Biologics and stem cell-based therapies for rotator cuff repair

Engineered Tendon-Fibrocartilage-Bone Composite With Mechanical Stimulation for Augmentation of Rotator Cuff Repair: A Study Using an In Vivo Canine Model With a 6-Month Follow-up

BACKGROUND

Rotator cuff repair augmentation using biological materials has become popular in clinical practice to reduce the high retear rates associated with traditional repair techniques. Tissue engineering approaches, such as engineered tendon-fibrocartilage-bone composite (TFBC), have shown promise in enhancing the biological healing of rotator cuff tears in animals. However, previous studies have provided limited long-term data on TFBC repair outcomes. The effect of mechanical stimulation on TFBC has not been explored extensively.

PURPOSE

To evaluate functional outcomes after rotator cuff repair with engineered TFBC subjected to mechanical stimulation in a 6-month follow-up using a canine in vivo model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 40 canines with an acute infraspinatus (ISP) tendon transection model were randomly allocated to 4 groups (n =10): (1) unilateral ISP tendon undergoing suture repair only (control surgery); (2) augmentation with engineered TFBC alone (TFBC); (3) augmentation with engineered TFBC and bone marrow-derived stem cells (BMSCs) (TFBC+C); and (4) augmentation with engineered TFBC and BMSCs, as well as mechanical stimulation (TFBC+C+M). Outcome measures-including biomechanical evaluations such as failure strength, stiffness, failure mode, gross appearance, ISP tendon and muscle morphological assessment, and histological analysis-were performed 6 months after surgery.

RESULTS

As shown in the mechanical test, the TFBC+C+M group exhibited higher failure strength compared with other repair techniques. The most common failure mode was avulsion fracture in the TFBC+C+M group, but tendon-bone junction rupture was observed predominantly in different groups. Engineered TFBC with mechanical stimulation showed over 70% relative failure strength compared with normal ISP, and the other groups showed about 50% relative failure strength. Histological analysis revealed less fat infiltration and closer-to-normal muscle fiber structure in the mechanical stimulation group.

CONCLUSION

This study provides evidence that mechanical stimulation of engineered TFBC promotes rotator cuff regeneration, thus supporting its potential for rotator cuff repair augmentation.

CLINICAL RELEVANCE

This study provides valuable evidence supporting the use of a novel tissue-engineered material (TFBC) in rotator cuff repair and paves the way for advancements in the field of rotator cuff regeneration.

Nanofiber Graft Therapy to Prevent Shoulder Stiffness and Adhesions after Rotator Cuff Tendon Repair: A Comprehensive Review

Stiffness and adhesions following rotator cuff tears (RCTs) are common complications that negatively affect surgical outcomes and impede healing, thereby increasing the risk of morbidity and failure of surgical interventions. Tissue engineering, particularly through the use of nanofiber scaffolds, has emerged as a promising regenerative medicine strategy to address these complications. This review critically assesses the efficacy and limitations of nanofiber-based methods in promoting rotator cuff (RC) regeneration and managing postrepair stiffness and adhesions. It also discusses the need for a multidisciplinary approach to advance this field and highlights important considerations for future clinical trials.

Biomimetic gradient scaffolds for the tissue engineering and regeneration of rotator cuff enthesis

Rotator cuff tear is one of the most common musculoskeletal disorders, which often results in recurrent shoulder pain and limited movement. Enthesis is a structurally complex and functionally critical interface connecting tendon and bone that plays an essential role in maintaining integrity of the shoulder joint. Despite the availability of advanced surgical procedures for rotator cuff repair, there is a high rate of failure following surgery due to suboptimal enthesis healing and regeneration. Novel strategies based on tissue engineering are gaining popularity in improving tendon-bone interface (TBI) regeneration. Through incorporating physical and biochemical cues into scaffold design which mimics the structure and composition of native enthesis is advantageous to guide specific differentiation of seeding cells and facilitate the formation of functional tissues. In this review, we summarize the current state of research in enthesis tissue engineering highlighting the development and application of biomimetic scaffolds that replicate the gradient TBI. We also discuss the latest techniques for fabricating potential translatable scaffolds such as 3D bioprinting and microfluidic device. While preclinical studies have demonstrated encouraging results of biomimetic gradient scaffolds, the translation of these findings into clinical applications necessitates a comprehensive understanding of their safety and long-term efficacy.

Recombinant Human Parathyroid Hormone Biocomposite Promotes Bone-to-Tendon Interface Healing by Enhancing Tenogenesis, Chondrogenesis, and Osteogenesis in a Rabbit Model of Chronic Rotator Cuff Tears

PURPOSE

To investigate the effect of recombinant human parathyroid hormone (rhPTH) biocomposite on bone-to-tendon interface (BTI) healing for surgical repair of a chronic rotator cuff tear (RCT) model of rabbit, focusing on genetic, histologic, biomechanical and micro-computed tomography (CT) evaluations.

METHODS

Sixty-four rabbits were equally assigned to the 4 groups: saline injection (group A), nanofiber sheet alone (group B), rhPTH-soaked nanofiber sheet (nanofiber sheet was soaked with rhPTH, group C), and rhPTH biocomposite (rhPTH permeated the nanofiber sheet by coaxial electrospinning, group D). The release kinetics of rhPTH (groups C and D) was examined for 6 weeks in vitro. Nanofiber scaffolds were implanted on the surface of the repair site 6 weeks after the induction of chronic RCT. Genetic and histologic analyses were conducted 4 weeks after surgery. Furthermore, genetic, histologic, biomechanical, micro-CT, and serologic analyses were performed 12 weeks after surgery.

RESULTS

In vivo, group D showed the highest collagen type I alpha 1 (COL1A1), collagen type III alpha 1 (COL3A1), and bone morphogenetic protein 2 (BMP-2) messenger RNA (mRNA) expression levels (all P < .001) 4 weeks after surgery; however, there were no differences between groups at 12 weeks postsurgery. After 12 weeks postsurgery, group D showed better collagen fiber continuity and orientation, denser collagen fibers, more mature bone-to-tendon junction, and greater fibrocartilage layer formation compared with the other groups (all P < .05). Furthermore, group D showed the highest load-to-failure rate (28.9 ± 2.0 N/kg for group A, 30.1 ± 3.3 N/kg for group B, 39.7 ± 2.7 N/kg for group C, and 48.2 ± 4.5 N/kg for group D, P < .001) and micro-CT outcomes, including bone and tissue mineral density, and bone volume/total volume rate (all P < .001) at 12 weeks postsurgery.

