Mechanobiology of the meniscus

Revealing Early Spatial Patterns of Cellular Responsivity in Fiber-Reinforced Microenvironments

Fiber-reinforcement approaches have been used to replace aligned tissues with engineered constructs after injury or surgical resection, strengthening soft biomaterial scaffolds and replicating anisotropic, load-bearing properties. However, most studies focus on the macroscale aspects of these scaffolds, rarely considering the cell-biomaterial interactions that govern remodeling and extracellular matrix organization toward aligned neo-tissues. As initial cell-biomaterial responses within fiber-reinforced microenvironments likely influence the long-term efficacy of repair and regeneration strategies, here we elucidate the roles of spatial orientation, substrate stiffness, and matrix remodeling on early cell-fiber interactions. Bovine mesenchymal stromal cells (MSCs) were cultured in soft fibrin gels reinforced with a stiff 100 µm polyglycolide-co-caprolactone fiber. Gel stiffness and remodeling capacity were modulated by fibrinogen concentration and aprotinin treatment, respectively. MSCs were imaged at 3 days and evaluated for morphology, mechanoresponsiveness (nuclear Yes-associated protein [YAP] localization), and spatial features including distance and angle deviation from fiber. Within these constructs, morphological conformity decreased as a function of distance from fiber. However, these correlations were weak (R2 = 0.01043 for conformity and R2 = 0.05542 for nuclear YAP localization), illustrating cellular heterogeneity within fiber-enforced microenvironments. To better assess cell-fiber interactions, we applied machine-learning strategies to our heterogeneous dataset of cell-shape and mechanoresponsive parameters. Principal component analysis (PCA) was used to project 23 input parameters (not including distance) onto 5 principal components (PCs), followed by agglomerative hierarchical clustering to classify cells into 3 groups. These clusters exhibited distinct levels of morpho-mechanoresponse (combination of morphological conformity and YAP signaling) and were classified as high response (HR), medium response (MR), and low response (LR) clusters. Cluster distribution varied spatially, with most cells (61%) closest to the fiber (0-75 µm) belonging to the HR cluster, and most cells (55%) furthest from the fiber (225-300 µm) belonging to the LR cluster. Modulation of gel stiffness and fibrin remodeling showed differential effects for HR cells, with stiffness influencing the level of mechanoresponse and remodeling capacity influencing the location of responding cells. Together, these novel findings demonstrate early trends in cellular patterning of the fiber-reinforced microenvironment, showing how spatial orientation, substrate biophysical properties, and matrix remodeling may guide the amplitude and localization of cellular mechanoresponses. These trends may guide approaches to optimize the design of microscale scaffold architecture and substrate properties for enhancing organized tissue assembly at the macroscale.

In Situ Loading and Time-Resolved Synchrotron-Based Phase Contrast Tomography for the Mechanical Investigation of Connective Knee Tissues: A Proof-of-Concept Study

Articular cartilage and meniscus transfer and distribute mechanical loads in the knee joint. Degeneration of these connective tissues occurs during the progression of knee osteoarthritis, which affects their composition, microstructure, and mechanical properties. A deeper understanding of disease progression can be obtained by studying them simultaneously. Time-resolved synchrotron-based X-ray phase-contrast tomography (SR-PhC-µCT) allows to capture the tissue dynamics. This proof-of-concept study presents a rheometer setup for simultaneous in situ unconfined compression and SR-PhC-µCT of connective knee tissues. The microstructural response of bovine cartilage (n = 16) and meniscus (n = 4) samples under axial continuously increased strain, or two steps of 15% strain (stress-relaxation) is studied. The chondrocyte distribution in cartilage and the collagen fiber orientation in the meniscus are assessed. Variations in chondrocyte density reveal an increase in the top 40% of the sample during loading, compared to the lower half. Meniscus collagen fibers reorient perpendicular to the loading direction during compression and partially redisperse during relaxation. Radiation damage, image repeatability, and image quality assessments show little to no effects on the results. In conclusion, this approach is highly promising for future studies of human knee tissues to understand their microstructure, mechanical response, and progression in degenerative diseases.

Reduced physiological extrusion of the medial meniscus in axial load-bearing condition in anterior cruciate ligament deficiency

PURPOSE

In this study, ultrasonography was used to measure medial meniscus (MM) extrusion under weight-bearing and nonweight-bearing conditions in both anterior cruciate ligament (ACL)-deficient and ACL-intact knee groups. This study aimed to determine the possible differences between these groups with an eventual impact on meniscal tears in ACL-deficient knees.

METHODS

A total of 107 patients who underwent ACL reconstructive surgery between June 2022 and April 2023 were enroled. After applying exclusion criteria, 37 patients met the conditions for inclusion in the study and formed the ACL deficiency group (Group D). Of the 141 patients presenting to an outpatient clinic who agreed to have ultrasonography conducted on their nondiscomforting contralateral knee, 37 patients matched for age, sex, hip-knee-ankle angle and body mass index with Group D patients were selected for the ACL intact group (Group I). Ultrasonography was used to measure MM extrusion in weight-bearing and nonweight-bearing conditions for all participants.

RESULTS

Seventy-four patients were included in the study (n = 37 per group). The supine position showed an MM extrusion of 1.2 ± 0.7 mm in Group I and 1.2 ± 0.7 mm in Group D (not significant). In the standing position, MM extrusion measured 2.0 ± 0.6 mm in Group I and 1.3 ± 0.8 mm in Group D. The difference in extrusion (Δextrusion) between the two positions was 0.8 ± 0.6 in Group I and 0.1 ± 0.2 in Group D, with statistical significance (p < 0.01). A consistent reduction in MM extrusion during weight-bearing was observed in patients with ACL deficiency, irrespective of the duration of ACL deficiency, age, sex and BMI.

CONCLUSION

ACL deficiency did not significantly impact MM extrusion during nonweight-bearing conditions; however, less MM extrusion was observed in response to axial loading conditions. These findings indicate altered MM biomechanics due to increased anterior-posterior meniscal motion and rotational instability after ACL injury.

LEVEL OF EVIDENCE

Level III.

Cyclic compressive loading induces a mature meniscal cell phenotype in mesenchymal stem cells with an atelocollagen-based scaffold

Introduction: Biomechanical stimulation is reportedly pivotal in meniscal regeneration, although its effect on mesenchymal stem cell (MSC) meniscal differentiation remains elusive. In this study, we investigated how cyclic compressive loading (CCL) could impact MSCs using three-dimensional cultures in atelocollagen-based meniscal substitute (ACMS). Methods: We extracted MSCs from the meniscus, synovium, and articular cartilage, cultured them in three-dimensional cultures, and exposed them to CCL for 7 days. We then compared the transcriptomes of MSCs treated with and without CCL. Results: Our RNA-seq analysis revealed that CCL induced significant transcriptome changes, significantly affecting chondrocyte-related genes, including SOX9, TGFB1, and PRG4 upregulation. CCL induced transcriptional differentiation of meniscus progenitors toward mature meniscal cells. Conclusion: This study unveils the potential of mechanical stress in promoting MSC meniscal differentiation within ACMS. Our investigations provide new insights for mechanisms underlying meniscal regeneration with ACMS.

Functional testing following isolated meniscus repair may help to identify patients who need additional physical therapy prior to a return to activity

OBJECTIVES

Functional testing (FT), commonly used to evaluate dynamic knee function and provide objective information about how well a patient, has progressed in rehabilitation following an anterior cruciate ligament (ACL) reconstruction. The purpose of the study was to determine whether a functional test could be used as an assessment tool for return to activity following isolated meniscus repair.

METHODS

The results of FT completed between 80 and 150 days post-operation (representing 4-months post-operative) in isolated meniscal repair patients were analysed for the involved limb, uninvolved limb, and limb symmetry index (LSI). Involved limb performance and LSI on FT were also recorded for a matched cohort of patients who underwent an isolated ACL reconstruction between 151 and 220 days post-operation (representing 6-months post-operative). The meniscus cohort was compared to the ACL cohort.

RESULTS

The meniscus cohort (n ​= ​26) performed well (LSI of 88% or better) on all functional test exercises, including all hop tests. There were patients in the meniscus cohort who did not achieve 90% LSI on the FT at 4 months. There was no statistically significant difference in any of the tests between the meniscus and ACL (n ​= ​39) cohorts.

