Repair of avascular meniscal injuries using juvenile meniscal fragments: an in vitro organ culture study

Minced Meniscus: Biologic Augmented Meniscal Implant Treatment

Applications of meniscus scaffolds are crucial for preserving articular cartilage tissue, restoring normal joint mechanics, and stabilizing joints with partial meniscus deficits. Studies are still being conducted to determine how meniscus scaffold applications can create viable and durable tissue. The surgical procedure described in this study uses the meniscus scaffold and minced meniscus tissue.

Regeneration of meniscal avascular zone using autogenous meniscal fragments in a rabbit model

Background

To investigate the effects of autologous meniscus fragment (AMF) implantation on injury in the meniscal avascular zone in mature rabbits.

Methods

Adult New Zealand white rabbits were randomly divided into two groups. Massive one-piece meniscus tissue was implanted in situ as control. In the experimental group, AMF was used to repair the meniscal injury in the avascular zone. Meniscal damage was assessed by gross observation of the degree of healing and histological semi-quantitative evaluation within 12 weeks postoperatively. The healing of meniscus interface was assessed by gross observation semiquantitative scoring and microscopic examination hematoxylin and eosin (H&E) staining at 2, 4, 8, and 12 weeks after surgery. The expressions of proliferating cell nuclear antigen (PCNA), collagen type I (COL1A1), and collagen type II (COL2) were detected by immunohistochemical staining.

Results

The degree of healing in the AMF group showed a significant increase over time (P < 0.05); the AMF group showed higher gross scores than the control group at 4, 8, and 12 weeks after surgery (P < 0.05). The histological scores in the AMF group were significantly higher than those in the control group at 4, 8, and 12 weeks after surgery (P < 0.05). The protein expression of PCNA in the AMF group was greater than that in the control group at 2, 4, and 8 weeks after surgery (P < 0.05). In addition, compared with the control group, the protein levels of COL1A1 and COL2 were significantly upregulated at each time-point. At 2 and 4 weeks after surgery, the expression level of COL1A1 increased in both groups followed by a gradual decrease after 8 weeks (P < 0.05). At 2, 4, 8, and 12 weeks after surgery, the expression levels of COL2 showed a gradual decrease in both groups (P < 0.05).

Conclusions

Our study demonstrated that the AMF method can promote the repair of rabbit meniscal injury in the avascular zone, and this method may potentially be used for clinical application.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12893-022-01663-3.

Implantation of autogenous meniscal fragments wrapped with a fascia sheath induces fibrocartilage regeneration in a large meniscal defect in sheep: A histological and biomechanical study

INTRODUCTION

Currently, various studies have been reported to regenerate the meniscus tissue in a large defect after partial meniscectomy using biological or synthetic scaffolds with or without fibrochondrocytes. However, the clinical utility of those treatments has not been established as of yet.

HYPOTHESIS

Purposes of this study were to develop a sheep model to evaluate feasibility of this new surgical strategy to treat the irreparable meniscus injury, and to test the hypothesis that implantation of autogenous meniscal fragments wrapped with a fascia sheath may significantly induce fibrocartilage regeneration in a large meniscal defect in the sheep model.

METHODS AND METHODS

Twenty Suffolk sheep were used. In each animal, an anterior 10-mm width of the right medial meniscus was resected. Then, the animals were divided into the following 2 groups. In Group I, the defect was enveloped with a fascia from the left thigh. In Group II, the resected meniscus fragmented into small pieces was grafted into the defect. Then the defect was enveloped with a fascia. In each group, 5 of 10 sheep were used for histological and biomechanical evaluations, respectively, at 12 weeks after surgery.

RESULTS

In Group I, the defect was incompletely filled with thin fibrous tissues, while fibrocartilage tissues rarely regenerated in the tissue. In Group II, all defects were completely filled with thick fibrocartilage tissues, which were richly stained with the safranin O staining. Both the gross and histological observation score of Group II was significantly (p=0.0005, p=0.0005) greater than that of Group I. Concerning the cross-sectional area of the regenerated tissue, Group II was significantly (p=0.0002) greater than Group I. In the biomechanical evaluation, the maximal load and the linear stiffness of the meniscus-tibia complex were significantly (p=0.0015, p=0.0283) greater in Group II than in Group I.

DISCUSSION

Implantation of autogenous meniscal fragments wrapped with a fascia sheath significantly induces fibrocartilage regeneration into a large meniscal defect in the sheep model.

LEVEL OF EVIDENCE

Not applicable; Controlled Laboratory Study, Experimental in vivo study.

