Pharmacologic Enhancement of Rotator Cuff Repair: A Narrative Review

Editorial Commentary: Suppression of Inflammatory Macrophages Is a Potential Strategy to Improve Rotator Cuff Healing and Has Shown Promise in Preclinical Models

The pathophysiology of rotator cuff disease is complex, involving intrinsic and extrinsic factors that contribute to mechanical alterations, inflammation, apoptosis, and neovascularization. These changes result in structural and cellular disruptions, including inflammatory cell infiltration and collagen disorganization. Macrophages recently have gained attention as critical mediators of tissue repair and regeneration. M1 macrophages traditionally have been associated with proinflammatory cytokines involved in the acute inflammatory process after injury, whereas M2 macrophages are thought to play a role in resolution of inflammation and tissue healing. Therefore, achieving a balance between M1 and M2 macrophage phenotypes may be crucial in influencing tendon healing outcomes. Strategies have ranged from mediating circulating macrophage recruitment with CCR2 inhibition to promoting M2 macrophage polarization, increasing secretion of transforming growth factor-β1 from M2 macrophages, and subsequently enhancing chondrogenesis of mesenchymal progenitor cells to improve tendon-to-bone healing. Modulating macrophage activity to favor the M2 phenotype also has been hypothesized to not only enhance healing but also to reduce adhesion formation, making it an attractive potential therapeutic strategy for tendon injuries. However, inflammation is complex and multifactorial, and identifying the optimal targets to modulate and at what time points in the healing process can be difficult. In addition, although preclinical models of tendon disorders can be helpful in identifying promising cellular and molecular targets, recapitulating the human disease process, which often consists of chronic, degenerative tendinopathies, remains challenging. Many studies use young, healthy small animal models with acute injuries, which do not fully recreate the chronic degenerative conditions commonly seen in human rotator cuff injuries. In addition, recent studies have used aged mice (∼18 to 20 months), which, although expensive, are likely closer in biological age relative to human patients and thus more representative of the changes in microstructure and composition seen in degenerative rotator cuff pathology.

Role of oxidative stress in the concurrent development of osteoporosis and tendinopathy: Emerging challenges and prospects for treatment modalities

Both osteoporosis and tendinopathy are widely prevalent disorders, encountered in diverse medical contexts. Whilst each condition has distinct pathophysiological characteristics, they share several risk factors and underlying causes. Notably, oxidative stress emerges as a crucial intersecting factor, playing a pivotal role in the onset and progression of both diseases. This imbalance arises from a dysregulation in generating and neutralising reactive oxygen species (ROS), leading to an abnormal oxidative environment. Elevated levels of ROS can induce multiple cellular disruptions, such as cytotoxicity, apoptosis activation and reduced cell function, contributing to tissue deterioration and weakening the structural integrity of bones and tendons. Antioxidants are substances that can prevent or slow down the oxidation process, including Vitamin C, melatonin, resveratrol, anthocyanins and so on, demonstrating potential in treating these overlapping disorders. This comprehensive review aims to elucidate the complex role of oxidative stress within the interlinked pathways of these comorbid conditions. By integrating contemporary research and empirical findings, our objective is to outline new conceptual models and innovative treatment strategies for effectively managing these prevalent diseases. This review underscores the importance of further in-depth research to validate the efficacy of antioxidants and traditional Chinese medicine in treatment plans, as well as to explore targeted interventions focused on oxidative stress as promising areas for future medical advancements.

Recent Advances in the Use of Stem Cells in Tissue Engineering and Adjunct Therapies for Tendon Reconstruction and Future Perspectives

Due to their function, tendons are exposed to acute injuries. This type of damage to the musculoskeletal system represents a challenge for clinicians when natural regeneration and treatment methods do not produce the expected results. Currently, treatment is long and associated with long-term complications. In this review, we discuss the use of stem cells in the treatment of tendons, including how to induce appropriate cell differentiation based on gene therapy, growth factors, tissue engineering, proteins involved in regenerative process, drugs and three-dimensional (3D) structures. A multidirectional approach as well as the incorporation of novel components of the therapy will improve the techniques used and benefit patients with tendon injuries in the future.