CONCLUSION

A majority of isolated meniscal repair patients perform well on FT by 4 months post-operatively and similar to patients undergoing isolated ACL reconstruction at 6 months post-operatively. Not all patients performed well on FT at 4 months post-operatively; however so, there may be a role for FT in isolated meniscal repair patients, and those patients may need further physical therapy prior to a return to sports.

LEVEL OF EVIDENCE

III; Retrospective cohort study.

LEVEL OF EVIDENCE

IV.

Bioprinting of scaled-up meniscal grafts by spatially patterning phenotypically distinct meniscus progenitor cells within melt electrowritten scaffolds

Meniscus injuries are a common problem in orthopedic medicine and are associated with a significantly increased risk of developing osteoarthritis. While developments have been made in the field of meniscus regeneration, the engineering of cell-laden constructs that mimic the complex structure, composition and biomechanics of the native tissue remains a significant challenge. This can be linked to the use of cells that are not phenotypically representative of the different zones of the meniscus, and an inability to direct the spatial organization of engineered meniscal tissues. In this study we investigated the potential of zone-specific meniscus progenitor cells (MPCs) to generate functional meniscal tissue following their deposition into melt electrowritten (MEW) scaffolds. We first confirmed that fibronectin selected MPCs from the inner and outer regions of the meniscus maintain their differentiation capacity with prolonged monolayer expansion, opening their use within advanced biofabrication strategies. By depositing MPCs within MEW scaffolds with elongated pore shapes, which functioned as physical boundaries to direct cell growth and extracellular matrix production, we were able to bioprint anisotropic fibrocartilaginous tissues with preferentially aligned collagen networks. Furthermore, by using MPCs isolated from the inner (iMPCs) and outer (oMPCs) zone of the meniscus, we were able to bioprint phenotypically distinct constructs mimicking aspects of the native tissue. An iterative MEW process was then implemented to print scaffolds with a similar wedged-shaped profile to that of the native meniscus, into which we deposited iMPCs and oMPCs in a spatially controlled manner. This process allowed us to engineer sulfated glycosaminoglycan and collagen rich constructs mimicking the geometry of the meniscus, with MPCs generating a more fibrocartilage-like tissue compared to the mesenchymal stromal/stem cells. Taken together, these results demonstrate how the convergence of emerging biofabrication platforms with tissue-specific progenitor cells can enable the engineering of complex tissues such as the meniscus.

Reduction in postnatal weight-bearing does not alter the trajectory of murine meniscus growth and maturation

The early postnatal period represents a critical window for the maturation and development of orthopedic tissues, including those within the knee joint. To understand how mechanical loading impacts the maturational trajectory of the meniscus and other tissues of the hindlimb, perturbation of postnatal weight bearing was achieved through surgical resection of the sciatic nerve in neonatal mice at 1 or 14 days old. Sciatic nerve resection (SNR) produced significant and persistent disruptions in gait, leading to reduced tibial length and reductions in Achilles tendon mechanical properties. However, SNR resulted in minimal disruptions in morphometric parameters of the menisci and other structures in the knee joint, with no detectable differences in Col1a1-YFP or Col2a1-CFP expressing cells within the menisci. Furthermore, micromechanical properties of the meniscus and cartilage (as assessed by atomic force microscopy-based nanoindentation testing) were not different between experimental groups. In contrast to our initial hypothesis, reduced hindlimb weight bearing via neonatal SNR did not significantly impact the growth and development of the knee meniscus. This unexpected finding demonstrates that the input mechanical threshold required to sustain meniscus development may be lower than previously hypothesized, though future studies incorporating skeletal kinematic models coupled with force plate measurements will be required to calculate the loads passing through the affected hindlimb and precisely define these thresholds. Collectively, these results provide insight into the mechanobiological responses of the meniscus to alterations in load, and contribute to our understanding of the factors that influence normal postnatal development.

Reconstruction of Fibrocartilage with Fibrous Alignment of Type I Collagen in Scaffold-Free Manner

For functional reconstruction of fibrocartilage, it is necessary to reproduce the essential mechanical property exhibited by natural fibrocartilage. The distinctive mechanical property of fibrocartilage is originated from the specific histological features of fibrocartilage composed of highly aligned type I collagen (Col I) and an abundant cartilaginous matrix. While the application of tensile stimulation induces highly aligned Col I, our study reveals that it also exerts an antichondrogenic effect on scaffold-free tissues constructed with meniscal chondrocytes (MCs) and induces downregulation of Sox-9 expression and attenuated glycosaminoglycan production. Modulation of mechanotransduction by blocking nuclear translocation of Yes-associated protein (YAP) ameliorated the antichondrogenic effect in the presence of tensile stimulation. Since MCs subjected to mechanical doses either by surface stiffness or tensile stimulation showed reversibility of YAP status even after a long-term exposure to mechanotransduction, fibrocartilage tissue was constructed by sequentially inducing tissue alignment by tensile stimulation followed by inducing cartilaginous matrix production in a tension-released state. The minimal tensile dose to constitute durable tissue alignment was screened by investigating the alignment of cytoskeleton and Col I after culturing the scaffold-free tissue constructs with various tensile doses (10% static tension for 1, 3, 7, and 10 days) followed by maintaining in a released state for 5 days. Fluorescence-conjugated phalloidin binding and immunofluorescence of Col I indicated that the duration of static tension for more than 7 days resulted in durable tissue alignment for at least 5 days in the tension-released state. The tissues subjected to tensile stimulation for 7 days followed by 14 days in a released state in chondrogenic media resulted in abundant cartilaginous matrix as well as uniaxial anisotropic alignment. Our results show that the optimized tensile dose can facilitate the successful reconstruction of fibrocartilage by modulating the characteristics of matrix production by MCs.

Postnatal morpho-functional development of a dog's meniscus

This study evaluates the morpho-functional modifications that characterize meniscal development from neonatal to adult dogs. Even if menisci are recognized as essential structures for the knee joint, poor information is available about their morphogenesis, in particular in dog models. Menisci from a group of Dobermann Pinchers aged 0, 10, 30 days, and 4 years (T0, T10, T30, adult, respectively) were analyzed by SEM, histochemistry (Safranin O and Picro Sirius Red Staining analyzed under a polarized light microscope), immunofluorescences (collagen type I and II), biomechanical (compression) and biochemical analyses (glycosaminoglycans, GAGs, and DNA content). SEM analyses revealed that the T0 meniscus is a bulgy structure that during growth tends to flatten, firstly in the inner zone (T10) and then even in the outer zone (T30), until the achievement of the completely smooth adult final shape. These results were further supported by the histochemistry analyses in which the deposition of GAGs started from T30, and the presence of type I birefringent collagen fibers was observed from T0 to T30, while poorly refringent type III collagen fibers were observed in the adult dogs. Double immunofluorescence analyses also evidenced that the neonatal meniscus contains mainly type I collagen fibers, as well as the T10 meniscus, and demonstrated a more evident regionalization and crimping in the T30 and adult meniscus. Young's elastic modulus of the meniscus in T0 and T10 animals was lower than the T30 animals, and this last group was also lower than adult ones (T0-T10 vs T30 vs adult). Biochemical analysis confirmed that cellularity decreases over time from neonatal to adult (p < 0.01). The same decreasing trend was observed in GAGs deposition. These results may suggest that the postnatal development of canine meniscus may be related to the progressive functional locomotory development: after birth, the meniscus acquires its functionality over time, through movement, load, and growth itself.

Introduction of an easy-to-operate arthroscopic test in detecting and treatment of meniscal instability: "suction drift" test

OBJECTIVE

To explore the surgical guidance value of "suction drift" in osteoarticular meniscal instability.

METHODS

The clinical data of 104 patients with significant knee symptoms following surgery were retrospectively analyzed. "Suction drift" was diagnosed in both groups. Depending on the treatment, patients treated with conventional debridement were assigned to group A, and those treated by meniscus suture until the disappearance of the "suction drift" phenomenon were included in group B. All patients were followed up for a minimum of 6 months after surgery. The postoperative Visual Analogue Scale (VAS) score, Lysholm knee score and the occurrence of meniscus-related symptoms were compared between the two groups.

