Outer Meniscus Research Articles

Steady state measurements in stress plateau region of entangled polymer solutions: Controlled-rate and controlled-stress modes

Despite decades of efforts, reliable measurements of nonlinear flow behavior of well-entangled polymers in continuous shear have been challenging to obtain. The present work attempts to accomplish three important tasks: (A) overcome this challenge by adopting a strategy of decoupling rheological measurements from the outer meniscus region in a cone-partitioned plate (C/PP) setup; (B) determine whether well-entangled solutions indeed undergo a flow transformation under creep that can be taken to phenomenologically define an entanglement-disentanglement transition (EDT); (C) provide the velocity profiles of such solutions undergoing either controlled-stress or controlled-rate shear by carrying out in situ particle-tracking velocimetric (PTV) measurements. Upon removing any influence of edge fracture and sample loss, we are able to reach steady state during continual shear and elucidate more reliably the nonlinear flow behavior of well entangled polymer solutions with little ambiguity. Three well-entangled s...

The effect of the pressure on the static meniscus shape in the case of tube growth by edge-defined film-fed growth (E.F.G.) method

In this paper explicit formulas prescribing inner and outer pressure limits are reported in the case of cylindrical tube growth by edge-defined film-fed growth (E.F.G.) method. These formulas are deduced in general for any growth configuration and for any material. If the value of the inner (the outer) pressure is less or more than the prescribed limit, then the inner (the outer) meniscus shape is convex or concave. The advantage of this kind of formulas is that from them special results can be gleaned. With this aim this study was undertaken. Numerical examples are given using the data of the first successful silicon tube growth experiment reported by Eriss et al.

Distale osteochondrale Femurimpressionsfrakturen

Chondral or osteochondral avulsions of the lateral distal femur edge after luxation of the patella are well known. Less common are impression fractures of the retropatellar joint or the lateral trochlea. Furthermore, on standard knee X-rays these injuries may not be seen and thus not properly be treated. By presenting our cases we show clinical symptoms, diagnostic pathways and the therapeutic approach for osteochondral fractures of the distal femur. The first patient had a large osteochondral impression fracture of the lateral femur trochlea and retropatellar surface. The second patient had a chondral depression of the lateral trochlea femoris after kicking a football. The further examinations showed no other knee injuries in the first case, but a rupture of the outer meniscus plus ACL rupture and distortion of the medial collateral complex in the other one. In both cases the whole degree of the injury was not seen on the standard X-rays, but only on MRI or CT scans. The clinical signs were also not so overwhelming, as both patients could walk with crutches, but suffered from haemarthrosis. Both patients were operated by arthroscopy first with surgery on the meniscus injury and ACL rupture. The impression was revised by an open procedure with elevation of the subchondral spongiosa. In the follow-up examination we saw no dissection of chondral flakes or local necrosis. Osteochondral lesions of the distal femur can be neglected, as it is an uncommon diagnosis and the radiological signs may not be impressing. The more important is a subtle anamnesis and further diagnostic regime via CT or MRI as it is a prearthrotic injury. Intraoperatively the impression must be elevated or in the case of a dislocation refixed. Further knee injuries have to be detected. In the follow-up one should check for signs of flake dissection or necrosis.

Repair Response of the Inner and Outer Regions of the Porcine Meniscus in Vitro

Background The menisci are essential intra-articular structures that contribute to knee function, and meniscal injury or loss is associated with joint degeneration. Tears of the outer vascularized zone have a greater potential for repair than do tears in the inner avascular region. Objective and Hypothesis Develop an in vitro explant model to examine the hypothesis that differences exist in the intrinsic repair response between the outer and inner region of the meniscus. Study Design Controlled laboratory study. Methods Cylindrical explants were harvested from the outer one third and inner two thirds of medial porcine menisci. To simulate a full-thickness defect, a central core was removed and reinserted immediately. Explants were cultured for 2, 4, or 6 weeks, and meniscal healing was investigated using mechanical testing, histologic analysis, and fluorescence confocal microscopy. Results Over the 6-week culture period, meniscal explants exhibited migration of cells into the repair site, followed by increased tissue formation that bridged the interface. The repair strength increased significantly over time, with no differences between the 2 regions. Conclusion The findings show that explants from the avascular inner zone and vascular outer zone of the meniscus exhibit similar healing potential and repair strength in vitro. Clinical Relevance These findings support the hypothesis that the regional differences in meniscal repair observed clinically are owed to the additional vascular supply of the outer meniscus rather than intrinsic differences between the extracellular matrix and cells from these 2 areas.

