The effect of adipose-derived stem cells on enthesis healing after repair of acute and chronic massive rotator cuff tears in rats

The role of injections of mesenchymal stem cells as an augmentation tool in rotator cuff repair: a systematic review

Background

Arthroscopic repair is currently the gold standard for the surgical treatment of rotator cuff tears, but the retear rates remain unacceptably high. Mesenchymal stem cells (MSCs) may play a role in the local biology and enhance tendon-to-bone healing during rotator cuff repair. However, the scientific literature is still not well systematized on the effects of injection of MSCs as an augmentation tool for rotator cuff repair. Our goal was to investigate the effect of injections of MSCs to augment rotator cuff repair in patients with rotator cuff tear.

Methods

PubMed and EMBASE were searched up to June 2022 for clinical studies that applied MSCs injections to augment rotator cuff repair. Imaging, patient-reported outcomes measures, shoulder range of motion and strength were collected. Quantitative synthesis included within- and between-group mean differences with the within-group percentage of minimal clinically important difference for each study and continuous outcomes, and relative risks (RR) for retears and adverse events. Quantitative synthesis was computed with 95% confidence intervals (CIs).

Results

We included 5 studies comprising a total of 228 individuals with a weighted mean age of 59.3 ± 1.2 years. Three studies used bone marrow MSCs and two studies applied adipose-derived MSCs. Patient-reported outcomes measures, shoulder range of motion, and strength improved significantly in all MSCs groups, with minimal clinically important differences ranging from 120% to 679% of established cut-off. When compared to rotator cuff repair alone, the MSCs groups did not result in improved outcomes. The MSCs group showed significant protective effect at the mid-term (RR = 0.52, 95% CI 0.27-0.98) and long-term (RR = 0.24, 95% CI 0.11-0.53).

Conclusion

There are no differences in clinical and functional outcomes between rotator cuff repair with or without augmentation with MSCs. However, there may be a protective effect against retear at the mid-term and long-term follow-up when augmenting the repair with MSCs. The literature on this topic is still preliminary and the quality and certainty of evidence is limited.

Adipose stromal cells in the human rotator cuff are resistant to fibrotic microenvironmental cues

Rotator cuff tears are the most common upper extremity orthopaedic injury, causing degenerative changes within the bone, tendon, joint capsule, bursa and muscle. These degenerative changes are linked to poor rehabilitative and surgical outcomes, which has launched investigations into co-therapeutic biologics. Specifically, mesenchymal stem cells (MSCs) have shown promise in mitigating degenerative changes in animal models of rotator cuff tears, but reports of their impact on clinical outcomes remain mixed. Here we describe an alternative source of MSCs in the human shoulder, adipose stromal cells (ASCs) from the subacromial fat (SAF) pad. Compared to the gold-standard subcutaneous (SQ) fat, we show that SAF ASCs are less sensitive to chemical and mechanical fibrotic cues, (1) retaining smaller cell area with reduced actin stress fibre alignment across a range of physiological and pathological stiffnesses, (2) having reduced traction forces and extracellular matrix production, and (3) having reduced myofibroblastic conversion in response to cytokine challenge. Furthermore, we show that SAF ASCs enhance fusion of primary human myoblasts via paracrine signalling. Despite a fibrotic signature in SAF from rotator cuffs with tendon tears, SAF ASCs sourced from torn rotator cuffs were equally effective at resisting fibroblastic conversion and promoting myogenesis as those from intact rotator cuffs, further supporting autologous clinical use of these cells. In conclusion, this study describes human SAF ASCs as an alternative, and potentially superior, cell source for rotator cuff therapies. KEY POINTS: Adipose tissue within the rotator cuff is a novel and understudied source of therapeutic adipose stromal cells. Here, we detail the impact rotator cuff tears have on adipose tissue within the shoulder, its resident adipose stromal cells, and make a comparison of shoulder adipose stromal cells to subcutaneous adipose stromal cells. Rotator cuff tears cause fibrosis of rotator cuff adipose tissue; this fibrosis does not impact downstream adipose stromal cell morphology or pro-myogenic signaling. Rotator cuff adipose stromal cells resist fibrotic microenvironmental cues and have enhanced pro-myogenic paracrine signaling compared with traditional subcutaneous adipose stromal cells. Rotator cuff adipose stromal cells represent a new cell type that can be impactful in advancing rotator cuff therapies.

Reliable Fabrication of Mineral-Graded Scaffolds by Spin-Coating and Laser Machining for Use in Tendon-to-Bone Insertion Repair

A reliable method for fabricating biomimetic scaffolds with a controllable mineral gradient to facilitate the surgical repair of tendon-to-bone injuries and the regeneration of the enthesis is reported. The gradient in mineral content is created by sequentially spin-coating with hydroxyapatite/poly(ε-caprolactone) suspensions containing hydroxyapatite nanoparticles in decreasing concentrations. To produce pores and facilitate cell infiltration, the spin-coated film is released and patterned with an array of funnel-shaped microchannels by laser machining. The unique design provided both mechanical (i.e., substrate stiffness) and biochemical (e.g., hydroxyapatite content) cues to spatially control the graded differentiation of mesenchymal stem cells. Immunocytochemical analysis of human mesenchymal stem cell-seeded scaffolds after 14 days of culture demonstrated the formation of a spatial phenotypic cell gradient from osteoblasts to mineralized chondrocytes based on the level of mineralization in the scaffold. By successfully recreating compositional and cellular features of the native tendon enthesis, the biomimetic scaffolds offer a promising avenue for improved tendon-to-bone repair.

Biomechanical properties of various rat rotator cuff repair techniques

While rat models are frequently used to study tendon healing, there is a lack of research comparing various rotator cuff repair methods in this animal model. Determining the most effective method to begin with is pivotal for biological studies focused on healing augmentation. No study to date has shown the superiority of one repair over the other for rotator cuff repair in a rat model. We performed a biomechanic study using a rat model to study the strength of four common grasping techniques. We assessed if the bone tunnel trajectory influenced the early biomechanics of the repair at postoperative day 0 (POD0). Sixty cadaveric rat shoulders were divided equally into 6 groups; 4 groups were allocated for the biomechanical strength testing based on either a (1) modified Mason Allen (MM), (2) modified Kessler loop (MK), (3) horizontal mattress (HM), or a (4) simple interrupted stitch (SS) technique. The remaining 2 groups were used to evaluate two tunneling angles: a transverse tunnel (TT) that was perpendicular to the long humeral axis, or a longitudinal tunnel (LT) that was 30◦ angle to the humerus. MM had the highest mean failure load, followed by MK, HM, and SS. Pairwise comparison revealed that MM was stronger than SS and HM (P = 0.025 and P = 0.026, respectively), although similar to the MK (P = 0.881). MM was stiffer than MK (P < 0.001), HM (P = 0.008), and SS (P < 0.001). The TT and LT had similar loads to failure and stiffness. Our study suggests that the MM technique provides a stronger and stiffer rotator cuff repair than the others.

