Advances in biologic augmentation for rotator cuff repair

Procyanidin-crosslinked gradient silk fibroin composite nanofiber scaffold with sandwich structure for rotator cuff repair

Improving the regeneration of the tendon-bone interface (TBI) helps to decrease the risk of rotator cuff retears after repair surgeries. Unfortunately, the lack of inherent healing capacity of the TBI, insufficient mechanical properties, and abnormal and persistent inflammation during repair are the key factors leading to suboptimal healing of the rotator cuff. Therefore, a high-strength rotator cuff repair material capable of regulating the unbalanced immune response and enhancing the regeneration of the TBI is urgently needed. In this study, a novel sandwiched silk fibroin composite nanofiber scaffold with a biomimetic gradient structure was prepared through layer-by-layer continuous electrospinning, and then procyanidin was utilized to further enhance the mechanical properties and biological activities of the scaffold. The physicochemical characterization revealed that the procyanidin-crosslinked sandwiched gradient scaffold (GMPC) possessed an appropriate porosity and pore size and superior mechanical properties. Cytocompatibility assessment and immunofluorescence staining indicated that GMPC allowed rapid adhesion, proliferation, and infiltration of osteoblasts. ELISA and macrophage polarization experiments further confirmed that GMPC could effectively inhibit excessive inflammation in injured tissues and regulate the polarization of macrophages to the beneficial phenotype. Therefore, the procyanidin-crosslinked sandwiched gradient nanofiber scaffold might be a promising candidate for rotator cuff repair.

Anti-Leukotriene Receptor Blockers Improve Tendon-Bone Interface Healing in a Rat Model of Acute Rotator Cuff Tear

BACKGROUND

Excessive expression of proinflammatory cytokines after rotator cuff (RC) surgery impairs the quality of tendon-bone interface (TBI) healing. There is evidence that the asthma drug montelukast (MS) inhibits the expression of proinflammatory cytokines. This study was conducted to verify the effect of MS administration on TBI healing after RC repair.

MATERIALS AND METHODS

Thirteen rats in the MS group were intraperitoneally administered 10 mg/kg of the drug daily for 2 weeks after RC surgery, and 13 rats in the control group were administered only 0.9% saline. The healing effect of the TBI was assessed through histologic and biomechanical analysis 4 weeks after tendon repair.

RESULTS

In the MS group, the expression of interleukin-1 beta (IL-1β; P<.01) and interleukin 6 (IL-6; P<.01) was significantly reduced compared with the control group. In the evaluation of supraspinatus fatty infiltration, the MS group showed significant inhibition of fatty infiltration compared with the control group (P<.001). Histologic analysis showed that the MS group had significant improvements in collagen density (P=.035) and alignment (P=.011). Biomechanical analysis after systemic administration of MS showed an increase in the cross-sectional area (P<.001) and elongation (P<.01) of the TBI.

CONCLUSION

The use of MS improved tendon elasticity through suppressing fatty infiltration and improving TBI collagen density and arrangement. The mechanism is down-regulation of IL-1β and IL-6. These results strongly support the use of MS as an anti-inflammatory agent that does not impair tendon healing. [Orthopedics. 2025;48(2):e105-e112.].

The continuous fragility index of outcomes in rotator cuff repair augmentation randomized trials: a systematic review

BACKGROUND

Symptomatic rotator cuff tears often undergo surgical repair, which may be paired with various augmentation strategies to enhance structural healing rates. While many randomized controlled trials (RCTs) evaluate augmentation techniques, the statistical robustness of many findings in these studies is unknown. This systematic review aims to evaluate the continuous fragility index (CFI) of RCTs on augmentation techniques for rotator cuff repairs.

METHODS

MEDLINE, Embase, and CENTRAL databases were comprehensively searched from inception to September 2023 for RCTs assessing the efficacy of at least 1 augmentation strategy during rotator cuff repair. Eligible studies reported at least 1 statistically significant finding for a continuous outcome. The CFI for eligible outcomes was calculated, with median CFI presented by type of augmentation and outcome. Multivariable regression was performed to identify associations between CFI and other outcome variables.

RESULTS

Nineteen RCTs (1305 patients) were included in the final analysis. The median CFI for the 86 outcomes analyzed was 5.85 (interquartile range [IQR]: 2.3-14.4). Augmentation-specific analysis demonstrated variability in CFIs, with the most robust outcomes found in platelet-rich plasma studies (median: 10.95; IQR: 3.3-19.0) and suture-spanning augmentation studies (median: 11.90; IQR: 11.45-14.35). Outcome-specific analysis demonstrated range of motion outcomes as most robust (median: 9.85; IQR: 7.58-14.0) and strength-related outcomes as most fragile (median: 2.00; IQR: 1.0-16.3). Multivariable regression identified larger sample size as a statistically significant predictor of greater CFI. Notably, loss to follow-up exceeded the CFI in 31.4% of outcomes.

CONCLUSION

The observed median CFI of 5.85 in augmentation trials is consistent with the CFI reported in orthopedic and sports medicine literature. However, almost a third of outcomes had a loss to follow-up exceeding their CFI, risking the reversal of study findings with more robust follow-up and outcomes. Clinicians and researchers should consider fragility in addition to P values when assessing study results, especially in the context of high loss to follow-up. Future trials should report the fragility of their findings.

The Clinical Application of Gel-Based Composite Scaffolds in Rotator Cuff Repair

Rotator cuff tears are a common injury that can be treated with or without surgical intervention. Gel-based scaffolds have gained significant attention in the field of tissue engineering, particularly for applications like rotator cuff repair. Scaffolds can be biological, synthetic, or a mixture of both materials. Collagen, a primary constituent of the extracellular matrix (ECM) in musculoskeletal tissues, is one of the most widely used materials for gel-based scaffolds in rotator cuff repair, but other ECM-based and synthetic-based composite scaffolds have also been utilized. These composite scaffolds can be engineered to mimic the biomechanical and biological properties of natural tissues, supporting the healing process and promoting regeneration. Various clinical studies examined the effectiveness of these composite scaffolds with collagen, ECM and synthetic polymers and provided outstanding results with remarkable improvements in range of motion (ROM), strength, and pain. This review explores the material composition, manufacturing process and material properties of gel-based composite scaffolds as well as their clinical outcomes for the treatment of rotator cuff injuries.

Causal relationship between sarcopenia and rotator cuff tears: a Mendelian randomization study

Background

Sarcopenia and rotator cuff tears are common among elderly patients. However, the role of sarcopenia in the management of rotator cuff tears has been often overlooked. This study aimed to elucidate the effects of sarcopenia-related traits on rotator cuff tears.

Methods

Two-sample Mendelian randomization (MR) analyses based on genome-wide association study data were used to evaluate the causal relationships among appendicular lean mass (ALM), usual walking pace, low hand grip strength, and rotator cuff tears. Multivariate Mendelian randomization (MVMR) analyses were used to evaluate the direct effects of each muscle trait on the causal relationship.

Results

Univariate MR analysis showed that ALM and usual walking pace were causally related to rotator cuff tears (odds ratio (OR) = 0.895; 95% confidence interval (CI), 0.758-0.966, P<0.001 and OR = 0.458, 95% CI, 0.276-0.762, P = 0.003, respectively), and there was no evidence of causality between low hand grip strength and rotator cuff tears (OR = 1.132, 95% CI, 0.913-1.404, P = 0.26). MVMR analysis confirmed the causal effects of ALM and walking pace on rotator cuff tears (OR = 0.918, 95% CI, 0.851-0.990, P = 0.03 and OR = 0.476, 95% CI, 0.304-0.746, P = 0.001, respectively).

Conclusion

A causal genetic relationship exists between sarcopenia and rotator cuff tears. Sarcopenia-related traits including low muscle mass and physical function, increase the risk of rotator cuff tears. These findings provide new clinical insights and evidence-based medicine to optimize management of rotator cuff tears.

Structure, ingredient, and function-based biomimetic scaffolds for accelerated healing of tendon-bone interface

Background

Tendon-bone interface (TBI) repair is slow and challenging owing to its hierarchical structure, gradient composition, and complex function. In this work, enlightened by the natural characteristics of TBI microstructure and the demands of TBI regeneration, a structure, composition, and function-based scaffold was fabricated. Methods: The biomimetic scaffold was designed based on the "tissue-inducing biomaterials" theory: (1) a porous scaffold was created with poly-lactic-co-glycolic-acid, nano-hydroxyapatite and loaded with BMP2-gelatinmp to simulate the bone (BP); (2) a hydrogel was produced from sodium alginate, type I collagen, and loaded with TGF-β3 to simulate the cartilage (CP); (3) the L-poly-lactic-acid fibers were oriented to simulate the tendon (TP). The morphology of tri-layered constructs, gelation kinetics, degradation rate, release kinetics and mechanical strength of the scaffold were characterized. Then, bone marrow mesenchymal stem cells (MSCs) and tenocytes (TT-D6) were cultured on the scaffold to evaluate its gradient differentiation inductivity. A rat Achilles tendon defect model was established, and BMSCs seeded on scaffolds were implanted into the lesionsite. The tendon-bone lesionsite of calcaneus at 4w and 8w post-operation were obtained for gross observation, radiological evaluation, biomechanical and histological assessment.

Results

The hierarchical microstructures not only endowed the scaffold with gradual composition and mechanical properties for matching the regional biophysical characteristics of TBI but also exhibited gradient differentiation inductivity through providing regional microenvironment for cells. Moreover, the scaffold seeded with cells could effectively accelerate healing in rat Achilles tendon defects, attributable to its enhanced differentiation performance.

Conclusion

The hierarchical scaffolds simulating the structural, compositional, and cellular heterogeneity of natural TBI tissue performed therapeutic effects on promoting regeneration of TBI and enhancing the healing quality of Achilles tendon.

