Properties Of Articular Cartilage Research Articles

Estimation of the mechanical property of meniscus using ultrasound: Examinations of native meniscus and effects of enzymatic digestion

We previously developed a novel ultrasound assessment system featuring wavelet transform to evaluate the material properties of articular cartilage. We aimed in this study to demonstrate the feasibility of quantitative evaluation of meniscus using ultrasound and to elucidate the relationships between its acoustic, mechanical, and biochemical properties. Meniscal disc specimens from mature pigs were assessed by ultrasound and compression testing, and their correlation was analyzed. A positive correlation was found between the ultrasound signal intensity and apparent Young's modulus (r=0.61). Subsequently, the porcine meniscal discs were treated with various enzymes and then characterized by ultrasound, by compression tests, by biochemical analyses, and by histology and immunohistochemistry. The signal intensity was decreased not by hyaluronidase but by collagenase treatment. Hyaluronidase-treated menisci showed a discrepancy between acoustic and mechanical properties, suggesting that the ultrasound reflection could not detect a reduction in proteoglycan content. Also, ultrasound signal intensity could only reflect superficial layers of the material. Several limitations exist at present, and further studies and improvements of the device are required. However, given the noninvasive nature and the requirement of only small equipment, this ultrasound assessment system will be an instrumental diagnostic tool for meniscal function in both research and clinical fields.

Effect of load variation on the friction properties of articular cartilage

Synovial joints are known for their remarkable load bearing capacity while maintaining very low friction and wear over their lifetime. Although other joint components play a role in the lubrication mechanisms, articular cartilage with its unique biphasic characteristics is believed to be largely responsible for the observed low friction properties in these joints. In the current study, a pin-on-plate machine was used in a cartilage loaded against cartilage configuration to study the effect of load variation on cartilage friction properties. Both static and dynamic loading conditions were tested under three different contact stress levels - 0.2, 0.3, and 0. 4 MPa with phosphate buffered saline as the lubricant. Indentation experiments were performed and modelled through finite-element (FE) method to determine the biphasic material properties of cartilage. A second FE model adopting the derived biphasic properties of cartilage was then used to simulate the static friction tests and determine the interstitial fluid load support in the cartilage tissue under different loads. An increase in contact stress was found to reduce the friction levels significantly ( p < 0.05) between the articulating cartilage surfaces in both dynamic and static models, while the percentage of fluid load support within the cartilage was almost identical. It was shown that while interstitial fluid pressurization of cartilage plays the major role, another extraneous factor or mechanism that influences the friction between cartilage surfaces is needed to completely explain the results observed.

In situ measurements of human articular cartilage stiffness by means of a scanning force microscope

Osteoarthritis is a painful and disabling progressive joint disease, characterized by degradation of articular cartilage. In order to study this disease at early stages, we have miniaturized and integrated a complete scanning force microscope into a standard arthroscopic device fitting through a standard orthopedic canula. This instrument will allow orthopedic surgeons to measure the mechanical properties of articular cartilage at the nanometer and micrometer scale in-vivo during a standard arthroscopy. An orthopedic surgeon assessed the handling of the instrument. First measurements of the elasticity-modulus of human cartilage were recorded in a cadaver knee non minimal invasive. Second, minimally invasive experiments were performed using arthroscopic instruments. Load-displacement curves were successfully recorded.

Investigation of articular cartilage and counterface compliance in multi-directional sliding as in orthopedic implants