Satellite myoblast and mesenchymal stem cell injections decrease fatty degeneration after rotator cuff tear in rats

Purpose

Rotator cuff (RC) tears cause fatty degeneration, aggravated by delayed treatment. Surgical repair alone cannot reverse fatty degeneration. It was aimed to test if local injections of satellite cell-derived myoblasts or satellite myoblasts (SM) from the deltoid region and mesenchymal stem cells (MSCs) from the subcutaneous abdominal fat pad would stimulate myogenesis and decrease adipogenesis in the rat model of fatty degenerated RC tear.

Methods

A standardized RC tear surgery was performed on both shoulders of 24 Wistar albino rats at t = 0, and rats were followed for 8 weeks to create a chronic degeneration model. The animals were randomly divided into repair + SM and MSC (n = 12) or repair only (n = 12) groups. Transosseous repair with or without stem cell-based injection was performed on the right shoulder of all rats on week 8, with additional injections on weeks 9 and 10. The left shoulders were used as control. The animals were followed until week 14 for recovery.

Results

Histological and histomorphometric analyses were performed in week 14. The repair + SM and MSC group had a significantly greater supraspinatus muscle mass than the repair only and control groups. The adipose tissue ratio was significantly lower in the repair + SM and MSC groups versus the repair only and control groups.

Conclusion

Histologically, the repair + SM and MSC group had improved muscle and tendon organization. In treating chronically degenerated RC tear in a rat model, surgical repair combined with injections of SM and MSC improved fatty degeneration, tendon healing and myogenesis.

Level of Evidence

Level III.

Adipose-derived stem cell-based optimization strategies for musculoskeletal regeneration: recent advances and perspectives

Musculoskeletal disorders are the leading causes of physical disabilities worldwide. The poor self-repair capacity of musculoskeletal tissues and the absence of effective therapies have driven the development of novel bioengineering-based therapeutic approaches. Adipose-derived stem cell (ADSC)-based therapies are being explored as new regenerative strategies for the repair and regeneration of bone, cartilage, and tendon owing to the accessibility, multipotency, and active paracrine activity of ADSCs. In this review, recent advances in ADSCs and their optimization strategies, including ADSC-derived exosomes (ADSC-Exos), biomaterials, and genetic modifications, are summarized. Furthermore, the preclinical and clinical applications of ADSCs and ADSC-Exos, either alone or in combination with growth factors or biomaterials or in genetically modified forms, for bone, cartilage, and tendon regeneration are reviewed. ADSC-based optimization strategies hold promise for the management of multiple types of musculoskeletal injuries. The timely summary and highlights provided here could offer guidance for further investigations to accelerate the development and clinical application of ADSC-based therapies in musculoskeletal regeneration.

Effects of adipose-derived cell supplementation on tendon-bone healing in a rat model of chronic rotator cuff tear with suprascapular nerve injury

OBJECTIVE

To investigate the effect of adipose-derived cells (ADCs) on tendon-bone healing in a rat model of chronic rotator cuff tear (RCT) with suprascapular nerve (SN) injury.

METHODS

Adult rats underwent right shoulder surgery whereby the supraspinatus was detached, and SN injury was induced. ADCs were cultured from the animals' abdominal fat. At 6 weeks post-surgery, the animals underwent surgical tendon repair; the ADC (+ve) group (n = 18) received an ADC injection, and the ADC (-ve) group (n = 18) received a saline injection. Shoulders were harvested at 10, 14, and 18 weeks and underwent histological, fluorescent, and biomechanical analyses.

RESULTS

In the ADC (+ve) group, a firm enthesis, including dense mature fibrocartilage and well-aligned cells, were observed in the bone-tendon junction and fatty infiltration was less than in the ADC (-ve) group. Mean maximum stress and linear stiffness was greater in the ADC (+ve) compared with the ADC (-ve) group at 18 weeks.

CONCLUSION

ADC supplementation showed a positive effect on tendon-bone healing in a rat model of chronic RCT with accompanying SN injury. Therefore, ADC injection may possibly accelerate recovery in massive RCT injuries.

Dual Growth Factor Delivery Using Photo-Cross-Linkable Gelatin Hydrogels for Effectively Reinforced Regeneration of the Rotator Cuff Tendon

Rotator cuff tears are currently treated with drugs (steroids and nonsteroidal anti-inflammatory drugs) and surgery. However, the damaged rotator cuff requires a considerable amount of time to regenerate, and the regenerated tissue cannot restore the same level of function as that before the damage. Although growth factors can accelerate regeneration, they are difficult to be used alone because of the risk of degradation and the difficulties in ensuring their sustained release. Thus, hydrogels such as gelatin are used, together with growth factors. Gelatin is a biocompatible and biodegradable hydrogel derived from collagen; therefore, it closely resembles the components of native tissues and can retain water and release drugs continuously, while also showing easily tunable mechanical properties by simple modifications. Moreover, gelatin is a natural biopolymer that possesses the ability to form hydrogels of varying compositions, thereby facilitating effective cross-linking. Therefore, gelatin can be considered to be suitable for rotator-to-tendon healing. In this study, we designed photo-cross-linkable gelatin hydrogels to enhance spacing and adhesive effects for rotator cuff repair. We mixed a ruthenium complex (Ru(II)bpy32+) and sodium persulfate into gelatin-based hydrogels and exposed them to blue light to induce gelation. Basic fibroblast growth factor and bone morphogenetic protein-12 were encapsulated in the gelatin hydrogel for localized and sustained release into the wound, thereby enhancing the cell proliferation. The effects of these dual growth factor-loaded hydrogels on cell cytotoxicity and tendon regeneration in rotator cuff tear models were evaluated using mechanical and histological assessments. The findings confirmed that the gelatin hydrogel was biocompatible and that treatment with the dual growth factor-loaded hydrogels in in vivo rotator cuff tear models promoted regeneration and functional restoration in comparison with the findings in the nontreated group. Therefore, growth factor-loaded gelatin-based hydrogels may be suitable for the treatment of rotator cuff tears.

Efficacy of transplantation of lipoaspired mesenchymal stem cells in the treatment of chronic rotator cuff tears. Experimental model in rats

BACKGROUND AND AIM

Rotator cuff tears emerge in approximately 30% of the population over 60 years of age. Arthroscopic surgical treatment of these lesions is the treatment of choice, however, despite the improved repair techniques, the rate of re-tears ranges between 11 and 94%. Therefore, researchers seek to improve the biological healing process through the use of different alternatives such as mesenchymal stem cells (MSCs). Our objective is to evaluate the efficacy of a Cellular Therapy Drug made from allogeneic stem cells derived from adipose tissue in a rat model of chronic rotator cuff injury.