The translational potential of this article

The novel scaffold showed the great efficacy on tendon to bone healing by offering a structural and compositional microenvironment. The results meant that the hierarchical scaffold with BMSCs may have a great potential for clinical application.

Circadian Rhythm-Regulated ADSC-Derived sEVs and a Triphasic Microneedle Delivery System to Enhance Tendon-to-Bone Healing

Modulating the inflammatory microenvironment to reconstruct the fibrocartilaginous layer while promoting tendon repair is crucial for enhancing tendon-to-bone healing in rotator cuff repair (RCR), a persistent challenge in orthopedics. Small extracellular vesicles (sEVs) hold significant potential to modulate inflammation, yet the efficient production of highly bioactive sEVs remains a substantial barrier to their clinical application. Moreover, achieving minimally invasive local delivery of sEVs to the tendon-to-bone interface presents significant technical difficulties. Herein, the circadian rhythm of adipose-derived stem cells is modulated to increase the yield and enhance the inflammatory regulatory capacity of sEVs. Circadian rhythm-regulated sEVs (CR-sEVs) enhance the cyclic adenosine monophosphate signaling pathway in macrophage (Mφ) via platelet factor 4 delivery, thereby inhibiting Mφ M1 polarization. Subsequently, a triphasic microneedle (MN) scaffold with a tip, stem, and base is designed for the local delivery of CR-sEVs (CR-sEVs/MN) at the tendon-to-bone junction, incorporating tendon-derived decellularized extracellular matrix in the base to facilitate tendon repair. CR-sEVs/MN mitigates inflammation, promotes fibrocartilage regeneration, and enhances tendon healing, thereby improving biomechanical strength and shoulder joint function in a rat RCR model. Combining CR-sEVs with this triphasic microneedle delivery system presents a promising strategy for enhancing tendon-to-bone healing in clinical settings.

Similar Healing Rates of Arthroscopic Rotator Cuff Repair With and Without Bone Marrow Stimulation: A Systematic Review and Meta-analysis of Randomized Controlled Trials

BACKGROUND

Bone marrow stimulation (BMS) techniques such as microfracture, nanofracture, and the crimson duvet procedure expose the bone marrow of the proximal humerus to the rotator cuff tendon footprint. The effect of performing BMS on tendon healing is a subject of interest.

PURPOSE

To compare studies on arthroscopic rotator cuff repair with BMS versus without BMS for rotator cuff tears according to healing rates and clinical and radiological outcomes.

STUDY DESIGN

Systematic review and meta-analysis; Level of evidence, 2.

METHODS

The 2020 PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines were followed in conducting a search. Studies that compared arthroscopic rotator cuff repair with and without BMS were included if they provided postoperative patient-reported outcomes and healing rates. Dichotomous outcomes were expressed as mean differences (MDs), while continuous outcomes were expressed as odds ratio.

RESULTS

Included were 5 studies (N = 499 shoulders); 4 studies had level 1 evidence, and 1 study had level 2 evidence. The healing rate of rotator cuff repair was similar between the 2 groups (ie, with and without BMS) (odds ratio, 1.58 [95% CI, 0.63 to 4.00]; P = .33). Furthermore, there were no significant differences in the postoperative Constant score (MD, 1.41 [95% CI, -0.58 to 3.39]; P = .16), American Shoulder and Elbow Surgeons score (MD, 0.77 [95% CI, -1.43 to 2.96]; P = .49), or range of motion for forward flexion (MD, 2.45 [95% CI, -0.66 to 5.57]; P = .12) and external rotation (MD, 0.81 [95% CI, -2.35 to 3.97]; P = .62) at the final follow-up between the 2 groups.

CONCLUSION

The healing rate of rotator cuff repair was similar, regardless of whether BMS was performed or not. Additionally, there was no significant difference in postoperative patient-reported outcome scores, range of motion, and complications.

REGISTRATION

CRD42023388427 (PROSPERO).

Age-different BMSCs-derived exosomes accelerate tendon-bone interface healing in rotator cuff tears model

BACKGROUND

Rotator cuff tears (RCTs) are culprit of shoulder pain and dysfunction. Tendon-bone interface (TBI) mal-healing is an essential contributor to retear after RCTs. Consequently, present project was conducted to investigate the role of bone marrow mesenchymal stem cells (BMSCs)-derived exosomes on TBI healing.

METHOD

Young BMSCs (Y-BMSCs) and Aged BMSCs (A-BMSCs) were isolated from Young (3-month-old) and old (24-month-old) SD rats, and their-derived exosomes (A-BMSCs-exo and Y-BMSCs-exo) were identified. RCTs model was established, and A-BMSCs-exo and Y-BMSCs-exo were injected at the rotator cuff using hydrogel as a vehicle. Pathological changes of TBI were observed by HE, Sirius Red and Oil Red O staining. Western blotting and RT-qPCR were applied to assess the expression of extracellular matrix (ECM)-, tendon cell (TCs)-, osteogenic-, tendon-derived stem cell (TDSCs)- and angiogenic-associated proteins and mRNAs in TBI.

RESULT

Y-BMSCs exhibited increased activity, osteogenic and lipogenic abilities than A-BMSCs. After A-BMSCs-exo and Y-BMSCs-exo treatment, TBI displayed massive sharpey's fibers growing along the tendon longitudinally, and a collagen fiber-chondrocyte migration zone forming a typical tendon-noncalcified fibrocartilage-calcified fibrocartilage-bone structure. A-BMSCs-exo and Y-BMSCs-exo significantly upregulated the expression of collagen Col I/II/III, Aggrecan, TNMD, SCX, Runx2, OPN, CD45, Sox2, CD31 and VEGFR2 in TBI. In vitro, A-BMSCs-exo and Y-BMSCs-exo significantly enhanced the activity of TCs and TDSCs, TDSCs stemness, and reduced the osteogenic and lipogenic capacity of TDSCs. The effect of Y-BMSCs-exo was significantly stronger than that of A-BMSCs-exo.

CONCLUSION

BMSCs-derived exosomes facilitate ECM remodeling, osteogenic differentiation, angiogenesis, and stemness of TDSCs, thereby accelerating TBI healing in RCTs, with better outcomes using young individual-derived BMSCs.

A novel and efficient murine model for investigating tendon-to-bone healing

BACKGROUND

Tendon-to-bone healing is a critical challenge in sports medicine, with its cellular and molecular mechanisms yet to be explored. An efficient murine model could significantly advance our understanding of this process. However, most existing murine animal models face limitations, including a propensity for bleeding, restricted operational space, and a steep learning curve. Thus, the need for a novel and efficient murine animal model to investigate the cellular and molecular mechanisms of tendon-to-bone healing is becoming increasingly evident.

METHODS

In our study, forty-four 9-week-old male C57/BL6 mice underwent transection and reattachment of the Achilles tendon insertion to investigate tendon-to-bone healing. At 2 and 4 weeks postoperatively, mice were killed for histological, Micro-CT, biomechanical, and real-time polymerase chain reaction tests.

RESULTS

Histological staining revealed that the original tissue structure was disrupted and replaced by a fibrovascular scar. Although glycosaminoglycan deposition was present in the cartilage area, the native structure had been destroyed. Biomechanical tests showed that the failure force constituted approximately 44.2% and 77.5% of that in intact tissues, and the ultimate tensile strength increased from 2 to 4 weeks postoperatively. Micro-CT imaging demonstrated a gradual healing process in the bone tunnel from 2 to 4 weeks postoperatively. The expression levels of ACAN, SOX9, Collagen I, and MMPs were detected, with all genes being overexpressed compared to the control group and maintaining high levels at 2 and 4 weeks postoperatively.

CONCLUSIONS

Our results demonstrate that the healing process in our model is aligned with the natural healing process, suggesting the potential for creating a new, efficient, and reproducible mouse animal model to investigate the cellular and molecular mechanisms of tendon-to-bone healing.

Electroconductivity, a regenerative engineering approach to reverse rotator cuff muscle degeneration

Muscle degeneration is one the main factors that lead to the high rate of retear after a successful repair of rotator cuff (RC) tears. The current surgical practices have failed to treat patients with chronic massive rotator cuff tears (RCTs). Therefore, regenerative engineering approaches are being studied to address the challenges. Recent studies showed the promising outcomes of electroactive materials (EAMs) on the regeneration of electrically excitable tissues such as skeletal muscle. Here, we review the most important biological mechanism of RC muscle degeneration. Further, the review covers the recent studies on EAMs for muscle regeneration including RC muscle. Finally, we will discuss the future direction toward the application of EAMs for the augmentation of RCTs.

Nanofibrous scaffolds for the healing of the fibrocartilaginous enthesis: advances and prospects

With the current developmental advancements in nanotechnology, nanofibrous scaffolds are being widely used. The healing of fibrocartilaginous enthesis is a slow and complex process, and while existing treatments have a certain effect on promoting their healing, these are associated with some limitations. The nanofibrous scaffold has the advantages of easy preparation, wide source of raw materials, easy adjustment, easy modification, can mimic the natural structure and morphology of the fibrocartilaginous enthesis, and has good biocompatibility, which can compensate for existing treatments and be combined with them to promote the repair of fibrocartilaginous enthesis. The nanofibrous scaffold can promote the healing of fibrocartilaginous enthesis by controlling the morphology and ensuring controlled drug release. Hence, the use of nanofibrous scaffold with stimulative response features in the musculoskeletal system has led us to imagine its potential application in fibrocartilaginous enthesis. Therefore, the healing of fibrocartilaginous enthesis based on a nanofibrous scaffold may be a novel therapeutic approach.

The long head of the biceps tendon: a valuable tool in shoulder surgery

ANATOMY AND FUNCTION

The long head of the biceps tendon (LHBT) has different properties and characteristics that render it a valuable tool in the hands of shoulder surgeons. Its accessibility, biomechanical strength, regenerative capabilities, and biocompatibility allow it to be a valuable autologous graft for repairing and augmenting ligamentous and muscular structures in the glenohumeral joint.

