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

Testing Hypoxia in Pig Meniscal Culture: Biological Role of the Vascular-Related Factors in the Differentiation and Viability of Neonatal Meniscus

Menisci play an essential role in shock absorption, joint stability, load resistance and its transmission thanks to their conformation. Adult menisci can be divided in three zones based on the vascularization: an avascular inner zone with no blood supply, a fully vascularized outer zone, and an intermediate zone. This organization, in addition to the incomplete knowledge about meniscal biology, composition, and gene expression, makes meniscal regeneration still one of the major challenges both in orthopedics and in tissue engineering. To overcome this issue, we aimed to investigate the role of hypoxia in the differentiation of the three anatomical areas of newborn piglet menisci (anterior horn (A), central body (C), and posterior horn (P)) and its effects on vascular factors. After sample collection, menisci were divided in A, C, P, and they were cultured in vitro under hypoxic (1% O₂) and normoxic (21% O₂) conditions at four different experimental time points (T0 = day of explant; T7 = day 7; T10 = day 10; T14 = day 14); samples were then evaluated through immune, histological, and molecular analyses, cell morpho-functional characteristics; with particular focus on matrix composition and expression of vascular factors. It was observed that hypoxia retained the initial phenotype of cells and induced extracellular matrix production resembling a mature tissue. Hypoxia also modulated the expression of angiogenic factors, especially in the early phase of the study. Thus, we observed that hypoxia contributes to the fibro-chondrogenic differentiation with the involvement of angiogenic factors, especially in the posterior horn, which corresponds to the predominant weight-bearing portion.

Biomaterials and Meniscal Lesions: Current Concepts and Future Perspective

Menisci are crucial structures for knee homeostasis. After a meniscal lesion, the golden rule, now, is to save as much meniscus as possible; only the meniscus tissue that is identified as unrepairable should be excised, and meniscal sutures find more and more indications. Several different methods have been proposed to improve meniscal healing. They include very basic techniques, such as needling, abrasion, trephination and gluing, or more complex methods, such as synovial flaps, meniscal wrapping or the application of fibrin clots. Basic research of meniscal substitutes has also become very active in the last decades. The aim of this literature review is to analyze possible therapeutic and surgical options that go beyond traditional meniscal surgery: from scaffolds, which are made of different kind of polymers, such as natural, synthetic or hydrogel components, to new technologies, such as 3-D printing construct or hybrid biomaterials made of scaffolds and specific cells. These recent advances show that there is great interest in the development of new materials for meniscal reconstruction and that, with the development of new biomaterials, there will be the possibility of better management of meniscal injuries

Multiscale finite element musculoskeletal model for intact knee dynamics

BACKGROUND AND OBJECTIVE

The dynamic characteristics of the intact knee joint are valuable for treating knee osteoarthritis and designing knee prostheses. However, it remains a challenge to elucidate the detailed dynamics of the knee due to its complexity of anatomical structure and complex interaction with body dynamics.

METHODS

In this study, a unique subject-specific musculoskeletal model with a concurrent high-accuracy intact finite element knee model was created and used to simultaneously evaluate the kinematics and mechanics of an intact knee joint during the gait cycle.

RESULTS

A medial pivot motion with external rotation, and a large parallel anterior translation were observed in the stance and swing phases, respectively, which is consistent with the in vivo fluoroscopy measurements. The maximum axial contact force on the knee joint, observed at 45% of the gait cycle, is approximately 2.89 times the body weight. The medial cartilage bears 65.7% of the total axial contact force. The results demonstrate that the cartilage-cartilage contact bears most of the joint load (62.5%) compared to the cartilage-meniscus-cartilage contact (37.5%). Regarding contact mechanics, the maximum contact pressure on both sides of the tibial cartilage (8.2 MPa) is almost similar to the first axial loading peak (14%) of the gait cycle. Additionally, the maximum contact pressure (6.01 MPa) was observed during the stance phase of the gait cycle on the patellofemoral joint.

CONCLUSIONS

The predicted results on the tibiofemoral and patellofemoral joints provide a theoretical basis for the treatment of knee joint diseases and knee prosthesis design. Moreover, this approach presents a comprehensive tool to evaluate the mechanics at both the body and tissue levels. Therefore, it has a high potential for application in human biomechanics.

Anisotropy and inhomogeneity of permeability and fibrous network response in the pars intermedia of the human lateral meniscus

Within the human tibiofemoral joint, meniscus plays a key role due to its peculiar time-dependent mechanical characteristics, inhomogeneous structure and compositional features. To better understand the pathophysiological mechanisms underlying this essential component, it is mandatory to analyze in depth the relationship between its structure and the function it performs in the joint. Accordingly, the aim of this study was to evaluate the behavior of both solid and fluid phases of human meniscus in response to compressive loads, by integrating mechanical assessment and histological analysis. Cubic specimens were harvested from seven knee lateral menisci, specifically from anterior horn, pars intermedia and posterior horn; unconfined compressive tests were then performed according to three main loading directions (i.e., radial, circumferential and vertical). Fibril modulus, matrix modulus and hydraulic permeability of the tissue were thence estimated through a fibril-network-reinforced biphasic model. Tissue porosity and collagen fibers arrangement were assessed through histology for each region and related to the loading directions adopted during mechanical tests. Regional and strain-dependent constitutive parameters were finally proposed for the human lateral meniscus, suggesting an isotropic behavior of both the horns, and a transversely isotropic response of the pars intermedia. Furthermore, the histological findings supported the evidences highlighted by the compressive tests. Indeed, this study provided novel insights concerning the functional behavior of human menisci by integrating mechanical and histological characterizations and thus highlighting the key role of this component in knee contact mechanics and presenting fundamental information that can be used in the development of tissue-engineered substitutes. STATEMENT OF SIGNIFICANCE: This work presents an integration to the approaches currently used to model the mechanical behavior of the meniscal tissue. This study assessed in detail the regional and directional contributions of both the meniscal solid and fluid phases during compressive response, providing also complementary histological evidence. Within this updated perspective, both knee computational modeling and meniscal tissue engineering can be improved to have an effective impact on the clinical practice.

3D Bioprinted Implants for Cartilage Repair in Intervertebral Discs and Knee Menisci

Cartilage defects pose a significant clinical challenge as they can lead to joint pain, swelling and stiffness, which reduces mobility and function thereby significantly affecting the quality of life of patients. More than 250,000 cartilage repair surgeries are performed in the United States every year. The current gold standard is the treatment of focal cartilage defects and bone damage with nonflexible metal or plastic prosthetics. However, these prosthetics are often made from hard and stiff materials that limits mobility and flexibility, and results in leaching of metal particles into the body, degeneration of adjacent soft bone tissues and possible failure of the implant with time. As a result, the patients may require revision surgeries to replace the worn implants or adjacent vertebrae. More recently, autograft - and allograft-based repair strategies have been studied, however these too are limited by donor site morbidity and the limited availability of tissues for surgery. There has been increasing interest in the past two decades in the area of cartilage tissue engineering where methods like 3D bioprinting may be implemented to generate functional constructs using a combination of cells, growth factors (GF) and biocompatible materials. 3D bioprinting allows for the modulation of mechanical properties of the developed constructs to maintain the required flexibility following implantation while also providing the stiffness needed to support body weight. In this review, we will provide a comprehensive overview of current advances in 3D bioprinting for cartilage tissue engineering for knee menisci and intervertebral disc repair. We will also discuss promising medical-grade materials and techniques that can be used for printing, and the future outlook of this emerging field.

Mechanotransduction in meniscus fibrochondrocytes: What about caveolae?

Meniscus fibrochondrocytes (MFCs) are an important cell population responsible for regulating the biomechanical properties of the knee meniscus. Despite their significance, not much is known about them, including how they sense and respond to mechanical stimuli. Due to the mechanical nature of the knee joint, it is therefore paramount to our understanding of the meniscus that its mechanotransductive mechanism be elucidated. In this review, we will summarize the current knowledge on mechanotransduction in MFCs and highlight the relevance of caveolae in lieu of a recent discovery. Additionally, we will discuss the importance of future studies in this area to help advance the field of meniscus research.

