Electromechanical probe and automated indentation maps are sensitive techniques in assessing early degenerated human articular cartilage

Non-invasive electroarthrography measures cartilage in live horses and correlates to direct measurements of cartilage streaming potentials in weight bearing regions of equine metacarpophalangeal joints

OBJECTIVE

To perform non-invasive Electroarthrography (EAG) on live horses and establish relationships between EAG and direct measurements of cartilage streaming potentials in weight bearing areas of the equine metacarpophalangeal joint.

DESIGN

EAG was performed bilaterally on the metacarpophalangeal joints of live horses (n = 3). Separate experiments used metacarpophalangeal joint explants (n = 11) to measure EAG obtained during simulated loading followed by direct measurements of cartilage streaming potentials on joint surfaces using the Arthro-BST probe. Joints were assigned to relatively normal (n = 5) and mildly degraded (n = 6) groups based on histological scoring of Safranin-O/Fast Green stained sections.

RESULTS

EAG, involving application of electrodes to skin surrounding the joint and repeated weight shifting, was well-tolerated in live horses. One pair of distal forelimbs were available for analogous ex vivo EAG testing and measurements were strongly correlated to in vivo EAG measurements obtained on the same joints (r = 0.804, p = 0.016, n = 8). Both indirect (EAG) and direct (Arthro-BST) measurements of cartilage streaming potentials distinguished between normal and mildly degraded cartilage with statistically significant differences at 5 of 6 and 4 of 6 electrodes during simulated standing and walking, respectively. Strong and moderate correlations for weight bearing regions on the dorsal phalanx and central metacarpus were detected during both standing and walking. At the metacarpus/sesamoid interface a moderate correlation occurred during walking.

CONCLUSION

Non-invasive EAG was used successfully in a clinical scenario and correlated to direct measurements of streaming potentials in weight bearing cartilage. These data support the potential of EAG to contribute to the diagnosis and treatment of degenerative joint diseases.

Arthroscopic Electromechanical Assessment of Human Articular Cartilage Injury Correlates with ICRS Scores

PURPOSE

This study aimed to conduct arthroscopic evaluation of cartilage electromechanical properties and establish their correlation with International Cartilage Repair Society (ICRS) grading scores.

METHODS

In 18 patients, quantitative parameter (QP) measurements were taken on the weight-bearing surface of the medial femoral condyle. Adjacently, the same site was graded using ICRS scores (0-4). Electromechanical QPs for ICRS grades 0 to 3 were obtained during arthroscopy, while complete grade 4 injuries were assessed using femur cartilage-bone blocks from knee arthroplasty. The QP values for ICRS grades 0 to 2 were compared with grades 3 and 4 using Welch t test. The corresponding QP values were assigned to ICRS grades 0 to 4 and compared using Welch ANOVA (analysis of variance). Pearson's coefficient evaluated QP-ICRS grade relationship.

RESULTS

Healthy grade 0 cartilage displayed a mean QP value of 10.5 (±2.8 SD, n = 4). The ICRS grade 1 and grade 2 injuries were associated with QP values of 12 (±0.7, n = 2) and 13.25 (±1.77, n = 2), respectively. The grade 3 defects had QP values of 20.43 (±4.84, n = 4), whereas complete grade 4 defects showed electromechanical values of 30.17 (±2.19, n = 6). Significant differences in QP values were observed between ICRS grades 0 to 2 (mean QP 11.56 ± 2.3, n = 8) and grades 3 and 4 (26.27 ± 6, n = 10; P < 0.0001). Pearson's correlation coefficient of 0.9 indicated a strong association between higher ICRS cartilage injury grades and elevated QP values (P < 0.0001).

CONCLUSION

Arthroscopic electromechanical QP assessment robustly correlates with ICRS scores. The QP values for ICRS grades 0 to 2 are significantly lower, compared with grades 3 and 4.

