will reduce fibroblast attachment and impart a lubrication effect for tendon gliding, while IBU will function as an anti-inflammation drug. For this purpose, we successfully fabricated HAIFB NFMs containing 20% (HAI20FB), 30% (HAI30FB), and 40% (HAI40FB) IBU and characterized their physico-chemical properties by scanning electron microscopy, Fourier transformed infrared spectroscopy, thermal gravimetric analysis, and mechanical testing. In vitro cell culture studies revealed that all NFMs except HAI40FB possessed excellent effects in preventing fibroblast attachment and penetration while preserving high biocompatibility without influencing cell proliferation. Although showing significant improvement in mechanical properties over other NFMs, the HAI40FB NFM exhibited cytotoxicity towards fibroblasts due to the higher percentage and concentration of IBU released form the membrane. In vivo studies in a rabbit flexor tendon rupture model demonstrated the efficacy of IBU-loaded NFMs (HAI30FB) over Seprafilm® and NFMs without IBU (HAFB) in reducing local inflammation and preventing tendon adhesion based on gross observation, histological analyses, and biomechanical functional assays. We concluded that an HAI30FB NFM will act as a multi-functional barrier membrane to prevent peritendinous adhesion after tendon surgery.

Battling adhesions: from understanding to prevention

Adhesions represent a major burden in clinical practice, particularly following abdominal, intrauterine, pericardial and tendon surgical procedures. Adhesions are initiated by a disruption in the epithelial or mesothelial layer of tissue, which leads to fibrin adhesion sites due to the downregulation of fibrinolytic activity and an increase in fibrin deposition. Hence, the metabolic events involved in tissue healing, coagulation, inflammation, fibrinolysis and angiogenesis play a pivotal role in adhesion formation. Understanding these events, their interactions and their influence on the development of post-surgical adhesion is crucial for the development of effective therapies to prevent them. Mechanical barriers, antiadhesive agents and combination thereof are customarily used in the battle against adhesions. Although these systems seem to be effective at reducing adhesions in clinical procedures, their prevention remains still elusive, imposing the need for new antiadhesive strategies.

Gene Silencing via PDA/ERK2-siRNA-Mediated Electrospun Fibers for Peritendinous Antiadhesion

Sustained delivery of small interfering RNA (siRNA) is a challenge in gene silencing for managing gene-related disorders. Although nanoparticle-mediated electrospun fibers enable sustainable gene silencing, low efficiency, loss of biological activity, toxicity issues, and complex electrospinning techniques are all bottlenecks of these systems. Preventing peritendinous adhesion is crucial for their successful use, which involves blocking cellular signaling via physical barriers. Here, a multifunctional, yet structurally simple, cationic 2,6-pyridinedicarboxaldehyde-polyethylenimine (PDA)-mediated extracellular signal-regulated kinase (ERK)2-siRNA polymeric delivery system is reported, in the form of peritendinous antiadhesion electrospun poly-l-lactic acid/hyaluronan membranes (P/H), with the ability to perform sustained release of bioactive siRNA for long-term prevention of adhesions and ERK2 silencing. After 4 days of culture, the cell area and proliferation rate of chicken embryonic fibroblasts on siRNA+PDA+P/H membrane are significantly less than those on P/H and siRNA+P/H membranes. The in vivo results of average optical density of collagen type III (Col III) and gene expression of ERK2 and its downstream SMAD3 in the siRNA+PDA+P/H group are less than those of P/H and siRNA+P/H groups. Consequently, siRNA+PDA+P/H electrospun membrane can protect the bioactivity of ERK2-siRNA and release it in a sustained manner. Moreover, adhesion formation is inhibited by reducing fibroblast proliferation and Col III deposition, and downregulating ERK2 and its downstream SMAD3.