RESULTS

After puncture, 78 patients (75.0%) had excessive displacement of the meniscus, with 53 (67.9%) of them being followed-up for at least 6 months. Twenty-five patients in group A and twenty-eight in group B were included in the final analysis (The number of patients with "suction drift" in two groups was tested to be comparable, P>0.05). VAS score was significantly decreased and Lysholm knee score was markedly increased in both groups after treatment, with lower VAS score and higher Lysholm knee score in group B compared with group A. In addition, group A had a significantly higher incidence of meniscus-related symptoms (joint space tenderness, joint clicks, and noose sensation) than group B.

CONCLUSIONS

"Suction drift" is a quick and easy-to-operate arthroscopic test, which can not only diagnose meniscus instability due to knee osteoarthrosis-induced meniscus degeneration, but also help determine the recovery of meniscus stability after suture, and significantly relieve symptoms.

Transient inhibition of meniscus cell migration following acute inflammatory challenge

Meniscus tears represent a common orthopedic injury that often requires surgery to restore pain-free function. The need for surgical intervention is due, in part, to the inflammatory and catabolic environment that inhibits meniscus healing after injury. In other organ systems, healing is dependent on the migration of cells to the site of injury; however, in the meniscus, it is currently unknown how the microenvironment dictates cell migration in the postinjury inflamed setting. Here, we investigated how inflammatory cytokines alter meniscal fibrochondrocyte (MFC) migration and sensation of microenvironmental stiffness. We further tested whether an FDA approved interleukin-1 receptor antagonist (IL-1Ra; Anakinra) could rescue migratory deficits caused by inflammatory challenge. When cultured in the presence of inflammatory cytokines (tumor necrosis factor-α [TNF-α] or interleukin-1β [IL-1β]) for 1 day, MFC migration was inhibited for 3 days before returning to control levels at Day 7. This migratory deficit was clear in three-dimensional as well, where fewer MFCs exposed to inflammatory cytokines migrated from a living meniscal explant compared with control. Notably, addition of IL-1Ra to MFCs previously exposed to IL-1β restored migration to baseline levels. This study demonstrates that joint inflammation can have negative impacts on meniscus cell migration and mechanosensation, affecting their potential for repair, and that resolution of this inflammation with concurrent anti-inflammatories can reverse these deficits. Future work will apply these findings to mitigate the negative consequences of joint inflammation and promote repair in a clinically relevant meniscus injury model.

A novel device for investigating structure-function relationships and mechanoadaptation of biological tissues

Exploring the structure-function relationships of cartilage on a microstructural level is crucial for tissue engineering approaches aiming to restore function. Therefore, a combination of mechanical testing with cell and tissue-level imaging would allow for longitudinal studying loading mechanisms, biological responses and mechanoadaptation of tissues at a microstructural level. This paper describes the design and validation of FELIX, a custom-built device for non-destructive image-guided micromechanical evaluation of biological tissues and tissue-engineered constructs. It combines multiphoton microscopy with non-destructive mechanical testing of native soft tissues. Ten silicone samples of the same size were mechanically tested with FELIX by different users to assess the repeatability and reproducibility. The results indicate that FELIX can successfully substitute mechanical testing protocols with a commercial device without compromising precision. Furthermore, FELIX demonstrated consistent results across repeated measurements, with very small deviations. Therefore, FELIX can be used to accurately measure biomechanical properties by different users for separate studies. Additionally, cell nuclei and collagen of porcine articular cartilage were successfully imaged under compression. Cell viability remained high in chondrocytes cultured in agarose over 21 days. Furthermore, there were no signs of contamination indicating a cell friendly, sterile environment for longitudinal studies. In conclusion, this work demonstrates that FELIX can consistently quantify mechanical measures without compromising precision. Furthermore, it is biocompatible allowing for longitudinal measurements.

Suspension bath bioprinting and maturation of anisotropic meniscal constructs

Due to limited intrinsic healing capacity of the meniscus, meniscal injuries pose a significant clinical challenge. The most common method for treatment of damaged meniscal tissues, meniscectomy, leads to improper loading within the knee joint, which can increase the risk of osteoarthritis. Thus, there is a clinical need for the development of constructs for meniscal repair that better replicate meniscal tissue organization to improve load distributions and function over time. Advanced three-dimensional bioprinting technologies such as suspension bath bioprinting provide some key advantages, such as the ability to support the fabrication of complex structures using non-viscous bioinks. In this work, the suspension bath printing process is utilized to print anisotropic constructs with a unique bioink that contains embedded hydrogel fibers that align via shear stresses during printing. Constructs with and without fibers are printed and then cultured for up to 56 din vitroin a custom clamping system. Printed constructs with fibers demonstrate increased cell and collagen alignment, as well as enhanced tensile moduli when compared to constructs printed without fibers. This work advances the use of biofabrication to develop anisotropic constructs that can be utilized for the repair of meniscal tissue.

Temporal application of lysyl oxidase during hierarchical collagen fiber formation differentially effects tissue mechanics

The primary source of strength in menisci, tendons, and ligaments are hierarchical collagen fibers; however, these fibers are not regenerated after injury nor in engineered replacements, resulting in limited repair options. Collagen strength is reliant on fiber alignment, density, diameter, and crosslinking. Recently, we developed a culture system which guides cells in high-density collagen gels to develop native-like hierarchically organized collagen fibers, which match native fiber alignment and diameters by 6 weeks. However, tensile moduli plateau at 1MPa, suggesting crosslinking may be lacking. Collagen crosslinking is regulated by lysyl oxidase (LOX) which forms immature crosslinks that condense into mature trivalent crosslinks. Trivalent crosslinks are thought to be the primarily source of strength in fibers, but it's not well understood how they form. The objective of this study was to evaluate the effect of exogenous LOX in our culture system at different stages of hierarchical fiber formation to produce stronger replacements and to better understand factors affecting crosslink maturation. We found treatment with LOX isoform LOXL2 did not restrict hierarchical fiber formation, with constructs still forming aligned collagen fibrils by 2 weeks, larger fibers by 4 weeks, and early fascicles by 6 weeks. However, LOXL2 treatment did significantly increase mature pyridinium (PYD) crosslink accumulation and tissue mechanics, with timing of LOXL2 supplementation during fiber formation having a significant effect. Overall, we found one week of LOXL2 supplementation at 4 weeks produced constructs with native-like fiber organization, increased PYD accumulation, and increased mechanics, ultimately matching the tensile modulus of immature bovine menisci. STATEMENT OF SIGNIFICANCE: Collagen fibers are the primary source of strength and function in connective tissues throughout the body, however it remains a challenge to develop these fibers in engineered replacements, greatly reducing treatment options. Here we demonstrate lysyl oxidase like 2 (LOXL2) can be used to significantly improve the mechanics of tissue engineered constructs, but timing of application is important and will most likely depend on degree of collagen organization or maturation. Currently there is limited understanding of how collagen crosslinking is regulated, and this system is a promising platform to further investigate cellular regulation of LOX crosslinking. Understanding the mechanism that regulates LOX production and activity is needed to ultimately regenerate functional repair or replacements for connective tissues throughout the body.

Controlling collagen gelation pH to enhance biochemical, structural, and biomechanical properties of tissue-engineered menisci

Collagen-based hydrogels have been widely used in biomedical applications due to their biocompatibility. Enhancing mechanical properties of collagen gels remains challenging while maintaining biocompatibility. Here, we demonstrate that gelation pH has profound effects on cellular activity, collagen fibril structure, and mechanical properties of the fibrochondrocyte-seeded collagen gels in both short- and long-terms. Acidic and basic gelation pH, below pH 7.0 and above 8.5, resulted in dramatic cell death. Gelation pH ranging from 7.0 to 8.5 showed a relatively high cell viability. Furthermore, physiologic gelation (pH 7.5) showed the greatest collagen deposition while glycosaminoglycan deposition appeared independent of gelation pH. Scanning electron microscopy showed that neutral and physiologic gelation pH, 7.0 and 7.5, exhibited well-aligned collagen fibril structure on day 0 and enhanced collagen fibril structure with laterally joined fibrils on day 30. However, basic pH, 8.0 and 8.5, displayed a densely packed collagen fibril structure on day 0, which was also persistent on day 30. Initial equilibrium modulus increased with increasing gelation pH. Notably, after 30 days of culture, gelation pH of 7.5 and 8.0 showed the highest equilibrium modulus, reaching 150 -160 kPa. While controlling gelation pH is simply achieved compared with other strategies to improve mechanical properties, its influences on biochemical and biomechanical properties of the collagen gel are long-lasting. As such, gelation pH is a useful means to modulate both biochemical and biomechanical properties of the collagen-based hydrogels and can be utilized for diverse types of tissue engineering due to its simple application.

