Characterization of synovial fluid cytokine profiles in chronic meniscal tear of the knee

Epigenetic Dynamics in Meniscus Cell Migration and its Zonal Dependency in Response to Inflammatory Conditions: Implications for Regeneration Strategies

Meniscus injuries pose significant challenges in clinical settings, primarily due to the intrinsic heterogeneity of the tissue and the limited efficacy of current treatments. Endogenous cell migration is crucial for the healing process, yet the regulatory mechanisms of meniscus cell migration and its zonal dependency within the meniscus are not fully understood. Thus, this study investigates the role of epigenetic mechanisms in governing meniscus cell migration under inflammatory conditions, with a focus on their implications for injury healing and regeneration. Here, we discovered that a proinflammatory cytokine, TNF-α treatment significantly impedes the migration speed of inner meniscus cells, while outer meniscus cells are unaffected, underscoring a zonal-dependent response within the meniscus. Our analysis identified distinct histone modification patterns and chromatin dynamics between inner and outer meniscus cells during migration, highlighting the necessity to consider these zonal-dependent properties in devising repair strategies. Specifically, we found that TNF-α differentially influences histone modifications, particularly H3K27me3, between the two cell types. Transcriptome analysis further revealed that TNF-α treatment induces substantial gene expression changes, with inner meniscus cells exhibiting more pronounced alterations than outer cells. Gene cluster analysis pointed to distinct responses in chromatin remodeling, extracellular matrix assembly, and wound healing processes between the zonal cell populations. Moreover, we identified potential therapeutic targets by employing existing epigenetic drugs, GSKJ4 (a histone demethylase inhibitor) and C646 (a histone acetyltransferase inhibitor), to successfully restore the migration speed of inner meniscus cells under inflammatory conditions. This highlights their potential utility in treating meniscus tear injuries. Overall, our findings elucidate the intricate interplay between epigenetic mechanisms and meniscus cell migration, along with its meniscus zonal dependency. This study provides insights into potential targets for enhancing meniscus repair and regeneration, which may lead to improved clinical outcomes for patients with meniscus injuries and osteoarthritis.

Biofabrication of Tissue-Engineered Cartilage Constructs Through Faraday Wave Bioassembly of Cell-Laden Gelatin Microcarriers

Acoustic biofabrication is an emerging strategy in tissue engineering due to its mild and fast manufacturing process. Herein, tissue-engineered cartilage constructs with high cell viability are fabricated from cell-laden gelatin microcarriers (GMs) through Faraday wave bioassembly, a typical acoustic "bottom-up" manufacturing process. Assembly modules are first prepared by incorporating cartilage precursor cells, the chondrogenic cell line ATDC5, or bone marrow-derived mesenchymal stem cells (BMSCs), into GMs. Patterned structures are formed by Faraday wave bioassembly of the cell-laden GMs. Due to the gentle and efficient assembly process and the protective effects of microcarriers, cells in the patterned structures maintain high activity. Subsequently, tissue-engineered cartilage constructs are obtained by inducing cell differentiation of the patterned structures. Comprehensive evaluations are conducted to verify chondrocyte differentiation and the formation of cartilage tissue constructs in terms of cell viability, morphological analysis, gene expression, and matrix production. Finally, implantation studies with a rat cartilage defect model demonstrate that these tissue-engineered cartilage constructs are beneficial for the repair of articular cartilage damage in vivo. This study provides the first biofabrication of cartilage tissue constructs using Faraday wave bioassembly, extending its application to engineering tissues with a low cell density.

Correlation of meniscus tear type with synovial inflammation and the therapeutic potential of docosapentaenoic acid

BACKGROUND

Synovitis, characterized by inflammation of the synovial membrane, is commonly induced by meniscus tears. However, significant differences in inflammatory responses and the key inflammatory mediators of synovium induced by different types of meniscal tears remain unclear.

METHODS

Magnetic resonance imaging (MRI) was employed to identify the type of meniscus tear, and the quantification of synovial inflammation was assessed through H&E staining assay. Transcription and expression levels of IL-1β and IL-6 were evaluated using bioinformatics, ELISA, RT-qPCR, and IHC of CD68 staining assays. The therapeutic potential of Docosapentaenoic Acid (DPA) was determined through network pharmacology, ELISA, and RT-qPCR assays. The safety of DPA was assessed using colony formation and EdU staining assays.

RESULTS

The results indicate that both IL-1β and IL-6 play pivotal roles in synovitis pathogenesis, with distinct expression levels across various subtypes. Among tested meniscus tears, oblique tear and bucket handle tear induced the most severe inflammation, followed by radial tear and longitudinal tear, while horizontal tear resulted in the least inflammation. Furthermore, in synovial inflammation induced by specific meniscus tears, the anterior medial tissues exhibited significantly higher local inflammation than the anterior lateral and suprapatellar regions, highlighting the clinical relevance and practical guidance of anterior medial tissues' inflammatory levels. Additionally, we identified the essential omega-3 fatty acid DPA as a potential therapeutic agent for synovitis, demonstrating efficacy in blocking the transcription and expression of IL-1β and IL-6 with minimal side effects.

CONCLUSION

These findings provide valuable insights into the nuanced nature of synovial inflammation induced by various meniscal tear classifications and contribute to the development of new adjunctive therapeutic agents in the management of synovitis.

Decay-Accelerating Factor Differentially Associates With Complement-Mediated Damage in Synovium After Meniscus Tear as Compared to Anterior Cruciate Ligament Injury

We have reported that anterior cruciate ligament (ACL) injury leads to the differential dysregulation of the complement system in the synovium as compared to meniscus tear (MT) and proposed this as a mechanism for a greater post-injury prevalence of post traumatic osteoarthritis (PTOA). To explore additional roles of complement proteins and regulators, we determined the presence of decay-accelerating factor (DAF), C5b, and membrane attack complexes (MACs, C5b-9) in discarded surgical synovial tissue (DSST) collected during arthroscopic ACL reconstructive surgery, MT-related meniscectomy, osteoarthritis (OA)-related knee replacement surgery and normal controls. Multiplexed immunohistochemistry was used to detect and quantify complement proteins. To explore the involvement of body mass index (BMI), after these 2 injuries, we examined correlations among DAF, C5b, MAC and BMI. Using these approaches, we found that synovial cells after ACL injury expressed a significantly lower level of DAF as compared to MT (p<0.049). In contrast, C5b staining synovial cells were significantly higher after ACL injury (p<0.0009) and in OA DSST (p<0.039) compared to MT. Interestingly, there were significantly positive correlations between DAF & C5b (r=0.75, p<0.018) and DAF & C5b (r=0.64 p<0.022) after ACL injury and MT, respectively. The data support that DAF, which should normally dampen C5b deposition due to its regulatory activities on C3/C5 convertases, does not appear to exhibit that function in inflamed synovia following either ACL injury or MT. Ineffective DAF regulation may be an additional mechanism by which relatively uncontrolled complement activation damages tissue in these injury states.

