An organ culture model for assaying wound repair of the fibrocartilaginous knee joint meniscus

Clinical Outcomes of Meniscus Repair with or without Multiple Intra-Articular Injections of Platelet Rich Plasma after Surgery

Preservation of the meniscal volume is crucial in meniscus repair. The goal of this study was to evaluate the clinical outcome of repeated intra-articular platelet-rich plasma (PRP) injections after arthroscopic repair of a traumatic meniscal tear. We retrospectively reviewed 61 primary meniscal repairs in 61 patients (PRP group: 30; non-PRP: 31) from 2017 to 2018. Patients in the PRP group received repeated intra-articular PRP injections in week 2,4,6 after the primary meniscus repair. Subsequent meniscal repair treatment or meniscectomy, knee arthroplasty, and IKDC changes of less than 11.5 points were defined as healing failures. After following up for at least 24 months, the IKDC score was 75.1 ± 13.6, and the Lysholm score was 80.6 ± 14.9 in the PRP group and 72.6 ± 15.8 (IKDC) and 77.7 ± 17.2 (Lysholm) in the non-PRP group. Healing rates of the PRP and the non-PRP groups were 93.3% (Kaplan-Meier 91.6%) and 87.1% (Kaplan-Meier 84.7%), respectively (log rank test p = 0.874). Our study is the first to use multiple intra-articular PRP injections to facilitate meniscal healing after meniscal repair. Though selection bias may be present in this study, the PRP group had similar functional outcome and healing rate compared to non-PRP group.

Which Contributes to Meniscal Repair, the Synovium or the Meniscus? An In Vivo Rabbit Model Study With the Freeze-Thaw Method

BACKGROUND

During meniscal tissue repair, the origin of the reparative cells of damaged meniscal tissue remains unclear.

HYPOTHESIS

Comparison of the influence between meniscal and synovial tissues on meniscal repair by the in vivo freeze-thaw method would clarify the origin of meniscal reparative cells.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 48 mature Japanese white rabbits were divided into 4 groups according to the tissue (meniscal or synovial) that received freeze-thaw treatment. The meniscus of each group had a 2 mm-diameter cylindrical defect filled with alginate gel. Macroscopic and histologic evaluations of the reparative tissues were performed at 1, 3, and 6 weeks postoperatively. Additional postoperative measurements included cell density, which was the number of meniscal cells in the cut area per cut area (mm²) of meniscus; cell density ratio, which was the cell density of the sample from each group per the average cell density of the intact meniscus; and cell death rate, which was the number of cells stained by propidium iodide per the number of cells stained by Hoechst 33342 of the meniscal tissue adjacent to the defect.

RESULTS

The macroscopic and histologic evaluations of the non-synovium freeze-thaw groups were significantly superior to those of the synovium freeze-thaw groups at 3 and 6 weeks postoperatively. Additionally, the meniscal cell density ratio and cell death rate in the freeze-thaw groups were significantly lower than those in the non-meniscal freeze-thaw groups at 3 and 6 weeks postoperatively.

CONCLUSION

The freeze-thawed meniscus recovered few cells in its tissue even after 6 weeks. However, the defect was filled with fibrochondrocytes and proteoglycan when the synovium was intact. On the basis of these results, it is concluded that synovial cells are the primary contributors to meniscal injury repair.

CLINICAL RELEVANCE

In meniscal tissue engineering, there is no consensus on the best cell source for meniscal repair. Based on this study, increasing the synovial activity and contribution should be the main objective of meniscal tissue engineering. This study can establish the foundation for future meniscal tissue engineering.

Effects of tissue culture on the biomechanical properties of porcine meniscus explants

BACKGROUND

The meniscus is critical for the normal functioning of the knee joint. The specific aim of this study was to validate an in vitro culture model of meniscus explants for testing the impact of culture conditions on meniscus biomechanical properties. We hypothesized that culturing menisci in the presence of intermediate and high concentration of serum would have a positive effect on the compressive stiffness of the meniscus.

METHODS

Unconstrained microindentation testing was performed on porcine meniscus explants cultured with varying concentrations 1%, 5%, or 10% of fetal bovine serum media. Meniscus explants that were not cultured were used as a control. These tests quantified the Young's Modulus of the listed groups of cultured and uncultured explant tissues.

FINDINGS

The Young's modulus for 10% cultured explants were significantly higher compared to the control, 1%, and 5% cultured meniscus explants. There was no statistical significance when the Young's modulus between control, 1%, and 5% cultured explants were compared.

INTERPRETATION

These results suggest that low concentrations of serum do not impart an anabolic effect on meniscus tissue explant biomechanical properties.

Novel organ-slice culturing system to simulate meniscal repair: Proof of concept using a synovium-based pool of meniscoprogenitor cells

Meniscal injuries can occur secondary to trauma or be instigated by the changes in knee-joint function that are associated with aging, osteo- and rheumatoid arthritis, disturbances in gait, and obesity. Sixty percent of persons over 50 years of age manifest signs of meniscal pathology. The surgical and arthroscopic measures that are currently implemented to treat meniscal deficiencies bring only transient relief from pain and effect but a temporary improvement in joint function. Although tissue-engineering-based approaches to meniscal repair are now being pursued, an appropriate in-vitro model has not been conceived. The aim of this study was to develop an organ-slice culturing system to simulate the repair of human meniscal lesions in vitro. The model consists of a ring of bovine meniscus enclosing a chamber that represents the defect and reproduces its sequestered physiological microenvironment. The defect, which is closed with a porous membrane, is filled with fragments of synovial tissue, as a source of meniscoprogenitor cells, and a fibrin-embedded, calcium-phosphate-entrapped depot of the meniscogenic agents BMP-2 and TGF-β1. After culturing for 2 to 6 weeks, the constructs were evaluated histochemically and histomorphometrically, as well as immunohistochemically, for the apoptotic marker caspase 3 and collagen types I and II. Under the defined conditions, the fragments of synovium underwent differentiation into meniscal tissue, which bonded with the parent meniscal wall. Both the parent and the neoformed meniscal tissue survived the duration of the culturing period without significant cell losses. The concept on which the in-vitro system is based was thus validated. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1588-1596, 2016.

Meniscal Repair of Degenerative Horizontal Cleavage Tears Using Fibrin Clots: Clinical and Arthroscopic Outcomes in 10 Cases

BACKGROUND

Presently, the treatment options available for patients with horizontal degenerative cleavage tears of the meniscus are limited. These tears are considered an indication for partial or subtotal meniscectomy because when the tear is located within an avascular area, it is difficult to induce healing. However, meniscectomy is not ideal because it disrupts the normal anatomical structure and function of the meniscus.

