Ongoing MRI remodeling 3-7 years after collagen meniscus implantation in stable knees

Advances in meniscus tissue engineering: Towards bridging the gaps from bench to bedside

Meniscus is vital for maintaining the anatomical and functional integrity of knee. Injuries to meniscus, commonly caused by trauma or degenerative processes, can result in knee joint dysfunction and secondary osteoarthritis, while current conservative and surgical interventions for meniscus injuries bear suboptimal outcomes. In the past decade, there has been a significant focus on advancing meniscus tissue engineering, encompassing isolated scaffold strategies, biological augmentation, physical stimulus, and meniscus organoids, to improve the prognosis of meniscus injuries. Despite noteworthy promising preclinical results, translational gaps and inconsistencies in the therapeutic efficiency between preclinical and clinical studies exist. This review comprehensively outlines the developments in meniscus tissue engineering over the past decade (Scheme 1). Reasons for the discordant results between preclinical and clinical trials, as well as potential strategies to expedite the translation of bench-to-bedside approaches are analyzed and discussed.

Meniscal Allograft versus Synthetic Graft in Treatment Outcomes of Meniscus Repair: A Mini-review and Meta-analysis

Meniscal injuries are highly correlated with osteoarthritis (OA) onset and progression. Although meniscal allograft transplantation (MAT) is a therapeutic option to restore meniscal anatomy, a shortage of donor material and the donor-derived infectious risk may be concerns in clinics. This review summarizes the literature reporting meniscus repair status in preclinical models and clinical practice using allografts or synthetic grafts. The advantages and limitations of biodegradable polymer-based meniscal scaffolds, applied in preclinical studies, are discussed. Then, the long-term treatment outcomes of patients with allografts or commercial synthetic scaffolds are compared. A total of 47 studies are included in our network meta-analysis. Compared with the meniscal allografts, the commercial synthetic products significantly improved clinical treatment outcomes in terms of the Knee Injury and Osteoarthritis Outcome Score (KOOS), Visual Analog Scale (VAS) scores, and Lysholm scores. In addition, development strategies for the next generation of novel synthetic scaffolds are proposed through optimization of structural design and fabrication, and selection of cell sources, external stimuli, and active ingredients. This review may inspire researchers and surgeons to design and fabricate clinic-orientated grafts with improved treatment outcomes.

The Current State of Meniscus Replacements

PURPOSE OF REVIEW

The field of meniscus replacement is changing continuously, with new devices emerging and others disappearing from the market. With the current tendency to preserve the knee joint, meniscus implants may become more relevant than ever. The purpose of this review is to provide an overview of the current state of partial and total meniscus replacements that have been developed beyond the academic phase. The available clinical and pre-clinical data is evaluated, and omissions are identified.

RECENT FINDINGS

Recent systematic reviews have shown a lack of homogenous clinical data on the CMI and Actifit meniscal scaffolds, especially regarding long-term performance without concomitant surgical interventions. Clinical studies on the medial total meniscus prostheses NUsurface and Artimis are ongoing, with the NUsurface being several years ahead. New techniques for meniscus replacement are rapidly developing, including the Artimis lateral meniscus prosthesis and the MeniscoFix 3D-printed scaffold. All evaluated clinical studies point towards improved clinical outcomes after implantation of partial and total meniscus replacements. Long-term data on survival and performance is of low quality for CMI and Actifit and is unavailable yet for NUsurface and Artimis. It is of major importance that future research focuses on optimizing fixation methods and identifying the optimal treatment strategy for each patient group. New techniques for total and partial replacement of the medial and lateral meniscus will be followed with interest.

Outcome comparison of meniscal allograft transplantation (MAT) and meniscal scaffold implantation (MSI): a systematic review

BACKGROUND

Although numerous studies have reported successful clinical outcomes of meniscal allograft transplantation (MAT) or meniscal scaffold implantation (MSI), the difference between the outcome of MAT and MSI remains unclear.

PURPOSE

To compare the overall outcomes and survival rates of MAT and MSI, aiming to provide comprehensive evidence for determining the optimal treatment strategy for meniscal defects.