Improved Cartilage Protection with Low Molecular Weight Hyaluronic Acid Hydrogel

Traumatic joint injuries are common, leading to progressive tissue degeneration and the development of osteoarthritis. The post-traumatic joint experiences a pro-inflammatory milieu, initiating a subtle but deteriorative process in cartilage tissue. To prevent or even reverse this process, our group previously developed a tissue-penetrating methacrylated hyaluronic acid (MeHA) hydrogel system, crosslinked within cartilage to restore and/or protect the tissue. In the current study, we further optimized this approach by investigating the impact of biomaterial molecular weight (MW; 20, 75, 100 kDa) on its integration within and reinforcement of cartilage, as well as its ability to protect tissue degradation in a catabolic state. Indeed, the low MW MeHA integrated and reinforced cartilage tissue better than the high MW counterparts. Furthermore, in a 2 week IL-1β explant culture model, the 20 kDa MeHA demonstrated the most protection from biphasic mechanical loss, best retention of proteoglycans (Safranin O staining), and least aggrecan breakdown (NITEGE). Thus, the lower MW MeHA gels integrated better into the tissue and provided the greatest protection of the cartilage matrix. Future work will test this formulation in a preclinical model, with the goal of translating this therapeutic approach for cartilage preservation.

Prokineticin 2 and Cytokine Content in the Synovial Fluid of Knee Osteoarthritis and Traumatic Meniscal Tear Patients: Preliminary Results

Knee osteoarthritis (OA) is a chronic degenerative inflammatory-based condition caused by a cascade of different intra-articular molecules including several cytokines. Among the cytokines, prokineticins (PKs) have recently been identified as important mediators of inflammation and pain. This observational study examined the potential involvement of PK2 in degenerative or traumatic knee disease. Fifteen patients presenting knee osteoarthritis (OA group) and 15 patients presenting a traumatic meniscal tear (TM group) were studied. Synovial fluid samples from affected knees were assessed for PK2, IL-10, and TNF-α using the ELISA method. At a long-term follow-up (minimum 5 years, mean = 6.1 years), patients in the TM group underwent clinical re-evaluation with PROMs (Tegner Activity Scale, IKDC, Lysholm, SKV); in addition, X-ray visualization was used to assess the presence of secondary OA. PK2 was detected in synovial fluids of both TM and OA patients and the levels were comparable between the two groups, while IL-10 levels were significantly greater in the OA group than those in TM patients. PK2 levels correlated with those of IL-10. PK2 levels were greater in blood effusions compared to clear samples, did not differ significantly between sexes, nor were they related to differences in weight, height, or injury (meniscal laterality, time since dosing). No correlation was found between PROMs and radiological classifications in patients in the TM group at final follow-up. These data are the first observations of PK2 in synovial fluid following traumatic meniscus injury. These findings suggest possible further prognostic indices and therapeutic targets to limit the development of secondary OA.

The Interplay of Biomechanical and Biological Changes Following Meniscus Injury

PURPOSE OF REVIEW

Meniscus injury often leads to joint degeneration and post-traumatic osteoarthritis (PTOA) development. Therefore, the purpose of this review is to outline the current understanding of biomechanical and biological repercussions following meniscus injury and how these changes impact meniscus repair and PTOA development. Moreover, we identify key gaps in knowledge that must be further investigated to improve meniscus healing and prevent PTOA.

RECENT FINDINGS

Following meniscus injury, both biomechanical and biological alterations frequently occur in multiple tissues in the joint. Biomechanically, meniscus tears compromise the ability of the meniscus to transfer load in the joint, making the cartilage more vulnerable to increased strain. Biologically, the post-injury environment is often characterized by an increase in pro-inflammatory cytokines, catabolic enzymes, and immune cells. These multi-faceted changes have a significant interplay and result in an environment that opposes tissue repair and contributes to PTOA development. Additionally, degenerative changes associated with OA may cause a feedback cycle, negatively impacting the healing capacity of the meniscus. Strides have been made towards understanding post-injury biological and biomechanical changes in the joint, their interplay, and how they affect healing and PTOA development. However, in order to improve clinical treatments to promote meniscus healing and prevent PTOA development, there is an urgent need to understand the physiologic changes in the joint following injury. In particular, work is needed on the in vivo characterization of the temporal biomechanical and biological changes that occur in patients following meniscus injury and how these changes contribute to PTOA development.

The Diagnostic and Prognostic Value of Synovial Fluid Analysis in Joint Diseases

Liquid biopsy is an emergent test method for the diagnosis and prognosis in the clinic. Joint fluid, also known as synovial fluid, contains a variety of bioactive constituents that can be selectively detected and further evaluated in a convenient fashion. Therefore, synovial fluid analysis functions as a specific form of liquid biopsy and plays a vital role in numerous joint diseases. In spite of the component analysis of aspirated synovial fluid beingconsidered as the gold standard for diagnosis of joint infections, biopsy of joint fluid benefits the initial diagnosis and long-term prognosis of degenerative, inflammatory, autoimmune, traumatic, congenital, and even neoplastic joint diseases. The convenience and accuracy for disease evaluation are significantly elevated as a result of the combination of synovial fluid analysis and other novel clinical technologies. In this review, we shed light on the latent role of synovial fluid in the diagnosis and prognosis of articular diseases and proposed future prospects for relevant research in this field.

Treatment-Monitoring Capabilities of Serum and Urine Biomarkers for Meniscal Allograft Transplantation in a Preclinical Canine Model

BACKGROUND

Meniscal allograft transplantation (MAT) has been developed as a treatment for meniscal deficiency. Despite promising outcomes, there are no real-time methods to evaluate graft survivorship and predict functional outcomes.

HYPOTHESIS

Assessment of serum and urine biomarkers could be used to develop biomarker panels-prognostic (1- and 3-month postsurgical time points) and diagnostic (6-month time point)-based on strong associations with clinically relevant outcome metrics obtained 6 months after surgery.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Twelve adult purpose-bred research hounds were included and underwent medial meniscal release to induce meniscal deficiency. Three months after meniscal release surgery, medial menisci were replaced with fresh-frozen meniscus (n = 4), fresh meniscus (n = 4), or fresh meniscotibial osteochondral allograft (n = 4) such that a spectrum of pain and functional outcomes could be anticipated. Serum and urine from all dogs were collected preoperatively and at 1, 3, and 6 months after MAT surgery. Dogs were assessed for pain-related and functional outcomes at the same time points. To develop a prognostic panel of biomarkers, biomarker data from the 1- and 3-month post-MAT surgery time points were used to model 6-month clinical outcomes. A diagnostic panel of biomarkers was developed using data from the 6-month post-MAT surgery to model 6-month clinical outcomes. Primary outcomes for pain and function were visual analog scale (VAS) and operated limb percentage total pressure index (%TPI), respectively. Using random subject effects, linear mixed models were used to develop prognostic biomarker panels, and linear fixed-effect models were used to develop diagnostic biomarker panels, with variance explained for each panel reported (R²) along with individual biomarker relationships.

RESULTS

Across prognostic biomarker panels, a panel including serum IL-6, IL-8, IL-10, and IL-18 was fit for the primary functional outcome, operated limb %TPI (R² = 0.450), whereas a panel including serum CTX-II and OPG was fit for the primary pain-related outcome, VAS (R² = 0.516). Across diagnostic biomarker panels, a panel including serum MMP-1 and MMP-3 and urine PINP and TIMP-1 was fit for %TPI (R² = 0.863). Separately, a panel including urine CTX-I, CTX-II, IL-8, MMP-2, and TIMP-1 was fit as diagnostic biomarkers for the VAS for pain (R² = 0.438).

CONCLUSION

Biomarker panels of selected serum and/or urine proteins can model clinically relevant metrics for function and pain in a preclinical model of MAT.

