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

Excessive mechanical loading promotes osteoarthritis development by upregulating Rcn2

Exposure of articular cartilage to excessive mechanical loading is closely related to the pathogenesis of osteoarthritis (OA). However, the exact molecular mechanism by which excessive mechanical loading drives OA remains unclear. In vitro, primary chondrocytes were exposed to cyclic tensile strain at 0.5 Hz and 10 % elongation for 30 min to simulate excessive mechanical loading in OA. In vivo experiments involved mice undergoing anterior cruciate ligament transection (ACLT) to model OA, followed by interventions on Rcn2 expression through adeno-associated virus (AAV) injection and tamoxifen-induced gene deletion. 10 μL AAV2/5 containing AAV-Rcn2 or AAV-shRcn2 was administered to the mice by articular injection at 1 week post ACLT surgery, and Col2a1-creERT: Rcn2flox/flox mice were injected with tamoxifen intraperitoneally to obtain Rcn2-conditional knockout mice. Finally, we explored the mechanism of Rcn2 affecting OA. Here, we identified reticulocalbin-2 (Rcn2) as a mechanosensitive factor in chondrocytes, which was significantly elevated in chondrocytes under mechanical overloading. PIEZO type mechanosensitive ion channel component 1 (Piezo1) is a critical mechanosensitive ion channel, which mediates the effect of mechanical loading on chondrocytes, and we found that increased Rcn2 could be suppressed through knocking down Piezo1 under excessive mechanical loading. Furthermore, chondrocyte-specific deletion of Rcn2 in adult mice alleviated OA progression in the mice receiving the surgery of ACLT. On the contrary, articular injection of Rcn2-expressing adeno-associated virus (AAV) accelerated the progression of ACLT-induced OA in mice. Mechanistically, Rcn2 accelerated the progression of OA through promoting the phosphorylation and nuclear translocation of signal transducer and activator of transcription 3 (Stat3).

Osteoarthritis Development Following Meniscectomy vs. Meniscal Repair for Posterior Medial Meniscus Injuries: A Systematic Review

This systematic review aims to evaluate critically and synthesize the existing literature on the outcomes of meniscectomy versus meniscal repair for posterior medial meniscus injuries, with a focus on osteoarthritis (OA) development. We sought to assess the incidence of OA following both treatment modalities, compare functional outcomes post-treatment, and identify factors influencing treatment choice, providing evidence-based recommendations for clinical decision-making. A comprehensive search strategy was employed across PubMed, Scopus, and Embase up until December 2023, adhering to PRISMA guidelines. The primary outcomes included OA development, functional knee outcomes, and quality of life measures. Six studies met the inclusion criteria, encompassing 298 patients. The systematic review revealed a significant association between meniscal repair and decreased progression of OA compared to meniscectomy. Meniscectomy patients demonstrated a 51.42% progression rate towards OA, significantly higher than the 21.28% observed in meniscal repair patients. Functional outcomes, as measured by the International Knee Documentation Committee (IKDC) and Lysholm scores, were notably better in the repair group, with average scores of 74.68 (IKDC) and 83.78 (Lysholm) compared to 67.55 (IKDC) and 74.56 (Lysholm) in the meniscectomy group. Furthermore, the rate of complete healing in the repair group was reported at 71.4%, as one study reported, indicating a favorable prognosis for meniscal preservation. However, these pooled data should be interpreted with consideration to the heterogeneity of the analyzed studies. Meniscal repair for posterior medial meniscus injuries is superior to meniscectomy in preventing OA development and achieving better functional outcomes and quality of life post-treatment. These findings strongly suggest the adoption of meniscal repair as the preferred treatment modality for such injuries, emphasizing the need for a paradigm shift in clinical practice towards preserving meniscal integrity to optimize patient outcomes.

[Design and validation of a novel knee biomechanical test method]

A novel structural dynamics test method and device were designed to test the biomechanical effects of dynamic axial loading on knee cartilage and meniscus. Firstly, the maximum acceleration signal-to-noise ratio of the experimental device was calculated by applying axial dynamic load to the experimental device under unloaded condition with different force hammers. Then the experimental samples were divided into non-specimen group (no specimen loaded), sham specimen group (loaded with polypropylene samples) and bovine knee joint specimen group (loaded with bovine knee joint samples) for testing. The test results show that the experimental device and method can provide stable axial dynamic load, and the experimental results have good repeatability. The final results confirm that the dynamic characteristics of experimental samples can be distinguished effectively by this device. The experimental method proposed in this study provides a new way to further study the biomechanical mechanism of knee joint structural response under axial dynamic load.

