Knee joint immobilization decreases aggrecan gene expression in 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.

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.

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.

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.

Explant models for meniscus metabolism, injury, repair, and healing

Purpose/Aim: Knee meniscus is a wedge-shaped fibrocartilaginous tissue, playing important roles in maintaining joint stability and function. Injuries to the meniscus, particularly with the avascular inner third zone, hardly heal and frequently progress into structural breakdown, followed by the initiation of osteoarthritis. As the importance of meniscus in joint function and diseases is being recognized, the field of meniscus research is growing. Not only development, biology, and metabolism but also injury, repair, and healing of meniscus are being actively investigated. As meniscus functions as an integrated unit of a knee joint, in vivo models with various species have been the predominant method for studying meniscus pathophysiology and for testing healing/regeneration strategies. However, in vivo models for meniscus studies suffer from low reproducibility and high cost. To complement the limitations of in vivo animal models, several types of meniscus explants have been applied as highly controlled, standardized in vitro models to investigate meniscus metabolism, pathophysiology, and repair or regeneration process. This review summarizes and compares the existing meniscus explant models. We also discuss the advantages and disadvantages of each explant model.Conclusion: Despite few outstanding challenges, meniscus explant models have potential to serve as an effective tool for investigations of meniscus metabolism, injury, repair and healing.

Knee and Hip Joint Cartilage Damage from Combined Spaceflight Hazards of Low-Dose Radiation Less than 1 Gy and Prolonged Hindlimb Unloading

Reduced weight bearing, and to a lesser extent radiation, during spaceflight have been shown as potential hazards to astronaut joint health. These hazards combined effect to the knee and hip joints are not well defined, particularly with low-dose exposure to radiation. In this study, we examined the individual and combined effects of varying low-dose radiation (≤1 Gy) and reduced weight bearing on the cartilage of the knee and hip joints. C57BL/6J mice (n = 80) were either tail suspended via hindlimb unloading (HLU) or remained full-weight bearing (ground). On day 6, each group was divided and irradiated with 0 Gy (sham), 0.1 Gy, 0.5 Gy or 1.0 Gy (n = 10/group), yielding eight groups: ground-sham; ground-0.1 Gy; ground-0.5 Gy; ground-1.0 Gy; HLU-sham; HLU-0.1 Gy; HLU-0.5 Gy; and HLU-1.0 Gy. On day 30, the hindlimbs, hip cartilage and serum were collected from the mice. Significant differences were identified statistically between treatment groups and the ground-sham control group, but no significant differences were observed between HLU and/or radiation groups. Contrast-enhanced micro-computed tomography (microCECT) demonstrated decrease in volume and thickness at the weight-bearing femoral-tibial cartilage-cartilage contact point in all treatment groups compared to ground-sham. Lower collagen was observed in all groups compared to ground-sham. Circulating serum cartilage oligomeric matrix protein (sCOMP), a biomarker for ongoing cartilage degradation, was increased in all of the irradiated groups compared to ground-sham, regardless of unloading. Mass spectrometry of the cartilage lining the femoral head and subsequent Ingenuity Pathway Analysis (IPA) identified a decrease in cartilage compositional proteins indicative of osteoarthritis. Our findings demonstrate that both individually and combined, HLU and exposure to spaceflight relevant radiation doses lead to cartilage degradation of the knee and hip with expression of an arthritic phenotype. Moreover, early administration of low-dose irradiation (0.1, 0.5 or 1.0 Gy) causes an active catabolic response in cartilage 24 days postirradiation. Further research is warranted with a focus on the prevention of cartilage degradation from long-term periods of reduced weight bearing and spaceflight-relevant low doses and qualities of radiation.

Biomechanical Stimulus Based Strategies for Meniscus Tissue Engineering and Regeneration

Meniscus injuries are very common in the knee joint. Treating a damaged meniscus continues to be a scientific challenge in sport medicine because of its poor self-healing potential and few clinical therapeutic options. Tissue engineering strategies are very promising solutions for repairing and regenerating a damaged meniscus. Meniscus is exposed to a complex biomechanical microenvironment, and it plays a crucial role in meniscal development, growth, and repairing. Over the past decades, increasing attention has been focused on the use of biomechanical stimulus to enhance biomechanical properties of the engineered meniscus. Further understanding the influence of mechanical stimulation on cell proliferation and differentiation, metabolism, relevant gene expression, and pro/anti-inflammatory responses may be beneficial to enhance meniscal repair and regeneration. On the one hand, this review describes some basic information about meniscus; on the other hand, we sum up the various biomechanical stimulus based strategies applied in meniscus tissue engineering and how these factors affect meniscal regeneration. We hope this review will provide researchers with inspiration on tissue engineering strategies for meniscus regeneration in the future.

Mechanoadaptation: articular cartilage through thick and thin

The articular cartilage is exquisitely sensitive to mechanical load. Its structure is largely defined by the mechanical environment and destruction in osteoarthritis is the pathophysiological consequence of abnormal mechanics. It is often overlooked that disuse of joints causes profound loss of volume in the articular cartilage, a clinical observation first described in polio patients and stroke victims. Through the 1980s, the results of studies exploiting experimental joint immobilisation supported this. Importantly, this substantial body of work was also the first to describe metabolic changes that resulted in decreased synthesis of matrix molecules, especially sulfated proteoglycans. The molecular mechanisms that underlie disuse atrophy are poorly understood despite the identification of multiple mechanosensing mechanisms in cartilage. Moreover, there has been a tendency to equate cartilage loss with osteoarthritic degeneration. Here, we review the historic literature and clarify the structural, metabolic and clinical features that clearly distinguish cartilage loss due to disuse atrophy and those due to osteoarthritis. We speculate on the molecular sensing pathways in cartilage that may be responsible for cartilage mechanoadaptation.