MATERIAL AND METHODS

The supraspinatus lesion was created in 48 rats for subsequent suturing at 4 weeks. MSCs in suspension were added to 24 animals after suturing, and HypoThermosol-FRS® (HTS) to 24 animals as a control group. Histology (Åström and Rausing scale) and the maximum load, displacement and elastic constant of the supraspinatus tendon were analyzed in both groups 4 months after the repair.

RESULTS

No statistically significant differences were found in the histological score comparing the tendons treated with MSCs with respect to the tendons treated with HTS (P=.811) nor in the results of maximum load (P=.770), displacement (P=.852) or elastic constant (P=.669) of the tendon in both groups.

CONCLUSIONS

The addition of adipose-derived cells in suspension to the repair of a chronic cuff injury does not improve the histology or biomechanics of the sutured tendon.

[Translated article] Efficacy of transplantation of lipoaspired mesenchymal stem cells in the treatment of chronic rotator cuff tears. Experimental model in rats

BACKGROUND AND AIM

Rotator cuff tears emerge in approximately 30% of the population over 60 years of age. Arthroscopic surgical treatment of these lesions is the treatment of choice, however, despite the improved repair techniques, the rate of re-tears ranges between 11 and 94%. Therefore, researchers seek to improve the biological healing process through the use of different alternatives such as mesenchymal stem cells (MSCs). Our objective is to evaluate the efficacy of a cellular therapy drug made from allogeneic stem cells derived from adipose tissue in a rat model of chronic rotator cuff injury.

MATERIAL AND METHODS

The supraspinatus lesion was created in 48 rats for subsequent suturing at 4 weeks. MSCs in suspension were added to 24 animals after suturing, and HypoThermosol-FRS® (HTS) to 24 animals as a control group. Histology (Åström and Rausing scale) and the maximum load, displacement and elastic constant of the supraspinatus tendon were analysed in both groups 4 months after the repair.

RESULTS

No statistically significant differences were found in the histological score comparing the tendons treated with MSCs with respect to the tendons treated with HTS (P=0.811) nor in the results of maximum load (P=0.770), displacement (P=0.852) or elastic constant (P=0.669) of the tendon in both groups.

CONCLUSIONS

The addition of adipose-derived cells in suspension to the repair of a chronic cuff injury does not improve the histology or biomechanics of the sutured tendon.

Rotator Cuff Augmentation: Its Role and Best Practices

Rotator cuff tears are a common source of pain and impairment in the shoulder. Healing of the rotator cuff tendons following repair has been associated with improved patient outcomes. While there have been many technical improvements in surgical techniques for rotator cuff repair, failure rates are still surprisingly high. Augmentation of these repairs has been shown to help with fixation biomechanics as well as healing rates. The described types of augments include autograft, allograft, xenograft, and synthetic options. This report reviews the commonly available types of augments and some of the outcomes associated with their use.

The Effect of Pulling Angle on Rotator Cuff Mechanical Properties in a Canine In Vitro Model

The objective of this study was to examine the effect of pulling angle on time-zero mechanical properties of intact infraspinatus tendon or infraspinatus tendon repaired with the modified Mason-Allen technique in a canine model in vitro. Thirty-six canine shoulder samples were used. Twenty intact samples were randomly allocated into functional pull (135°) and anatomic pull (70°) groups (n = 10 per group). The remaining sixteen infraspinatus tendons were transected from the insertion and repaired using the modified Mason-Allen technique before being randomly allocated into functional pull or anatomic pull groups (n = 8 per group). Load to failure testing was performed on all specimens. The ultimate failure load and ultimate stress of the functional pulled intact tendons were significantly lower compared with anatomic pulled tendons (1310.2 ± 167.6 N vs. 1687.4 ± 228.2 N, p = 0.0005: 55.6 ± 8.4 MPa vs. 67.1 ± 13.3 MPa, p = 0.0334). For the tendons repaired with the modified Mason-Allen technique, no significant differences were observed in ultimate failure load, ultimate stress or stiffness between functional pull and anatomic pull groups. The variance of pulling angle had a significant influence on the biomechanical properties of the rotator cuff tendon in a canine shoulder model in vitro. Load to failure of the intact infraspinatus tendon was lower at the functional pulling position compared to the anatomic pulling position. This result indicates that uneven load distribution across tendon fibers under functional pull may predispose the tendon to tear. However, this mechanical character is not presented after rotator cuff repair using the modified Mason-Allen technique.

Evidence for Utilization of Injectable Biologic Augmentation in Primary Rotator Cuff Repair: A Systematic Review of Data From 2010 to 2022

Background

Biologic healing after rotator cuff repair remains a significant challenge. Injectable biologic augmentation may improve tissue quality at the suture-tendon interface.

Purpose

To investigate the effect of injectable biologic supplementation in rotator cuff repair and to assess the quality and adherence to evolving reporting standards.

Study Design

Systematic review; Level of evidence, 3.

Methods

A systematic review was conducted following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Included were 40 studies: 29 preclinical (in vivo animal models) and 11 clinical. Each clinical study was assessed for quality, risk of bias, and adherence to relevant MIBO (Minimum Information for Studies Evaluating Biologics in Orthopaedics) guidelines. The outcomes of interest were reported load to failure, load to gap, gap size, and stiffness in the preclinical studies, and healing rate and any patient-reported outcome measures in the clinical studies.

Results

Injectables reported included growth factors (eg, transforming growth factor-beta 3, erythropoietin), bone marrow-derived mesenchymal stem cells and adipose-derived mesenchymal stem cells (ADSCs), and other agents such as platelet-rich plasma (PRP) and hyaluronic acid. The most common findings for preclinical injectables were increased load to failure (16/29 studies; 55.2%) and improved collagen histological quality (11/29 studies; 37.9%). All 11 clinical studies (10 PRP, 1 ADSC) indicated no adverse events, with similar or improved patient-reported outcomes compared with repairs in the control groups. In 1 study utilizing an innovative delivery technique, a concentrated PRP globule with fibrin matrix was shuttled over a suture to maintain concentrated PRP at the repair site and demonstrated a significant decrease in retears (P = .03) at a 31-month follow-up. A matched-cohort study investigating augmentation with ADSCs demonstrated a significantly lower retear rate in the ADSC-augmented group than the control group at a 28-month follow-up (P < .001). On average, the clinical studies adhered to 66% of relevant MIBO reporting guidelines and had a low risk of bias.