CONCLUSIONS

In comparison to rhPTH-soaked nanofiber sheet and the other control groups, rhPTH biocomposite effectively accelerated BTI healing by enhancing the mRNA expression levels of COL1A1, COL3A1, and BMP-2 at an early stage and achieving tenogenesis, chondrogenesis, and osteogenesis at 12 weeks after surgical repair of a chronic RCT model of rabbit.

CLINICAL RELEVANCE

The present study might be a transitional study to demonstrate the efficacy of rhPTH biocomposites on BTI healing for surgical repair of chronic RCTs as an adaptable polymer biomaterial in humans.

Translational Research on Orthobiologics in the Treatment of Rotator Cuff Disease: From the Laboratory to the Operating Room

Rotator cuff disease is one of the most common human tendinopathies and can lead to significant shoulder dysfunction. Despite efforts to improve symptoms in patients with rotator cuff tears and healing rates after rotator cuff repair, high rates of failed healing and persistent shoulder morbidity exist. Increasing interest has been placed on the utilization of orthobiologics-scaffolds, cell-based augmentation, platelet right plasma (platelet-rich plasma), and small molecule-based strategies-in the management of rotator cuff disease and the augmentation of rotator cuff repairs. This is a complex topic that involves novel treatment strategies, including patches/scaffolds, small molecule-based, cellular-based, and tissue-derived augmentation techniques. Ultimately, translational research, with a particular focus on preclinical models, has allowed us to gain some insights into the utility of orthobiologics in the treatment of rotator cuff disease and will continue to be critical to our further understanding of the underlying cellular mechanisms moving forward.

Regenerative Medicine Solutions for Rotator Cuff Injuries in Athletes: Indications and Outcomes

Rotator cuff (RC) injuries include a wide range of pathologic states. Athletes are perhaps the most susceptible to RC injuries ranging from tendinopathy to partial or full-thickness tears, due to functional overload and repetitive movements, causing abstention from sports for long periods. Regenerative medicine keeps giving us multiple choices to fight the disability caused by these pathologies. A literature search was performed, and findings related to the structure-function of rotator cuff units, pathophysiology of injuries, regenerative medicine treatments, and future strategies were outlined. Platelet-rich plasma (PRP) has a greater number of articles and clinical trials, accompanied by stem cells progenitor, prolotherapy, and new approaches such as microfragmented adipose tissue and exosomes. RC injuries in athletes can cause pain, functional impotence, and the risk of recurrence, and can lead them to stop playing sports. Regenerative medicine offers a range of treatments, but some of them need further studies to underline their actual validity.

Tendon stem cells seeded on dynamic chondroitin sulfate and chitosan hydrogel scaffold with BMP2 enhance tendon-to-bone healing

Failure to adequately reconstruct the tendon-to-bone interface constitutes the primary etiology underlying rotator cuff retear after surgery. The purpose of this study is to construct a dynamic chondroitin sulfate and chitosan hydrogel scaffold (CHS) with bone morphogenetic protein 2 (BMP2), then seed tendon stem cells (TSCs) on BMP2-CHS for the rotator cuff reconstruction of tendon-to-bone interface. In this dynamic hydrogel system, the scaffold could not only have good biocompatibility and degradability but also significantly promote the proliferation and differentiation of TSCs. The ability of BMP2-CHS combined with TSCs to promote regeneration of tendon-to-bone interface was further verified in the rabbit rotator cuff tear model. The results showed that BMP2-CHS combined with TSCs could induce considerable collagen, fibrocartilage, and bone arrangement and growth at the tendon-to-bone interface and promote the biomechanical properties. Overall, TSCs seeded on CHS with BMP2 can enhance tendon-to-bone healing and provide a new possibility for improving the poor prognosis of rotator cuff surgery.

Ultrasound-Controlled Delivery of Growth Factor-Loaded Cerasomes Combined with Polycaprolactone Scaffolds Seeded with Bone Marrow Mesenchymal Stem Cells for Biomimetic Tendon-to-Bone Interface Engineering

Rotator cuff tear (RCT) is a prevalent shoulder injury that poses challenges for achieving continuous and functional regeneration of the tendon-to-bone interface (TBI). In this study, we controlled the delivery of growth factors (GFs) from liposomal nanohybrid cerasomes by ultrasound and implanted three-dimensional printed polycaprolactone (PCL) scaffolds modified with polydopamine loaded with bone marrow mesenchymal stem cells (BMSCs) to repair tears of the infraspinatus tendon in a lapine model. Direct suturing (control, CTL) was used as a control. The PCL/BMSC/cerasome (PBC) devices are sutured with the enthesis of the infraspinatus tendon. The cerasomes and PCL scaffolds are highly stable with excellent biocompatibility. The roles of GFs BMP2, TGFβ1, and FGF2 in tissue-specific differentiation are validated. Compared with the CTL group, the PBC group had significantly greater proteoglycan deposition (P = 0.0218), collagen volume fraction (P = 0.0078), and proportions of collagen I (P = 0.0085) and collagen III (P = 0.0048). Biotin-labeled in situ hybridization revealed a high rate of survival for transplanted BMSCs. Collagen type co-staining at the TBI is consistent with multiple collagen regeneration. Our studies demonstrate the validity of biomimetic scaffolds of TBI with BMSC-seeded PCL scaffolds and GF-loaded cerasomes to enhance the treatment outcomes for RCTs.

Comparison of mesenchymal stem cells from bone marrow, umbilical cord blood, and umbilical cord tissue in regeneration of a full-thickness tendon defect in vitro and in vivo

Although mesenchymal stem cells (MSCs) can be obtained from various tissues such as bone marrow (BM), umbilical cord blood (UCB) and umbilical cord tissue (UC), the comparative efficacy of each MSC in tendon regeneration is unknown. Therefore, we investigated the efficacy of MSCs isolated from three different sources on tendon regeneration after injury. We evaluated the potential of BM-, UCB- and UC-MSC to differentiate into tendon-like cells in tensioned three-dimensional construct (T-3D) using gene and histological analysis. In animal experiments, full-thickness tendon defect (FTD) was created in supraspinatus of rats, and injected with Saline and BM-, UCB- and UC-MSC. After two and four weeks, histological evaluations were performed. After inducing tenogenic differentiation, the gene expression of scleraxis, mohawk, type I collagen and tenascin-C was upregulated by 3.12-, 5.92-, 6.01- and 1.61-fold respectively and formation of tendon-like matrix was increased 4.22-fold in UC-MSC compared to BM-MSC in T-3D. In animal experiments, the total degeneration score was lower in the UC-MSC group than in BM-MSC group at both weeks. In heterotopic matrix formation, glycosaminoglycan-rich area was reduced in the UC-MSC group, whereas area was larger in the BM-MSC group than in Saline group at four weeks. In conclusion, UC-MSC is superior to other MSCs in differentiating into tendon-like lineage cells and forming a well-organized tendon-like matrix under T-3D conditions. UC-MSC enhances regeneration of FTD in terms of histological properties compared to BM- and UCB-MSC.