The Human Meniscus Behaves as a Functionally Graded Fractional Porous Medium under Confined Compression Conditions

In this study, we observe that the poromechanical parameters in human meniscus vary spatially throughout the tissue. The response is anisotropic and the porosity is functionally graded. To draw these conclusions, we measured the anisotropic permeability and the “aggregate modulus” of the tissue, i.e., the stiffness of the material at equilibrium, after the interstitial fluid has ceased flowing. We estimated those parameters within the central portion of the meniscus in three directions (i.e., vertical, radial and circumferential) by fitting an enhanced model on stress relation confined compression tests. We noticed that a classical biphasic model was not sufficient to reproduce the observed experimental behaviour. We propose a poroelastic model based on the assumption that the fluid flow inside the human meniscus is described by a fractional porous medium equation analogous to Darcy’s law, which involves fractional operators. The fluid flux is then time-dependent for a constant applied pressure gradient (in contrast with the classical Darcy’s law, which describes a time independent fluid flux relation). We show that a fractional poroelastic model is well-suited to describe the flow within the meniscus and to identify the associated parameters (i.e., the order of the time derivative and the permeability). The results indicate that mean values of λβ,β in the central body are λβ=5.5443×10−10m4Ns1−β, β=0.0434, while, in the posterior and anterior regions, are λβ=2.851×10−10m4Ns1−β, β=0.0326 and λβ=1.2636×10−10m4Ns1−β, β=0.0232, respectively. Furthermore, numerical simulations show that the fluid flux diffusion is facilitated in the central part of the meniscus and hindered in the posterior and anterior regions.

Advances in electrospun scaffolds for meniscus tissue engineering and regeneration

The meniscus plays a critical role in maintaining the homeostasis, biomechanics, and structural stability of the knee joint. Unfortunately, it is predisposed to damages either from sports-related trauma or age-related degeneration. The meniscus has an inherently limited capacity for tissue regeneration. Self-healing of injured adult menisci only occurs in the peripheral vascularized portion, while the spontaneous repair of the inner avascular region seems never happens. Repair, replacement, and regeneration of menisci through tissue engineering strategies are promising to address this problem. Recently, many scaffolds for meniscus tissue engineering have been proposed for both experimental and preclinical investigations. Electrospinning is a feasible and versatile technique to produce nano- to micro-scale fibers that mimic the microarchitecture of native extracellular matrix and is an effective approach to prepare nanofibrous scaffolds for constructing engineered meniscus. Electrospun scaffolds are reported to be capable of inducing colonization of meniscus cells by modulating local extracellular density and stimulating endogenous regeneration by driving reprogramming of meniscus wound microenvironment. Electrospun nanofibrous scaffolds with tunable mechanical properties, controllable anisotropy, and various porosities have shown promises for meniscus repair and regeneration and will undoubtedly inspire more efforts in exploring effective therapeutic approaches towards clinical applications. In this article, we review the current advances in the use of electrospun nanofibrous scaffolds for meniscus tissue engineering and repair and discuss prospects for future studies.

Shear Wave Elastography Evaluation of Meniscus Degeneration with Magnetic Resonance Imaging Correlation

RATIONALE AND OBJECTIVES

The objective of the study was to assess the diagnostic efficiency of shear wave elastography in the grading of meniscal degeneration compared to magnetic resonance imaging (MRI) as a reference standard.

MATERIALS AND METHODS

Fifty patients were included in the study (who had bilateral knee MRI). Tissue elasticity was measured in the coronal plane from the meniscus body in kilopascal. Nonparametric testing (Mann-Whitney U) was utilized to assess the differences between mean elasticity of the meniscus tissue, gender. The inter-intraobserver agreement was determined by the intraclass correlation coefficient. The correlations between the mean elasticity of the meniscus versus age, height, and body mass index were calculated via the "Pearson Correlation Coefficient Test." The relationship between MRI meniscal degeneration grading and elastography elasticity module was determined via the "Spearman Correlation Test." A p value less than 0.05 was considered statistically significant.

RESULTS

İnter-intraobserver intraclass correlation coefficient of the lateral and medial meniscus mean stiffness values were good or excellent (>0.8). A statistically significant increase in stiffness of meniscus tissue was observed with an increase in age (p = 0.003 for medial menisci, 0.006 for lateral menisci). Tissue stiffness was higher in the medial meniscus than the lateral meniscus (p < 0.001). A positive correlation was observed between the MRI meniscal degeneration grade and tissue stiffness (p < 0.05). Additionally, mean stiffness values from lateral and medial menisci were higher in the group with degeneration (p < 0.0001).

CONCLUSION

Meniscus stiffness is increased with aging. There was a statistically significant positive correlation between meniscal stiffness and degeneration grading in MRI.

The effect of meniscal pathology and management with ACL reconstruction on patient-reported outcomes, strength, and jump performance ten months post-surgery

BACKGROUND

The purpose of this study was to examine the differences in patient-reported outcome measures, isokinetic strength, plyometric ability and ability to meet return to play criteria ten months after anterior cruciate ligament (ACL) reconstruction surgery between those who underwent meniscectomy, those who underwent meniscal repair and those with no meniscal intervention alongside ACL reconstruction surgery.

METHODS

Three hundred and thirteen athletes with clinically and radiologically confirmed ACL ruptures were included in this study. Participants were grouped according to their intra-operative procedures (isolated ACL reconstruction surgery n = 155, ACL reconstruction surgery with meniscectomy n = 128, ACL reconstruction surgery with meniscal repair n = 30). Participants completed patient-reported outcome measures questionnaires (Marx Activity Rating Scale, the ACL Return to Sport after Injury and the International Knee Documentation Committee Score) and completed a battery of objective functional testing including isokinetic dynamometry and jump performance testing (countermovement jump and drop jump) between 9 and 11 months after surgery.

RESULTS

No significant between-group differences were identified in any metric relating to patient-reported outcome measures (p = .611), strength and jump measures (p = .411) or the ability to achieve symmetry-based return to play criteria (p = .575).

CONCLUSIONS

Clinically, these results suggest that concomitant meniscal surgery has no significant effects on patient-reported outcome measures, strength and jump metrics at the return to play stage post-operatively and can inform the pre-operative counselling of those awaiting ACL reconstruction surgery with likely meniscal intervention.

Mechano-Hypoxia Conditioning of Engineered Human Meniscus

Meniscus fibrochondrocytes (MFCs) experience simultaneous hypoxia and mechanical loading in the knee joint. Experimental conditions based on these aspects of the native MFC environment may have promising applications in human meniscus tissue engineering. We hypothesized that in vitro “mechano-hypoxia conditioning” with mechanical loading such as dynamic compression (DC) and cyclic hydrostatic pressure (CHP) would enhance development of human meniscus fibrocartilage extracellular matrix in vitro. MFCs from inner human meniscus surgical discards were pre-cultured on porous type I collagen scaffolds with TGF-β3 supplementation to form baseline tissues with newly formed matrix that were used in a series of experiments. First, baseline tissues were treated with DC or CHP under hypoxia (HYP, 3% O₂) for 5 days. DC was the more effective load regime in inducing gene expression changes, and combined HYP/DC enhanced gene expression of fibrocartilage precursors. The individual treatments of DC and HYP regulated thousands of genes, such as chondrogenic markers SOX5/6, in an overwhelmingly additive rather than synergistic manner. Similar baseline tissues were then treated with a short course of DC (5 vs 60 min, 10–20% vs 30–40% strain) with different pre-culture duration (3 vs 6 weeks). The longer course of loading (60 min) had diminishing returns in regulating mechano-sensitive and inflammatory genes such as c-FOS and PTGS2, suggesting that as few as 5 min of DC was adequate. There was a dose-effect in gene regulation by higher DC strains, whereas outcomes were inconsistent for different MFC donors in pre-culture durations. A final set of baseline tissues was then cultured for 3 weeks with mechano-hypoxia conditioning to assess mechanical and protein-level outcomes. There were 1.8–5.1-fold gains in the dynamic modulus relative to baseline in HYP/DC, but matrix outcomes were equal or inferior to static controls. Long-term mechano-hypoxia conditioning was effective in suppressing hypertrophic markers (e.g., COL10A1 10-fold suppression vs static/normoxia). Taken together, these results indicate that appropriately applied mechano-hypoxia conditioning can support meniscus fibrocartilage development in vitro and may be useful as a strategy for developing non-hypertrophic articular cartilage using mesenchymal stem cells.