METHODS

A systematic review was performed via a comprehensive search of PubMed, Embase, and the Cochrane Library. Studies of MAT or MSI were included according to the inclusion and exclusion criteria. The Lysholm score was chosen as the primary outcome measure, while secondary outcomes encompassed patient-reported outcome measures (PROMs), return to sports (RTS) rates, survival rates, and complication rates. The outcomes were stratified into two groups: MAT group and MSI group, followed by statistical comparison ( P <0.05). The quality of the included studies was assessed by the Cochrane Risk of Bias 2 (RoB2) assessment tool for randomized controlled trials (RCTs) and the Coleman Methodology Score (CMS) for non-randomized controlled trials.

RESULTS

A total of 3932 patients (2859 MAT, 1073 MSI) in 83 studies (51 MAT, 32 MSI) had the overall significant improvement in all clinical scores. The group MSI had a higher Lysholm score of both preoperative ( P =0.002) and postoperative ( P <0.001) than group MAT; however, the mean improvements were similar between the two groups ( P =0.105). Additionally, MSI had higher improvements of IKDC ( P <0.001), KOOS symptom ( P =0.010), KOOS pain ( P =0.036), and KOOS ADL ( P =0.004) than MAT. Interestingly, MAT had higher preoperative ( P =0.018) and less postoperative VAS pain ( P =0.006), which was more improved in MAT ( P <0.001). Compared with MAT, MSI had a higher 10-year survival rate ( P =0.034), a similar mid-term survival rate MAT ( P =0.964), and a lower complication rate ( P <0.001).

CONCLUSION

Both MAT and MSI could have good clinical outcomes after surgery with a similar improvement in Lysholm score. MSI had a higher 10-year survival rate and fewer complications than MAT.

LEVEL OF EVIDENCE

Level IV, systematic review.

Biologic Augmentation of Isolated Meniscal Repair

PURPOSE OF REVIEW

The limited blood supply and intrinsic healing capacity of the meniscus contributes to suboptimal tissue regeneration following injury and surgical repair. Biologic augmentation techniques have been utilized in combination with isolated meniscal repair to improve tissue regeneration. Several innovative strategies such as Platelet-Rich Plasma (PRP), fibrin clots, mesenchymal stem cells (MSCs), bone marrow stimulation, meniscal scaffolds, and meniscal wrapping, are being explored to enhance repair outcomes. This article provides a comprehensive review of recent findings and conclusions regarding biologic augmentation techniques.

RECENT FINDINGS

Studies on PRP reveal mixed outcomes, with some suggesting benefits in reducing failure rates of isolated meniscal repair, while others question its efficacy. Fibrin clots and PRF (Platelet-rich fibrin), although promising, show inconsistent results and lack sufficient evidence for definitive conclusions. MSCs demonstrate potential in preclinical studies, but clinical trials have been limited and inconclusive. Bone marrow stimulation appears effective in certain contexts, but its broader applicability remains uncertain. Meniscal scaffolds, including CMI (Collagen Meniscal Implants) and Actifit (polyurethane scaffolds), show encouraging short- and mid-term outcomes but have not consistently surpassed traditional methods in the long term. Meniscal wrapping is infrequently studied but demonstrates positive short-term results with certain applications. The review reveals a diverse range of outcomes for biologic augmentation in meniscal repair. While certain techniques show promise, particularly in specific scenarios, the overall efficacy of these methods has yet to reach a consensus. The review underscores the necessity for standardized, high-quality research to establish the definitive effectiveness of these biologic augmentation methods.

Loss of chondroprotection of medial collagen meniscus implant (CMI) at 20-year follow-up

OBJECTIVE

The mid-term results of the collagen meniscus implant (CMI) procedure for the replacement of partial meniscus defects have already been described. However, there is a paucity of long-term comparative studies. This study aimed to compare the clinical outcomes, failures, and osteoarthritis progression of patients who underwent partial medial meniscectomy and medial CMI implantation.

METHODS

Thirty-six nonconsecutive patients with medial meniscus injuries that underwent medial CMI (MCMI) implantation or partial medial meniscectomy (PMM) between 1997 and 2000 were included in a prospective study with an intermediate 10-year follow-up examination and a final follow-up examination at 20-year follow-up. Outcome measures at the 20-year follow-up included the Lysholm score, visual analogue scale (VAS) for pain, International Knee Documentation Committee (IKDC) knee form , and Tegner activity level. Bilateral weight-bearing radiographs were also performed to evaluate hip-knee-angle (HKA) and the medial joint line height (JL). Data regarding complications and failures were also collected.