PURPOSE

To examine the clinical and arthroscopic outcomes following meniscal repair of degenerative horizontal cleavage tears using fibrin clots.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Vertical sutures were placed in the meniscal tear, and the cleft was filled with fibrin clots before the sutures were tightened. We repaired 18 menisci in 18 consecutive eligible patients using a previously described technique. Three patients with anterior cruciate ligament (ACL) injury who underwent simultaneous ACL reconstruction and 5 patients who did not undergo follow-up arthroscopy within 12 months were excluded. The remaining 10 menisci in 10 patients were evaluated in this study. The mean age of the patients was 35.8 ± 16.5 years, and the mean postoperative follow-up time was 40.8 ± 5.4 months. Pre- and postoperative Lysholm scores, International Knee Documentation Committee (IKDC) subjective scores, and Tegner activity levels were compared. The arthroscopy findings were evaluated at a mean postoperative time of 6.7 ± 2.9 months.

RESULTS

The mean Lysholm score improved significantly from 69.3 ± 16.3 points preoperatively to 95.4 ± 3.6 points postoperatively (P < .005). The mean IKDC subjective score also improved significantly from 26.5% ± 19.0% preoperatively to 87.8% ± 7.5% postoperatively (P < .001). The Tegner activity level recovered to the preinjury level in 6 patients and to 1 level below the preinjury level in 4 patients. The follow-up arthroscopies showed complete healing in 7 patients (70%) and incomplete healing in 3 patients (30%).

CONCLUSION

Meniscal repair of degenerative horizontal cleavage tears using fibrin clots resulted in improved Lysholm and IKDC subjective scores, but the complete healing rate on follow-up arthroscopy was only 70%.

CLINICAL RELEVANCE

If we are to prevent osteoarthritis, we should minimize resection and restore the contact area of the meniscus to preserve the original shape.

Human migratory meniscus progenitor cells are controlled via the TGF-β pathway

Degeneration of the knee joint during osteoarthritis often begins with meniscal lesions. Meniscectomy, previously performed extensively after meniscal injury, is now obsolete because of the inevitable osteoarthritis that occurs following this procedure. Clinically, meniscus self-renewal is well documented as long as the outer, vascularized meniscal ring remains intact. In contrast, regeneration of the inner, avascular meniscus does not occur. Here, we show that cartilage tissue harvested from the avascular inner human meniscus during the late stages of osteoarthritis harbors a unique progenitor cell population. These meniscus progenitor cells (MPCs) are clonogenic and multipotent and exhibit migratory activity. We also determined that MPCs are likely to be controlled by canonical transforming growth factor β (TGF-β) signaling that leads to an increase in SOX9 and a decrease in RUNX2, thereby enhancing the chondrogenic potential of MPC. Therefore, our work is relevant for the development of novel cell biological, regenerative therapies for meniscus repair.

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Progenitor cells are found in the inner avascular part of human osteoarthritic menisci

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These meniscus progenitor cells (MPCs) are clonogenic, migratory, and multipotent

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MPCs are governed via the canonical TGF-β pathway

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TGF-β3 via Smad2 reduces Runx2 to enhance the chondrogenic potential of MPCs

Xenoimplantation of an extracellular-matrix-derived, biphasic, cell-scaffold construct for repairing a large femoral-head high-load-bearing osteochondral defect in a canine model

This study was aimed to develop an ECM-derived biphasic scaffold and to investigate its regeneration potential loaded with BM-MSCs in repair of large, high-load-bearing osteochondral defects of the canine femoral head. The scaffolds were fabricated using cartilage and bone ECM as a cartilage and bone layer, respectively. Osteochondral constructs were fabricated using induced BM-MSCs and the scaffold. Osteochondral defects (11 mm diameter × 10 mm depth) were created on femoral heads of canine and treated with the constructs. The repaired tissue was evaluated for gross morphology, radiography, histological, biomechanics at 3 and 6 months after implantation. Radiography revealed that femoral heads slightly collapsed at 3 months and severely collapsed at 6 months. Histology revealed that some defects in femoral heads were repaired, but with fibrous tissue or fibrocartilage, and femoral heads with different degrees of collapse. The bone volume fraction was lower for subchondral bone than normal femoral bone at 3 and 6 months. Rigidity was lower in repaired subchondral bone than normal femoral bone at 6 months. The ECM-derived, biphasic scaffold combined with induced BM-MSCs did not successfully repair large, high-load-bearing osteochondral defects of the canine femoral head. However, the experience can help improve the technique of scaffold fabrication and vascularization.

Optimization strategies on the structural modeling of gelatin/chitosan scaffolds to mimic human meniscus tissue

Meniscus lesions are frequently occurring injuries with poor ability to heal. Typical treatment procedure includes removal of damaged regions, which can lead to sub-optimal knee biomechanics and early onset of osteoarthritis. Some of the drawbacks of current treatment approach present an opportunity for a tissue engineering solution. In this study, gelatin (G)/chitosan (Cs) scaffolds were synthesized via gel casting method and cross-linked with naturally derived cross-linker, genipin, through scaffold cross-linking method. Based on the characteristics of native meniscus tissue microstructure and function, three different layers were chosen to design the macroporous multilayered scaffolds. The multi-layered scaffolds were investigated for their ability to support human-derived meniscus cells by evaluating their morphology and proliferation using MTT assay at various time points. Based on structural, mechanical and cell compatibility considerations, laminated scaffolds composed of G60/Cs40, G80/Cs20 and G40/Cs60 samples, for the first, second and third layers, respectively, could be an appropriate combination for meniscus tissue engineering applications.

Chondrogenesis of myoblasts in biodegradable poly-lactide-co-glycolide scaffolds

Myoblasts are considered to be an alternative cell source for cell-based meniscal repair due to their multiple differentiation potentials. This study addresses the chondrogenic differentiation of myoblasts seeded into poly-lactide-co-glycolide (PLGA) scaffolds following implantation in a subcutaneous pocket of nude mice. Canine myoblasts isolated from a Beagle were expanded and seeded into PLGA scaffolds and cultured in cartilage-derived morphogenetic protein-2 (CDMP-2) and transforming growth factor-β1 (TGF-β1)-containing medium for 2 weeks in vitro. The constructs were implanted into a subcutaneous pocket of 24 combined immunodeficiency mice and harvested after 8 and 12 weeks, respectively. Hematoxylin and eosin staining of the sections of the engineered cartilage at 8 and 12 weeks revealed the regeneration of fibrocartilage. Immunohistochemical staining confirmed a similar distribution of collagen type Ⅱ in the engineered cartilage as the normal meniscus. At 12 weeks, expression of mRNAs for type Ⅰ collagen, type Ⅱ collagen and aggrecan was detected by RT-PCR. The compressive moduli of engineered cartilage reached 85.72% of the normal meniscus at 12 weeks, with a high level of glycosaminoglycan (GAG) content (no statistical difference from normal). Myoblast-seeded PLGA scaffolds express a stable chondrogenic phenotype in a heterotopic model of cartilage transplantation and represent a suitable tool for tissue engineering of cartilage.