The menisci are not shock absorbers: A biomechanical and comparative perspective

The lateral and medial menisci are fibrocartilaginous structures in the knee that play a crucial role in normal knee biomechanics. However, one commonly cited role of the menisci is that they function as "shock absorbers." Here we provide a critique of this notion, drawing upon a review of comparative anatomical and biomechanical data from humans and other tetrapods. We first review those commonly, and often exclusively, cited studies in support of a shock absorption function and show that evidence for a shock absorptive function is dubious. We then review the evolutionary and comparative evidence to show that (1) the human menisci are unremarkable in morphology compared with most other tetrapods, and (2) "shock" during locomotion is uncommon, with humans standing out as one of the only tetrapods that regularly experiences high levels of shock during locomotion. A shock-absorption function does not explain the origin of menisci, nor are human menisci specialized in any way that would explain a unique shock-absorbing function during human gait. Finally, we show that (3) the material properties of menisci are distinctly poorly suited for energy dissipation and that (4) estimations of meniscal energy absorption based on published data are negligible, both in their absolute amount and in comparison to other well-accepted structures which mitigate shock during locomotion. The menisci are evolutionarily ancient structures crucial for joint congruity, load distribution, and stress reduction, among a number of other functions. However, the menisci are not meaningful shock absorbers, neither in tetrapods broadly, nor in humans.

Meniscus Anatomy and Basic Science

A basic understanding of meniscal anatomy and biomechanics is important for physicians evaluating knee injuries and surgeons treating meniscal injuries. This chapter provides a concise review of meniscal anatomy and biomechanics relevant for the evaluation and treatment of meniscus injuries. Anatomic landmarks relevant for meniscal root repair and transplant are discussed, along with the gross, microscopic, vascular, and neuroanatomy of the menisci.

Mesenchymal stem cells for enhancing biological healing after meniscal injuries

The meniscus is a semilunar fibrocartilage structure that plays important roles in maintaining normal knee biomechanics and function. The roles of the meniscus, including load distribution, force transmission, shock absorption, joint stability, lubrication, and proprioception, have been well established. Injury to the meniscus can disrupt overall joint stability and cause various symptoms including pain, swelling, giving-way, and locking. Unless treated properly, it can lead to early degeneration of the knee joint. Because meniscal injuries remain a significant challenge due to its low intrinsic healing potential, most notably in avascular and aneural inner two-thirds of the area, more efficient repair methods are needed. Mesenchymal stem cells (MSCs) have been investigated for their therapeutic potential in vitro and in vivo. Thus far, the application of MSCs, including bone marrow-derived, synovium-derived, and adipose-derived MSCs, has shown promising results in preclinical studies in different animal models. These preclinical studies could be categorized into intra-articular injection and tissue-engineered construct application according to delivery method. Despite promising results in preclinical studies, there is still a lack of clinical evidence. This review describes the basic knowledge, current treatment, and recent studies regarding the application of MSCs in treating meniscal injuries. Future directions for MSC-based approaches to enhance meniscal healing are suggested.

Degenerative Joint Disease After Meniscectomy

The meniscus has an important role in stabilizing the knee joint and protecting the articular cartilage from shear forces. Meniscus tears are common injuries and can disrupt these protective properties, leading to an increased risk of articular cartilage damage and eventual osteoarthritis. Certain tear patterns are often treated with arthroscopic partial meniscectomy, which can effectively relieve symptoms. However, removal of meniscal tissue can also diminish the ability of the meniscus to dissipate hoop stresses, resulting in altered biomechanics of the knee joint including increased contact pressures. This makes meniscal repair an important treatment consideration whenever possible. Understanding the incidence and mechanism of osteoarthritis development after arthroscopic partial meniscectomy as it relates to different tear morphologies and other treatment alternatives (ie, meniscus repair) is important to appropriately treat meniscus tears.

Intrinsic and growth-mediated cell and matrix specialization during murine meniscus tissue assembly

The incredible mechanical strength and durability of mature fibrous tissues and their extremely limited turnover and regenerative capacity underscores the importance of proper matrix assembly during early postnatal growth. In tissues with composite extracellular matrix (ECM) structures, such as the adult knee meniscus, fibrous (Collagen-I rich), and cartilaginous (Collagen-II, proteoglycan-rich) matrix components are regionally segregated to the outer and inner portions of the tissue, respectively. While this spatial variation in composition is appreciated to be functionally important for resisting complex mechanical loads associated with gait, the establishment of these specialized zones is poorly understood. To address this issue, the following study tracked the growth of the murine meniscus from its embryonic formation through its first month of growth, encompassing the critical time-window during which animals begin to ambulate and weight bear. Using histological analysis, region specific high-throughput qPCR, and Col-1, and Col-2 fluorescent reporter mice, we found that matrix and cellular features defining specific tissue zones were already present at birth, before continuous weight-bearing had occurred. These differences in meniscus zones were further refined with postnatal growth and maturation, resulting in specialization of mature tissue regions. Taken together, this work establishes a detailed timeline of the concurrent spatiotemporal changes that occur at both the cellular and matrix level throughout meniscus maturation. The findings of this study provide a framework for investigating the reciprocal feedback between cells and their evolving microenvironments during assembly of a mechanically robust fibrocartilage tissue, thus providing insight into mechanisms of tissue degeneration and effective regenerative strategies.

Regenerative Engineering Animal Models for Knee Osteoarthritis

Abstract

Osteoarthritis (OA) of the knee is the most common synovial joint disorder worldwide, with a growing incidence due to increasing rates of obesity and an aging population. A significant amount of research is currently being conducted to further our understanding of the pathophysiology of knee osteoarthritis to design less invasive and more effective treatment options once conservative management has failed. Regenerative engineering techniques have shown promising preclinical results in treating OA due to their innovative approaches and have emerged as a popular area of study. To investigate these therapeutics, animal models of OA have been used in preclinical trials. There are various mechanisms by which OA can be induced in the knee/stifle of animals that are classified by the etiology of the OA that they are designed to recapitulate. Thus, it is essential to utilize the correct animal model in studies that are investigating regenerative engineering techniques for proper translation of efficacy into clinical trials. This review discusses the various animal models of OA that may be used in preclinical regenerative engineering trials and the corresponding classification system.

Lay Summary

Osteoarthritis (OA) of the knee is the most common synovial joint disease worldwide, with high rates of occurrence due to an increase in obesity and an aging population. A great deal of research is currently underway to further our understanding of the causes of osteoarthritis, to design more effective treatments. The emergence of regenerative engineering has provided physicians and investigators with unique opportunities to join ideas in tackling human diseases such as OA. Once the concept is proven to work, the initial procedure for the evaluation of a treatment solution begins with an animal model. Thus, it is essential to utilize a suitable animal model that reflects the particular ailment in regenerative engineering studies for proper translation to human patients as each model has associated advantages and disadvantages. There are various ways by which OA can occur in the knee joint, which are classified according to the particular cause of the OA. This review discusses the various animal models of OA that may be used in preclinical regenerative engineering investigations and the corresponding classification system.

Posterior Root Avulsion Fracture of the Medial Meniscus in a Skeletally Immature Child: A Case Report

CASE

We describe a rare case of posterior root avulsion fracture of the medial meniscus in an 11-year-old boy. Previous reports have demonstrated delayed diagnosis, but in this case, multiplanar computed tomography (CT) combined with magnetic resonance imaging (MRI) enabled early diagnosis and treatment. Gradual ossification was observed after arthroscopic suture fixation, and meniscal extrusion did not progress. He returned to sports without any symptoms and showed no degenerative changes at 2.5 years postoperatively.

CONCLUSION

This is the first case report of early diagnosis and time-course analysis of a rare avulsion fracture, emphasizing the usefulness of CT combined with MRI.

Ultrashort echo time adiabatic T1ρ (UTE-Adiab-T1ρ) is sensitive to human cadaveric knee joint deformation induced by mechanical loading and unloading

PURPOSE

The development of ultrashort echo time (UTE) MRI sequences has led to improved imaging of tissues with short T2 relaxation times, such as the deep layer cartilage and meniscus. UTE combined with adiabatic T1ρ preparation (UTE-Adiab-T1ρ) is an MRI measure with low sensitivity to the magic angle effect. This study aimed to investigate the sensitivity of UTE-Adiab-T1ρ to mechanical load-induced deformations in the tibiofemoral cartilage and meniscus of human cadaveric knee joints.

