Doxycycline-mediated inhibition of matrix metalloproteinases improves healing after rotator cuff repair

TGF-β1 Improves Biomechanical Strength by Extracellular Matrix Accumulation Without Increasing the Number of Tenogenic Lineage Cells in a Rat Rotator Cuff Repair Model

BACKGROUND

Transforming growth factor β1 (TGF-β1) positively regulates the tenogenic marker genes scleraxis ( Scx) and tenomodulin ( Tnmd) in mesenchymal progenitors in vitro. However, little is known about the effect of TGF-β1 on the expression of tenogenic markers during rotator cuff (RC) healing in rats.

HYPOTHESIS

TGF-β1 improves the biomechanical properties and histological maturity of reparative tissue in a rat RC repair model by stimulating the growth of tenogenic cells.

STUDY DESIGN

Controlled laboratory study.

METHODS

Adult male Sprague-Dawley rats (N = 180) underwent unilateral supraspinatus tendon-to-bone surgical repair and were randomly treated with a gelatin hydrogel presoaked in TGF-β1 (100 ng) or phosphate-buffered saline. The effects of TGF-β1 on RC healing were investigated at 2, 4, 6, 8, and 12 weeks postoperatively by immunostaining for proliferating cell nuclear antigen, by real-time reverse transcription polymerase chain reaction and in situ hybridization or immunostaining for enthesis-related markers (SRY-box containing gene 9 [ Sox9], Scx, and Tnmd), and by real-time reverse transcription polymerase chain reaction and immunostaining for type I and III collagen. At 6 and 12 weeks postoperatively, biomechanical testing, micro-computed tomography, and biochemical analysis were also performed. At 2 and 4 weeks postoperatively, mesenchymal stem cell-related markers, phospho-Smad2, and matrix metalloproteinase 9 (MMP-9) and MMP-13 were assessed by immunostaining.

RESULTS

The TGF-β1-treated group had significantly higher ultimate load to failure and tissue volume at 6 and 12 weeks postoperatively and a higher collagen content at 12 weeks compared with the saline group. Tendon-related gene expression, histological maturity, cell proliferation, and mesenchymal stem cell-related marker immunoreactivity were not affected by exogenously administrated TGF-β1 at all time points. In the TGF-β1-treated group, the percentage of phospho-Smad2-positive cells within the healing tissue increased, whereas the expression of MMP-9 and MMP-13 significantly decreased at 2 and 4 weeks postoperatively.

CONCLUSION

TGF-β1 enhances formation of tough fibrous tissues at the healing site by inhibiting MMP-9 and MMP-13 expression to increase collagen accumulation but without the growth of tenogenic lineage cells.

CLINICAL RELEVANCE

These findings suggest that TGF-β1 could be used for enhancing biomechanical strength after RC surgical repair.

Tendon stem/progenitor cells regulate inflammation in tendon healing via JNK and STAT3 signaling

Tendon stem/progenitor cells (TSCs) have been found in different anatomic locations and showed a promising regenerative potential. We identified a role of TSCs in the regulation of inflammation during healing of acute tendon injuries. Delivery of connective tissue growth factor (CTGF) into full-transected rat patellar tendons significantly increased the number of CD146⁺ TSCs, leading to enhanced healing. In parallel, CTGF delivery significantly reduced the number of iNOS⁺ M1 macrophages and increased the expression of anti-inflammatory IL-10 at 2 d after surgery, with over 85% CD146⁺ TSCs expressing IL-10. By 1 wk, the elevated IL-10 expression remained, and IL-6 expression was significantly attenuated in CTGF-delivered tendon healing. Matrix metalloproteinase (MMP)-3 expression in CTGF-delivered tendon was organized along with the reorienting collagen fibers by 1 wk after surgery, in comparison with the control group showing the abundant MMP-3 expression localized at healing junction. Tissue inhibitor of metalloprotease (TIMP)-3 was expressed in CD146⁺ TSCs at 1 wk with CTGF, in contrast to control with no TIMP-3 expression. In vitro, IL-10 expression was detected only when tendon cells were stimulated with IL-1β, and CTGF and significantly higher in CD146⁺ TSCs than CD146^- tendon cells. Similarly, TIMP-3 expression was detected only when treated with CTGF or CTGF and IL-1β that is significantly higher in CD146⁺ TSCs compared to CD146^- tendon cells. Signaling study with specific inhibitors and Western blot analysis demonstrated that CTGF-induced expression of IL-10 and TIMP-3 in CD146⁺ TSCs are regulated by JNK/signal transducer and activator of transcription 3 signaling. Taken together, these findings suggest anti-inflammatory roles of CTGF-stimulated TSCs that are likely associated with improved tendon healing.-Tarafder, S., Chen, E., Jun, Y., Kao, K., Sim, K. H., Back, J., Lee, F. Y., Lee, C. H. Tendon stem/progenitor cells regulate inflammation in tendon healing via JNK and STAT3 signaling.

Effectiveness of Biologic Factors in Shoulder Disorders

Background:

Shoulder pathology can cause significant pain, discomfort, and loss of function that all interfere with activities of daily living and may lead to poor quality of life. Primary osteoarthritis and rotator cuff diseases with its sequalae are the main culprits. Management of shoulder disorders using biological factors gained an increasing interest over the last years. This interest reveals the need of effective treatments for shoulder degenerative disorders, and highlights the importance of a comprehensive and detailed understanding of the rapidly increasing knowledge in the field.

Methods:

This study will describe most of the available biology-based strategies that have been recently developed, focusing on their effectiveness in animal and clinical studies.

Results:

Data from in vitro work will also be briefly presented; in order to further elucidate newly acquired knowledge regarding mechanisms of tissue degeneration and repair that would probably drive translational work in the next decade. The role of platelet rich-plasma, growth factors, stem cells and other alternative treatments will be described in an evidence-based approach, in an attempt to provide guidelines for their clinical application. Finally, certain challenges that biologic treatments face today will be described as an initiative for future strategies.

Conclusion:

The application of different growth factors and mesenchymal stem cells appears as promising approaches for enhancing biologic repair. However, data from clinical studies are still limited, and future studies need to improve understanding of the repair process in cellular and molecular level and evaluate the effectiveness of biologic factors in the management of shoulder disorders.

The Rotator Cuff Organ: Integrating Developmental Biology, Tissue Engineering, and Surgical Considerations to Treat Chronic Massive Rotator Cuff Tears

The torn rotator cuff remains a persistent orthopedic challenge, with poor outcomes disproportionately associated with chronic, massive tears. Degenerative changes in the tissues that comprise the rotator cuff organ, including muscle, tendon, and bone, contribute to the poor healing capacity of chronic tears, resulting in poor function and an increased risk for repair failure. Tissue engineering strategies to augment rotator cuff repair have been developed in an effort to improve rotator cuff healing and have focused on three principal aims: (1) immediate mechanical augmentation of the surgical repair, (2) restoration of muscle quality and contractility, and (3) regeneration of native enthesis structure. Work in these areas will be reviewed in sequence, highlighting the relevant pathophysiology, developmental biology, and biomechanics, which must be considered when designing therapeutic applications. While the independent use of these strategies has shown promise, synergistic benefits may emerge from their combined application given the interdependence of the tissues that constitute the rotator cuff organ. Furthermore, controlled mobilization of augmented rotator cuff repairs during postoperative rehabilitation may provide mechanotransductive cues capable of guiding tissue regeneration and restoration of rotator cuff function. Present challenges and future possibilities will be identified, which if realized, may provide solutions to the vexing condition of chronic massive rotator cuff tears.

Editorial Commentary: Should I Order Prophylactic Antibiotics for My Next Knee Scope?

Postoperative infections are going to happen. The question of whether prophylactic antibiotics can lower the infection rate in routine knee arthroscopy is investigated. Although a large number of cases were included in the study, the results did not reach statistical significance. Nevertheless, a significant trend toward a lower incidence of deep infection was seen when antibiotics were given.

Nanoparticulate delivery of agents for induced elastogenesis in three-dimensional collagenous matrices

The degradation of elastic matrix in the infrarenal aortic wall is a critical parameter underlying the formation and progression of abdominal aortic aneurysms. It is mediated by the chronic overexpression of matrix metalloprotease (MMP)-2 and MMP-9, leading to a progressive loss of elasticity and weakening of the aortic wall. Delivery of therapeutic agents to inhibit MMPs, while concurrently coaxing cell-based regenerative repair of the elastic matrix represents a potential strategy for slowing or arresting abdominal aortic aneurysm growth. Previous studies have demonstrated elastogenic induction of healthy and aneurysmal aortic smooth muscle cells and inhibition of MMPs, following exogenous delivery of elastogenic factors such as transforming growth factor (TGF)-β1, as well as MMP-inhibitors such as doxycycline (DOX) in two-dimensional culture. Based on these findings, and others that demonstrated elastogenic benefits of nanoparticulate delivery of these agents in two-dimensional culture, poly(lactide-co-glycolide) nanoparticles were developed for localized, controlled and sustained delivery of DOX and TGF-β1 to human aortic smooth muscle cells within a three-dimensional gels of type I collagen, which closely simulate the arterial tissue microenvironment. DOX and TGF-β1 released from these nanoparticles influenced elastogenic outcomes positively within the collagen constructs over 21 days of culture, which were comparable to that induced by exogenous supplementation of DOX and TGF-β1 within the culture medium. However, this was accomplished at doses ~20-fold lower than the exogenous dosages of the agents, illustrating that their localized, controlled and sustained delivery from nanoparticles embedded within a three-dimensional scaffold is an efficient strategy for directed elastogenesis. Copyright © 2014 John Wiley & Sons, Ltd.