Human meniscus cells express hypoxia inducible factor-1α and increased SOX9 in response to low oxygen tension in cell aggregate culture

In previous work we demonstrated that the matrix-forming phenotype of cultured human cells from whole meniscus was enhanced by hypoxia (5% oxygen). Because the meniscus contains an inner region that is devoid of vasculature and an outer vascular region, here we investigate, by gene expression analysis, the separate responses of cells isolated from the inner and outer meniscus to lowered oxygen, and compared it with the response of articular chondrocytes. In aggregate culture of outer meniscus cells, hypoxia (5% oxygen) increased the expression of type II collagen and SOX9 (Sry-related HMG box-9), and decreased the expression of type I collagen. In contrast, with inner meniscus cells, there was no increase in SOX9, but type II collagen and type I collagen increased. The articular chondrocytes exhibited little response to 5% oxygen in aggregate culture, with no significant differences in the expression of these matrix genes and SOX9. In both aggregate cultures of outer and inner meniscus cells, but not in chondrocytes, there was increased expression of collagen prolyl 4-hydroxylase (P4H)α(I) in response to 5% oxygen, and this hypoxia-induced expression of P4Hα(I) was blocked in monolayer cultures of meniscus cells by the hypoxia-inducible factor (HIF)-1α inhibitor (YC-1). In fresh tissue from the outer and inner meniscus, the levels of expression of the HIF-1α gene and downstream target genes (namely, those encoding P4Hα(I) and HIF prolyl 4-hydroxylase) were significantly higher in the inner meniscus than in the outer meniscus. Thus, this study revealed that inner meniscus cells were less responsive to 5% oxygen tension than were outer meniscus cells, and they were both more sensitive than articular chondrocytes from a similar joint. These results suggest that the vasculature and greater oxygen tension in the outer meniscus may help to suppress cartilage-like matrix formation.

Differential cartilaginous tissue formation by human synovial membrane, fat pad, meniscus cells and articular chondrocytes

To identify an appropriate cell source for the generation of meniscus substitutes, among those which would be available by arthroscopy of injured knee joints. Human inner meniscus cells, fat pad cells (FPC), synovial membrane cells (SMC) and articular chondrocytes (AC) were expanded with or without specific growth factors (Transforming growth factor-beta1, Fibroblast growth factor-2 and Platelet-derived growth factor bb, TFP) and then induced to form three-dimensional cartilaginous tissues in pellet cultures, or using a hyaluronan-based scaffold (Hyaff-11), in culture or in nude mice. Human native menisci were assessed as reference. Cell expansion with TFP enhanced glycosaminoglycan (GAG) deposition by all cell types (up to 4.1-fold) and messenger RNA expression of collagen type II by FPC and SMC (up to 472-fold) following pellet culture. In all models, tissues generated by AC contained the highest fractions of GAG (up to 1.9% of wet weight) and were positively stained for collagen type II (specific of the inner avascular region of meniscus), type IV (mainly present in the outer vascularized region of meniscus) and types I, III and VI (common to both meniscus regions). Instead, inner meniscus, FPC and SMC developed tissues containing negligible GAG and no detectable collagen type II protein. Tissues generated by AC remained biochemically and phenotypically stable upon ectopic implantation. Under our experimental conditions, only AC generated tissues containing relevant amounts of GAG and with cell phenotypes compatible with those of the inner and outer meniscus regions. Instead, the other investigated cell sources formed tissues resembling only the outer region of meniscus. It remains to be determined whether grafts based on AC will have the ability to reach the complex structural and functional organization typical of meniscus tissue.

Finite Element Modeling Predictions of Region-specific Cell-matrix Mechanics in the Meniscus

The knee meniscus exhibits significant spatial variations in biochemical composition and cell morphology that reflect distinct phenotypes of cells located in the radial inner and outer regions. Associated with these cell phenotypes is a spatially heterogeneous microstructure and mechanical environment with the innermost regions experiencing higher fluid pressures and lower tensile strains than the outer regions. It is presently unknown, however, how meniscus tissue mechanics correlate with the local micromechanical environment of cells. In this study, theoretical models were developed to study mechanics of inner and outer meniscus cells with varying geometries. The results for an applied biaxial strain predict significant regional differences in the cellular mechanical environment with evidence of tensile strains along the collagen fiber direction of approximately 0.07 for the rounded inner cells, as compared to levels of 0.02-0.04 for the elongated outer meniscus cells. The results demonstrate an important mechanical role of extracellular matrix anisotropy and cell morphology in regulating the region-specific micromechanics of meniscus cells, that may further play a role in modulating cellular responses to mechanical stimuli.