Periosteum-derived skeletal stem cells encapsulated in platelet-rich plasma enhance the repair of bone defect

BACKGROUND

Spontaneous restoration of large bone defects remains a challenge under infections, tumors, and crushing conditions. Current stem cell-based therapies for treating bone defects need improvement, because the used stem cells are isolated by a traditional protocol, which is based on their properties of in-vitro plastic adherence and fibroblastic colony formation. The stem cells isolated by the traditional protocol belong to a multicellular type mixture, individual cells vary in proliferative and osteogenic potential. Thus, developing a protocol capable of isolating stem cell subset with higher purity is required and urgent.

AIM

This study aimed to sort a subpopulation of stem cells from periosteum using flow cytometry (named as FC-PSCs), and evaluate the proliferative and osteogenic capacity of FC-PSCs in-vitro, and then establish a new stem cell-based therapies for treating bone defects by delivering the FC-PSCs within platelet-rich plasma (PRP).

METHODS

Mouse periosteum was used to sort FC-PSCs using flow cytometry with CD45-TER119-TIE2-ITGAV+CD90 + 6C3-CD105- markers, or isolate periosteum-derived stem cells with the traditional protocol (TP-PSCs) as control. After evaluating the FC-PSCs proliferation and osteogenic differentiation in-vitro as well as the promotive efficacy of platelet-rich plasma (PRP) on FC-PSCs proliferation and osteogenic differentiation, the FC-PSCs were delivered into the femoral epiphysis bone defect site of a mouse model by platelet-rich plasma (PRP). At postoperative 14 or 28 days, these mice were euthanized for harvest the femur specimens for micro-CT, histological evaluation.

RESULTS

In-vitro results determined that the FC-PSCs showed more capacity for proliferation and osteogenic differentiation compared with the TP-PSCs. In addition, in-vitro results showed the promotive efficacy of PRP on FC-PSCs proliferation and osteogenic differentiation. In-vivo results showed that the FC-PSCs delivered by PRP was able to facilitate the repair of bone defects by stimulating new bone formation and remodeling.

CONCLUSION

FC-PSCs delivered by PRP enhance the repair of bone defects by stimulating new bone formation and remodeling.

Menstrual Blood-Derived Mesenchymal Stem Cells Encapsulated in Autologous Platelet-Rich Gel Facilitate Rotator Cuff Healing in a Rabbit Model of Chronic Tears

BACKGROUND

Successful management of chronic rotator cuff (RC) tears remains a challenge owing to its limited intrinsic healing capacity and unsatisfactory failure rate. Menstrual blood-derived mesenchymal stem cells (MenSCs) have the potential to differentiate into the chondrogenic or osteogenic lineage. Autologous platelet-rich gel (APG), a gel material derived from platelet-rich plasma (PRP), can be applied as a carrier system for cell delivery and also as a releasing system for endogenous growth factors.

PURPOSE

To investigate the effect of human MenSCs encapsulated in APG (MenSCs@APG) on the healing of chronic RC tears in a rabbit model.

STUDY DESIGN

Controlled laboratory study.

METHODS

After evaluation of the effect of PRP on MenSC proliferation or differentiation, the stem cells were encapsulated in APG for in vivo injection. Supraspinatus tenotomy from the right greater tuberosity was performed on 45 New Zealand White rabbits. After 6 weeks, these rabbits were randomly allocated to 3 supplemental treatments during supraspinatus repair: saline injection (control [CTL] group), APG injection (APG group), and MenSCs@APG injection (MenSCs@APG group). At week 18, these rabbits were sacrificed to harvest the humerus-supraspinatus tendon complexes for micro-computed tomography (CT), histological evaluation, tensile test, and MenSC tracking.

RESULTS

In vitro results showed that APG can stimulate MenSC proliferation and enhance chondrogenic or osteogenic differentiation. In vivo results showed that APG can act as a carrier for delivering MenSCs into the healing site, and also as a stimulator for enhancing the in vivo performance of MenSCs. Micro-CT showed that bone volume/total volume and trabecular thickness of the new bone in the MenSCs@APG group presented significantly larger values than those of the APG or CTL group (P < .05 for all). Histologically, compared with the CTL or APG group, significantly more mature fibrocartilage regenerated at the healing site in the MenSCs@APG group. A large number of human nuclei-stained cells were observed in the MenSCs@APG group, presenting a similar appearance to fibrochondrocytes or osteocytes. Biomechanically, the MenSCs@APG group showed significantly higher failure load and stiffness than the APG or CTL group (P < .05 for all).

CONCLUSION

Human MenSCs@APG facilitated RC healing in a rabbit model of chronic tears.

CLINICAL RELEVANCE

Autogenous MenSCs@APG may be a new stem cell-based therapy for augmenting RC healing in the clinic.

Human hair follicle-derived mesenchymal stem cells promote tendon repair in a rabbit Achilles tendinopathy model

BACKGROUND

Hair follicles are easily accessible and contain stem cells with different developmental origins, including mesenchymal stem cells (MSCs), that consequently reveal the potential of human hair follicle (hHF)-derived MSCs in repair and regeneration. However, the role of hHF-MSCs in Achilles tendinopathy (AT) remains unclear. The present study investigated the effects of hHF-MSCs on Achilles tendon repair in rabbits.

METHODS

First, we extracted and characterized hHF-MSCs. Then, a rabbit tendinopathy model was constructed to analyze the ability of hHF-MSCs to promote repair in vivo . Anatomical observation and pathological and biomechanical analyses were performed to determine the effect of hHF-MSCs on AT, and quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and immunohistochemical staining were performed to explore the molecular mechanisms through which hHF-MSCs affects AT. Furthermore, statistical analyses were performed using independent sample t test, one-way analysis of variance (ANOVA), and one-way repeated measures multivariate ANOVA as appropriate.