RESULTS

At the 20-year follow-up, 31 patients (83% follow-up rate) with a mean age of 60.7 ​± ​8.9 years were included in the final analysis (21.1 ​± ​1.2 years follow-up). Four reoperations and one failure per group were reported. When comparing the clinical results of the two groups, no difference was found considering the Lysholm score, Knee Injury and Osteoarthritis Outcome Score (KOOS), Tegner, and the IKDC. Moreover, 20 patients underwent radiographic examination (10 MCMI, 10 ​MM), and no statistically significant difference was reported concerning the JL, HKA, and the presence and incidence of osteoarthritis between the two groups.

CONCLUSION

The CMI implant for partial medial meniscectomy provided good long-term results and a low failure rate. However, differently from the 10 years follow-up, the clinical and the radiological outcomes were not superior compared to the medial meniscectomy group. The present study's result suggests that using a medial scaffold is not chondroprotective.

LEVEL OF EVIDENCE

III, Prospective case-control study.

Short-Term but Not Long-Term Knee Symptoms and Functional Improvements of Tissue Engineering Strategy for Meniscus Defects: A Systematic Review of Clinical Studies

PURPOSE

To investigate the up-to-date clinical outcomes of tissue-engineered meniscus implants for meniscus defects.

METHODS

A search was performed by 3 independent reviewers on PubMed, MEDLINE, EMBASE, and Cochrane from 2016 to June 18, 2023, with the term "meniscus" with all the following terms: "scaffolds," "constructs," "implant," and "tissue engineering." Inclusion criteria included "Clinical trials" and "English language articles" that involved isolated meniscus tissue engineering strategies for meniscus injuries. Only Level I to IV clinical studies were considered. The modified Coleman Methodology score was used for quality analysis of included clinical trials. The Methodological Index for Non-Randomized Studies was employed for analysis of the risk of study bias and methodological quality.

RESULTS

The search identified 2,280 articles, and finally 19 original clinical trials meeting the inclusion criteria were included. Three types of tissue-engineered meniscus implants (CMI-Menaflex, Actifit, and NUsurface) have been clinically evaluated for meniscus reconstruction. Lack of standardized outcome measures and imaging protocols limits comparison between studies.

CONCLUSIONS

Tissue-engineered meniscus implants can provide short-term knee symptom and function improvements, but no implants have been shown to propose significant long-term benefits for meniscus defects.

LEVEL OF EVIDENCE

Level IV, systematic review of Level I to IV studies.

MRI follow up of bilateral partial meniscal substitution with a demineralized bone block. A case report

The case of a 60-year-old male is described, who presented in 2020 with a symptomatic degenerative bilateral posterior horn lesion of the medial meniscus. On MRI both lesions appeared identical as 60%-70% incomplete radial tears in the posterior horn of the medial meniscus with a flap tear component. The patient was arthroscopically treated with bilateral implantation of a demineralized bone block as a partial medial meniscus substitute. A complete isointense and homogenous signal was recorded after 16 weeks and 12 months on the right knee and after 12 weeks on the left knee, indicating a complete ingrowth and remodeling of the implant. KOOS and IKDC score improved from 81 and 66% presurgery to 94 and 93%, respectively, 6 months after the second partial medial meniscus substitution on the left knee.

Natural biopolymer scaffold for meniscus tissue engineering

Meniscal injuries caused by trauma, degeneration, osteoarthritis, or other diseases always result in severe joint pain and motor dysfunction. Due to the unique anatomy of the human meniscus, the damaged meniscus lacks the ability to repair itself. Moreover, current clinical treatments for meniscal injuries, including meniscal suturing or resection, have significant limitations and drawbacks. With developments in tissue engineering, biopolymer scaffolds have shown promise in meniscal injury repair. They act as templates for tissue repair and regeneration, interacting with surrounding cells and providing structural support for newly formed meniscal tissue. Biomaterials offer tremendous advantages in terms of biocompatibility, bioactivity, and modifiable mechanical and degradation kinetics. In this study, the preparation and composition of meniscal biopolymer scaffolds, as well as their properties, are summarized. The current status of research and future research prospects for meniscal biopolymer scaffolds are reviewed in terms of collagen, silk, hyaluronic acid, chitosan, and extracellular matrix (ECM) materials. Overall, such a comprehensive summary provides constructive suggestions for the development of meniscal biopolymer scaffolds in tissue engineering.