SHOULDER SURGERY APPLICATIONS

Numerous applications of the LHBT have been described in the shoulder surgery literature, including augmentation of posterior-superior rotator cuff repair, augmentation of subscapularis peel repair, dynamic anterior stabilization, anterior capsule reconstruction, post-stroke stabilization, and superior capsular reconstruction. Some of these applications have been described meticulously in technical notes and case reports, whereas others may require additional research to confirm clinical benefit and efficacy.

CONCLUSION

This review examines the role of the LHBT as a source of local autograft, with biological and biomechanical properties, in aiding outcomes of complex primary and revision shoulder surgery procedures.

Present situation and development prospects of the diagnosis and treatment of rotator cuff tears

Rotator cuff tears are an important cause of shoulder pain and are caused by degeneration or trauma of the shoulder tendon at the anatomical neck of the humeral head. The understanding and research of rotator cuff tears have a history of hundreds of years, and their etiology, diagnosis, and treatment have a complete system, but some detailed rules of diagnosis and treatment still have room for development. This research paper briefly introduces the diagnosis and treatment of rotator cuff tears. The current situation and its valuable research direction are described.

Bioprinted living tissue constructs with layer-specific, growth factor-loaded microspheres for improved enthesis healing of a rotator cuff

Substantial challenges remain in constructing the native tendon-to-bone interface for rotator cuff healing owing to the enthesis tissues' highly organized structural and compositional gradients. Herein, we propose to bioprint living tissue constructs with layer-specific growth factors (GFs) to promote enthesis regeneration by guiding the zonal differentiation of the loaded stem cells in situ. The sustained release of tenogenic, chondrogenic, and osteogenic GFs was achieved via microsphere-based delivery carriers embedded in the bioprinted constructs. Compared to the basal construct without GFs, the layer-specific tissue analogs realized region-specific differentiation of stem cells in vitro. More importantly, bioprinted living tissue constructs with layer-specific GFs rapidly enhanced the enthesis regeneration in a rabbit rotator cuff tear model in terms of biomechanical restoration, collagen deposition, and alignment, showing gradient interface of fibrocartilage structures with aligned collagen fibrils and an ultimate load failure of 154.3 ± 9.5 N resembling those of native enthesis tissues in 12 weeks. This exploration provides a feasible strategy to engineer living tissue constructions with region-specific differentiation potentials for the functional repair of gradient enthesis tissues. STATEMENT OF SIGNIFICANCE: Previous studies that employed acellular layer-specific scaffolds or stem cells for the reconstruction of the rotator cuff faced challenges due to their insufficient capability to rebuild the anisotropic compositional and structural gradients of native enthesis tissues. This manuscript proposed a living tissue construct with layer-specific, GFs-loaded µS, which can direct in situ and region-specific differentiation of the embedded stem cells to tenogenic, chondrogenic, and osteogenic lineages for functional regeneration of the enthesis tissues. This bioprinted living tissue construct with the unique capability to reduce fibrovascular scar tissue formation and simultaneously facilitate enthesis tissue remodeling might provide a promising strategy to repair complex and gradient tissues in the future.

Tendon progenitor cells as biological augmentation improve functional gait and reduce scar formation after rotator cuff repair

BACKGROUND

High rates of structural failure are reported after rotator cuff repairs due to inability to recreate the native enthesis during healing. The development of biological augmentation methods that mitigate scar formation and regenerate the enthesis is still an unmet need. Since neonatal enthesis is capable of regeneration after injury, this study tested whether delivery of neonatal tendon progenitor cells (TPCs) into the adult injured environment can enhance functional and structural supraspinatus enthesis and tendon healing.

METHODS

TPCs were isolated from Ai14 Rosa26-TdTomato mouse Achilles tendons and labeled using adenovirus-Cre. Fifty-two CB57BL/6J mice underwent detachment and acute repair of the supraspinatus tendon and received either a fibrin-only or TPC-fibrin gel. Immunofluorescence analysis was carried out to determine cellularity (DAPI), fibrocartilage (SOX9), macrophages (F4/80), myofibroblasts (α-smooth muscle actin), and scar (laminin). Assays for function (gait and biomechanical testing) and structure (micro-computed tomography imaging, picrosirius red/Alcian Blue staining, type I and III collagen staining) were carried out.

RESULTS

Analysis of TdTomato cells after injury showed minimal retention of TPCs by day 7 and day 14, with detected cells localized near the bursa and deltoid rather than the enthesis/tendon. However, TPC delivery led to significantly increased %Sox9+ cells in the enthesis at day 7 after injury and decreased laminin intensity across almost all time points compared to fibrin-only treatment. Similarly, TPC-treated mice showed gait recovery by day 14 (paw area and stride length) and day 28 (stance time), while fibrin-treated mice failed to recover gait parameters. Despite improved gait, biomechanical testing showed no differences between groups. Structural analysis by micro-computed tomography suggests that TPC application improves cortical thickness after surgery compared to fibrin. Superior collagen alignment at the neo-enthesis was also observed in the TPC-augmented group at day 28, but no difference was detected in type I and III collagen intensity.

CONCLUSION

We found that neonatal TPCs improved and restored functional gait by reducing overall scar formation, improving enthesis collagen alignment, and altering bony composition response after supraspinatus tendon repair. TPCs did not appear to integrate into the healing tissue, suggesting improved healing may be due to paracrine effects at early stages. Future work will determine the factors secreted by TPCs to develop translational targets.

Association of Preoperative Vitamin D Deficiency With Retear Rate and Early Pain After Arthroscopic Rotator Cuff Repair: A Retrospective Cohort Study

Background

Although the function of vitamin D in bone metabolism has been well studied, the question remains whether vitamin D deficiency impairs tendon healing after rotator cuff repair.

Purpose

To investigate the correlation between preoperative vitamin D deficiency and the retear rate and pain after arthroscopic rotator cuff repair.

Study Design

Cohort study; Level of evidence, 3.

Methods

Patients with full-thickness rotator cuff tears who underwent arthroscopic rotator cuff repair between January 2018 and August 2019 were enrolled. Included patients were divided into a control group (vitamin D level ≥20 μg/L) and a deficiency group (vitamin D level <20 μg/L). We investigated the association between preoperative vitamin D level and patient characteristics, MRI findings, pain and function scores (visual analog scale [VAS] for pain; Constant-Murley; University of California, Los Angeles; and American Shoulder and Elbow Surgeons scores), and healing status using the Pearson or Spearman correlation coefficient. The clinical characteristics were compared between the groups using the chi-square test or Fisher exact test.

Results

Included were 89 patients (control group, 44 patients; deficiency group, 45 patients). The mean vitamin D levels were 25.07 ± 5.38 and 14.61 ± 3.43 μg/L in the control and deficiency groups, respectively (P < .001); otherwise, there were no significant differences between the groups in the variables under study. Vitamin D levels were not related to age, symptom duration, tear size, extent of retraction, VAS pain score preoperatively and at 6 and 24 months postoperatively, or any function scores. Supraspinatus fatty infiltration and VAS scores at 1 and 3 months postoperatively were significantly associated with vitamin D level (r = -0.360, -0.362, and -0.316, respectively; P < .05 for all). VAS scores were significantly lower in the control group than in the deficiency group at postoperative 1 month (1.09 ± 0.56 vs 1.47 ± 0.66, respectively) and 3 months (1.14 ± 0.77 vs 1.44 ± 0.66) (P < .05 for both). The retear rate was significantly lower in the control group than in the deficiency group (9.09% vs 26.67%, respectively; P < .05).

Conclusion

Our study revealed that preoperative vitamin D deficiency was associated with a higher retear rate and early pain (1 and 3 months) after arthroscopic rotator cuff repair.

Does the critical shoulder angle influence retear and functional outcome after arthroscopic rotator cuff repair? A systematic review and meta-analysis

PURPOSE

This systematic review and meta-analysis aimed to evaluate the correlation between increased critical shoulder angle (CSA) and higher retear rates and functional outcomes after arthroscopic rotator cuff repair (ARCR).

METHODS

PubMed, Embase, Web of Science, and Cochrane Library databases published before January 2022 were comprehensively searched. Two reviewers independently reviewed the titles and abstracts using the specified criteria. Studies were included if the authors clearly described the correlation between the CSA and rotator cuff repair. Data on patient characteristics, mean CSA, retear rate, and the functional score was pooled from the selected articles. A meta-analysis was performed using Review Manager (RevMan) 5.4.1 software, 2020 (Cochrane Collaboration, Copenhagen, Denmark).

RESULTS

Eleven articles involving 1449 patients from 7 countries were included. The ages of the patients ranged from 45 to 75 years. The follow-up period ranged from 6 to 96 months. The mean CSA was greater in the retear group than in the non-retear group after ARCR (mean difference 2.73°; 95% confidence interval [CI] 0.69-4.77) (p = 0.009). Three studies evaluated the association between increased CSA and the postoperative retear rate. All three studies showed a higher postoperative retear rate in patients with an increased CSA (odds ratio 5.35; 95% CI 2.02-14.15; p = 0.0007). No association was found between CSA and Constant-Murley (Constant), the University of California at Los Angeles (UCLA), or Visual Analog Scale (VAS) scores during the follow-up period of 24-96 months (p > 0.05).

CONCLUSIONS

This systematic review and meta-analysis showed that CSA correlates highly with rotator cuff retear after ARCR. In addition, the postoperative retear rate of the rotator cuff increased with increased CSA. CSA appeared to not affect worse functional outcomes in patients after ARCR.

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.