As the use of total-joint replacement devices has become widespread, debris-induced osteolysis from ultra-high molecular weight polyethylene (UHMWPE) is still the primary challenge to lengthening the pain-free lifetime of these implants. Investigators have long suspected that the natural cartilage-on-cartilage interface found in synnovial joints is an optimal system, but technology has not advanced to the point of producing such an implant for use in total-joint replacement. The authors have investigated the performance of such a joint by developing an in vitro model of a cartilage-on-cartilage system. Bovine articular cartilage was fabricated into pins and subjected to multi-directional sliding in the Dual Axis Wear Simulator (DAWS), a machine developed by the authors to simulate conditions in an in vivo joint. The pins were worn against a rigid stainless steel counterface, similar to that found in conventional total-joint implants, and these results were compared to wear against a compliant polymeric counterface. The rigid counterface produced cartilage wear amounts with a mean of 25.65 mg after 100,000 cycles of 39 N loading and a 6.4-mm square wear path. However, use of the compliant counterface yielded a mean wear value of 9.97 mg for the same testing conditions. It is likely that the mechanism responsible for this wear involves the generation and subsequent depletion of a fluid layer at the interface between the cartilage pin and the counterface such that the majority of material removal occurred during the fluid deficient portions of the wear cycle. This difference in wear amounts was attributed to the substantial difference in contact pressures between the rigid and compliant counterfaces. To estimate the contact pressures in each case, the storage and loss moduli were measured for cartilage samples through dynamic mechanical analysis (DMA). It was found that over a frequency range from 0.1 to 10 Hz, the storage modulus ranged from 470 to 1010 kPa, while the loss modulus increased more modestly, from 176 to 249 kPa. The results of wear testing and the measurement of the viscoelastic properties of articular cartilage suggest the possibility of successful cartilage-on-metal implant systems where the contact pressures are kept low through joint geometry or the use of a biocompatible compliant surface on the metallic component.

B113 関節軟骨の超音波特性とその計測法の検討(B1-4 関節4)

B113 関節軟骨の超音波特性とその計測法の検討(B1-4 関節4)

Effect of a single impact loading on the structure and mechanical properties of articular cartilage

Aim To study the effect of a single impact on the structure and mechanical properties of cartilage. Materials and method Osteochondral plugs harvested from bovine femora were subjected each to a single impact using an in-house designed drop-tower. Impact masses of different values were released from different drop heights in selected combinations to apply stresses at strain rates and impact energies within specific ranges. Changes in the storage and loss moduli were estimated from cyclic compressive loading test undertaken before and after impact. The conditions of these tests were set to those occurring during walking and running. The extent of the damage on cartilage surface and depth was assessed using optical and confocal microscopy. Results The storage modulus varied slightly at level walking and running after performing impact tests up to the impact energy of 0.736 J. However, the decrease in the storage modulus was considerable at the impact energy of 1.962 J for test conditions representing both walking and running. This impact energy resulted in strain rate of 1500 s −1, stress of 25 MPa and energy absorbed per unit volume of 12.79 mJ/mm 3. After impact the loss modulus increased over the loading cycles at all energies. Severe fissures were observed across the cartilage surface and through its thickness at levels of impact energy equal or grater than 1.472 J. Conclusions This study identified thresholds for the strain rate, impact stress and impact energy, which caused permanent changes in the mechanical properties and damage to structure of cartilage.

Biomechanical properties of articular cartilage as a standard for biologically integrated interfaces

Articular cartilage integration has been described in in-vitro models, which compare mechanical to biochemical behaviour and histological analysis, respectively. The emphasis of these findings is mainly on the biochemical and histological analysis, rather than on the mechanical performance. The complex in vitro loading conditions and high deviations in the mechanical results due to the biological variance, make interpretations difficult. The aim of this study is to analyse and define the mechanical stress and strain distribution in a single lap configuration by means of an optical strain measurement system. Supportive finite element computation is performed to indicate the heterogeneous stress strain distribution in the integration area. The optical failure analysis of the experiment reveals crack propagation through the integration area comparable to plane shear in fracture mode two. Using the optical strain measurement set up a direct estimation of the shear modulus is achievable by analysing the relative displacement within the bonded joint before the onset of delamination in the adhesive layer. This result lead to a better interpretation of the mechanical behaviour of articular cartilage integration in vitro.