Prevention of Peritendinous Adhesion Formation After the Flexor Tendon Surgery in Rabbits: A Comparative Study Between Use of Local Interferon-α, Interferon-β, and 5-Fluorouracil

BACKGROUND

Peritendinous adhesion is the most common complication after tendon surgery, particularly in zone II of the hand. Prevention of inflammation around the tendon, which develops after trauma and surgery, can decrease the tendon adhesion formation. This study compares the effect of some anti-inflammatory cytokines with 5-fluorouracil (5-FU) on the tensile strength and in prevention of peritendinous adhesion formation.

METHODS

Sixteen rabbits were allocated equally into 4 groups. Tendons of the index and ring fingers in zone II of the right hind paw were cut in all animals and then repaired. Interferon (IFN)-α in group 1, 5-FU in group 2, normal saline in group 3, and IFN-β in group 4 were locally applied to the repaired sites. Three weeks later, tensometric and histopathologic evaluations were performed.

RESULTS

The force required for removing the tendon from the sheath was not different between the groups (P = 0.130), but the time required for removal was significantly shorter in 5-FU group (P = 0.049). The strength of repair was not different between the groups in terms of force and time needed for rupture (P = 0.11 and 0.67, respectively). In histopathologic examination, normal architecture of the tendon and peritendon environment was less disturbed in the IFN groups, especially in IFN-β specimens.

CONCLUSIONS

Local application of 5-FU significantly reduced peritendinous adhesion. Local IFN-α and IFN-β had no significant effect on the prevention of peritendinous adhesion formation. The strength of the repair was not affected by these cytokines and 5-FU.

Multi-functional electrospun antibacterial core-shell nanofibrous membranes for prolonged prevention of post-surgical tendon adhesion and inflammation

The possibility of endowing an electrospun anti-adhesive barrier membrane with multi-functionality, such as lubrication, prevention of fibroblast attachment and anti-infection and anti-inflammation properties, is highly desirable for the management of post-surgical tendon adhesion. To this end, we fabricated core-shell nanofibrous membranes (CSNMs) with embedded silver nanoparticles (Ag NPs) in the poly(ethylene glycol) (PEG)/poly(caprolactone) (PCL) shell and hyaluronic acid (HA)/ibuprofen in the core. HA imparted a lubrication effect for smooth tendon gliding and reduced fibroblast attachment, while Ag NPs and ibuprofen functioned as anti-infection and anti-inflammation agents, respectively. CSNMs with a PEG/PCL/Ag shell (PPA) and HA core containing 0% (H/PPA), 10% (HI10/PPA), 30% (HI30/PPA) and 50% (HI50/PPA) ibuprofen were fabricated through co-axial electrospinning and assessed through microscopic, spectroscopic, thermal, mechanical and drug release analyses. Considering nutrient passage through the barrier, the microporous CSNMs exerted the same barrier effect but drastically increased the mass transfer coefficients of bovine serum albumin compared with the commercial anti-adhesive membrane SurgiWrap®. Cell attachment/focal adhesion formation of fibroblasts revealed effective reduction of initial cell attachment on the CSNM surface with minimum cytotoxicity (except HI50/PPA). The anti-bacterial effect against both Gram-negative and Gram-positive bacteria was verified to be due to the Ag NPs in the membranes. In vivo studies using H/PPA and HI30/PPA CSNMs and SurgiWrap® in a rabbit flexor tendon rupture model demonstrated the improved efficacy of HI30/PPA CSNMs in reducing inflammation and tendon adhesion formation based on gross observation, histological analysis and functional assays. We conclude that HI30/PPA CSNMs can act as a multifunctional barrier membrane to prevent peritendinous adhesion after tendon surgery.

STATEMENT OF SIGNIFICANCE

A multi-functional anti-adhesion barrier membrane that could reduce fibroblasts attachment and penetration while simultaneously prevent post-surgical infection and inflammation is urgently needed. To this end, we prepared electrospun core-shell hyaluronic acid + ibuprofen/polyethylene glycol + polycaprolactone + Ag nanoparticles nanofibrous membranes by co-axial electrospinning as an ideal anti-adhesive membrane. The core-shell structure could meet the need of a desirable anti-adhesion barrier through release of ibuprofen and Ag nanoparticles to reduce infection and inflammation while hyaluronic acid can reduce fibroblasts adhesion. The superior performance of this multi-functional core-shell nanofibrous membrane in preventing peritendinous adhesion and post-surgical inflammation was demonstrated in a rabbit flexor tendon rupture model.