Mechanobiology of the meniscus

The meniscus plays a critical biomechanical role in the knee, providing load support, joint stability, and congruity. Importantly, growing evidence indicates that the mechanobiologic response of meniscal cells plays a critical role in the physiologic, pathologic, and repair responses of the meniscus. Here we review experimental and theoretical studies that have begun to directly measure the biomechanical effects of joint loading on the meniscus under physiologic and pathologic conditions, showing that the menisci are exposed to high contact stresses, resulting in a complex and nonuniform stress-strain environment within the tissue. By combining microscale measurements of the mechanical properties of meniscal cells and their pericellular and extracellular matrix regions, theoretical and experimental models indicate that the cells in the meniscus are exposed to a complex and inhomogeneous environment of stress, strain, fluid pressure, fluid flow, and a variety of physicochemical factors. Studies across a range of culture systems from isolated cells to tissues have revealed that the biological response of meniscal cells is directly influenced by physical factors, such as tension, compression, and hydrostatic pressure. In addition, these studies have provided new insights into the mechanotransduction mechanisms by which physical signals are converted into metabolic or pro/anti-inflammatory responses. Taken together, these in vivo and in vitro studies show that mechanical factors play an important role in the health, degeneration, and regeneration of the meniscus. A more thorough understanding of the mechanobiologic responses of the meniscus will hopefully lead to therapeutic approaches to prevent degeneration and enhance repair of the meniscus.

Chronic changes in the articular cartilage and meniscus following traumatic impact to the lapine knee

The objective of this study was to induce anterior cruciate ligament (ACL) and meniscal damage, via a single tibiofemoral compressive impact, in order to document articular cartilage and meniscal changes post-impact. Tibiofemoral joints of Flemish Giant rabbits were subjected to a single blunt impact that ruptured the ACL and produced acute meniscal damage. Animals were allowed unrestricted cage activity for 12 weeks before euthanasia. India ink analysis of the articular cartilage revealed higher degrees of surface damage on the impacted tibias (p=0.018) and femurs (p<0.0001) compared to controls. Chronic meniscal damage was most prevalent in the medial central and medial posterior regions. Mechanical tests revealed an overall 19.4% increase in tibial plateau cartilage thickness (p=0.026), 34.8% increase in tibial plateau permeability (p=0.054), 40.8% increase in femoral condyle permeability (p=0.029), and 20.1% decrease in femoral condyle matrix modulus (p=0.012) in impacted joints compared to controls. Both instantaneous and equilibrium moduli of the lateral and medial menisci were decreased compared to control (p<0.02). Histological analyses revealed significantly increased presence of fissures in the medial femur (p=0.036). In both meniscus and cartilage there was a significant decrease in GAG coverage for the impacted limbs. Based on these results it is clear that an unattended combined meniscal and ACL injury results in significant changes to the soft tissues in this experimental joint 12 weeks post-injury. Such changes are consistent with a clinical description of mid to late stage PTOA of the knee.

Decreased hypertrophic differentiation accompanies enhanced matrix formation in co-cultures of outer meniscus cells with bone marrow mesenchymal stromal cells

Introduction

The main objective of this study was to determine whether meniscus cells from the outer (MCO) and inner (MCI) regions of the meniscus interact similarly to or differently with mesenchymal stromal stem cells (MSCs). Previous study had shown that co-culture of meniscus cells with bone marrow-derived MSCs result in enhanced matrix formation relative to mono-cultures of meniscus cells and MSCs. However, the study did not examine if cells from the different regions of the meniscus interacted similarly to or differently with MSCs.

Methods

Human menisci were harvested from four patients undergoing total knee replacements. Tissue from the outer and inner regions represented pieces taken from one third and two thirds of the radial distance of the meniscus, respectively. Meniscus cells were released from the menisci after collagenase treatment. Bone marrow MSCs were obtained from the iliac crest of two patients after plastic adherence and in vitro culture until passage 2. Primary meniscus cells from the outer (MCO) or inner (MCI) regions of the meniscus were co-cultured with MSCs in three-dimensional (3D) pellet cultures at 1:3 ratio, respectively, for 3 weeks in the presence of serum-free chondrogenic medium containing TGF-β1. Mono-cultures of MCO, MCI and MSCs served as experimental control groups. The tissue formed after 3 weeks was assessed biochemically, histochemically and by quantitative RT-PCR.

Results

Co-culture of inner (MCI) or outer (MCO) meniscus cells with MSCs resulted in neo-tissue with increased (up to 2.2-fold) proteoglycan (GAG) matrix content relative to tissues formed from mono-cultures of MSCs, MCI and MCO. Co-cultures of MCI or MCO with MSCs produced the same amount of matrix in the tissue formed. However, the expression level of aggrecan was highest in mono-cultures of MSCs but similar in the other four groups. The DNA content of the tissues from co-cultured cells was not statistically different from tissues formed from mono-cultures of MSCs, MCI and MCO. The expression of collagen I (COL1A2) mRNA increased in co-cultured cells relative to mono-cultures of MCO and MCI but not compared to MSC mono-cultures. Collagen II (COL2A1) mRNA expression increased significantly in co-cultures of both MCO and MCI with MSCs compared to their own controls (mono-cultures of MCO and MCI respectively) but only the co-cultures of MCO:MSCs were significantly increased compared to MSC control mono-cultures. Increased collagen II protein expression was visible by collagen II immuno-histochemistry. The mRNA expression level of Sox9 was similar in all pellet cultures. The expression of collagen × (COL10A1) mRNA was 2-fold higher in co-cultures of MCI:MSCs relative to co-cultures of MCO:MSCs. Additionally, other hypertrophic genes, MMP-13 and Indian Hedgehog (IHh), were highly expressed by 4-fold and 18-fold, respectively, in co-cultures of MCI:MSCs relative to co-cultures of MCO:MSCs.

Conclusions

Co-culture of primary MCI or MCO with MSCs resulted in enhanced matrix formation. MCI and MCO increased matrix formation similarly after co-culture with MSCs. However, MCO was more potent than MCI in suppressing hypertrophic differentiation of MSCs. These findings suggest that meniscus cells from the outer-vascular regions of the meniscus can be supplemented with MSCs in order to engineer functional grafts to reconstruct inner-avascular meniscus.