"Slow walk" mimetic tensile loading maintains human meniscus tissue resident progenitor cells homeostasis in photocrosslinked gelatin hydrogel

Meniscus, the cushion in knee joint, is a load-bearing tissue that transfers mechanical forces to extracellular matrix (ECM) and tissue resident cells. The mechanoresponse of human tissue resident stem/progenitor cells in meniscus (hMeSPCs) is significant to tissue homeostasis and regeneration but is not well understood. This study reports that a mild cyclic tensile loading regimen of ∼1800 loads/day on hMeSPCs seeded in 3-dimensional (3D) photocrosslinked gelatin methacryloyl (GelMA) hydrogel is critical in maintaining cellular homeostasis. Experimentally, a "slow walk" biomimetic cyclic loading regimen (10% tensile strain, 0.5 Hz, 1 h/day, up to 15 days) is applied to hMeSPCs encapsulated in GelMA hydrogel with a magnetic force-controlled loading actuator. The loading significantly increases cell differentiation and fibrocartilage-like ECM deposition without affecting cell viability. Transcriptomic analysis reveals 332 mechanoresponsive genes, clustered into cell senescence, mechanical sensitivity, and ECM dynamics, associated with interleukins, integrins, and collagens/matrix metalloproteinase pathways. The cell-GelMA constructs show active ECM remodeling, traced using a green fluorescence tagged (GFT)-GelMA hydrogel. Loading enhances nascent pericellular matrix production by the encapsulated hMeSPCs, which gradually compensates for the hydrogel loss in the cultures. These findings demonstrate the strong tissue-forming ability of hMeSPCs, and the importance of mechanical factors in maintaining meniscus homeostasis.

The Interplay of Biomechanical and Biological Changes Following Meniscus Injury

PURPOSE OF REVIEW

Meniscus injury often leads to joint degeneration and post-traumatic osteoarthritis (PTOA) development. Therefore, the purpose of this review is to outline the current understanding of biomechanical and biological repercussions following meniscus injury and how these changes impact meniscus repair and PTOA development. Moreover, we identify key gaps in knowledge that must be further investigated to improve meniscus healing and prevent PTOA.

RECENT FINDINGS

Following meniscus injury, both biomechanical and biological alterations frequently occur in multiple tissues in the joint. Biomechanically, meniscus tears compromise the ability of the meniscus to transfer load in the joint, making the cartilage more vulnerable to increased strain. Biologically, the post-injury environment is often characterized by an increase in pro-inflammatory cytokines, catabolic enzymes, and immune cells. These multi-faceted changes have a significant interplay and result in an environment that opposes tissue repair and contributes to PTOA development. Additionally, degenerative changes associated with OA may cause a feedback cycle, negatively impacting the healing capacity of the meniscus. Strides have been made towards understanding post-injury biological and biomechanical changes in the joint, their interplay, and how they affect healing and PTOA development. However, in order to improve clinical treatments to promote meniscus healing and prevent PTOA development, there is an urgent need to understand the physiologic changes in the joint following injury. In particular, work is needed on the in vivo characterization of the temporal biomechanical and biological changes that occur in patients following meniscus injury and how these changes contribute to PTOA development.

The triply periodic minimal surface-based 3D printed engineering scaffold for meniscus function reconstruction

Background

The meniscus injury is a common disease in the area of sports medicine. The main treatment for this disease is the pain relief, rather than the meniscal function recovery. It may lead to a poor prognosis and accelerate the progression of osteoarthritis. In this study, we designed a meniscal scaffold to achieve the purposes of meniscal function recovery and cartilage protection.

Methods

The meniscal scaffold was designed using the triply periodic minimal surface (TPMS) method. The scaffold was simulated as a three-dimensional (3D) intact knee model using a finite element analysis software to obtain the results of different mechanical tests. The mechanical properties were gained through the universal machine. Finally, an in vivo model was established to evaluate the effects of the TPMS-based meniscal scaffold on the cartilage protection. The radiography and histological examinations were performed to assess the cartilage and bony structures. Different regions of the regenerated meniscus were tested using the universal machine to assess the biomechanical functions.

Results

The TPMS-based meniscal scaffold with a larger volume fraction and a longer functional periodicity demonstrated a better mechanical performance, and the load transmission and stress distribution were closer to the native biomechanical environment. The radiographic images and histological results of the TPMS group exhibited a better performance in terms of cartilage protection than the grid group. The regenerated meniscus in the TPMS group also had similar mechanical properties to the native meniscus.

Conclusion

The TPMS method can affect the mechanical properties by adjusting the volume fraction and functional periodicity. The TPMS-based meniscal scaffold showed appropriate features for meniscal regeneration and cartilage protection.

The Effects of Korean Medicine Treatment for Meniscus Tears: A Retrospective Chart Review

Changes in symptoms and dysfunction related to meniscus tears following the use of Korean medicine for ≥ 4 days were studied. The medical charts of 53 cases of diagnosed meniscus tears (magnetic resonance imaging) with an admission Numeric Rating Scale (NRS) score ≥ 4, between 2017 and 2022 were retrospectively reviewed. Treatments included acupuncture, pharmacopuncture, herbal treatment, Chuna therapy, and physiotherapy. The NRS, Western Ontario and McMaster Universities Osteoarthritis Index, and European Quality of Life 5 Dimensions were performed at admission and discharge. There were 42 females and 11 males in this study. Patients were more likely to be in their 60s (38.18%), have an unknown etiology (81.13%), and have complex tears (50.94%). After receiving a combination of alternative Korean medicine during hospitalization, the mean NRS score improved from 6.82 ± 1.19 to 3.66 ± 1.83 (p < 0.001), the Western Ontario and McMaster Universities Osteoarthritis Index score improved from 46.47 ± 20.99 to 37.98 ± 19.23 (p < 0.001), and the mean European Quality of Life Five Dimensions score improved from 0.61 ± 0.18 to 0.68 ± 0.14 (p < 0.001) after treatment. These results suggest that Korean medicine treatment of meniscus tears alleviated pain and improved physical function.

Management Strategies and Imaging Observation of Early and Delayed Intelligent Treatment of Meniscus Sports Injury under Knee Osteoarthroscopy

Objective

To investigate the meniscus characteristics of knee osteoarthritis and its guiding significance for minimally invasive surgery.

Methods

A total of 100 patients with knee meniscus sports injuries who were treated in our hospital from January 2019 to January 2022 were selected as the research subjects and were grouped according to the interval between injury and surgery, with an interval of 2 months: the early group (53 cases) within 2 months and the delayed group (47 cases) with an interval of more than 2 months. The distribution of intraoperative complications in the two groups was observed and recorded, and the changes in pain degree, joint range of motion, knee joint function, and quality of life scores before and after operation were compared between the two groups.

Results

The postoperative VAS score, range of motion, Lysholm score, IKDC knee subjective function score, and quality of life score were significantly improved in both groups (P < 0.05). The incidence of intra-articular cartilage injury in the delayed group was significantly higher than that in the early group (P < 0.05). The patellofemoral cartilage injury was the main part of intra-articular cartilage injury in the two groups, and the incidence of patellofemoral cartilage injury in the delayed group was significantly higher than that in the early group (P < 0.05). The cartilage damage was mainly cartilage damage, and the grades I-II and III-IV cartilage damages were significantly increased in the extension group.

Conclusion

Meniscal injury in knee osteoarthritis has certain microscopic characteristics. In this paper, the microscopic classification of meniscus injury in knee osteoarthritis is helpful to guide microscopic surgery and improve the minimally invasive knee osteoarthritis effect of surgical treatment.

The Current Role of Biologics for Meniscus Injury and Treatment

PURPOSE OF REVIEW

There is little doubt that the consensus has changed to favor preservation of meniscal function where possible. Accordingly, the indications for meniscal repair strategies have been refocused on the long-term interest of knee joint health. The development and refinements in surgical technique have been complemented by biological augmentation strategies to address intrinsic challenges in healing capacity of meniscal tissue, with variable effects.