Localized delivery of miRNAs targets cyclooxygenases and reduces flexor tendon adhesions

The formation of adhesions during healing of an injured tendon remains a difficult problem in clinical practice. Local anti-inflammation gene delivery provides high local gene concentration, reduces the inflammatory response of the injured tendon microenvironment, and decreases systemic side effects to enhance in vivo efficacy. In this study, we designed a novel local sustained gene delivery system by using cyclooxygenase (COX-1 and COX-2)-engineered miRNA plasmid/nanoparticles embedded in hyaluronic acid (HA) hydrogel to reduce flexor tendon adhesions. The local sustained gene delivery system significantly downregulates COX-1 and COX-2 expression in the tendon tissue and the surrounding subcutaneous tissue. More importantly, this plasmid/nanoparticle hydrogel system significantly reduced tissue adhesion formation. This approach offers an effective therapeutic strategy to reduce tendon adhesions by directly targeting the down-regulation of COX-1 and COX-2 expression within the microenvironment of the injured tendon.

STATEMENT OF SIGNIFICANCE

A local sustained gene delivery system was developed to regulate the expression of targeted genes in the specific time and location for tendon adhesion treatment. The engineered miRNA plasmid/nanoparticles embedded in hyaluronic acid hydrogel were synthesized to downregulate the expression of cyclooxygenases in the tendon tissue during the early stage of tendon healing with inflammatory response. This plasmid/nanoparticle hydrogel system offers an effective therapeutic strategy to attenuate the formation of tendon adhesion through direct downregulation of COX-1 and COX-2 expression within the microenvironment of the injured tendon.

Flexor Tendon Injuries

Flexor tendon injuries of the hand are uncommon, and they are among the most challenging orthopaedic injuries to manage. Proper management is essential to ensure optimal outcomes. Consistent, successful management of flexor tendon injuries relies on understanding the anatomy, characteristics and repair of tendons in the different zones, potential complications, rehabilitation protocols, recent advances in treatment, and future directions, including tissue engineering and biologic modification of the repair site.

Molecular Biology of Flexor Tendon Healing in Relation to Reduction of Tendon Adhesions

Tendon injuries are encountered after major and minor hand trauma. Despite meticulous repair technique, adhesion formation can occur, limiting recovery. Although a great deal of progress has been made toward understanding the mechanism of tendon healing and adhesions, clinically applicable solutions to prevent adhesions remain elusive. The goal of this paper is to review the most recent literature relating to the tendon healing and adhesion prevention.

An Experimental Model on the Biomechanical Behaviour of the Flexor Tendons in New Zealand Rabbits

BACKGROUND

In order to introduce new pharmacological agents with the intent to inhibit the adhesion formation, it is important to test such products on laboratory animals under a protocol that can evaluate the quantitative and qualitative aspects of healing of the tendons. Most experimental models focus on the tensile strength and histological analysis of the tendons, failing to sufficiently quantify the degree of the adhesion formation.

METHODS

The experiment included six male New Zealand rabbits that underwent surgery of their right forepaws. The deep flexor tendon of the middle finger was transected and repaired and after six weeks the rabbits were killed. In order to assess the extent of adhesions, the functional stiffness of the tendons and the range of motion of the specimens' fingers was studied using a tensile testing machine. The setup used allowed the simultaneous recording of the specimens' motion and the pulling force values.

RESULTS

The mean values of the left and right forepaws were expressed in the same chart showing a clear difference between the operated and non operated forepaws.

CONCLUSIONS

Using a relatively simple set up in the laboratory we had the chance to focus on a more elaborate analysis of the data with the help of low cost and accessible software.