Icariin Promotes Tendon-Bone Healing during Repair of Rotator Cuff Tears: A Biomechanical and Histological Study

To investigate whether the systematic administration of icariin (ICA) promotes tendon-bone healing after rotator cuff reconstruction in vivo, a total of 64 male Sprague Dawley rats were used in a rotator cuff injury model and underwent rotator cuff reconstruction (bone tunnel suture fixation). Rats from the ICA group (n = 32) were gavage-fed daily with ICA at 0.125 mg/g, while rats in the control group (n = 32) received saline only. Micro-computed tomography, biomechanical tests, serum ELISA (calcium; Ca, alkaline phosphatase; AP, osteocalcin; OCN) and histological examinations (Safranin O and Fast Green staining, type I, II and III collagen (Col1, Col2, and Col3), CD31, and vascular endothelial growth factor (VEGF)) were analyzed two and four weeks after surgery. In the ICA group, the serum levels of AP and OCN were higher than in the control group. More Col1-, Col2-, CD31-, and VEGF-positive cells, together with a greater degree of osteogenesis, were detected in the ICA group compared with the control group. During mechanical testing, the ICA group showed a significantly higher ultimate failure load than the control group at both two and four weeks. Our results indicate that the systematic administration of ICA could promote angiogenesis and tendon-bone healing after rotator cuff reconstruction, with superior mechanical strength compared with the controls. Treatment for rotator cuff injury using systematically-administered ICA could be a promising strategy.

Advances in biologic augmentation for rotator cuff repair

Rotator cuff tear is a very common shoulder injury that often necessitates surgical intervention for repair. Despite advances in surgical techniques for rotator cuff repair, there is a high incidence of failure after surgery because of poor healing capacity attributed to many factors. The complexity of tendon-to-bone integration inherently presents a challenge for repair because of a large biomechanical mismatch between the tendon and bone and insufficient regeneration of native tissue, leading to the formation of fibrovascular scar tissue. Therefore, various biological augmentation approaches have been investigated to improve rotator cuff repair healing. This review highlights recent advances in three fundamental approaches for biological augmentation for functional and integrative tendon-bone repair. First, the exploration, application, and delivery of growth factors to improve regeneration of native tissue are discussed. Second, applications of stem cell and other cell-based therapies to replenish damaged tissue for better healing are covered. Finally, this review will highlight the development and applications of compatible biomaterials to both better recapitulate the tendon-bone interface and improve delivery of biological factors for enhanced integrative repair.

The Role of Platelet Rich Plasma (PRP) and Other Biologics for Rotator Cuff Repair

BACKGROUND

Surgical treatment of rotator cuff tears has consistently demonstrated good clinical and functional outcomes. However, in some cases, the rotator cuff fails to heal. While improvements in rotator cuff constructs and biomechanics have been made, the role of biologics to aid healing is currently being investigated.

METHODS

A selective literature search was performed and personal surgical experiences are reported.

RESULTS

Biologic augmentation of rotator cuff repairs can for example be performed wtableith platelet-rich plasma (PRP) and mesenchymal stem cells (MSCs). Clinical results on PRP application have been controversial. Application of MSCs has shown promise in animal studies, but clinical data on its effectiveness is presently lacking. The role of Matrix Metalloproteinase (MMP) inhibitors is another interesting field for potential targeted drug therapy after rotator cuff repair.

CONCLUSIONS

Large randomized clinical studies need to confirm the benefit of these approaches, in order to eventually lower retear rates and improve clinical outcomes after rotator cuff repair.

AAOS Research Symposium Updates and Consensus: Biologic Treatment of Orthopaedic Injuries

Strategies that seek to enhance musculoskeletal tissue regeneration and repair by modulating the biologic microenvironment at the site of injury have considerable therapeutic potential. Current and emerging biologic approaches include the use of growth factors, platelet-rich plasma, stem cell therapy, and scaffolds. The American Academy of Orthopaedic Surgeons hosted a research symposium in November 2015 to review the current state-of-the-art biologic treatments of articular cartilage, muscle, tendon, and bone injuries and identify knowledge gaps related to these emerging treatments. This review outlines the findings of the symposium and summarizes the consensus reached on how best to advance research on biologic treatment of orthopaedic injuries.

Vitamin D and the immunomodulation of rotator cuff injury

Tendon-to-bone healing after rotator cuff repair surgery has a failure rate of 20%–94%. There has been a recent interest to determine the factors that act as determinants between successful and unsuccessful rotator cuff repair. Vitamin D level in patients is one of the factors that have been linked to bone and muscle proliferation and healing, and it may have an effect on tendon-to-bone healing. The purpose of this article is to critically review relevant published research that relates to the effect of vitamin D on rotator cuff tears and subsequent healing. A review of the literature was conducted to identify all studies that investigate the relationship between vitamin D and tendon healing, in addition to its mechanism of action. The data were then analyzed in order to summarize what is currently known about vitamin D, rotator cuff pathology, and tendon-to-bone healing. The activated metabolite of vitamin D, 1α,25-dihydroxyvitamin D₃, affects osteoblast proliferation and differentiation. Likewise, vitamin D plays a significant role in the tendon-to-bone healing process by increasing the bone mineral density and strengthening the skeletal muscles. The 1α,25-dihydroxyvitamin D₃ binds to vitamin D receptors on myocytes to stimulate growth and proliferation. The form of vitamin D produced by the liver, calcifediol, is a key initiator of the myocyte healing process by moving phosphate into myocytes, which improves function and metabolism. Investigation into the effect of vitamin D on tendons has been sparse, but limited studies have been promising. Matrix metalloproteinases play an active role in remodeling the extracellular matrix (ECM) of tendons, particularly deleterious remodeling of the collagen fibers. Also, the levels of transforming growth factor-β3 positively influence the success of the surgery for rotator cuff repair. In the tendon-to-bone healing process, vitamin D has been shown to successfully influence bone and muscle healing, but more research is needed to delve into the mechanisms of vitamin D as a factor in skeletal tendon health and healing.

Association of synovial inflammation and inflammatory mediators with glenohumeral rotator cuff pathology

HYPOTHESIS

We hypothesized that patients with full-thickness rotator cuff tears would have greater synovial inflammation compared with those without rotator cuff tear pathology, with gene expression relating to histologic findings.

METHODS

Synovial sampling was performed in 19 patients with full-thickness rotator cuff tears (RTC group) and in 11 patients without rotator cuff pathology (control group). Cryosections were stained and examined under light microscopy and confocal fluorescent microscopy for anti-cluster CD45 (common leukocyte antigen), anti-CD31 (endothelial), and anti-CD68 (macrophage) cell surface markers. A grading system was used to quantitate synovitis under light microscopy, and digital image analysis was used to quantify the immunofluorescence staining area. Quantitative polymerase chain reaction was performed for validated inflammatory markers. Data were analyzed with analysis of covariance, Mann-Whitney U, and Spearman rank order testing, with significance set at α = .05.

RESULTS

The synovitis score was significantly increased in the RTC group compared with controls. Immunofluorescence demonstrated significantly increased staining for CD31, CD45, and CD68 in the RTC vs control group. CD45+/68- cells were found perivascularly, with CD45+/68+ cells toward the joint lining edge of the synovium. Levels of matrix metalloproteinase-3 (MMP-3) and interleukin-6 were significantly increased in the RTC group, with a positive correlation between the synovitis score and MMP-3 expression.

CONCLUSIONS

Patients with full-thickness rotator cuff tears have greater levels of synovial inflammation, angiogenesis, and MMP-3 upregulation compared with controls. Gene expression of MMP-3 correlates with the degree of synovitis.

Magnesium inference screw supports early graft incorporation with inhibition of graft degradation in anterior cruciate ligament reconstruction

Patients after anterior cruciate ligament (ACL) reconstruction surgery commonly encounters graft failure in the initial phase of rehabilitation. The inhibition of graft degradation is crucial for the successful reconstruction of the ACL. Here, we used biodegradable high-purity magnesium (HP Mg) screws in the rabbit model of ACL reconstruction with titanium (Ti) screws as a control and analyzed the graft degradation and screw corrosion using direct pull-out tests, microCT scanning, and histological and immunohistochemical staining. The most noteworthy finding was that tendon graft fixed by HP Mg screws exhibited biomechanical properties substantially superior to that by Ti screws and the relative area of collagen fiber at the tendon-bone interface was much larger in the Mg group, when severe graft degradation was identified in the histological analysis at 3 weeks. Semi-quantitative immunohistochemical results further elucidated that the MMP-13 expression significantly decreased surrounding HP Mg screws with relatively higher Collagen II expression. And HP Mg screws exhibited uniform corrosion behavior without displacement or loosening in the femoral tunnel. Therefore, our results demonstrated that Mg screw inhibited graft degradation and improved biomechanical properties of tendon graft during the early phase of graft healing and highlighted its potential in ACL reconstruction.

Biologic Treatments for Sports Injuries II Think Tank-Current Concepts, Future Research, and Barriers to Advancement, Part 2: Rotator Cuff

Rotator cuff tears are common and result in considerable morbidity. Tears within the tendon substance or at its insertion into the humeral head represent a considerable clinical challenge because of the hostile local environment that precludes healing. Tears often progress without intervention, and current surgical treatments are inadequate. Although surgical implants, instrumentation, and techniques have improved, healing rates have not improved, and a high failure rate remains for large and massive rotator cuff tears. The use of biologic adjuvants that contribute to a regenerative microenvironment have great potential for improving healing rates and function after surgery. This article presents a review of current and emerging biologic approaches to augment rotator cuff tendon and muscle regeneration focusing on the scientific rationale, preclinical, and clinical evidence for efficacy, areas for future research, and current barriers to advancement and implementation.

