Measurements of nonhomogeneous, directional mechanical properties of articular cartilage in tension

The purpose of this investigation is to develop an accurate experimental procedure to measure the elastic properties of articular cartilage in uniaxial tension. Standardized, dumbbell shaped specimens, 250–325 μm thick, were taken from the surface, middle, and deep zones of the articular cartilage at 0°, 45°, and 90° from axis of the cleavage line pattern for the study of the zonal and directional properties of articular cartilage. A total of 75 specimens were tested to failure in this study. The use of a video dimensional analyzer system in this study makes accurate monitoring of the deformation of articular cartilage specimens possible. Nonlinear stress-strain relationships of the articular cartilage samples were mathematically approximated by exponential law similar to Fung (1967). Higher stiffness for the 0° specimens in the surface and middle zones was found. The experimental findings are in general agreement with the interpretations of low magnification scanning electron microscopy.     

A transversely isotropic, transversely homogeneous microstructural-statistical model of articular cartilage

Articular cartilage is a multi-phasic, composite, fibre-reinforced material. Therefore, its mechanical properties are determined by the tissue microstructure. The presence of cells (chondrocytes) and collagen fibres within the proteoglycan matrix influences, at a local and a global level, the material symmetries. The volumetric concentration and shape of chondrocytes, and the volumetric concentration and spatial arrangement of collagen fibres have been observed to change as a function of depth in articular cartilage. In particular, collagen fibres are perpendicular to the bone-cartilage interface in the deep zone, their orientation is almost random in the middle zone, and they are parallel to the surface in the superficial zone. The aim of this work is to develop a model of elastic properties of articular cartilage based on its microstructure. In previous work, we addressed this problem based on Piola's notation for fourth-order tensors. Here, mathematical tools initially developed for transversely isotropic composite materials comprised of a statistical orientation of spheroidal inclusions are extended to articular cartilage, while taking into account the dependence of the elastic properties on cartilage depth. The resulting model is transversely isotropic and transversely homogeneous (TITH), the transverse plane being parallel to the bone-cartilage interface and the articular surface. Our results demonstrate that the axial elastic modulus decreases from the deep zone to the articular surface, a result that is in good agreement with experimental findings. Finite element simulations were carried out, in order to explore the TITH model's behaviour in articular cartilage compression tests. The force response, fluid flow and displacement fields obtained with the TITH model were compared with the classical linear elastic, isotropic, homogeneous (IH) model, showing that the IH model is unable to predict the non-uniform behaviour of the tissue. Based on considerations that the mechanical stability of the tissue depends on its topological and microstructural properties, our long-term goal is to clearly understand the stability conditions in topological terms, and the relationship with the growth and remodelling mechanisms in the healthy and diseased tissue.     

A “coupled” subchondral bone-articular cartilage tissue culture system for the study of cartilage proteoglycan metabolism

Summary Current evidence suggests that interactions between the subchondral bone and the articular cartilage of mammalian diarthrodial joints may occur through the action of bone-associated peptide factors. However, there is no suitable organ culture model for studying these interactions. This study defines a long-term tissue culture system where the articular cartilage is coupled to the adjacent subchondral bone obtained from the proximal ends of bovine metacarpals. Autoradiography done over 3 mo., by utilizing [³⁵S]SO₄ incorporation into cartilage proteoglycan (PG) and a procedure for cutting non-decalcified bone, demonstrated similar numbers of silver grains over chondrocytes in all cartilage zones, including the bone-cartilage interface. Newly synthesized PG (NSPG) from the cartilage of the “coupled” system over a 3-wk period was primarily of large hydrodynamic size (Kav of 0.34). Comparable bovine articular and nasal cartilage slice systems, incubated for short periods of time, yielded similar and somewhat larger NSPG, respectively. Labeled chondroitin sulphate PG accumulating in the medium of primary chondrocyte monolayer cultures, derived from the cartilage of the coupled system at 0, 1, 2, and 3 wk, revealed two polydisperse subpopulations (Kav of 0.30 to 0.38 and 0.51 to 0.68). We conclude that this coupled bone-cartilage system is viable for prolonged periods, is suitable for studies on the metabolism of articular cartilage PGs, and seems to have some advantages over the cultured articular cartilage slice system.     