RESULTS

Flow cytometry, a trilineage-induced differentiation test, confirmed that hHF-derived stem cells were derived from MSCs. The effect of hHF-MSCs on AT revealed that the Achilles tendon was anatomically healthy, as well as the maximum load carried by the Achilles tendon and hydroxyproline proteomic levels were increased. Moreover, collagen I and III were upregulated in rabbit AT treated with hHF-MSCs (compared with AT group; P  < 0.05). Analysis of the molecular mechanisms revealed that hHF-MSCs promoted collagen fiber regeneration, possibly through Tenascin-C (TNC) upregulation and matrix metalloproteinase (MMP)-9 downregulation.

CONCLUSIONS

hHF-MSCs can be a treatment modality to promote AT repair in rabbits by upregulating collagen I and III. Further analysis revealed that treatment of AT using hHF-MSCs promoted the regeneration of collagen fiber, possibly because of upregulation of TNC and downregulation of MMP-9, thus suggesting that hHF-MSCs are more promising for AT.

Assessment of a Synergistic Effect of Platelet-Rich Plasma and Stem Cell-Seeded Hydrogel for Healing of Rat Chronic Rotator Cuff Injuries

Outcomes after repair of chronic rotator cuff injuries remain suboptimal. Type-1 collagen-rich tendon hydrogel was previously reported to improve healing in a rat chronic rotator cuff injury model. Stem cell seeding of the tendon hydrogel improved bone quality in the same model. This study aimed to examine whether there was a synergistic and dose-dependent effect of platelet-rich plasma (PRP) on tendon-bone interface healing by combining PRP with stem cell-seeded tendon hydrogel. Human cadaveric tendons were processed into a hydrogel. PRP was prepared at two different platelet concentrations: an initial concentration (initial PRP group) and a higher concentration (concentrated PRP group). Tendon hydrogel was mixed with adipose-derived stem cells and one of the platelet concentrations. Methylcellulose, as opposed to saline, was used as a negative control due to comparable viscosity. The supraspinatus tendon was detached bilaterally in 33 Sprague-Dawley rats (66 shoulders). Eight weeks later, each detached tendon was repaired, and a hydrogel mixture or control was injected at the repair site. Eight weeks after repair, shoulder samples were harvested and assigned for biomechanical testing (n = 42 shoulders) or a combination of bone morphological and histological assessment (n = 24 shoulders). Biomechanical testing showed significantly higher failure load and stiffness in the concentrated PRP group than in control. Yield load in the initial and concentrated PRP groups were significantly higher than that in the control. There were no statistically significant differences between the initial and concentrated PRP groups. The addition of the highly concentrated PRP to stem cells-seeded tendon hydrogel improved healing biomechanically after chronic rotator cuff injury in rats compared to control. However, synergistic and dose-dependent effects were not seen.

Rotator cuff healing is regulated by the lymphatic vasculature

Background

Despite great advances in surgical techniques for rotator cuff tear (RCT) over the past decades, the postoperative failure rate of RCT is still high due to the poor healing competence of bone-tendon interface (BTI). The lymphatic vasculature plays a regulatory role in inflammatory disease and affects tissue healing. However, whether lymphangiogenesis and the role of lymphatic vasculature in the physiopathological process of rotator cuff （RC）injury remains unknown.

Methods

In this study, we constructed a mouse RC injury model and the BTI samples were collected for measurement. Firstly, immunofluorescence was used to investigate the temporal and spatial distribution of lymphangiogenesis in BTI area at different post-injury time points. Subsequently, the mice of experimental group were gavaged with the lymphatic inhibitors (SAR131675) on the first postoperative day to inhibit lymphangiogenesis, while the control group was treated with the vehicle. At postoperative week 2 and 4, the samples were collected for immunofluorescence staining to evaluate lymphatic angiogenesis inhibition. At postoperative week 4 and 8, The supraspinatus (SS) tendon-humeral complexes were collected for bone morphometric, histological and biomechanical tests to assess the healing outcome of the BTI.

Results

Immunofluorescence results showed that the lymphatic proliferation in the BTI injury area and increased in consistence with the healing time, and the lymphatic hyperplasia area significantly diminished at postoperative week 4. The lymphatic hyperplasia area in the SAR group was significantly lower than that in the control group both at 2 and 4 weeks postoperatively. Moreover, the administration of SAR131675 significantly impeded RC healing, as evidenced by lower histological scores, lower bone morphometric parameters, and worse biomechanical properties in comparison with that in control group at postoperative weeks 4 and 8.

Conclusion

Lymphangiogenesis plays a positive role in RC healing, and targeting the lymphatic drainage at healing site may be a new therapeutic approach to promote RC injury repair.

The translational potential of this article

This is the first study to assess the specific role of lymphatic vessels in RC healing, and improving lymphatic drainage may be a potential new therapeutic approach to facilitate repair of BTI. Further, our study provides a reference for possible future treatment of BTI by intervening the lymphatic system.

Engineering an enthesis-like graft for rotator cuff repair: An approach to fabricate highly biomimetic scaffold capable of zone-specifically releasing stem cell differentiation inducers

Rotator cuff (RC) attaches to humerus across a triphasic yet continuous tissue zones (bone-fibrocartilage-tendon), termed "enthesis". Regrettably, rapid and functional enthesis regeneration is challenging after RC tear. The existing grafts bioengineered for RC repair are insufficient, as they were engineered by a scaffold that did not mimic normal enthesis in morphology, composition, and tensile property, meanwhile cannot simultaneously stimulate the formation of bone-fibrocartilage-tendon tissues. Herein, an optimized decellularization approach based on a vacuum aspiration device (VAD) was developed to fabricate a book-shaped decellularized enthesis matrix (O-BDEM). Then, three recombinant growth factors (CBP-GFs) capable of binding collagen were synthesized by fusing a collagen-binding peptide (CBP) into the N-terminal of BMP-2, TGF-β3, or GDF-7, and zone-specifically tethered to the collagen of O-BDEM to fabricate a novel scaffold (CBP-GFs/O-BDEM) satisfying the above-mentioned requirements. After ensuring the low immunogenicity of CBP-GFs/O-BDEM by a novel single-cell mass cytometry in a mouse model, we interleaved urine-derived stem cell-sheets into this CBP-GFs/O-BDEM to bioengineer an enthesis-like graft. Its high-performance on regenerating enthesis was determined in a canine model. These findings indicate this CBP-GFs/O-BDEM may be an excellent scaffold for constructing enthesis-like graft to patch large/massive RC tears, and provide breakthroughs in fabricating graded interfacial tissue.