Tracking of autologous adipose tissue-derived mesenchymal stromal cells with in vivo magnetic resonance imaging and histology after intralesional treatment of artificial equine tendon lesions--a pilot study

BACKGROUND

Adipose tissue-derived mesenchymal stromal cells (AT-MSCs) are frequently used to treat equine tendinopathies. Up to now, knowledge about the fate of autologous AT-MSCs after intralesional injection into equine superficial digital flexor tendons (SDFTs) is very limited. The purpose of this study was to monitor the presence of intralesionally injected autologous AT-MSCs labelled with superparamagnetic iron oxide (SPIO) nanoparticles and green fluorescent protein (GFP) over a staggered period of 3 to 9 weeks with standing magnetic resonance imaging (MRI) and histology.

METHODS

Four adult warmblood horses received a unilateral injection of 10 × 10(6) autologous AT-MSCs into surgically created front-limb SDFT lesions. Administered AT-MSCs expressed lentivirally transduced reporter genes for GFP and were co-labelled with SPIO particles in three horses. The presence of AT-MSCs in SDFTs was evaluated by repeated examinations with standing low-field MRI in two horses and post-mortem in all horses with Prussian blue staining, fluorescence microscopy and with immunofluorescence and immunohistochemistry using anti-GFP antibodies at 3, 5, 7 and 9 weeks after treatment.

RESULTS

AT-MSCs labelled with SPIO particles were detectable in treated SDFTs during each MRI in T2*- and T1-weighted sequences until the end of the observation period. Post-mortem examinations revealed that all treated tendons contained high numbers of SPIO- and GFP-labelled cells.

CONCLUSIONS

Standing low-field MRI has the potential to track SPIO-labelled AT-MSCs successfully. Histology, fluorescence microscopy, immunofluorescence and immunohistochemistry are efficient tools to detect labelled AT-MSCs after intralesional injection into surgically created equine SDFT lesions. Intralesional injection of 10 × 10(6) AT-MSCs leads to the presence of high numbers of AT-MSCs in and around surgically created tendon lesions for up to 9 weeks. Integration of injected AT-MSCs into healing tendon tissue is an essential pathway after intralesional administration. Injection techniques have to be chosen deliberately to avoid reflux of the cell substrate injected. In vivo low-field MRI may be used as a non-invasive tool to monitor homing and engraftment of AT-MSCs in horses with tendinopathy of the SDFT.

Do Matrix Metalloproteases and Tissue Inhibitors of Metalloproteases in Tenocytes of the Rotator Cuff Differ with Varying Donor Characteristics?

An imbalance between matrix metalloproteases (MMPs) and the tissue inhibitors of metalloproteases (TIMPs) may have a negative impact on the healing of rotator cuff tears. The aim of the project was to assess a possible relationship between clinical and radiographic characteristics of patients such as the age, sex, as well as the degenerative status of the tendon and the MMPs and TIMPs in their tenocyte-like cells (TLCs). TLCs were isolated from ruptured supraspinatus tendons and quantitative Real-Time PCR and ELISA was performed to analyze the expression and secretion of MMPs and TIMPs. In the present study, MMPs, mostly gelatinases and collagenases such as MMP-2, -9 and -13 showed an increased expression and protein secretion in TLCs of donors with higher age or degenerative status of the tendon. Furthermore, the expression and secretion of TIMP-1, -2 and -3 was enhanced with age, muscle fatty infiltration and tear size. The interaction between MMPs and TIMPs is a complex process, since TIMPs are not only inhibitors, but also activators of MMPs. This study shows that MMPs and TIMPs might play an important role in degenerative tendon pathologies.

Tendon basic science: Development, repair, regeneration, and healing

Tendinopathy and tendon rupture are common and disabling musculoskeletal conditions. Despite the prevalence of these injuries, a limited number of investigators are conducting fundamental, basic science studies focused on understanding processes governing tendinopathies and tendon healing. Development of effective therapeutics is hindered by the lack of fundamental guiding data on the biology of tendon development, signal transduction, mechanotransduction, and basic mechanisms underlying tendon pathogenesis and healing. To propel much needed progress, the New Frontiers in Tendon Research Conference, co-sponsored by NIAMS/NIH, the Orthopaedic Research Society, and the Icahn School of Medicine at Mount Sinai, was held to promote exchange of ideas between tendon researchers and basic science experts from outside the tendon field. Discussed research areas that are underdeveloped and represent major hurdles to the progress of the field will be presented in this review. To address some of these outstanding questions, conference discussions and breakout sessions focused on six topic areas (Cell Biology and Mechanics, Functional Extracellular Matrix, Development, Mechano-biology, Scarless Healing, and Mechanisms of Injury and Repair), which are reviewed in this special issue and briefly presented in this review. Review articles in this special issue summarize the progress in the field and identify essential new research directions.

Tendon mechanobiology: Current knowledge and future research opportunities

Tendons mainly function as load-bearing tissues in the muscloskeletal system; transmitting loads from muscle to bone. Tendons are dynamic structures that respond to the magnitude, direction, frequency, and duration of physiologic as well as pathologic mechanical loads via complex interactions between cellular pathways and the highly specialized extracellular matrix. This paper reviews the evolution and current knowledge of mechanobiology in tendon development, homeostasis, disease, and repair. In addition, we review several novel mechanotransduction pathways that have been identified recently in other tissues and cell types, providing potential research opportunities in the field of tendon mechanobiology. We also highlight current methods, models, and technologies being used in a wide variety of mechanobiology research that could be investigated in the context of their potential applicability for answering some of the fundamental unanswered questions in this field. The article concludes with a review of the major questions and future goals discussed during the recent ORS/ISMMS New Frontiers in Tendon Research Conference held on September 10 and 11, 2014 in New York City.

Stem cell therapy in the management of shoulder rotator cuff disorders

Rotator cuff tears are frequent shoulder problems that are usually dealt with surgical repair. Despite improved surgical techniques, the tendon-to-bone healing rate is unsatisfactory due to difficulties in restoring the delicate transitional tissue between bone and tendon. It is essential to understand the molecular mechanisms that determine this failure. The study of the molecular environment during embryogenesis and during normal healing after injury is key in devising strategies to get a successful repair. Mesenchymal stem cells (MSC) can differentiate into different mesodermal tissues and have a strong paracrine, anti-inflammatory, immunoregulatory and angiogenic potential. Stem cell therapy is thus a potentially effective therapy to enhance rotator cuff healing. Promising results have been reported with the use of autologous MSC of different origins in animal studies: they have shown to have better healing properties, increasing the amount of fibrocartilage formation and improving the orientation of fibrocartilage fibers with less immunologic response and reduced lymphocyte infiltration. All these changes lead to an increase in biomechanical strength. However, animal research is still inconclusive and more experimental studies are needed before human application. Future directions include expanded stem cell therapy in combination with growth factors or different scaffolds as well as new stem cell types and gene therapy.

The effect of granulocyte-colony stimulating factor on rotator cuff healing after injury and repair

BACKGROUND

The failure rate of tendon-bone healing after repair of rotator cuff tears remains high. A variety of biologic- and cell-based therapies aimed at improving rotator cuff healing have been investigated, and stem cell-based techniques have become increasingly more common. However, most studies have focused on the implantation of exogenous cells, which introduces higher risk and cost. We aimed to improve rotator cuff healing by inducing endogenous stem cell mobilization with systemic administration of granulocyte-colony stimulating factor (G-CSF).

QUESTIONS/PURPOSES

We asked: (1) Does G-CSF administration increase local cellularity after acute rotator cuff repair? (2) Is there histologic evidence that G-CSF improved organization at the healing enthesis? (3) Does G-CSF administration improve biomechanical properties of the healing supraspinatus tendon-bone complex? (4) Are there micro-MRI-based observations indicating G-CSF-augmented tendon-bone healing?

METHODS

After creation of full-thickness supraspinatus tendon defects with immediate repair, 52 rats were randomized to control or G-CSF-treated groups. G-CSF was administered for 5 days after repair and rats were euthanized at 12 or 19 postoperative days. Shoulders were subjected to micro-MR imaging, stress relaxation, and load-to-failure as well as blinded histologic and histomorphometric analyses.

RESULTS

G-CSF-treated animals had significantly higher cellularity composite scores at 12 and 19 days compared with both control (12 days: 7.40 ± 1.14 [confidence interval {CI}, 5.98-8.81] versus 4.50 ± 0.57 [CI, 3.58-5.41], p = 0.038; 19 days: 8.00 ± 1.00 [CI, 6.75-9.24] versus 5.40 ± 0.89 [CI, 4.28-6.51], p = 0.023) and normal animals (12 days: p = 0.029; 19 days: p = 0.019). There was no significant difference between G-CSF-treated animals or control animals in ultimate stress (MPa) and strain, modulus (MPa), or yield stress (MPa) and strain at either 12 days (p = 1.000, p = 0.104, p = 1.000, p = 0.909, and p = 0.483, respectively) or 19 days (p = 0.999, p = 0.964, p = 1.000, p = 0.988, and p = 0.904, respectively). There was no difference in MRI score between G-CSF and control animals at either 12 days (2.7 ± 1.8 [CI, 1.08-4.24] versus 2.3 ± 1.8 [CI, 0.49-4.17], p = 0.623) or 19 days (2.5 ± 1.4 [CI, 1.05-3.94] versus 2.3 ± 1.5 [CI, 0.75-3.91], p = 0.737). G-CSF-treated animals exhibited significantly lower relative bone volume compared with normal animals in the entire humeral head (24.89 ± 3.80 [CI, 20.17-29.60) versus 32.50 ± 2.38 [CI, 29.99-35.01], p = 0.009) and at the supraspinatus insertion (25.67 ± 5.33 [CI, 19.04-32.29] versus 33.36 ± 1.69 [CI, 31.58-35.14], p = 0.027) at 12 days. Further analysis did not reveal any additional significant relationships with respect to regional bone volume or trabecular thickness between groups and time points (p > 0.05).