Histological examination of collagen and proteoglycan changes in osteoarthritic menisci

This study sought to examine collagen and proteoglycan changes in the menisci of patients with osteoarthritis (OA). Collagens were examined using picrosirius red, and hematoxylin and eosin. Proteoglycans were examined using safranin-O and alcian blue. Types I and II collagens and aggrecan were examined using immunochemistry. Severe loss of collagens was observed to occur in OA menisci, particularly in the middle and deep zones and collagen networks were less organized than those of normal menisci. In contrast, proteoglycan staining in the middle and deep zones of OA meniscus increased compared to normal control menisci. Immunohistochemistry indicated that types I and II collagens were co-localized and the loss of types I collagen in OA menisci appeared more severe in the middle and deep zones than that in the surface zones. The loss of type II collagen however was severe across all three zones. Immunohistochemistry also indicated elevated aggrecan staining in OA menisci. These findings together indicate that severe loss of collagens and intrameniscal degeneration are hallmarks of OA menisci and that extracellular matrix degeneration occurred in OA menisci follows a pathway different from that occurred in OA articular cartilage. These findings are not only important for a better understanding of the disease process but also important for the development of novel structure-modifying drugs for OA therapy.

Biological basis of exercise-based treatments for musculoskeletal conditions

Exercise-based therapies are the cornerstone of rehabilitation programs. While the benefits of exercise on systemic and tissue function are generally accepted, mechanisms underlying these benefits are sometimes poorly understood. An improved understanding of the effects of mechanical loading on molecular and cellular processes has the potential to lead to more disease-specific and efficacious exercise-based therapies. The purpose of this paper is to review the current literature examining the role of mechanical signaling on muscle and cartilage biology.

Meniscal tissue explants response depends on level of dynamic compressive strain

OBJECTIVE

Following partial meniscectomy, the remaining meniscus is exposed to an altered loading environment. In vitro 20% dynamic compressive strains on meniscal tissue explants has been shown to lead to an increase in release of glycosaminoglycans from the tissue and increased expression of interleukin-1alpha (IL-1alpha). The goal of this study was to determine if compressive loading which induces endogenously expressed IL-1 results in downstream changes in gene expression of anabolic and catabolic molecules in meniscal tissue, such as MMP expression.

METHOD

Relative changes in gene expression of MMP-1, MMP-3, MMP-9, MMP-13, A Disintegrin and Metalloproteinase with ThromboSpondin 4 (ADAMTS4), ADAMTS5, TNFalpha, TGFbeta, COX-2, Type I collagen (COL-1) and aggrecan and subsequent changes in the concentration of prostaglandin E(2) released by meniscal tissue in response to varying levels of dynamic compression (0%, 10%, and 20%) were measured. Porcine meniscal explants were dynamically compressed for 2h at 1Hz.

RESULTS

20% dynamic compressive strains upregulated MMP-1, MMP-3, MMP-13 and ADAMTS4 compared to no dynamic loading. Aggrecan, COX-2, and ADAMTS5 gene expression were upregulated under 10% strain compared to no dynamic loading while COL-1, TIMP-1, and TGFbeta gene expression were not dependent on the magnitude of loading.

CONCLUSION

This data suggests that changes in mechanical loading of the knee joint meniscus from 10% to 20% dynamic strain can increase the catabolic activity of the meniscus.

IL-1 and iNOS gene expression and NO synthesis in the superior region of meniscal explants are dependent on the magnitude of compressive strains

OBJECTIVE

Partial meniscectomy is known to cause osteoarthritis (OA) of the underlying cartilage as well as alter the load on the remaining meniscus. Removal of 30-60% of the medial meniscus increases compressive strains from a maximum of approximately 10% to almost 20%. The goal of this study is to determine if meniscal cells produce catabolic molecules in response to the altered loading that results from a partial meniscectomy.

METHOD

Relative changes in gene expression of interleukin-1 (IL-1), inducible nitric oxide synthase (iNOS) and subsequent changes in the concentration of nitric oxide (NO) released by meniscal tissue in response to compression were measured. Porcine meniscal explants were dynamically compressed for 2 h at 1 Hz to simulate physiological stimulation at either 10% strain or 0.05 MPa stress. Additional explants were pathologically stimulated to either 0% strain, 20% strain or, 0.1 MPa stress.

RESULTS

iNOS and IL-1 gene expression and NO release into the surrounding media were increased at 20% compressive strain compared to other conditions. Pathological unloading (0% compressive strain) of meniscal explants did not significantly change expression of IL-1 or iNOS genes, but did result in an increased amount of NO released compared to physiological strain of 10%.

CONCLUSION

These data suggest that meniscectomies which reduce the surface area of the meniscus by 30-60% will increase the catabolic activity of the meniscus which may contribute to the progression of OA.

Transfer of macroscale tissue strain to microscale cell regions in the deformed meniscus

Cells within fibrocartilaginous tissues, including chondrocytes and fibroblasts of the meniscus, ligament, and tendon, regulate cell biosynthesis in response to local mechanical stimuli. The processes by which an applied mechanical load is transferred through the extracellular matrix to the environment of a cell are not fully understood. To better understand the role of mechanics in controlling cell phenotype and biosynthetic activity, this study was conducted to measure strain at different length scales in tissue of the fibrocartilaginous meniscus of the knee joint, and to define a quantitative parameter that describes the strain transferred from the far-field tissue to a microenvironment surrounding a cell. Experiments were performed to apply a controlled uniaxial tensile deformation to explants of porcine meniscus containing live cells. Using texture correlation analyses of confocal microscopy images, two-dimensional Lagrangian and principal strains were measured at length scales representative of the tissue (macroscale) and microenvironment in the region of a cell (microscale) to yield a strain transfer ratio as a measure of median microscale to macroscale strain. The data demonstrate that principal strains at the microscale are coupled to and amplified from macroscale principal strains for a majority of cell microenvironments located across diverse microstructural regions, with average strain transfer ratios of 1.6 and 2.9 for the maximum and minimum principal strains, respectively. Lagrangian strain components calculated along the experimental axes of applied deformations exhibited considerable spatial heterogeneity and intersample variability, and suggest the existence of both strain amplification and attenuation. This feature is consistent with an in-plane rotation of the principal strain axes relative to the experimental axes at the microscale that may result from fiber sliding, fiber twisting, and fiber-matrix interactions that are believed to be important for regulating deformation in other fibrocartilaginous tissues. The findings for consistent amplification of macroscale to microscale principal strains suggest a coordinated pattern of strain transfer from applied deformation to the microscale environment of a cell that is largely independent of these microstructural features in the fibrocartilaginous meniscus.