Clinical perspectives for repairing rotator cuff injuries with multi-tissue regenerative approaches

Background

In the musculoskeletal system, bone, tendon, and muscle form highly integrated multi-tissue units such as the rotator cuff complex, which facilitates functional and dynamic movement of the shoulder joint. Understanding the intricate interplay among these tissues within clinical, biological, and engineering contexts is vital for addressing challenging issues in treatment of musculoskeletal disorders and injuries.

Methods

A wide-ranging literature search was performed, and findings related to the socioeconomic impact of rotator cuff tears, the structure-function relationship of rotator cuff bone-tendon-muscle units, pathophysiology of injury, current clinical treatments, recent state-of-the-art advances (stem cells, growth factors, and exosomes) as well as their regulatory approval, and future strategies aimed at engineering bone-tendon-muscle musculoskeletal units are outlined.

Results

Rotator cuff injuries are a significant socioeconomic burden on numerous healthcare systems that may be addressed by treating the rotator cuff as a single complex, given its highly integrated structure-function relationship as well as degenerative pathophysiology and limited healing in bone-tendon-muscle musculoskeletal tissues. Current clinical practices for treating rotator cuff injuries, including the use of commercially available devices and evolving trends in surgical management have benefited patients while advances in application of stem/progenitor cells, growth factors, and exosomes hold clinical potential. However, such efforts do not emphasize targeted regeneration of bone-tendon-muscle units. Strategies aimed at regenerating bone-tendon-muscle units are thus expected to address challenging issues in rotator cuff repair.

Conclusions

The rotator cuff is a highly integrated complex of bone-tendon-muscle units that when injured, has severe consequences for patients and healthcare systems. State-of-the-art clinical treatment as well as recent advances have resulted in improved patient outcome and may be further enhanced by engineering bone-tendon-muscle multi-tissue grafts as a potential strategy for rotator cuff injuries.

Translational Potential of this Article

This review aims to bridge clinical, tissue engineering, and biological aspects of rotator cuff repair and propose a novel therapeutic strategy by targeted regeneration of multi-tissue units. The presentation of these wide-ranging and multi-disciplinary concepts are broadly applicable to regenerative medicine applications for musculoskeletal and non-musculoskeletal tissues.

Mesenchymal Stem Cell Use in Acute Tendon Injury: In Vitro Tenogenic Potential vs. In Vivo Dose Response

Stem cell therapy for the treatment of tendon injury is an emerging clinical practice in the fields of human and veterinary sports medicine; however, the therapeutic benefit of intralesional transplantation of mesenchymal stem cells in tendonitis cases is not well designed. Questions persist regarding the overall tenogenic potential and efficacy of this treatment alone. In this study, we aimed to isolate a rat mesenchymal stem cell lineage for in vitro and in vivo use, to assess the effects of growth factor exposure in vitro on cell morphology, behavior, and tendon-associated glycoprotein production, and to assess the therapeutic potential of intralesional stem cells, as a function of dose, in vivo. First, rat adipose-derived (rAdMSC) and bone marrow-derived (rBMSC) stem cell lineages were isolated, characterized with flow cytometric analysis, and compared in terms of proliferation (MTS assay) and cellular viability (calcein AM staining). Rat AdMSCs displayed superior proliferation and more homogenous CD 73, CD 44H, and CD 90 expression as compared to rBMSC. Next, the tenogenic differentiation potential of the rAdMSC lineage was tested in vitro through isolated and combined stimulation with reported tenogenic growth factors, transforming growth factor (TGF)-β3 and connective tissue growth factor (CTGF). We found that the most effective tenogenic factor in terms of cellular morphologic change, cell alignment/orientation, sustained cellular viability, and tendon-associated glycoprotein upregulation was TGFβ3, and we confirmed that rAdMSC could be induced toward a tenogenic lineage in vitro. Finally, the therapeutic potential of rAdMSCs as a function of dose was assessed using a rat acute Achilles tendon injury model. Amounts of 5 × 10⁵ (low dose) and 4 × 10⁶ (high dose) were used. Subjectively, on the gross morphology, the rAdMSC-treated tendons exhibited fewer adhesions and less scar tissue than the control tendons; however, regardless of the rAdMSC dose, no significant differences in histological grade or tissue collagen I deposition were noted between the rAdMSC-treated and control tendons. Collectively, rAdMSCs exhibited appropriate stem cell markers and tenogenic potential in vitro, but the clinical efficacy of intralesional implantation of undifferentiated cells in acute tendonitis cases could not be proven. Further investigation into complementary therapeutics or specialized culture conditions prior to implantation are warranted.

Injection of Leukocyte-Poor Platelet-Rich Plasma for Moderate-to-Large Rotator Cuff Tears Does Not Improve Clinical Outcomes but Reduces Retear Rates and Fatty Infiltration: A Prospective, Single-Blinded Randomized Study

OBJECTIVES

To determine whether leukocyte-poor platelet-rich plasma (Lp-PRP) reduced retear rates, reduced fatty infiltration, and improved functional outcomes in patients with degenerative moderate-to-large rotator cuff tears.

METHODS

This was a randomized controlled study at a single center. A consecutive series of 104 patients with moderate-to-large rotator cuff tears was enrolled and randomly allocated to a control group (double-row suture-bridge arthroscopic rotator cuff repair alone, n = 52) and a study group (double-row suture-bridge repair followed by 3 Lp-PRP injections at the tendon repair site during surgery, at days 7 and 14 after surgery, n = 52). All patients were followed up for 27.2 months (range 24-36 months), with University of California at Los Angeles (UCLA) shoulder rating scale, the Constant score, and a visual analog scale (VAS) evaluated respectively. The integrity and fatty infiltration of repaired tissue were assessed by magnetic resonance imaging using the Sugaya classification and Goutallier grade classification at 24 months after surgery. Statistical analysis was performed based on the t test, χ² test, and the Kendall tau-b correlation coefficient.