Biomaterials for meniscus and cartilage in knee surgery: state of the art

Meniscus and cartilage injuries of the knee joint lead to cartilage degeneration and osteoarthritis (OA). The research on biomaterials and artificial implants as substitutes in reconstruction and regeneration has become a main international focus in order to solve clinical problems such as irreparable meniscus injury, postmeniscectomy syndrome, osteochondral lesions and generalised chronic OA. In this review, we provide a summary of biomaterials currently used in clinical practice as well as state-of-the-art tissue engineering strategies and technologies that are developed for articular cartilage and meniscus repair and regeneration. The literature was reviewed over the last 5 years on clinically used meniscus and cartilage repair biomaterials, such as Collagen Meniscal Implant, Actifit, NUsurface, TruFit, Agili-C and MaioRegen. There are clinical advantages for these biomaterials and the application of these treatment options should be considered individually. Standardised evaluation protocols are needed for biological and mechanical assessment and comparison between different scaffolds, and long-term randomised independent clinical trials with large study numbers are needed to provide more insight into the use of these biomaterials. Surgeons should become familiar and stay up to date with evolving repair options to improve their armamentarium for meniscal and cartilage defects.

Clinical Replacement Strategies for Meniscus Tissue Deficiency

Meniscus tissue deficiency resulting from primary meniscectomy or meniscectomy after failed repair is a clinical challenge because the meniscus has little to no capacity for regeneration. Loss of meniscus tissue has been associated with early-onset knee osteoarthritis due to an increase in joint contact pressures in meniscectomized knees. Clinically available replacement strategies range from allograft transplantation to synthetic implants, including the collagen meniscus implant, ACTIfit, and NUSurface. Although short-term efficacy has been demonstrated with some of these treatments, factors such as long-term durability, chondroprotective efficacy, and return to sport activities in young patients remain unpredictable. Investigations of cell-based and tissue-engineered strategies to treat meniscus tissue deficiency are ongoing.

Biosynthetic scaffolds for partial meniscal loss: A systematic review from animal models to clinical practice

Acute or degenerative meniscus tears are the most common knee lesions. Meniscectomy provides symptomatic relief and functional recovery only in the short- to mid-term follow-up but significantly increases the risk of osteoarthritis. For this reason, preserving the meniscus is key, although it remains a challenge. Allograft transplants present many disadvantages, so during the last 20 years preclinical and clinical research focused on developing and investigating meniscal scaffolds. The aim of this systematic review was to collect and evaluate all the available evidence on biosynthetic scaffolds for meniscus regeneration both in vivo and in clinical studies. Three databases were searched: 46 in vivo preclinical studies and 30 clinical ones were found. Sixteen natural, 15 synthetic, and 15 hybrid scaffolds were studied in vivo. Among them, only 2 were translated into clinic: the Collagen Meniscus Implant, used in 11 studies, and the polyurethane-based scaffold Actifit®, applied in 19 studies. Although positive outcomes were described in the short- to mid-term, the number of concurrent procedures and the lack of randomized trials are the major limitations of the available clinical literature. Few in vivo studies also combined the use of cells or growth factors, but these augmentation strategies have not been applied in the clinical practice yet. Current solutions offer a significant but incomplete clinical improvement, and the regeneration potential is still unsatisfactory. Building upon the overall positive results of these "old" technologies to address partial meniscal loss, further innovation is urgently needed in this field to provide patients better joint sparing treatment options.