Muscle degeneration in chronic massive rotator cuff tears of the shoulder: Addressing the real problem using a graphene matrix

Massive rotator cuff tears (MRCTs) of the shoulder cause disability and pain among the adult population. In chronic injuries, the tendon retraction and subsequently the loss of mechanical load lead to muscle atrophy, fat accumulation, and fibrosis formation over time. The intrinsic repair mechanism of muscle and the successful repair of the torn tendon cannot reverse the muscle degeneration following MRCTs. To address these limitations, we developed an electroconductive matrix by incorporating graphene nanoplatelets (GnPs) into aligned poly(l-lactic acid) (PLLA) nanofibers. This study aimed to understand 1) the effects of GnP matrices on muscle regeneration and inhibition of fat formation in vitro and 2) the ability of GnP matrices to reverse muscle degenerative changes in vivo following an MRCT. The GnP matrix significantly increased myotube formation, which can be attributed to enhanced intracellular calcium ions in myoblasts. Moreover, the GnP matrix suppressed adipogenesis in adipose-derived stem cells. These results supported the clinical effects of the GnP matrix on reducing fat accumulation and muscle atrophy. The histological evaluation showed the potential of the GnP matrix to reverse muscle atrophy, fat accumulation, and fibrosis in both supraspinatus and infraspinatus muscles at 24 and 32 wk after the chronic MRCTs of the rat shoulder. The pathological evaluation of internal organs confirmed the long-term biocompatibility of the GnP matrix. We found that reversing muscle degenerative changes improved the morphology and tensile properties of the tendon compared with current surgical techniques. The long-term biocompatibility and the ability of the GnP matrix to treat muscle degeneration are promising for the realization of MRCT healing and regeneration.

Clinical Outcomes After Arthroscopic Rotator Cuff Repair With a Fibrin Scaffold Containing Growth Factors and Autologous Progenitor Cells Derived from cBMA

Purpose

To report the clinical outcomes after biologically augmented rotator cuff repair (RCR) with a fibrin scaffold derived from autologous whole blood and supplemented with concentrated bone marrow aspirate (cBMA) harvested at the proximal humerus.

Methods

Patients who underwent arthroscopic RCR with biologic augmentation using a fibrin clot scaffold (“Mega- Clot”) containing progenitor cells and growth factors from proximal humerus BMA and autologous whole blood between April 2015 and January 2018 were prospectively followed. Only high-risk patients in primary and revision cases that possessed relevant comorbidities or physically demanding occupation were included. Minimum follow-up for inclusion was 1 year. The visual analog score for pain (VAS), American Shoulder and Elbow Surgeons (ASES), Simple Shoulder Test (SST), Single Assessment Numerical Evaluation (SANE), and Constant-Murley scores were collected preoperatively and at final follow-up. In vitro analyses of the cBMA and fibrin clot using nucleated cell count, colony forming units, and live/dead assays were used to quantify the substrates.

Results

Thirteen patients (56.9 ± 7.7 years) were included. The mean follow-up was 26.9 ± 17.7 months (n = 13). There were significant improvements in all outcome scores from the preoperative to the postoperative state: VAS (5.6 ± 2.5 to 3.1 ± 3.2; P < .001), ASES (42.0 ± 17.1 to 65.5 ± 30.6; P < .001), SST (3.2 ± 2.8 to 6.5 ± 4.7; P = .002), SANE (11.5 ± 15.6 to 50.3 ± 36.5; P < .001), and Constant-Murley (38.9 ± 17.5 to 58.1 ± 26.3; P < .001). Six patients (46%) had retears on postoperative MRI, despite all having improvements in pain and function except one. All failures were chronic rotator cuff tears, and all were revision cases except one (1.6 ± 0.5 previous RCRs). The representative sample of harvested cBMA showed an average of 28.5 ± 9.1 × 10⁶ nucleated cells per mL.

Conclusions

Arthroscopic rotator cuff repairs that are biologically augmented with a fibrin scaffold containing growth factors and autologous progenitor cells derived from autologous whole blood and humeral cBMA can improve clinical outcomes in primary, as well as revision cases in high-risk patients. However, the incidence of retears remains a concern in this population, demanding further improvements in biologic augmentation.

Level of Evidence

IV, therapeutic case series.

Functional and radiologic results of the crimson duvet procedure in rotator cuff treatment: a randomized controlled clinical trial

BACKGROUND

Rotator cuff tears are one of the more frequent pathologies of the shoulder. Arthroscopic techniques and biologic augmentation have been developed to improve the rate and quality of healing. The crimson duvet procedure (CDP) theoretically provides mesenchymal stem cells through microfracture treatment of the footprint. The aim of this research was to evaluate the effect of CDP in patients who had undergone arthroscopic surgery for complete rotator cuff repair.

METHODS

A prospective randomized clinical trial was performed in a total of 123 patients, consisting of 59 women and 64 men, with a mean age of 58 years. We included patients with a clinical and radiologic diagnosis of a complete rotator cuff tear. All patients were treated with arthroscopic rotator cuff repair. In group 1, the surface of the footprint was débrided; in group 2, the footprint underwent microfracture. The primary outcome was the nonhealing rate, which was detected by magnetic resonance imaging (MRI) or ultrasonography, and the secondary outcome was the functional result. A Sugaya classification of I to III was considered to indicate healing. For clinical evaluation, the American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) and Constant scores were evaluated, along with the range of motion. The functional evaluation was performed preoperatively and at 6 months and 1 year postoperatively. The radiologic (MRI or ultrasonography) evaluation was performed at 6 months. Neither the patients nor the radiologists and physical therapists who performed the postoperative evaluations were informed of the random selection.

RESULTS

We observed a healing rate of 85.11% in the control group and 93.7% in the CDP group, which was not significant (P = .19). However, a significant improvement in function was observed in all patients. The ASES score improved from 68.9 (SD 13.8) preoperatively to 92.2 at 6 months and to 96.4 (SD 6.2) at 12 months (P < .05), but no difference was observed between the groups. A similar level of improvement was observed in the Constant score.

CONCLUSION

The arthroscopic repair of complete rotator cuff tears presents good and excellent clinical results in most patients. Nevertheless, nonhealing occurs at a rate that depends mainly on the age of the patient and the size of the tear. The addition of CDP did not improve the functional results or the healing rate.

Bioactive Film-Guided Soft-Hard Interface Design Technology for Multi-Tissue Integrative Regeneration

Control over soft-to-hard tissue interfaces is attracting intensive worldwide research efforts. Herein, a bioactive film-guided soft-hard interface design (SHID) for multi-tissue integrative regeneration is shown. Briefly, a soft bioactive film with good elasticity matchable to native ligament tissue, is incorporated with bone-mimic components (calcium phosphate cement, CPC) to partially endow the soft-film with hard-tissue mimicking feature. The hybrid film is elegantly compounded with a clinical artificial ligament to act as a buffer zone to bridge the soft (ligament) and hard tissues (bone). Moreover, the bioactive film-decorated ligament can be rolled into a 3D bio-instructive implant with spatial-controllable distribution of CPC bioactive motifs. CPC then promotes the recruitment and differentiation of endogenous cells in to the implant inside part, which enables a vascularized bone growth into the implant, and forms a structure mimicking the biological ligament-bone interface, thereby significantly improving osteointegration and biomechanical property. Thus, this special design provides an effective SHID-guided implant-bioactivation strategy unreached by the traditional manufacturing methods, enlightening a promising technology to develop an ideal SHID for translational use in the future.

Current concepts on management of cuff tear

Among pathologies of the shoulder, rotator cuff tear is the most common. Diagnosis of cuff tear around mid twenties is unusual, but the prevalence increases significantly after the age of forty. The prevalence after the age of 60 is around 20-30%. A well recognised feature of cuff tear is being asymptomatic but, tear progression in asymptomatic is a known consequence. The spectrum of cuff tear ranges from partial, full thickness cuff tear with or without retraction. The mainstay of treatment for partial thickness cuff tear is systematic rehabilitation and for the full thickness cuff tear an initial rehabilitation is an accepted management. Failed rehabilitation for 3 months, acute traumatic tear, younger age, intractable pain, good quality muscle would be the indications for repair of a full thickness cuff tear. Though there are defined indications for surgical intervention in the full thickness rotator cuff tear, differentiating an asymptomatic tear that would not progress or identifying a tear that would become better with rehabilitation is an undeniable challenge for even the most experienced surgeon. Rehabilitation in cuff tear consists of strengthening the core stabilizers along with rotator cuff and deltoid muscles. In a symptomatic cuff tear that merits surgical intervention the objective is to do an anatomical foot print repair. In scenarios where the cuff is retracted, one has to settle for a medialised repair. As, a repair done in tension is more likely to fail than a tensionless medialised repair. The success rate of all these non anatomical procedures varies from series to series but it approximates around 60-80%. Augmenting cuff repair to enhance biological healing is a recent advance in rotator cuff repair surgery. The augmentation factors can be growth factors like PRP, scaffolds both auto and allografts. The outcome of these procedures from literature has been variable. As there are no major harmful effects, it can be viewed as another future step in bringing better outcomes to patients having rotator cuff tear surgery. Despite being the commonest shoulder pathology, the rotator cuff tear still remains as a condition with varied presenting features and a wide variety of management options. The goal of the treatment is to achieve pain free shoulders with good function. Correcting altered scapular kinematics by systematic rehabilitation of the shoulder would be the first choice in all partial thickness cuff tear and also as an initial management of full thickness cuff tears. Failure of rehabilitation would be the step forward for a surgical intervention. While embarking on a surgical procedure, correct patient selection, sound surgical technique, appropriate counselling about expected outcome are the most essential in patient satisfaction.

Autograft Long Head Biceps Tendon Can Be Used as a Scaffold for Biologically Augmenting Rotator Cuff Repairs

PURPOSE

We create a viable, mechanically expanded autograft long head biceps tendon (LHBT) scaffold for biologically augmenting the repair of torn rotator cuffs.