RECENT FINDINGS

A contemporary approach to meniscal healing includes adequate surgical fixation, meniscal and synovial tissue stimulation, and management of the intraarticular milieu. Overall, evidence supporting the use of autogenous or allogeneic cell sources remains limited. The use of FDA-approved medications to effect biologically favorable mechanisms during meniscal healing holds promise. Development and characterization of biologics continue to advance with translational research focused on specific growth factors, cell and tissue behaviors in meniscal healing, and joint homeostasis. Although significant strides have been made in laboratory and pre-clinical studies, translation to clinical application remains challenging. Finally, expert consensus and standardization of nomenclature related to orthobiologics for meniscal preservation will be important for the advancement of this field.

Inside-Out Approach to Meniscus Repair: Still the Gold Standard?

PURPOSE OF REVIEW

The purpose of this review is to provide an up-to-date summary on the current literature and trends regarding use of the inside-out approach to meniscus repair. Additionally, the paper describes the authors preferred techniques for inside-out meniscus repair utilizing posteromedial and posterolateral exposures.

RECENT FINDINGS

There has been a substantial increase in recent publications regarding meniscus repair. However, comparisons regarding the optimal repair technique have not been conclusive. Despite the recent increase in use of all-inside devices, multiple investigations with short-to-mid-term follow-up have demonstrated similar rates of meniscus healing between inside-out and all-inside repair techniques. Similarly, current literature describes comparable failure rates of around 20%. There are variations in the profile of complications, with all-inside devices having more implant-related complications and inside-out techniques with higher neurovascular injuries. Inside-out meniscus repair is a versatile, cost-effective technique that remains the gold standard for management of most meniscus tear patterns. Through a thoughtful approach, efficient suture retrieval and repair can be performed while protecting critical neurovascular structures. All-inside meniscus repair devices have increased in popularity and surgeon access, but this technique is not without limitations and comparisons to inside-out meniscus repair demonstrates equivocal outcomes.

Meniscus Matrix Structural and Biomechanical Evaluation: Age-Dependent Properties in a Swine Model

The analysis of the morphological, structural, biochemical, and mechanical changes of the Extracellular Matrix (ECM), which occur during meniscus development, represents the goal of the present study. Medial fully developed menisci (FD, 9-month-old pigs), partially developed menisci (PD, 1-month-old piglets), and not developed menisci (ND, from stillbirths) were collected. Cellularity and glycosaminoglycans (GAGs) deposition were evaluated by ELISA, while Collagen 1 and aggrecan were investigated by immunohistochemistry and Western blot analyses in order to be compared to the biomechanical properties of traction and compression tensile forces, respectively. Cellularity decreased from ND to FD and GAGs showed the opposite trend (p < 0.01 both). Collagen 1 decreased from ND to FD, as well as the ability to resist to tensile traction forces (p < 0.01), while aggrecan showed the opposite trend, in accordance with the biomechanics: compression test showed that FD meniscus greatly resists to deformation (p < 0.01). This study demonstrated that in swine meniscus, clear morphological and biomechanical changes follow the meniscal maturation and specialization during growth, starting with an immature pattern (ND) to the mature organized meniscus of the FD, and they could be useful to understand the behavior of this structure in the light of its tissue bioengineering.

Performance and Return to Sports After Meniscectomy in Professional Baseball Players

BACKGROUND

Meniscal injuries are common in athletes across many sports. How professional baseball players respond to partial meniscectomy is not well documented.

PURPOSE/HYPOTHESIS

The purpose was to determine the performance and return-to-sports (RTS) rate in professional baseball players after arthroscopic partial knee meniscectomy and compare the results of partial medial meniscectomy versus partial lateral meniscectomy. The hypothesis was that there would be a high RTS rate in professional baseball players after partial meniscectomy with no difference in the RTS rate or timing of RTS between players who underwent partial medial meniscectomy versus partial lateral meniscectomy.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

All professional baseball players who underwent arthroscopic partial meniscectomy between 2010 and 2017 were identified using the Major League Baseball Health and Injury Tracking System database. Demographic and performance data (before and after injury) for each player were recorded. The RTS rate and timing of RTS were then compared between players who underwent partial medial meniscectomy versus partial lateral meniscectomy.

RESULTS

A total of 168 knees (168 players) underwent arthroscopic partial meniscectomy (mean age, 25 ± 5 years; 46% medial meniscectomy, 45% lateral meniscectomy, and 9% both medial and lateral meniscectomy). The most common mechanism of injury was fielding in the infield on natural grass. Injuries were spread evenly across positions: 18% catchers, 24% infielders, 20% outfielders, and 38% pitchers. The overall RTS rate was 80% (76% returned to the same or a higher level, and 4% returned to a lower level). For performance, pitchers saw significant decreases in usage but significant improvements in performance using the advanced statistics of fielding independent pitching (P < .001) and wins above replacement (P = .011). Hitters saw significant decreases in usage but increases in efficiency as seen by improvements in wins above replacement (P = .003). Of the 79 athletes who returned during the same season, the median time to return to play was 42 days.

CONCLUSION

The RTS rate after meniscectomy in professional baseball players was 80%. Player efficiency improved after surgery in pitchers and position players. No difference in the RTS rate or timing of RTS existed between players who underwent partial medial meniscectomy versus partial lateral meniscectomy.

A Tale of Two Loads: Modulation of IL-1 Induced Inflammatory Responses of Meniscal Cells in Two Models of Dynamic Physiologic Loading

Meniscus injuries are highly prevalent, and both meniscus injury and subsequent surgery are linked to the development of post-traumatic osteoarthritis (PTOA). Although the pathogenesis of PTOA remains poorly understood, the inflammatory cytokine IL-1 is elevated in synovial fluid following acute knee injuries and causes degradation of meniscus tissue and inhibits meniscus repair. Dynamic mechanical compression of meniscus tissue improves integrative meniscus repair in the presence of IL-1 and dynamic tensile strain modulates the response of meniscus cells to IL-1. Despite the promising observed effects of physiologic mechanical loading on suppressing inflammatory responses of meniscus cells, there is a lack of knowledge on the global effects of loading on meniscus transcriptomic profiles. In this study, we compared two established models of physiologic mechanical stimulation, dynamic compression of tissue explants and cyclic tensile stretch of isolated meniscus cells, to identify conserved responses to mechanical loading. RNA sequencing was performed on loaded and unloaded meniscus tissue or isolated cells from inner and outer zones, with and without IL-1. Overall, results from both models showed significant modulation of inflammation-related pathways with mechanical stimulation. Anti-inflammatory effects of loading were well-conserved between the tissue compression and cell stretch models for inner zone; however, the cell stretch model resulted in a larger number of differentially regulated genes. Our findings on the global transcriptomic profiles of two models of mechanical stimulation lay the groundwork for future mechanistic studies of meniscus mechanotransduction, which may lead to the discovery of novel therapeutic targets for the treatment of meniscus injuries.

Engineered Human Meniscus in Modeling Sex Differences of Knee Osteoarthritis in Vitro

Background: Osteoarthritis (OA) primarily affects mechanical load-bearing joints. The knee joint is the most impacted by OA. Knee OA (KOA) occurs in almost all demographic groups, but the prevalence and severity are disproportionately higher in females. The molecular mechanism underlying the pathogenesis and progression of KOA is unknown. The molecular basis of biological sex matters of KOA is not fully understood. Mechanical stimulation plays a vital role in modulating OA-related responses of load-bearing tissues. Mechanical unloading by simulated microgravity (SMG) induced OA-like gene expression in engineered cartilage, while mechanical loading by cyclic hydrostatic pressure (CHP), on the other hand, exerted a pro-chondrogenic effect. This study aimed to evaluate the effects of mechanical loading and unloading via CHP and SMG, respectively, on the OA-related profile changes of engineered meniscus tissues and explore biological sex-related differences.

Methods: Tissue-engineered menisci were made from female and male meniscus fibrochondrocytes (MFCs) under static conditions of normal gravity in chondrogenic media and subjected to SMG and CHP culture. Constructs were assayed via histology, immunofluorescence, GAG/DNA assays, RNA sequencing, and testing of mechanical properties.