Towards an analytical model of soft biological tissues

In the past years, soft-tissue modelling research has seen substantial developments, a significant part of which can be ascribed to the refinement of numerical techniques, such as Finite Element analysis. A large class of physico-mechanical properties can be effectively simulated and predictions can be made for a variety of phenomena. However, there is still much that can be conceptually explored by means of fundamental theoretical analysis. In the past few years, driven by our interest in articular cartilage mechanics, we have developed theoretical microstructural models for linear elasticity and permeability that accounted for the presence and arrangement of collagen fibres in cartilage. In this paper, we investigate analytically the non-linear elasticity of soft tissues with collagen fibres arranged according to a given distribution of orientation, a problem that, aside from the case of fibres aligned in a finite number of distinct directions, has been treated exclusively numerically in the literature. We show that, for the case of a tissue with complex fibre arrangement, such as articular cartilage, the theoretical framework commonly used leads to an integral expression of the elastic strain energy potential. The present model is a first attempt in the development of a unified analytical microstructural model for non-linear elasticity and permeability of hydrated, fibre-reinforced soft tissues.     

Bicarbonate-dependent pH(i) regulation by chondrocytes within the superficial zone of bovine articular cartilage

Control of chondrocyte pH (pH(i)) determines articular cartilage matrix metabolism. However, the transporters of chondrocytes in situ throughout cartilage zones are unclear, and we tested the hypothesis that chondocytes within the superficial zone (SZ) utilise a HCO(3) (-)-dependent system absent from other zones. Imaging of single BCECF-labelled cells was used to monitor the pH(i) of in situ chondrocytes within the cartilage zones, and also that of cells isolated from the SZ or full depth (FD) explants. Resting pH(i) and intrinsic buffering power (beta(i)) in HEPES-buffered saline was not different between SZ and DZ cells, however the pH(i) of SZ chondrocytes was lower in HCO(3) (-) saline. Ammonium pre-pulse was used to acid-load cells and pH(i) recovery by in situ or isolated SZ chondrocytes shown to be totally dependent on HCO(3) (-). pH(i) recovery rate was significantly (P < 0.05) greater for in situ cells, suggesting that isolation damaged the HCO(3) (-)-dependent system. Recovery of pH(i) by in situ cells was blocked by the anion transport inhibitor DIDS, and partially inhibited by EIPA probably non-specifically. Recovery of pH(i) by acidified MZ or DZ cells or those isolated from FD explants was not affected by HCO(3) (-) (P > 0.05). Na(+)-dependent HCO(3) (-)-(NBC) transporters were identified in SZ chondrocytes by fluorescence immunohistochemistry suggesting that this system might account for the HCO(3) (-)-dependent recovery of pH(i). Bovine articular cartilage chondrocytes possess a HCO(3) (-)-dependent transporter which plays a key role in pH(i) regulation in cells in the SZ, but not in chondrocytes within deeper cartilage zones.     

Do changes in the mechanical properties of articular cartilage promote catabolic destruction of cartilage and osteoarthritis?