Porosity and cell preseeding influence electrospun scaffold maturation and meniscus integration in vitro

Electrospinning generates fibrous scaffolds ideal for engineering soft orthopedic tissues. By modifying the electrospinning process, scaffolds with different structural organization and content can be generated. For example, fibers can be aligned in a single direction, or the porosity of the scaffold can be modified through the use of multi-jet electrospinning and the removal of sacrificial fibers. In this work, we investigated the role of fiber alignment and scaffold porosity on construct maturation and integration within in vitro meniscus defects. Further, we explored the effect of preseeding expanded meniscus fibrochondrocytes (MFCs) onto the scaffold at a high density before in vitro repair. Our results demonstrate that highly porous electropun scaffolds integrate better with a native tissue and mature to a greater extent than low-porosity scaffolds, while scaffold alignment does not influence integration or maturation. The addition of expanded MFCs to scaffolds before in vitro repair improved integration with the native tissue, but did not influence maturation. In contrast, preculture of these same scaffolds for 1 month before repair decreased integration with the native tissue, but resulted in a more mature scaffold compared to implantation of cellular scaffolds or acellular scaffolds. This work will inform scaffold selection in future in vivo studies by identifying the ideal scaffold and seeding methods for meniscus tissue engineering.

Growth factor supplementation improves native and engineered meniscus repair in vitro

Few therapeutic options exist for meniscus repair after injury. Local delivery of growth factors may stimulate repair and create a favorable environment for engineered replacement materials. In this study we assessed the effect of basic fibroblast growth factor (bFGF) (a pro-mitotic agent) and transforming growth factor β3 (TGF-β3) (a pro-matrix formation agent) on meniscus repair and the integration/maturation of electrospun poly(ε-caprolactone) (PCL) scaffolds for meniscus tissue engineering. Circular meniscus repair constructs were formed and refilled with either native tissue or scaffolds. Repair constructs were cultured in serum-containing medium for 4 and 8weeks with various growth factor formulations, and assessed for mechanical strength, biochemical content, and histological appearance. Results showed that either short-term delivery of bFGF or sustained delivery of TGF-β3 increased integration strength for both juvenile and adult bovine tissue, with similar findings for engineered materials. While TGF-β3 increased proteoglycan content in the explants, bFGF did not increase DNA content after 8weeks of culture. This work suggests that in vivo delivery of bFGF or TGF-β3 may stimulate meniscus repair, but that the time course of delivery will strongly influence success. Further, this study demonstrates that electrospun scaffolds are a promising material for meniscus tissue engineering, achieving comparable or superior integration compared with native tissue.

The basic science of human knee menisci: structure, composition, and function

CONTEXT

Information regarding the structure, composition, and function of the knee menisci has been scattered across multiple sources and fields. This review contains a concise, detailed description of the knee menisci-including anatomy, etymology, phylogeny, ultrastructure and biochemistry, vascular anatomy and neuroanatomy, biomechanical function, maturation and aging, and imaging modalities.

EVIDENCE ACQUISITION

A literature search was performed by a review of PubMed and OVID articles published from 1858 to 2011.

RESULTS

This study highlights the structural, compositional, and functional characteristics of the menisci, which may be relevant to clinical presentations, diagnosis, and surgical repairs.

CONCLUSIONS

An understanding of the normal anatomy and biomechanics of the menisci is a necessary prerequisite to understanding the pathogenesis of disorders involving the knee.

Repair of meniscal defect using an induced myoblast-loaded polyglycolic acid mesh in a canine model

Defects of the meniscus greatly alter knee function and predispose the joint to degenerative changes. The purpose of this study was to test a recently developed cell-scaffold combination for the repair of a critical-size defect in the canine medial meniscus. A bilateral, complete resection of the anterior horn of the medial meniscus was performed in 18 Beagle canines. A PLGA scaffold was implanted into the defect of one knee of 6 canines and the contralateral defect was left untreated. Scaffolds loaded with autologous myoblasts and cultured in a chondrogenic medium for 14 days were implanted in a second series of 12 canines. Empty scaffolds were implanted in the contralateral knees. Menisci were harvested at 12 weeks. Untreated defects had a muted fibrous healing response. Defects treated with cell-free implants also showed predominantly fibrous tissue, whereas fibrocartilage was present in several scaffolds. The thickness of the repair tissue after treatment with cell-free scaffolds was significantly greater compared to the controls (p<0.05). Pre-cultured implants integrated with the host tissue, and 9 of 12 contained meniscus-like fibrocartilage when compared to 2 of the 12 controls (p<0.05). The thickness of the pre-cultured implant repair tissue was greater compared to the controls (p<0.05). This study demonstrates the repair of a critical size meniscal defect using a stem cell and scaffold-based tissue engineering approach.

Cell-based meniscal tissue engineering: a case for synoviocytes

BACKGROUND

Avascular meniscal injuries are largely incapable of healing; the most common treatment remains partial meniscectomy despite the risk of subsequent osteoarthritis. Meniscal responses to injury are partially mediated through synovial activity and strategies have been investigated to encourage healing through stimulating or transplanting adjacent synovial lining. However, with their potential for chondrogenesis, synovial fibroblast-like stem cells hold promise for meniscal cartilage tissue engineering.

QUESTIONS/PURPOSES

Thus, specific purposes of this review were to (1) examine how the synovial intima and synoviomeniscal junction affect current meniscal treatment modalities; and (2) examine the components of tissue engineering (cells, scaffolds, bioactive agents, and bioreactors) in the specific context of how cells of synovial origin may be used for meniscal healing or regeneration.

METHODS

An online bibliographic search through PubMed was performed in March 2010. Studies were subjectively evaluated and reviewed if they addressed the question posed. Fifty-four resources were initially retrieved, which offered information on the chondrogenic potential of synovial-based cells that could prove valuable for meniscal fibrocartilage engineering.

RESULTS

Based on the positive effects of adjoining synovium on meniscal healing as used in some current treatment modalities, the chondrogenic potential of fibroblast-like stem cells of synovial origin make this cell source a promising candidate for cell-based tissue engineering strategies.

CONCLUSIONS

The abundance of autologous synovial lining, its ability to regenerate, and the potential of synovial-derived stem cells to produce a wide spectrum of chondral matrix components make it an ideal candidate for future meniscal engineering investigations.

Repair of horizontal meniscal cleavage tears with exogenous fibrin clots

PURPOSE

A novel indication and technique using exogenous fibrin clots to repair horizontal cleavage tears of the meniscus is presented.

METHODS

Vertical sutures were placed on the meniscus using FasT-Fix (Smith & Nephew Endoscopy, Andover, MA, USA), and exogenous fibrin clots were inserted within the cleft to promote healing and to preserve function.

RESULTS

Repeat arthroscopy showed healing and closure of the cleft of the meniscus without affecting the articular cartilage. Three medial and six lateral menisci were treated, and all of the patients showed improvements in their functional scores and their quality of life.

CONCLUSIONS

It appears that the exogenous fibrin clots act as a scaffold to promote the healing process and that growth factors in the fibrin clots had a beneficial effect on meniscal healing. This procedure should be considered to treat degenerative menisci for which repair options have been limited until now.

LEVEL OF EVIDENCE

IV.