CLINICAL RELEVANCE

Postoperative stem cell mobilization agents may be an effective way to enhance rotator cuff repair. Future studies regarding the kinetics of mobilization, the homing capacity of mobilized cells to injured tissues, and the ability of homing cells to participate in regenerative pathways are necessary.

Peri-tunnel bone loss: does it affect early tendon graft to bone tunnel healing after ACL reconstruction?

PURPOSE

The clinical relevance and mechanisms of local bone loss early post-anterior cruciate ligament (ACL) reconstruction remain unclear. The early spatial and temporal changes of peri-tunnel bone, its molecular mechanisms and its relationships with graft-bone tunnel healing were investigated in a 12-week-old rat model.

METHODS

At various times, the reconstructed ACL complex was harvested for vivaCT imaging, biomechanical test, histology and immunohistochemical staining of CD68+ cells (a monocyte-macrophage lineage marker), MMP1 and MMP13.

RESULTS

The peri-tunnel bone resorbed simultaneously with improvement of graft-bone tunnel healing. There were 30.1 ± 17.4, 46.8 ± 10.5 and 81.5 ± 12.3 % loss of peri-tunnel BMD as well as 43.2 ± 21.7, 78.7 ± 8.5 and 92.4 ± 17.7 % loss of peri-tunnel bone volume/total volume (BV/TV) at week 6 at the distal femur, epiphysis and metaphysis of tibia, respectively. MMP1, MMP13 and CD68+ cells were expressed at the graft-bone tunnel interface and peri-tunnel bone and increased with time post-reconstruction at the tibia. The ultimate load and stiffness of the healing complex positively correlated with tibial tunnel bone formation and negatively correlated with tibial peri-tunnel bone. Tunnel BV/TV at the tibial metaphysis and epiphysis showed the highest correlation with ultimate load (ρ = 0.591; p = 0.001) and stiffness (ρ = 0.427; p = 0.026) of the complex, respectively.

CONCLUSION

There was time-dependent loss of peri-tunnel bone early post-reconstruction, with the greatest loss occurring at the tibial metaphysis. This was consistent with high expression of MMP1, MMP13 and CD68+ cells at the graft-bone tunnel interface and the peri-tunnel region. The significant loss of peri-tunnel bone, though not critically affecting early tunnel healing, suggested the need to protect the knee joint early post-reconstruction.

A hierarchical, stretchable and stiff fibrous biotemplate engineered using stagger-electrospinning for augmentation of rotator cuff tendon-healing

The regeneration of fibrocartilage at the tendon-bone insertion site in rotator cuff tears (RCTs) is challenging due to the complexity of its composition and mechanical properties. In this study, hierarchical, stretchable and stiff fibrous scaffolds composed of microfibers of poly(ε-caprolactone) (PCL) and nanofibers of chitosan (CS) were fabricated using stagger-electrospinning for the augmentation of RCT-healing. It was found that the composite PCL-CS scaffolds had significantly improved strength and failure strain compared to the control CS scaffolds and increased stiffness compared to the control PCL scaffolds. These scaffolds also showed enhanced hydrophilicity, water absorption and a faster degradation rate compared to the PCL scaffolds. Moreover, they demonstrated better fibroblast attachment and proliferation compared to the PCL scaffolds. Radiological and histological analysis revealed that the PCL-CS scaffolds enhanced new bone formation (mineralization) and collagen and glycosaminoglycan expression (major components of extracellular matrix) compared to the PCL scaffolds. Furthermore, the torn tissues at the tendon-bone insertion site regenerated with the PCL-CS scaffolds showed higher strength and failure strain as well as stiffness compared to those repaired using only the PCL scaffolds. The above mentioned results suggest that the hierarchical, stretchable and stiff fibrous scaffolds engineered using stagger-electrospinning have great potential for the augmentation of RCT-healing.

Inhibition of 5-LOX, COX-1, and COX-2 increases tendon healing and reduces muscle fibrosis and lipid accumulation after rotator cuff repair

BACKGROUND

The repair and restoration of function after chronic rotator cuff tears are often complicated by muscle atrophy, fibrosis, and fatty degeneration of the diseased muscle. The inflammatory response has been implicated in the development of fatty degeneration after cuff injuries. Licofelone is a novel anti-inflammatory drug that inhibits 5-lipoxygenase (5-LOX), as well as cyclooxygenase (COX)-1 and COX-2 enzymes, which play important roles in inducing inflammation after injuries. While previous studies have demonstrated that nonsteroidal anti-inflammatory drugs and selective inhibitors of COX-2 (coxibs) may prevent the proper healing of muscles and tendons, studies about bone and cartilage have demonstrated that drugs that inhibit 5-LOX concurrently with COX-1 and COX-2 may enhance tissue regeneration.

HYPOTHESIS

After the repair of a chronic rotator cuff tear in rats, licofelone would increase the load to failure of repaired tendons and increase the force production of muscle fibers.

STUDY DESIGN

Controlled laboratory study.

METHODS

Rats underwent supraspinatus release followed by repair 28 days later. After repair, rats began a treatment regimen of either licofelone or a vehicle for 14 days, at which time animals were euthanized. Supraspinatus muscles and tendons were then subjected to contractile, mechanical, histological, and biochemical analyses.

RESULTS

Compared with controls, licofelone-treated rats had a grossly apparent decrease in inflammation and increased fibrocartilage formation at the enthesis, along with a 62% increase in the maximum load to failure and a 51% increase in peak stress to failure. Licofelone resulted in a marked reduction in fibrosis and lipid content in supraspinatus muscles as well as reduced expression of several genes involved in fatty infiltration. Despite the decline in fibrosis and fat accumulation, muscle fiber specific force production was reduced by 23%.

CONCLUSION

The postoperative treatment of cuff repair with licofelone may reduce fatty degeneration and enhance the development of a stable bone-tendon interface, although decreases in muscle fiber specific force production were observed, and force production in fact declined.

CLINICAL RELEVANCE

This study demonstrates that the inhibition of 5-LOX, COX-1, and COX-2 modulates the healing process of repaired rotator cuff tendons. Although further studies are necessary, the treatment of patients with licofelone after cuff repair may improve the development of a stable enthesis and enhance postoperative outcomes.

The effect of diclofenac on matrix metalloproteinase levels in the rotator cuff

INTRODUCTION

Matrix metalloproteinases (MMPs) are involved in physiological events such as restructuring of the tissue, morphogenesis, wound healing and normal developmental process. Use of diclofenac sodium following rotator cuff repair can disrupt healing of tendon through acting on MMPs.

MATERIALS AND METHODS

Supraspinatus tendons of rats (n = 84) were detached from their insertion on humerus, and repaired to anatomic footprint. Rats were divided into study group (n = 42) and control group (n = 42). Study group received a dose of 1 mg/kg daily diclofenac sodium subcutaneously. The rats were killed at weeks 1, 3 and 6, and seven rats from each groups were included in biomechanical and immunohistological examinations. Immunohistological staining of MMP-2, MMP-3 and MMP13 were used.

RESULTS

Maximum load was reduced in the study group at the end of week 1 (8.76 vs. 5.28 N) (p = 0.01). MMP-3 level was statistically significantly lower in the study group at the end of week 1. MMP-13 level and stiffness decreased towards week 6 in the study group while in the control group the level of MMP-2 decreased towards week 6.

CONCLUSION

Diclofenac has an impact on the levels of MMP-2, MMP-3 and MMP-13, which are needed for normal healing process, and it can also lead to disruption of tendon healing.

Fluoroquinolones impair tendon healing in a rat rotator cuff repair model: a preliminary study

BACKGROUND

Recent studies suggest that fluoroquinolone antibiotics predispose tendons to tendinopathy and/or rupture. However, no investigations on the reparative capacity of tendons exposed to fluoroquinolones have been conducted.

HYPOTHESIS

Fluoroquinolone-treated animals will have inferior biochemical, histological, and biomechanical properties at the healing tendon-bone enthesis compared with controls.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ninety-two rats underwent rotator cuff repair and were randomly assigned to 1 of 4 groups: (1) preoperative (Preop), whereby animals received fleroxacin for 1 week preoperatively; (2) pre- and postoperative (Pre/Postop), whereby animals received fleroxacin for 1 week preoperatively and for 2 weeks postoperatively; (3) postoperative (Postop), whereby animals received fleroxacin for 2 weeks postoperatively; and (4) control, whereby animals received vehicle for 1 week preoperatively and for 2 weeks postoperatively. Rats were euthanized at 2 weeks postoperatively for biochemical, histological, and biomechanical analysis. All data were expressed as mean ± standard error of the mean (SEM). Statistical comparisons were performed using either 1-way or 2-way ANOVA, with P < .05 considered significant.

RESULTS

Reverse transcriptase quantitative polymerase chain reaction (RTqPCR) analysis revealed a 30-fold increase in expression of matrix metalloproteinase (MMP)-3, a 7-fold increase in MMP-13, and a 4-fold increase in tissue inhibitor of metalloproteinases (TIMP)-1 in the Pre/Postop group compared with the other groups. The appearance of the healing enthesis in all treated animals was qualitatively different than that in controls. The tendons were friable and atrophic. All 3 treated groups showed significantly less fibrocartilage and poorly organized collagen at the healing enthesis compared with control animals. There was a significant difference in the mode of failure, with treated animals demonstrating an intrasubstance failure of the supraspinatus tendon during testing. In contrast, only 1 of 10 control samples failed within the tendon substance. The healing enthesis of the Pre/Postop group displayed significantly reduced ultimate load to failure compared with the Preop, Postop, and control groups. There was no significant difference in load to failure in the Preop group compared with the Postop group. Pre/Postop animals demonstrated significantly reduced cross-sectional area compared with the Postop and control groups. There was also a significant reduction in area between the Preop and control groups.

CONCLUSION

In this preliminary study, fluoroquinolone treatment negatively influenced tendon healing.