Osteoarthritis (OA) is a joint disease characterized by cartilage degeneration, a thickening of subchondral bone, and formation of marginal osteophytes. Previous mechanical characterization of cartilage in our laboratory suggests that energy storage and dissipation is reduced in osteoarthritis as the extent of fibrillation and fissure formation increases. It is not clear whether the loss of energy storage and dissipation characteristics is a result of biochemical and/or biophysical changes that occur to hyaline cartilage in joints. The purpose of this study is to present data, on the strain rate dependence of the elastic and viscous behaviors of cartilage, in order to further characterize changes that occur in the mechanical properties that are associated with OA. We have previously hypothesized that the changes seen in the mechanical properties of cartilage may be due to altered mechanochemical transduction by chondrocytes. Results of incremental tensile stress-strain tests at strain rates between 100%/min and 10,000%/min conducted on OA cartilage indicate that the slope of the elastic stress-strain curve increases with increasing strain rate, unlike the reported behavior of skin and self-assembled collagen fibers. It is suggested that the strain-rate dependence of the elastic stress-strain curve is due to the presence of large quantities of proteoglycans (PGs), which protect articular cartilage by increasing the apparent stiffness. The increased apparent stiffness of articular cartilage at high strain rates may limit the stresses borne and prolong the onset of OA. It is further hypothesized that increased compressive loading of chondrocytes in the intermediate zone of articular cartilage occurs as a result of normal wear to the superficial zone or from excessive impact loading. Once the superficial zone of articular cartilage is worn away, the tension is decreased throughout all cartilage zones leading to increased chondrocyte compressive loading and up-regulation of mechanochemical transduction processes that elaborate catabolic enzymes.     

Lubrication of the human ankle joint in walking with the synovial fluid filtrated by the cartilage with the surface zone worn out: steady pure sliding motion.

A mixture model of synovial fluid filtration by cartilage in the human ankle joint during walking is presented for steady sliding motion of the articular surfaces. In the paper the cartilage surface zone is assumed worn out. The same model has been recently applied to the squeeze-film problem for the human hip joint loaded by the body weight during standing (Hlavácek, Journal of Biomechanics 26, 1145-1150, 1151-1160, 1993; Hlavácek and Novák, Journal of Biomechanics 28, 1193-1198, 1199-1205, 1995). The linear biphasic model for cartilage (elastic porous matrix + ideal fluid) due to Prof. V. C. Mow and his co-workers and the biphasic model for synovial fluid (viscous fluid + ideal fluid), as used in the above-mentioned squeeze-film problem, are applied. For the physiologic parameters of the ankle joint during walking, a continuous synovial fluid film about 1 microm thick is maintained under steady entraining motion according to the classical model without the fluid transport across the articular surface. This is not the case in the filtration model with the cartilage surface zones worn out. On the contrary, this filtration model indicates that synovial fluid is intensively filtrated by such cartilage, so that no continuous fluid film is maintained and a synovial gel layer, about 10(-8) m thick, develops over the majority of the contact. Thus, if the cartilage surface zones are worn out, boundary lubrication should prevail in the ankle joint under steady sliding motion for the mean values of loading and the sliding velocity encountered in walking cycle.     

FGF2 and dexamethasone increase the production of hyaluronan in two-dimensional culture of elastic cartilage-derived cells: in vitro analyses and in vivo cartilage formation

Elastic cartilage-derived cells cultured two-dimensionally with FGF2 and corticosteroid produce gel-type masses that become mature cartilage when injected into a subcutaneous pocket. This unique method has previously been clinically applied for treatments of nasal augmentation. However, the components of the gel-type mass and the mechanism of its synthesis remain unknown. Here, we have investigated the components of the gel-type mass produced by elastic cartilage-derived cells, and whether this gel-type mass can be produced by using other cell sources or other media. Human elastic cartilage-derived cells from auricular cartilage, hyaline cartilage-derived cells from articular cartilage, and mesenchymal stem cells from synovium were cultured in three media: “redifferentiation medium” containing FGF2 and dexamethasone; “chondrogenic medium” containing bone morphogenetic protein-2, transforming growth factor-β3, and dexamethasone specific for in vitro chondrogenesis of mesenchymal stem cells; control medium. The elastic cartilage-derived cells cultured in redifferentiation medium produced a gelatinous matrix positive for Alcian blue. During culture, the amount of chondroitin 4-sulfate, chondroitin 6-sulfate, and especially hyaluronan increased. However, the expression of RNAs for most chondrogenic genes did not increase. We also reproduced cartilage tissue formation by the injection of elastic cartilage-derived cells with the gelatinous mass into the subcutaneous space of the nude mouse. The synthesis of gelatinous matrix in vitro and the formation of cartilage tissue in vivo could be obtained only for the combination of elastic cartilage-derived cells with redifferentiation medium. This study was supported in part by grants from the “Japan Society for the Promotion of Science (19591752)” and “Center of Excellence Program for Frontier Research on Molecular Destruction and Reconstruction of Tooth and Bone in Tokyo Medical and Dental University” to Takeshi Muneta, and the “Japan Society for the Promotion of Science (18591657)” to Ichiro Sekiya.     