Effects of biomimetic surfaces and oxygen tension on redifferentiation of passaged human fibrochondrocytes in 2D and 3D cultures

Due to its limited healing potential within the inner avascular region, functional repair of the meniscus remains a significant challenge in orthopaedic surgery. Tissue engineering of a meniscus implant using meniscal cells offers the promise of enhancing the reparative process and achieving functional meniscal repair. In this work, using quantitative real-time reverse transcriptase polymerase chain reaction (RT-qPCR) analysis, we show that human fibrochondrocytes rapidly dedifferentiate during monolayer expansion on standard tissue culture flasks, representing a significant limit to clinical use of this cell population for meniscal repair. Previously, we have characterized and described the feasibility of a tailored biomimetic surface (C6S surface) for reversing dedifferentiation of monolayer-expanded rat meniscal cells. The surface is comprised of major meniscal extracellular matrix (ECM) components in the inner region, namely collagen I/II (at a 2:3 ratio) and chondroitin-6-sulfate. We thus have further evaluated the effects of the C6S surface, alongside a number of other tailored surfaces, on cell adhesion, proliferation, matrix synthesis and relevant marker gene expression (collagen I, -II, aggrecan and Sox-9 etc) of passaged human fibrochondrocytes in 2D (coated glass coverslips) and 3D (surface-modified polymeric scaffolds) environments. We show that the C6S surface is permissive for cell adhesion, proliferation and ECM synthesis, as demonstrated using DNA quantification, 1,9-dimethylmethylene blue (DMMB) assay, histology and immunohistochemistry. More importantly, RT-qPCR analyses corroborate the feasibility of the C6S surface for reversing phenotypic changes, especially the downregulation of collagen II, of dedifferentiated human fibrochondrocytes. Furthermore, human fibrochondrocyte redifferentiation was enhanced by hypoxia in the 3D cultures, independent of hypoxia inducible factor (HIF) transcriptional activity and was shown to potentially involve the transcriptional activation of Sox-9.

Interactions of meniscal cells with extracellular matrix molecules: towards the generation of tissue engineered menisci

Menisci are one of the most commonly injured parts of the knee. Conventional surgical interventions are often associated with a long-term increased risk of osteoarthritis. Meniscal tissue engineering utilizes natural or synthetic matrices as a scaffold to guide tissue repair or regeneration in three dimensions. Studies have shown that a diverse cellular response can be triggered depending on the composition of the surrounding extracellular matrix (ECM) components. As such, attempts have been made to replace or repair meniscus defects using tissue grafts or reconstituted ECM components prepared from a multitude of tissues. This commentary summarizes the most recent data on the response of meniscal cells to ECM components, both in vivo and in vitro, and focuses on their potential roles in meniscal repair and regeneration. We also discuss our recent investigations into the interactions of meniscal cells and a self assembled biomimetic surface composed of meniscal ECM molecules. The biological effects conferred by the biomimetic surface, in terms of cell adhesion, proliferation, gene expression profiles and matrix synthesis, were evaluated. Finally, some suggested directions for future research in this field are outlined.

Maturation state-dependent alterations in meniscus integration: implications for scaffold design and tissue engineering

The knee meniscus is a crucial component of the knee that functions to stabilize the joint, distribute load, and maintain congruency. Meniscus tears and degeneration are common, and natural healing is limited. Notably, few children present with meniscus injuries and other related fibrocartilaginous tissues heal regeneratively in immature animals and in the fetus. In this work, we evaluated fetal, juvenile, and adult bovine meniscus properties and repair capacity in vitro. Although no changes in cell behavior (migration and proliferation) were noted with age, drastic alterations in the density and distribution of the major components of meniscus tissue (proteoglycan, collagen, and DNA) occurred with development. Coincident with these marked tissue changes, the in vitro healing capacity of the tissue decreased with age. Fetal and juvenile meniscus formed a robust repair over 8 weeks on both a histological and mechanical basis, despite a lack of vascular supply. In contrast, adult meniscus did not integrate over this period. However, integration was improved significantly with the addition of the growth factor transforming growth factor-beta 3. Finally, to evaluate engineered scaffold integration in the context of aging, we monitored cellular infiltration from native tissue into engineered nanofibrous constructs. Our findings suggest that maturation processes that enable load bearing in the adult limit endogenous healing potential and identify new metrics for the development of tissue-engineered meniscus implants.

Effect of gelatin hydrogel incorporating fibroblast growth factor 2 on human meniscal cells in an organ culture model

Efforts to use growth factors to enhance the healing potential of the meniscus have been impeded because their half-lives are too short to maintain the biological activity. The thread was coated with gelatin hydrogel and fibroblast growth factor 2 (FGF 2) was biologically stabilized by incorporating in a gelatin hydrogel-coated thread. The purpose of this study is to investigate the effect of gelatin hydrogel-coated thread incorporating FGF 2 on human meniscal cells in an organ culture. Twenty-five menisci were cut into small pieces, and selected pieces were sutured with gelatin hydrogel-coated thread incorporating FGF 2 (FGF(+) group) or physiologic saline (FGF(-) group), followed by organ culture. The meniscal samples histologically evaluated 4, 7, and 14 days later. The cell density and the number of PCNA-positive cells for the FGF(+) group were higher than those of the FGF(-) group, while the number of TUNEL-positive cells was lower. These results suggest that FGF 2 stimulates the proliferation of meniscal cells and inhibits meniscal cell death. Gelatin hydrogel-coated threads releasable FGF 2 may be useful to promote repairing of human meniscus.

Evaluation criteria for musculoskeletal and craniofacial tissue engineering constructs: a conference report

Over the past 20 years, tissue engineering (TE) has evolved into a thriving research and commercial development field. However, applying TE strategies to musculoskeletal (MSK) and craniofacial tissues has been particularly challenging since these tissues must also transmit loads during activities of daily living. To address this need, organizers invited a small group of bioengineers, surgeons, biologists, and material scientists from academia, industry, and government to participate in a two and half-day conference to develop general and tissue-specific criteria for evaluating new concepts and tissue-engineered constructs, including threshold values of success. Participants were assigned to four breakout groups representing commonly injured tissues, including tendon and ligament, articular cartilage, meniscus and temporomandibular joint, and bone and intervertebral disc. Working in multidisciplinary teams, participants first carefully defined one or two important unmet clinical needs for each tissue type, including current standards of care and the potential impact of TE solutions. The groups then sought to identify important parameters for evaluating repair outcomes in preclinical studies and to specify minimally acceptable values for these parameters. The importance of in vitro TE studies was then discussed in the context of these preclinical studies. Where data were not currently available from clinical, preclinical, or culture studies, the groups sought to identify important areas of preclinical research needed to speed the development process. This report summarizes the findings of the conference.

Interleukin-1 and tumor necrosis factor alpha inhibit repair of the porcine meniscus in vitro

OBJECTIVE

Injury or removal of the knee meniscus leads to progressive joint degeneration, and current surgical therapies for meniscal tears seek to maximally preserve meniscal structure and function. However, the factors that influence intrinsic repair of the meniscus are not well understood. The goal of this study was to investigate the capacity of meniscus tissue to repair a simulated defect in vitro and to examine the effect of pro-inflammatory cytokines on this process.