RESULTS

Four patients refused follow-up, and 11 patients had incomplete data. Eventually, a total of 89 patients were available for 24 months follow-up. The mean UCLA score increased from 14.80 ± 2.53 to 29.37 ± 2.06 in control group and from 13.74 ± 3.30 to 30.14 ± 2.32 in study group (P = .103). The mean Constant score increased from 46.56 ± 5.90 to 86.83 ± 4.94 in control group and from 44.37 ± 7.92 to 88.80 ± 4.92 in study group (P = .063). The VAS score decreased from 3.22 ± 1.24 to 0.97 ± 1.12 in control group and in 3.49 ± 1.52 to 1.16 ± 0.99 in study group (P = .41). All differences in UCLA score, Constant score, and VAS between pre- and postoperation achieved minimal clinically important differences proposed for arthroscopic rotator cuff repair. Of the 89 patients, 76 had magnetic resonance imaging performed at 24 months after surgery. The retear rate was 17.6% in study group, which was lower than that in control group (38.1%, P = .049). In addition, the Goutallier grade was found to be significant difference between groups postoperatively (Kendall tau-b -0.24, P = .03) but no significant difference preoperatively (Kendall tau-b -0.18, P = .11). There were no complications in the patients.

CONCLUSIONS

Our procedures involving repeated injections of Lp-PRP during surgery and at days 7 and 14, as described in this study, have positive effects on reducing retear rate and promoting Goutallier grade in patients following arthroscopic rotator cuff repair and could also provide substantial clinical outcomes that reach the minimal clinically important difference for surgical treatment. However, given the numbers available for analysis, it did not promote better clinical results when compared with the control group.

LEVEL OF EVIDENCE

II, randomized controlled study.

Innate and adaptive immune system cells implicated in tendon healing and disease

Tendons perform a critical function in the musculoskeletal system by integrating muscle with skeleton and enabling force transmission. Damage or degeneration of these tissues lead to impaired structure and function, which often persist despite surgical intervention. While the immune response and inflammation are important drivers of both tendon healing and disease progression, there have been relatively few studies of the diverse immune cell types that may regulate these processes in these tissues. To date, most of the studies have focused on macrophages, but emerging research indicate that other immune cell types may also play a role in tendon healing, either by regulating the immune environment or through direct interactions with resident tenocytes. The present review synthesises the literature on innate and adaptive immune system cells that have been implicated in tendon healing or disease, in the context of animal injury models, human clinical samples or in vitro experiments.

"Smart Exosomes": A Smart Approach for Tendon Regeneration

Shoulder tendon injuries are the common musculoskeletal disorder resulting in significant pain and disability. These injuries are characterized by chronic inflammation and tissue degeneration. Tendon pathology exhibits poor innate healing ability, enhanced inflammation, disorganized collagen fibers, calcification, and scar tissue formation affecting the normal healing process. Extracellular vesicle, especially exosomes, treatment has been emerging as a potential regenerative strategy improving the outcomes and biomechanical properties, accelerating tenocyte proliferation and migration, reducing inflammation, and facilitating the healing at tendon-bone interface. In this article, we critically reviewed the potential role of exosomes in tendon regeneration and their applications to accelerate the healing response following injury. In addition, the article provides novel insights on the concept of "Smart Exosomes" by programming/manipulating the secretome contents and functions of exosomes in the management of shoulder tendon injury.

Mesenchymal stem cell-derived exosomes: therapeutic implications for rotator cuff injury

Rotator cuff injuries are a common clinical condition of the shoulder joint. Surgery that involves reattaching the torn tendon to its humeral head bony attachment has a somewhat lower success rate. The scar tissue formed during healing of the rotator cuff leads to poor tendon-related mechanical properties. To promote healing, a range of genetic interventions, as well as cell transplantation, and many other techniques have been explored. In recent years, the therapeutic promise of mesenchymal stem cells (MSCs) has been well documented in animal and clinical studies. Some data have suggested that MSCs can promote angiogenesis, reduce inflammation and cell proliferation and increase collagen deposition. These functions are likely paracrine effects of MSCs, particularly mediated through exosomes. Here, we review the use of MSCs-related exosomes in tissues and organs. We also discuss their potential utility for treating rotator cuff injuries, and explore the underlying mechanisms of their effects.

Acceleration of Bone-Tendon Interface Healing by Low-Intensity Pulsed Ultrasound Is Mediated by Macrophages

OBJECTIVE

Low-intensity pulsed ultrasound (LIPUS) has been proven to facilitate bone-tendon interface (BTI) healing and regulate some inflammatory cytokines. However, the role of macrophages, a key type of inflammatory cell, during treatment remains unknown. This study aimed to investigate the role of macrophages in the treatment of BTI injury with LIPUS in a rotator cuff tear animal model.

METHODS

In this experimental and comparative study, a total of 160 C57BL/6 mature male mice that underwent supraspinatus tendon detachment and repair were randomly assigned to 4 groups: daily ultrasonic treatment and liposomal clodronate (LIPUS+LC), daily ultrasonic treatment and liposomes (LIPUS), daily mock sonication and liposomal clodronate (LC), and daily mock sonication and liposomes (control [CTL]). LIPUS treatment was initiated immediately postoperatively and continued daily until the end of the experimental period.

RESULTS

The failure load and stiffness of the supraspinatus tendon-humerus junction were significantly higher in the LIPUS group than in the other groups at postoperative weeks 2 and 4, whereas those in the LIPUS+LC and LC groups were lower than those in the CTL group at postoperative week 4. The LIPUS, LIPUS+LC, and LC groups exhibited significantly more fibrocartilage than the CTL group at 2 weeks. Only the LIPUS group had more fibrocartilage than the CTL group at 4 weeks. Micro-computed tomography results indicated that LIPUS treatment could improve the bone quality of the attachment site after both 2 and 4 weeks. When macrophages were depleted by LC, the bone quality-promoting effect of LIPUS treatment was significantly reduced.

CONCLUSION

The enhancement of BTI healing by LIPUS might be mediated by macrophages.

IMPACT

In our study, LIPUS treatment appeared to accelerate BTI healing, which was associated with macrophages based on our murine rotator cuff repair model. The expressions of macrophage under LIPUS treatment may offer a potential mechanism to explain BTI healing and the effects of LIPUS on BTI healing.

Current Biological Strategies to Enhance Surgical Treatment for Rotator Cuff Repair

Rotator cuff tear is one of the most common shoulder problems encountered by orthopedic surgeons. Due to the slow healing process and high retear rate, rotator cuff tear has distressed millions of people all around the world every year, especially for the elderly and active athletes. This disease significantly impairs patients' motor ability and reduces their quality of life. Besides conservative treatment, open and arthroscopic surgery contributes a lot to accelerate the healing process of rotator cuff tear. Currently, there are many emerging novel treatment methods to promote rotator cuff repair. A variety of biological stimulus has been utilized in clinical practice. Among them, platelet-rich plasma, growth factors, stem cells, and exosomes are the most popular biologics in laboratory research and clinical trials. This review will focus on the biologics of bioaugmentation methods for rotator cuff repair and tendon healing, including platelet-rich plasma, growth factors, exosomes and stem cells, etc. Relevant studies are summarized in this review and future research perspectives are introduced.