CLINICAL RELEVANCE

These findings indicate that there was an active but inadequate repair response that has potential clinical implications for patients who are exposed to fluoroquinolones before tendon repair surgery.

Healing improvement after rotator cuff repair using gelatin-grafted poly(L-lactide) electrospun fibrous membranes

BACKGROUND

Rotator cuff tears (RCTs) are a common cause of shoulder pain and disability in middle and older age. Despite improvements in the understanding of this disease process and advances in surgical treatment, rotator cuff (RC) repair failure rates remain high. Insufficient healing capacity is likely the main factor for failure of reconstruction.

MATERIALS AND METHODS

We fabricated implantable biodegradable gelatin-grafted poly(L-lactide) (PLLA) fibrous membranes using electrospinning technology and evaluated them using in vitro cell proliferation assays. Then, we established chronic rat RCT models and randomly assigned rats into one of three groups. In group 1 (n = 48), the detached supraspinatus tendon was repaired to its anatomic footprint (transosseous repair). In groups 2 and 3, the rats underwent transosseous repair and were implanted with either pure PLLA membranes (n = 48) or gelatin-PLLA membranes (n = 48) to augment the repairs. The animals were killed at 2, 4, and 8 wk postoperatively, which was followed by histomorphometric and biomechanical evaluation.

RESULTS

Histologic observations revealed that gelatin-PLLA membranes have excellent biocompatibility and biodegradability. At 2, 4, and 8 wk postoperatively, the gelatin-PLLA membranes significantly increased the area of glycosaminoglycan staining at the tendon-bone interface compared with the control group (P < 0.05) and significantly improved collagen organization, as measured by birefringence under polarized light at the healing enthesis compared with the control and PLLA groups (P < 0.05). Biomechanical testing revealed that the gelatin-PLLA group had a greater ultimate load to failure and stiffness than the control group at 4 and 8 wk (P < 0.05). The gelatin-PLLA membranes had the highest stress of the healing enthesis.

CONCLUSIONS

Local application of gelatin-PLLA fibrous membranes to the healing tendon-bone interface after RC repair in a rat chronic RCT model was found to strengthen the healing enthesis, increase the area of fibrocartilage, and improve collagen organization compared with repair alone. Augmentation with gelatin-grafted PLLA may enhance healing after RC repair and might eventually lead to improvement of clinical surgical outcomes.

Effect of the Interposition of Calcium Phosphate Materials on Tendon-Bone Healing During Repair of Chronic Rotator Cuff Tear

BACKGROUND

The current nature of tendon-bone healing after rotator cuff (RC) repair is still the formation of granulation tissue at the tendon-bone interface rather than the formation of fibrocartilage, which is the crucial structure in native tendon insertion and can be observed after knee ligament reconstruction. The interposition of calcium phosphate materials has been found to be able to enhance tendon-bone healing in knee ligament reconstruction. However, whether the interposition of these kinds of materials can enhance tendon-bone healing or even change the current nature of tendon-bone healing after RC repair still needs to be explored.

HYPOTHESIS

The interposition of calcium phosphate materials during RC repair would enhance tendon-bone healing or change its current nature of granulation tissue formation into a more favorable process.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 144 male Sprague-Dawley rats underwent unilateral detachment of the supraspinatus tendon, followed by delayed repair after 3 weeks. The animals were allocated into 1 of 3 groups: (1) repair alone, (2) repair with Ca5(PO4)2SiO4 (CPS) bioceramic interposition, or (3) repair with hydroxyapatite (HA) bioceramic interposition at the tendon-bone interface. Animals were sacrificed at 2, 4, or 8 weeks postoperatively, and microcomputed tomography (micro-CT) was used to quantify the new bone formation at the repair site. New fibrocartilage formation and collagen organization at the tendon-bone interface was evaluated by histomorphometric analysis. Biomechanical testing of the supraspinatus tendon-bone complex was performed. Statistical analysis was performed using 1-way analysis of variance. Significance was set at P < .05.

RESULTS

The micro-CT analysis demonstrated remarkable osteogenic activity and osteoconductivity to promote new bone formation and ingrowth of CPS and HA bioceramic, with CPS bioceramic showing better results than HA. Histological observations indicated that CPS bioceramic had excellent biocompatibility and biodegradability. At early time points after the RC repair, CPS bioceramic significantly increased the area of fibrocartilage at the tendon-bone interface compared with the control and HA groups. Moreover, CPS and HA bioceramics had significantly improved collagen organization. Biomechanical tests indicated that the CPS and HA groups have greater ultimate load to failure and stiffness than the control group at 4 and 8 weeks, and the CPS specimens exhibited the maximum ultimate load to failure, stiffness, and stress of the healing enthesis.

CONCLUSION

Both CPS and HA bioceramics aid in cell attachment and proliferation and accelerate new bone formation, and CPS bioceramic has a more prominent effect on tendon-to-bone healing.

CLINICAL RELEVANCE

Local application of CPS and HA bioceramic at the tendon-bone interface shows promise in improving healing after rotator cuff tear repair.

Biological augmentation of rotator cuff repair using bFGF-loaded electrospun poly(lactide-co-glycolide) fibrous membranes

Clinically, rotator cuff tear (RCT) is among the most common shoulder pathologies. Despite significant advances in surgical techniques, the re-tear rate after rotator cuff (RC) repair remains high. Insufficient healing capacity is likely the main factor for reconstruction failure. This study reports on a basic fibroblast growth factor (bFGF)-loaded electrospun poly(lactide-co-glycolide) (PLGA) fibrous membrane for repairing RCT. Implantable biodegradable bFGF-PLGA fibrous membranes were successfully fabricated using emulsion electrospinning technology and then characterized and evaluated with in vitro and in vivo cell proliferation assays and repairs of rat chronic RCTs. Emulsion electrospinning fabricated ultrafine fibers with a core-sheath structure which secured the bioactivity of bFGF in a sustained manner for 3 weeks. Histological observations showed that electrospun fibrous membranes have excellent biocompatibility and biodegradability. At 2, 4, and 8 weeks after in vivo RCT repair surgery, electrospun fibrous membranes significantly increased the area of glycosaminoglycan staining at the tendon-bone interface compared with the control group, and bFGF-PLGA significantly improved collagen organization, as measured by birefringence under polarized light at the healing enthesis compared with the control and PLGA groups. Biomechanical testing showed that the electrospun fibrous membrane groups had a greater ultimate load-to-failure and stiffness than the control group at 4 and 8 weeks. The bFGF-PLGA membranes had the highest ultimate load-to-failure, stiffness, and stress of the healing enthesis, and their superiority compared to PLGA alone was significant. These results demonstrated that electrospun fibrous membranes aid in cell attachment and proliferation, as well as accelerating tendon-bone remodeling, and bFGF-loaded PLGA fibrous membranes have a more pronounced effect on tendon-bone healing. Therefore, augmentation using bFGF-PLGA electrospun fibrous membranes is a promising treatment for RCT.

Effect of immediate and delayed high-strain loading on tendon-to-bone healing after anterior cruciate ligament reconstruction

BACKGROUND

We previously demonstrated, in a rat anterior cruciate ligament (ACL) graft reconstruction model, that the delayed application of low-magnitude-strain loading resulted in improved tendon-to-bone healing compared with that observed after immediate loading and after prolonged immobilization. The purpose of this study was to determine the effect of higher levels of strain loading on tendon-to-bone healing.

METHODS

ACL reconstruction was carried out in a rat model in three randomly assigned groups: high-strain daily loading beginning on either (1) postoperative day one (immediate-loading group; n = 7) or (2) postoperative day four (delayed-loading group; n = 11) or (3) after prolonged immobilization (immobilized group; n = 8). Animals were killed two weeks after surgery and micro-computed tomography (micro-CT) and biomechanical testing of the bone-tendon-bone complex were carried out.

RESULTS

The delayed-loading group had greater tissue mineral density than either the immediate-loading or immobilized group (mean [and standard deviation], 813.0 ± 24.9 mg/mL compared with 778.4 ± 32.6 mg/mL and 784.9 ± 26.4 mg/mL, respectively; p &lt; 0.05). There was a trend toward greater bone volume per total volume fraction in both the immobilized and the delayed-loading group compared with the immediate-loading group (0.24 ± 0.03 and 0.23 ± 0.06 compared with 0.20 ± 0.05; p = 0.06). Trabecular thickness was greater in the immobilized group compared with the immediate-loading group (106.5 ± 23.0 μm compared with 72.6 ± 10.6 μm; p &lt; 0.01). There were no significant differences in failure load or stiffness between the immobilized group and either high-strain cyclic-loading group.

CONCLUSIONS

Immediate application of high-strain loading appears to have a detrimental effect on healing in this rat model. Any beneficial effects of delayed loading on the healing tendon-bone interface (after a brief period of immobilization) may be offset by the detrimental effects of excessive strain levels or by the detrimental effects of stress deprivation on the graft.

CLINICAL RELEVANCE

The timing and magnitude of mechanical load on a healing rat ACL reconstruction graft may have important implications for postoperative rehabilitation. Avoidance of exercises that cause high graft strain in the early postoperative period may lead to improved tendon-to-bone healing in humans.

Matrix metalloproteinase content and activity in low-platelet, low-leukocyte and high-platelet, high-leukocyte platelet rich plasma (PRP) and the biologic response to PRP by human ligament fibroblasts

BACKGROUND

Recent work has shown the presence of catabolic cytokines in platelet-rich plasma (PRP), but little is known about endogenous catabolic proteases such as matrix metalloproteinases (MMPs). Hypothesis/

PURPOSE

To quantify MMP content in 2 commercially available PRP preparation systems: Arthrex Double Syringe System autologous conditioned plasma (ACP) and Biomet GPS (GPS). The hypothesis was that MMPs are actively secreted from PRP immediately after preparation.

STUDY DESIGN

Controlled laboratory study.