Region-specific constitutive gene expression in the adult porcine meniscus

The knee meniscus exhibits extensive spatial variations in native healing capacity, biochemical composition, and cell morphology that suggest the existence of distinct phenotypes for meniscus cells. Constitutive gene expression levels of appropriate extracellular matrix proteins may serve as useful molecular markers of cellular phenotypes; however, relatively little is known of variations in the gene expression for meniscus cells of different regions of the tissue. The objective of the present study was to evaluate constitutive differences between radial inner and outer regions in gene expression for extracellular matrix proteins relevant to the meniscus. A secondary objective was to determine if these region-specific differences in gene expression are maintained after periods of monolayer culture. The innermost regions of the meniscus were found to constitutively express higher mRNA levels for proteins highly expressed in articular cartilage, including aggrecan, type II collagen, and NOS2. In contrast, the outer meniscus was found to contain higher gene expression for proteins associated with fibrous tissues including type I collagen, and the proteases MMP2 and MMP3. Isolated inner and outer meniscus cells maintained these region-specific gene expression patterns for collagens and proteoglycans during short-term monolayer culture. The results provide new information that suggests the utility of constitutive gene expression levels as molecular markers to distinguish tissue and cells of the inner and outer meniscus.

Biaxial Strain Effects on Cells from the Inner and Outer Regions of the Meniscus

During knee joint loading, the fibrocartilaginous menisci experience significant spatial variations in mechanical stimuli. Meniscus cells also exhibit significant variations in biosynthesis and gene expression depending on their location within the tissue. These metabolic patterns are consistent with a more chondrocytic phenotype for cells located within the avascular inner two-thirds compared with a more fibroblastic phenotype for cells within the vascularized outer periphery. The spatial distribution of cell biosynthesis and gene expression patterns within the meniscus suggest that cells may exhibit intrinsically different responses to mechanical stimuli. The objective of our study was to test for intrinsic differences in the responsiveness of these meniscus cell populations to an equivalent mechanical stimulus. Cellular biosynthesis and gene expression for extracellular matrix proteins in isolated inner and outer meniscus cells in monolayer were quantified following cyclic biaxial stretch. The results demonstrate that inner and outer meniscus cells exhibit significant differences in matrix biosynthesis and gene expression regardless of stretching condition. Both inner and outer meniscus cells responded to stretch with increased nitric oxide production and total protein synthesis. The results suggest that inner and outer meniscus cells may respond similarly to biaxial stretch in vitro with measures of biosynthesis and gene expression.

Coaxial jets generated from electrified Taylor cones. Scaling laws

An experimental investigation on the electrified co-axial jets of two immiscible liquids issuing from a structured Taylor cone (Science 295 (5560) (2002) 1695) has been carried out. The structure of these almost conical electrified menisci consists of an outer meniscus surrounding an inner one. The liquid threads which issue from the vertex of each one of the menisci give rise to a two-concentric layered jet whose eventual breakup results in an aerosol of relatively monodisperse compound droplets with the outer liquid encapsulating the inner one. The effect of the flow rates of both liquids on the current transported by these coaxial jets and on the size of the compound droplets has been investigated. Several couples of liquids have been used to explore the influence on the spraying process of the properties of the liquids: i.e. the electrical conductivity K, dielectric constant β, interfacial tension of the liquid couple γ, viscosity μ, etc. We have found that the measurements of the current emitted through the coaxial jet when they are made dimensionless fit satisfactorily the current scaling law of regular electrosprays. Data of the mean diameter of the compound droplets have been obtained using a non-intrusive laser system. As expected the breakup process and therefore the droplet size are strongly dependent on the liquid viscosities and on the ratio of the liquid flow rates.