CLINICAL RELEVANCE

Biomarker panels could be used to provide real-time diagnostic and prognostic data regarding outcomes after MAT.

Prospective Randomized Controlled Clinical Trial Comparing Hyperosmolar Saline to Standard Isotonic Irrigation Fluid for Arthroscopic Knee Surgery: Initial Clinical Outcomes

Numerous in vitro studies suggest higher osmolarity irrigation fluids potentiate a chondroprotective environment, and a recent clinical study using hyperosmolar saline for shoulder arthroscopy reported potential clinical advantages. This prospective randomized double-blind controlled clinical trial was designed to assess initial clinical outcomes associated with use of a hyperosmolar irrigation solution in patients undergoing arthroscopic knee surgery. With institutional review board approval and informed consent, patients scheduled for arthroscopic knee surgery were randomized to surgery with either isotonic lactated Ringer's (273 mOsm/L) or hyperosmolar saline (593 mOsm/L) irrigation solution. Outcomes included perioperative blood pressure, knee girth, visual analogue scale (VAS) pain scores, and narcotic pain medication consumption. Forty-six patients underwent arthroscopic knee surgery with isotonic (n = 23) or hyperosmolar (n = 23) irrigation fluids. There were 11 males and 12 females (mean age = 44.0 years) in the isotonic cohort and 8 males and 15 females (mean age = 40.2 years) in the hyperosmolar cohort. There were no significant differences with respect to surgical duration (pump time) or amount of irrigation fluid used between the two cohorts. There were no significant differences with respect to change in knee girth, blood pressure, or VAS pain scores. However, patients treated with hyperosmolar saline consumed less narcotic medication on postoperative day 3 (4.0 ± 7.6 vs. 15.5 ± 17.4 mg, p = 0.01). The results of this randomized clinical trial suggest that a hyperosmolar irrigation solution is safe and relatively inexpensive for use in patients undergoing arthroscopic knee surgery and contributes to a reduction in initial postoperative narcotic pain medication consumption. A hyperosmolar saline irrigation fluid was not associated with any detrimental effects on the execution of the surgical procedure, postoperative pain, or periarticular fluid extravasation. Taken together with previous basic science, translational, and clinical studies, hyperosmolar saline irrigation fluid is promising alternative to traditional isotonic irrigation fluids for knee arthroscopy. This study is a prospective trial and reflects level of evidence I.

Combination of Lidocaine and IL-1Ra Is Effective at Reducing Degradation of Porcine Cartilage Explants

BACKGROUND

Posttraumatic inflammation after joint injury, ranging from sprains to articular fracture, contributes to the development of arthritis, and the administration of interleukin 1 (IL-1) receptor antagonist (IL-1Ra) is a potential intervention to mitigate this response. Although IL-1Ra mitigates cartilage degenerative changes induced by IL-1, lidocaine is used for local pain management in acute joint injury. Intra-articular delivery of both drugs in combination would be a novel and possibly disease-modifying treatment. However, it is not known whether the interaction with lidocaine at clinical concentrations (1%) would alter the efficacy of IL-1Ra to protect cartilage from the catabolic effects of IL-1.

HYPOTHESIS

Treatment of articular cartilage with IL-1Ra in combination with a clinically relevant concentration of lidocaine (1%) will inhibit the catabolic effects of IL-1α in a manner similar to treatment with IL-1Ra alone.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fresh porcine cartilage explants were harvested, challenged with IL-1α, and incubated for 72 hours with IL-1Ra or a combination of IL-1Ra and lidocaine. The primary outcome was total sulfated glycosaminoglycan (sGAG) release. Additional experiments assessed the effect of storage temperature and premixing of IL-1Ra and lidocaine on sGAG release. All explants were histologically assessed for cartilage degradation using a modified Mankin grading scale.

RESULTS

The combination of IL-1Ra and lidocaine, premixed at various time points and stored at room temperature or 4°C, was as effective as IL-1Ra alone at inhibiting IL-1α-mediated sGAG release. Mankin histopathology scores supported these findings.

CONCLUSION

Our hypothesis was supported, and results indicated that the combination of IL-1Ra and lidocaine was as efficacious as IL-1Ra treatment alone in acutely mitigating biological cartilage injury due to IL-1α in an explant model.

CLINICAL SIGNIFICANCE

The combination of IL-1Ra and lidocaine is stable when reagents are stored in advance of administration at varying temperatures, providing clinically relevant information about storage of medications. The ability to premix and store this drug combination for intra-articular delivery may provide a novel treatment after joint injury to provide pain relief and block inflammation-induced catabolism of joint tissues.

A Tale of Two Loads: Modulation of IL-1 Induced Inflammatory Responses of Meniscal Cells in Two Models of Dynamic Physiologic Loading

Meniscus injuries are highly prevalent, and both meniscus injury and subsequent surgery are linked to the development of post-traumatic osteoarthritis (PTOA). Although the pathogenesis of PTOA remains poorly understood, the inflammatory cytokine IL-1 is elevated in synovial fluid following acute knee injuries and causes degradation of meniscus tissue and inhibits meniscus repair. Dynamic mechanical compression of meniscus tissue improves integrative meniscus repair in the presence of IL-1 and dynamic tensile strain modulates the response of meniscus cells to IL-1. Despite the promising observed effects of physiologic mechanical loading on suppressing inflammatory responses of meniscus cells, there is a lack of knowledge on the global effects of loading on meniscus transcriptomic profiles. In this study, we compared two established models of physiologic mechanical stimulation, dynamic compression of tissue explants and cyclic tensile stretch of isolated meniscus cells, to identify conserved responses to mechanical loading. RNA sequencing was performed on loaded and unloaded meniscus tissue or isolated cells from inner and outer zones, with and without IL-1. Overall, results from both models showed significant modulation of inflammation-related pathways with mechanical stimulation. Anti-inflammatory effects of loading were well-conserved between the tissue compression and cell stretch models for inner zone; however, the cell stretch model resulted in a larger number of differentially regulated genes. Our findings on the global transcriptomic profiles of two models of mechanical stimulation lay the groundwork for future mechanistic studies of meniscus mechanotransduction, which may lead to the discovery of novel therapeutic targets for the treatment of meniscus injuries.

A Hyperosmolar Saline Solution Fortified with Anti-Inflammatory Components Mitigates Articular Cartilage Pro-Inflammatory and Degradative Responses in an In Vitro Model of Knee Arthroscopy

OBJECTIVE

To evaluate differences in pro-inflammatory and degradative mediator production from osteoarthritic knee articular cartilage explants treated with a hyperosmolar saline solution supplemented with anti-inflammatory components (l-glutamine, ascorbic acid, sodium pyruvate, epigallocatechin gallate [EGCG], and dexamethasone) or normal saline using an in vitro model for knee arthroscopy.

DESIGN

Full-thickness 6 mm articular cartilage explants (n = 12/patient) were created from femoral condyle and tibial plateau samples collected from patients who received knee arthroplasty. One explant half was treated for 3 hours with hyperosmolar saline (600 mOsm/L) supplemented with anti-inflammatory components and the corresponding half with normal saline (308 mOsm/L). Explants were cultured for 3 days and then collected for biomarker analyses. Media biomarker concentrations were normalized to the wet weight of the tissue (mg) and were analyzed by a paired t test with significance set at P < 0.05.