Results: The mRNA expression of ACAN and COL2A1, was upregulated by CHP but downregulated by SMG. COL10A1, a marker for chondrocyte hypertrophy, was downregulated by CHP compared to SMG. Furthermore, CHP increased GAG/DNA levels and wet weight in both female and male donors, but only significantly in females. From the transcriptomics, CHP and SMG significantly modulated genes related to the ossification, regulation of ossification, extracellular matrix, and angiogenesis Gene Ontology (GO) terms. A clear difference in fold-change magnitude and direction was seen between the two treatments for many of the genes. Furthermore, differences in fold-change magnitudes were seen between male and female donors within each treatment. SMG and CHP also significantly modulated genes in OA-related KEGG pathways, such as mineral absorption, Wnt signalling pathway, and HIF-1 signalling pathway.

Conclusion: Engineered menisci responded to CHP and SMG in a sex-dependent manner. SMG may induce an OA-like profile, while CHP promotes chondrogenesis. The combination of SMG and CHP could serve as a model to study the early molecular events of KOA and potential drug-targetable pathways.

Multiscale Strain Transfer in Cartilage

The transfer of stress and strain signals between the extracellular matrix (ECM) and cells is crucial for biochemical and biomechanical cues that are required for tissue morphogenesis, differentiation, growth, and homeostasis. In cartilage tissue, the heterogeneity in spatial variation of ECM molecules leads to a depth-dependent non-uniform strain transfer and alters the magnitude of forces sensed by cells in articular and fibrocartilage, influencing chondrocyte metabolism and biochemical response. It is not fully established how these nonuniform forces ultimately influence cartilage health, maintenance, and integrity. To comprehend tissue remodelling in health and disease, it is fundamental to investigate how these forces, the ECM, and cells interrelate. However, not much is known about the relationship between applied mechanical stimulus and resulting spatial variations in magnitude and sense of mechanical stimuli within the chondrocyte’s microenvironment. Investigating multiscale strain transfer and hierarchical structure-function relationships in cartilage is key to unravelling how cells receive signals and how they are transformed into biosynthetic responses. Therefore, this article first reviews different cartilage types and chondrocyte mechanosensing. Following this, multiscale strain transfer through cartilage tissue and the involvement of individual ECM components are discussed. Finally, insights to further understand multiscale strain transfer in cartilage are outlined.

Meniscus regeneration by 3D printing technologies: Current advances and future perspectives

Meniscal tears are a frequent orthopedic injury commonly managed by conservative strategies to avoid osteoarthritis development descending from altered biomechanics. Among cutting-edge approaches in tissue engineering, 3D printing technologies are extremely promising guaranteeing for complex biomimetic architectures mimicking native tissues. Considering the anisotropic characteristics of the menisci, and the ability of printing over structural control, it descends the intriguing potential of such vanguard techniques to meet individual joints’ requirements within personalized medicine. This literature review provides a state-of-the-art on 3D printing for meniscus reconstruction. Experiences in printing materials/technologies, scaffold types, augmentation strategies, cellular conditioning have been compared/discussed; outcomes of pre-clinical studies allowed for further considerations. To date, translation to clinic of 3D printed meniscal devices is still a challenge: meniscus reconstruction is once again clear expression of how the integration of different expertise (e.g., anatomy, engineering, biomaterials science, cell biology, and medicine) is required to successfully address native tissues complexities.

Post-Traumatic Osteoarthritis Assessment in Emerging and Advanced Pre-Clinical Meniscus Repair Strategies: A Review

Surgical repair of meniscus injury is intended to help alleviate pain, prevent further exacerbation of the injury, restore normal knee function, and inhibit the accelerated development of post-traumatic osteoarthritis (PTOA). Meniscus injuries that are treated poorly or left untreated are reported to significantly increase the risk of PTOA in patients. Current surgical approaches for the treatment of meniscus injuries do not eliminate the risk of accelerated PTOA development. Through recent efforts by scientists to develop innovative and more effective meniscus repair strategies, the use of biologics, allografts, and scaffolds have come into the forefront in pre-clinical investigations. However, gauging the extent to which these (and other) approaches inhibit the development of PTOA in the knee joint is often overlooked, yet an important consideration for determining the overall efficacy of potential treatments. In this review, we catalog recent advancements in pre-clinical therapies for meniscus injuries and discuss the assessment methodologies that are used for gauging the success of these treatments based on their effect on PTOA severity. Methodologies include histopathological evaluation of cartilage, radiographic evaluation of the knee, analysis of knee function, and quantification of OA predictive biomarkers. Lastly, we analyze the prevalence of these methodologies using a systemic PubMed® search for original scientific journal articles published in the last 3-years. We indexed 37 meniscus repair/replacement studies conducted in live animal models. Overall, our findings show that approximately 75% of these studies have performed at least one assessment for PTOA following meniscus injury repair. Out of this, 84% studies have reported an improvement in PTOA resulting from treatment.

Contrast-Enhanced Micro-Computed Tomography for 3D Visualization and Quantification of Glycosaminoglycans in Different Cartilage Types

OBJECTIVE

To compare CA4+-enhanced micro-computed tomography (microCT) of bovine articular, meniscal, nasal, and auricular cartilage, each of which possesses a different extracellular matrix (ECM) composition and structure.

DESIGN

The diffusion kinetics of CA4+ in different native cartilage types were assessed over 20 hours. The feasibility of CA4+-enhanced microCT to visualize and quantify glycosaminoglycans (GAGs) in these different tissues was tested using safranin-O staining and 1,9-dimethylmethylene blue assay.

RESULTS

The diffusion kinetics of CA4+ in auricular cartilage are significantly slower compared with all other cartilage types. Total GAG content per volume correlates to microCT attenuation with an R² value of 0.79 for all cartilage types. Three-dimensional contrast-enhanced microCT images of spatial GAG distribution reflect safranin-O staining and highlight the differences in ECM structure, with heterogeneous regions with higher GAG concentrations highlighted by the contrast agent.

CONCLUSIONS

CA4+-enhanced microCT enables assessment of 3-dimensiona distribution and GAG content in different types of cartilage and has promise as an ex vivo diagnostic technique to monitor matrix development in different tissues over time as well as tissue-engineered constructs.

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.

Effects of and Response to Mechanical Loading on the Knee

Mechanical loading to the knee joint results in a differential response based on the local capacity of the tissues (ligament, tendon, meniscus, cartilage, and bone) and how those tissues subsequently adapt to that load at the molecular and cellular level. Participation in cutting, pivoting, and jumping sports predisposes the knee to the risk of injury. In this narrative review, we describe different mechanisms of loading that can result in excessive loads to the knee, leading to ligamentous, musculotendinous, meniscal, and chondral injuries or maladaptations. Following injury (or surgery) to structures around the knee, the primary goal of rehabilitation is to maximize the patient's response to exercise at the current level of function, while minimizing the risk of re-injury to the healing tissue. Clinicians should have a clear understanding of the specific injured tissue(s), and rehabilitation should be driven by knowledge of tissue-healing constraints, knee complex and lower extremity biomechanics, neuromuscular physiology, task-specific activities involving weight-bearing and non-weight-bearing conditions, and training principles. We provide a practical application for prescribing loading progressions of exercises, functional activities, and mobility tasks based on their mechanical load profile to knee-specific structures during the rehabilitation process. Various loading interventions can be used by clinicians to produce physical stress to address body function, physical impairments, activity limitations, and participation restrictions. By modifying the mechanical load elements, clinicians can alter the tissue adaptations, facilitate motor learning, and resolve corresponding physical impairments. Providing different loads that create variable tensile, compressive, and shear deformation on the tissue through mechanotransduction and specificity can promote the appropriate stress adaptations to increase tissue capacity and injury tolerance. Tools for monitoring rehabilitation training loads to the knee are proposed to assess the reactivity of the knee joint to mechanical loading to monitor excessive mechanical loads and facilitate optimal rehabilitation.

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.

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.