Conclusion

Approximately 83% of preclinical studies found a positive biomechanical or histological effect, with no studies showing an overall negative effect. Clinically, utilization of innovative delivery techniques may reduce the risk of arthroscopic washout of PRP and improve retear rates. ADSCs were shown to reduce retear rates at a 28-month follow-up.

Therapeutic potential and mechanisms of mesenchymal stem cell-derived exosomes as bioactive materials in tendon-bone healing

Tendon-bone insertion (TBI) injuries, such as anterior cruciate ligament injury and rotator cuff injury, are the most common soft tissue injuries. In most situations, surgical tendon/ligament reconstruction is necessary for treating such injuries. However, a significant number of cases failed because healing of the enthesis occurs through scar tissue formation rather than the regeneration of transitional tissue. In recent years, the therapeutic potential of mesenchymal stem cells (MSCs) has been well documented in animal and clinical studies, such as chronic paraplegia, non-ischemic heart failure, and osteoarthritis of the knee. MSCs are multipotent stem cells, which have self-renewability and the ability to differentiate into a wide variety of cells such as chondrocytes, osteoblasts, and adipocytes. Numerous studies have suggested that MSCs could promote angiogenesis and cell proliferation, reduce inflammation, and produce a large number of bioactive molecules involved in the repair. These effects are likely mediated by the paracrine mechanisms of MSCs, particularly through the release of exosomes. Exosomes, nano-sized extracellular vesicles (EVs) with a lipid bilayer and a membrane structure, are naturally released by various cell types. They play an essential role in intercellular communication by transferring bioactive lipids, proteins, and nucleic acids, such as mRNAs and miRNAs, between cells to influence the physiological and pathological processes of recipient cells. Exosomes have been shown to facilitate tissue repair and regeneration. Herein, we discuss the prospective applications of MSC-derived exosomes in TBI injuries. We also review the roles of MSC-EVs and the underlying mechanisms of their effects on promoting tendon-bone healing. At last, we discuss the present challenges and future research directions.

Milk-derived small extracellular vesicles: nanomaterials to promote bone formation

Small extracellular vesicles (sEVs) are an important component in the paracrine pathway. They can be used as a substitute for seed cells and have shown good application prospects in promoting bone regeneration. Cow’s milk could be used as a source of sEVs with good biocompatibility and cost-effectiveness, with easy availability, low cost and low toxicity. This study focused on the role and mechanism of small extracellular vesicles derived from milk in bone repair. In order to explore the mechanism via which Milk-sEVs promote bone repair, we screened the differential gene GJA1 in Milk-sEV-treated osteoblasts through transcriptome chips, and verified the transcript AP3B1 of GJA1 through chromatin immunoprecipitation (CHIP). We have proved by in vivo and in vitro experiments that milk-derived sEVs (Milk-sEVs) increase the repair ability of bone tissue, and promote expression of the osteogenic gene GJA1 through the transcript AP3B1.

Hydrogel Development for Rotator Cuff Repair

Rotator cuff tears (RCTs) are common in shoulder disease and disability. Despite significant advances in surgical repair techniques, 20–70% of patients still have postoperative rotator cuff dysfunction. These functional defects may be related to retear or rotator cuff quality deterioration due to tendon retraction and scar tissue at the repair site. As an effective delivery system, hydrogel scaffolds may improve the healing of RCTs and be a useful treatment for irreparable rotator cuff injuries. Although many studies have tested this hypothesis, most are limited to laboratory animal experiments. This review summarizes differences in hydrogel scaffold construction, active ingredients, and application methods in recent research. Efforts to determine the indications of hydrogel scaffolds (with different constructions and cargos) for various types of RCTs, as well as the effectiveness and reliability of application methods and devices, are also discussed.

Advances in Stem Cell Therapies for Rotator Cuff Injuries

Rotator cuff injury is a common upper extremity musculoskeletal disease that may lead to persistent pain and functional impairment. Despite the clinical outcomes of the surgical procedures being satisfactory, the repair of the rotator cuff remains problematic, such as through failure of healing, adhesion formation, and fatty infiltration. Stem cells have high proliferation, strong paracrine action, and multiple differentiation potential, which promote tendon remodeling and fibrocartilage formation and increase biomechanical strength. Additionally, stem cell-derived extracellular vesicles (EVs) can increase collagen synthesis and inhibit inflammation and adhesion formation by carrying regulatory proteins and microRNAs. Therefore, stem cell-based therapy is a promising therapeutic strategy that has great potential for rotator cuff healing. In this review, we summarize the advances of stem cells and stem cell-derived EVs in rotator cuff repair and highlight the underlying mechanism of stem cells and stem cell-derived EVs and biomaterial delivery systems. Future studies need to explore stem cell therapy in combination with cellular factors, gene therapy, and novel biomaterial delivery systems.

Injection of adipose stem cells in the treatment of rotator cuff disease - a narrative review of current evidence

The purpose of this study is to summarize evidence for the use of adipose stem cell (ASC) injections in the treatment of rotator cuff tears (RCT) and identify future areas of study. A thorough literature search was performed to identify studies investigating the use of ASC injections in the treatment of RCTs. Among animal trials, it is unclear whether ASCs are of benefit for rotator cuff repair. In clinical trials, ASC injection may reduce retear rate with otherwise equivocal clinical outcomes. Although ASC injection may be safe, the literature does not provide a clear consensus as to the efficacy of ASC injections, nor does it delineate which patients would benefit most from this treatment.

Evaluation of patches for rotator cuff repair: A systematic review and meta-analysis based on animal studies

Based on the published animal studies, we systematically evaluated the outcomes of various materials for rotator cuff repair in animal models and the potentials of their clinical translation. 74 animal studies were finally included, of which naturally derived biomaterials were applied the most widely (50.0%), rats were the most commonly used animal model (47.0%), and autologous tissue demonstrated the best outcomes in all animal models. The biomechanical properties of naturally derived biomaterials (maximum failure load: WMD 18.68 [95%CI 7.71-29.66]; P = 0.001, and stiffness: WMD 1.30 [95%CI 0.01-2.60]; P = 0.048) was statistically significant in the rabbit model. The rabbit model showed better outcomes even though the injury was severer compared with the rat model.