Nitric oxide synthase and cyclooxygenase interactions in cartilage and meniscus: relationships to joint physiology, arthritis, and tissue repair

Rheumatoid arthritis and osteoarthritis are painful and debilitating diseases with complex pathophysiology. There is growing evidence that pro-inflammatory cytokines (e.g., interleukin-1 and tumor necrosis factor alpha) and mediators (e.g., prostaglandins, leukotrienes, and nitric oxide) play critical roles in the development and perpetuation of tissue inflammation and damage in joint tissues such as articular cartilage and meniscus. While earlier studies have generally focused on cells of the synovium (especially macrophages), there is increasing evidence that chondrocytes and meniscal cells actively contribute to inflammatory processes. In particular, it is now apparent that mechanical forces engendered by joint loading are transduced to biological signals at the cellular level and that these signals modulate gene expression and biochemical processes. Here we give an overview of the interplay of cytokines and mechanical stress in the production of cyclooxygenases and prostaglandins; lipoxygenases and leukotrienes; and nitric oxide synthases and nitric oxide in arthritis, with particular focus on the interactions of these pathways in articular cartilage and meniscus.

Proteoglycan breakdown of meniscal explants following dynamic compression using a novel bioreactor

Motivated by our interest in examining meniscal mechanotransduction processes, we report on the validation of a new tissue engineering bioreactor. This paper describes the design and performance capabilities of a tissue engineering bioreactor for cyclic compression of meniscal explants. We showed that the system maintains a tissue culture environment equivalent to that provided by conventional incubators and that its strain output was uniform and reproducible. The system incorporates a linear actuator and load cell aligned together in a frame that is contained within an incubator and allows for large loads and small displacements. A plunger with six Teflon-filled Delrin compression rods is attached to the actuator compressing up to six tissue explants simultaneously and with even pressure. The bioreactor system was used to study proteoglycan (PG) breakdown in porcine meniscal explants following various input loading tests (0–20% strain, 0–0.1 MPa). The greatest PG breakdown was measured following 20% compressive strain. These strain and stress levels have been shown to correspond to partial meniscectomy. Thus, these data suggest that removing 30–60% of meniscal tissue will result in the breakdown of meniscal tissue proteoglycans.

Role of cell location and morphology in the mechanical environment around meniscal cells

Fibrochondrocytes within meniscal tissue have been shown to alter their biochemical activity in response to changes in their mechanical environment. Meniscal tissue is known to contain both spherical (chondrocytic-like) and elliptical (fibroblastic-like) cells. We hypothesize that a cell's mechanical environment is governed by local material properties of the tissue around the cell, the cell morphology and the cell's position within the tissue. A two-dimensional, non-linear, fiber (collagen) reinforced, multi-scale, finite element model was utilized to quantify changes in the stress, strain, fluid velocity and fluid flow induced shear stress (FFISS) within and around fibrochondrocytes. Cells differing in morphology and size were modeled at different locations within an explant 6mm in diameter and 5mm thick, under 5% unconfined compression. Cellular stresses were an order of magnitude less than surrounding extracellular matrix stresses but cellular strains were higher. Cell size affected both the stress and strain levels within the cell, with smaller cells being exposed to smaller principal stresses and strains than larger cells of the same shape. The pericellular matrix of an elliptical cell was less effective at shielding the cell from large principal strains and stresses. FFISS were largest around small circular cells ( approximately 0.13Pa), and were dramatically affected by the position of the cell relative to the axis of the explant, with cells closer to the periphery experiencing greater FFISS than cells near the central axis of the explant. These results will allow biosynthetic activity of fibrochondrocytes to be correlated with position and morphology in the future.

A Direct Compression Stimulator for Articular Cartilage and Meniscal Explants

This paper describes the development and use of a direct compression stimulator for culturing explants from the meniscus of the knee and articular cartilage. Following design and fabrication of the instrument along with its data acquisition system, the function of the machine was verified by both mechanical means and tissue effect. The loading chamber can hold up to 45 5 mm diameter samples. While designed to stimulate samples up to 4 mm thick, axial displacements as little as 0.127 microm are within the theoretical capacity of the stimulator. In gene expression studies, collagen II and aggrecan expression were examined in explants from articular cartilage as well as medial and lateral menisci subjected to dynamic stimulation and static compression. These results were then compared to free swelling samples. It was found that static compression to cut thickness down-regulated aggrecan and collagen II expression in articular cartilage explants compared to free swelling controls by 94% and 90%, respectively. The application of a dynamic, intermittent, 2% oscillation around the cut thickness returned expression levels to those of free swelling controls at 4 h but not at 76 h. In medial meniscus samples, dynamic compression up-regulated aggrecan expression by 108%, but not collagen II expression, at 4 and 76 h compared to static controls. No difference in gene expression was observed for lateral meniscal explants. Thus, effects of direct compression seen in articular cartilage may not necessarily translate to the knee meniscus. The design of this stimulator will allow a variety of tissues and loading regimens to be examined. It is hoped that regimens can be found that not only return samples to the production levels of free swelling controls, but also surpass them in terms of gene expression, protein synthesis, and functional properties.

The matrix-forming phenotype of cultured human meniscus cells is enhanced after culture with fibroblast growth factor 2 and is further stimulated by hypoxia

Human meniscus cells have a predominantly fibrogenic pattern of gene expression, but like chondrocytes they proliferate in monolayer culture and lose the expression of type II collagen. We have investigated the potential of human meniscus cells, which were expanded with or without fibroblast growth factor 2 (FGF2), to produce matrix in three-dimensional cell aggregate cultures with a chondrogenic medium at low (5%) and normal (20%) oxygen tension. The presence of FGF2 during the expansion of meniscus cells enhanced the re-expression of type II collagen 200-fold in subsequent three-dimensional cell aggregate cultures. This was increased further (400-fold) by culture in 5% oxygen. Cell aggregates of FGF2-expanded meniscus cells accumulated more proteoglycan (total glycosaminoglycan) over 14 days and deposited a collagen II-rich matrix. The gene expression of matrix-associated proteoglycans (biglycan and fibromodulin) was also increased by FGF2 and hypoxia. Meniscus cells after expansion in monolayer can therefore respond to chondrogenic signals, and this is enhanced by FGF2 during expansion and low oxygen tension during aggregate cultures.