RESULTS

Cartilage was collected from 9 females and 2 males (mean age = 68 years). Concentrations of MCP-1 (P < 0.001), IL-8 (P = 0.03), GRO-α (P = 0.02), MMP-1 (P < 0.001), MMP-2 (P < 0.001), and MMP-3 (P < 0.001) were significantly lower in explant halves treated with the enhanced hyperosmolar solution. When considering only those cartilage explants in the top tercile of tissue metabolism, IL-6 (P = 0.005), IL-8 (P = 0.0001), MCP-1 (P < 0.001), GRO-α (P = 0.0003), MMP-1 (P < 0.001), MMP-2 (P < 0.001), MMP-3 (P < 0.001), and GAG expression (P = 0.0001) was significantly lower in cartilage explant halves treated with the enhanced hyperosmolar solution.

CONCLUSIONS

Treatment of cartilage explants with a hyperosmolar saline arthroscopic irrigation solution supplemented with anti-inflammatory components was associated with significant decreases in inflammatory and degradative mediator production and mitigation of proteoglycan loss.

Advances in the Mechanisms Affecting Meniscal Avascular Zone Repair and Therapies

Injuries to menisci are the most common disease among knee joint-related morbidities and cover a widespread population ranging from children and the general population to the old and athletes. Repair of the injuries in the meniscal avascular zone remains a significant challenge due to the limited intrinsic healing capacity compared to the peripheral vascularized zone. The current surgical strategies for avascular zone injuries remain insufficient to prevent the development of cartilage degeneration and the ultimate emergence of osteoarthritis (OA). Due to the drawbacks of current surgical methods, the research interest has been transferred toward facilitating meniscal avascular zone repair, where it is expected to maintain meniscal tissue integrity, prevent secondary cartilage degeneration and improve knee joint function, which is consistent with the current prevailing management idea to maintain the integrity of meniscal tissue whenever possible. Biological augmentations have emerged as an alternative to current surgical methods for meniscal avascular zone repair. However, understanding the specific biological mechanisms that affect meniscal avascular zone repair is critical for the development of novel and comprehensive biological augmentations. For this reason, this review firstly summarized the current surgical techniques, including meniscectomies and meniscal substitution. We then discuss the state-of-the-art biological mechanisms, including vascularization, inflammation, extracellular matrix degradation and cellular component that were associated with meniscal avascular zone healing and the advances in therapeutic strategies. Finally, perspectives for the future biological augmentations for meniscal avascular zone injuries will be given.

Current State of Synovial Fluid Biomarkers in Sports Medicine

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While the gross mechanical abnormalities contributing to posttraumatic osteoarthritis (PTOA) have been well described, new research is demonstrating that these insults to the articular cartilage may also initiate changes in the joint microenvironment that seed the development of PTOA.

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A growing amount of literature has identified key biomarkers that exhibit altered expression in the synovial fluid following a knee injury, with a portion of these molecules remaining elevated in the years following an injury.

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These biomarkers have the potential to aid in the early detection of PTOA before radiographic evidence becomes apparent. Furthermore, deciphering the processes that occur within the articular microenvironment after trauma may allow for better identification of therapeutic targets for the prevention and earlier treatment of PTOA.

Meniscal Regenerative Scaffolds Based on Biopolymers and Polymers: Recent Status and Applications

Knee menisci are structurally complex components that preserve appropriate biomechanics of the knee. Meniscal tissue is susceptible to injury and cannot heal spontaneously from most pathologies, especially considering the limited regenerative capacity of the inner avascular region. Conventional clinical treatments span from conservative therapy to meniscus implantation, all with limitations. There have been advances in meniscal tissue engineering and regenerative medicine in terms of potential combinations of polymeric biomaterials, endogenous cells and stimuli, resulting in innovative strategies. Recently, polymeric scaffolds have provided researchers with a powerful instrument to rationally support the requirements for meniscal tissue regeneration, ranging from an ideal architecture to biocompatibility and bioactivity. However, multiple challenges involving the anisotropic structure, sophisticated regenerative process, and challenging healing environment of the meniscus still create barriers to clinical application. Advances in scaffold manufacturing technology, temporal regulation of molecular signaling and investigation of host immunoresponses to scaffolds in tissue engineering provide alternative strategies, and studies have shed light on this field. Accordingly, this review aims to summarize the current polymers used to fabricate meniscal scaffolds and their applications in vivo and in vitro to evaluate their potential utility in meniscal tissue engineering. Recent progress on combinations of two or more types of polymers is described, with a focus on advanced strategies associated with technologies and immune compatibility and tunability. Finally, we discuss the current challenges and future prospects for regenerating injured meniscal tissues.

Discoid meniscus in human fetuses: A systematic review

BACKGROUND

Discoid meniscus (DM) is a rare variant of regular knee anatomy. Compared to standard meniscus it is thicker and abnormal in shape; these characteristics make it more prone to tear. It is a congenital defect whose correct etiology is still debated and far from being clarified. The purpose of this systematic review is to evaluate evidences of DM in human fetuses in order to assess whether embryological development may have a role.

METHODS

A systematic review was performed on PubMed, Scopus, and Embase with different combinations of the keywords "discoid meniscus", "embryology", "fetus", "neonatal". Search yielded 1013 studies, on which we performed a primary evaluation.

RESULTS

Seven studies were considered including a total of 1378 fetal menisci specimens, from 396 different fetuses. Discoid shape was not found represented as a normal stage of prenatal development. From 782 lateral menisci analyzed, only 86 (10.86%) were discoid (13 complete, 73 incomplete type). None of medial menisci was found to be discoid. Lateral meniscus was observed to cover a larger surface of tibial plateau than medial one until 28th gestational week.

CONCLUSION

Lateral meniscus seems to be more prone to discoid shape for its natural tendency of covering a larger surface of the tibial plateau during fetal stages. However the fact that a discoid shape was not found in the majority of fetuses suggests that it is not a normal stage of fetal development. To support a single etiological factor it will be appropriate to have further morphological and morphometric studies.

Use of a Hyperosmolar Saline Solution to Mitigate Proinflammatory and Degradative Responses of Articular Cartilage and Meniscus for Application to Arthroscopic Surgery

PURPOSE

This study was designed to evaluate differences in proinflammatory and degradative mediator production and extracellular matrix degradation from osteoarthritic knee articular cartilage and meniscus explants treated with either hyperosmolar saline or isotonic saline.

METHODS

6 mm-diameter full-thickness explants were created from articular cartilage and menisci recovered after patients underwent knee surgery. One explant half was treated for 3 hours with hyperosmolar saline (600 mOsm/L) and the corresponding half with isotonic saline (300 mOsm/L). Explants were subsequently cultured for 3 days in tissue culture media. On day 3, media were collected for biomarker analyses. Results were normalized to tissue wet weight and analyzed statistically.

RESULTS

Articular cartilage was collected from 10 patients (5 male, 5 female; mean age = 66.9 years) and menisci were collected from 8 patients (2 male, 6 female; mean age = 66 years). Articular cartilage media concentrations of monocyte chemoattractant protein-1 (P = .001) and interleukin (IL)-6 (P = .049) were significantly lower in explants treated with hyperosmolar saline. Meniscus media concentrations of prostaglandin E₂ (P = .008), monocyte chemoattractant protein-1 (P = .011), IL-6 (P = .029), IL-8 (P = .012), matrix metalloproteinase-2 (P = .011), and glycosaminoglycan (P = .008) were significantly lower in explants treated with hyperosmolar saline.