METHODS

PRP was prepared using either ACP (low platelet, low leukocyte) or GPS (high platelet, high leukocyte). MMP-2, MMP-3, and MMP-9 concentrations were measured using multiplex enzyme-linked immunosorbent assays for up to 6 days in 2 donors, and MMP activity was measured in 3 donors using kinetic activity kits able to detect the enzymatic cleavage of a fluorogenic peptide. Human ligament fibroblasts were cultured and exposed to both ACP and GPS from 1 donor each. MMP-2, -3, and -9 concentrations were assayed in culture media at 24 and 48 hours after exposure.

RESULTS

GPS exhibited higher total MMP-2, -3, and -9 concentrations for up to 144 hours of release, while ACP had higher platelet-normalized MMP-2 and MMP-3 concentrations. GPS had significantly higher total and endogenous MMP-2 activity (P = .004 and .014, respectively), MMP-3 activity (P = .020 and .015, respectively), and MMP-9 activity (P = .004 and .002, respectively) compared with ACP. Once normalized to platelet count, differences in MMP activity were not significant between ACP and GPS. Compared with controls, cells stimulated with interleukin-1 beta (IL-1β) and treated with ACP showed significantly higher fold changes of MMP-2 (P = .001) and MMP-3 (P = .003) concentrations at 24 hours than did cells treated with GPS. Total MMP-9 content was higher in the media of GPS-treated, IL-1β-stimulated cells compared with ACP-treated cells (P = .001). At 48 hours, IL-1β-stimulated cells treated with GPS exhibited higher fold changes of MMP-2 concentration (P = .002) compared with controls, but no difference in MMP-3 concentration was found. At 48 hours, there was a significantly higher concentration of MMP-9 in the cell culture media of ACP-treated cells compared with GPS-treated cells (P = .003).

CONCLUSION

PRP prepared as both ACP and GPS contains MMP-2, -3, and -9, which is released over a period of at least 6 days. Furthermore, a large proportion of these MMPs are in their active form, and MMP activity is dependent on platelet count within the PRP preparation. Once exposed to ligament fibroblasts, both ACP and GPS cause the fibroblasts to release MMPs, most notably 24 hours after PRP exposure, and this release is dependent on prior IL-1β stimulation.

CLINICAL RELEVANCE

The results of this study demonstrate that PRP therapy delivers ng/mL-range concentrations of catabolic proteases, which could perpetuate inflammation and inhibit tissue healing.

Advanced age diminishes tendon-to-bone healing in a rat model of rotator cuff repair

BACKGROUND

Advanced patient age is associated with recurrent tearing and failure of rotator cuff repairs clinically; however, basic science studies have not evaluated the influence of aging on tendon-to-bone healing after rotator cuff repair in an animal model. Hypothesis/

PURPOSE

This study examined the effect of aging on tendon-to-bone healing in an established rat model of rotator cuff repair using the aged animal colony from the National Institute on Aging of the National Institutes of Health. The authors hypothesized that normal aging decreases biomechanical strength and histologic organization at the tendon-to-bone junction after acute repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

In 56 F344xBN rats, 28 old and 28 young (24 and 8 months of age, respectively), the supraspinatus tendon was transected and repaired. At 2 or 8 weeks after surgery, shoulder specimens underwent biomechanical testing to compare load-to-failure and load-relaxation response between age groups. Histologic sections of the tendon-to-bone interface were assessed with hematoxylin and eosin staining, and collagen fiber organization was assessed by semiquantitative analysis of picrosirius red birefringence under polarized light.

RESULTS

Peak failure load was similar between young and old animals at 2 weeks after repair (31% vs 26% of age-matched uninjured controls, respectively; P > .05) but significantly higher in young animals compared with old animals 8 weeks after repair (86% vs 65% of age-matched uninjured controls, respectively; P < .01). Eight weeks after repair, fibroblasts appeared more organized and uniformly aligned in young animals on hematoxylin and eosin slides compared with old animals. Collagen birefringence analysis of the tendon-to-bone junction demonstrated that young animals had increased collagen fiber organization and similar histologic structure compared with age-matched controls (53.7 ± 2.4 gray scales; P > .05). In contrast, old animals had decreased collagen fiber organization and altered structure compared with age-matched controls (49.8 ± 3.1 gray scales; P < .01).

DISCUSSION

In a rat model of aging, old animals demonstrated diminished tendon-to-bone healing after rotator cuff injury and repair. Old animals had significantly decreased failure strength and collagen fiber organization at the tendon-to-bone junction compared with young animals. This study implies that animal age may need to be considered in future studies of rotator cuff repair in animal models.

CLINICAL RELEVANCE

With increasing age and activity level of the population, the incidence of rotator cuff tears is predicted to rise. Despite advances in rotator cuff repair technique, the retear rate remains specifically high in elderly patients. The findings of this research suggest that aging negatively influences tendon-to-bone healing after rotator cuff repair in a validated animal model.

Enhancement of Achilles tendon repair mediated by matrix metalloproteinase inhibition via systemic administration of doxycycline

Collagenases or matrix metalloproteinases (MMPs) have been shown to play an important role in the matrix degradation cascade associated with Achilles tendon rupture and disease. The goal of this study was to examine the effects of daily administration of doxycycline (Doxy) through oral gavage on MMP activity and on the repair quality of Achilles tendons in vivo. Our findings indicate that Achilles tendon transection resulted in increasing MMP-8 activity from 2 to 6 weeks post-injury, with peak increases in activity occurring at 4 weeks post-injury. Doxy adiministration at clinically relevant serum concentrations was found to significantly inhibit MMP activity after continuous treatment for 4 weeks, but not for continuous administration for shorter durations (96 h or 2 weeks). Extended doxy administration was also associated with improved collagen fibril organization, and enhanced biomechanical properties (stiffness, ultimate tensile strength, maximum load to failure, and elastic toughness). Our findings indicate that a temporal delay exists between Achilles tendon transection and associated increases in MMP-8 activity in situ. Our findings suggest that inhibition of MMP-8 at its peak activity levels ameliorates fibrosis development and improves biomechanical properties of the Achilles tendon.

Augmentation of tendon-to-bone healing

Tendon-to-bone healing is vital to the ultimate success of the various surgical procedures performed to repair injured tendons. Achieving tendon-to-bone healing that is functionally and biologically similar to native anatomy can be challenging because of the limited regeneration capacity of the tendon-bone interface. Orthopaedic basic-science research strategies aiming to augment tendon-to-bone healing include the use of osteoinductive growth factors, platelet-rich plasma, gene therapy, enveloping the grafts with periosteum, osteoconductive materials, cell-based therapies, biodegradable scaffolds, and biomimetic patches. Low-intensity pulsed ultrasound and extracorporeal shockwave treatment may affect tendon-to-bone healing by means of mechanical forces that stimulate biological cascades at the insertion site. Application of various loading methods and immobilization times influence the stress forces acting on the recently repaired tendon-to-bone attachment, which eventually may change the biological dynamics of the interface. Other approaches, such as the use of coated sutures and interference screws, aim to deliver biological factors while achieving mechanical stability by means of various fixators. Controlled Level-I human trials are required to confirm the promising results from in vitro or animal research studies elucidating the mechanisms underlying tendon-to-bone healing and to translate these results into clinical practice.

Effect of diet-induced vitamin D deficiency on rotator cuff healing in a rat model

BACKGROUND

Few studies have considered hormonal influences, particularly vitamin D, on healing.

HYPOTHESIS

Vitamin D deficiency would have a negative effect on the structure of the healing tendon-bone interface in a rat model and would result in decreased tendon attachment strength.

STUDY DESIGN

Controlled laboratory study.

METHODS

Vitamin D deficiency was induced in 28 male Sprague-Dawley rats using a specialized vitamin D-deficient diet and ultraviolet light restriction. Serum levels of vitamin D were measured after 6 weeks. These vitamin D-deficient animals (experimental group) plus 32 rats with normal vitamin D levels (controls) underwent unilateral detachment of the right supraspinatus tendon from the greater tuberosity of the humerus, followed by immediate repair using bone tunnel suture fixation. The animals were sacrificed at 2- and 4-week intervals after surgery for biomechanical analysis. A paired t test was used to compare serum vitamin D levels at day 0 and at 6 weeks. A nonparametric Mann-Whitney U test was used to compare load-to-failure and stiffness values between the experimental group and controls. Bone density and new bone formation at the tendon insertion site on the greater tuberosity were assessed with micro-computed tomography (CT). The organization of collagen tissue, new bone formation, vascularity at the tendon-bone interface, fibrocartilage at the tendon-bone interface, and collagen fiber continuity between the tendon and bone tissue were evaluated with safranin O and picrosirius red staining.

RESULTS

Blood draws confirmed vitamin D deficiency at 6 weeks compared with time zero/baseline for rats in the experimental group (10.9 ng/mL vs 6.5 ng/mL, respectively; P < .001). Biomechanical testing demonstrated a significant decrease in load to failure in the experimental group compared with controls at 2 weeks (5.8 ± 2.0 N vs 10.5 ± 4.4 N, respectively; P < .006). There was no difference in stiffness at 2 weeks between the control and experimental groups. At 4 weeks, there was no significant difference in load to failure or stiffness between the control and experimental groups. Histological analysis showed less bone formation and less collagen fiber organization in the vitamin D-deficient specimens at 4 weeks as compared with controls. Micro-CT analysis showed no significant difference between groups for total mineral density and bone volume fraction of cortical, whole, or trabecular bone at 4 weeks.

CONCLUSION

The biomechanical and histological data from this study suggest that low vitamin D levels may negatively affect early healing at the rotator cuff repair site.

CLINICAL RELEVANCE

It is estimated that 1 billion people worldwide are vitamin D deficient. In the deficient state, acutely injured rotator cuffs may have a reduced ability for tendon healing. Further studies are needed to determine the exact mechanism by which vitamin D affects tendon healing and whether vitamin D supplementation can improve rotator cuff tendon healing and reduce the incidence of retears.