Transplantable stem cell nanobridge scaffolds for accelerating articular cartilage regeneration

Microfracture technique for treating articular cartilage defects usually has poor clinical outcomes due to critical heterogeneity and extremely limited in quality. To improve the effects of current surgical technique (i.e., microfracture technique), we propose the transplantable stem cell nanobridge scaffold, acting as a protective bridge between host tissue and defected cartilage as well as microfracture-derived cells. Nanobridge scaffolds have a sophisticated nanoaligned structure with freestanding and flexible shapes for imposing direct structural guidance to cells including transplanted stem cells and host cells, and it can induce not only chondrocyte migration but also stem cell differentiation, maturation, and growth factor secretion. The transplantable stem cell nanobridge scaffold is capable of reconstructing the defected cartilage with homogeneous architecture and highly enhanced adhesive stress similar with native cartilage tissue by the synergistic effects of stem cells-based chondro-induction and nanotopography-based chondro-conduction. Our findings demonstrate a significant advancement in the traditional treatment technique by using a nanoengineered tool for achieving successful cartilage regeneration.

The stability of repaired meniscal root can affect postoperative cartilage status following medial meniscus posterior root repair

BACKGROUND

Transtibial pullout repair yields beneficial clinical outcomes in patients with medial meniscus (MM) posterior root tear. However, the relationship between repaired meniscal root healing status and postoperative clinical outcomes remains unclear. We aimed to evaluate changes in articular cartilage damage and clinical scores after pullout repair using two simple stitches (TSS).

METHODS

Thirty-three patients who underwent pullout repair using TSS were assessed. Healing status was assessed by a semi-quantitative second-look arthroscopic scoring system comprising three evaluation criteria (width of bridging tissues, stability of the repaired root, and synovial coverage), 1 year postoperatively. MM medial extrusion (MMME) and cartilage damage were assessed preoperatively and 1 year postoperatively. The medial compartment was divided into 8 zones (A-H) for comparison of preoperative and 1-year postoperative cartilage damage. Clinical outcomes were evaluated using the Knee Injury and Osteoarthritis Outcome score, Lysholm score, International Knee Documentation Committee scores, and visual analogue scale pain score.

RESULTS

Although cartilage damage did not aggravate significantly in most medial compartment areas, MMME progressed at 1 year postoperatively. No statistical differences were observed in cartilage damage between the central-to-medial area of the medial femoral condyle and the medial tibial plateau area at 1 year postoperatively. Regarding semi-quantitative healing scores, the stability score was significantly correlated with the International Cartilage Repair Society grade at 1 year postoperatively. All 1-year and 2-year clinical scores significantly improved compared with the preoperative scores.

CONCLUSION

Regarding TSS repair, stability of repaired meniscal root negatively correlated with cartilage damage in the medial compartment loading area. All 1-year and 2-year clinical scores significantly improved than those of the preoperative scores. Achieving MM stability is crucial for suppressing cartilage degeneration.

LEVEL OF EVIDENCE

IV case series study.

Advances in Use of Nanomaterials for Musculoskeletal Regeneration

Since the worldwide incidence of bone disorders and cartilage damage has been increasing and traditional therapy has reached its limits, nanomaterials can provide a new strategy in the regeneration of bones and cartilage. The nanoscale modifies the properties of materials, and many of the recently prepared nanocomposites can be used in tissue engineering as scaffolds for the development of biomimetic materials involved in the repair and healing of damaged tissues and organs. In addition, some nanomaterials represent a noteworthy alternative for treatment and alleviating inflammation or infections caused by microbial pathogens. On the other hand, some nanomaterials induce inflammation processes, especially by the generation of reactive oxygen species. Therefore, it is necessary to know and understand their effects in living systems and use surface modifications to prevent these negative effects. This contribution is focused on nanostructured scaffolds, providing a closer structural support approximation to native tissue architecture for cells and regulating cell proliferation, differentiation, and migration, which results in cartilage and bone healing and regeneration.