METHODS

Cylindrical explants were harvested from the outer one-third of medial porcine menisci. To simulate a full-thickness defect, a central core was removed and reinserted immediately into the defect. Explants were cultured for 2, 4, or 6 weeks in serum-containing media in the presence or absence of interleukin-1 (IL-1) or tumor necrosis factor alpha (TNF-alpha), and meniscal repair was investigated using mechanical testing and fluorescence confocal microscopy.

RESULTS

Meniscal lesions in untreated samples showed a significant capacity for intrinsic repair in vitro, with increasing cell accumulation and repair strength over time in culture. In the presence of IL-1 or TNF-alpha, no repair was observed despite the presence of abundant viable cells.

CONCLUSIONS

This study demonstrates that the meniscus exhibits an intrinsic repair response in vitro. However, the presence of pro-inflammatory cytokines completely inhibited repair. These findings suggest that increased levels of pro-inflammatory cytokines post-injury or under arthritic conditions may inhibit meniscal repair. Therefore, inhibition of these cytokines may provide a means of accelerating repair of damaged or injured menisci in vivo.

Regional multilineage differentiation potential of meniscal fibrochondrocytes: implications for meniscus repair

The knee menisci are wedge-shaped semilunar fibrocartilaginous structures that reside between the femur and tibia and function to transmit and distribute load. These structures have characteristics of both fibrous and cartilaginous tissues. The cartilage-like inner region and the fibrous vascularized outer region each has a distinct extracellular matrix, and resident meniscal fibrochondrocytes (MFCs) with distinct morphologies dependent on their location. Damage to the meniscus is common, and disruption of tissue structure and function result in erosion of the underlying articular cartilage. It has been observed that damage in the vascular periphery undergoes spontaneous repair, whereas damage of the inner region does not heal. While vascularity of the peripheral region plays a role in healing, recent findings have also suggested that local cellular composition influences local healing capacity. This study examined the variation in multipotential characteristics of cell populations isolated from different regions of the bovine meniscus. MFCs were isolated from the outer (vascular), inner (avascular), and horn (mixed) regions and induced toward chondrogenic, adipogenic, and osteogenic lineages. The results of this study suggest that MFCs from all regions of the meniscus possess a multilineage differentiation capability, particularly toward chondrogenesis and adipogenesis. MFCs from the outer region were most plastic, differentiating along all three mesenchymal lineages. These findings may underlie the experimental observation of improved integration of meniscus grafts from the outer zone and may have implications for developing strategies of cell-based meniscus repair.

Repair response of the inner and outer regions of the porcine meniscus in vitro

BACKGROUND

The menisci are essential intra-articular structures that contribute to knee function, and meniscal injury or loss is associated with joint degeneration. Tears of the outer vascularized zone have a greater potential for repair than do tears in the inner avascular region.

OBJECTIVE AND HYPOTHESIS

Develop an in vitro explant model to examine the hypothesis that differences exist in the intrinsic repair response between the outer and inner region of the meniscus.

STUDY DESIGN

Controlled laboratory study.

METHODS

Cylindrical explants were harvested from the outer one third and inner two thirds of medial porcine menisci. To simulate a full-thickness defect, a central core was removed and reinserted immediately. Explants were cultured for 2, 4, or 6 weeks, and meniscal healing was investigated using mechanical testing, histologic analysis, and fluorescence confocal microscopy.

RESULTS

Over the 6-week culture period, meniscal explants exhibited migration of cells into the repair site, followed by increased tissue formation that bridged the interface. The repair strength increased significantly over time, with no differences between the 2 regions.

CONCLUSION

The findings show that explants from the avascular inner zone and vascular outer zone of the meniscus exhibit similar healing potential and repair strength in vitro.

CLINICAL RELEVANCE

These findings support the hypothesis that the regional differences in meniscal repair observed clinically are owed to the additional vascular supply of the outer meniscus rather than intrinsic differences between the extracellular matrix and cells from these 2 areas.

Effects of hepatocyte growth factor and platelet-derived growth factor on the repair of meniscal defects in vitro

Injuries to the avascular region of the meniscus occur frequently and may be difficult to repair. This study was designed to determine whether growth factors could diffuse from a collagen sponge or a collagen gel into meniscal tissue and stimulate healing of defects using an in vitro model. The diffusion of platelet-derived growth factor (PDGF) from the collagen carriers into the medium was rapid with approximately 50% being released from the collagen sponge within the first hour. After 5 d of incubation, 8% of the PDGF was present in the meniscus, 11% in the collagen sponge, and 62% had been released into the medium. Similar results were obtained when a collagen gel was used as a carrier. Histological evaluation of the meniscal explants after 2 wk in culture revealed extensive proteoglycan staining in the areas surrounding defects treated with either hepatocyte growth factor (HGF) or PDGF compared with controls without growth factor. The HGF-PDGF treatment resulted in alignment and migration of meniscal cells toward the defect, which was not observed in untreated controls. At 3-7 d, increased number of cells were observed in defects treated with collagen gels (but not the sponge) with PDGF-HGF. At 4 wk, combined HGF-PDGF treatment resulted in the formation of tissue with birefringence by polarized microscopy, suggestive of organized collagen. The data suggest that use of specific PDGF-HGF may enhance the repair of meniscal injuries.

Meniscal repair using bone marrow-derived mesenchymal stem cells: experimental study using green fluorescent protein transgenic rats

Meniscal tears in the avascular zone have very limited potential to heal because of a poor blood supply. Although there have been many attempts to promote the healing potential of the torn meniscus, no established treatments have achieved sufficient meniscal healing. In this study, we evaluated the efficacy of mesenchymal stem cell transplantation as a cell source to promote meniscal healing, using cells from the green fluorescent protein (GFP) transgenic rat and organ culture model. Mesenchymal stem cells from bone marrow were isolated and expanded in monolayer culture. They were embedded in fibrin glue and were transplanted into the meniscal defects of Sprague-Dawley rats. In the control groups, the defects remained untreated, or only fibrin glue without cells was transplanted. The GFP-positive cells enabled us to detect the transplanted cells from recipient cells easily. As a result, transplanted mesenchymal stem cells could survive and proliferate in the meniscal defects in the organ culture model. They also could produce an abundant extracellular matrix stained by toluidine blue around the cells which contributed to meniscal healing in the avascular status. We could detect transplanted GFP cells under a fluorescent microscope until 8 weeks after transplantation. In a clinical situation, mesenchymal stem cell transplantation is a promising new clinical strategy for the treatment of meniscal tears in the avascular zone.