Increased matrix metalloprotease-3 gene expression in ruptured rotator cuff tendons is associated with postoperative tendon retear

PURPOSE

The role of matrix metalloproteases (MMPs) in ruptured rotator cuff tendons remains unknown. This study aimed to investigate the gene expression of MMPs in ruptured rotator cuff tendons and to compare their expression levels between patients with and without postoperative tendon retear.

METHODS

Twenty-four patients (a median age of 61 years: interquartile range, 55-66 years) with full-thickness rotator cuff tears were examined in this study. The marginal site of the ruptured tendon was harvested during surgery. The mRNA expression levels of collagen types I and III, MMP-1, MMP-3, MMP-7, MMP-9, MMP-13, tissue inhibitor of MMP (TIMP)-1, and TIMP-2 were analysed by real-time reverse transcription polymerase chain reaction. Postoperative retear was evaluated by magnetic resonance imaging at a minimum of 1 year following surgery.

RESULTS

The mRNA expression levels of MMP-3 and TIMP-1 in ruptured rotator cuff tendons were significantly increased in patients with postoperative retear (n = 6), compared with patients without retear (n = 18) (P = 0.04). For collagens, MMP-1, MMP-7, MMP-9, MMP-13, and TIMP-2, there were no significant differences in the mRNA expression levels in ruptured tendons between patients with and without retear.

CONCLUSIONS

These results suggest that, in addition to up-regulation of TIMP-1 gene expression, increased MMP-3 gene expression in ruptured rotator cuff tendons is associated with postoperative tendon retear. Thus, drug therapy specifically targeting MMP-3 after rotator cuff repair should be considered in the future.

The science of rotator cuff tears: translating animal models to clinical recommendations using simulation analysis

PURPOSE

The purpose of this article is to review basic science studies using various animal models for rotator cuff research and to describe structural, biomechanical, and functional changes to muscle following rotator cuff tears. The use of computational simulations to translate the findings from animal models to human scale is further detailed.

METHODS

A comprehensive review was performed of the basic science literature describing the use of animal models and simulation analysis to examine muscle function following rotator cuff injury and repair in the ageing population.

RESULTS

The findings from various studies of rotator cuff pathology emphasize the importance of preventing permanent muscular changes with detrimental results. In vivo muscle function, electromyography, and passive muscle-tendon unit properties were studied before and after supraspinatus tenotomy in a rodent rotator cuff injury model (acute vs chronic). Then, a series of simulation experiments were conducted using a validated computational human musculoskeletal shoulder model to assess both passive and active tension of rotator cuff repairs based on surgical positioning.

CONCLUSION

Outcomes of rotator cuff repair may be improved by earlier surgical intervention, with lower surgical repair tensions and fewer electromyographic neuromuscular changes. An integrated approach of animal experiments, computer simulation analyses, and clinical studies may allow us to gain a fundamental understanding of the underlying pathology and interpret the results for clinical translation.

Metalloproteases and tendinopathy

Matrix metalloproteinases (MMP) are involved in the development of tendinopathy. These potent enzymes completely degrade all components of the connective tissue, modify the extracellular matrix (ECM), and mediate the development of painful tendinopathy. To control the local activity of activated proteinases, the same cells produce tissue inhibitors of metalloproteinases (TIMP). These latter bind to the enzyme and prevent degradation. The balance between the activities of MMPs and TIMPs regulates tendon remodeling, whereas an imbalance produces a collagen dis-regulation and disturbances in tendons. ADAMs (a disintegrin and metalloproteinase) are cell membrane-linked enzymes with proteolytic and cell signaling functions. ADAMTSs (ADAM with thrombospondin motifs) are secreted into the circulation and constitute a heterogenous family of proteases with both anabolic and catabolic functions. Further studies are needed to better define the mechanism of action, and whether these new strategies are safe and effective in larger models.

MMP inhibition as a potential method to augment the healing of skeletal muscle and tendon extracellular matrix

The extracellular matrix (ECM) of skeletal muscle and tendon is composed of different types of collagen molecules that play important roles in the transmission of forces throughout the body, and in the repair and regeneration of injured tissues. Fibroblasts are the primary cells in muscle and tendon that maintain, repair, and modify the ECM in response to mechanical loading, injury, and inactivity. Matrix metalloproteinases (MMPs) are enzymes that digest collagen and other structural molecules, which are synthesized and excreted by fibroblasts. MMPs are required for baseline ECM homeostasis, but disruption of MMP regulation due to injury or disease can alter the normal ECM architecture and prevent proper force transmission. Chronic injuries and diseases of muscles and tendons can be severely debilitating, and current therapeutic modalities to enhance healing are quite limited. This review will discuss the mechanobiology of MMPs, and the potential use of MMP inhibitors to improve the treatment of injured and diseased skeletal muscle and tendon tissue.

Human growth hormone may be detrimental when used to accelerate recovery from acute tendon-bone interface injuries

BACKGROUND

There have been few scientific studies that have examined usage of human growth hormone to accelerate recovery from injury. The hypothesis of this study was that human growth hormone would accelerate tendon-to-bone healing compared with control animals treated with placebo in a rat model of acute rotator cuff injury repair.

METHODS

Seventy-two rats underwent repair of acute rotator cuff injuries and were randomized into the following postoperative dosing regimens: placebo, and human growth hormone at 0.1, 1, 2, 5, and 10 mg/kg/day, administered subcutaneously once per day for fourteen days (Protocol 1). An additional twenty-four rats were randomized to receive either (1) placebo or (2) human growth hormone at 5 mg/kg, administered subcutaneously twice per day for seven days preoperatively and twenty-eight days postoperatively (Protocol 2). All rats were killed twenty-eight days postoperatively. Mechanical testing was performed. Ultimate stress, ultimate force, stiffness, energy to failure, and ultimate distension were determined.

RESULTS

For Protocol 1, analysis of variance testing showed no significant difference between the groups with regard to ultimate stress, ultimate force, stiffness, energy to failure, or ultimate distension. In Protocol 2, ultimate force to failure was significantly worse in the human growth hormone group compared with the placebo group (21.1 ± 5.85 versus 26.3 ± 5.47 N; p = 0.035). Failure was more likely to occur through the bone than the tendon-bone interface in the human growth hormone group compared with the placebo group (p = 0.001). No significant difference was found for ultimate stress, ultimate force, stiffness, energy to failure, or ultimate distension between the groups in Protocol 2.

CONCLUSIONS

In this rat model of acute tendon-bone injury repair, daily subcutaneous postoperative human growth hormone treatment for fourteen days failed to demonstrate a significant difference in any biomechanical parameter compared with placebo. Furthermore, subcutaneous administration of 5 mg/kg of human growth hormone twice daily from seven days preoperatively until twenty-eight days postoperatively demonstrated lower loads to ultimate failure and a higher risk of bone fracture failure compared with placebo.

Metalloproteases and their inhibitors are altered in both torn and intact rotator cuff tendons

BACKGROUND

We evaluated the role of matrix metalloproteases (MMPs) and their inhibitors which are involved in extracellular matrix remodeling and degradation, in the pathogenesis of chronic rotator cuff tears.

MATERIALS AND METHODS

Tendon samples were harvested from 13 patients who underwent arthroscopic repair of a rotator cuff tear. Supraspinatus biopsy specimens were harvested en bloc from the arthroscopically intact middle portion of the tendon more than 1 cm from the torn edge, from the lateral edge of the tear, and from the superior one third of the macroscopically intact subscapularis tendon used as control. Histological analysis and an evaluation of the activity of specific metalloproteases and the tissue inhibitors of metalloprotease (TIMP-1, TIMP-2) was done blindly by multiplex sandwich ELISA (Search-Light technology) in each specimen

RESULTS

Histological evidence of tendinopathy was present in all patients with a tear of the rotator cuff, and not in the macroscopically intact subscapularis tendon. There was a significant increase in MMP 1, MMP 2, MMP 3 and in TIMP-1, TIMP-2 levels in all specimens examined, including the macroscopically intact portion of the supraspinatus tendon and in the control specimens

CONCLUSIONS

The tissue in the ruptured area of the supraspinatus tendon undergoes marked rearrangement at molecular levels. This involves the activity of MMP 1, 2 and 3, and supports the critical role of MMPs in the tendon physiology. Seemingly intact parts of the injured supraspinatus tendon can present tendinopathic features, with altered cellular metabolism.

ACL graft healing and biologics

Operative reconstruction of a torn anterior cruciate ligament (ACL) has become the most broadly accepted treatment. An important, but underreported, outcome of ACL reconstruction is graft failure, which poses a challenge for the orthopedic surgeon. An understanding of the tendon-bone healing and the intra-articular ligamentization process is crucial for orthopedic surgeons to make appropriate graft choices and to be able to initiate optimal rehabilitation protocols after surgical ACL reconstruction. This article focuses on the current understanding of the tendon-to-bone healing process for both autografts and allografts and discusses strategies to biologically augment healing.

Tenocytes of chronic rotator cuff tendon tears can be stimulated by platelet-released growth factors

BACKGROUND

Bone-to-tendon healing after rotator cuff repairs is mainly impaired by poor tissue quality. The tenocytes of chronic rotator cuff tendon tears are not able to synthesize normal fibrocartilaginous extracellular matrix (ECM). We hypothesized that in the presence of platelet-released growth factors (PRGF), tenocytes from chronically retracted rotator cuff tendons proliferate and synthesize the appropriate ECM proteins.