Advances in biomechanical and biochemical engineering methods to stimulate meniscus tissue

Meniscal injuries can cause cartilage degeneration, which usually leads to the development of osteoarthritis (OA) and results in progressive destruction of the knee joint. Therefore, it is important to identify methods to stop or slow the development of OA after the onset of meniscal defects. The current surgical techniques for meniscal injuries are insufficient to prevent the progression of knee OA, which has accelerated the development of alternative tissue engineering strategies. Much progress has been made in the use of biomechanical and biochemical stimuli in the past decades to engineer neotissue akin to native meniscus. In this review, we focus on the current progress in biomechanical and biochemical stimuli-based strategies applied to meniscal tissue engineering, and explore how these factors influence meniscal regeneration. By understanding the functional mechanism that can stimulate regeneration in the meniscus, we hope that this review will provide a theoretical basis and strategies for meniscus tissue engineering.

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.

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.

Spaceflight and hind limb unloading induces an arthritic phenotype in knee articular cartilage and menisci of rodents

Reduced knee weight-bearing from prescription or sedentary lifestyles are associated with cartilage degradation; effects on the meniscus are unclear. Rodents exposed to spaceflight or hind limb unloading (HLU) represent unique opportunities to evaluate this question. This study evaluated arthritic changes in the medial knee compartment that bears the highest loads across the knee after actual and simulated spaceflight, and recovery with subsequent full weight-bearing. Cartilage and meniscal degradation in mice were measured via microCT, histology, and proteomics and/or biochemically after: (1) ~ 35 days on the International Space Station (ISS); (2) 13-days aboard the Space Shuttle Atlantis; or (3) 30 days of HLU, followed by a 49-day weight-bearing readaptation with/without exercise. Cartilage degradation post-ISS and HLU occurred at similar spatial locations, the tibial-femoral cartilage-cartilage contact point, with meniscal volume decline. Cartilage and meniscal glycosaminoglycan content were decreased in unloaded mice, with elevated catabolic enzymes (e.g., matrix metalloproteinases), and elevated oxidative stress and catabolic molecular pathway responses in menisci. After the 13-day Shuttle flight, meniscal degradation was observed. During readaptation, recovery of cartilage volume and thickness occurred with exercise. Reduced weight-bearing from either spaceflight or HLU induced an arthritic phenotype in cartilage and menisci, and exercise promoted recovery.

Shear wave elastography of the knee menisci

OBJECTIVE

To determine the ability of shear wave elastography to measure the stiffness of the knee menisci in healthy adults.

METHODS

This observational cross-sectional study evaluated knee joints in healthy adults. Shear wave elastography was used to evaluate the anterior horn of the medial menisci bilaterally. The correlations between the mean elasticity bilaterally and age, weight, height and body mass index (BMI) were calculated using Pearson's correlation coefficient test.

RESULTS

A total of 34 knee joints in 17 healthy subjects were evaluated. The mean ± SD shear elastic modulus of the anterior horn of the right medial meniscus was 24.86 ± 6.35 kPa and of the anterior horn of the left medial meniscus was 23.86 ± 4.49 kPa. A significant inverse correlation was observed between the right medial meniscus elasticity and height. Other demographic factors showed no significant relationship to the anterior horn of the right medial meniscus elasticity. A significant inverse correlation was observed between the anterior horn of the left medial meniscus elasticity and age, while a significant positive correlation was observed between left medial meniscus elasticity and BMI.

CONCLUSION

These preliminary results suggest that shear wave elastography could be a potential tool to aid in studying the stiffness of the knee menisci.

Finite element analysis of biomechanical effects of residual varus/valgus malunion after femoral fracture on knee joint

OBJECTIVE

Post-operative femoral shaft fractures are often accompanied by a residual varus/valgus deformity, which can result in osteoarthritis in severe cases. The purpose of this study was to investigate the biomechanical effects of residual varus/valgus deformities after middle and lower femoral fracture on the stress distribution and contact area of knee joint.

METHODS

Thin-slice CT scanning of lower extremities and MRI imaging of knee joints were obtained from a healthy adult male to establish normal lower limb model (neutral position). Then, the models of 3°, 5°, and 10° of varus/valgus were established respectively by modifying middle and lower femur of normal model. To validate the modifying, a patient-specific model, whose BMI was same to former and had 10° of varus deformity of tibia, was built and simulated under the same boundary conditions.

RESULT

The contact area and maximum stress of modified models were similar to those of patient-specific model. The contact area and maximum stress of medial tibial cartilage in normal neutral position were 244.36 mm² and 0.64 MPa, while those of lateral were 196.25 mm² and 0.76 MPa. From 10° of valgus neutral position to 10° of varus, the contact area and maximum stress of medial tibial cartilage increased, and the lateral gradually decreased. The contact area and maximum stress of medial meniscus in normal neutral position were 110.91 mm² and 3.24 MPa, while those of lateral were 135.83 mm² and 3.45 MPa. The maximum stress of medial tibia subchondral bone in normal neutral position was 1.47 MPa, while that of lateral was 0.65 MPa. The variation trend of medial/lateral meniscus and subchondral bone was consistent with that of tibial plateau cartilage in the contact area and maximum stress.

CONCLUSION

This study suggested that varus/valgus deformity of femur had an obvious effect on the contact area and stress distribution of knee joint, providing biomechanical evidence and deepening understanding when performing orthopedic trauma surgery or surgical correction of the already existing varus/valgus deformity.

Moderate mechanical stimulation rescues degenerative annulus fibrosus by suppressing caveolin-1 mediated pro-inflammatory signaling pathway

Mechanical loading can induce or antagonize the extracellular matrix (ECM) synthesis, proliferation, migration, and inflammatory responses of annulus fibrosus cells (AFCs), depending on the loading mode and level. Caveolin-1 (Cav1), the core protein of caveolae, plays an important role in cellular mechanotransduction and inflammatory responses. In the present study, we presented that AFCs demonstrated different behaviors when subjected to cyclic tensile strain (CTS) for 24 h at a magnitude of 0%, 2%, 5% and 12%, respectively. It was found that 5% CTS had positive effects on cell proliferation, migration and anabolism, while 12% CTS had the opposite effects. Besides, cells exposed to interleukin-1β stimulus exhibited an increase expression in inflammatory genes, and the expression of these genes decreased after exposure to moderate mechanical loading with 5% CTS. In addition, 5% CTS decreased the level of Cav1 and integrin β1 and exhibited anti-inflammatory effects. Moreover, the expression of integrin β1 and p-p65 increased in AFCs transfected with Cav1 plasmids. In vivo results revealed that moderate mechanical stimulation could recover the water content and morphology of the discs. In conclusion, moderate mechanical stimulation restrained Cav1-mediated signaling pathway and exhibited anti-inflammatory effects on AFCs. Together with in vivo results, this study expounds the underlying molecular mechanisms on the effect of moderate mechanical stimulation on intervertebral discs (IVDs) and may provide a new therapeutic strategy for the treatment of IVD degeneration.

Engineered human meniscus' matrix-forming phenotype is unaffected by low strain dynamic compression under hypoxic conditions

Low oxygen and mechanical loading may play roles in regulating the fibrocartilaginous phenotype of the human inner meniscus, but their combination in engineered tissues remains unstudied. Here, we investigated how continuous low oxygen (“hypoxia”) combined with dynamic compression would affect the fibrocartilaginous “inner meniscus-like” matrix-forming phenotype of human meniscus fibrochondrocytes (MFCs) in a porous type I collagen scaffold. Freshly-seeded MFC scaffolds were cultured for 4 weeks in either 3 or 20% O₂ or pre-cultured for 2 weeks in 3% O₂ and then dynamically compressed for 2 weeks (10% strain, 1 Hz, 1 h/day, 5 days/week), all with or without TGF-β3 supplementation. TGF-β3 supplementation was found necessary to induce matrix formation by MFCs in the collagen scaffold regardless of oxygen tension and application of the dynamic compression loading regime. Neither hypoxia under static culture nor hypoxia combined with dynamic compression had significant effects on expression of specific protein and mRNA markers for the fibrocartilaginous matrix-forming phenotype. Mechanical properties significantly increased over the two-week loading period but were not different between static and dynamic-loaded tissues after the loading period. These findings indicate that 3% O₂ applied immediately after scaffold seeding and dynamic compression to 10% strain do not affect the fibrocartilaginous matrix-forming phenotype of human MFCs in this type I collagen scaffold. It is possible that a delayed hypoxia treatment and an optimized pre-culture period and loading regime combination would have led to different outcomes.