Translational therapy from preclinical animal models for muscle degeneration after rotator cuff injury

Chronic rotator cuff tears are debilitating diseases which significantly affect patients’ quality of life and pose substantial financial burden to the society. The intraoperative reparability of injured tendon and postoperative probability of tendon retear are highly associated with the quality of torn muscles, specifically, the severity of muscle atrophy and fatty infiltration. Animal models that reproduce the characteristic muscle pathology after rotator cuff injury have been developed and used to provide insight into the underlying biology and pathophysiology. In this review, we briefly summarize the current information obtained from preclinical animal studies regarding the degenerative change of cuff muscle subsequent to tendon release and/or suprascapular nerve denervation. Importantly, we focus on the potential translational therapeutic targets or agents for the prevention or reversal of muscle atrophy and fatty infiltration. While further studies are warranted to assess the safety and efficacy of novel therapies derived from these preclinical animal research, we believe that their clinical translation for the treatment of rotator cuff disorders is on the horizon.

The Translational potential of this article

Novel therapeutic strategies described in this review from preclinical animal studies hold a great translational potential for preventing or reversing rotator cuff muscle pathology, while further assessments on their safety and efficacy are warranted.

Augmentation of Rotator Cuff Healing With Orthobiologics

The limited regenerative capacity of the tendon-bone enthesis after surgical repair poses a significant challenge to achieving desired clinical outcomes. Biologic augmentation of the repair site has the potential to enhance the biomechanical and histological integrity of the enthesis, leading to lower retear rates and greater patient satisfaction. Platelet-rich plasma, stem cells and bone marrow aspirate concentrate, growth factors, biodegradable or biomimetic scaffolds, and amniotic products have been investigated in preclinical and, in some cases, clinical studies aimed at augmenting tendon-bone healing. Although many of these therapies have achieved some degree of success in improving structural, histological, and clinical outcomes after surgical tendon-bone enthesis repair, none have reliably and consistently lead to clinical improvement. High-quality randomized controlled clinical studies are needed to definitively evaluate the efficacy of these biologic therapies and ultimately determine which, if any, are capable of achieving a tendon-bone repair that is structurally noninferior to the native enthesis before 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.

Common animal models lack a distinct glenoid labrum: a comparative anatomy study

Purpose

Development and validation of an animal model of labral healing would facilitate translation of novel surgical and biological strategies to improve glenolabral healing. The purpose of this study was to characterize the anatomic and histological properties of the shoulder labrum in rat, rabbit, dog, pig, goat, and humans. Given the demonstrated similarities in size and structural morphology in other joints, it was hypothesized that the goat glenoid with surrounding capsulolabral complex would most closely resemble that of humans in terms of dimensions and structure, as observed grossly and histologically.

Methods

Cadaveric glenohumeral joints from rats (n = 8), New Zealand white rabbits (n = 13), Mongrel dogs (n = 9), Spanish goats (n = 10), Yorkshire pigs (n = 10), and humans (n = 9) were freshly harvested. Photographs were taken of the glenoid with its surrounding capsulolabral complex. Linear dimensions of the glenoid articular surface were measured. It was determined where the capsulolabral complex was continuous with, or recessed from, the articular glenoid surface. The glenoid was divided into 6 equal segments radiating out toward 12, 2, 4, 6, 8, and 10 o’clock positions. Samples were sectioned and stained with Safranin O/Fast green and Mallory Trichrome. Insertion of the capsulolabral tissue onto the glenoid was qualitatively assessed and compared with gross morphology.

Results

Dimensions of the goat glenoid most closely paralleled dimensions of the human glenoid. A capsulolabral complex was continuous with the glenoid surface from ~ 9 to 12 o’clock in the rats, 7 to 12 o’clock in rabbits, 5 to 12 o’clock in the dogs, and 9 to 12 o’clock in goats, 6 to 12 o’clock in pigs, and 2 to 8 o’clock in humans. In contrast to humans, no other species demonstrated an organized fibrocartilaginous labrum either macroscopically or histologically.

Conclusion

The animals in the present study did not possess a discrete fibrocartilaginous labrum by gross or histological evaluation, as directly compared to humans. While models using these animals may be acceptable for examining other shoulder pathologies, they are not adequate to evaluate labral pathology.

Level of evidence

Basic Science Study; Anatomy and Histology; Cadaveric Animal Model.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-021-00383-6.

Stem cell therapies in tendon-bone healing

Tendon-bone insertion injuries such as rotator cuff and anterior cruciate ligament injuries are currently highly common and severe. The key method of treating this kind of injury is the reconstruction operation. The success of this reconstructive process depends on the ability of the graft to incorporate into the bone. Recently, there has been substantial discussion about how to enhance the integration of tendon and bone through biological methods. Stem cells like bone marrow mesenchymal stem cells (MSCs), tendon stem/progenitor cells, synovium-derived MSCs, adipose-derived stem cells, or periosteum-derived periosteal stem cells can self-regenerate and potentially differentiate into different cell types, which have been widely used in tissue repair and regeneration. Thus, we concentrate in this review on the current circumstances of tendon-bone healing using stem cell therapy.

Engineering multi-tissue units for regenerative Medicine: Bone-tendon-muscle units of the rotator cuff

Our body systems are comprised of numerous multi-tissue units. For the musculoskeletal system, one of the predominant functional units is comprised of bone, tendon/ligament, and muscle tissues working in tandem to facilitate locomotion. To successfully treat musculoskeletal injuries and diseases, critical consideration and thoughtful integration of clinical, biological, and engineering aspects are necessary to achieve translational bench-to-bedside research. In particular, identifying ideal biomaterial design specifications, understanding prior and recent tissue engineering advances, and judicious application of biomaterial and fabrication technologies will be crucial for addressing current clinical challenges in engineering multi-tissue units. Using rotator cuff tears as an example, insights relevant for engineering a bone-tendon-muscle multi-tissue unit are presented. This review highlights the tissue engineering strategies for musculoskeletal repair and regeneration with implications for other bone-tendon-muscle units, their derivatives, and analogous non-musculoskeletal tissue structures.

Fibrin Glue-Kartogenin Complex Promotes the Regeneration of the Tendon-Bone Interface in Rotator Cuff Injury

Objective

Rotator cuff injury healing is problematic because the tendon-bone junction often forms cicatricial tissues, rather than fibrocartilage, which leads to mechanical impairment and is prone to redamage. Kartogenin (KGN) is a newly discovered small molecule compound which can induce cartilage formation through chondrogenesis of endogenous mesenchymal stem cells.

Methods

In this study, we used KGN with fibrin glue (FG) to repair the rotator cuff injury by promoting the formation of fibrocartilage at the tendon to bone interface. Firstly, we assessed the release rate of KGN from the FG-KGN complex and then created a rabbit rotator cuff tendon graft-bone tunnel model. The rabbits received saline, FG-KGN, or FG injections onto the tendon to bone interface after injury. Shoulder tissues were harvested at 6 and 12 weeks, and the sections were stained with HE and Safranin O/Fast green. The samples were assessed by histologic evaluation and biomechanical testing. Synovial mesenchymal stem cells derived from the synovial tissue around the rotator cuff were harvested for western blotting and qRT-PCR analysis.