Optimization of Lyophilized Hyperacute Serum (HAS) as a Regenerative Therapeutic in Osteoarthritis

Hyperacute serum (HAS) is a blood derivative product that promotes the proliferation of various cell types and controls inflammation in vitro. The aim of this study is to investigate the regenerative potential of different formulations of HAS, including lyophilized and hyaluronic acid combined versions, to obtain a stable and standardized therapeutic in osteoarthritis (OA), which may be able to overcome the variability limitations of platelet-rich plasma (PRP). Primary human osteoarthritic chondrocytes were used for testing cellular viability and gene expression of OA-related genes. Moreover, a co-culture of human explants of cartilage, bone and synovium under inflammatory conditions was used for investigating the inflammatory control capacities of the different therapeutics. In this study, one formulation of lyophilized HAS achieved the high cell viability rates of liquid HAS and PRP. Gene expression analysis showed that HAS induced higher Col1a1 expression than PRP. Cytokine quantification from supernatant fluids revealed that HAS treatment of inflamed co-cultures significantly reduced levels of IL-5, IL-15, IL-2, TNFα, IL-7 and IL-12. To conclude, lyophilized HAS is a stable and standardized therapeutic with high potential in joint regeneration.

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.

EZH2 is associated with cartilage degeneration in osteoarthritis by promoting SDC1 expression via histone methylation of the microRNA-138 promoter

Cartilage degeneration has been reported to deteriorate osteoarthritis (OA), a prevalent joint disease caused by intrinsic and epigenetic factors. This study aimed to examine the molecular mechanism of enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2)/microRNA-138 (miR-138)/syndecan 1 (SDC1) and its epigenetic regulation in cartilage degeneration in OA. An OA cell model was induced by stimulating chondrocytes with interleukin (IL)-1β at a final concentration of 10 ng/mL, followed by alterations in EZH2 and miR-138 expression. Afterwards, cell apoptosis was analyzed using flow cytometry. The expression patterns of cartilage catabolism-related factors (MMP-13, ADAMTS-4, and ADAMTS-5) were determined using RT-qPCR and western blot analyses. The EZH2 and H3K27me3 enrichment at the miR-138 promoter region were determined using ChIP-qPCR. Finally, an OA mouse model was constructed to verify the function of EZH2 in vivo. EZH2 was expressed at high levels in OA models. EZH2 depletion ameliorated OA, as evidenced by reduced cell apoptosis in IL-1β-treated chondrocytes and decreased levels of cartilage catabolism-related factors. Moreover, EZH2 promoted histone methylation at the miR-138 promoter to suppress miR-138 expression, thereby upregulating the expression of SDC1, a target gene of miR-138. Changes in this pathway increased the expression of cartilage catabolism-related factors in vitro while promoting cartilage degeneration in vivo. Our data provided evidence that EZH2 inhibits miR-138 expression by promoting the histone methylation of its promoter, which induces cartilage degeneration in OA models by upregulating SDC1 expression, suggesting a novel mechanistic strategy for OA treatment.

Ex Vivo Generation and Characterization of Human Hyaline and Elastic Cartilaginous Microtissues for Tissue Engineering Applications

Considering the high prevalence of cartilage-associated pathologies, low self-repair capacity and limitations of current repair techniques, tissue engineering (TE) strategies have emerged as a promising alternative in this field. Three-dimensional culture techniques have gained attention in recent years, showing their ability to provide the most biomimetic environment for the cells under culture conditions, enabling the cells to fabricate natural, 3D functional microtissues (MTs). In this sense, the aim of this study was to generate, characterize and compare scaffold-free human hyaline and elastic cartilage-derived MTs (HC-MTs and EC-MTs, respectively) under expansion (EM) and chondrogenic media (CM). MTs were generated by using agarose microchips and evaluated ex vivo for 28 days. The MTs generated were subjected to morphometric assessment and cell viability, metabolic activity and histological analyses. Results suggest that the use of CM improves the biomimicry of the MTs obtained in terms of morphology, viability and extracellular matrix (ECM) synthesis with respect to the use of EM. Moreover, the overall results indicate a faster and more sensitive response of the EC-derived cells to the use of CM as compared to HC chondrocytes. Finally, future preclinical in vivo studies are still needed to determine the potential clinical usefulness of these novel advanced therapy products.