METHODS

The proximal aspect of the tenotomized LHBTs was harvested from patients during rotator cuff repair surgery and was mechanically formed into porous scaffolds using a surgical graft expander. LHBT scaffolds were evaluated for change in area, tensile properties, and tenocyte viability before and after expansion. The ability of endogenous tenocytes derived from the LHBT scaffold to promote tenogenic differentiation of human adipose-derived mesenchymal stromal cells (ADMSCs) was also determined.

RESULTS

Autograft LHBTs were successfully expanded using a modified surgical graft expander to create a porous scaffold containing viable resident tenoctyes from patients undergoing rotator cuff repair. LHBT scaffolds had significantly increased area (length: 24.91 mm [13.91, 35.90] × width: 22.69 mm [1.87, 34.50]; P = .011) compared with the native LHBT tendon (length: 27.16 mm [2.70, 33.62] × width: 6.68 mm [5.62, 7.74]). The structural properties of the autograft were altered, including the ultimate tensile strength (LHBT scaffold: .56 MPa [.06, 1.06] vs. native LHBT: 2.35 MPa [1.36, 3.33]; P = .002) and tensile modulus (LHBT scaffold: 4.72 MPa [-.80, 1.24] versus native LHBT: 37.17 MPa [24.56, 49.78]; P = .001). There was also a reduction in resident tenocyte percent viability (LHBT scaffold: 38.52% [17.94, 59.09] vs. native LHBT: 68.87% [63.67, 74.37]; P =.004). Tenocytes derived from the LHBT scaffold produced soluble signals that initiated ADMSC differentiation into an immature tenocyte-like phenotype, as indicated by an 8.7× increase in scleraxis (P = .040) and a 3.6× increase in collagen type III mRNA expression (P = .050) compared with undifferentiated ADMSC controls.

CONCLUSIONS

The ability to produce a viable autologous scaffold from the proximal biceps tendon having dimensions, porosity, mechanical characteristics, native ECM components, and viable tenocytes that produce bioactive signals conducive to supporting the biologic augmentation of rotator cuff repair surgery has been demonstrated.

CLINICAL RELEVANCE

This biologically active construct may help to improve the quality of healing and regeneration at the repair site of rotator cuff tears, especially those at high risk for retear.

What Factors Are Associated with Symptomatic Rotator Cuff Tears: A Meta-analysis

BACKGROUND

Rotator cuff tears are common. A previous systematic review reported on factors associated with rotator cuff tears; however, it included relatively few studies and few variables, and in addition, it had considerable heterogeneity. To identify the factors associated with symptomatic rotator cuff tears and to help guide clinicians to potentially modifiable factors, we felt a broader and more inclusive meta-analysis would be useful.

QUESTIONS/PURPOSES

In this systematic review and meta-analysis, we asked what (1) demographic, (2) disease, and (3) imaging factors are associated with symptomatic rotator cuff tears?

METHODS

PubMed, Embase, and Web of Science were searched, and the search period were from the inception of each database through February 2021. The keywords included "risk factor," "rotator cuff injury," "rotator cuff tears," and "rotator cuff tendinitis." All comparative studies on symptomatic rotator cuff tears were included. We considered that the diagnosis of rotator cuff tear could be made by any imaging tool (MRI or ultrasound). We considered either partial- or full-thickness tears to be a rotator cuff tear. No language restrictions were applied. Twenty-six articles from 14 countries involving 9809 individuals, consisting of 3164 patients and 6645 controls, were included. The Newcastle-Ottawa Scale and the Agency for Healthcare Research and Quality (AHRQ) scale were used to evaluate the risk of bias of the included studies, and the highest scores were 9 and 11, respectively. The Newcastle-Ottawa Scale was used for retrospective comparative studies, and the AHRQ was used to evaluate prospective comparative studies. The eight retrospective comparative studies we included were scored from 4 to 9. The quality score of the 18 prospective comparative studies ranged from 6 to 9. Publication bias was explored using the Egger test. Heterogeneity was estimated using the I2 value. If there was no heterogeneity (I2 ≤ 50%), a fixed-effects model was used to determine the overall effect size; if there was heterogeneity (I2 > 50%), a random-effects model was used to merge the effect values. A meta-analysis was performed with RevMan 5.3, and the risk ratio (RR) and weighted mean difference of related factors were calculated.

RESULTS

Our meta-analysis identified the following demographic factors associated with an increased risk of rotator cuff tears: older age (mean difference 3.1 [95% CI 1.4 to 4.8]; p < 0.001), greater BMI (mean difference 0.77 [95% CI 0.37 to 1.17]; p < 0.001), smoking (RR 1.32 [95% CI 1.17 to 1.49]; p < 0.001), dominant arm (RR 1.15 [95% CI 1.06 to 1.24]; p < 0.001), greater height (mean difference 0.9 [95% CI 0.4 to 1.4]; p < 0.001), and heavier weight (mean difference 2.24 [95% CI 0.82 to 3.66]; p = 0.002). Regarding disease factors, we found that traumatic events (RR 1.91 [95% CI 1.40 to 2.54]; p < 0.001) and hypertension (RR 1.50 [95% CI 1.32 to 1.70]; p < 0.001) were associated with symptomatic rotator cuff tears. Regarding imaging factors, we found that the following three factors were associated with symptomatic rotator cuff tears: greater acromion index (mean difference 0.11 [95% CI 0.06 to 0.16]; p < 0.001), greater critical shoulder angle (mean difference 1.9 [95% CI 1.5 to 2.3]; p < 0.001), and smaller glenoid version angle (mean difference -1.3 [95% CI -1.9 to -0.8]; p < 0.001). We found no association between the patient's sex or the presence or absence of thyroid disease and the likelihood of a rotator cuff tear being present.

CONCLUSION

This study identified several factors associated with symptomatic rotator cuff tears, including blood glucose, blood pressure, weight, and smoking. Clinicians may seek to modify these factors, possibly in patients with symptomatic rotator cuff tears, but also in symptomatic patients who have not yet been diagnosed with rotator cuff tears because there would be no harm or risk associated with modifying any of the factors we identified. Future research should further study whether addressing these factors can delay the progression and size of rotator cuff tears.Level of Evidence Level III, prognostic study.

Risk factors for full-thickness rotator cuff tears: a systematic review and meta-analysis

Rotator cuff tears are a common condition of the shoulder, and 20.7% of people with the condition have a full-thickness rotator cuff tear. The purpose of this study was to explore the risk factors for full-thickness rotator cuff tears and to provide evidence to support the accurate diagnosis of full-thickness rotator cuff tears.

Studies from PubMed, Embase and Web of Science published before 30 January 2021 were retrieved. All cohort studies and cross-sectional studies on risk factors for full-thickness rotator cuff tears were included. A meta-analysis was performed in RevMan 5.3 to calculate the relative risks (RRs) or weighted mean differences (WMDs) of related risk factors. Stata 15.1 was used for the quantitative analysis of publication bias.

In total, 11 articles from six countries, including 4047 cases, with 1518 cases and 2529 controls, were included. The meta-analysis showed that age (MD = 0.76, 95% CI: 0.24 to 1.28, P = 0.004), hypertension (RR = 1.46, 95% CI: 1.17 to 1.81, P = 0.0007) and critical shoulder angle (CSA) (MD = 2.02, 95% CI: 1.55 to 2.48, P < 0.00001) were risk factors for full-thickness rotator cuff tears.

Our results also suggested that body mass index, sex, dominant hand, smoking, diabetes mellitus and thyroid disease were not risk factors for full-thickness rotator cuff tears. Early identification of risk factors for full-thickness rotator cuff tears is helpful in identifying high-risk patients and choosing the appropriate treatment.

Cite this article: EFORT Open Rev 2021;6:1087-1096. DOI: 10.1302/2058-5241.6.210027

The Regenerative Role of Gelatin in PLLA Electrospun Membranes for the Treatment of Chronic Massive Rotator Cuff Injuries

Failing to regenerate native tendon tissue in chronic massive rotator cuff tears (CMRCTs) results in high retear rates after surgery. Gelatin is a hydrolyzed form of collagen which is bioactive and biocompatible. This study intends to investigate the suitability of integrating gelatin to poly (l-lactic acid) (PLLA) fibrous membranes for promoting the healing of CMRCTs. PLLA/Gelatin electrospun membranes (PGEM) are fabricated using electrospinning technology. The fourier transform infrared, static contact angles are tested sequentially. Cytocompatibility is evaluated with rat tendon fibroblasts and human umbilical endothelial cells (HUEVCs) lines. CMRCTs rat models are established and assigned into three groups (the sham group, the repaired group, and the augmentation group) to perform histomorphological and biomechanical evaluations. Gelatin is successfully integrated into PLLA fibrous membranes by the electrospinning technique. In vitro studies indicate that PGEM shows a great cytocompatibility for rat tendon fibroblasts and HUEVCs. In vivo studies find that applications of PGEM significantly promote well-aligned collagen I fibers formation and enhance biomechanical properties of the repaired tendon in CMRCTs rat models. In summary, gelatin promotes tendon fibroblasts and HUEVCs adhesion, migration, and proliferation on the PLLA fibrous membranes, and PGEM may provide a great prospect for clinical application.

Risk Factors for Supraspinatus Tears: A Meta-analysis of Observational Studies

Background:

The pathogenesis of rotator cuff tears remains unclear, and there is a lack of high-quality evidence-based research on the risk factors for supraspinatus tears.

Purpose:

To explore 10 potential risk factors for supraspinatus muscle tears.

Study Design:

Systematic review; Level of evidence, 3.

Methods:

This review was conducted according to the MOOSE (Meta-analysis Of Observational Studies in Epidemiology) guidelines. PubMed, Embase, and Web of Science were searched for cohort, case-control and cross-sectional studies published before January 2021 on supraspinatus tears. The following potential risk factors were analyzed: age, body mass index, male sex, female sex, arm dominance, diabetes mellitus, smoking, hypertension, thyroid disease, and the critical shoulder angle (CSA). Risk ratios (RRs) or weighted mean differences (WMDs) of related risk were calculated. The Egger test was used to evaluate publication bias.