METHODS

Eight knee joints from young (42 ± 12 years at death) donors were evaluated on a 3 T scanner using the UTE-Adiab-T1ρ sequence under four sequential loading conditions: load = 0 N (Load0), load = 300 N (Load1), load = 500 N (Load2), and load = 0 N (Unload). UTE-Adiab-T1ρ was measured in the meniscus (M), femoral articular cartilage (FAC), tibial articular cartilage (TAC), articular cartilage regions uncovered by meniscus (AC-UC), and articular cartilage regions covered by meniscus (AC-MC) within region of interests (ROIs) manually selected by an experienced MR scientist. The Kruskal-Wallis test, with corrected significance level for multiple comparisons, was used to examine the UTE-Adiab-T1ρ differences between different loading conditions.

RESULTS

UTE-Adiab-T1ρ decreased in all grouped ROIs under both Load1 and Load2 conditions (-18.7% and - 16.9% for M, -18.8% and - 12.6% for FAC, -21.4% and - 10.7% for TAC, -26.2% and - 13.9% for AC-UC, and - 16.9% and - 10.7% for AC-MC). After unloading, average UTE-Adiab-T1ρ increased across all ROIs and within a lower range compared with the average UTE-Adiab-T1ρ decreases induced by the two previous loading conditions. The loading-induced differences were statistically non-significant.

CONCLUSIONS

While UTE-Adiab-T1ρ reduction by loading is likely an indication of tissue deformation, the increase of UTE-Adiab-T1ρ within a lower range by unloading implies partial tissue restoration. This study highlights the UTE-Adiab-T1ρ technique as an imaging marker of tissue function for detecting deformation patterns under loading.

Development of a decellularized meniscus matrix-based nanofibrous scaffold for meniscus tissue engineering

The meniscus plays a critical role in knee mechanical function but is commonly injured given its central load bearing role. In the adult, meniscus repair is limited, given the low number of endogenous cells, the density of the matrix, and the limited vascularity. Menisci are fibrocartilaginous tissues composed of a micro-/nano- fibrous extracellular matrix (ECM) and a mixture of chondrocyte-like and fibroblast-like cells. Here, we developed a fibrous scaffold system that consists of bioactive components (decellularized meniscus ECM (dME) within a poly(e-caprolactone) material) fashioned into a biomimetic morphology (via electrospinning) to support and enhance meniscus cell function and matrix production. This work supports that the incorporation of dME into synthetic nanofibers increased hydrophilicity of the scaffold, leading to enhanced meniscus cell spreading, proliferation, and fibrochondrogenic gene expression. This work identifies a new biomimetic scaffold for therapeutic strategies to substitute or replace injured meniscus tissue. STATEMENT OF SIGNIFICANCE: In this study, we show that a scaffold electrospun from a combination of synthetic materials and bovine decellularized meniscus ECM provides appropriate signals and a suitable template for meniscus fibrochondrocyte spreading, proliferation, and secretion of collagen and proteoglycans. Material characterization and in vitro cell studies support that this new bioactive material is susceptible to enzymatic digestion and supports meniscus-like tissue formation.

The association of meniscal body height with knee structural changes in middle-aged and elderly patients with symptomatic knee osteoarthritis

OBJECTIVES

To investigate whether and how meniscal height is associated with osteoarthritis (OA)-related knee structural changes in symptomatic knee OA.

METHODS

We studied 106 patients (61 female, aged 40-73 years) with symptomatic knee OA. X-ray was used for Kellgren-Lawrence score. Meniscal body heights and extrusion were measured on coronal sections of intermediate-weighted MRI sequence. Knee structural changes were assessed using the modified whole-organ magnetic resonance imaging score (WORMS). Associations between meniscal body height and knee structural changes were assessed using linear regression analysis.

RESULTS

Higher medial meniscal body height was significantly associated with severe medial meniscal lesions (p = 0.001-0.023), medial compartmental cartilage lesions (p = 0.045), patellofemoral compartmental and medial compartmental bone marrow edema patterns (p = 0.001-0.037), anterior cruciate ligament and patellar ligament abnormalities (p = 0.020-0.023), and loose bodies (p = 0.017). However, lateral meniscal body height was negatively correlated with WORMS scores for lateral meniscal lesions (p ≤ 0.018), lateral compartmental cartilage lesions (p ≤ 0.011), and lateral compartmental bone marrow edema patterns (p = 0.038).

CONCLUSION

Higher medial meniscal body height was associated with more severe medial compartment structural abnormalities and patellofemoral bone marrow edema patterns, while lateral meniscal body height was inversely correlated with the severity of lateral compartment structural abnormalities.

ADVANCES IN KNOWLEDGE

Our study revealed that meniscal body height was associated with multiple OA-related knee structural changes, which would be beneficial in identifying patients with or at risks for knee OA.

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

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

Analysis of spatial osteochondral heterogeneity in advanced knee osteoarthritis exposes influence of joint alignment

Osteoarthritis (OA) is considerably affected by joint alignment. Here, we investigate the patterns of spatial osteochondral heterogeneity in patients with advanced varus knee OA together with clinical data. We report strong correlations of osteochondral parameters within individual topographical patterns, highlighting their fundamental and location-dependent interactions in OA. We further identify site-specific effects of varus malalignment on the lesser loaded compartment and, conversely, an unresponsive overloaded compartment. Last, we trace compensatory mechanisms to the overloaded subarticular spongiosa in patients with additional high body weight. We therefore propose to consider and to determine axial alignment in clinical trials when selecting the location to assess structural changes in OA. Together, these findings broaden the scientific basis of therapeutic load redistribution and weight loss in varus knee OA.

Five Overlooked Injuries on Knee MRI

This article highlights five knee injuries that, in the author's experience, are commonly overlooked by readers inexperienced in knee MRI: ramp lesions, meniscocapsular tears, meniscal root ligament tears, posterior capsular ligament tears, and partial anterior cruciate ligament tear. While these injuries are readily apparent when the images are assessed for the given abnormality, the author's belief is that these may be overlooked because either the injury is not considered, or the affected area is not closely inspected. While these injuries may not alter immediate clinical management or require surgical intervention, they may, nevertheless, result in patient symptoms and may potentially increase the risk of further knee injury. Further, these injuries are difficult to recognize clinically and arthroscopically. In this review, we present these five injuries, emphasising relevant anatomy, normal MRI appearances, common injury patterns, and tips to avoid their being overlooked. Routine review of these areas when interpreting knee MRI, with additional imaging as necessary, will allow these injuries to be recognized more regularly.

Osteoarthritis-Related Degeneration Alters the Biomechanical Properties of Human Menisci Before the Articular Cartilage

An exact understanding of the interplay between the articulating tissues of the knee joint in relation to the osteoarthritis (OA)-related degeneration process is of considerable interest. Therefore, the aim of the present study was to characterize the biomechanical properties of mildly and severely degenerated human knee joints, including their menisci and tibial and femoral articular cartilage (AC) surfaces. A spatial biomechanical mapping of the articulating knee joint surfaces of 12 mildly and 12 severely degenerated human cadaveric knee joints was assessed using a multiaxial mechanical testing machine. To do so, indentation stress relaxation tests were combined with thickness and water content measurements at the lateral and medial menisci and the AC of the tibial plateau and femoral condyles to calculate the instantaneous modulus (IM), relaxation modulus, relaxation percentage, maximum applied force during the indentation, and the water content. With progressing joint degeneration, we found an increase in the lateral and the medial meniscal instantaneous moduli (p < 0.02), relaxation moduli (p < 0.01), and maximum applied forces (p < 0.01), while for the underlying tibial AC, the IM (p = 0.01) and maximum applied force (p < 0.01) decreased only at the medial compartment. Degeneration had no influence on the relaxation percentage of the soft tissues. While the water content of the menisci did not change with progressing degeneration, the severely degenerated tibial AC contained more water (p < 0.04) compared to the mildly degenerated tibial cartilage. The results of this study indicate that degeneration-related (bio-)mechanical changes seem likely to be first detectable in the menisci before the articular knee joint cartilage is affected. Should these findings be further reinforced by structural and imaging analyses, the treatment and diagnostic paradigms of OA might be modified, focusing on the early detection of meniscal degeneration and its respective treatment, with the final aim to delay osteoarthritis onset.