Oscillatory fluid flow regulates glycosaminoglycan production via an intracellular calcium pathway in meniscal cells

Mechanical loading in the form of oscillatory fluid flow-induced shear stress was applied to meniscal cells while the biochemical response [intracellular calcium mobilization and sulfated glycosaminoglycan (GAG) production] was studied. Isolated rabbit meniscal cells were cultured onto microscope slides and placed in a parallel plate flow chamber. Cells were exposed to oscillating fluid flow-induced shear stresses of 4 Pa for sulfated GAG studies and 0-6.5 Pa for calcium studies. The calcium response was monitored using a fluorescent probe and imaging techniques, sulfated GAG production was measured using the modified 1,9-dimethylmethylene blue method, and thapsigargin was used to block intracellular calcium ([Ca2+]i) mobilization. A significant dose-dependent relationship was found for the percentage of cells responding to oscillating fluid flow with an increase in [Ca2+]i versus shear stress level. The percentage of cells responding decreased linearly from 72% +/- 17% at 6.5 Pa to 28% +/- 7% at 2.0 Pa to 2% +/- 1% for baseline no-flow (0 Pa). No differences were found in the amplitude of the calcium response of responding cells for any shear stress level. Oscillating fluid flow-induced shear stresses of 4 Pa produced a significantly greater amount of sulfated GAGs (253 +/- 95 ng GAG/microg cell protein) compared to the no-flow control (158 +/- 86 ng/microg). The addition of thapsigargin to the media inhibited both the intracellular calcium response to oscillating fluid flow (less than 1.5% of the cells responded) and the increase in GAG production following oscillating fluid flow, which was returned to control levels (170 +/- 72 ng/microg). These findings suggest that oscillatory fluid flow-induced shear stress increases intracellular calcium levels and sulfated GAG production. Furthermore, they suggests that calcium may modulate the biochemical pathway that leads to sulfated GAG production.

Anti-inflammatory effects of continuous passive motion on meniscal fibrocartilage

Motion-based therapies have been applied to promote healing of arthritic joints. The goal of the current study was to determine the early molecular events that are responsible for the beneficial actions of motion-based therapies on meniscal fibrocartilage. Rabbit knees with Antigen-Induced-Arthritis (AIA) were exposed to continuous passive motion (CPM) for 24 or 48 h and compared to immobilized knees. The menisci were harvested and glycosaminoglycans (GAG), interleukin-1beta (IL-1beta), matrix metalloproteinase-1 (MMP-1), cyclooxygenase-2 (COX-2), and interleukin-10 (IL-10) were determined by histochemical analysis. Within 24 h, immobilized knees exhibited marked GAG degradation. The expression of proinflammatory mediators MMP-1, COX-2, and IL-1beta was notably increased within 24 h and continued to increase during the next 24 h in immobilized knees. Knees subjected to CPM revealed a rapid and sustained decrease in GAG degradation and the expression of all proinflammatory mediators during the entire period of CPM treatment. More importantly, CPM induced synthesis of the anti-inflammatory cytokine IL-10. The results demonstrate that mechanical signals generated by CPM exert potent anti-inflammatory signals on meniscal fibrochondrocytes. Furthermore, these studies explain the molecular basis of the beneficial effects of CPM observed on articular cartilage and suggest that CPM suppresses the inflammatory process of arthritis more efficiently than immobilization.

Menisci of the rabbit knee require mechanical loading to maintain homeostasis: cyclic hydrostatic compression in vitro prevents derepression of catabolic genes

BACKGROUND

The purpose of this study was to examine the influence of removing menisci from their in vivo loading environment on gene expression patterns and to determine whether in vitro loading can maintain the tissues in their in vivo phenotype.

METHODS

Lateral and medial rabbit meniscal explants from one leg were cultured in vitro and subjected to intermittent cyclic hydrostatic pressure (CHP) of 1 MPa at 0.5 Hz for 1 min and a rest period of 14 min (4 h of culture). The contralateral menisci were incubated at atmospheric pressure for 4 h. Menisci from both legs of another set of rabbits were frozen immediately to yield time zero values reflective of in vivo mRNA levels. Total RNA was isolated from all groups and processed for reverse transcription-polymerase chain reaction analysis for a subset of relevant genes (matrix molecules, cytokines, proteinases and inhibitors, enzymes).

RESULTS

It was found that mRNA levels for MMP-1, MMP-3, TIMPs, iNOS, COX-2, interleukin-1beta in both menisci, and interleukin-6 in medial menisci were significantly elevated in tissues cultured under nonloading conditions compared to the time zero controls. Subjecting menisci to CHP significantly prevented these increases in mRNA levels for nearly all of the indicated molecules. In contrast, there were no significant differences in mRNA levels for collagens, biglycan, MMP-13, or TIMP-4 between the time zero values and those cultured under either nonloading or loading conditions.

CONCLUSIONS

These studies demonstrate that removing rabbit menisci from their normal in vivo mechanical environment leads to an apparent up-regulation of a subset of potent effector molecules that could mediate catabolic activities, and that in vitro CHP can largely prevent this apparent up-regulation.