Results:

A total of 9 articles from 8 countries were included; among the 3240 patients, 687 were included in the supraspinatus tear group, and 2553 were included in the nonsupraspinatus tear group. The meta-analysis showed that older age (WMD, 3.36 [95% confidence interval (CI), 0.53-6.20]; P = .02), male sex (RR, 0.87 [95% CI, 0.78-0.97]; P = .01), smoking (RR, 2.21 [95% CI, 1.56-3.14]; P < .00001), diabetes (RR, 1.67 [95% CI, 1.03-2.70]; P = .04), hypertension (RR, 1.51 [95% CI, 1.16-1.97]; P = .002), and the CSA (WMD, 2.25 [95% CI, 1.39-3.12]; P < .00001) were risk factors for supraspinatus tears.

Conclusion:

Older age, male sex, smoking, diabetes, hypertension, and a higher CSA were found to be risk factors for supraspinatus tears in this meta-analysis review. Identifying risk factors for supraspinatus tears early can help clinicians identify these high-risk patients and choose appropriate treatments.

Effects of purified exosome product on rotator cuff tendon-bone healing in vitro and in vivo

Exosomes have multiple therapeutic targets, but the effects on healing rotator cuff tear (RCT) remain unclear. As a circulating exosome, purified exosome product (PEP) has the potential to lead to biomechanical improvement in RCT. Here, we have established a simple and efficient approach that identifies the function and underlying mechanisms of PEP on cell-cell interaction using a co-culture model in vitro. In the in vivo trial, adult female Sprague-Dawley rats underwent unilateral surgery to transect and repair the supraspinatus tendon to its insertion site with or without PEP. PEP promoted the migration and confluence of osteoblast cells and tenocytes, especially during direct cell-cell contact. Expression of potential genes for RCT in vitro and in vivo models were consistent with biomechanical tests and semiquantitative histologic scores, indicating accelerated strength and healing of the RC in response to PEP. Our observations suggest that circulating exosomes provide an effective option to improve the healing speed of RCT after surgical repair. The regeneration of enthesis following PEP treatment appears to be related to a mutually reinforcing relationship between direct cell-cell contact and PEP activity, suggesting a dual approach to the healing process.

Decreased Colony-Forming Ability of Subacromial Bursa-Derived Cells During Revision Arthroscopic Rotator Cuff Repair

Purpose

To compare the cellular viability and differentiation potential of subacromial bursa-derived cells (SBDCs) located over the rotator cuff muscle and tendon of patients undergoing primary versus revision arthroscopic rotator cuff repair (ARCR).

Methods

Subacromial bursa was harvested from 18 primary (57.1 ± 4.6 years) and 12 revision ARCRs (57.3 ± 6.7 years). Bursa was collected from 2 sites (over rotator cuff tendon and muscle), digested with collagenase, and grown in culture. The number of nucleated cells, colony-forming units (CFUs), differentiation potential, and mesenchymal stem cell surface markers were compared in primary and revision cases.

Results

There was no difference in the number of nucleated cells between primary and revision ARCR harvested from the subacromial bursa overlying the tendon (3019.3 ± 1420.6 cells/mg and 3541.7 ± 2244.2 cells/mg, respectively; P = .912) or muscle (2753.5 ± 1547.1 cells/mg and 2989.0 ± 2231.4 cells/mg, respectively; P = .777). There was no difference in the number of CFUs between primary and revision ARCR over the rotator cuff tendon (81.5 ± 49.5 CFUs and 53.0 ± 36.9 CFUs, respectively; P = .138), but there were significantly fewer CFUs over the muscle in revision cases (28.1 ± 22.7 CFUs) compared with primary cases (55.7 ± 34.5 CFUs) (P = .031). SBDCs from revision ARCR expressed characteristic mesenchymal stem cell surface epitopes and had multidifferentiation potentials for chondrogenesis, osteogenesis, and adipogenesis.

Conclusions

SBDCs harvested over the rotator cuff muscle demonstrated significantly decreased colony-forming abilities in revision arthroscopic rotator cuff repairs compared with primary repairs. However, the subacromial bursa retains its pluripotent differentiation potential for chondrogenic, osteogenic, and adipogenic lineages in the revision setting.

Clinical Relevance

The subacromial bursa may play a role in the healing response of the repaired rotator cuff. This capacity is not necessarily diminished in the revision setting and may be harnessed as an orthobiologic.

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.

Gradient bimetallic ion-based hydrogels for tissue microstructure reconstruction of tendon-to-bone insertion

Although gradients play an essential role in guiding the function of tissues, achieving synchronous regeneration of gradient tissue injuries remains a challenge. Here, a gradient bimetallic (Cu and Zn) ion-based hydrogel was first constructed via the one-step coordinative crosslinking of sulfhydryl groups with copper and zinc ions for the microstructure reconstruction of the tendon-to-bone insertion. In this bimetallic hydrogel system, zinc and copper ions could not only act as crosslinkers but also provide strong antibacterial effects and induce regenerative capacity in vitro. The capability of hydrogels in simultaneously promoting tenogenesis and osteogenesis was further verified in a rat rotator cuff tear model. It was found that the Cu/Zn gradient layer could induce considerable collagen and fibrocartilage arrangement and ingrowth at the tendon-to-bone interface. Overall, the gradient bimetallic ion-based hydrogel ensures accessibility and provides opportunities to regenerate inhomogeneous tissue with physiological complexity or interface tissue.

Electrospun polycaprolactone/hydroxyapatite/ZnO films as potential biomaterials for application in bone-tendon interface repair

The bone-tendon interface (BTI) is a graded structure consisting of bone, mineralized and nonmineralized fibrocartilage, and tendons. Due to the complexity of the BTI structure, BTI healing is particularly challenging. To achieve a better material for BTI healing, polycaprolactone (PCL)/hydroxyapatite (HA)/ZnO films were constructed by the electrospinning method; in addition, the relevant material characteristics were tested. After culturing MC3T-E1 cells, ATDC5 cells, mouse primary fibrochondrocytes, and mouse primary tenocytes on films, PCL-5%HA-1%ZnO films (HA and ZnO weight ratios of 5% and 1%, respectively) displayed superior cell compatibility and cell adhesion. PCL-5%HA-1%ZnO films also promoted osteogenesis, chondrogenesis, fibrocartilage formation, and tendon healing. The antibacterial characteristics of PCL-5%HA-1%ZnO films were also identified in this study. The PCL-5%HA-1%ZnO films have great application potential in the field of BTI repair.

Rotator cuff anchor repair: Histological changes associated with the recovering mechanical properties in a rabbit model

Rotator cuff anchor repair is an increasingly common surgical procedure but the failure rate remains high. In order to improve surgical outcomes, a better understanding of postrepair histological and cellular responses at the tendon-bone attachment site (enthesis) is needed. We examined operated shoulders from 42 New Zealand female white rabbits. The animals underwent unilateral supraspinatus detachment followed by anchor repair a week later. To assess enthesis reformation, fibrocartilage staining area and the number of chondrocytes or nonchondrocytes were quantified at 0, 1, 2, and 4 weeks postrepair. Using linear regression, we correlated these results with the load to failure and stiffness recorded during mechanical testing of the tendons. Fibrocartilage staining and chondrocyte number increased during the first 2 weeks of enthesis formation. Between 2 and 4 weeks, fibrocartilage staining plateaued while chondrocyte number decreased. The presence of nonchondrocytes remained similar between 0- and 1-week postrepair but then decreased abruptly at 2 weeks. There was a linear correlation between fibrocartilage staining area and load to failure as well as stiffness. Nonchondrocyte number negatively correlated with stiffness. Early plateau of fibrocartilage staining and decrease in chondrocytes between 2 and 4 weeks postrepair suggest a blunted enthesis formation response in our animal model.

Nanoparticle-coated sutures providing sustained growth factor delivery to improve the healing strength of injured tendons

Tendon injuries are common diseases. The healing capacity of tendon is limited due to its special composition of extra-cellular matrix and hypocellularity and hypovascularity. The purpose of this study was to evaluate the effectiveness of nanoparticle-coated sutures carrying growth factors for accelerating tendon repair. A variety of experimental methods had been used to investigate the characteristics and therapeutic effects of the modified sutures. Nanoparticles could adhere uniformly to the surface of the suture through polydopamine. Even sutured in the tendon, most of nanoparticles were still remained on the surface of suture, and the loaded proteins could spread into the tendon tissues. In vivo study, the ultimate strength of repaired tendons treated with bFGF and VEGFA-releasing sutures was significantly greater than the tendons repaired with control sutures at multiple time-points, whether in the chicken model of flexor tendon injury or the rat model of Achilles tendon injury. At week 6, the adhesion score in the bFGF and VEGFA-releasing suture group was significantly lower than those of the control suture group. Tendon gliding excursion was significantly longer in the bFGF and VEGFA-releasing suture group than that in the control bare sutures. Work of digital flexion was significantly decreased in the bFGF and VEGFA-releasing suture group. In a word, we developed a platform for local and continuous delivery of growth factors based on the nanoparticle-coated sutures, which could effectively deliver growth factors to tissues and control the release of growth factors. This growth factors delivery system is an attractive therapeutic tool to repair injured tendons. STATEMENT OF SIGNIFICANCE: Tendon rupture is a common clinical injury, due to the special character of the tendon with mainly extra cellular matrix and hypocellularity and hypovascularity, the healing capacity of the injured tendon is limited. In this study, nanoparticle-coated surgical sutures carrying growth factors were prepared to accelerate tendon repair. After treatment, bFGF and VEGFA loaded nanoparticle-coated sutures can significantly enhance tendon healing, and significantly improve tendon gliding function and effectively inhibit the formation of adhesion. Moreover, these nanoparticle-coated sutures have good biocompatibility and no obvious tissue reaction, which provides more guarantee for further clinical application. This is an attractive and promising approach that uses surgical suture as a growth factor delivery tool to repair tendon injury, which can simplify the treatment. And this kind of bioactive sutures may be applied to other tissue repair, such as muscle, nerve, intestinal canal, blood vessel, skin, and so on.