Results

KGN was released rapidly from the FG-KGN complex during first 4 hrs and followed by a slow release until 7 days. The tendon graft-bone interface in the control (saline) group and the FG group was filled with scar tissue, rather than cartilage-like tissue, and only a small number of chondrocytes were found at the adjacent bone surface. In the FG-KGN group, the tendon to bone interface was fully integrated and populated by chondrocytes with proteoglycan deposition, indicating the formation of fibrocartilage-like tissues. At 12 weeks, the maximum tensile strength of the FG-KGN group was significantly higher than that of the FG and control groups (P < 0.01). The RNA expression levels of tendinous genes such as Tenascin C and the chondrogenic gene Sox-9 were substantially elevated in SMSCs treated with the FG-KGN complex compared to the other two groups.

Conclusion

These results indicated that fibrin glue is an effective carrier for KGN, allowing for the sustained release of KGN. The FG-KGN complex could effectively promote the regeneration and formation of fibrocartilage tissue of the tendon-bone interface in the rabbit rotator cuff tendon graft-bone tunnel model.

Editorial Commentary: Mesenchymal Stem Cell Preparation Methods Affect the Properties of Shoulder Subacromial Bursa-Derived Cells

Augmentation of mesenchymal stem cells (MSCs) from the subacromial bursa in the setting of irreparable rotator cuff tears is a powerful candidate for future regenerative medicine. However, little is known about whether the preparation technique affects the individual differences and potentials of subacromial bursa-derived MSCs. The yields obtained by chopping or cell-expansion techniques with a high-density of initial nucleated cells seem to be lower than those obtained with low-density cell-expansion techniques. Differences in cell-preparation methods may affect whether individual differences in their properties exist. Further studies are required using a low-density cell-expansion technique to establish a new regenerative treatment using subacromial bursa-derived MSCs for irreparable rotator cuff tears.

Engineered Cell Sheets for the Effective Delivery of Adipose-Derived Stem Cells for Tendon-to-Bone Healing

BACKGROUND

Efforts are being made to treat rotator cuff tears (RCTs) that exhibit poor healing and high retear rates. Tendon-to-bone healing using mesenchymal stem cells is being explored, but research is needed to establish effective delivery options.

PURPOSE

To evaluate the effects of an adipose-derived stem cell (ADSC) sheet on mesenchymal stem cell delivery for tendon-to-bone healing of a chronic RCT in rats and to demonstrate that ADSC sheets enhance tendon-to-bone healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Mesenchymal stem cells were obtained from rat adipose tissue, and a cell sheet was prepared using a temperature-responsive dish. To evaluate the efficacy of stem cells produced in a sheet for the lesion, the experiment was conducted with 3 groups: repair group, cell sheet transplantation after repair group, and cell sheet-only group. Histological, biomechanical, and micro-computed tomography (micro-CT) results were compared among the groups.

RESULTS

Hematoxylin and eosin staining for histomorphological analysis revealed that the cell sheet transplantation after repair group (5.75 ± 0.95) showed statistically significant higher scores than the repair (2.75 ± 0.50) and cell sheet-only (3.25 ± 0.50) groups (P < .001). On safranin O staining, the cell sheet transplantation after repair group (0.51 ± 0.04 mm²) had a larger fibrocartilage area than the repair (0.31 ± 0.06 mm²) and cell sheet-only (0.32 ± 0.03 mm²) groups (P = .001). On micro-CT, bone volume/total volume values were significantly higher in the cell sheet transplantation after repair group (23.98% ± 1.75%) than in the other groups (P < .039); there was no significant difference in the other values. On the biomechanical test, the cell sheet transplantation after repair group (4 weeks after repair) showed significantly higher results than the other groups (P < .005).

CONCLUSION

Our study shows that engineered stem cells are a clinically feasible stem cell delivery tool for rotator cuff repair.

CLINICAL RELEVANCE

This laboratory study provides evidence that ADSCs are effective in repairing RCTs, which are common sports injuries.

Injectable hydrogels for tendon and ligament tissue engineering

The problem of tendon and ligament (T/L) regeneration in musculoskeletal diseases has long constituted a major challenge. In situ injection of formable biodegradable hydrogels, however, has been demonstrated to treat T/L injury and reduce patient suffering in a minimally invasive manner. An injectable hydrogel is more suitable than other biological materials due to the special physiological structure of T/L. Most other materials utilized to repair T/L are cell-based, growth factor-based materials, with few material properties. In addition, the mechanical property of the gel cannot reach the normal T/L level. This review summarizes advances in natural and synthetic polymeric injectable hydrogels for tissue engineering in T/L and presents prospects for injectable and biodegradable hydrogels for its treatment. In future T/L applications, it is necessary develop an injectable hydrogel with mechanics, tissue damage-specific binding, and disease response. Simultaneously, the advantages of various biological materials must be combined in order to achieve personalized precision therapy.

In Vitro Cultures of Adipose-Derived Stem Cells: An Overview of Methods, Molecular Analyses, and Clinical Applications

Adipose-derived stem cells (ASCs) exhibiting mesenchymal stem cell (MSC) characteristics, have been extensively studied in recent years. Because they have been shown to differentiate into lineages such as osteogenic, chondrogenic, neurogenic or myogenic, the focus of most of the current research concerns either their potential to replace bone marrow as a readily available and abundant source of MSCs, or to employ them in regenerative and reconstructive medicine. There is close to consensus regarding the methodology used for ASC isolation and culture, whereas a number of molecular analyses implicates them in potential therapies of a number of pathologies. When it comes to clinical application, there is a range of examples of animal trials and clinical studies employing ASCs, further emphasizing the advancement of studies leading to their more widespread use. Nevertheless, in vitro studies will most likely continue to play a significant role in ASC studies, both providing the molecular knowledge of their ex vivo properties and possibly serving as an important step in purification and application of those cells in a clinical setting. Therefore, it is important to consider current methods of ASC isolation, culture, and processing. Furthermore, molecular analyses and cell surface properties of ASCs are essential for animal studies, clinical studies, and therapeutic applications of the MSC properties.

The role of adipose derived stem cells in the treatment of rotator cuff tears: from basic science to clinical application

Over the last decade, regenerative medicine has become increasingly popular throughout the scientific community. The poor healing capacity at the tendon-bone interface makes the rotator cuff an appealing target for biologic agents. Adipose derived stem cells are mesenchymal cells with the capacity for self-renewal and multipotential differentiation. They have been recently proposed, both in isolation and as adjuvants to existing surgical therapies, for the treatment of rotator cuff tears. Several studies have been carried out in this research field, starting from the biological characteristics of adipose derived stem cells, their preparation and culture, up to the application in the experimental field on animal models and on humans. The purpose of this study was to provide a state of the art about the current basic science and clinical literature for the effectiveness of adipose derived stem cells in the treatment of rotator cuff tears.