Macrophage infiltration of electrospun polyester fibers

Ibuprofen (IBU)-loaded fibrous PLA membranes can prevent peritendinous adhesion/granuloma formation and inflammation by reducing macrophage infiltration.

The Biology of Bone and Ligament Healing

This review describes the normal healing process for bone, ligaments, and tendons, including primary and secondary healing as well as bone-to-bone fusion. It depicts the important mediators and cell types involved in the inflammatory, reparative, and remodeling stages of each healing process. It also describes the main challenges for clinicians when trying to repair bone, ligaments, and tendons with a specific emphasis on Charcot neuropathy, fifth metatarsal fractures, arthrodesis, and tendon sheath and adhesions. Current treatment options and research areas are also reviewed.

Rabbit Achilles tendon full transection model - wound healing, adhesion formation and biomechanics at 3, 6 and 12 weeks post-surgery

After tendon rupture repair, two main problems may occur: re-rupture and adhesion formation. Suitable non-murine animal models are needed to study the healing tendon in terms of biomechanical properties and extent of adhesion formation. In this study 24 New Zealand White rabbits received a full transection of the Achilles tendon 2 cm above the calcaneus, sutured with a 4-strand Becker suture. Post-surgical analysis was performed at 3, 6 and 12 weeks. In the 6-week group, animals received a cast either in a 180 deg stretched position during 6 weeks (adhesion provoking immobilization), or were re-casted with a 150 deg position after 3 weeks (adhesion inhibiting immobilization), while in the other groups (3 and 12 weeks) a 180 deg position cast was applied for 3 weeks. Adhesion extent was analyzed by histology and ultrasound. Histopathological scoring was performed according to a method by Stoll et al. (2011), and the main biomechanical properties were assessed. Histopathological scores increased as a function of time, but did not reach values of healthy tendons after 12 weeks (only around 15 out of 20 points). Adhesion provoking immobilization led to an adhesion extent of 82.7±9.7%, while adhesion inhibiting immobilization led to 31.9±9.8% after 6 weeks. Biomechanical properties increased over time, however, they did not reach full strength nor elastic modulus at 12 weeks post-operation. Furthermore, the rabbit Achilles tendon model can be modulated in terms of adhesion formation to the surrounding tissue. It clearly shows the different healing stages in terms of histopathology and offers a suitable model regarding biomechanics because it exhibits similar biomechanics as the human flexor tendons of the hand.

Summary: The rabbit Achilles tendon full transection model can be used to study adhesion extent in a controlled way. It also mimics the biomechanics of human hand flexor tendons.

Cell and Biologic-Based Treatment of Flexor Tendon Injuries

The two primary factors leading to poor clinical results after intrasynovial tendon repair are adhesion formation within the digital sheath and repair-site elongation and rupture. As the outcomes following modern tendon multi-strand repair and controlled rehabilitation techniques are often unsatisfactory, alternative approaches, such as the application of growth factors and mesenchymal stem cells (MSCs), have become increasingly attractive treatment options. Successful biological therapies require carefully controlled spatiotemporal delivery of cells, growth factors, and biocompatible scaffold matrices in order to simultaneously (1) promote matrix synthesis at the tendon repair site leading to increased biomechanical strength and stiffness and (2) suppress matrix synthesis along the tendon surface and synovial sheath preventing adhesion formation. This review summarizes recent cell and biologic-based experimental treatments for flexor tendon injury, with an emphasis on large animal translational studies.

The effect of a collagen-elastin matrix on adhesion formation after flexor tendon repair in a rabbit model

PURPOSE

The outcome of flexor tendon surgery is negatively affected by the formation of adhesions which can occur during the healing of the tendon repair. In this experimental study, we sought to prevent adhesion formation by wrapping a collagen-elastin scaffold around the repaired tendon segment.