The clinical efficacy of leukocyte-poor platelet-rich plasma in arthroscopic rotator cuff repair: a meta-analysis of randomized controlled trials

BACKGROUND

The efficacy of platelet-rich plasma (PRP) in the arthroscopic treatment of rotator cuff injury has been reported in the literature. However, conclusions have been inconsistent and more often related to differences in the types of PRP used. Therefore, to minimize these differences, we performed a meta-analysis of only studies investigating leukocyte-poor PRP to evaluate whether PRP promotes and improves the effects of arthroscopic rotator cuff repair.

METHODS

A comprehensive search of the PubMed, Embase, and Cochrane Library databases was conducted to evaluate the efficacy of leukocyte-poor PRP in arthroscopic rotator cuff repair. The available data were extracted, and the methodologic quality of the included studies was evaluated by the Cochrane risk-of-bias assessment tool.

RESULTS

In total, 10 randomized controlled trials involving 742 patients were included. The results of the meta-analysis showed that treatment with leukocyte-poor PRP performed better than the control treatment in relieving postoperative pain in the short-term (mean difference [MD], -0.57; 95% confidence interval [CI], -0.79 to -0.35; P < .0001) and medium- and long-term (MD, -0.18; 95% CI, -0.34 to -0.03; P = .02) follow-up groups. However, the changes in the MD in the visual analog scale score were below the minimal clinically important difference. Regarding the Constant shoulder (MD, 3.35; 95% CI, 1.68-5.02; P < .0001) and University of California, Los Angeles (MD, 1.73; 95% CI, 0.94-2.52; P < .0001) scores, statistically significant differences were found in favor of leukocyte-poor PRP over the control treatment. However, the changes in the MD in both the Constant and University of California, Los Angeles scores were below the minimal clinically important difference. Moreover, during medium- and long-term follow-up, the retear rate in the leukocyte-poor PRP group was lower than that in the control group regardless of the rotator cuff tear size (small and medium [<3 cm] [risk ratio (RR), 0.64; 95% CI, 0.43-0.97; P = .03] vs. medium and large [>3 cm] [RR, 0.51; 95% CI, 0.34-0.77; P = .001]) and surgical repair method (single-row repair [RR, 0.61; 95% CI, 0.43-0.87; P = .007] vs. double-row suture bridge repair [RR, 0.57; 95% CI, 0.38-0.84; P = .005]).

CONCLUSION

According to our study, leukocyte-poor PRP can significantly reduce the postoperative retear rate in the medium and long term regardless of the tear size and the method used for rotator cuff repair. However, the use of leukocyte-poor PRP failed to show clinically meaningful effects in terms of postoperative pain and patient-reported outcomes.

Hip abductor tendon tears: where are we now?

Hip abductor tendon tear is a difficult problem to manage. The hip abductor mechanism is made up of the gluteus medius and minimus muscles, both of which contribute to stabilising the pelvis through the gait cycle. Tears of these tendons are likely due to iatrogenic injury during arthroplasty and chronic degenerative tendinopathy. Ultrasound and magnetic resonance imaging have provided limited clues regarding the pattern of disease and further work is required to clarify both the macro and microscopic pattern of disease. While surgery has been attempted over the last 2 decades, the outcomes are variable and the lack of high-quality studies have limited the uptake of surgical repair. Hip abductor tendon tears share many features with rotator cuff tears, hence, innovations in surgical techniques, materials and biologics may apply to both pathologies.

Three-dimensional printed multiphasic scaffolds with stratified cell-laden gelatin methacrylate hydrogels for biomimetic tendon-to-bone interface engineering

Background

The anatomical properties of the enthesis of the rotator cuff are hardly regained during the process of healing. The tendon-to-bone interface is normally replaced by fibrovascular tissue instead of interposition fibrocartilage, which impairs biomechanics in the shoulder and causes dysfunction. Tissue engineering offers a promising strategy to regenerate a biomimetic interface. Here, we report heterogeneous tendon-to-bone interface engineering based on a 3D-printed multiphasic scaffold.

Methods

A multiphasic poly(ε-caprolactone) (PCL)–PCL/tricalcium phosphate (TCP)–PCL/TCP porous scaffold was manufactured using 3D printing technology. The three phases of the scaffold were designed to mimic the graded tissue regions in the tendon-to-bone interface—tendon, fibrocartilage, and bone. Fibroblasts, bone marrow–derived mesenchymal stem cells, and osteoblasts were separately encapsulated in gelatin methacrylate (GelMA) and loaded seriatim on the relevant phases of the scaffold, by which a cells/GelMA-multiphasic scaffold (C/G-MS) construct, replicating the native interface, was fabricated. Cell proliferation, viability, and chondrogenic differentiation were evaluated in vitro. The C/G-MS constructs were further examined to determine the potential of regenerating a continuous interface with gradual transition of teno-, fibrocartilage- and osteo-like tissues in vivo.

Results

In vitro tests confirmed the good cytocompatibility of the constructs. After seven days in culture, cellular microfilament staining indicated that not only could cells well proliferate in GelMA hydrogels ​but also efficiently attach to and grow on scaffold fibres. Moreover, by immunolocalizing collagen type II, chondrogenesis was identified in the intermediate phase of the C/G-MS construct that had been treated with transforming growth factor β3 for 21 days. After subcutaneous implantation in mice, the C/G-MS construct exhibited a heterogeneous and graded structure up to eight weeks, with distinguished matrix distribution observed at one week. Overall, gene expression of tenogenic, chondrogenic, and osteogenic markers showed increasing patterns for eight weeks. Among them, expression of collagen type X gene was found drastically increasing during eight weeks, indicating progressive formation of calcifying cartilage within the constructs.

Conclusion

Our findings demonstrate that the stratified manner of fabrication based on the 3D-printed multiphasic scaffold is an effective strategy for tendon-to-bone interface engineering in terms of efficient cell seeding, chondrogenic potential, and distinct matrix deposition in varying phases.

The translational potential of this article

We fabricated a biomimetic tendon-to-bone interface by using a 3D-printed multiphasic scaffold and adopting a stratified cell-seeding manner with GelMA. The biomimetic interface might have applications in tendon-to-bone repair in the rotator cuff. It can not only be an alternative to a biological fixation device ​but also offer an ex vivo living graft to replace the damaged enthesis.

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.

A Practical Guide for the Current Use of Biologic Therapies in Sports Medicine

Over the past decade, there has been an increased interest in the use of biologic therapies in sports medicine. Although these technologies are in relatively early stages of development, there have been substantial increases in marketing, patient demand, and clinical utilization of biologics, including platelet-rich plasma, bone marrow aspirate concentrate, and other cell-derived therapies. Direct-to-consumer marketing of biologics has also proliferated but is largely unregulated, and clinicians must accurately convey the safety and efficacy profiles of these therapies to patients. Because most insurance companies consider biologic treatments to be experimental or investigational for orthopaedic applications given the lack of high-quality evidence to support their efficacy, patients receiving these treatments often make substantial out-of-pocket payments. With a range of treatment costs among centers offering biologics, there is a need for appropriate and sustainable pricing and reimbursement models. Clinicians utilizing biologics must also have a thorough understanding of the recently clarified Food and Drug Administration guidelines that regulate the clinical use of cell and tissue products. There is a lack of consensus on the optimal preparation, source, delivery method, and dosing of biologic therapies, which has been exacerbated by a lack of sufficient experimental detail in most published studies. Future research must better identify the biologic target of treatment, adhere to better standards of reporting, and better integrate researchers, industry, and regulatory bodies to optimize applications.

The "other" 15-40%: The Role of Non-Collagenous Extracellular Matrix Proteins and Minor Collagens in Tendon

Extracellular matrix (ECM) determines the physiological function of all tissues, including musculoskeletal tissues. In tendon, ECM provides overall tissue architecture, which is tailored to match the biomechanical requirements of their physiological function, that is, force transmission from muscle to bone. Tendon ECM also constitutes the microenvironment that allows tendon-resident cells to maintain their phenotype and that transmits biomechanical forces from the macro-level to the micro-level. The structure and function of adult tendons is largely determined by the hierarchical organization of collagen type I fibrils. However, non-collagenous ECM proteins such as small leucine-rich proteoglycans (SLRPs), ADAMTS proteases, and cross-linking enzymes play critical roles in collagen fibrillogenesis and guide the hierarchical bundling of collagen fibrils into tendon fascicles. Other non-collagenous ECM proteins such as the less abundant collagens, fibrillins, or elastin, contribute to tendon formation or determine some of their biomechanical properties. The interfascicular matrix or endotenon and the outer layer of tendons, the epi- and paratenon, includes collagens and non-collagenous ECM proteins, but their function is less well understood. The ECM proteins in the epi- and paratenon may provide the appropriate microenvironment to maintain the identity of distinct tendon cell populations that are thought to play a role during repair processes after injury. The aim of this review is to provide an overview of the role of non-collagenous ECM proteins and less abundant collagens in tendon development and homeostasis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:23-35, 2020.