Systemic hypoxia alters gene expression levels of structural proteins and growth factors in knee joint cartilage

We investigated the effects of short- (8- and 24-h) and long-term (3 weeks) exposure to systemic normobaric hypoxia (13%) on the gene expression level of structural proteins and growth factors in knee joint cartilage of rabbits. Collagen type Ia2, II, and Va1, TGF-beta1, and b-FGF were upregulated after short-term hypoxia in both menisci, but not in articular cartilage. In contrast, long-term hypoxia downregulated gene expression level of collagens, aggrecan, and growth factors in articular cartilage and meniscal fibrocartilage. Interestingly, gene expression levels of non-collagenous proteins biglycan, decorin, and versican were not affected by short-term or by long-term hypoxia in knee joint cartilage. The present study suggests that changes in oxygen level differentially affect gene expression levels of growth factors, collagens, and non-collagenous proteins in normal knee joint cartilage in rabbits.

Etiology and pathophysiology of osteoarthritis

Acute or chronic insult, including normal wear and tear, age, obesity, and joint injury, may initiate an imbalance between matrix synthesis and matrix degradation in healthy cartilage that promotes chondral loss and prevents cartilage self-repair. The structure of healthy cartilage and the pathophysiological mechanisms of its degradation are described, followed by descriptions of endogenous and exogenous factors believed to be involved in the progressive course of osteoarthritis. Studies cited include research from the community of sports medicine.

The concentration, gene expression, and spatial distribution of aggrecan in canine articular cartilage, meniscus, and anterior and posterior cruciate ligaments: a new molecular distinction between hyaline cartilage and fibrocartilage in the knee joint

The concentration, spatial distribution, and gene expression of aggrecan in meniscus, articular cartilage, and the anterior and posterior cruciate ligaments (ACL and PCL) was determined in the knee joints of five mature dogs. An anti-serum against peptide sequences specific to the G1 domain of aggrecan was employed in competitive-inhibition ELISA of guanidine HCl extracts and immunofluorescence microscopy. Gene expression was determined by Taqman real-time PCR. The concentration of aggrecan in articular cartilage (240.1 +/- 32 nMol/g dry weight) was higher than that in meniscus (medial meniscus: 33.4 +/- 4.3 nMol/g) and ligaments (ACL: 6.8 +/- 0.9 nMol/g). Aggrecan was more concentrated in the inner than the outer zone of the meniscus. Aggrecan in meniscus showed an organized, spatial network, in contrast to its diffuse distribution in articular cartilage. Thus, differences in the concentration, gene expression, and spatial distribution of aggrecan constitute another molecular distinction between hyaline cartilage and fibrocartilage of the knee.

The effects of cyclic mechanical strain and tumor necrosis factor alpha on the response of cells of the meniscus

OBJECTIVES

Cells of the knee meniscus respond to changes in their biochemical and biomechanical environments with alterations in the biosynthesis of matrix constituents and inflammatory mediators. Tumor necrosis factor alpha (TNF-alpha) is a pro-inflammatory cytokine that is involved in the pathogenesis of both osteoarthritis and rheumatoid arthritis, but its influence on meniscal physiology or mechanobiology is not fully understood. The objectives of this study were to examine the hypothesis that cyclic mechanical strain of meniscal cells modulates the biosynthesis of matrix macromolecules and pro-inflammatory mediators, and to determine if this response is altered by TNF-alpha.

METHODS

Cells were isolated from the inner two-thirds of porcine medial menisci and subjected to biaxial tensile strain of 5-15% at a frequency of 0.5Hz. The synthesis of proteoglycan, protein, nitric oxide (NO), and prostaglandin E(2) were determined.

RESULTS

Cyclic tensile strain increased the production of nitric oxide through the upregulation of nitric oxide synthase 2 (NOS2) and also increased synthesis rates of prostaglandin E(2), proteoglycan, and total protein in a manner that depended on strain magnitude. TNF-alpha increased the production of NO and total protein, but inhibited proteoglycan synthesis rates. TNF-alpha prevented the mechanical stimulation of proteoglycan synthesis, and this effect was not dependent on NOS2.

CONCLUSIONS

These findings indicate that pro-inflammatory cytokines can modulate the responses of meniscal cells to mechanical signals, suggesting that both biomechanical and inflammatory factors could contribute to the progression of joint disease as a consequence of altered loading of the meniscus.

Return to play following surgical treatment of meniscal and chondral injuries to the knee

Much has been written in the sports medicine literature regarding return to competition following anterior cruciate ligament reconstruction; however, little scientific work has been done regarding the return to competition following meniscal surgery or cartilage surgery. This article reviews the basic science of meniscal surgery and cartilage surgery in an attempt to promote rational rehabilitative protocols rooted in scientific investigation. A twofold approach is used. One approach is from a biologic standpoint; that is, when are the repaired tissues healed enough to withstand physiologic activity? The second approach is from a rehabilitative standpoint; when is the patient strong enough to play without recurrent injury?

Differential effects of static and dynamic compression on meniscal cell gene expression

Cells of the meniscus are exposed to a wide range of time-varying mechanical stimuli that may regulate their metabolic activity in vivo. In this study, the biological response of the meniscus to compressive stimuli was evaluated in vitro, using a well-controlled explant culture system. Gene expression for relevant extracellular matrix proteins was quantified using real-time RT-PCR following a 24 h period of applied static (0.1 MPa compressive stress) or dynamic compression (0.08-0.16 MPa). Static and dynamic compression were found to differentially regulate mRNA levels for specific proteins of the extracellular matrix. Decreased mRNA levels were observed for decorin ( approximately 2.1 fold-difference) and type II collagen ( approximately 4.0 fold-difference) following 24 h of dynamic compression. Decorin mRNA levels also decreased following static compression ( approximately 4.5 fold-difference), as did mRNA levels for both types I ( approximately 3.3 fold-difference) and II collagen ( approximately 4.0 fold-difference). Following either static or dynamic compression, mRNA levels for aggrecan, biglycan and cytoskeletal proteins were unchanged. It is noteworthy that static compression was associated with a 2.6 fold-increase in mRNA levels for collagenase, or MMP-1, suggesting that the homeostatic balance between collagen biosynthesis and catabolism was altered by the mechanical stimuli. These findings demonstrate that the biosynthetic response of the meniscus to compression is regulated, in part, at the transcriptional level and that transcription of types I and II collagen as well as decorin may be regulated by common mechanical stimuli.