CONCLUSIONS

Treatment of cartilage and meniscus explants with hyperosmolar saline effectively mitigated key proinflammatory mediator production, as well as degradative mediator production and glycosaminoglycan loss from meniscus, with no detrimental effects noted compared to isotonic saline.

CLINICAL RELEVANCE

These results suggest that hyperosmolar saline irrigation fluid may provide a safe alternative to standard isotonic saline irrigation fluid, and could mitigate untoward effects associated with inflammatory responses after standard-of-care knee arthroscopy.

Characterization of Synovial Cytokine Patterns in Bucket-Handle and Posterior Horn Meniscal Tears

The specific etiology of meniscal tears, including the mechanism of lesion, location, and orientation, is considered for its contribution to subsequent joint cytokine responsiveness, healing outcomes, and by extension, appropriate lesion-specific surgical remediation. Meniscal repair is desirable to reduce the probability of development of posttraumatic osteoarthritis (PTOA) which is strongly influenced by the coordinate generation of pro- and anti-inflammatory cytokines by the injured cartilage. We now present biochemical data on variation in cytokine levels arising from two particular meniscal tears: bucket-handle (BH) and posterior horn (PH) isolated meniscal tears. We selected these two groups due to the different clinical presentations. We measured the concentrations of TNF-α, IL-1β, IL-6, IL-8, and IL-10 in knee synovial fluid of 45 patients with isolated meniscal lesions (BH tear, n = 12; PH tear, n = 33). TNF-α levels were significantly (p < 0.05) greater in the BH group compared with the PH group, whereas IL-1β levels were significantly greater (p < 0.05) in the PH group compared with the BH group. Both BH and PH groups were consistent in presenting a positive correlation between concentrations of IL-6 and IL-1β. A fundamental difference in IL-10 responsiveness between the two groups was noted; specifically, levels of IL-10 were positively correlated with IL-6 in the BH group, whereas in the PH group, levels of IL-10 were positively correlated with IL-1β. Collectively, our data suggest a possible influence of the meniscal tear pattern to the articular cytokine responsiveness. This differential expression of inflammatory cytokines may influence the risk of developing PTOA in the long term.

Molecular biology of meniscus pathology: Lessons learned from translational studies and mouse models

Injury to any individual structure in the knee interrupts the overall function of the joint and initiates a cascade of biological and biomechanical changes whose endpoint is often osteoarthritis (OA). The knee meniscus is an integral component of knee biomechanics and may also contribute to the biological homeostasis of the joint. Meniscus injury altering knee function is associated with a high risk of OA progression, and may also be involved in the initiation of OA. As the relationship between meniscus injury and OA is very complex; despite the availability of transcript level data on human meniscus injury and meniscus mediated OA, mechanistic studies are lacking, and available human data are difficult to validate in the absence of patient-matched noninjured control tissues. As similarities exist between human and mouse knee joint structure and function, investigators have begun to use cutting-edge genetic and genomic tools to examine the usefulness of the mouse as a model to study the intricate relationship between meniscus injury and OA. In this review, we use evidence from human meniscus research to identify critical barriers hampering our understanding of meniscus injury induced OA and discuss strategies to overcome these barriers, including those that can be examined in a mouse model of injury-mediated OA.

Amniotic Suspension Allograft Modulates Inflammation in a Rat Pain Model of Osteoarthritis

Osteoarthritis (OA) affects over 301 million adults worldwide. Inflammation is a recognized component of the OA process; two potent pro-inflammatory cytokines involved in OA are interleukin-1β and tumor necrosis factor-α. Placental-derived tissues and fluids are known to contain anti-inflammatory and immunomodulatory cytokines and growth factors. The objective of this study was to evaluate the anti-inflammatory effects of amniotic suspension allograft (ASA) in an in vivo model of OA; we evaluated pain, function, and cytokine levels following ASA treatment in the rat monosodium iodoacetate (MIA) OA pain model. Rats were injected with 2 mg of MIA, which causes pain, cartilage degeneration, and inflammation, followed by treatment with saline, triamcinolone (positive control), or ASA 7 days following disease induction with MIA. Behavioral assays, including gait analysis, mechanical pain threshold, incapacitance, and swelling were evaluated, along with histology and serum and synovial fluid biomarkers. Treatment with ASA resulted in significant improvements in pain threshold, while weight bearing aversion and swelling were significantly decreased. There were no differences between groups in total joint score after histological grading. Serum biomarkers did not show differences, indicating a lack of systemic response; however, synovial fluid levels of IL-10 were significantly increased in animals treated with ASA. ASA treatment significantly reduced pain, weight-bearing aversion and swelling. This study provides mechanistic data regarding potential therapeutic effects of ASA in OA and preliminary evidence of the anti-inflammatory nature of ASA. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:1141-1149, 2020.

Osteoarthritis-related biomarkers profile in chronic anterior cruciate ligament injured knee

OBJECTIVE

Increasing evidence has shown the involvement of the innate immune system and inflammatory response in osteoarthritis (OA) pathogenesis; however, anterior cruciate ligament (ACL) tears are recognized risk factors for development of post-traumatic OA. We investigated (1) whether inflammatory mediators involved in OA pathogenesis are also present at significant concentrations in the knee joint sometime after ACL complete tear and may be considered as prognostic biomarkers of progression to secondary OA; and (2) whether quantification in serum may surrogate synovial fluid (SF) measurements in both cases.

METHODS

Thirty-seven end-stage OA patients and 33 patients with ACL complete tear that were included on the waiting list for knee surgery were consecutively recruited. Serum and SF samples were taken before surgery, and tumor necrosis factor-alpha, (TNF-α), interleukin-6 (IL-6), interleukin-8 (IL-8), matrix metalloproteinase-1 (MMP1), matrix metalloproteinase-3 (MMP3), tissue inhibitor of metalloproteinase-1 (TIMP1), bone morphogenetic protein-7 (BMP7), regulated upon activation normal t-cell expressed and secreted (RANTES), cytokine interferon-γ-induced protein 10 (IP-10) and heat shock protein family A (Hsp70) member 1A (HSPA1A) were quantified by enzyme-linked immunosorbent assay (ELISA.) Normally distributed data were compared using a one-way analysis of variance (ANOVA) test. Data not normally distributed were analyzed using a nonparametric Mann-Whitney rank sum test. Differences in means were compared using a Student's t-test. Correlations were analyzed using Pearson's coefficient of variation.

RESULTS

Eighty-seven percent of patients with OA and 86% of those with ACL tear had quantifiable levels of biomarkers in SF. SF levels of IL-6, IL-8, MMP1, MMP3, RANTES, IP-10, BMP7 and HSPA1A were significantly lower in ACL injury knees compared with those with OA, but much higher than those reported in control subjects. Serum levels of IL-6, IP-10, and MMP1 were also lower in patients with ACL tears, who had, however, significantly higher TNF-α, HSPA1A, and TIMP1 levels when compared with OA patients. Levels of biomarkers tested in serum and SF samples were significantly different.

CONCLUSIONS

Our data propose that cytokines IL-6 and IL-8 and the chemokines RANTES, IP-10, MMP1, MMP3, and HSPA1A may be involved in the inflammatory process leading to synovitis, the central lesion in OA onset and development; persistent high levels of these substances sometime after ACL injury suggest that they could play an etiopathogenic role in the maintenance of the inflammatory environment leading to post-traumatic OA. Serum biomarker levels do not appear to faithfully reflect what occurs inside the joint. Thus, most biomarkers cannot yet be considered as useful inflammatory biomarkers of knee joint diseases.