Adipose-derived stem cell exosomes facilitate rotator cuff repair by mediating tendon-derived stem cells

Aim: To evaluate the potential capability of adipose-derived stem cell exosomes (ADSC-exos) on rotator cuff repair by mediating the tendon-derived stem cells (TDSCs) and explored the mechanism. Methods: First, we investigated the growth, survival and migration of TDSCs in the presence of ADSC-exos in vitro. Using a rat rotator cuff injury model to analyze the ability of the ADSC-exos to promote rotator cuff healing in vivo. Results: The hydrogel with ADSC-exos significantly improved the osteogenic and adipogenesis differentiation and enhanced the expression of RUNX2, Sox-9, TNMD, TNC and Scx and the mechanical properties of the articular portion. Conclusion: The ADSC-exos have the potential to promote the rotator cuff repair by mediating the TDSCs.

Biomimetic strategies for tendon/ligament-to-bone interface regeneration

Tendon/ligament-to-bone healing poses a formidable clinical challenge due to the complex structure, composition, cell population and mechanics of the interface. With rapid advances in tissue engineering, a variety of strategies including advanced biomaterials, bioactive growth factors and multiple stem cell lineages have been developed to facilitate the healing of this tissue interface. Given the important role of structure-function relationship, the review begins with a brief description of enthesis structure and composition. Next, the biomimetic biomaterials including decellularized extracellular matrix scaffolds and synthetic-/natural-origin scaffolds are critically examined. Then, the key roles of the combination, concentration and location of various growth factors in biomimetic application are emphasized. After that, the various stem cell sources and culture systems are described. At last, we discuss unmet needs and existing challenges in the ideal strategies for tendon/ligament-to-bone regeneration and highlight emerging strategies in the field.

Application of Autogenous Urine-Derived Stem Cell Sheet Enhances Rotator Cuff Healing in a Canine Model

BACKGROUND

A repaired rotator cuff (RC) often heals with interposed scar tissue, making repairs prone to failure. Urine-derived stem cells (USCs), with robust proliferation ability and multilineage differentiation, can be isolated from urine, avoiding invasive and painful surgical procedures for harvesting the cells. These advantages make it a novel cell source for autologous transplantation to enhance RC healing.

HYPOTHESIS

Implantation of an autogenous USC sheet to the injury site will enhance RC healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

USCs isolated from urine were cultured using ascorbic acid and transforming growth factor β3 to form a cell sheet. Sixteen male mature beagles underwent bilateral shoulder surgery. The right shoulder underwent infraspinatus tendon (IT) insertion detachment and repair only, and the other was subjected to IT insertion detachment and repair, followed by autogenous USC sheet implantation. Among the animals, 3 received a Dil (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate)- labeled USC sheet implant in the right shoulder and were sacrificed at postoperative 6 weeks for cell tracking. The other animals were sacrificed at postoperative 12 weeks, and the IT-humerus complexes were harvested for gross observation, micro-computed tomography evaluation and histological analysis (n = 5), and mechanical testing (n = 8). Additionally, 13 unpaired canine cadaveric shoulders were included as native controls.

RESULTS

Micro-computed tomography analysis showed that the USC sheet group had a significant increase in bone volume/total volume and trabecular thickness at the RC healing site when compared with the control group (P < .05 for all). Histologically, the Dil-labeled USC sheet was still visible at the RC healing site, which suggested that the implanted USCs remained viable at postoperative 6 weeks. Meanwhile, the healing interface in the USC sheet group regenerated significantly more enthesis-like tissue than did that of the control group (P < .05). Additionally, the healing interface in the USC sheet group presented a larger fibrocartilage area, more proteoglycan deposition, and higher collagen birefringence than did that of the control group (P < .05 for all). Biomechanically, the USC sheet group showed significantly higher failure load and stiffness versus the control group (P < .05 for all).

CONCLUSION

A USC sheet was able to enhance RC healing in a canine model.

CLINICAL RELEVANCE

The findings of the study showed that USC sheet implantation could serve as a practical application for RC healing.

Regeneration of a full-thickness defect in rotator cuff tendon with umbilical cord-derived mesenchymal stem cells in a rat model

Although rotator cuff disease is a common cause of shoulder pain, there is still no treatment method that could halt or reveres its development and progression. The purpose of this study was to investigate the efficacy of umbilical cord-derived mesenchymal stem cells (UC MSCs) on the regeneration of a full-thickness rotator cuff defect (FTD) in a rat model. We injected either UC MSCs or saline to the FTD and investigated macroscopic, histological and biomechanical results and cell trafficking. Treatment with UC MSCs improved macroscopic appearance in terms of tendon thickness at two weeks, and inflammation, defect size, swelling/redness and connection surrounding tissue and slidability at four weeks compared to the saline group. Histologically, UC MSCs induced the tendon matrix formation recovering collagen organization, nuclear aspect ratio and orientation angle of fibroblast as well as suppressing cartilage-related glycosaminoglycan compared to saline group at four weeks. The UC MSCs group also improved ultimate failure load by 25.0% and 19.0% and ultimate stress by 27.3% and 26.8% at two and four weeks compared to saline group. UC MSCs labeled with PKH26 exhibited 5.3% survival at four weeks compared to three hours after injection. This study demonstrated that UC MSCs regenerated the FTD with tendon tissue similar properties to the normal tendon in terms of macroscopic, histological and biomechanical characteristics in a rat model.

Regeneration of a full-thickness defect of rotator cuff tendon with freshly thawed umbilical cord-derived mesenchymal stem cells in a rat model

BACKGROUND

It is difficult to immediately use mesenchymal stem cells (MSCs) for the patient with rotator cuff disease because isolation and culture time are required. Thus, the MSCs would be prepared in advanced in cryopreserved condition for an "off-the-shelf" usage in clinic. This study investigated the efficacy of freshly thawed MSCs on the regeneration of a full-thickness tendon defect (FTD) of rotator cuff tendon in a rat model.