Nuclear envelope wrinkling predicts mesenchymal progenitor cell mechano-response in 2D and 3D microenvironments

Exogenous mechanical cues are transmitted from the extracellular matrix to the nuclear envelope (NE), where mechanical stress on the NE mediates shuttling of transcription factors and other signaling cascades that dictate downstream cellular behavior and fate decisions. To systematically study how nuclear morphology can change across various physiologic microenvironmental contexts, we cultured mesenchymal progenitor cells (MSCs) in engineered 2D and 3D hyaluronic acid hydrogel systems. Across multiple contexts we observed highly 'wrinkled' nuclear envelopes, and subsequently developed a quantitative single-cell imaging metric to better evaluate how wrinkles in the nuclear envelope relate to progenitor cell mechanotransduction. We determined that in soft 2D environments the NE is predominately wrinkled, and that increases in cellular mechanosensing (indicated by cellular spreading, adhesion complex growth, and nuclear localization of YAP/TAZ) occurred only in absence of nuclear envelope wrinkling. Conversely, in 3D hydrogel and tissue contexts, we found NE wrinkling occurred along with increased YAP/TAZ nuclear localization. We further determined that these NE wrinkles in 3D were largely generated by actin impingement, and compared to other nuclear morphometrics, the degree of nuclear wrinkling showed the greatest correlation with nuclear YAP/TAZ localization. These findings suggest that the degree of nuclear envelope wrinkling can predict mechanotransduction state in mesenchymal progenitor cells and highlights the differential mechanisms of NE stress generation operative in 2D and 3D microenvironmental contexts.

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.

Driving Hierarchical Collagen Fiber Formation for Functional Tendon, Ligament, and Meniscus Replacement

Hierarchical collagen fibers are the primary source of strength in musculoskeletal tendons, ligaments, and menisci. It has remained a challenge to develop these large fibers in engineered replacements or in vivo after injury. The objective of this study was to investigate the ability of restrained cell-seeded high density collagen gels to drive hierarchical fiber formation for multiple musculoskeletal tissues. We found boundary conditions applied to high density collagen gels were capable of driving tenocytes, ligament fibroblasts, and meniscal fibrochondrocytes to develop native-sized hierarchical collagen fibers 20-40 μm in diameter. The fibers organize similar to bovine juvenile collagen with native fibril banding patterns and hierarchical fiber bundles 50-350 μm in diameter by 6 weeks. Mirroring fiber organization, tensile properties of restrained samples improved significantly with time, reaching ~1 MPa. Additionally, tendon, ligament, and meniscal cells produced significantly different sized fibers, different degrees of crimp, and different GAG concentrations, which corresponded with respective juvenile tissue. To our knowledge, these are some of the largest, most organized fibers produced to date in vitro. Further, cells produced tissue specific hierarchical fibers, suggesting this system is a promising tool to better understand cellular regulation of fiber formation to better stimulate it in vivo after injury.

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.

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

Purpose

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

Methods

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

Results

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

Conclusions

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

Level of Evidence

Level III, retrospective cohort study.

Small medial femoral condyle morphotype is associated with medial compartment degeneration and distinct morphological characteristics: a comparative pilot study

PURPOSE

Early-onset degeneration of the knee is linked to genetics, overload, injury, and potentially, knee morphology. The purpose of this study is to explore the characteristics of the small medial femoral condyle, as a distinct knee morphotype, by means of a landmark-based three-dimensional (3D) analysis and statistical parametric mapping.

METHODS

Sixteen knees with a small medial femoral condyle (SMC) were selected from a database of patients with distinct knee joint anatomy and 16 gender-matched knees were selected from a control group database. 3D models were generated from the medical imaging. After normalization for size, a set of pre-defined landmark-based parameters was analysed for the femur and tibia. Local shape differences were evaluated by matching all bone surfaces onto each other and comparing the distances to the mean control group bone shape.

RESULTS

The small medial condyle group showed a significant association with medial compartment degeneration and had a 4% and 13% smaller medial condyle anteroposteriorly and mediolaterally, whereas the distal femur was 3% wider mediolaterally. The lateral condyle was 2% smaller anteroposteriorly and 8% wider mediolaterally. The complete tibial plateau was 3% smaller mediolaterally and the medial tibial plateau was 6% smaller.

CONCLUSION

A new knee morphotype demonstrated an increased risk for medial compartment degeneration and was differentiated from a healthy control group based on the following morphological characteristics: a smaller medial femoral condyle and medial tibial plateau, a wider lateral femoral condyle and a wider distal femur on a smaller tibial plateau. This pilot study suggests a role for the SMC knee morphotype in the multifactorial process of medial compartment degeneration.

LEVEL OF EVIDENCE

III.

Exercise as an Adjuvant to Cartilage Regeneration Therapy

This article provides a brief review of the pathophysiology of osteoarthritis and the ontogeny of chondrocytes and details how physical exercise improves the health of osteoarthritic joints and enhances the potential of autologous chondrocyte implants, matrix-induced autologous chondrocyte implants, and mesenchymal stem cell implants for the successful treatment of damaged articular cartilage and subchondral bone. In response to exercise, articular chondrocytes increase their production of glycosaminoglycans, bone morphogenic proteins, and anti-inflammatory cytokines and decrease their production of proinflammatory cytokines and matrix-degrading metalloproteinases. These changes are associated with improvements in cartilage organization and reductions in cartilage degeneration. Studies in humans indicate that exercise enhances joint recruitment of bone marrow-derived mesenchymal stem cells and upregulates their expression of osteogenic and chondrogenic genes, osteogenic microRNAs, and osteogenic growth factors. Rodent experiments demonstrate that exercise enhances the osteogenic potential of bone marrow-derived mesenchymal stem cells while diminishing their adipogenic potential, and that exercise done after stem cell implantation may benefit stem cell transplant viability. Physical exercise also exerts a beneficial effect on the skeletal system by decreasing immune cell production of osteoclastogenic cytokines interleukin-1β, tumor necrosis factor-α, and interferon-γ, while increasing their production of antiosteoclastogenic cytokines interleukin-10 and transforming growth factor-β. In conclusion, physical exercise done both by bone marrow-derived mesenchymal stem cell donors and recipients and by autologous chondrocyte donor recipients may improve the outcome of osteochondral regeneration therapy and improve skeletal health by downregulating osteoclastogenic cytokine production and upregulating antiosteoclastogenic cytokine production by circulating immune cells.

Efficacy of Arthroscopic Treatment for Concurrent Medial Meniscus Posterior Horn and Lateral Meniscus Anterior Horn Injury: A Retrospective Single Center Study

Objective

To investigate the effectiveness of arthroscopic surgery for combined tears of the posterior horn of the medial meniscus (PHMM) and the anterior horn of the lateral meniscus (AHLM).

Methods

Between September 2009 and December 2013, a retrospective investigation was performed on 48 patients (48 knees) with combined tears of PHMM and AHLM who underwent arthroscopic surgery. All patients underwent magnetic resonance imaging (MRI) diagnosis in the outpatient department. After admission, other basic examinations were performed. PHMM was treated with partial meniscectomy and AHLM was treated with external–internal suture or partial meniscectomy. Curative effect was evaluated according to Lysholm score and IKDC score. The differences of the functions as well as Lysholm and IKDC scores pre‐ and postoperatively were compared, while the diagnostic accuracy of MRI and arthroscopy for PHMM and AHLM were compared.

Results

Seven patients with combined tears of PHMM and AHLM were misdiagnosed during MRI examination when arthroscopy was used as the gold standard. All patients were followed up for an average of 34.58 months (range 10–52 months) and all incisions healed by first intention with no obvious complication. The preoperative and postoperative Lysholm scores were 47.22 ± 2.77 and 87.36 ± 5.45, respectively. The IKDC scores are 54.73 ± 4.65 preoperatively and 89.62 ± 3.71 postoperatively. The positive rates of the diagnosis through MRI and arthroscopic surgery is 85.42% and 100%, respectively. At the last follow‐up, the patients had no pain, weakness, and instability, and tenderness in medial and lateral joint space disappeared. Mcmurray test was weakly positive in four patients. Excellent outcome was achieved in 39 cases, and a good outcome was achieved in five cases; the good to excellent rate was 91.67%.

Conclusion

MRI examination of combined tears of PHMM and AHLM may result in misdiagnosis. Arthroscopic primary repair seemed to be an effective surgical option for treatment of combined tears of PHMM and AHLM.