METHODS

In 28 rabbit hind legs, the flexor tendons of the third and fourth digits were cut and then repaired using a two-strand suture technique on the fourth digit and a four-strand technique on the third digit. Rabbits were randomly assigned to study and control groups. In the control group, the operation ended by closing the tendon sheath and the skin. In the study group, a collagen-elastin scaffold was wrapped around the repaired tendon segment in both digits. After 3 and 8 weeks, the tendons were harvested and processed histologically. The range of motion of the digits and the gap formation between the repaired tendon ends were measured. The formation of adhesions, infiltration of leucocytes and extracellular inflammatory response were quantified.

RESULTS

At the time of tendon harvesting, all joints of the operated toes showed free range of motion. Four-strand core sutures lead to significantly less diastasis between the repaired tendon ends than two-strand core suture repairs. The collagen-elastin scaffold leads to greater gapping after 3 weeks compared to the controls treated without the matrix. Within the tendons treated with the collagen-elastin matrix, a significant boost of cellular and extracellular inflammation could be stated after 3 weeks which was reflected by a higher level of CAE positive cells and more formation of myofibroblasts in the αSMA stain in the study group. The inflammatory response subsided gradually and significantly until the late stage of the study. Both the cellular and extracellular inflammatory response was emphasized with the amount of material used for the repair.

CONCLUSION

The use of a collagen-elastin matrix cannot be advised for the prevention of adhesion formation in flexor tendon surgery, because it enhances both cellular and extracellular inflammation. Four-strand core sutures lead to less gapping than two-strand core sutures, but at the same time, the cellular and extracellular inflammatory response is more pronounced.

Controlled release of curcumin from curcumin-loaded nanomicelles to prevent peritendinous adhesion during Achilles tendon healing in rats

We introduced curcumin-loaded nanomicelles into a tendon-healing model to evaluate their effects on tendon healing and adhesion. Three groups consisting of 36 rats underwent rupture and repair of the Achilles tendon. The treatment group received an injection of curcumin-loaded nanomicelles (gold nanorods [GNRs]-1/curcumin in polymeric nanomicelles [curc@PMs] at a dosage of 0.44 mg curcumin/kg in 0.1 mL saline) into the surgical site and exposed to laser postoperatively at weeks 1, 2, and 3, for three times 10 seconds each, on the surgical site in the rats that underwent tendon rupture and repair, while the other two groups received 0.44 mg curcumin/kg in 0.1 mL saline and 0.1 mL of saline, respectively. The specimens were harvested at 4 weeks and subjected to biomechanical and histological evaluation. The scoring results of tendon adhesion indicated that GNRs-1/curc@PMs group was in the lowest grade of peritendinous adhesions compared to the other groups. Histological assessment further confirmed the preventive effect of GNRs-1/curc@PMs on tendon adhesion. These findings indicated greater tendon strength with less adhesion in the group treated with GNRs-1/curc@PMs combined with laser exposure, and that nanoparticle-based therapy may be applied to prevent adhesion in clinical patients.

Ibuprofen-conjugated hyaluronate/polygalacturonic acid hydrogel for the prevention of epidural fibrosis

The formation of fibrous tissue is part of the natural healing response following a laminectomy. Severe scar tissue adhesion, known as epidural fibrosis, is a common cause of failed back surgery syndrome. In this study, by combining the advantages of drug treatment with a physical barrier, an ibuprofen-conjugated crosslinkable polygalacturonic acid and hyaluronic acid hydrogel was developed for epidural fibrosis prevention. Conjugation was confirmed and measured by 1D 1H NMR spectroscopy. In vitro analysis showed that the ibuprofen-conjugated polygalacturonic acid–hyaluronic acid hydrogel showed low cytotoxicity. In addition, the conjugated ibuprofen decreased prostaglandin E2 production of the lipopolysaccharide-induced RAW264.7 cells. Histological data in in vivo studies indicated that the scar tissue adhesion of laminectomized male adult rats was reduced by the application of our ibuprofen-conjugated polygalacturonic acid-hyaluronic acid hydrogel. Its use also reduced the population of giant cells and collagen deposition of scar tissue without inducing extensive cell recruitment. The results of this study therefore suggest that the local delivery of ibuprofen via a polygalacturonic acid-hyaluronic acid-based hydrogel reduces the possibility of epidural fibrosis.