Anticitrullinated protein antibodies facilitate migration of synovial tissue-derived fibroblasts

OBJECTIVES

Rheumatoid arthritis (RA)-specific anti-citrullinated protein/peptide antibodies (ACPAs) might contribute to bone loss and arthralgia before the onset of joint inflammation. We aimed to dissect additional mechanisms by which ACPAs might contribute to development of joint pathology.

METHODS

Fibroblast-like synoviocytes (FLS) were isolated from the synovial membrane of patients with RA. The FLS cultures were stimulated with polyclonal ACPAs (anti-CCP-2 antibodies) purified from the peripheral blood of patients with RA or with monoclonal ACPAs derived from single synovial fluid B cells. We analysed how ACPAs modulate FLS by measuring cell adhesion and mobility as well as cytokine production. Expression of protein arginine deiminase (PAD) enzymes and protein citrullination were analysed by immunofluorescence, and signal transduction was studied using immunoblotting.

RESULTS

Challenge of FLS by starvation-induced stress or by exposure to the chemokine interleukin-8 was essential to sensitise the cells to ACPAs. These challenges led to an increased PAD expression and protein citrullination and an ACPA-mediated induction of FLS migration through a mechanism involving phosphoinositide 3-kinase activation. Inhibition of the PAD enzymes or competition with soluble citrullinated proteins or peptides completely abolished the ACPA-induced FLS migration. Different monoclonal ACPAs triggered distinct cellular effects in either fibroblasts or osteoclasts, suggesting unique roles for individual ACPA clones in disease pathogenesis.

CONCLUSION

We propose that transient synovial insults in the presence of a certain pre-existing ACPA repertoire might result in an ACPA-mediated increase of FLS migration.

Metabolic responses of meniscal tissue to focal collagenase degeneration

Purpose: The objective of this study was to determine the responses of normal meniscus to collagenase activity. It was hypothesized that meniscal explants exposed to collagenase would significantly increase release of pro-inflammatory cytokines and degradative enzymes, in a dose-dependent manner, compared to control.Methods: Menisci were harvested from adult dogs (n = 6) euthanized for reasons unrelated to this study. Meniscal explants were created from the central portion of lateral and medial meniscus. Explants were injected with 100 µl collagenase at a concentration of 50 µg/ml, 5 µg/ml, or 0 µg/ml of collagenase. Explants were cultured for 12 days, and media were changed and collected every 3 days for biomarker analyses. Differences among collagenase concentrations were determined by a three factor ANOVA with adjustment for multiple comparisons, with pre-adjustment statistical significance set at p < 0.05.Results: When data from all explants were compared, the 50 µg group released significantly higher IL-6 and PGE2, and the 5 µg group released significantly higher levels of MMP-3 and CTX-II compared to the 0 µg group. Explants from the medial meniscus released significantly more MMP-1, MMP-2, MMP-3, and MMP-13 in response to stimulation with 5 µg/ml of collagenase compared to explants from the lateral meniscus.Discussion: The data from this study indicate that in response to localized degradative enzyme activity, the meniscus increases the release of pro-inflammatory and degradative biomarkers in a dose-dependent manner. Further, these data indicate potential differences in metabolic responses of lateral versus medial menisci to collagenase insult.

The Meniscus in Normal and Osteoarthritic Tissues: Facing the Structure Property Challenges and Current Treatment Trends

The treatment of meniscus injuries has recently been facing a paradigm shift toward the field of tissue engineering, with the aim of regenerating damaged and diseased menisci as opposed to current treatment techniques. This review focuses on the structure and mechanics associated with the meniscus. The meniscus is defined in terms of its biological structure and composition. Biomechanics of the meniscus are discussed in detail, as an understanding of the mechanics is fundamental for the development of new meniscal treatment strategies. Key meniscal characteristics such as biological function, damage (tears), and disease are critically analyzed. The latest technologies behind meniscal repair and regeneration are assessed.

Evaluation of the effect of experimentally induced cartilage defect and intra-articular hyaluronan on synovial fluid biomarkers in intercarpal joints of horses

BACKGROUND

Inflammatory and degenerative activity inside the joint can be studied in vivo by analysis of synovial fluid biomarkers. In addition to pro-inflammatory mediators, several anabolic and anti-inflammatory substances are produced during the disease process. They counteract the catabolic effects of the pro-inflammatory cytokines and thus diminish the cartilage damage. The response of synovial fluid biomarkers after intra-articular hyaluronan injection, alone or in combination with other substances, has been examined only in a few equine studies. The effects of hyaluronan on some pro-inflammatory mediators, such as prostaglandin E2, have been documented but especially the effects on synovial fluid anti-inflammatory mediators are less studied. In animal models hyaluronan has been demonstrated to reduce pain via protecting nociceptive nerve endings and by blocking pain receptor channels. However, the results obtained for pain-relief of human osteoarthritis are contradictory. The aim of the study was to measure the synovial fluid IL-1ra, PDGF-BB, TGF-β1 and TNF-α concentrations before and after surgically induced cartilage defect, and following intra-articular hyaluronan injection in horses. Eight Standardbred horses underwent bilateral arthroscopic surgeries of their intercarpal joints under general anaesthesia, and cartilage defect was created on the dorsal edge of the third carpal bone of one randomly selected intercarpal joint of each horse. Five days post-surgery, one randomly selected intercarpal joint was injected intra-articular with 3 mL HA (20 mg/mL).

RESULTS

Operation type had no significant effect on the synovial fluid IL-1ra, PDGF-BB, TGF-β1 and TNF-α concentrations but compared with baseline, synovial fluid IL-1ra and TNF-α concentrations increased. Intra-articular hyaluronan had no significant effect on the biomarker concentrations but a trend of mild improvement in the clinical signs of intra-articular inflammation was seen.

CONCLUSIONS

Creation of the cartilage defect and sham-operation lead to an increase of synovial fluid IL-1ra and TNF-α concentrations but changes in concentrations of anabolic growth factors TGF-β1 and PDGF-BB could not be documented 5 days after the arthroscopy. Intra-articular hyaluronan was well tolerated. Further research is needed to document possible treatment effects of intra-articular hyaluronan on the synovial fluid biomarkers of inflammation and cartilage metabolism.

Continuous low-intensity ultrasound attenuates IL-6 and TNFα-induced catabolic effects and repairs chondral fissures in bovine osteochondral explants

BACKGROUND

Cartilage repair outcomes are compromised in a pro-inflammatory environment; therefore, the mitigation of pro-inflammatory responses is beneficial. Treatment with continuous low-intensity ultrasound (cLIUS) at the resonant frequency of 5 MHz is proposed for the repair of chondral fissures under pro-inflammatory conditions.

METHODS

Bovine osteochondral explants, concentrically incised to create chondral fissures, were maintained under cLIUS (14 kPa (5 MHz, 2.5 Vpp), 20 min, 4 times/day) for a period of 28 days in the presence or absence of cytokines, interleukin-6 (IL-6) or tumor necrosis factor (TNF)α. Outcome assessments included histological and immunohistochemical staining of the explants; and the expression of catabolic and anabolic genes by qRT-PCR in bovine chondrocytes. Cell migration was assessed by scratch assays, and by visualizing migrating cells into the hydrogel core of cartilage-hydrogel constructs.