METHODS

We evaluated morphology, viability, and proliferation of cultured umbilical cord-derived MSCs (C-UC MSCs) and freshly thawed umbilical cord-derived MSCs (T-UC MSCs) at passage 10 in vitro. In animal experiments, we created a FTD in the supraspinatus of rats and injected the injured tendon with saline, cryopreserved agent (CPA; control), C-UC MSCs, and T-UC MSCs, respectively. Two and 4 weeks later, macroscopic, histological, biomechanical, and cell trafficking were evaluated. T test and ANOVA were used with SPSS. Differences with p < .05 were considered statistically significant.

RESULTS

T-UC MSCs had fibroblast-like morphology and showed greater than 97% viability and stable proliferation comparable to the C-UC MSCs at passage 10. In animal experiments, compared with the control group, the macroscopic appearance of the T-UC MSCs was more recovered at 2 and 4 weeks such as inflammation, defect size, neighboring tendon, swelling/redness, the connecting surrounding tissue and slidability. Histologically, the nuclear aspect ratio, orientation angle of fibroblasts, collagen organization, and fiber coherence were improved by 33.33%, 42.75%, 1.86-fold, and 1.99-fold at 4 weeks, and GAG-rich area decreased by 88.13% and 94.70% at 2 and 4 weeks respectively. Further, the T-UC MSCs showed enhanced ultimate failure load by 1.55- and 1.25-fold compared with the control group at both 2 and 4 weeks. All the improved values of T-UC MSCs were comparable to those of C-UC MSCs. Moreover, T-UC MSCs remained 8.77% at 4 weeks after injury, and there was no significant difference between C-UC MSCs and T-UC MSCs.

CONCLUSIONS

The morphology, viability, and proliferation of T-UC MSCs were comparable to those of C-UC MSCs. Treatment with T-UC MSCs could induce tendon regeneration of FTD at the macroscopic, histological, and biomechanical levels comparable to treatment with C-UC MSCs.

3D printing of multilayered scaffolds for rotator cuff tendon regeneration

Repairing massive rotator cuff tendon defects remains a challenge due to the high retear rate after surgical intervention. 3D printing has emerged as a promising technique that enables the fabrication of engineered tissues with heterogeneous structures and mechanical properties, as well as controllable microenvironments for tendon regeneration. In this study, we developed a new strategy for rotator cuff tendon repair by combining a 3D printed scaffold of polylactic-co-glycolic acid (PLGA) with cell-laden collagen-fibrin hydrogels. We designed and fabricated two types of scaffolds: one featuring a separate layer-by-layer structure and another with a tri-layered structure as a whole. Uniaxial tensile tests showed that both types of scaffolds had improved mechanical properties compared to single-layered PLGA scaffolds. The printed scaffold with collagen-fibrin hydrogels effectively supported the growth, proliferation, and tenogenic differentiation of human adipose-derived mesenchymal stem cells. Subcutaneous implantation of the multilayered scaffolds demonstrated their excellent in vivo biocompatibility. This study demonstrates the feasibility of 3D printing multilayered scaffolds for application in rotator cuff tendon regeneration.

TGF-β3 Loaded Electrospun Polycaprolacton Fibre Scaffolds for Rotator Cuff Tear Repair: An in Vivo Study in Rats

Biological factors such as TGF-β3 are possible supporters of the healing process in chronic rotator cuff tears. In the present study, electrospun chitosan coated polycaprolacton (CS-g-PCL) fibre scaffolds were loaded with TGF-β3 and their effect on tendon healing was compared biomechanically and histologically to unloaded fibre scaffolds in a chronic tendon defect rat model. The biomechanical analysis revealed that tendon-bone constructs with unloaded scaffolds had significantly lower values for maximum force compared to native tendons. Tendon-bone constructs with TGF-β3-loaded fibre scaffolds showed only slightly lower values. In histological evaluation minor differences could be observed. Both groups showed advanced fibre scaffold degradation driven partly by foreign body giant cell accumulation and high cellular numbers in the reconstructed area. Normal levels of neutrophils indicate that present mast cells mediated rather phagocytosis than inflammation. Fibrosis as sign of foreign body encapsulation and scar formation was only minorly present. In conclusion, TGF-β3-loading of electrospun PCL fibre scaffolds resulted in more robust constructs without causing significant advantages on a cellular level. A deeper investigation with special focus on macrophages and foreign body giant cells interactions is one of the major foci in further investigations.

Effect of Fatty Acid-Binding Protein 4 Inhibition on Rotator Cuff Muscle Quality: Histological, Biomechanical, and Biomolecular Analysis

BACKGROUND

A rotator cuff tear (RCT) induces fatty acid-binding protein 4 (FABP4) expression, resulting in ectopic fat accumulation in the rotator cuff muscle.

PURPOSE

To evaluate whether FABP4 inhibition reduces fatty infiltration and improves muscle physiology after RCT in a rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Human supraspinatus muscle and deltoid muscle tissues were acquired from patients with RCTs during arthroscopic surgery, and FABP4 expression in the supraspinatus muscle was evaluated as compared with the intact deltoid muscle. A rat RCT model was established by detaching the supraspinatus tendon, after which a specific FABP4 inhibitor was locally injected into the supraspinatus muscle 4 times at 3-day intervals starting 2 weeks after the surgery. Body weight and blood glucose levels were measured at 2 and 4 weeks after the RCT, and the mRNA and protein expressions of various target molecules (including FABP4), histological changes, and biomechanical tensile strength were assessed in the supraspinatus muscles at 4 weeks after the RCT.

RESULTS

The expression of human FABP4 was significantly increased in the torn rotator cuff muscle as compared with the intact deltoid muscle. In the rat model, the mRNA and protein expressions of FABP4 and HIF1α were significantly increased by the RCT as compared with the control. The FABP4 inhibitor treatment significantly decreased FABP4 expression when compared with the vehicle treatment; however, HIF1α expression was not significantly decreased versus the vehicle treatment. Histologically, RCT induced noticeable muscle fatty infiltration, which was remarkably reduced by the local injection of the FABP4 inhibitor. Biomechanically, the tensile strength of the rotator cuff muscle after the RCT was significantly improved by the FABP4 inhibitor in terms of load to failure and total energy to failure.

CONCLUSION

RCT induces FABP4 expression in human and rat rotator cuff muscles. The FABP4 inhibitor drastically decreased the histological fatty infiltration caused by RCT and improved the tensile strength of the rotator cuff muscle.

CLINICAL RELEVANCE

FABP4 inhibitor may have a beneficial effect on the muscle quality after RCT.