A review of strategies for development of tissue engineered meniscal implants

The meniscus is a key stabilizing tissue of the knee that facilitates proper tracking and movement of the knee joint and absorbs stresses related to physical activity. This review article describes the biology, structure, and functions of the human knee meniscus, common tears and repair approaches, and current research and development approaches using modern methods to fabricate a scaffold or tissue engineered meniscal replacement. Meniscal tears are quite common, often resulting from sports or physical training, though injury can result without specific contact during normal physical activity such as bending or squatting. Meniscal injuries often require surgical intervention to repair, restore basic functionality and relieve pain, and severe damage may warrant reconstruction using allograft transplants or commercial implant devices. Ongoing research is attempting to develop alternative scaffold and tissue engineered devices using modern fabrication techniques including three-dimensional (3D) printing which can fabricate a patient-specific meniscus replacement. An ideal meniscal substitute should have mechanical properties that are close to that of natural human meniscus, and also be easily adapted for surgical procedures and fixation. A better understanding of the organization and structure of the meniscus as well as its potential points of failure will lead to improved design approaches to generate a suitable and functional replacement.

The regenerative effect of different growth factors and platelet lysate on meniscus cells and mesenchymal stromal cells and proof of concept with a functionalized meniscus implant

Meniscus regeneration could be enhanced by targeting meniscus cells and mesenchymal stromal cells (MSCs) with the right growth factors. Combining these growth factors with the Collagen Meniscus Implant (CMI®) could accelerate cell ingrowth and tissue formation in the implant and thereby improve clinical outcomes. Using a transwell migration assay and a micro-wound assay, the effect of insulin-like growth factor-1, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), transforming growth factor beta 1 (TGF-β1), fibroblast growth factor, and platelet lysate (PL) on migration and proliferation of meniscus cells and MSCs was assessed. The formation of extracellular matrix under influence of the above-mentioned growth factors was assessed after 28 days of culture of both MSCs and meniscus cells. As a proof of concept, the CMI® was functionalized with a VEGF binding peptide and coated with platelet-rich plasma (PRP) for clinical application. Our results demonstrate that PDGF, TGF-β1, and PL stimulate migration, proliferation, and/or extracellular matrix production of meniscus cells and MSCs. Additionally, the CMI® was successfully functionalized with a VEGF binding peptide and PRP which increased migration of meniscus cell and MSC into the implant. This study demonstrates proof of concept of functionalizing the CMI® with growth factor binding peptides. A CMI® functionalized with the right growth factors holds great potential for meniscus replacement after partial meniscectomy.

A professional athlete functionally active 10 years after an arthroscopic lateral collagen meniscus implant

The case of a former high-level professional soccer player is presented at 10-year follow-up after arthroscopically implanted lateral Collagen Meniscus Implant (CMI). The patient achieved a full-knee functional recovery and a complete sport resumption to the same pre-injury level for several soccer seasons and he is still performing semi-professional soccer activity (minor league) 10 years after surgery.Level of evidence Case Report. Level IV.

Meniscal substitution, a developing and long-awaited demand

The menisci represent indispensable intraarticular components of a well-functioning knee joint. Sports activities, traumatic incidents, or simply degenerative conditions can cause meniscal injuries, which often require surgical intervention. Efforts in biomechanical and clinical research have led to the recommendation of a meniscus-preserving rather than a meniscus-resecting treatment approach. Nevertheless, partial or even total meniscal resection is sometimes inevitable. In such circumstances, techniques of meniscal substitution are required. Autologous, allogenic, and artificial meniscal substitutes are available which have evolved in recent years. Basic anatomical and biomechanical knowledge, clinical application, radiological and clinical outcomes as well as future perspectives of meniscal substitutes are presented in this article. A comprehensive knowledge of the different approaches to meniscal substitution is required in order to integrate these evolving techniques in daily clinical practice to prevent the devastating effects of lost meniscal tissue.

Lateral Meniscus Replacement Using Peroneus Longus Tendon Autograft

Nowadays, several techniques are available for preserving the lateral aspect of the knee after meniscectomy; meniscus transplantation is the gold standard, and meniscus scaffold implantation is an effective alternative. However, meniscus transplantation is technically difficult and has many potential complications, whereas scaffolds resorb over time. Autografts are commonly used for labroplasty in shoulder and hip surgeries. We attempted to adapt this technique to the knee, using autografts for meniscus replacement. In this report, we describe a meniscus-replacement technique, using a peroneus longus autograft, for lateral meniscus deficits. This technique significantly simplifies the procedure and is cost effective, and thus can be considered as an alternative technique for preventing osteoarthritis of the lateral aspect of the knee.