Meniscus Forces and Profiles: Theory and Its Applications to Liquid-Mediated Interfaces

A theory for obtaining meniscus forces and profiles for any given liquid-mediated interface is presented that includes the effects of surface interactions, adsorption and evaporation of liquid films. The meniscus force is obtained from the derivative of the total free energy of liquid-mediated interface, which requires the meniscus profile to be known. The meniscus profile is the solution of a second-order differential equation, as derived from Pascal’s law for static incompressible liquids with inclusion of surface interactions. For nonvolatile liquid films, the total liquid amount at the interface is a conserved quantity, whereas for volatile liquids, the liquid films are in thermodynamic equilibrium with their respective vapor phase. Two typical types of initial liquid conditions are considered. Type I represents the case in which one surface is wet and the other is initially dry, having a finite contact angle with the liquid. Type II represents the situation in which both surfaces are wet by either a liquid or by two different liquids before making contact. If two or more types of liquids are involved at the interface, miscibility of the liquids and interactions due to other liquid(s) have to be also considered. For contacts with azimuthal geometry, which is merely a mathematical convenience, such as ellipsoidal/spherical, conical or crater, the theory generates several analytical formulae for calculating meniscus forces without involving meniscus profiles. These formulae can be handily applied to various surface probes techniques such as Scanning Probe Microscopy or Surface Force Apparatus. The proposed theory is also applicable to “meniscus rings” formed around crater geometry, such as encountered in laser-textured magnetic disks. In this case, the outer meniscus ring can be asymmetric to the inner meniscus ring if no liquid passage exists between the inner and outer meniscus ring. Even for the case of spherical contact geometry, the calculated meniscus profile is very nonspherical with a much larger volume than that of the widely assumed spherical meniscus profile for Type I conditions, leading to an under-estimation of the meniscus force in the previous models. It is found that for a spherical or a crater contact geometry, the surface interactions have little effect on the meniscus force provided the lateral meniscus dimension is much smaller than the radius of the sphere or of the crater. However the surface interactions have a large effect on the meniscus force for other contact geometries, such as conical contact geometry. The calculated meniscus forces are compared with the normal component of the stiction force measured at the laser textured surfaces and good agreement is found. The calculated meniscus profiles are also found in good agreement with that measured using light interferometer technique between two cross cylinders. One very interesting finding of our theory is that the meniscus volume grows first and may then shrink, as observed experimentally by others, because the initially dry surface become wetted and the boundary conditions change over from Type I to Type II.

Numerical investigation of the dynamic influence of the contact line region on the macroscopic meniscus shape

The influence of different boundary conditions applied in the contact line region on the outer meniscus shape is analysed by means of a finite-element numerical simulation of the steady movement of a liquid-gas meniscus in a capillary tube. The free-surface steady shape is obtained by solving the unsteady creeping-flow approximation of the Navier–Stokes equations starting from some initial shape. Comparisons of the outer solutions obtained using two different inner models, together with that published by Lowndes (1980), indicate the relative insensitivity of the outer solution to the type of model utilized in the contact line region.

Cross-Validation of Cyanogen Bromide-Peptide Ratios to Measure the Proportion of Type II Collagen in Pepsin Digests of Equine Articular Cartilage, Meniscus, and Cartilage Repair Tissue

Collagen type I and type II were purified from equine flexor tendon and articular cartilage, respectively. Equal amounts of these collagens were cleaved with cyanogen bromide, and 11 mixtures containing increasing proportions of type II collagen were separated in seven identical sodium dodecyl sulfate-polyacrylamide gels. The density of bands was measured in wet gels and the peak areas were used to form six ratios of peptide bands that had polynomial relationships with the known proportions of type I and type II collagen in the mixtures. Calibration curves for determining the proportion of type II collagen in the mixtures were constructed using ratios and combinations of ratios of peak areas. Cross-validation was used to identify calibration curves with the smallest squared prediction error or squared average prediction error for all combinations of ratios. Ratios of peak areas of each one of the seven gels were treated, in turn, as the "unknown," and a prediction was carried out using these unknowns and the ratios from the other six gels. Two ratios had the smallest squared average prediction error and calibration curves were computed for these ratios with all seven gels. These curves were used to estimate the proportion of type II collagen in the pepsin-soluble and the pepsin-resistant fractions of articular cartilage, inner and outer meniscus, and cartilage repair tissue. Cross-validation enabled selection of the cyanogen bromide-peptide ratios for calibration curves that resulted in the most accurate estimation of the proportion of type II collagen in pepsin digests of tissues.