Spatial Mapping of the Biomechanical Properties of the Pericellular Matrix of Articular Cartilage Measured In Situ via Atomic Force Microscopy

In articular cartilage, chondrocytes are surrounded by a narrow region called the pericellular matrix (PCM), which is biochemically, structurally, and mechanically distinct from the bulk extracellular matrix (ECM). Although multiple techniques have been used to measure the mechanical properties of the PCM using isolated chondrons (the PCM with enclosed cells), few studies have measured the biomechanical properties of the PCM in situ. The objective of this study was to quantify the in situ mechanical properties of the PCM and ECM of human, porcine, and murine articular cartilage using atomic force microscopy (AFM). Microscale elastic moduli were quantitatively measured for a region of interest using stiffness mapping, or force-volume mapping, via AFM. This technique was first validated by means of elastomeric models (polyacrylamide or polydimethylsiloxane) of a soft inclusion surrounded by a stiff medium. The elastic properties of the PCM were evaluated for regions surrounding cell voids in the middle/deep zone of sectioned articular cartilage samples. ECM elastic properties were evaluated in regions visually devoid of PCM. Stiffness mapping successfully depicted the spatial arrangement of moduli in both model and cartilage surfaces. The modulus of the PCM was significantly lower than that of the ECM in human, porcine, and murine articular cartilage, with a ratio of PCM to ECM properties of ∼0.35 for all species. These findings are consistent with previous studies of mechanically isolated chondrons, and suggest that stiffness mapping via AFM can provide a means of determining microscale inhomogeneities in the mechanical properties of articular cartilage in situ.     

Immunolocalisation of BPTI-like serine proteinase inhibitory proteins in mast cells, chondrocytes and intervertebral disc fibrochondrocytes of ovine and bovine connective tissues. An immunohistochemical and biochemical study

A polyclonal anti-bovine pancreatic trypsin inhibitor (BPTI) IgY was raised in chickens immunised with aprotinin. The anti-BPTI IgY was subsequently isolated from egg yolks and purified to homogeneity by affinity chromatography on immobilised aprotinin and by Superose 6 size exclusion fast protein liquid chromatography (FPLC). Immunoblotting with the chicken IgY demonstrated its specificity for BPTI; 3.9 ng BPTI could be detected by this technique. There was no crossreactivity against alpha1-proteinase inhibitor (human and sheep), inter-alpha-trypsin inhibitor (human and sheep), secretory leucocyte proteinase inhibitor or a range of serine proteinase inhibitory proteins (SPIs) isolated from plant sources (soybean and lima bean trypsin inhibitor, potato trypsin and chymotrypsin inhibitors) or serum SPIs (antithrombin-III, alpha2-macroglobulin). Immunoblotting using the anti-BPTI IgY identified the 6- to 12- and 58-kDa forms of endogenous ovine cartilage SPIs in cartilage extracts, confirming the interrelationship of the ovine cartilage SPIs with BPTI. BPTI-domain SPIs were immunolocalised within mast cells of ovine and bovine duodenum, lung and pancreas, and in ovine and bovine bronchial cartilage chondrocytes, chondrocytes of the superficial and intermediate zones of articular cartilage and in the fibrochondrocytes/chondrocytes of the nucleus     