Quantitative three-dimensional collagen orientation analysis of human meniscus posterior horn in health and osteoarthritis using micro-computed tomography

OBJECTIVE

Knee osteoarthritis (OA) is associated with meniscal degeneration that may involve disorganization of the meniscal collagen fiber network. Our aims were to quantitatively analyze the microstructural organization of human meniscus samples in 3D using micro-computed tomography (μCT), and to compare the local microstructural organization between OA and donor samples.

METHOD

We collected posterior horns of both medial and lateral human menisci from 10 end-stage medial compartment knee OA patients undergoing total knee replacement (medial & lateral OA) and 10 deceased donors without knee OA (medial & lateral donor). Posterior horns were dissected and fixed in formalin, dehydrated in ascending ethanol concentrations, treated with hexamethyldisilazane (HMDS), and imaged with μCT. We performed local orientation analysis of collagenous microstructure in 3D by calculating structure tensors from greyscale gradients within selected integration window to determine the polar angle for each voxel.

RESULTS

In donor samples, meniscus bundles were aligned circumferentially around the inner border of meniscus. In medial OA menisci, the organized structure of collagen network was lost, and main orientation was shifted away from the circumferential alignment. Quantitatively, medial OA menisci had the lowest mean orientation angle compared to all groups, -24° (95%CI -31 to -18) vs medial donor and -25° (95%CI -34 to -15) vs lateral OA.

CONCLUSIONS

HMDS-based μCT imaging enabled quantitative analysis of meniscal collagen fiber bundles and their orientations in 3D. In human medial OA menisci, the collagen disorganization was profound with overall lower orientation angles, suggesting collagenous microstructure disorganization as an important part of meniscus degradation.

Outcomes at 20 Years After Meniscectomy in Patients Aged 50 to 70 Years

PURPOSE

To report the outcomes of arthroscopic meniscectomy (AM) at 20 years of follow-up through timing/rate of conversion to total knee replacement (TKR) and Knee Injury and Osteoarthritis Outcome Score (KOOS), focusing on detection of specific predictor variables for these outcomes, in patients 50 to 70 years old.

METHODS

We performed a retrospective study of 289 patients, ages at surgery 50 to 70 years, with diagnosis of degenerative meniscal tear who underwent arthroscopic meniscectomy. We collected the following baseline data: age, sex, injured meniscus (medial, lateral, or both), knee alignment, osteoarthritis (OA), associated lesion identified during arthroscopy, and associated procedure performed during arthroscopy. At 20 years of follow-up, we collected rate and timing of TKR conversion, and we evaluated clinical outcomes with KOOS.

RESULTS

Female sex (P < .01), older age (P < .01), lateral meniscectomy (P = .02), malalignment (P = .03), and advanced chondral lesion (P < .01) were found to be significantly related to subsequent TKR. No significant correlation was found between amount of resection and subsequent TKR (P = .26). Negative predictor factors to obtain equal or superior to age- and sex-adjusted KOOS scores were age 60 to 70 years at time of AM (P = .03) and lateral meniscectomy (P = .02).

CONCLUSIONS

We report a 15.7% conversion rate at 20 years from AM to TKR and a mean time between surgeries of 7 years. Subsequent TKR in the 20 years after AM for degenerative meniscus tears were significantly associated with preoperative OA and chondral lesion (Kellgren Lawrence 2; Outerbridge >2), lateral meniscectomy, age at surgery, female sex, and malalignment. Furthermore, age >60 years, lateral meniscectomy, and concurrent anterior cruciate ligament reconstruction were negative predictors for poor clinical outcomes at 20 years. Therefore, if patients present with negative predictor factors, the AM should not be proposed as second-line treatment, and nonoperative management should be continued until TKR is unavoidable.

LEVEL OF EVIDENCE

IV, case series.

Osteoarthritis: Novel Molecular Mechanisms Increase Our Understanding of the Disease Pathology

Although osteoarthritis (OA) is the most common musculoskeletal condition that causes significant health and social problems worldwide, its exact etiology is still unclear. With an aging and increasingly obese population, OA is becoming even more prevalent than in previous decades. Up to 35% of the world’s population over 60 years of age suffers from symptomatic (painful, disabling) OA. The disease poses a tremendous economic burden on the health-care system and society for diagnosis, treatment, sick leave, rehabilitation, and early retirement. Most patients also experience sleep disturbances, reduced capability for exercising, lifting, and walking and are less capable of working, and maintaining an independent lifestyle. For patients, the major problem is disability, resulting from joint tissue destruction and pain. So far, there is no therapy available that effectively arrests structural deterioration of cartilage and bone or is able to successfully reverse any of the existing structural defects. Here, we elucidate novel concepts and hypotheses regarding disease progression and pathology, which are relevant for understanding underlying the molecular mechanisms as a prerequisite for future therapeutic approaches. Emphasis is placed on topographical modeling of the disease, the role of proteases and cytokines in OA, and the impact of the peripheral nervous system and its neuropeptides.

3D Printed Poly(ε-Caprolactone)/Meniscus Extracellular Matrix Composite Scaffold Functionalized With Kartogenin-Releasing PLGA Microspheres for Meniscus Tissue Engineering

Meniscus tissue engineering (MTE) aims to fabricate ideal scaffolds to stimulate the microenvironment for recreating the damaged meniscal tissue. Indeed, favorable mechanical properties, suitable biocompatibility, and inherent chondrogenic capability are crucial in MTE. In this study, we present a composite scaffold by 3D printing a poly(ε-caprolactone) (PCL) scaffold as backbone, followed by injection with the meniscus extracellular matrix (MECM), and modification with kartogenin (KGN)-loaded poly(lactic-co-glycolic) acid (PLGA) microsphere (μS), which serves as a drug delivery system. Therefore, we propose a plan to improve meniscus regeneration via KGN released from the 3D porous PCL/MECM scaffold. The final results showed that the hydrophilicity and bioactivity of the resulting PCL/MECM scaffold were remarkably enhanced. In vitro synovium-derived mesenchymal stem cells (SMSCs) experiments suggested that introducing MECM components helped cell adhesion and proliferation and maintained promising ability to induce cell migration. Moreover, KGN-incorporating PLGA microspheres, which were loaded on scaffolds, showed a prolonged release profile and improved the chondrogenic differentiation of SMSCs during the 14-day culture. Particularly, the PCL/MECM-KGN μS seeded by SMSCs showed the highest secretion of total collagen and aggrecan. More importantly, the synergistic effect of the MECM and sustained release of KGN can endow the PCL/MECM-KGN μS scaffolds with not only excellent cell affinity and cell vitality preservation but also chondrogenic activity. Thus, the PCL/MECM-KGN μS scaffolds are expected to have good application prospects in the field of MTE.

High Resolution Micro-Computed Tomography Reveals a Network of Collagen Channels in the Body Region of the Knee Meniscus

The meniscus is an integral part of the human knee, preventing joint degradation by distributing load from the femoral condyles to the tibial plateau. Recent qualitative studies suggested that the meniscus is constituted by an intricate net of collagen channels inside which the fluid flows during loading. The aim of this study is to describe in detail the structure in which this fluid flows by quantifying the orientation and morphology of the collagen channels of the meniscal tissue. A 7 mm cylindrical sample, extracted vertically from the central part of a lateral porcine meniscus was freeze-dried and scanned using the highest-to-date resolution Microscopic Computed Tomography. The orientation of the collagen channels, their size and distribution was calculated. Comparisons with confocal multi-photon microscopy imaging performed on portions of fresh tissue have shown that the freeze-dried procedure adopted here ensures that the native architecture of the tissue is maintained. Sections of the probe at different heights were examined to determine differences in composition and structure along the sample from the superficial to the internal layers. Results reveal a different arrangement of the collagen channels in the superficial layers with respect to the internal layers with the internal layers showing a more ordered structure of the channels oriented at 30[Formula: see text] with respect to the vertical, a porosity of 66.28% and the mean size of the channels of 22.14 [Formula: see text].