RESULTS

Both in the presence and absence of cytokines, higher percent apposition along with closure of fissures were noted in cLIUS-stimulated explants as compared to non-cLIUS-stimulated explants on day 14. On day 28, the percent apposition was not significantly different between unstimulated and cLIUS-stimulated explants exposed to cytokines. As compared to non-cLIUS-stimulated controls, on day 28, cLIUS preserved the distribution of proteoglycans and collagen II in explants despite exposure to cytokines. cLIUS enhanced the cell migration irrespective of cytokine treatment. IL-6 or TNFα-induced increases in MMP13 and ADAMTS4 gene expression was rescued by cLIUS stimulation in chondrocytes. Under cLIUS, TNFα-induced increase in NF-κB expression was suppressed, and the expression of collagen II and TIMP1 genes were upregulated.

CONCLUSION

cLIUS repaired chondral fissures, and elicited pro-anabolic and anti-catabolic effects, thus demonstrating the potential of cLIUS in improving cartilage repair outcomes.

The Importance of the Knee Joint Meniscal Fibrocartilages as Stabilizing Weight Bearing Structures Providing Global Protection to Human Knee-Joint Tissues

The aim of this study was to review aspects of the pathobiology of the meniscus in health and disease and show how degeneration of the meniscus can contribute to deleterious changes in other knee joint components. The menisci, distinctive semilunar weight bearing fibrocartilages, provide knee joint stability, co-ordinating functional contributions from articular cartilage, ligaments/tendons, synovium, subchondral bone and infra-patellar fat pad during knee joint articulation. The meniscus contains metabolically active cell populations responsive to growth factors, chemokines and inflammatory cytokines such as interleukin-1 and tumour necrosis factor-alpha, resulting in the synthesis of matrix metalloproteases and A Disintegrin and Metalloprotease with ThromboSpondin type 1 repeats (ADAMTS)-4 and 5 which can degrade structural glycoproteins and proteoglycans leading to function-limiting changes in meniscal and other knee joint tissues. Such degradative changes are hall-marks of osteoarthritis (OA). No drugs are currently approved that change the natural course of OA and translate to long-term, clinically relevant benefits. For any pharmaceutical therapeutic intervention in OA to be effective, disease modifying drugs will have to be developed which actively modulate the many different cell types present in the knee to provide a global therapeutic. Many individual and combinatorial approaches are being developed to treat or replace degenerate menisci using 3D printing, bioscaffolds and hydrogel delivery systems for therapeutic drugs, growth factors and replacement progenitor cell populations recognising the central role the menisci play in knee joint health.

Gene expression, protein profiling, and chemotactic activity of infrapatellar fat pad mesenchymal stem cells in pathologies of the knee joint

The infrapatellar fat pad (IPFP) is a periarticular adipose knee tissue. This tissue contains a large number of mesenchymal stem cells (MSCs). In the present work, we wanted to study the IPFP MSCs and their relationship and differences in two groups, anterior cruciate ligament (ACL) ruptures knees and ostheoarthrosis (OA). The IPFP of 42 patients with OA or ACL rupture were analyzed. Isolation, primary culture, and a genetic and proteomic study of MSCs from IPFP were performed. Gene expression of IL-6, tumor necrosis factor (TNF), IL-8, HSPA1A (Hsp70), CXCL10, RANTES, MMP1, MMP3, TIMP1, and BMP7 was analyzed by real-time quantitative polymerase chain reaction (RT-qPCR). We analyzed MSCs from from 12 diferents patients in two cellular pools (6 from AO disease and 6 from ALC rupture to form two cell pool), for the iTRAQ Proteomic Assay. The conditional media were used in quantitative analysis of MSC soluble factors by Luminex and for de migration assay. A higher gene expression of IL-6, TNF, CXCL10, RANTES, and MMP1 and OPG in MSCs from OA versus ACL (p < 0.05) was observed. Conversely HSPA1A, TIMP1, and RANKL showed a significant lower expression in OA-MSCs (p < 0.05). In the secretome analysis, adipsin and visfantin levels in the supernatants from OA-MSCs were lower (p < 0.05) respect to ACL-MSCs. Also, the monocytic cells migrated two-folds in the presence of conditioned media from OA-MSCs patients versus patients with ACL-MSC. The infrapatellar pad should be considered as an adipose tissue capable of producing and excreting inflammatory mediators directly in the knee joint, influencing the development and progression of knee joint pathologies.

Arthroscopic repair of the meniscus: Surgical management and clinical outcomes

From the biomechanical and biological points of view, an arthroscopic meniscal repair (AMR) should always be considered as an option. However, AMR has a higher reoperation rate compared with arthroscopic partial meniscectomy, so it should be carefully indicated.

Compared with meniscectomy, AMR outcomes are better and the incidence of osteoarthritis is lower when it is well indicated.

Factors influencing healing and satisfactory results must be carefully evaluated before indicating an AMR.

Tears in the peripheral third are more likely to heal than those in the inner thirds.

Vertical peripheral longitudinal tears are the best scenario in terms of success when facing an AMR.

‘Inside-out’ techniques were considered as the gold standard for large repairs on mid-body and posterior parts of the meniscus. However, recent studies do not demonstrate differences regarding failure rate, functional outcomes and complications, when compared with the ‘all-inside’ techniques.

Some biological therapies try to enhance meniscal repair success but their efficacy needs further research. These are: mechanical stimulation, supplemental bone marrow stimulation, platelet rich plasma, stem cell therapy, and scaffolds and membranes.

Meniscal root tear/avulsion dramatically compromises meniscal stability, accelerating cartilage degeneration. Several options for reattachment have been proposed, but no differences between them have been established. However, repair of these lesions is actually the reference of the treatment.

Meniscal ramp lesions consist of disruption of the peripheral attachment of the meniscus. In contrast, with meniscal root tears, the treatment of reference has not yet been well established.

Cite this article: EFORT Open Rev 2018;3:584-594. DOI: 10.1302/2058-5241.3.170059

Metabolic responses of meniscal explants to injury and inflammation ex vivo

This study was designed to characterize metabolic responses of meniscal tissue explants to injury and inflammation. We hypothesized that impact injury and interleukin (IL-1β) stimulation of meniscal explants would result in significant increases in matrix metalloproteinase (MMP) activity and relevant cytokine production compared to controls. Mature canine meniscal explants (n = 9/group) were randomly assigned to: (i) IL-1β (0.1 ng/ml) treated (IL); (ii) 25% strain (25); (iii) 75% strain (75); (iv) 25% + IL-1β (25IL); (v) 75% + IL-1β (75IL); or (vi) 0% + no IL-1β control (NC). Explants were impacted at 100 mm/s to 0%, 25%, or 75% strain and then cultured for 12 days with or without 0.1 ng/ml rcIL-1β. Media were refreshed every 3 days and analyzed for MMP activity, ADAMTS-4 activity, MMP-1, MMP-2, MMP-3, GAG, NO, PGE₂ , IL-6, IL-8, MCP-1, and KC concentrations. Treatment with IL-1β alone significantly increased NO, PGE2, general MMP activity, IL-6, IL-8, KC, and MCP-1 media concentrations compared to negative controls. Impact at 75% significantly increased PGE2, IL-6, IL-8, and KC media concentrations compared to negative controls. The combination of IL-1β and 75% strain significantly increased production of PGE2 compared to IL-1β or 75% strain alone. Impact injury to meniscal explants ex vivo is associated with increased production of pro-inflammatory mediators and degradative enzyme activity, which are exacerbated by stimulation with IL-1β. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2657-2663, 2018.