Ultrastructure of elastic cartilage in the rat external ear

Summary The structure of elastic cartilage in the external ear of the rat was investigated by transmission and scanning electron microscopy.The narrow subperichondrial, boundary zone contains predominantly ovoid cells rich in cell organelles: mitochondria, Golgi complex, granular endoplasmic reticulum and small (40–100 nm) vesicles. Scarce glycogen granules and bundles of 6–7 nm cytoplasmic filaments are also present. Deeper in the boundary zone, one or more cytoplasmic lipid droplets appear and cytofilaments become more abundant.Fully differentiated chondrocytes in the central zone of the cartilage plate resemble white adipose cells. They are globular and contain a single, large cytoplasmic lipid droplet. The cytoplasm is reduced to a thin peripheral rim; it contains a flattened nucleus, few cytoplasmic organelles and abundant, densely packed, cytoplasmic filaments.The intercellular matrix is very sparse. The pericellular ring consists of collagen fibrils about 20 nm in diameter and a proteoglycan cartilage matrix in the form of a stellate reticulum. The complex of these two structures appears in the scanning electron micrographs as a network of randomly oriented, ca 100 nm thick fibrils. Spaces between pericellular rings of matrix also contain thick elastic fibers or plates, apparently devoid of microfibrils. In scanning electron micrographs elastic fibers could be detected only in a few areas, in which they were not obscured by other constituents of the matrix. Immature forms of elastic fibers, oxytalan (pre-elastic) and elaunin fibers, were found in the perichondrial and boundary zones.     

Abnormalities of DNA in human osteoarthritic articular cartilage

The normal amount of DNA in human diploid nuclei was determined by the use of the Feulgen reaction measured by microdensitometry. The DNA-content of nuclei in normal human articular cartilage was determined in nuclei of zones 3 and 4 of cartilage of the femoral head removed from osteoporotic fractured necks of femur. Analysis of the results indicated that a degree of synthesis of DNA occurred even in these zones of very elderly persons. Results on these zones in the articular cartilage of osteoarthritic joints indicated that different populations occurred. In some there was DNA-synthesis related to tetraploidy; in others, the DNA was very stable to acid hydrolysis with no sign of biosynthetic activity; in the last group, which contained erosions of the superficial zones, the DNA was unstable to hydrolysis.     

Alterations in the mechanical properties of the human chondrocyte pericellular matrix with osteoarthritis

In articular cartilage, chondrocytes are surrounded by a pericellular matrix (PCM), which together with the chondrocyte have been termed the "chondron." While the precise function of the PCM is not know there has been considerable speculation that it plays a role in regulating the biomechanical environment of the chondrocyte. In this study, we measured the Young's modulus of the PCM from normal and osteoarthritic cartilage using the micropipette aspiration technique, coupled with a newly developed axisymmetric elastic layered half-space model of the experimental configuration. Viable, intact chondrons were extracted from human articular cartilage using a new microaspiration-based isolation technique. In normal cartilage, the Young's modulus of the PCM was similar in chondrons isolated from the surface zone (68.9 +/- 18.9 kPa) as compared to the middle and deep layers (62.0 +/- 30.5 kPa). However, the mean Young's modulus of the PCM (pooled for the two zones) was significantly decreased in osteoarthritic cartilage (66.5 +/- 23.3 kPa versus 41.3 +/- 21.1 kPa, p < 0.001). In combination with previous theoretical models of cell-matrix interactions in cartilage, these findings suggest that the PCM has an important influence on the stress-strain environment of the chondrocyte that potentially varies with depth from the cartilage surface. Furthermore, the significant loss of PCM stiffness that was observed in osteoarthritic cartilage may affect the magnitude and distribution of biomechanical signals perceived by the chondrocytes.     