Flexor Tendon Repair: Healing, Biomechanics, and Suture Configurations

Successful outcome after flexor tendon repair requires a delicate balance between tendon healing and limiting scar tissue formation. Recent studies have highlighted the importance of the number of core sutures crossing the repair and the benefits of specific suture configurations in determining the strength of tendon repair. Researchers have attempted to augment the biological environment to improve the speed and strength of tendon repair.

Adeno-associated virus-2-mediated TGF-β1 microRNA transfection inhibits adhesion formation after digital flexor tendon injury

Adhesion formation after digital flexor tendon injury greatly affects gliding function of the tendon, which is a major clinical complication after hand surgery. Transforming growth factor beta 1 (TGF-β1) has a critical role in adhesion formation during tendon healing. Persistent regulation of TGF-β1 through application of microRNA (miRNA) specifically inhibiting the function of TGF-β1 (TGF-β1-miRNA) holds promise for treatment of such a complication. Adeno-associated virus (AAV) was used to transfer TGF-β1-miRNA to the chicken digital flexor tendons, which had been injured and surgically repaired. Four doses of AAV2-TGF-β1-miRNA (2 × 10¹¹, 2 × 10¹⁰, 2 × 10⁹ and 2 × 10⁸ vector genomes (vg)) were used to determine the transfection efficiency. At postoperative 3 weeks, we found a positive correlation between the administered AAV2-TGF-β1-miRNA doses and transfection efficiency. The transfection rate ranged from 10% to 77% as the doses increased. Production of TGF-β1 protein in the tendons decreased on increasing vector dosage. When 2 × 10¹¹ and 2 × 10¹⁰) vg were injected into the tendon, gliding excursion of the repaired tendon and work of flexion of chicken toes were significantly increased and adhesion score decreased 6 and 8 weeks later, indicating the improvement of tendon gliding and decreases in adhesion formations. However, the ultimate strength of the tendons transfected at the dose of 2 × 10¹⁰ vg was 12-24% lower than that of the control tendons. The results of this study demonstrate that application of TGF-β1-miRNA had a mixed impact on tendon healing: adhesion around the tendon is reduced but strength of the tendon healing is adversely affected. Future studies should aim at maintaining the beneficial effects of reducing tendon adhesions, while eliminating the adverse effects of decreasing the healing strength.

Effect of Heparin on Post-Operative Adhesion in Flexor Tendon Surgery of the Hand

Flexor tendon laceration is a common hand injury. Timely and correct diagnosis of this defect is an important factor for restoring hand function. Post-operative adhesion is a frequent problem after tendon repair and its prevention is difficult in some types of tendon lacerations. There have been some controversial studies on the positive effect of some materials and substances on prevention of these adhesions. This study aims to evaluate effects of the Heparin in postoperative tendon adhesions. In this clinical trial, 100 patients with laceration of flexor tendons in zone II of the hand were enrolled. The patients were randomly divided into two groups. In the first group, 0.5 cc Heparin (5000 IU/cc) was injected into each tendon ends before tendon repair. In the control group, repair was carried out without any heparin injection. After 3 months the total active range of motion (TAROM), mean extension gap (MEG) and mean flexion gap (MFG) were measured and compared between these two groups. The TAROM and MEGs were not significantly different between two groups; but MFGs were significantly better in Heparin treated group (P < 0.02). However rupture rate was significantly higher in heparin treated group (P = 0.003). Heparin may improve the tendons function and reduce the postoperative adhesions in zone II of the hand; however there is a significant risk of tendon rupture.

5-Fluorouracil loaded thermosensitive PLGA–PEG–PLGA hydrogels for the prevention of postoperative tendon adhesion

Thermosensitive PLGA–PEG–PLGA hydrogels containing 5-fluorouracil were applied to cover the sutured Achilles tendon of rats, leading to a significant reduction in adhesion formation during the tendon healing.