Clinical application of polyurethane meniscal scaffold: A meta-analysis

OBJECTIVE

In patients with partial meniscus defect, the implantation of polyurethane meniscal scaffold has become a common method for the treatment of meniscus vascular entry and tissue regeneration. However, it is unclear whether polyurethane meniscal scaffold will yield better clinical and MRI results after surgery. This meta-analysis compared the clinical and MRI results of polyurethane meniscal scaffold in some patients with meniscus defects.

METHODS

By searching PubMed, Embase, and Cochrane Library, a systematic review of studies evaluating the clinical outcomes of patients with polyurethane meniscal scaffold implantation. The search terms used are: "meniscus", "meniscal", "scaffold", "Actifit" "polyurethane" and "implant". The study was evaluated based on the patient's reported outcome score, accompanying surgery, and radiology results. Genovese scale was used to evaluate morphology and signal intensity, and Yulish score was used to evaluate the imaging performance of articular cartilage.

RESULTS

There were 16 studies that met the inclusion criteria, a total of 613 patients, and the overall average follow-up time was 41 months. The clinical scores at the final follow-up, such as VAS, IKDC, Tegner, and KOOS, were significantly improved compared with preoperatively. The MS, SI, and IIRMC scores evaluated in MRI showed no significant difference between preoperative and final follow-up. However, for AC (OR 0.34, 95% CI 0.11-1.00; P = 0.05) and AME (OR 0.08, 95% CI 0.03-0.22; P < 0.01), the final follow-up results were worse than preoperatively.

CONCLUSIONS

This meta-analysis found that compared with preoperative, the clinical effect of the final follow-up was significantly improved. However, MS, SI, and IIRMC in MRI parameters did not change significantly. In addition, the final follow-up results of AC and AME showed a deteriorating trend. Therefore, for patients with partial meniscus defects, polyurethane meniscal scaffold seem to be a viable option, and further research is needed to determine whether the deterioration of AC and AME is clinically relevant.

Higher Incidence of Complete Lateral Meniscal Root Tears in Revision Compared With Primary Anterior Cruciate Ligament Reconstruction

Purpose

To evaluate the incidence of complete lateral meniscal posterior root tears (LMPRTs) repaired at revision as compared with primary anterior cruciate ligament (ACL) reconstruction (PACLR) and to determine whether other demographic or surgical characteristics were associated with LMPRTs needing repair.

Methods

A chart review was performed to identify the PACLR and revision ACL reconstruction (RACLR) cohorts. Demographic and surgical characteristics were recorded. Cases with concurrent lateral meniscal posterior root repair were identified. Cases were classified as acute (<5 months) or chronic (>5 months) based on the time from reported injury to surgery. Tunnel malposition in revision cases was recorded if either tunnel or both tunnels were malpositioned on radiographs and magnetic resonance imaging.

Results

Data from 167 cases, 140 PACLR and 27 RACLR cases, were included. The cohorts had similar demographic characteristics including age, sex, and lateral meniscal injury. The overall incidence of lateral meniscal root repair in ACL reconstruction patients was 12.6% (21 of 167 patients). The incidence of LMPRT repair was 7.1% (10 of 140 patients) in the PACLR cohort versus 40.7% (11 of 27 patients) in the RACLR cohort. The revision cohort was significantly more likely to have a chronic injury (66.7% [18 of 27 patients] vs 31.4% [44 of 140 patients]). The most significant predictor of concurrent lateral meniscal posterior root repair was RACLR versus PACLR for both univariate and multivariate logistic regression analyses (χ² = 20.603; P < .0001; odds ratio, 13.887; 95% confidence interval, 1.531-125.993). Analysis of tunnel positions for the revision group revealed that PACLR tunnel malposition was a significant predictor of LMPRTs (χ² = 4.91, P = .027).

Conclusions

Complete LMPRTs warranting repair are encountered with a significantly greater frequency at RACLR as compared with PACLR. The overall incidence of LMPRT repair at RACLR is high. In this cohort, LMPRT repair in RACLR cases was associated with tunnel malposition of the PACLR.

Level of Evidence

Level III, retrospective cohort study.

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.