Regulation of matrix turnover in meniscal explants: role of mechanical stress, interleukin-1, and nitric oxide

The meniscus is an intra-articular fibrocartilaginous structure that serves essential biomechanical roles in the knee. With injury or arthritis, the meniscus may be exposed to significant changes in its biochemical and biomechanical environments that likely contribute to the progression of joint disease. The goal of this study was to examine the influence of mechanical stress on matrix turnover in the meniscus in the presence of interleukin-1 (IL-1) and to determine the role of nitric oxide (NO) in these processes. Explants of porcine menisci were subjected to dynamic compressive stresses at 0.1 MPa for 24 h at 0.5 Hz with 1 ng/ml IL-1, and the synthesis of total protein, proteoglycan, and NO was measured. The effects of a nitric oxide synthase 2 (NOS2) inhibitor were determined. Dynamic compression significantly increased protein and proteoglycan synthesis by 68 and 58%, respectively, compared with uncompressed explants. This stimulatory effect of mechanical stress was prevented by the presence of IL-1 but was restored by specifically inhibiting NOS2. Release of proteoglycans into the medium was increased by IL-1 or mechanical compression and further enhanced by IL-1 and compression together. Stimulation of proteoglycan release in response to compression was dependent on NOS2 regardless of the presence of IL-1. These finding suggest that IL-1 may modulate the effects of mechanical stress on extracellular matrix turnover through a pathway that is dependent on NO.

Mechanical induction in limb morphogenesis: the role of growth-generated strains and pressures

Morphogenesis is regulated by intrinsic factors within cells and by inductive signals transmitted through direct contact, diffusible molecules, and gap junctions. In addition, connected tissues growing at different rates necessarily generate complicated distributions of physical deformations (strains) and pressures. In this Perspective we present the hypothesis that growth-generated strains and pressures in developing tissues regulate morphogenesis throughout development. We propose that these local mechanical cues influence morphogenesis by: (1) modulating growth rates; (2) modulating tissue differentiation; (3) influencing the direction of growth; and (4) deforming tissues. It is in this context that we review concepts and experiments of cell signaling and gene expression in various mechanical environments. Tissue and organ culture experiments are interpreted in light of the developmental events associated with the growth of the limb buds and provide initial support for the presence and morphological importance of growth-generated strains and pressures. The concepts presented are used to suggest future lines of research that may give rise to a more integrated mechanobiological view of early embryonic musculoskeletal morphogenesis.

Insulin-like growth factor-I gene expression patterns during spontaneous repair of acute articular cartilage injury

This study evaluated the constitutive insulin-like growth factor-I (IGF-I) gene expression pattern in spontaneously healing cartilage defects over the course of 16 weeks, and correlated the tissue morphology and matrix gene expression with IGF-I mRNA levels. Full-thickness 15 mm cartilage defects were debrided in the femoral trochlea of both femoropatellar joints of 8 horses and the healing defects examined 2, 4, 8, or 16 weeks after surgery. Samples were harvested for histologic assessment of tissue healing using H&E staining, toluidine blue histochemical reaction for proteoglycan deposition, and in situ hybridization and immunohistochemistry procedures to demonstrate collagen type II mRNA and protein expression. Total RNA was isolated for Northern analysis to measure cartilage matrix molecule expression, and for semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) to determine IGF-I gene expression patterns in healing cartilage defects. Full-thickness cartilage defects in horses were slow to heal compared to smaller lesions in similar locations in other animals. However, a progressive decline in tissue cellularity and vascularity, and increased tissue organization were observed on H&E stained specimens over the 16-week experiment. Evidence of early chondrogenic repair was detected through collagen type II in situ hybridization and immunohistochemistry. However, levels of collagen type II and aggrecan mRNA in lesions were not abundant on Northern analysis indicating incomplete chondrogenesis. IGF-I message expression followed a cyclic pattern with low levels at 2 weeks, followed by an increase at 4 and 8 weeks, and a subsequent decline at 16 weeks. There was no direct correlation between the stage of healing and cartilage matrix message expression, and the abundance of IGF-I mRNA in the healing lesions. In conclusion, this study demonstrated that the spontaneous healing of articular defects was accompanied by a temporal fluctuation in IGF-I gene expression which was discoordinate to the steady rise in expression of cartilage matrix molecules such as procollagen type II.

The effect of dynamic mechanical compression on nitric oxide production in the meniscus

OBJECTIVE

The menisci play an important role in the biomechanics of the knee, and loss of meniscal function has been associated with progressive degenerative changes of the joint in rheumatoid arthritis as well as in osteoarthritis. However, little is known about the underlying mechanisms that link meniscal injury or degeneration to arthritis. Meniscal fibrochondrocytes respond to environmental mediators such as growth factors and cytokines, but the influence of mechanical stress on their metabolic activity is not well understood. Nitric oxide (NO) is believed to play a role in mechanical signal transduction, and there is also significant evidence of its role in cartilage and meniscus degeneration. The goal of this study was to determine if meniscal fibrochondrocytes respond to mechanical stress by increasing NO production in vitro.

DESIGN

Explants of lateral and medial porcine menisci were dynamically compressed in a precisely controlled manner, and NO production, nitric oxide synthase antigen expression and cell viability were measured. The relative responses of the meniscal surface and deep layers to dynamic compression were also investigated separately.

RESULTS

Meniscal NO production was significantly (P< 0.01) increased by dynamic compression in both the medial and lateral menisci. Dynamically compressed menisci contained inducible nitric oxide synthase antigen, while uncompressed menisci did not. Significant (P< 0.05) zonal differences were observed in basal and compression-induced NO production.

DISCUSSION

Our findings provide direct evidence that dynamic mechanical stress influences the biological activity of meniscal cells. These results suggest that NO production in vivo may be in part regulated by mechanical stress acting upon the menisci. Since NO affects matrix metabolism in various intraarticular tissues, alterations in the distribution and magnitude of stress in the menisci may have important metabolic as well as biomechanical consequences on joint physiology and function.