Estrogen and testosterone supplementation improves tendon healing and functional recovery after rotator cuff repair

Failure of healing after rotator cuff repair (RCR) is common. The purpose of the current study was to evaluate the effect of systemic estrogen or testosterone supplementation on tendon healing after RCR. Seventy-two adult male mice were utilized for all experiments. The supraspinatus tendon was transected and repaired with 6-0 Prolene suture on the left shoulder of 51 animals. Mice were segregated into three groups postoperative: (1) vehicle group (VG; n = 18), (2) estrogen group (EST; n = 17), and (3) testosterone group (TST; n = 16). An unrepaired control group (unrepaired, n = 21) did not have surgery. Utilizing these animals, histological analysis, activity testing, biomechanical testing and RNA sequencing (RNA-seq) was performed. At 8 weeks post-RCR, TST, and EST supplementation improved the overall histologic structure of the repaired enthesis site. No differences in ultimate failure loads or stiffness were detected between VG, EST, and TST groups after biomechanical testing. RCR caused a reduction in wheel activity compared to unrepaired controls and supplementation with TST restored wheel activity. RNA-seq analysis indicated that estrogen and testosterone regulated different pathways associated with enthesis healing, including a suppression of inflammatory signaling. Supplementation with sex hormones improved the structure of the repaired tendon enthesis and significantly regulated expression of diverse pathways regulating multiple biological processes. Testosterone administration following RCR restored wheel activity without having a detrimental impact on biomechanical strength. Future human studies of sex hormone supplementation after RCR are warranted as supplementation in an animal model may improve tendon enthesis healing.

In Vitro and In Vivo Effects of IGF-1 Delivery Strategies on Tendon Healing: A Review

Tendon injuries suffer from a slow healing, often ending up in fibrovascular scar formation, leading to inferior mechanical properties and even re-rupture upon resumption of daily work or sports. Strategies including the application of growth factors have been under view for decades. Insulin-like growth factor-1 (IGF-1) is one of the used growth factors and has been applied to tenocyte in vitro cultures as well as in animal preclinical models and to human patients due to its anabolic and matrix stimulating effects. In this narrative review, we cover the current literature on IGF-1, its mechanism of action, in vitro cell cultures (tenocytes and mesenchymal stem cells), as well as in vivo experiments. We conclude from this overview that IGF-1 is a potent stimulus for improving tendon healing due to its inherent support of cell proliferation, DNA and matrix synthesis, particularly collagen I, which is the main component of tendon tissue. Nevertheless, more in vivo studies have to be performed in order to pave the way for an IGF-1 application in orthopedic clinics.

Comparison of Six-strand and Four-strand Techniques on the Repair of Injured Deep Flexor Tendons of Zone II of the Hand: A Randomized Controlled Clinical Trial

Background

Hand zone II flexor tendon repair had been associated with many complications thereby it was previously called no man's land. Although there is some agreement on the primary repair of flexor tendons in this area, it is challenging due to certain complications. We compared the six and four-strand techniques in the repair of flexor digitorum profundus (FDP) tendons of zone II.

Methods

This randomized controlled clinical trial was registered with the Iranian Registry of Clinical Trials (IRCT20130812014333N139). Fifty patients with damaged FDP in zone II of the hand who were referred to Taleghani Hospital, Kermanshah, Iran in 2020 were included and divided into two groups (n=25). In group 1, the damaged tendons were repaired using the four-strand technique and prolene suture while in group 2, the six-strand technique was used. Postoperatively, the patients were examined every week for the first three weeks. In the second and third weeks, sutures were removed. At the end of 3rd month, the outcomes of surgery were compared in the groups.

Results

Fifty patients (74% male) with 85 damaged fingers were investigated. Based on Buck-Gramcko criteria, the outcomes of surgery were excellent in 78%, good in 16%, fair in 4%, and bad in 2%. Complications after surgery were adhesion (8%) and 2 cases of rupture. There was no significant difference between 4 and 6-strand sutures regarding tendon adhesion and range of motion.

Conclusion

Both 4 and 6-strand sutures were associated with favorable outcomes in patients with damaged FDP in zone II of the hand.