Extraction of Mechanical Properties of Articular Cartilage From Osmotic Swelling Behavior Monitored Using High Frequency Ultrasound

Articular cartilage is a biological weight-bearing tissue covering the bony ends of articulating joints. Negatively charged proteoglycan (PG) in articular cartilage is one of the main factors that govern its compressive mechanical behavior and swelling phenomenon. PG is nonuniformly distributed throughout the depth direction, and its amount or distribution may change in the degenerated articular cartilage such as osteoarthritis. In this paper, we used a 50 MHz ultrasound system to study the depth-dependent strain of articular cartilage under the osmotic loading induced by the decrease of the bathing saline concentration. The swelling-induced strains under the osmotic loading were used to determine the layered material properties of articular cartilage based on a triphasic model of the free-swelling. Fourteen cylindrical cartilage-bone samples prepared from fresh normal bovine patellae were tested in situ in this study. A layered triphasic model was proposed to describe the depth distribution of the swelling strain for the cartilage and to determine its aggregate modulus H(a) at two different layers, within which H(a) was assumed to be linearly dependent on the depth. The results showed that H(a) was 3.0+/-3.2, 7.0+/-7.4, 24.5+/-11.1 MPa at the cartilage surface, layer interface, and deep region, respectively. They are significantly different (p<0.01). The layer interface located at 70%+/-20% of the overall thickness from the uncalcified-calcified cartilage interface. Parametric analysis demonstrated that the depth-dependent distribution of the water fraction had a significant effect on the modeling results but not the fixed charge density. This study showed that high-frequency ultrasound measurement together with triphasic modeling is practical for quantifying the layered mechanical properties of articular cartilage nondestructively and has the potential for providing useful information for the detection of the early signs of osteoarthritis.

Nanoindentation differentiates tissue‐scale functional properties of native articular cartilage

Cartilage mechanical properties are typically tested at the macroscale. To demonstrate the ability of nanoindentation to characterize in situ articular cartilage properties at the tissue scale, we investigated the local structure-property relationships of intact articular cartilage of a normal rabbit metacarpophalangeal joint. We calculated the mechanical parameters of stiffness, S, resistance to penetration, R, and volumetric creep strain, dV/V, from nanoindentation of the articular surface at specific regions of interest. We measured morphological parameters of superficial zone thickness, middle zone thickness, total uncalcified thickness, and cell density from corresponding regions with light and polarized light microscopy. Mechanical parameters were compared to morphological parameters. There were significant positive correlations (r = 0.98, p < 0.05) between superficial zone thickness and both S and R. However, we found no significant correlation between dV/V and the zone sizes. There were moderate, negative correlations between cell density and both S and R, suggesting an effect of cell volume on cartilage behavior at the tissue scale. We opine that the superficial zone plays important role in load support, as evidenced by correlations between zone size and intact cartilage mechanical properties.

Depth-dependent Compressive Equilibrium Properties of Articular Cartilage Explained by its Composition

For this study, we hypothesized that the depth-dependent compressive equilibrium properties of articular cartilage are the inherent consequence of its depth-dependent composition, and not the result of depth-dependent material properties. To test this hypothesis, our recently developed fibril-reinforced poroviscoelastic swelling model was expanded to include the influence of intra- and extra-fibrillar water content, and the influence of the solid fraction on the compressive properties of the tissue. With this model, the depth-dependent compressive equilibrium properties of articular cartilage were determined, and compared with experimental data from the literature. The typical depth-dependent behavior of articular cartilage was predicted by this model. The effective aggregate modulus was highly strain-dependent. It decreased with increasing strain for low strains, and increases with increasing strain for high strains. This effect was more pronounced with increasing distance from the articular surface. The main insight from this study is that the depth-dependent material behavior of articular cartilage can be obtained from its depth-dependent composition only. This eliminates the need for the assumption that the material properties of the different constituents themselves vary with depth. Such insights are important for understanding cartilage mechanical behavior, cartilage damage mechanisms and tissue engineering studies.

Compressive Properties of Mouse Articular Cartilage Determined in a Novel Micro-Indentation Test Method and Biphasic Finite Element Model