Distribution of biglycan and decorin in collateral and cruciate ligaments and menisci of the rabbit knee joint

The small leucine-rich proteoglycans (PGs) biglycan and decorin, and their mRNAs, have been localized during neonatal development and aging (3 weeks to 2 years) of collateral and cruciate ligaments and of menisci of the rabbit knee joint. In the collateral ligaments, biglycan and decorin are found between the bundles of collagen fibers at all ages. In cruciate ligaments the PGs are primarily around the cells. In neonatal ligaments all the cells express the mRNAs for biglycan and decorin, but in the collateral ligaments the number expressing the mRNAs is reduced at 8 months. In 3--week menisci the PGs are uniformly distributed in the matrix, but by 8 months biglycan is present primarily in the central fibrocartilaginous regions, whereas decorin is found peripherally. In neonates, all the cells express the mRNAs but the number is reduced in 8-month menisci. The results illustrate the precise localizations of biglycan and decorin in healthy rabbit ligaments and menisci which, after injury, must be reproduced in the repair tissue for normal strength to be regained. (J Histochem Cytochem 49:877-885, 2001)

Absolute concentrations of mRNA for type I and type VI collagen in the canine meniscus in normal and ACL-deficient knee joints obtained by RNase protection assay

Relatively little is known about the cellular and molecular responses of the knee joint meniscus to joint injury, despite the functional importance of the tissue. We investigated how meniscus cells respond to joint injury in the early stages of post-traumatic osteoarthritis by characterizing the changes in matrix gene expression in menisci at 3 and 12 weeks post-surgery in dogs in which the anterior cruciate ligament (ACL) in one joint was transected and the other unoperated joint served as a control. Changes in the total RNA and DNA concentrations of the menisci were determined. Absolute concentrations of the mRNA of the COL1A1 gene of type 1 collagen, the major fibrillar collagen of the meniscus, and the COL6A3 gene of type VI collagen, a major repair molecule, were determined by quantitative ribonuclease (RNase) protection assay. The concentration of total RNA in medial and lateral menisci increased from 40 to 60 microg RNA/g wet wt in unoperated, control joints to 200-350 microg RNA/g wet wt in ACL-deficient joints. No significant changes were detected in the concentration of DNA (900-1200 microg DNA/g wet wt). Low concentrations of COL1A1 (2-3 pmol mRNA/g DNA) and COL6A3 (0.3-0.6 pmol mRNA/g DNA) mRNA transcripts were measured in normal menisci. ACL-deficiency induced a 20-38 fold increase in COL1A1 and COL6A3 mRNA concentration at 3 weeks, and an 11-19 fold increase at 12 weeks post-surgery. In general, the increase in COL1A1 and COL6A3 mRNA concentrations was greater in medial menisci than in lateral menisci. These results demonstrate that the menisci initiate a vigorous biosynthetic response to transection of the ACL.

In-vitro cyclic tensile loading of an immobilized and mobilized ligament autograft selectively inhibits mRNA levels for collagenase (MMP-1)

To test the hypothesis that loading conditions can be used to "engineer" ligament autograft behaviors, the effect of cyclic tension on the mRNA levels of matrix molecules and collagenase in in-vivo immobilized and mobilized 6-week rabbit medial collateral ligament (MCL) autografts was examined using an in-vitro system. Femur-[autograft MCL]-tibia complexes were subjected to a tensile stress of 4 MPa at 0.5 Hz for 1 min, followed by 14 min of rest. This 15-min testing cycle was repeated for 4 h. Semi-quantitative reverse transcrip-tase polymerase chain reaction (RT-PCR) was performed on RNA from mechanically treated MCL autografts, using rabbit-specific primer sets for types I and III collagen, biglycan, decorin, fibromodulin, lumican, versican, matrix metalloproteinase-1 (MMP-1, collagenase-1), MMP-13 (collagenase-3), and a housekeeping gene, glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Interestingly, 4 h of culture of normal control MCLs led to increased mRNA levels for MMP-1 (P < 0.05), but there were no significant changes in MMP-13 mRNA levels. Total RNA levels in that normal MCL tissue were, however, decreased after culture (P < 0.05). In-vitro tensile loading of in-vivo mobilized autografts resulted in a significant increase in total RNA (185% of in-vitro non-loaded autografts). On the other hand, in-vitro tensile loading of in-vivo immobilized autografts resulted in no significant changes in total RNA levels compared with levels in non-loaded control grafts. MMP-1 mRNA levels in both the in-vivo mobilized (47% of non-loaded autograft) and in-vivo immobilized (38% of non-loaded autograft) MCL autografts were significantly lower than those in non-loaded control tissue following in-vitro tensile loading, but there were no significant changes in the mRNA levels for the seven other matrix molecules assessed. These results show that it is possible to selectively inhibit MMP-1 mRNA levels in autograft ligaments by supplying mechanical stimuli in vitro. The results also demonstrate that in-vivo immobilization leads to a decrease in the effects of subsequent in-vitro mechanical loading in such autografts with respect to total RNA levels. Collectively, these results demonstrate that both in-vivo and in-vitro loading have implications in the engineering of an ideal ligament graft.

Postural control and torque of the knee joint after healed tibial shaft fracture

Muscular atrophy occurs as a consequence of trauma and immobilisation. This cohort comparison study was conducted to evaluate the limb function after healed tibial shaft fractures, which were treated by casting versus nailing. Balance (as centre of pressure) and muscle strength (as torque of the knee joint during knee extension) have been measured in 27 patients with tibial shaft fractures with a mean age of 39 (19-73) years, 1 year after fracture healing. Fourteen patients were treated by intramedullary nailing 'nailed group' and 13 by plaster cast with or without minimal internal fixation 'casted group'. Centre of pressure was measured on a force platform. Knee extension torque was measured during isometric and concentric muscle actions by an isokinetic dynamometer. Centre of pressure tended to be more towards the uninjured leg in patients who had been treated by plaster cast (P<0.05). Side-to-side differences for isometric torque were significantly higher within the casted group (P<0.05). Patients with tibial shaft fractures treated by intramedullary nailing showed better postural control, one-leg standing test, and side-to-side differences for isometric muscle strength compared with patients treated by cast. Therefore, we recommend intramedullary nailing as a better method of treatment for tibial shaft fractures, with regard to recovery of muscle function.