Lack of chondroitin sulphate epitope in the proliferating zone of the growth plate of chicken tibia

Summary Monoclonal antibodies specific to chondroitin sulphate (CS-56) and keratan sulphate (AH12) were used to localize proteoglycans in the proximal tibial articular cartilage and growth plate of broiler chickens. There was no CS-56 labelling in the proliferative zone of the growth plate. In contrast, intense labelling with this antibody was observed in the transitional and hypertrophic zones of the growth plate and the articular cartilage. This was confirmed by extracting chondroitin sulphate fractions from different zones of the growth plate and articular cartilage, and examining their antigenicities to CS-56 by ELISA inhibition assay. It was suggested that the maturation of chondrocytes in the growth plate is related to the production of chondroitin sulphate with CS-56 epitope, which may be a prerequisite for normal endochondral bone formation in the chicken tibia. The role of chondroitin sulphate recognized by CS-56 in the articular cartilage is unknown.     

Resident mesenchymal progenitors of articular cartilage

Articular cartilage has poor capacity of self-renewal and repair. Insufficient number and activity of resident mesenchymal (connective tissue) progenitors is likely one of the underlying reasons. Chondroprogenitors reside not only in the superficial zone of articular cartilage but also in other zones of articular cartilage and in the neighboring tissues, including perichondrium (groove of Ranvier), synovium and fat pad. These cells may respond to injury and contribute to articular cartilage healing. In addition, marrow stromal cells can migrate through subchondral bone when articular cartilage is damaged. We should develop drugs and methods that correctly stimulate resident progenitors for improvement of repair and inhibition of degenerative changes in articular cartilage.     

Treatment of cartilage defects by Low-intensity pulsed ultrasound in a sheep model

Aim of this study was to evaluate effects of Low-intensity pulsed ultrasound on repair of articular cartilage defects. Low-intensity pulsed ultrasound (Lipus) can induce the differentiation and activation of chondrocytes. This study was designed to evaluate the effect of Lipus on articular cartilage defects in a sheep. Eight sheep were divided in to two groups. The animals received bilateraly, articular cartilage defects 4 mm in diameter and 2 mm in deep on the patellar groove and experimental groups were treated with intensity 200 mW/cm², 20 min/day with low-intensity pulsed ultrasound for 2 month. Then both knee joints underwent surgery for remove of formed tissue sample from defects.The samples were evaluated by Quantitative real-time polymerase chain reaction (qRT-PCR), Safranin-o staining, Immunofluorescence Staining and Morphological characterization. The best and worst sample per group according to Macroscopic and micriscopic scoring were icentified. The results showed that the operated groups with-Lipus-treatment and without-Lipus treatment had considered statistically significant. Gross photography revealed that the defects in experimental groups were filled with proliferative tissue, while in control groups, a thin layer of proliferative tissue was formed in defects. qRT-PCR results showed the expression of coll2, sox9, aggrecan and Osteocalcin in experimental groups. Intense safranin-O staining show the formation cartilage tissue in ultrasound treated group, while loose safranin-o-staining were observed at the control groups. Immunofluorescence staining showed the type 2 Collagen protein expression. We suggest that low-intensity pulsed ultrasound provide the mechanistic basis force for articular cartilage repair and effective treatment modality for improving of articular cartilage defects.

     

Development and growth of long bones in European water frogs (Amphibia: Anura: Ranidae), with remarks on age determination