Tendon regeneration induced by umbilical cord graft in a rabbit tendon defect model

Whether tendon regeneration can be induced using the umbilical cord as a whole-graft structure is unknown. In this study, we explored the potential for tendon regeneration induction using an umbilical cord graft in a rabbit model of patella tendon defects. In 52 of 54 New Zealand White rabbits, the central third of the patella tendons of both hind legs was removed to create tendon defects. The rabbits were randomly divided into four groups, nonfilling (empty defect), refilling (defect refilled with resected tendon portion), Wharton's jelly (WJ) outside (WJO; defect filled with umbilical cord graft, WJ side facing outward), and WJ inside (WJI; same as WJO with WJ side facing inward) groups. Four rabbits from WJO and WJI groups were sacrificed for human CD 105 evaluation 1 month after surgery. Further histological, biomechanical, and gene expression analyses were performed at 3 and 6 months after surgery. The untreated patella tendons in the remaining two rabbits were harvested as normal biomechanical controls. Histological evaluation showed that the formed tissue structure fibers in the tendon defect area were much denser and more mature in the WJI group than in all other groups. Biomechanical testing showed that the failure load of the final tissue structure was the highest in the WJI group. Real-time polymerase chain reaction indicated that the expression of most tendon-related genes was upregulated in the WJI group at 6 months after surgery. We concluded that umbilical cord grafting induces effective tendon regeneration, particularly when the WJ side faces inward.

Microcurrent and adipose-derived stem cells modulate genes expression involved in the structural recovery of transected tendon of rats

Tendon injuries are common and have a high incidence of re-rupture that can cause loss of functionality. Therapies with adipose-derived stem cells (ASC) and the microcurrent (low-intensity electrical stimulation) application present promising effects on the tissue repair. We analyzed the expression of genes and the participation of some molecules potentially involved in the structural recovery of the Achilles tendon of rats, in response to the application of both therapies, isolated and combined. The tendons were distributed in five groups: normal (N), transected (T), transected and ASC (C) or microcurrent (M) or with ASC, and microcurrent (MC). Microcurrent therapy was beneficial for tendon repair, as it was observed a statistically significant increase in the organization of the collagen fibers, with involvement of the TNC, CTGF, FN, FMDO, and COL3A1 genes as well as PCNA, IL-10, and TNF-α. ASC therapy significantly increased the TNC and FMDO genes expression with no changes in the molecular organization of collagen. With the association of therapies, a significant greater collagen fibers organization was observed with involvement of the FMOD gene. The therapies did not affect the expression of COL1A1, SMAD2, SMAD3, MKX, and EGR1 genes, nor did they influence the amount of collagen I and III, caspase-3, tenomodulin (Tnmd), and hydroxyproline. In conclusion, the application of the microcurrent isolated or associated with ASC increased the organization of the collagen fibers, which can result in a greater biomechanical resistance in relation to the tendons treated only with ASC. Future studies will be needed to demonstrate the biological effects of these therapies on the functional recovery of injured tendons.

Mesenchymal stem cells and their application to rotator cuff pathology: A meta-analysis of pre-clinical studies

Background

Rotator cuff injury (RCI) is a leading cause of morbidity in orthopaedics. Advances in regenerative medicine have led to the novel pleiotropic effects of mesenchymal stromal cells (MSCs) as therapeutic agents for RCI.

Objective

Conduct a systematic evaluation of available preclinical studies to quantify the effects of MSCs on RCI.

Methods

A literature search was performed in PubMed, Scopus, Cochrane, CINAHL, and Google Scholar. At least two independent investigators screened animal studies assessing the therapeutic effects of MSCs on: (i) biomechanical testing, imaging, and/or range-of-motion (primary outcome), and (ii) histologic analyses of wound healing, gene/protein expression of regenerative factors, and safety/long-term outcomes (secondary outcome). Meta-analysis data is reported as standardized mean difference (SMD) with 95% confidence interval (CI).

Results

A total of 858 titles and abstracts were screened; 18 studies (n=576) met inclusion criteria. MSC therapy improved ultimate load failure [SMD -0.43 (95% CI -0.65, -0.22), p<0.0001; 15 studies, 28 comparisons], site stiffness [SMD -0.29 (95% CI -0.55, -0.04), p<0.05; 9 studies, 17 comparisons], bone mineral density [SMD -0.77 (95% CI -1.16, -0.38), p<0.0001; 2 studies, 6 comparisons], and stimulated fibrocartilage formation [SMD of -1.37 (95% CI -1.99, -0.74), p<0.0001; 4 studies, 7 comparisons]. Heterogeneity between studies was high and risk of bias was unclear.

Conclusion

Administration of MSCs in preclinical models recapitulating RCI improved aspects of shoulder biomechanics, imaging, and collagen formation. Although these findings are promising, future studies should attempt to limit the risk of bias and focus on optimizing MSCs by standardizing methodologies.

Intratendinous Injection of Mesenchymal Stem Cells for the Treatment of Rotator Cuff Disease: A 2-Year Follow-Up Study

PURPOSE

To assess the mid-term safety and efficacy of an intratendinous injection of autologous adipose tissue-derived mesenchymal stem cells (AD MSCs) for rotator cuff disease at 2-year follow-up.

METHODS

The first part of the study consisted of 3 dose-escalation groups, with 3 patients each, for the evaluation of safety: low-dose (1.0 × 10⁷ cells), mid-dose (5.0 × 10⁷), and high-dose (1.0 × 10⁸) groups. For the second part, we planned to include 9 patients receiving the high dose for the evaluation of exploratory efficacy. Clinical outcomes were assessed according to pain, range of motion, muscle strength, functional scores, overall satisfaction and function, and presence of failure. Structural outcomes included changes in volume of tendon defects measured using magnetic resonance imaging.

RESULTS

This study enrolled 19 patients (9 for the first part and 10 for the second part) with partial-thickness rotator cuff tears. There were no treatment-related adverse events at minimum 2-year follow-up. Intratendinous injection of AD MSCs reduced shoulder pain by approximately 90% at 1 and 2 years in the mid- and high-dose groups. The strength of the supraspinatus, infraspinatus, and teres minor significantly increased by greater than 50% at 2 years in the high-dose group. Shoulder function measured with 6 commonly used scores improved for up to 2 years in all dose groups. Structural outcomes evaluated with magnetic resonance imaging showed that the volume of bursal-sided defects in the high-dose group nearly disappeared at 1 year and did not recur at up to 2 years. No failures-defined as the performance of any kind of shoulder surgery or return of the Shoulder Pain and Disability Index score to the preinjection level-occurred during follow-up.