Regional differences in the healing potential of the meniscus-an organ culture model to eliminate the influence of microvasculature and the synovium

Meniscal healing is well known to be region-specific, and this is thought to be mainly due to its specific vascularity. The purpose of this study was to assess regional differences in the intrinsic healing potential of the meniscus, using an organ culture model to eliminate the influence of microvasculature and the synovium. A full-thickness circular defect, 1.5 mm in diameter, was created in the inner avascular zone in meniscal explants from rabbits. As a control, a column of 1.5 mm in diameter was removed then replanted in the area where it had been obtained (Group C). In the experimental group, a 1.5 mm-diameter meniscal graft obtained from the peripheral zone of the same specimen was implanted in the damaged area (Group T). These meniscal explants were cultured for 2, 4 or 6 weeks, and the relationship between the recipient tissue and the graft was examined using both gross and histological semiquantitative scoring. The 6-week gross-examination showed that the openings were more apparent in Group C, and the score of Group T was significantly higher than that of Group C (P=0.0152). Histologically, the healing responses after both 4 and 6 weeks of incubation were significantly better in Group T than in Group C (P=0.0237, 0.0281). These results using organ culture demonstrate that intrinsic healing potential differs even without the influence of vascular supply and the synovium, indicating that the superior healing potential in the peripheral zone may contribute to the good meniscal healing in this location.

Tissue engineering of the meniscus

Meniscus lesions are among the most frequent injuries in orthopaedic practice and they will inevitably lead to degeneration of the knee articular cartilage. The fibro-cartilage-like tissue of the meniscus is notorious for its limited regenerative capacity. Tissue engineering could offer new treatment modalities for repair of meniscus tears and eventually will enable the replacement of a whole meniscus by a tissue-engineered construct. Many questions remain to be answered before the final goal, a tissue-engineered meniscus is available for clinical implementation. These questions are related to the selection of an optimal cell type, the source of the cells, the need to use growth factor(s) and the type of scaffold that can be used for stimulation of differentiation of cells into tissues with optimal phenotypes. Particularly in a loaded, highly complex environment of the knee, optimal mechanical properties of such a scaffold seem to be of utmost importance. With respect to cells, autologous meniscus cells seems the optimal cell source for tissue engineering of meniscus tissue, but their availability is limited. Therefore research should be stimulated to investigate the suitability of other cell sources for the creation of meniscus tissue. Bone marrow stroma cells could be useful since it is well known that they can differentiate into bone and cartilage cells. With respect to growth factors, TGF-beta could be a suitable growth factor to stimulate cells into a fibroblastic phenotype but the problems of TGF-beta introduced into a joint environment should then be solved. Polyurethane scaffolds with optimal mechanical properties and with optimal interconnective macro-porosity have been shown to facilitate ingrowth and differentiation of tissue into fibro-cartilage. However, even these materials cannot prevent cartilage degeneration in animal models. Surface modification and/or seeding of cells into the scaffolds before implantation may offer a solution for this problem in the future.This review focuses on a number of specific questions; what is the status of the development of procedures for lesion healing and how far are we from replacing the entire meniscus by a (tissue-engineered) prosthesis. Subquestions related to the type of scaffold used are: is the degree of tissue ingrowth and differentiation related to the initial mechanical properties and if so, what is the influence of those properties on the subsequent remodelling of the tissue into fibro-cartilage; what is the ideal pore geometry and what is the optimal degradation period to allow biological remodelling of the tissue in the scaffold. Finally, we will finish with our latest results of the effect of tear reconstruction and the insertion of prostheses on articular cartilage degradation.

Marrow stimulating technique to augment meniscus repair

Several techniques exist to increase the rate of healing of meniscal tears after repair. We describe a simple arthroscopic technique of microfracture to the intercondylar notch. This technique can provide marrow elements to the site of meniscus repair to aid in meniscal healing at the time of repair.

Effects of selected growth factors on porcine meniscus in chemically defined medium

Some evidence shows that selected growth factors can increase proteoglycan synthesis and that fibrin clot aids in the repair of meniscal tears. A significant (P<.05) dose-dependent stimulation of proteoglycan synthesis was found with platelet-derived growth factor AB (PDGF-[AB]), transforming growth factor-beta1 and bone morphogenetic protein-7 (osteogenic protein-I). In separate experiments, a significant increase in cellularity was found in the deep and superficial aspects of the explants treated with PDGF-(AB) compared with those treated with basal medium alone. The current study provides data as to which growth factors might prove most useful in the maintenance and repair of menisci.

Results of rasping of meniscal tears with and without anterior cruciate ligament injury as evaluated by second-look arthroscopy

PURPOSE

Meniscal rasping without suturing has been experimentally shown to stimulate vascular induction in tears in the avascular zone of menisci, resulting in meniscal healing. The goals of this study were to arthroscopically assess the results of meniscal rasping and analyze the factors affecting meniscal healing.

TYPE OF STUDY

Retrospective cohort study.

METHODS

Forty-eight torn menisci in 47 patients (age range, 14-47 years; average, 24 years) treated arthroscopically with the meniscal rasping technique were evaluated by second-look arthroscopy. The interval between the injury and the time of surgery ranged from 3 weeks to 13 years. There were 35 lateral and 13 medial meniscal tears associated with 44 anterior cruciate ligament injuries; 28 of the menisci had a full-thickness longitudinal tear and the other 20 had a partial-thickness tear. The length of the tears ranged from 10 to 33 mm (mean, 14.4 mm). The distance from the capsule to the tear ranged from 1 to 9 mm (mean, 5.0 mm).

RESULTS

Thirty-four menisci (71%) healed completely (without a marked visible unhealed area), 10 (21%) healed incompletely, and 4 (8%) showed no evidence of healing. There were no relationships between outcome and age, gender, injured side, or time from injury and rasping. Both the distance from the capsule to the tear and the length of the tear were longer in the unhealed menisci. Stable tears had a high healing rate after meniscal rasping.

CONCLUSIONS

Meniscal rasping without suturing is an easy procedure to perform and seems to be a reliable way to repair longitudinal tears in the avascular region of the meniscus, although the healing potential of the procedure is affected by the distance from the capsule to the tear site and the length and the stability of the tear.

Contractile actin expression in torn human menisci

The human meniscus is subject to injury that necessitates repair or removal. Many aspects of the cellular response to injury have not been well characterized. The purpose of this study was to describe the cellular distributions within the torn human meniscus. In addition to evaluating the cell density in selected regions, we investigated the cellular expression of a contractile actin isoform that has recently been found in the intact human meniscus. Included as a contemporaneous comparative group were torn human meniscal allografts. We hypothesized that a hypercellular surface zone would be found in the torn menisci, with a higher percentage of cells in this peripheral region expressing alpha-smooth muscle actin compared with other locations in the interior of the remnant. The rationale for this hypothesis was based on prior immunohistochemical investigations of the distribution of alpha-smooth muscle actin-containing cells in the torn human anterior cruciate ligament. Eighteen torn meniscal specimens were obtained from 17 patients, 0.5 to 84 months after injury, and four torn allograft meniscal samples were retrieved from three patients, 11 to 49 months after implantation. Microtomed sections of paraffin-embedded tissue were stained with hematoxylin and eosin and a monoclonal antibody to alpha-smooth muscle actin. The cell density and percentage of cells containing alpha-smooth muscle actin were determined in the following zones: synovial, vascular, hypercellular with loose collagen, hypocellular with dense collagen, and organized collagen. A cellular layer that resembled synovium was present on the surface of all but two of the specimens. Vascular regions were often continuous with the synovium abutting the more interior loose collagen zones. The total cell density was greatest in each of the zones closest to the periphery (synovium, vascular, and loose collagen; p < 0.001), when compared to the interior of the tissue. The synovium-like layer was found to have the highest percentage of alpha-smooth muscle actin-expressing cells and the highest alpha-smooth muscle actin-containing cell density (p < 0.05). Similar results were found for the torn allograft menisci. These findings confirm the working hypothesis and suggest that the torn human meniscus is capable of mounting a reparative response, including the proliferation of cells capable of contributing to wound closure. This underscores the importance of providing a bridging scaffold into which such cells can migrate.