Differentiation and development of long bones were studied in European water frogs: Rana lessonae, R. ridibunda, and R. esculenta. The study included premetamorphic larvae (Gosner Stage 40) to frogs that were 5 years old. Femora, metatarsal bones, and proximal phalanges of the hindlimb exhibit the same pattern of periosteal bone differentiation and the same pattern of growth. Longitudinal and radial growth of these bones was studied by examination of the diaphyses and epiphyses, particularly where the edge of periosteal bone is inserted into the epiphysis. The periosteum seems to be responsible for both longitudinal and radial growth. Investigation of the formation, length, and arrangement of lines of arrested growth reveals that the first line is present only in the middle 25-35% of the length of the diaphysis of an adult bone; therefore, only the central portion of the diaphysis should be used for age estimation in skeletochronological studies. Comparison of the shapes and histological structures of epiphyses in the femur, metatarsal bones, and phalanges revealed that epiphyseal cartilages are composed of an inner and outer part. The inner metaphyseal cartilage has distinct zones and plugs the end of the periosteal bone cylinder; its role in longitudinal growth is questioned. The outer epiphyseal cartilage is composed of articular cartilages proper, in addition to lateral articular cartilages. Differences in the symmetry of the lateral articular cartilages of distal epiphyses of the femur and toes may reflect adaptations to different kinds of movements at the knee and in the foot.     

The distribution patterns of COMP and matrilin-3 in septal,alar and triangular cartilages of the human nose

The biomechanical characteristics of septal cartilage depend strongly on the distinct extracellular matrix of cartilage tissue; therefore, it is essential that the components of this matrix are identified and understood. Cartilage oligomeric matrix protein (COMP) and matrilin-3 are localised in articular cartilage. This study was the first to examine all subtypes of mature human nasal cartilages (alar, triangular and septal) with specific attention to the distribution of COMP and matrilin-3. Three whole fresh-frozen noses from human donors were dissected, and exemplary biopsies were examined using histochemical staining (haematoxylin and eosin and Alcian blue) and immunohistochemistry (collagen II, COMP and matrilin-3). The following three zones within the nasal cartilage were identified: superficial, intermediate and central. COMP was detected as highest in the intermediate zones in all three subtypes of nasal cartilage, whereas matrilin-3 was detected with pericellular deposition mainly within septal cartilage predominantly in the superficial zones. The distinct staining patterns of COMP and matrilin-3 underscore the different functional roles of both proteins in nasal cartilage. According to the literature, COMP might be involved with collagen II in the formation of networks, whereas matrilin-3 is reported to prevent ossification or regulate mechanosensitivity. The predominant staining observed in septal cartilage suggests matrilin-3’s modulatory role because of its presence in the osteochondral junctional zone and given that the biomechanical load in septal cartilage is different from that in alar or triangular cartilage. In conclusion, COMP and matrilin-3 were detected in mature human nasal cartilage but displayed different staining patterns that might be explained by the functional roles of the respective matrix protein; however, further research is necessary to identify and define the functional aspects of this morphological difference.     

Comparison of nonlinear mechanical properties of bovine articular cartilage and meniscus

Nonlinear, linear and failure properties of articular cartilage and meniscus in opposing contact surfaces are poorly known in tension. Relationships between the tensile properties of articular cartilage and meniscus in contact with each other within knee joints are also not known. In the present study, rectangular samples were prepared from the superficial lateral femoral condyle cartilage and lateral meniscus of bovine knee joints. Tensile tests were carried out with a loading rate of 5 mm/min until the tissue rupture. Nonlinear properties of the toe region, linear properties in larger strains, and failure properties of both tissues were analysed. The strain-dependent tensile modulus of the toe region, Young's modulus of the linear region, ultimate tensile stress and toughness were on average 98.2, 8.3, 4.0 and 1.9 times greater (p<0.05) for meniscus than for articular cartilage. In contrast, the toe region strain, yield strain and failure strain were on average 9.4, 3.1 and 2.3 times greater (p<0.05) for cartilage than for meniscus. There was a significant negative correlation between the strain-dependent tensile moduli of meniscus and articular cartilage samples within the same joints (r=−0.690, p=0.014). In conclusion, the meniscus possesses higher nonlinear and linear elastic stiffness and energy absorption capability before rupture than contacting articular cartilage, while cartilage has longer nonlinear region and can withstand greater strains before failure. These findings point out different load carrying demands that both articular cartilage and meniscus have to fulfil during normal physiological loading activities of knee joints.