The mechanical properties of articular cartilage serve as important measures of tissue function or degeneration, and are known to change significantly with osteoarthritis. Interest in small animal and mouse models of osteoarthritis has increased as studies reveal the importance of genetic background in determining predisposition to osteoarthritis. While indentation testing provides a method of determining cartilage mechanical properties in situ, it has been of limited value in studying mouse joints due to the relatively small size of the joint and thickness of the cartilage layer. In this study, we developed a micro-indentation testing system to determine the compressive and biphasic mechanical properties of cartilage in the small joints of the mouse. A nonlinear optimization program employing a genetic algorithm for parameter estimation, combined with a biphasic finite element model of the micro-indentation test, was developed to obtain the biphasic, compressive material properties of articular cartilage. The creep response and material properties of lateral tibial plateau cartilage were obtained for wild-type mouse knee joints, by the micro-indentation testing and optimization algorithm. The newly developed genetic algorithm was found to be efficient and accurate when used with the finite element simulations for nonlinear optimization to the experimental creep data. The biphasic mechanical properties of mouse cartilage in compression (average values: Young's modulus, 2.0 MPa; Poisson's ratio, 0.20; and hydraulic permeability, 1.1 x 10(-16) m4/N-s) were found to be of similar orders of magnitude as previous findings for other animal cartilages, including human, bovine, rat, and rabbit and demonstrate the utility of the new test methods. This study provides the first available data for biphasic compressive properties in mouse cartilage and suggests a promising method for detecting altered cartilage mechanics in small animal models of osteoarthritis.

Mechanical properties of articular cartilage covered by the meniscus

To investigate the mechanical properties and morphological characteristics of articular cartilage on the tibial plateau of human knees, including the region covered by the meniscus. Using a 1-mm diameter flat-ended cylindrical probe to apply a constant load (0.6 MPa) at specific sites on the tibial plateau, the mechanical properties of articular cartilage were studied using seven cadaver knees. Comparison was made between data obtained by the cartilage covered by the meniscus and that not covered. This was done for both the medial and lateral plateaus. Histological sections of the articular cartilage were also performed to study differences between cartilage from these regions of the tibial plateau. Compared to cartilage that was not covered by the meniscus, the articular cartilage beneath the meniscus showed a significantly (P<0.05) larger modulus by as much as 70%, and was less thick by about 40%. Also, the subchondral bone quantity and calcified layer thickness were observed to be significantly lesser in the regions covered by the meniscus. Our findings revealed a significant difference between the mechanical properties and associated structures of articular cartilage in the region covered by the meniscus compared with the articular cartilage not covered by the meniscus.

Effects of Ageing on the Biomechanical Properties of Rat Articular Cartilage

Previous studies have demonstrated that male Sprague Dawley (SD) rats experience age-related bone loss with the same characteristics as that in ageing men. As articular cartilage, like bone, is a critical component of the health and function of the musculoskeletal system, the authors hypothesized that articular cartilage in the untreated male SD rats could be a suitable model for studying the age-related deterioration of articular cartilage in men. To test this hypothesis, male SD rats were killed at between 6 and 27 months. The right femur of each rat was removed. The effects of ageing on the structural integrity of the distal femoral articular cartilage were studied by biomechanical testing with a creep indentation apparatus. The aggregate modulus, Poisson's ratio, permeability, thickness, and percentage recovery of articular cartilage were determined using finite element/non-linear optimization modelling. No significant differences were observed in these biomechanical properties of the distal femoral articular cartilage as a function of age. Therefore, untreated male SD rats appear to be unsuitable for studying the age-related changes of articular cartilage as they occur in men. However, and more intriguingly, it is also possible that ageing does not affect the biomechanical properties of articular cartilage in the absence of cartilage pathology.

Determination of characteristics of degenerative joint disease using optical coherence tomography and polarization sensitive optical coherence tomography