Development of a novel automatable fabrication method based on electrospinning co electrospraying for rotator cuff augmentation patches

Rotator cuff tear is one of the most common shoulder diseases. Rotator cuff augmentation (RCA) is trying to solve the high retear failure percentage after the surgery procedures (20-90%). The ideal augmentation patch must provide a temporal mechanical support during the healing process. In this work, we proposed a simple method for the fabrication of synthetic RCA patches. This method combines the use of electrospraying to produce poly-L-lactic-co-ε-caprolactone (PLC) films in an organogel form and electrospinning to produce poly(lactic) acid (PLA) nanofibers. The device consists in a combination of layers, creating a multilayered construct, enabling the possibility of tuning its mechanical properties and thickness. Besides, both techniques are simple to escalate for industrial production. A complete characterization has been performed to optimize the involved number of layers and production time of PLC films and PLA nanofibers fabrication, obtaining a final optimal configuration for RCA devices. Structural, mechanical and suture properties were evaluated. Also, the possibility of surface functionalization to improve the bioactivity of the scaffold was studied, adding aligned electrospun PLA nanofibers on the surface of the device to mimic the natural tendon topography. Surface modification was characterized by culturing adult normal human dermal fibroblasts. Lack of toxicity was detected for material presented, and cell alignment shape orientation guided by aligned fibers, mimicking tendon structure, was obtained. Cell proliferation and protein production were also evaluated.

Pro-chondrogenic and immunomodulatory melatonin-loaded electrospun membranes for tendon-to-bone healing

Reconstructing the native structure of the tendon-to-bone insertion site (enthesis) in rotator cuff repair has always been a great challenge for orthopedic surgeons. Difficulty arises mainly due to the limited enthesis regenerative capability and severe inflammatory cell infiltration, which result in fibrovascular scar formation instead of native cartilage-like enthesis. Therefore, tissue engineering scaffolds with pro-chondrogenic and immunomodulatory capabilities may offer a new strategy for native enthesis regeneration. In this study, melatonin-loaded aligned polycaprolactone (PCL) electrospun fibrous membranes were fabricated. The sustained release of melatonin from this membrane significantly promoted the chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs) in a long-term chondroid pellet model. After the membranes were implanted in a rat acute rotator cuff tear model, melatonin-loaded PCL membranes inhibited macrophage infiltration in the tendon-to-bone interface at the early healing phase, increasing chondroid zone formation, promoting collagen maturation, decreasing fibrovascular tissue formation and eventually improving the biomechanical strength of the regenerated enthesis. Taken together, melatonin-loaded PCL membranes possess great clinical application potential for tendon-to-bone healing.

Nanofiber-based matrices for rotator cuff regenerative engineering

The rotator cuff consists of a cuff of soft tissue responsible for rotating the shoulder. Rotator cuff tendon tears are responsible for a significant source of disability and pain in the adult population. Most rotator cuff tendon tears occur at the bone-tendon interface. Tear size, patient age, fatty infiltration of muscle, have a major influence on the rate of retear after surgical repair. The high incidence of retears (up to 94% in some studies) after surgery makes rotator cuff injuries a critical musculoskeletal problem to address. The limitations of current treatments motivate regenerative engineering approaches for rotator cuff regeneration. Various fiber-based matrices are currently being investigated due to their structural similarity with native tendons and their ability to promote regeneration. This review will discuss the current approaches for rotator cuff regeneration, recent advances in fabrication and enhancement of nanofiber-based matrices and the development and use of complex nano/microstructures for rotator cuff regeneration. STATEMENT OF SIGNIFICANCE: Regeneration paradigms for musculoskeletal tissues involving the rotator cuff of the shoulder have received great interest. Novel technologies based on nanomaterials have emerged as possible robust solutions for rotator cuff injury and treatment due to structure/property relationships. The aim of the review submitted is to comprehensively describe and evaluate the development and use of nano-based material technologies for applications to rotator cuff tendon healing and regeneration.

Tendon healing affects the multiscale mechanical, structural and compositional response of tendon to quasi-static tensile loading

Tendon experiences a variety of multiscale changes to its extracellular matrix during mechanical loading at the fascicle, fibre and fibril levels. For example, tensile loading of tendon increases its stiffness, with organization of collagen fibres, and increases cell strain in the direction of loading. Although applied macroscale strains correlate to cell and nuclear strains in uninjured tendon, the multiscale response during tendon healing remains unknown and may affect cell mechanosensing and response. Therefore, this study evaluated multiscale structure-function mechanisms in response to quasi-static tensile loading in uninjured and healing tendons. We found that tendon healing affected the macroscale mechanical and structural response to mechanical loading, evidenced by decreases in strain stiffening and collagen fibre realignment. At the micro- and nanoscales, healing resulted in increased collagen fibre disorganization, nuclear disorganization, decreased change in nuclear aspect ratio with loading, and decreased indentation modulus compared to uninjured tendons. Taken together, this work supports a new concept of nuclear strain transfer attenuation during tendon healing and identifies several multiscale properties that may contribute. Our work also provides benchmarks for the biomechanical microenvironments that tendon cells may experience following cell delivery therapies.

Overlay repair with a synthetic collagen scaffold improves the quality of healing in a rat rotator cuff repair model

BACKGROUND

Augmenting repairs with extracellular matrix-based scaffolds is a common option for rotator cuff tears. In this study, a new collagen scaffold was assessed for its efficacy in augmenting rotator cuff repair.

METHODS

The collagen scaffold was assessed in vitro for cytocompatibility and retention of tenocyte phenotype using alamarBlue assays, fluorescent imaging, and real-time polymerase chain reaction. Immunogenicity was assessed in vitro by the activation of human monocytes. In vivo, by use of a modified rat rotator cuff defect model, supraspinatus tendon repairs were carried out in 40 animals. Overlay augmentation with the collagen scaffold was compared with unaugmented repairs. At 6 and 12 weeks postoperatively, the repairs were tested biomechanically to evaluate repair strength, as well as histologically to assess quality of healing.

RESULTS

The collagen scaffold supported human tendon-derived cell growth in vitro, with cells demonstrating proliferation and appearing morphologically tenocytic over the experimental period. No immunogenic responses were provoked compared with suture material control. In vivo, augmentation with the scaffold improved the histologic scores at 12 weeks (8.4 of 15 vs 6.4 of 15, P = .032). However, no significant difference was detected with mechanical testing.

CONCLUSION

The new collagen scaffold was supportive of cell growth in vitro and generated a minimal acute inflammatory response. In vivo, we observed an improvement in the histologic appearance of the repair at 12 weeks. However, a meaningful increase in biomechanical strength was not achieved. Further modification and improvement of the scaffold are required prior to consideration for clinical use.

Promoting tendon to bone integration using graphene oxide-doped electrospun poly(lactic-co-glycolic acid) nanofibrous membrane

Background

These normal entheses are not reestablished after repair despite significant advances in surgical techniques. There is a significant need to develop integrative biomaterials, facilitating functional tendon-to-bone integration.

Materials and methods

We fabricated a highly interconnective graphene oxide-doped electrospun poly(lactide-co-glycolide acid) (GO-PLGA) nanofibrous membrane by electrospinning technique and evaluated them using in vitro cell assays. Then, we established rabbit models, the PLGA and GO-PLGA nanofibrous membranes were used to augment the rotator cuff repairs. The animals were killed postoperatively, which was followed by micro-computed tomography, histological and biomechanical evaluation.

Results

GO was easily mixed into PLGA filament without changing the three dimensional microstructure. An in vitro evaluation demonstrated that the PLGA membranes incorporated with GO accelerated the proliferation of BMSCs and furthered the Osteogenic differentiation of BMSCs. In addition, an in vivo assessment further revealed that the local application of GO-PLGA membrane to the gap between the tendon and the bone in a rabbit model promoted the healing enthesis, increased new bone and cartilage generation, and improved collagen arrangement and biomechanical properties in comparison with repair with PLGA only.

Conclusion

The electrospun GO-PLGA fibrous membrane provides an effective approach for the regeneration of tendon to bone enthesis.

Reduced Myogenic and Increased Adipogenic Differentiation Capacity of Rotator Cuff Muscle Stem Cells

BACKGROUND

Fat accumulation commonly occurs in chronically torn rotator cuff muscles, and increased fat within the rotator cuff is correlated with poor clinical outcomes. The extent of lipid deposition is particularly pronounced in injured rotator cuff muscles compared with other commonly injured muscles such as the gastrocnemius. Satellite cells, which are a tissue-resident muscle stem-cell population, can differentiate into fat cells. We hypothesized that satellite cells from the rotator cuff have greater intrinsic adipogenic differentiation potential than do gastrocnemius satellite cells, and this difference is due to variations in epigenetic imprinting between the cells.

METHODS

Satellite cells from gastrocnemius and rotator cuff muscles of mice were cultured in adipogenic media, and the capacity to differentiate into mature muscle cells and adipogenic cells was assessed (n ≥ 9 plates per muscle group). We also performed DNA methylation analysis of gastrocnemius and rotator cuff satellite cells to determine whether epigenetic differences were present between the 2 groups (n = 5 mice per group).

RESULTS

Compared with the gastrocnemius, satellite cells from the rotator cuff had a 23% reduction in myogenic differentiation and an 87% decrease in the expression of the differentiated muscle cell marker MRF4 (myogenic regulatory factor 4). With respect to adipogenesis, rotator cuff satellite cells had a 4.3-fold increase in adipogenesis, a 12-fold increase in the adipogenic transcription factor PPARγ (peroxisome proliferator-activated receptor gamma), and a 65-fold increase in the adipogenic marker FABP4 (fatty-acid binding protein 4). Epigenetic analysis identified 355 differentially methylated regions of DNA between rotator cuff and gastrocnemius satellite cells, and pathway enrichment analysis suggested that these regions were involved with lipid metabolism and adipogenesis.

CONCLUSIONS

Satellite cells from rotator cuff muscles have reduced myogenic and increased adipogenic differentiation potential compared with gastrocnemius muscles. There appears to be a cellular and genetic basis behind the generally poor rates of rotator cuff muscle healing.

CLINICAL RELEVANCE

The reduced myogenic and increased adipogenic capacity of rotator cuff satellite cells is consistent with the increased fat content and poor muscle healing rates often observed for chronically torn rotator cuff muscles. For patients undergoing rotator cuff repair, transplantation of autologous satellite cells from other muscles less prone to fatty infiltration may improve clinical outcomes.