Knee immobilization on meniscal healing after suture: an experimental study in sheep

Immobilization and nonweightbearing may influence the healing of sutured meniscal lesions in the avascular zone. In 12 sheep, 3 to 4 months of age, a 0.5-cm longitudinal lesion was made in the middle segment and posterior portion of the medial meniscus of the left knee in the avascular zone. The lesion was sutured immediately. The knees of six sheep were immobilized with a monolateral external fixator, which crossed the knee, and the knees in the other six sheep were not immobilized. The animals were sacrificed 6 weeks after the operation. Specimens from the anterior meniscus were used for histologic and vascular studies, and the posterior meniscus was used for mechanical testing. Repair was observed in two of 12 sheep in the form of fibrous tissue. Fibrochondrocytes and synovial cells were involved. Meniscal fibrochondrocytes from the nearest meniscal tissue, synovial cells from the femoral and tibial meniscal surfaces, and fibroblastic cells migrating through the suture channel provide cell access to the meniscus lesion. Sutured menisci, immobilized or not, support less than 50% of a normal load and are mechanically weak.

Genetic engineering of meniscal allografts

Allograft meniscal transplantation represents one of the few available treatment options after menisectomy. Despite acceptable early results, a considerable controversy exists with regard to poor graft regeneration, shrinkage and biomechanical failure of transplanted menisci. Transfer of specific growth factor genes may improve the regeneration process of meniscal allografts. The aim of this study was to investigate the feasibility of gene transfer in meniscal allografts in rabbits. Four different viral vectors encoding marker genes, including lacZ, luciferase, and green fluorescence protein were used to investigate viral transduction in 50 lapine menisci for 4 weeks in vitro. Subsequently, 16 unilateral meniscus replacements were performed with ex vivo retrovirally transduced meniscal allografts, and the expression of the lacZ gene was examined histologically at 2, 4, 6, and 8 weeks after transplantation. Gene expression in the superficial cell layers of the menisci can be detected for up to 4 weeks in vitro, but the level of gene transfer declined over time. The transduction with retrovirus showed better persistence and deep penetration of the menisci with infected cells. In vivo, declining numbers of beta-galactosidase-positive cells were also detected in retrovirally transduced allografts up to 8 weeks. Consistently, transduced cells were found at the menisco-synovial junction of the transplants and in deeper layers of the menisci. There was no evidence of cellular immune response in the transduced transplants. This investigation showed a prospective for growth factor delivery in auto- and allografts. In further experiments, vectors expressing therapeutic proteins such as growth factors will be investigated to assess their potential to improve remodeling and healing of meniscal allografts.

Expression of cytokines after meniscal rasping to promote meniscal healing

PURPOSE

We have developed a new surgical procedure of rasping a meniscal surface to repair a tear in the avascular zone. This procedure stimulates vascular induction to the tear, resulting in meniscal healing. The purpose of this study was to elucidate the mechanism of vascular induction and meniscal healing.

TYPE OF STUDY

Randomized trial.

METHODS

A full-thickness longitudinal tear of 5 mm in length was created in the avascular zone of the anterior segment of both medial menisci of rabbits. Meniscal rasping of about 0.5 mm in depth was then done on the femoral surface of the left meniscus from the parameniscal synovium to the inner portion including the longitudinal tear, and the right meniscus was left untreated as a control. After surgery, at 1, 7, 14, 28, 56, and 112 days, 4 rabbits were killed, both medial menisci were resected, and immunohistochemical staining with monoclonal antibodies was used to quantify expression of interleukin-1alpha (IL-1alpha), transforming growth factor-beta1 (TGF-beta1), platelet-derived growth factor (PDGF), and proliferating-cell nuclear antigen (PCNA) on the femoral surface of the menisci. A positive ratio of immunostaining was encountered.

RESULTS

The positive ratio of IL-1alpha, TGF-beta1, PDGF, and PCNA on the rasped surface area reached its peak at 1, 7, 14, and 7 days, respectively, after surgery, and thereafter gradually declined. Although the time course of the positive ratio was different among these cytokines, the positive ratio on the rasped surface was significantly higher than that on the control surface at the early stage of the observation period.

CONCLUSIONS

The cytokine network on the rasped meniscal surface appears to be the key to explaining the mechanism of vascular induction and meniscal healing by meniscal rasping.

Toward tissue engineering of the knee meniscus

This review details current efforts to tissue engineer the knee meniscus successfully. The meniscus is a fibrocartilaginous tissue found within the knee joint that is responsible for shock absorption, load transmission, and stability within the knee joint. If this tissue is damaged, either through tears or degenerative processes, then deterioration of the articular cartilage can occur. Unfortunately, there is a dearth in the amount of work done to tissue engineer the meniscus when compared to other musculoskeletal tissues, such as bone. This review gives a brief overview of meniscal anatomy, biochemical properties, biomechanical properties, and wound repair techniques. The discussion centers primarily on the different components of attempting to tissue engineer the meniscus, such as scaffold materials, growth factors, animal models, and culturing conditions. Our approach for tissue engineering the meniscus is also discussed.

Effect of CO2 laser on healing of cultured meniscus

BACKGROUND AND OBJECTIVE

A new method to improve cartilage repair is clinically important. The enhancement of meniscal healing by low power CO2 laser was investigated in an organ culture system.

STUDY DESIGN/MATERIALS AND METHODS

A longitudinal or a radial defect was made in the avascular zone of rabbit menisci. Irradiation by CO2 laser with 1 W (energy density 50 J/cm2) and 2 W (energy density 100 J/cm2) was used.

RESULTS

Histologic and scanning electron microscopic evaluations revealed that both energy densities of laser irradiation and the type of and the site of meniscal defect can influence the course and the outcome of meniscal healing. A marked increase in fibrochondrocytic proliferation and regeneration of collagen fibers were demonstrated in the meniscal defects irradiated by 100 J of CO2 laser energy.

CONCLUSIONS

The healing of meniscal defects could be promoted by low power CO2 laser irradiation.