Intra-Articular Cytokine Levels in Adolescent Patients after Anterior Cruciate Ligament Tear

The treatment of anterior cruciate ligament (ACL) injuries in children and adolescents is challenging. Preclinical and clinical studies investigated ACL repairing techniques in skeletally immature subjects. However, intra-articular bioenvironment following ACL tear has not yet been defined in skeletally immature patients. The aim of this study was to measure cytokine concentrations in the synovial fluid in adolescent population. Synovial levels of IL-1β, IL-1ra, IL-6, IL-8, IL-10, and TNF-α were measured in 17 adolescent patients (15 boys) with ACL tears who underwent ACL reconstruction including acute (5), subacute (7), and chronic (5) phases. Femoral growth plates were classified as “open” in three patients, “closing” in eight, and “closed” in six. Eleven patients presented an ACL tear associated with a meniscal tear. The mean Tegner and Lysholm scores (mean ± SD) of all patients were 8 ± 1 and 50.76 ± 26, respectively. IL-8, TNF-α, and IL-1β levels were significantly greater in patients with “open” physes. IL-1ra and IL-1β levels were significantly higher in patients with ACL tear associated with a meniscal tear. Poor Lysholm scores were associated with elevated IL-6 and IL-10 levels. IL-10 levels positively correlated with IL-6 and IL-8 levels, whereas TNF-α concentration negatively correlated with IL-6 levels. Skeletally immature patients with meniscal tears and open growth plates have a characteristic cytokine profile with particularly elevated levels of proinflammatory cytokines including IL-8, TNF-α, and IL-1β. This picture suggests that the ACL tear could promote an intra-articular catabolic response in adolescent patients greater than that generally reported for adult subjects. The study lacks the comparison with synovial samples from healthy skeletally immature knees due to ethical reasons. Overall, these data contribute to a better knowledge of adolescent intra-articular bioenvironment following ACL injuries.

Radiofrequency Ablation for Mucoid Degeneration of the Anterior Cruciate Ligament

Mucoid degeneration of the anterior cruciate ligament (MD-ACL) is an underdiagnosed ACL pathology. When recognized, one potential management strategy involves arthroscopic debridement to "debulk" the ACL. Here, with the addition of video footage, we describe our arthroscopic technique for MD-ACL debridement using radiofrequency ablation. We show the engorged, stranded MD-ACL during arthroscopy and how this engorgement causes impingement in the femoral notch, resulting in the symptoms described by the patient. After radiofrequency ablation, we show a reduction in impingement and assess the stability of the cruciate ligaments. This Technical Note aims to raise awareness of this pathology and show the technique of arthroscopic radiofrequency ablation to reduce impingement of the ACL within the femoral notch.

Inflammatory and degenerative phases resulting from anterior cruciate rupture in a non-invasive murine model of post-traumatic osteoarthritis

Joint injury is the predominant risk factor for post-traumatic osteoarthritis development (PTOA). Several non-invasive mouse models mimicking human PTOA investigate molecular mechanisms of disease development; none have characterized the inflammatory response to this acute traumatic injury. Our aim was to characterize the early inflammatory phase and later degenerative component in our in vivo non-invasive murine model of PTOA induced by anterior cruciate ligament (ACL) rupture. Right knees of 12-week-old C57Bl6 mice were placed in flexion at a 30° offset position and subjected to a single compressive load (12N, 1.4 mm/s) to induce ACL rupture with no obvious damage to surrounding tissues. Tissue was harvested 4 h post-injury and on days 3, 14, and 21; contralateral left knees served as controls. Histological, immunohistochemical, and gene analyzes were performed to evaluate inflammatory and degenerative changes. Immunohistochemistry revealed time-dependent expression of mature (F4/80 positive) and inflammatory (CD11b positive) macrophage populations within the sub-synovial infiltrate, developing osteophytes, and inflammation surrounding the ACL in response to injury. Up-regulation of genes encoding acute pro-inflammatory markers, inducible nitric oxide synthase, interleukin-6 and interleukin-17, and the matrix degrading enzymes, ADAMTS-4 and MMP3 was detected in femoral cartilage, concomitant with extensive cartilage damage and bone remodelling over 21-days post-injury. Our non-invasive model describes pathologically distinct phases of the disease, increasing our understanding of inflammatory episodes, the tissues/cells producing inflammatory mediators and the early molecular changes in the joint, thereby defining the early phenotype of PTOA. This knowledge will guide appropriate interventions to delay or arrest disease progression following joint injury. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society. J Orthop Res 9999:1-10, 2018.

Models to define the stages of articular cartilage degradation in osteoarthritis development

Osteoarthritis (OA) is a common chronic disorder that affects an increasing number of the ageing population. Despite the prevalence, there are currently no therapies. Defining new therapies that target specific pathogenic phases of disease development relies on the effective separation of the different stages of OA. This manuscript reviews the tissues and models that are being used to separate these stages of disease, in particular initiation and early and late progression. These models include human tissues with known initiating factors, the use of anatomical locations with defined relationships to the primary cartilage lesion area, timing of OA development in well-described animal models and the versatility of a non-invasive model of murine knee joint trauma.

Inflammatory Microenvironment Persists After Bone Healing in Intra-articular Ankle Fractures

BACKGROUND

Post-traumatic osteoarthritis (PTOA) is responsible for the majority of cases of ankle arthritis. While acute and end-stage intra-articular inflammation has previously been described, the state of the joint between fracture healing and end-stage PTOA remains undefined. This study characterized synovial fluid (SF) composition of ankles after bone healing of an intra-articular fracture to identify factors that may contribute to the development of PTOA.

METHODS

Of an original 21 patients whose SF was characterized acutely following intra-articular ankle fractures, 7 returned for planned hardware (syndesmotic screw) removal after bone healing (approximately 6 months) and consented to a second bilateral SF collection. SF concentrations of 15 cytokines and matrix metalloproteinases (MMPs) and 2 markers each of cartilage catabolism (CTXII and glycosaminoglycan) and hemarthrosis (biliverdin and bilirubin) were compared for previously fractured and contralateral, uninjured ankles from the same patient. Analysis was also performed to determine the effect of the number of fracture lines and involvement of soft tissue on SF composition.

RESULTS

Interleukin (IL)-6, IL-8, MMP-1, MMP-2, and MMP-3 were significantly elevated in the SF from healed ankles compared to matched contralateral uninjured ankles at approximately 6 months after fracture. There were no differences in markers of cartilage catabolism or hemarthrosis. Only IL-1α was affected by the number of fracture lines while differences were not detected for other analytes or with respect to the involvment of soft tissue.

CONCLUSIONS

Sustained intra-articular inflammation, even after complete bone healing, was suggested by elevations of pro-inflammatory cytokines (IL-6 and IL-8). In addition, elevated concentrations of MMPs were also noted and were consistent with a persistent inflammatory environment. This study suggests new evidence of persistent intra-articular inflammation after intra-articular ankle fracture healing and suggests potential mediators for PTOA development.

CLINICAL RELEVANCE

This work may be relevant to the clinical diagnosis and treatment of post-traumatic osteoarthritis.