Graphene Oxide-Doped Gellan Gum-PEGDA Bilayered Hydrogel Mimicking the Mechanical and Lubrication Properties of Articular Cartilage

Articular cartilage (AC) is a specialized connective tissue able to provide a low-friction gliding surface supporting shock-absorption, reducing stresses, and guaranteeing wear-resistance thanks to its structure and mechanical and lubrication properties. Being an avascular tissue, AC has a limited ability to heal defects. Nowadays, conventional strategies show several limitations, which results in ineffective restoration of chondral defects. Several tissue engineering approaches have been proposed to restore the AC's native properties without reproducing its mechanical and lubrication properties yet. This work reports the fabrication of a bilayered structure made of gellan gum (GG) and poly (ethylene glycol) diacrylate (PEGDA), able to mimic the mechanical and lubrication features of both AC superficial and deep zones. Through appropriate combinations of GG and PEGDA, cartilage Young's modulus is effectively mimicked for both zones. Graphene oxide is used as a dopant agent for the superficial hydrogel layer, demonstrating a lower friction than the nondoped counterpart. The bilayered hydrogel's antiwear properties are confirmed by using a knee simulator, following ISO 14243. Finally, in vitro tests with human chondrocytes confirm the absence of cytotoxicity effects. The results shown in this paper open the way to a multilayered synthetic injectable or surgically implantable filler for restoring AC defects.

Imaging of meniscal allograft transplantation: what the radiologist needs to know

Meniscal allograft transplantation is an emerging surgical option for younger patients with symptomatic meniscal deficiency, which aims to restore anatomic biomechanics and load distribution in the knee joint, and by so doing to potentially delay accelerated osteoarthritis. In this review article, we summarize the structure and biomechanics of the native meniscus, describe indications and procedure technique for meniscal allograft transplantation, and demonstrate the spectrum of expected postoperative imaging and role of imaging to identify potential complications.

Tuning the Phenotype of Cartilage Tissue Mimics by Varying Spheroid Maturation and Methacrylamide-Modified Gelatin Hydrogel Characteristics

In hybrid bioprinting of cartilage tissue constructs, spheroids are used as cellular building blocks and combined with biomaterials for dispensing. However, biomaterial intrinsic cues can deeply affect cell fate and to date, the influence of hydrogel encapsulation on spheroid viability and phenotype has received limited attention. This study assesses this need and unravels 1) how the phenotype of spheroid-laden constructs can be tuned through adjusting the hydrogel physico-chemical properties and 2) if the spheroid maturation stage prior to encapsulation is a determining factor for the construct phenotype. Articular chondrocyte spheroids with a cartilage specific extracellular matrix (ECM) are generated and different maturation stages, early-, mid-, and late-stage (3, 7, and 14 days, respectively), are harvested and encapsulated in 10, 15, or 20 w/v% methacrylamide-modified gelatin (gelMA) for 14 days. The encapsulation of immature spheroids do not lead to a cartilage-like ECM production but when more mature mid- or late-stage spheroids are combined with a certain concentration of gelMA, a fibrocartilage-like as well as a hyaline cartilage-like phenotype can be induced. As a proof of concept, late-stage spheroids are bioprinted using a 10 w/v% gelMA-Irgacure 2959 solution with the aim to test the processing potential of the spheroid-laden bioink.

Comparison of medial and lateral tibial tunnel in pullout repair of posterior root tear of medial meniscus: Radiologic, clinical, and arthroscopic outcomes

PURPOSE

Medial meniscus posterior root tear (MMPRT) should be repaired to the correct position as possible to maintain hoop tension of the meniscus. In this study, we propose a comparison of the outcome between the medial tunnel and the lateral tunnel in the pullout suture technique using the tibial tunnel for anatomical repair of posterior root tear of medial meniscus.

METHODS

From April 2010, of patients who underwent pullout suture, 51 cases (24 medial tunnel group (MTG) and 27 lateral tunnel group (LTG)) were able to follow-up with second look arthroscopy. Original Coronal Ratio of Root Attachment (CRORA) was defined as the ratio of the distance from the medial edge of the tibial plateau to the root attach site divided by the entire tibial medial-lateral width on preoperative computed tomography. Error between postoperative CRORA and original CRORA was calculated. We compared this error, clinical outcome, and arthroscopic finding between MTG and LTG.

RESULTS

The mean error ratio of postoperative CRORA divided by original CRORA was 0.86 ± 0.11 in MTG, which was significantly (p = 0.001) lower than that (1.02 ± 0.06) in LTG. The mean value of the root attach point in the MTG with a post/original CRORA value of 0.86 ± 0.11 means statistically significant medialization after the operation. There was no statistically significant difference in changes of International Knee Documentation Committee (IKDC) and Lysholom score between MTG and LTG. The difference between the two groups of arthritis progression was not statistically significant.

CONCLUSION

In patients with MMPRT, CRORA may provide a basis for coronal assessment of root repair position before and after surgery, and lateral tibial tunnel technique can help anatomical repair by reducing technical error due to guide pin slip medially compared to medial tibial tunnel technique.

Non-anatomical placement adversely affects the functional performance of the meniscal implant: a finite element study

Non-anatomical placement may occur during the surgical implantation of the meniscal implant, and its influence on the resulting biomechanics of the knee joint has not been systematically studied. The purpose of this study was to evaluate the biomechanical effects of non-anatomical placement of the meniscal implant on the knee joint during a complete walking cycle. Three-dimensional finite element (FE) analyses of the knee joint were performed, based on the model developed from magnetic resonance images and the loading conditions derived from the gait pattern of a healthy male subject, for the following physiological conditions: (i) knee joint with intact native meniscus, (ii) medial meniscectomized knee joint, (iii) knee joint with anatomically placed meniscal implant, and (iv) knee joint with the meniscal implant placed in four different in vitro determined non-anatomical locations. While the native menisci were modeled using the nonlinear hyperelastic Holzapfel-Gasser-Ogden (HGO) constitutive model, the meniscal implant was modeled using the isotropic hyperelastic neo-Hookean model. Placement of the meniscal implant in the non-anatomical lateral-posterior and lateral-anterior locations significantly increased the peak contact pressure in the medial compartment. Placement of the meniscal implant in non-anatomical locations significantly altered the tibial rotational kinematics and increased the total force acting at the meniscal horns. Results suggest that placement of the meniscal implant in non-anatomical locations may restrain its ability to be chondroprotective and may initiate or accelerate cartilage degeneration. In conclusion, clinicians should endeavor to place the implant as closest as possible to the anatomical location to restore the normal knee biomechanics.

Outcomes at 20 years after meniscectomy in young patients

AIM

To define arthroscopic meniscectomy (AM) outcomes in young patients at 20 years follow up in terms of predictors of poor clinical results, rate and timing of conversion to total knee replacement (TKR).

METHODS

The following data were collected for 225 patients aged between 18 and 50 years with meniscal tear (MT) who underwent AM: age at surgery, gender, injured meniscus, knee alignment, associated lesions, amount of meniscal resection. At 20 years follow up, rate and timing of TKR conversion and clinical outcomes with Knee injury and Osteoarthritis Outcome Score (KOOS) score were reviewed.

RESULTS

Ten patients (4.4%) required TKR in the follow up period. The mean time from AM to TKR was 7.0 years (standard deviation 3.87). Age between 40 and 50 years at AM (P < 0.01), malalignment (P < 0.01), lateral meniscectomy (any size, P = 0.01), advanced chondral lesion (Outerbridge > 2, P < 0.01) and total meniscectomy (P < 0.01) were significantly related to subsequent TKR. Negative predicting factors to obtaining equal or superior to age/sex-adjusted KOOS score were age between 40 and 50 years old at time of AM (P < 0.01), female sex (P < 0.01), malalignment (P = 0.04), and advanced chondral lesion (Outerbridge > 2, P = 0.02).

CONCLUSIONS

Twenty years conversion rate to TKR after AM for MT is 4.4% and TKR was performed after a mean time of 7 years. Significant association between TKR surgery and advanced chondral lesion (Outerbridge > 2), total meniscectomy, lateral meniscectomy, age at surgery between 40 and 50 years old, and malalignment were found. Age between 40 and 50 years at time of AM, female, malalignment, advanced chondral lesion were all factors significantly related to poor clinical results.