A clinical study of collagen meniscus implants to restore the injured meniscus

The meniscus performs critical functions within the knee, and its loss frequently leads to osteoarthritis and irreversible joint damage. Because prosthetic replacement of the meniscus has proven ineffective, the authors used tissue engineering techniques to develop a resorbable collagen scaffold (collagen meniscus implant) that supports ingrowth of new tissue and eventual regeneration of the lost meniscus. Eight patients underwent arthroscopic placement the collagen meniscus implant to reconstruct and restore the irreparably damaged medial meniscus of one knee. Seven patients had one or more prior meniscectomies, and one patient had an acute meniscus injury. Patients were observed with frequent clinical, serologic, radiographic, and magnetic resonance imaging examinations for at least 24 months (range, 24-32 months). All patients underwent relook arthroscopy and biopsy of the implant regenerated tissue at either 6 or 12 months after implantation. All patients improved clinically from preoperatively to 1 and 2 years postoperatively based on pain, Lysholm scores, Tegner activity scale, and self assessment. Relook arthroscopy revealed tissue regeneration in all patients with apparent preservation of the joint surfaces based on visual observations. Histologic analysis confirmed new fibrocartilage matrix formation. Radiographs confirmed no progression of degenerative joint disease. The collagen meniscus implant is implantable, biocompatible, resorbable, and supports new tissue regeneration as it is resorbed. This tissue seems to function similar to meniscus tissue by protecting the chondral surfaces.

The effect of cytokines on the proliferation and migration of bovine meniscal cells

We determined the effect of cytokines on the proliferation and migration of cells isolated from the inner-third (white-white), middle-third (red-white), and outer-third (red-red) regions of bovine meniscus. Cells from the outer, or peripheral, region of the meniscus exhibited higher DNA synthesis in the presence of 10% serum compared with cells from the inner or central regions. Recombinant human platelet-derived growth factor-AB, hepatocyte growth factor/scatter factor, and bone morphogenic protein-2 stimulated DNA synthesis of all meniscal cells in a dose-dependent manner, with a two- to threefold maximal stimulation at 10 ng/ml. Cell migration was also stimulated by addition of cytokines. Platelet-derived growth factor and hepatocyte growth factor caused an increase in the migration of cells derived from all three zones, while interleukin-1 selectively stimulated the migration of outer-zone meniscal cells. Epidermal growth factor was much less effective and stimulated the migration of cells in the inner and outer zones by 40% to 50%, while bone morphogenic protein-2 and insulin-like growth factor-1 stimulated the migration of meniscal cells from the middle zone by 40% to 50%. The identification of cytokines that stimulate both the growth and migration of meniscal cells may provide new tools for modulation of meniscal healing.

Function of the normal meniscus and consequences of meniscal resection

The principal functions of the meniscus are load transmission and shock absorption, based on the meniscal collagen architecture, the biochemical fluid composition, and the proteoglucan-collagen meshwork. The mobile menisci transmit 50-90% of load over the knee joint, depending on knee flexion angle, femoral translation and rotation. The meniscus contributes to knee joint proprioception and probably also to joint stability. Late consequences of total and partial meniscectomy are radiographic osteoarthritis, with a varying percentage of these patients having symptoms. Malalignment, concomitant articular cartilage lesions, and ligament instability are absolute risk factors, while age, lateral compartment, and continued sport activity are relative risk factors. Acute reinsertion of meniscal tears in the red-red or red-white zones can be performed successfully by arthroscopic technique. Also in chronic tears stable healing can be expected in most cases, if the scar tissue is resected.

Meniscal rasping for repair of meniscal tear in the avascular zone

We examined experimentally whether a longitudinal tear in the avascular zone of a rabbit meniscus can be healed by meniscal rasping. A full-thickness longitudinal tear 5-mm long was artificially created in the avascular zone of the anterior segment of both medial menisci. Meniscal rasping was then done on the femoral surface of the right meniscus from the parameniscal synovium to the inner segment including the tear. The left meniscus was left without further treatment as control. Two to 4 weeks after surgery, the hypertrophic synovium was observed invading from the parameniscal region to the injured portion. Eight to 16 weeks after surgery, the tear was almost completely healed. In contrast, neither hypertrophy of the synovium covering the tear nor healing was induced in the control meniscus. The mechanical test showed that there was a significant difference in the tensile strength and the stiffness of the injured portion between the rasped meniscus and the control meniscus. Meniscal rasping is easy to do, is effective, and causes few adverse effects with menisci. This procedure may be a treatment option for clinical cases of meniscal tear in the avascular zone for which we have no effective and clinically applicable methods at present, although further investigation is needed before clinical application.

Trephination and suturing of avascular meniscal tears: a clinical study of the trephination procedure

On the basis of animal studies, an arthroscopic surgical system and procedure of trephination plus suturing were designed for clinical practice. The system consists of a trephine with a tooth-like tip, a guide, and an ordinary arthroscopic power handle. The guide introduces the trephine to the tear without abrading articular cartilage and controls the depth of the trephination. The power handle connected to a suction system provides an inside-out cut core of meniscal tissue. Thirty-six patients with meniscal tears underwent arthroscopic trephination plus suturing (group TS) and 28 patients had suturing alone (group S). The follow-up was 25 to 78 months. Two symptomatic retears have occurred in group TS and 7 symptomatic retears in group S. The symptomatic retear rate of group TS was significantly smaller than group S (P < .01). It is indicated that the patients treated with trephination have fewer symptoms and lower clinical failure rate. Arthroscopic trephination is a safe and easy procedure.

Augmented meniscal healing with free synovial autografts: an organ culture model

We examined whether or not free synovial autografts can augment the healing of lesions artificially created in the human knee meniscus in an organ culture model. The effectiveness of free synovial autografts was also compared with that of fibrin glue (Tisseel). In the control group, the accumulation of cellular components increased at the edge of a 4-mm meniscal defect following culture, although no cells were found to invade the defect. In the fibrin glue group, an increased migration of cells into fibrin glue packed into the defect was observed until 4 weeks following cultivation. However, newly formed collagen produced by the cells in the fibrin glue was minimal even 4 weeks after cultivation. In contrast, in the synovial group, newly formed collagen production, as well as cellular proliferation, increased in the grafted synovium with time after cultivation. By 4 weeks, the gap between the edge of the defect and the grafted synovium was bridged by newly formed collagen tissue, indicating improved histologic repair. Our results suggest that free autogenous synovial tissue grafts in meniscal lesions are superior to fibrin glue, and that interpositional synovial autografts to augment repair of meniscal tears in the avascular zone may be clinically useful.

Autogenous replacement of the meniscus cartilage: analysis of results and mechanisms of failure

Autogenous replantation of meniscal cartilage (resection of 80% of the meniscus cartilage followed by immediate replantation) was performed in 14 dogs as a control arm of a meniscal replacement study. The purpose was to assess the ability of the excised tissue to heal to the intact rim and function as a meniscus cartilage. This procedure is an idealized model of allografting meniscus cartilage in that the tissue is fresh, autogenous, and perfectly sized. If this procedure did not succeed, it seemed likely to the authors that allografting meniscal cartilage would have diminished chances for success. Evaluation of these replant failures led us to speculate that the causes and mechanisms might include slow or incomplete revascularization, inadequate mechanical fixation or stabilization, and, perhaps, some type of rejection phenomenon not examined or confirmed in the present study. We believe these mechanisms will be particularly deleterious for allografted meniscal cartilages and recommend further extensive evaluation of meniscal allografts before wide clinical use.