CONCLUSIONS

This study showed continued safety and efficacy of an intratendinous injection of AD MSCs for the treatment of partial-thickness rotator cuff tears over a 2-year period through regeneration of tendon defects.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Tendon and Ligament Healing and Current Approaches to Tendon and Ligament Regeneration

Ligament and tendon injuries are common problems in orthopedics. There is a need for treatments that can expedite nonoperative healing or improve the efficacy of surgical repair or reconstruction of ligaments and tendons. Successful biologically-based attempts at repair and reconstruction would require a thorough understanding of normal tendon and ligament healing. The inflammatory, proliferative, and remodeling phases, and the cells involved in tendon and ligament healing will be reviewed. Then, current research efforts focusing on biologically-based treatments of ligament and tendon injuries will be summarized, with a focus on stem cells endogenous to tendons and ligaments. Statement of clinical significance: This paper details mechanisms of ligament and tendon healing, as well as attempts to apply stem cells to ligament and tendon healing. Understanding of these topics could lead to more efficacious therapies to treat ligament and tendon injuries. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:7-12, 2020.

Editorial Commentary: Are We Ready to Apply Stem Cell Therapy in Rotator Cuff Tear Surgery?

For rotator cuff tear surgery, application of mesenchymal stem cells (MSCs) is a promising new option. Among various MSC sources, synovial tissue contains a high number of MSCs with high chondrogenic potential. Because chondrogenic formation is an important factor in enthesis healing in rotator cuff repair, synovial MSCs derived from the subacromial bursa are superior candidates for the augmentation of rotator cuff tear surgery.

Cell Therapy-a Basic Science Primer for the Sports Medicine Clinician

PURPOSE OF REVIEW

The emergence of cell-based therapies has brought much excitement to the field of orthopedic sports medicine. However, the significant inconsistency of reporting has led to the poor understanding, misinformation, and false expectations for patients and clinicians alike. In this paper, we aim to clarify the available cell-therapy treatments and summarize some of the latest research.

RECENT FINDINGS

Although this technology is in early development, our understanding of cell biology has grown significantly over the last decade. Furthermore, it is becoming evident that tissue specificity may play a significant role in determining the effectiveness and overall clinical benefit attributed to cell therapy. Cell therapy is an emerging field with tremendous potential for clinically significant benefit. However, in its current state, clinical application of these treatments is limited by federal regulations, variability in formulation, and limited understanding of the biologic activity of various cell formulations.

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.

The role of biologic agents in the management of common shoulder pathologies: current state and future directions

The field of orthopedic surgery has seen a rapid increase in the use of various biologic agents for the treatment of common musculoskeletal injuries. Most biologic agents attempt to harness or mimic naturally occurring growth factors, cytokines, and anti-inflammatory mediators to improve tissue healing and recovery. The most commonly used biologic agents are platelet-rich plasma and cells derived from bone marrow aspirate and adipose tissue. These agents have become increasingly popular despite a relative dearth of clinical data to support their use. Much confusion exists among patients and physicians in determining the role of these agents in treating common shoulder pathologies, such as glenohumeral osteoarthritis, rotator cuff tears, and tendinopathy. This article reviews the basic science and clinical evidence for the most commonly used biologic agents in the management of common shoulder pathology.

No healing improvement after rotator cuff reconstruction augmented with an autologous periosteal flap

PURPOSE

To show descriptive clinical and magnetic resonance (MR) imaging results after an additional periosteal flap augmentation in mini-open rotator cuff reconstruction and to evaluate potential healing improvement at long-term follow-up.

METHODS

Twenty-three patients with degenerative rotator cuff tears were followed after receiving a mini-open single-row repair with a subtendinous periosteal flap augmentation. Data were collected preoperatively, after 12 months and after 11 years. Clinical examination, simple shoulder test (SST), Constant-Murley Score (CS), ultrasonography examination and 3T MR imaging were performed.

RESULTS

Out of 23 patients, 20 were available for short-term and 19 for final follow-up at a median of 11.5 years (range 10.4-13.0). Questions answered with "yes" in SST improved from baseline 5.0 (range 1.0-8.0) to short 10.5 (range 8.0-12.0) and final follow-up 12.0 (range 7.0-12.0). CS improved from 53.5 (range 25.0-66.0) to 80.8 (range 75.9-89.3) and finally to 79.8 points (range 42.3-95.4). Improvement was highly significant (p < 0.05). Severe retears were found in 9/19 patients. Ossifications along the refixed tendon were noticed in 8/19 cases. Ossifications did not correlate with clinical outcome. At final follow-up, patients with retears seemed likely to have lower strength values in CS (mean ± SD) than patients without retears (7.3 ± 4.1 vs. 12.8 ± 5.3; p < 0.05).

CONCLUSION

No positive effect on improving healing response in rotator cuff refixation with a periosteal flap augmentation could be found. Retear rate is comparable to that of conventional rotator cuff refixation in the published literature. Ossifications along the tendon, without negatively affecting the clinical outcome, were seen. This invasive technique cannot be advised and should not be used anymore.

LEVEL OF EVIDENCE

IV.

Stem Cells in Rotator Cuff Injuries and Reconstructions: A Systematic Review and Meta-Analysis

BACKGROUND

Multiple studies have focused on stem cell-based treatments for rotator cuff disorders; however, the outcomes are not consistent.

OBJECTIVES

This systematic review and meta-analysis were performed to evaluate the effects of stem cells on rotator cuff healing.

METHODS

A detailed search of relevant studies was conducted in three databases including Pubmed/ Medline, Cochrane library, and Embase databases, using the following keywords: "rotator cuff" or "Tissue Engineering" AND "stem cell" from inception to January 01, 2019. The standard mean difference (SMD) and 95% confidence interval (CI) for each individual study were extracted from the original studies or calculated based on relevant data and pooled to obtain integrated estimates using random effects modeling.

RESULTS

A total of 22 studies were identified. The results demonstrated that the ultimate strain in the stem cell group was significantly higher than that in the control group at 4 and 8 weeks. Muscle weight in the stem cell group was higher than the control group at 8 weeks, while no significant differences were detected at 16 weeks. The stem cell group had lower visual analog scale scores (VAS) at 1, 3, and 6 months, and higher American shoulder and elbow surgeons score (ASES) at 3 months. In addition, the walking distance, time, and speed in the stem cell group were significantly superior to those in the control group.

CONCLUSIONS

This meta-analysis confirms that stem cells improved the rehabilitation of rotator cuff disorders. However, larger-scale studies are needed to further support these findings.