Viscoelastic and equilibrium shear properties of human meniscus: Relationships with tissue structure and composition

The meniscus is crucial in maintaining the knee function and protecting the joint from secondary pathologies, including osteoarthritis. Although most of the mechanical properties of human menisci have been characterized, to our knowledge, its dynamic shear properties have never been reported. Moreover, little is known about meniscal shear properties in relation to tissue structure and composition. This is crucial to understand mechanisms of meniscal injury, as well as, in regenerative medicine, for the design and development of tissue engineered scaffolds mimicking the native tissue. Hence, the objective of this study was to characterize the dynamic and equilibrium shear properties of human meniscus in relation to its anisotropy and composition. Specimens were prepared from the axial and the circumferential anatomical planes of medial and lateral menisci. Frequency sweeps and stress relaxation tests yielded storage (G') and loss moduli (G″), and equilibrium shear modulus (G). Correlations of moduli with water, glycosaminoglycans (GAGs), and collagen content were investigated. The meniscus exhibited viscoelastic behavior. Dynamic shear properties were related to tissue composition: negative correlations were found between G', G″ and G, and meniscal water content; positive correlations were found for G' and G″ with GAG and collagen (only in circumferential samples). Circumferential samples, with collagen fibers orthogonal to the shear plane, exhibited superior dynamic mechanical properties, with G' ~70 kPa and G″ ~10 kPa, compared to those of the axial plane ~15 kPa and ~1 kPa, respectively. Fiber orientation did not affect the values of G, which ranged from ~50 to ~100 kPa.

Forces at the Anterior Meniscus Attachments Strongly Increase Under Dynamic Knee Joint Loading

BACKGROUND

The anatomic appearance and biomechanical and clinical importance of the anterior meniscus roots are well described. However, little is known about the loads that act on these attachment structures under physiological joint loads and movements.

HYPOTHESES

As compared with uniaxial loading conditions under static knee flexion angles or at very low flexion-extension speeds, more realistic continuous movement simulations in combination with physiological muscle force simulations lead to significantly higher anterior meniscus attachment forces. This increase is even more pronounced in combination with a longitudinal meniscal tear or after total medial meniscectomy.

STUDY DESIGN

Controlled laboratory study.

METHODS

A validated Oxford Rig-like knee simulator was used to perform a slow squat, a fast squat, and jump landing maneuvers on 9 cadaveric human knee joints, with and without muscle force simulation. The strains in the anterior medial and lateral meniscal periphery and the respective attachments were determined in 3 states: intact meniscus, medial longitudinal tear, and total medial meniscectomy. To determine the attachment forces, a subsequent in situ tensile test was performed.

RESULTS

Muscle force simulation resulted in a significant strain increase at the anterior meniscus attachments of up to 308% (P < .038) and the anterior meniscal periphery of up to 276%. This corresponded to significantly increased forces (P < .038) acting in the anteromedial attachment with a maximum force of 140 N, as determined during the jump landing simulation. Meniscus attachment strains and forces were significantly influenced (P = .008) by the longitudinal tear and meniscectomy during the drop jump simulation.

CONCLUSION

Medial and lateral anterior meniscus attachment strains and forces were significantly increased with physiological muscle force simulation, corroborating our hypothesis. Therefore, in vitro tests applying uniaxial loads combined with static knee flexion angles or very low flexion-extension speeds appear to underestimate meniscus attachment forces.

CLINICAL RELEVANCE

The data of the present study might help to optimize the anchoring of meniscal allografts and artificial meniscal substitutes to the tibial plateau. Furthermore, this is the first in vitro study to indicate reasonable minimum stability requirements regarding the reattachment of torn anterior meniscus roots.

The role of MRI in evaluation of arthroscopic transtibial pullout repair for medial meniscus posterior root tears

Medial meniscus posterior root tears (MMPRT) can lead to meniscal extrusion, loss of hoop tension, loss of load-sharing ability and increased contact pressure. Currently, the most commonly used technique for root repair is arthroscopic transtibial pullout repair (ATPR). This article aims to illustrate both normal and abnormal postoperative imaging findings of the MMPRT repair performed with ATPR, with emphasis on MRI. The radiologist must highlight the tunnel position, the reduction of the medial meniscus posterior root to its anatomical attachment, the signs of root healing (continuity and lower signal intensity), and eventual meniscal extrusion or signs of osteoarthritis.

Arthroscopic-Assisted Lateral Meniscal Allograft Transplantation With Open Ligamentous Extra-Articular Tenodesis

Lateral meniscus allograft transplantation is performed in predominantly young, active patients and is an option to stabilize the joint in lateral meniscus-deficient patients after anterior cruciate ligament reconstruction. The lateral meniscus functions as an important restraint to anterior tibial translation, and meniscal transplant in such a patient may improve survivability of the graft in addition to preserving the patient's articular cartilage in the long term. A ligamentous extra-articular tenodesis procedure may be performed simultaneously to augment rotational stability of the joint, particularly in a patient with underlying ligamentous hyperlaxity.

Human engineered meniscus transcriptome after short-term combined hypoxia and dynamic compression

This study investigates the transcriptome response of meniscus fibrochondrocytes (MFCs) to the low oxygen and mechanical loading signals experienced in the knee joint using a model system. We hypothesized that short term exposure to the combined treatment would promote a matrix-forming phenotype supportive of inner meniscus tissue formation. Human MFCs on a collagen scaffold were stimulated to form fibrocartilage over 6 weeks under normoxic (NRX, 20% O₂) conditions with supplemented TGF-β3. Tissues experienced a delayed 24h hypoxia treatment (HYP, 3% O₂) and then 5 min of dynamic compression (DC) between 30 and 40% strain. Delayed HYP induced an anabolic and anti-catabolic expression profile for hyaline cartilage matrix markers, while DC induced an inflammatory matrix remodeling response along with upregulation of both SOX9 and COL1A1. There were 41 genes regulated by both HYP and DC. Overall, the combined treatment supported a unique gene expression profile favouring the hyaline cartilage aspect of inner meniscus matrix and matrix remodeling.

Different effects of the lateral meniscus complete radial tear on the load distribution and transmission functions depending on the tear site

PURPOSE

To compare the effect of the lateral meniscus (LM) complete radial tear at different tear sites on the load distribution and transmission functions.

METHODS

A compressive load of 300 N was applied to the intact porcine knees (n = 30) at 15°, 30°, 60°, 90°, and 120° of flexion. The LM complete radial tears were created at the middle portion (group M), the posterior portion (group P), or the posterior root (group R) (n = 10, each group), and the same loading procedure was followed. Finally, the recorded three-dimensional paths were reproduced on the LM-removed knees. The peak contact pressure (contact area) in the lateral compartment and the calculated in situ force of the LM under the principle of superposition were compared among the four groups (intact, group M, group P, and group R).

RESULTS

At all the flexion angles, the peak contact pressure (contact area) was significantly higher (lower) after creating the LM complete radial tear as compared to that in the intact state (p < 0.01). At 120° of flexion, group R represented the highest peak contact pressure (lowest contact area), followed by group P and group M (p < 0.05). The results of the in situ force carried by the LM were similar to those of the tibiofemoral contact mechanics.

CONCLUSION

The detrimental effect of the LM complete radial tear on the load distribution and transmission functions was greatest in the posterior root tear, followed by the posterior portion tear and the middle portion tear in the deep-flexed position. Complete radial tars of the meniscus, especially at the posterior root, should be repaired to restore the biomechanical function.

Microstructure Analysis and Reconstruction of a Meniscus

OBJECTIVE

To analyze the characteristics of menicus microstructure and to reconstruct a microstructure-mimicing 3D model of the menicus.

METHODS

Human and sheep meniscus were collected and prepared for this study. Hematoxylin-eosin staining (HE) and Masson staining were conducted for histological analysis of the meniscus. For submicroscopic structure analysis, the meniscus was first freeze-dried and then scanned by scanning electron microscopy (SEM). The porosity of the meniscus was determined according to SEM images. A micro-MRI was used to scan each meniscus, immersed in distilled water, and a 3D digital model was reconstructed afterwards. A three-dimensional (3D) resin model was printed out based on the digital model. Before high-resolution micro-CT scanning, each meniscus was freeze-dried. Then, micro-scale two-dimensional (2D) CT projection images were obtained. The porosity of the meniscus was calculated according to micro-CT images. With micro-CT, multiple 2D projection images were collected. A 3D digital model based on 2D CT pictures was also reconstructed. The 3D digital model was exported as STL format. A 3D resin model was printed by 3D printer based on the 3D digital model.