Articular Cartilage Fragmentation Improves Chondrocyte Migration by Upregulating Membrane Type 1 Matrix Metalloprotease

OBJECTIVE

This study was undertaken to elucidate the mechanism of improved chondrocyte migration after juvenile articular cartilage fragmentation.

DESIGN

In vitro organ culture with rabbit cartilage fragments and cell culture with rabbit chondrocytes were performed. In part A, minced juvenile cartilage fragments (~0.5 × 0.5 × 0.5 mm) from rabbits, planted in gelatin sponge and fibrin glue, were cultured for 2, 4, or 6 weeks in vitro and compared with the cartilage chunks (~4 × 4 × 1 mm) and membrane type 1 matrix metalloprotease (MT1-MMP) inhibitor groups. Chondrocyte outgrowth was evaluated on histology and confocal laser scanning microscopy. MT1-MMP expression was compared between the cartilage fragment group and the cartilage chunks group. In part B, articular chondrocytes were harvested from juvenile rabbits, MT1-MMP was transfected into the cells, and cell migration was evaluated using the Transwell and wound healing tests.

RESULTS

The histology and confocal microscopy results revealed that cell accumulation occurred at the edge of cartilage fragments, and outgrowth was better in the cartilage fragment group than those in the cartilage chunks group. Similar results were observed for MT1-MMP expression. After MT1-MMP inhibition, cells did not accumulate at the edge of the cartilage fragments, and chondrocyte outgrowth did not occur. Furthermore, overexpression of MT1-MMP enhanced the migration of articular chondrocytes.

CONCLUSIONS

Juvenile articular cartilage fragmentation improved chondrocyte migration by upregulating MT1-MMP.

Hypoxia as a Stimulus for the Maturation of Meniscal Cells: Highway to Novel Tissue Engineering Strategies?

The meniscus possesses low self-healing properties. A perfect regenerative technique for this tissue has not yet been developed. This work aims to evaluate the role of hypoxia in meniscal development in vitro. Menisci from neonatal pigs (day 0) were harvested and cultured under two different atmospheric conditions: hypoxia (1% O₂) and normoxia (21% O₂) for up to 14 days. Samples were analysed at 0, 7 and 14 days by histochemical (Safranin-O staining), immunofluorescence and RT-PCR (in both methods for SOX-9, HIF-1α, collagen I and II), and biochemical (DNA, GAGs, DNA/GAGs ratio) techniques to record any possible differences in the maturation of meniscal cells. Safranin-O staining showed increments in matrix deposition and round-shape “fibro-chondrocytic” cells in hypoxia-cultured menisci compared with controls under normal atmospheric conditions. The same maturation shifting was observed by immunofluorescence and RT-PCR analysis: SOX-9 and collagen II increased from day zero up to 14 days under a hypoxic environment. An increment of DNA/GAGs ratio typical of mature meniscal tissue (characterized by fewer cells and more GAGs) was observed by biochemical analysis. This study shows that hypoxia can be considered as a booster to achieve meniscal cell maturation, and opens new opportunities in the field of meniscus tissue engineering.

Autologous meniscus fragments embedded in atelocollagen gel enhance meniscus repair in a rabbit model

Aims

Meniscal injuries are common and often induce knee pain requiring surgical intervention. To develop effective strategies for meniscus regeneration, we hypothesized that a minced meniscus embedded in an atelocollagen gel, a firm gel-like material, may enhance meniscus regeneration through cell migration and proliferation in the gel. Hence, the objective of this study was to investigate cell migration and proliferation in atelocollagen gels seeded with autologous meniscus fragments in vitro and examine the therapeutic potential of this combination in an in vivo rabbit model of massive meniscus defect.

Methods

A total of 34 Japanese white rabbits (divided into defect and atelocollagen groups) were used to produce the massive meniscus defect model through a medial patellar approach. Cell migration and proliferation were evaluated using immunohistochemistry. Furthermore, histological evaluation of the sections was performed, and a modified Pauli’s scoring system was used for the quantitative evaluation of the regenerated meniscus.

Results

In vitro immunohistochemistry revealed that the meniscus cells migrated from the minced meniscus and proliferated in the gel. Furthermore, histological analysis suggested that the minced meniscus embedded in the atelocollagen gel produced tissue resembling the native meniscus in vivo. The minced meniscus group also had a higher Pauli’s score compared to the defect and atelocollagen groups.

Conclusion

Our data show that cells in minced meniscus can proliferate, and that implantation of the minced meniscus within atelocollagen induces meniscus regeneration, thus suggesting a novel therapeutic alternative for meniscus tears.

Cite this article: Bone Joint Res 2021;10(4):269–276.