Previous studies have demonstrated that optical coherence tomography (OCT) could be used to delineate alterations in the microstructure of cartilage, and have suggested that changes in the polarization state of light as detected by OCT could provide information on the birefringence properties of articular cartilage as influenced by disease. In this study we have used both OCT and polarization sensitive optical coherence tomography (PS-OCT) technologies to evaluate normal and abnormal bovine articular cartilage according to established structural, organizational, and birefringent characteristics of degenerative joint disease (DJD) in order to determine if this technology can be used to differentiate various stages of DJD as a minimally invasive imaging tool. Fresh bovine femoral-tibial joints were obtained from an abattoir, and 45 cartilage specimens were harvested from 8 tibial plateaus. Whole ex vivo specimens of normal and degenerative articular cartilage were imaged by both OCT and PS-OCT, then fixed and processed for histological evaluation. OCT/PS-OCT images and corresponding histology sections of each specimen were scored according to a modified Mankin structural grading scale and compared. OCT and PS-OCT imaging allowed structural evaluation of intact articular cartilage along a 6 mm surface length to a depth of 2 mm with a transverse resolution of 12 microm and an axial resolution of 10 microm. The OCT and PS-OCT images demonstrated characteristic alterations in the structure of articular cartilage with a high correlation to histological evaluation (kappa = 0.776). The OCT images were able to demonstrate early to advanced structural changes of articular cartilage while the optical phase retardation images obtained by PS-OCT imaging were able to discriminate areas where disorganization of the cartilage matrix was present, however, these characteristics are much different than those reported where OCT images alone were used to characterize tissue birefringence. No evidence of differences in OCT or PS-OCT images were detected between specimens of similar structural characteristics where proteoglycan was judged present or absent by safranin-O Fast Green staining. The combined use of OCT and PS-OCT technologies to obtain images from a single system is able to demonstrate and discriminate between characteristics of very early stages of surface irregularities not previously reported for OCT imaging, to deep clefts and collagen matrix disorganization for tissue at depths of up to 2 mm with good correlation to histology. PS-OCT and accumulated optical phase retardation images of articular cartilage as constructed from alterations in Stokes vector parameters appear to give a valuable but different assessment of alterations in tissue birefringence and organization than have been reported for OCT images obtained with the use of polarized or non-polarized light sources. This is the first time that alterations in the polarization state of light reflected from within the tissue have been demonstrated to be consistent with changes observed in the orientation and organization of the collagen matrix in advanced stages of DJD. The degree of phase transformation of light reflected from within the tissue as determined by PS-OCT imaging does not appear to be altered by the presence or absence of proteoglycan.

In vivo study on the short-term effect of radiofrequency energy on chondromalacic patellar cartilage and its correlation with calcified cartilage pathology in an equine model

Chondromalacia can cause joint pain and synovial effusion with the potential for developing into osteoarthritis. Thermal chondroplasty using radiofrequency energy (RFE) has been reported to be superior to mechanical debridement for treating chondromalacia. We compared short-term changes in biomechanical properties of articular cartilage after treatment with monopolar (mRFE) or bipolar RFE (bRFE) or mechanical debridement (MD) on experimentally created grade II chondromalacia patellae. Chondromalacia patellae was created arthroscopically in both patellae of 15 ponies. Ten months after surgery, each patella was randomly assigned to one of four experimental groups: sham operated, untreated control; MD; bRFE; and mRFE. Animals were euthanized 6 months after treatment and fresh osteochondral sections were collected from the treated area, the border of the chondromalacic and nonchondromalacic area, and from two untreated areas for analysis of mechanical properties. The same areas were harvested from an additional six untreated ponies. The aggregate modulus (H(A)), Poisson's ratio (nu(s)), and permeability (k) were determined for each area under creep indentation, and cartilage thickness was measured with a needle probe. The relation between zone of calcified cartilage (ZCC) and mechanical properties of hyaline cartilage (HC) was assessed histomorphometrically. Treated areas of all four groups had inferior mechanical properties compared at the same location. The treated and border areas had significantly lower H(A) values than the untreated areas. Permeability values showed significant differences between bRFE and other treated groups. Chondromalacic areas showed thinning of cartilage compared to nonchondromalacic areas. Biomechanical properties of the injured cartilage were inferior to nonchondromalacic cartilage regardless of the treatment type. mRFE had the highest stiffness value compared to other treatments and significantly higher values than MD. A significant correlation was observed between the mechanical properties of HC and ZCC thickness.

Application of acrylic split-hopkinson-bar method for determining mechanical properties of articular cartilage at high strain rate

Application of acrylic split-hopkinson-bar method for determining mechanical properties of articular cartilage at high strain rate

Determination of elastic properties of articular cartilage by aspiration test

Determination of elastic properties of articular cartilage by aspiration test

Biochemical and Biomechanical Properties of Lesion and Adjacent Articular Cartilage after Chondral Defect Repair in an Equine Model