RESULTS

As revealed in the HE and Masson images, a meniscus is mostly composed of collagen, with a few cells disseminated between the collagen fiber bundles at the micro-scale. The SEM image clearly shows the path of highly cross-linked collagen fibers, and massive pores exist between the fibers. According to the SEM images, the porosity of the meniscus was 34.1% (34.1% ± 0.032%) and the diameters of the collagen fibers were varied. In addition, the cross-linking pattern of the fibers was irregular. The scanning accuracy of micro-MRI was 50 μm. The micro-MRI demonstrated the outline of the meniscus, but the microstructure was obscure. The micro-CT clearly displayed microfibers in the meniscus with a voxel size of 11.4 μm. The surface layer, lamellar layer, circumferential fibers, and radial fibers could be identified. The mean porosity of the meniscus according to micro-CT images was 33.92% (33.92% ± 0.03%). Moreover, a 3D model of the microstructure based on the micro-CT images was built. The microscale fibers could be displayed in the micro-CT image and the reconstructed 3D digital model. In addition, a 3D resin model was printed out based on the 3D digital model.

CONCLUSION

It is extremely difficult to artificially simulate the microstructure of the meniscus because of the irregularity of the diameter and cross-linking pattern of fibers. The micro-MRI images failed to demonstrate the meniscus microstructure. Freeze-drying and micro-CT scanning are effective methods for 3D microstructure reconstruction of the meniscus, which is an important step towards mechanically functional 3D-printed meniscus grafts.

Prognostic Factors of Mid- to Long-term Clinical Outcomes after Arthroscopic Partial Meniscectomy for Medial Meniscal Tears

Backgroud

Arthroscopic partial meniscectomy (APM) continues to be the popular treatment for meniscal tears, but recent randomized controlled trials have questioned its efficacy. To provide more evidence-based criteria for patient selection, we undertook this study to identify prognostic factors associated with clinical failure after APM for medial meniscus tears.

Methods

Medical records of 160 patients followed up for at least 5 years after APM for medial meniscal tears were retrospectively reviewed. Demographic data (age, sex, and body mass index), radiographic variables (Kellgren-Lawrence [K-L] grade and hip-knee-ankle [HKA] angle), and clinical scores (International Knee Documentation Committee score, Tegner activity scale score, Lysholm score, and Knee injury and Osteoarthritis Outcome Score) were recorded. Clinical failure was defined as the need for an additional surgical procedure (arthroscopy, osteotomy, or arthroplasty) or the presence of intolerable pain. Survivorship analysis with clinical failure as an end point was performed using Kaplan-Meier survival curves. Factors related to clinical failure were analyzed using a Cox proportional hazard model. Cutoff values were determined using areas under receiver operating characteristic (ROC) curves. Radiographic progression of osteoarthritis was analyzed using the chi-square test, and serial changes of clinical scores were analyzed using a linear mixed model.

Results

Clinical success rates were 95.7% at 5 years, 75.6% at 10 years, and 46.3% at 15 years. Age, HKA angle, and K-L grade (p = 0.01, p = 0.02, and p = 0.04, respectively) were found to be significant risk factors of clinical failure. Cutoff values at 10 years postoperatively as determined by ROC analysis were 50 years for age (sensitivity = 0.778, 1−specificity = 0.589), grade 2 for K-L grade (sensitivity = 0.778, 1−specificity = 0.109), and 5.5° for HKA angle (sensitivity = 0.667, 1−specificity = 0.258). In patients who had clinical success until 10 years after APM, radiological osteoarthritis progressed gradually. However, the clinical scores of patients who achieved clinical success did not decrease significantly over the 10-year follow-up.

Conclusions

The poor prognostic factors found to be related to clinical failure after APM for a medial meniscal tear were patient age (≥ 50 years), preoperative K-L grade (≥ grade 2), and preoperative HKA angle (≥ varus 5.5°).

All-inside versus inside-out meniscal repair: A systematic review and meta-analysis

BACKGROUND

Meniscal repair using all-inside devices has garnered popularity compared to inside-out repair, yet few studies directly compare the two techniques in terms meniscal healing rates, surgical time, patient outcomes and incidence of complications.

METHODS

A systematic literature review was performed using the Medline, Cochrane and Embase databases. English-language studies comparing all-inside and inside-out arthroscopic meniscal repair techniques directly were included. Randomised controlled trials (RCTs) and observational studies with at least 10 patients in each treatment arm were included. Meta-analyses were performed using a fixed effect (when I2 < 50%) or random effects model (I2 ≥ 50%).

RESULTS

A total of 1042 studies were identified with seven being sui for inclusion (n = 505 patients). These comprised of one RCT two prospective and four retrospective, comparative, observational studies. Meta-analyses demonstrated that there was a significant reduction in operating time favouring all-inside repair (ratio of means [ROM] 0.62, 95% confidence interval [CI] 0.48-0.79; p = 0.0002) based on 3 studies (n = 208 patients). Based on 5 studies (n = 370 patients), there was no significant difference in meniscal healing rates between the groups (OR 1.26, 95% CI 0.52-3.10; p = 0.61). Nerve injury was more common after inside-out repair. There was a 85% reduction in the odds of nerve injury with the all-inside technique (OR 0.15, 95% CI 0.05-0.47; p = 0.0013). A qualitative data analysis suggested no difference in functional outcomes between the two techniques.

CONCLUSIONS

All-inside meniscal repair is associated with reduced operative time and a lower odds of nerve injury complications compared to inside-out repair, without compromising meniscal healing or functional results.

Editorial Commentary: Discovery: Progenitor Cells and Endothelial Cells Are Found in the White-White Zone of the Meniscus, But This Does Not Mean That These Tears Heal or Should Be Repaired

More than 35 years ago, the concept of vascular zones of the meniscus was introduced. It has been shown that blood supply is limited to the peripheral 25% of the lateral and 30% of the medial meniscus. This obviously has repercussions with regard to the healing potential of meniscus tears, whether repaired or not. In general, tears that extend into the white-white zone, such as flaps, cleavage tears, and radial tears, are deemed irreparable. However, several recent reports have suggested that radial tears in the white-white zone, when repaired, heal and have good clinical outcomes. Now progenitor mesenchymal cells have been identified in the white-white zones, confirming the potential of the meniscus to heal. However, blood supply was demonstrated only by indirect signs such as the presence of endothelial cells and the presence of endothelial surface markers.

Work-Related Risk Factors of Knee Meniscal Tears in Korean Farmers: A Cross-Sectional Study

Background

Meniscal tears are among the major risk factors for knee osteoarthritis progression. This study aimed to investigate the relationship between meniscal tears and work-related factors in the farming occupation.

Methods

The participants included 486 farmers (238 men and 248 women), aged 40–69 years, who were among the 550 farmers registered in the Korea Farmer's Knee Cohort (KFKC). Data such as those on gender, age, body mass index (BMI), mechanical axis, cumulative heavy-lifting working time (CLWT), cumulative squatting working time (CSWT), and previous knee injury history were collected from the questionnaire, along with whole leg radiographic findings. Two radiologists assessed the magnetic resonance images of both knees to confirm the presence of meniscal tears. The factors related to meniscal tears were analyzed by multiple logistic regression.

Results

A total of 54.5% of the farmers (48.7% of men and 60.1% of women) had meniscal tears. These tears were associated with gender, age, and BMI. We also identified an association between meniscal tears and CSWT, an especially important factor in farming [10,000–19,999 working hours, odds ratio = 2.16, 95% confidence interval (CI): 1.14-4.07, ≥20,000 working hours, odds ratio = 2.35, 1.45-3.80]. However, mechanical axis, knee injury history, and CLWT were not significantly related to meniscal tears.

Conclusion

This study's findings show that squatting for long periods, as an occupational factor, is related to meniscal tears.

Structure, function, and defect tolerance with maturation of the radial tie fiber network in the knee meniscus

The knee menisci are comprised of two orthogonal collagenous networks-circumferential and radial-that combine to enable efficient load bearing by the tissue in adults. Here, we assessed how the structural and functional characteristics of these networks developed over the course of skeletal maturation and determined the role of these fiber networks in defect tolerance with tissue injury. Imaging of the radial tie fiber (RTF) collagen structure in medial bovine menisci from fetal, juvenile, and adult specimens showed increasing heterogeneity, anisotropy, thickness, and density with skeletal development. The mechanical analysis showed that the tensile modulus in the radial direction did not change with skeletal development, though the resilience (in the radial direction) increased and the tolerance to defects in the circumferential direction decreased, in adult compared to fetal tissues. This loss of defect tolerance correlated with increased order in the RTF network in adult tissue. These data provide new insights into the role of the radial fiber network in meniscus function, will lead to improved clinical decision-making in the presence of a tear and may improve engineering efforts to reproduce this critical load-bearing structure in the knee.