Engineered Healing of Avascular Meniscus Tears by Stem Cell Recruitment

Meniscus injuries are extremely common with approximately one million patients undergoing surgical treatment annually in the U.S. alone. Upon injury, the outer zone of the meniscus can be repaired and expected to functionally heal but tears in the inner avascular region are unlikely to heal. To date, no regenerative therapy has been proven successful for consistently promoting healing in inner-zone meniscus tears. Here, we show that controlled applications of connective tissue growth factor (CTGF) and transforming growth factor beta 3 (TGFβ3) can induce seamless healing of avascular meniscus tears by inducing recruitment and step-wise differentiation of synovial mesenchymal stem/progenitor cells (syMSCs). A short-term release of CTGF, a selected chemotactic and profibrogenic cue, successfully recruited syMSCs into the incision site and formed an integrated fibrous matrix. Sustain-released TGFβ3 then led to a remodeling of the intermediate fibrous matrix into fibrocartilaginous matrix, fully integrating incised meniscal tissues with improved functional properties. Our data may represent a novel clinically relevant strategy to improve healing of avascular meniscus tears by recruiting endogenous stem/progenitor cells.

3D Porous Gelatin/PVA Hydrogel as Meniscus Substitute Using Alginate Micro-Particles as Porogens

One of the current major challenges in orthopedic surgery is the treatment of meniscal lesions. Some of the main issues include mechanical consistency of meniscal implants, besides their fixation methods and integration with the host tissues. To tackle these aspects we realized a micro-porous, gelatin/polyvinyl alcohol (PVA)-based hydrogel to approach the high percentage of water present in the native meniscal tissue, recapitulating its biomechanical features, and, at the same time, realizing a porous implant, permissive to cell infiltration and tissue integration. In particular, we adopted aerodynamically-assisted jetting technology to realize sodium alginate micro-particles with controlled dimensions to be used as porogens. The porous hydrogels were realized through freezing-thawing cycles, followed by alginate particles leaching. Composite hydrogels showed a high porosity (74%) and an open porous structure, while preserving the elasticity behavior (E = 0.25 MPa) and high water content, typical of PVA-based hydrogels. The ex vivo animal model validation proved that the addition of gelatin, combined with the micro-porosity of the hydrogel, enhanced implant integration with the host tissue, allowing penetration of host cells within the construct boundaries. Altogether, these results show that the combined use of a water-insoluble micro-porogen and gelatin, as a bioactive agent, allowed the realization of a porous composite PVA-based hydrogel to be envisaged as a potential meniscal substitute.

Rapidly dissociated autologous meniscus tissue enhances meniscus healing: An in vitro study

PURPOSE

Treatment of meniscus tears is a persistent challenge in orthopedics. Although cell therapies have shown promise in promoting fibrocartilage formation in in vitro and preclinical studies, clinical application has been limited by the paucity of autologous tissue and the need for ex vivo cell expansion. Rapid dissociation of the free edges of the anterior and posterior meniscus with subsequent implantation in a meniscus lesion may overcome these limitations. The purpose of this study was to explore the effect of rapidly dissociated meniscus tissue in enhancing neotissue formation in a radial meniscus tear, as simulated in an in vitro explant model.

MATERIALS AND METHODS

All experiments in this study, performed at minimum with biological triplicates, utilized meniscal tissues from hind limbs of young cows. The effect of varying collagenase concentration (0.1%, 0.2% and 0.5% w/v) and treatment duration (overnight and 30 minutes) on meniscus cell viability, organization of the extracellular matrix (ECM), and gene expression was assessed through a cell metabolism assay, microscopic examination, and quantitative real-time reverse transcription polymerase chain reaction analysis, respectively. Thereafter, an explant model of a radial meniscus tear was used to evaluate the effect of a fibrin gel seeded with one of the following: (1) fibrin alone, (2) isolated and passaged (P2) meniscus cells, (3) overnight digested tissue, and (4) rapidly dissociated tissue. The quality of in vitro healing was determined through histological analysis and derivation of an adhesion index.

RESULTS

Rapid dissociation in 0.2% collagenase yielded cells with higher levels of metabolism than either 0.1% or 0.5% collagenase. When seeded in a three-dimensional fibrin hydrogel, both overnight digested and rapidly dissociated cells expressed greater levels of collagens type I and II than P2 meniscal cells at 1 week. At 4 and 8 weeks, collagen type II expression remained elevated only in the rapid dissociation group. Histological examination revealed enhanced healing in all cell-seeded treatment groups over cell-free fibrin controls at weeks 1, 4, and 8, but there were no significant differences across the treatment groups.

CONCLUSIONS

Rapid dissociation of meniscus tissue may provide a single-step approach to augment regenerative healing of meniscus repairs.