Background Chondral defects may lead to degradative changes in the surrounding cartilage, predisposing patients to developing osteoarthritis. Purpose To quantify changes in the biomechanical and biochemical properties of the articular cartilage adjacent to chondral defects after experimental defect repair. Study Design Controlled laboratory study. Methods Specimens were harvested from tissue within (lesion), immediately adjacent to, and at a distance from (remote area) a full-thickness cartilage defect 8 months after cartilage repair with genetically modified chondrocytes expressing insulin-like growth factor-I or unmodified, control chondrocytes. Biomechanical properties, including instantaneous Young's and equilibrium aggregate moduli, were determined by confined compression testing. Biochemical properties, such as water and proteoglycan content, were also measured. Results The instantaneous Young's modulus, equilibrium modulus, and proteoglycan content increased, whereas water content decreased with increasing distance from the repaired lesion. The instantaneous Young's and equilibrium moduli of the adjacent articular cartilage were 80% and 50% that of remote area samples, respectively, whereas water content increased 0.9% and proteoglycan content was decreased by 35%. No significant changes in biomechanical and biochemical properties were found either in the lesion tissue or in adjacent cartilage with genetic modification of the chondrocytes. Conclusion Articular cartilage adjacent to repaired chondral defects showed significant remodeling 8 months after chondral defect repair, regardless of whether genetically modified or unmodified cells were implanted. Clinical Relevance Changes in the biochemical and biomechanical properties of articular cartilage adjacent to repaired chondral defects may represent remodeling as part of an adaptive process or degeneration secondary to an altered distribution of joint forces. Quantification of these changes could provide important parameters for assessing progress after operative chondral defect repair.

Material properties of articular cartilage in the rabbit tibial plateau

The material properties of articular cartilage in the rabbit tibial plateau were determined using biphasic indentation creep tests. Cartilage specimens from matched-pair hind limbs of rabbits approximately 4 months of age and greater than 12 months of age were tested on two locations within each compartment using a custom built materials testing apparatus. A three-way ANOVA was used to determine the effect of leg, compartment, and test location on the material properties (aggregate modulus, permeability, and Poisson's ratio) and thickness of the cartilage for each set of specimens. While no differences were observed in cartilage properties between the left and right legs, differences between compartments were found in each set of specimens. For cartilage from the adolescent group, values for aggregate modulus were 40% less in the medial compartment compared to the lateral compartment, while values for permeability and thickness were greater in the medial compartment compared to the lateral compartment (57% and 30%, respectively). Values for Poisson's ratio were 19% less in the medial compartment compared to the lateral compartment. There was also a strong trend for thickness to differ between test locations. Similar findings were observed for cartilage from the mature group with values for permeability and thickness being greater in the medial compartment compared to the lateral compartment (66% and 34%, respectively). Values for Poisson's ratio were 22% less in the medial compartment compared to the lateral compartment.

Method of Evaluation a Basic Mechanic Property of Cartilage

Many osteoarthritis animal models have been studied, attempting to model these findings after those of humans. an animal model that could develop naturally occurring osteoarthritis in a manner similar to humans would be of great benefit for future research. Studies with cynomologous macaques have shown that these animals develop naturally occurring os� teoarthritis similar to that in humans. The goal of the current project was to examine the basic biome� chanical characteristics of normal cynomologous macaque distal femoral articular cartilage as well as to develop a proper biomechanical testing protocol. Testing was performed with the EnduraTEC machine. Using a 0.5mm radius nonpermeable cylindrical indenter, instantaneous linear ramp compressions were applied to the cartilage specimens at a rate of 10 mm/sec to a depth of 0.15 mm. The thickness of the articular cartilage specimen was determined by using the needle probe. A load deformation curve was obtained and analyzed to determine the thickness. Using a linear elastic model, we assumed that compression was instantaneous. Young's Modulus (N/ mm2 = MPa) was calculated by plotting stress (load/crosssectional area) vs. strain (displacement/ thickness) and calculating the equation of the line. Stiffness (N/mm) was obtained by plotting load vs. displacement. Both were reached calculating the bestfit line form the speed compression ramp. Only one previous published experiment attempted to characterize the biomechanical properties of nor� mal cynomologous macaque monkey articular cartilage. Our study attempted to use a more simplified approach to calculate Young's modulus and stiffness. By assuming that the compression was instantane� ous and using an impermeable indenter we were able to calculate what we feel are important biome� chanical properties of articular cartilage.