MATERIALS AND METHODS

Tenocytes from 8 patients with chronic rotator cuff tears were cultured for 4 weeks in 2 different media: standard medium (Iscove's Modified Dulbecco's Media + 10% fetal calf serum + 1% nonessential amino acids + 0.5 μg/mL ascorbic acid) and media with an additional 10% PRGF. Cell proliferation was assessed at 7, 14, 21, and 28 days. Messenger (m)RNA levels of collagens I, II, and X, decorin, biglycan, and aggrecan were analyzed using real time reverse-transcription polymerase chain reaction. Immunocytochemistry was also performed.

RESULTS

The proliferation rate of tenocytes was significantly higher at all time points when cultured with PRGF. At 21 days, the mRNA levels for collagens I, II, and X, decorin, aggrecan, and biglycan were significantly higher in the PRGF group. The mRNA data were confirmed at protein level by immunocytochemistry.

CONCLUSIONS

PRGFs enhance tenocyte proliferation in vitro and promote synthesis of ECM to levels similar to those found with insertion of the normal human rotator cuffs.

CLINICAL RELEVANCE

Biologic augmentation of repaired rotator cuffs with PRGF may enhance the properties of the repair tissue. However, further studies are needed to determine if application of PRGF remains safe and effective in long-term clinical studies.

LEVEL OF EVIDENCE

Basic Science Study, Cell Biology.

Isolation and characterization of human mesenchymal stem cells derived from shoulder tissues involved in rotator cuff tears

BACKGROUND

Recent studies report a relatively high failure rate for tendon-bone healing after rotator cuff repair. Several studies have investigated biologically augmented rotator cuff repair; however, none has shown the application of synovial mesenchymal stem cells for such repair.

PURPOSE

To demonstrate whether cells derived from shoulder tissues have mesenchymal stem cell properties and to identify which tissue is the best source of the mesenchymal stem cells.

STUDY DESIGN

Controlled laboratory study.

METHODS

Forty-two patients with a diagnosed rotator cuff tear preoperatively were enrolled in this study. Human mesenchymal tissues were obtained during arthroscopic surgery for rotator cuff tears from 19 donors who met the inclusion criteria and had investigable amounts of tissue. Colony-forming units, yield obtained, expandability, differentiation potential, epitope profile, and gene expression were compared among the cells from 4 shoulder tissues: synovium of the glenohumeral joint, subacromial bursa, margin of the ruptured supraspinatus tendon, and residual tendon stump on the greater tuberosity (enthesis).

RESULTS

The number of live passage 0 cells from whole tissue was significantly higher in cells derived from the subacromial bursa (P < .05). Subacromial bursa-derived cells retained their expandability even at passage 10. In adipogenesis experiments, the frequency of Oil Red O-positive colonies was significantly higher for synovium- and subacromial bursa-derived cells than for tendon- and enthesis-derived cells (P < .0001). In studies of osteogenesis, the rate of von Kossa- and alkaline phosphatase-positive colonies was highest in subacromial bursa-derived cells (P < .0001). The chondrogenic potential was highest in cells derived from the enthesis. For epitope profiling, 11 surface antigens were measured, and most had similar epitope profiles, irrespective of cell source.

CONCLUSION

The findings indicate that the subacromial bursa is a good candidate for the source of mesenchymal stem cells in rotator cuff tears.

CLINICAL RELEVANCE

Synovial cells from the subacromial bursa in patients with rotator cuff tears are a superior cell source in vitro, suggesting that mesenchymal stem cells from this tissue could be good candidates for biological augmentation of rotator cuff repair.

Effects of doxycycline on mesenchymal stem cell chondrogenesis and cartilage repair

OBJECTIVE

Strategies to improve cartilage repair tissue quality after bone marrow cell-based procedures may reduce later development of osteoarthritis. Doxycycline is inexpensive, well-tolerated, and has been shown to reduce matrix-metalloproteinases (MMPs) and osteoarthritis progression. This study tests the hypotheses that doxycycline reduces MMP, enhances chondrogenesis of human bone marrow-derived mesenchymal stem cells (hMSC), and improves in vivo cartilage repair.

DESIGN

Ninety hMSC pellets were cultured in chondrogenic media with either 0-, 1- or 2-μg/mL doxycycline. Pellets were evaluated with stereomicroscopy, proteoglycan assay, qRT-PCR, and histology. Osteochondral defects (OCDs) were created in the trochlear grooves of 24-Sprague-Dawley rats treated with/without oral doxycycline. Rats were sacrificed at 12-weeks and repair tissues were examined grossly and histologically.

RESULTS

hMSC pellets with 1-μg/mL (P = 0.014) and 2-μg/mL (P = 0.002) doxycycline had larger areas than pellets without doxycycline. hMSC pellets with 2-μg/mL doxycycline showed reduced mmp-13 mRNA (P = 0.010) and protein at 21-days. Proteoglycan, DNA contents, and mRNA expressions of chondrogenic genes were similar (P > 0.05). For the in vivo study, while the histological scores were similar between the two groups (P = 0.116), the gross scores of the OCD repair tissues in doxycycline-treated rats were higher at 12-weeks (P = 0.017), reflective of improved repair quality. The doxycycline-treated repairs also showed lower MMP-13 protein (P = 0.029).

CONCLUSIONS

This study shows that doxycycline improves hMSC chondrogenesis and decreases MMP-13 in pellet cultures and within rat OCDs. Doxycycline exerted no negative effect on multiple measures of chondrogenesis and cartilage repair. These data support potential use of doxycycline to improve cartilage repair to delay the onset of osteoarthritis.

Metalloproteinases and their associated genes contribute to the functional integrity and noise-induced damage in the cochlear sensory epithelium

Matrix metalloproteinases (MMPs) and their related gene products regulate essential cellular functions. An imbalance in MMPs has been implicated in various neurological disorders, including traumatic injuries. Here, we report a role for MMPs and their related gene products in the modulation of cochlear responses to acoustic trauma in rats. The normal cochlea was shown to be enriched in MMP enzymatic activity, and this activity was reduced in a time-dependent manner after traumatic noise injury. The analysis of gene expression by RNA sequencing and qRT-PCR revealed the differential expression of MMPs and their related genes between functionally specialized regions of the sensory epithelium. The expression of these genes was dynamically regulated between the acute and chronic phases of noise-induced hearing loss. Moreover, noise-induced expression changes in two endogenous MMP inhibitors, Timp1 and Timp2, in sensory cells were dependent on the stage of nuclear condensation, suggesting a specific role for MMP activity in sensory cell apoptosis. A short-term application of doxycycline, a broad-spectrum inhibitor of MMPs, before noise exposure reduced noise-induced hearing loss and sensory cell death. In contrast, a 7 d treatment compromised hearing sensitivity and potentiated noise-induced hearing loss. This detrimental effect of the long-term inhibition of MMPs on noise-induced hearing loss was further confirmed using targeted Mmp7 knock-out mice. Together, these observations suggest that MMPs and their related genes participate in the regulation of cochlear responses to acoustic overstimulation and that the modulation of MMP activity can serve as a novel therapeutic target for the reduction of noise-induced cochlear damage.

Biologics in the management of rotator cuff surgery

The rotator cuff enthesis is not reestablished after a rotator cuff repair. Instead, a scar-mediated healing response occurs at the tendon-bone interface, which is notably weaker than the native enthesis and thus more prone to failure. Biological augmentation through growth factors, AASs, biomimetic scaffolds, or siRNA therapy has the potential to enhance the healing response. The ultimate key, however, is in determining which of these enables a more regenerative healing response of the native tissue rather than enhanced production of scar tissue. In addition, the optimal combination of factors, dosing, and delivery methods remains to be clearly elucidated. Biological augmentation and tissue engineering for tendon healing remains promising, but much work still needs to be done.

Biologically based strategies to augment rotator cuff tears

Lesions of the rotator cuff (RC) are among the most frequent tendon injuries. In spite of the developments in both open and arthroscopic surgery, RC repair still very often fails. In order to reduce the failure rate after surgery, several experimental in vitro and in vivo therapy methods have been developed for biological improvement of the reinsertion. This article provides an overview of the current evidence for augmentation of RC reconstruction with growth factors. Furthermore, potential future therapeutic approaches are discussed. We performed a comprehensive search of the PubMed database using various combinations of the keywords “tendon,” “rotator cuff,” “augmentation,” “growth factor,” “platelet-rich fibrin,” and “platelet-rich plasma” for publications up to 2011. Given the linguistic capabilities of the research team, we considered publications in English, German, French, and Spanish. We excluded literature reviews, case reports, and letters to the editor.

Elevated plasma levels of TIMP-1 in patients with rotator cuff tear

BACKGROUND AND PURPOSE

Extracellular matrix remodeling is altered in rotator cuff tears, partly due to altered expression of matrix metalloproteinases (MMPs) and their inhibitors. It is unclear whether this altered expression can be traced as changes in plasma protein levels. We measured the plasma levels of MMPs and their tissue inhibitors (TIMPs) in patients with rotator cuff tears and related changes in the pattern of MMP and TIMP levels to the extent of the rotator cuff tear.

METHODS

Blood samples were collected from 17 patients, median age 61 (39-77) years, with sonographically verified rotator cuff tears (partial- or full-thickness). These were compared with 16 age- and sex-matched control individuals with sonographically intact rotator cuffs. Plasma levels of MMPs and TIMPs were measured simultaneously using Luminex technology and ELISA.

RESULTS

The plasma levels of TIMP-1 were elevated in patients with rotator cuff tears, especially in those with full-thickness tears. The levels of TIMP-1, TIMP-3, and MMP-9 were higher in patients with full-thickness tears than in those with partial-thickness tears, but only the TIMP-1 levels were significantly different from those in the controls.

INTERPRETATION

The observed elevation of TIMP-1 in plasma might reflect local pathological processes in or around the rotator cuff, or a genetic predisposition in these patients. That the levels of TIMP-1 and of certain MMPs were found to differ significantly between partial and full-thickness tears may reflect the extent of the lesion or different etiology and pathomechanisms.