Ex vivo storage of human osteochondral allografts: Long-term analysis over 300 days using a Ringer-based solution

Large osteochondral defects are a major challenge in orthopedics, for which osteochondral allograft (OCA) transplantation is nowadays considered as an option, especially in young patients. However, a major issue with OCA is the need for graft storage, which ensures adequate cartilage integrity over time. The aim of this study was to test how long a Ringer-based storage solution can provide good graft quality after explantation and thus meet the requirements for OCA. For this purpose, human osteochondral allografts of the knee and ankle were analyzed. Live/Dead analysis was performed and glycosaminoglycan, as well as hydroxyproline content, were measured as crucial chondrocyte integrity factors. Furthermore, biomechanical tests focusing on stress relaxation and elastic compression modulus were performed. The critical value of 70% living chondrocytes, which corresponds to a number of 300 cells/mm², was reached after an average of 16 weeks of storage. In addition, a constant cell shrinkage was observed over time. The amount of glycosaminoglycan and hydroxyroline showed a slight and constant decrease over time, but no significant differences when compared from Day 0 to the values at Weeks 40-43. Biomechanical testing also revealed no significant differences at the different time points. Therefore, the results show that the Ringer-based storage solution at 4°C is able to provide a chondrocyte survival of 70% until Week 16. This is comparable to previously published storage solutions. Therefore, the study contributes to the establishment of a Ringer-based osteochondral allograft transplantation system for countries where medium-based storage solution cannot be approved.

Region partitioning of articular cartilage with streaming-potential-based parameters and indentation maps

Articular cartilage exhibits site-specific tissue inhomogeneity, for which the tissue properties may continuously vary across the articular surface. To facilitate practical applications such as studying site-specific cartilage degeneration, the inhomogeneity may be approximated with several distinct region-wise variations, with one set of tissue properties for one region. A clustering method was previously developed to partition such regions using cartilage indentation-relaxation and thickness mapping instead of simply using surface geometry. In the present study, a quantitative parameter based on streaming potential measurement was introduced as an additional feature to assess the applicability of the methodology with independent datasets. Experimental data were collected from 24 sets of femoral condyles, extracted from fresh porcine stifle joints, through streaming potential mapping, automated indentation, and needle penetration tests. K-means clustering and Elbow method were used to find optimal region partitions. Consistent with previous findings, three regions were suggested for either lateral or medial condyle regardless of left or right joint. The region shapes were approximately triangular or trapezoidal, which was similar to what was found previously. Streaming potentials were confirmed to be region-dependent, but not significantly different among joints. The cartilage was significantly thicker in the medial than lateral condyles. The region areas were consistent among joints, and comparable to that found in a previous study. The present study demonstrated the capability of region partitioning methods with different variables, which may facilitate new applications whenever site-specific tissue properties must be considered.

Site-specific elastic and viscoelastic biomechanical properties of healthy and osteoarthritic human knee joint articular cartilage

Articular cartilage exhibits site-specific biomechanical properties. However, no study has comprehensively characterized site-specific cartilage properties from the same knee joints at different stages of osteoarthritis (OA). Cylindrical osteochondral explants (n = 381) were harvested from donor-matched lateral and medial tibia, lateral and medial femur, patella, and trochlea of cadaveric knees (N = 17). Indentation test was used to measure the elastic and viscoelastic mechanical properties of the samples, and Osteoarthritis Research Society International (OARSI) grading system was used to categorize the samples into normal (OARSI 0-1), early OA (OARSI 2-3), and advanced OA (OARSI 4-5) groups. OA-related changes in cartilage mechanical properties were site-specific. In the lateral and medial tibia and trochlea sites, equilibrium, instantaneous and dynamic moduli were higher (p < 0.001) in normal tissue than in early and advanced OA tissue. In lateral and medial femur, equilibrium, instantaneous and dynamic moduli were smaller in advanced OA, but not in early OA, than in normal tissue. The phase difference (0.1-0.25 Hz) between stress and strain was significantly smaller (p < 0.05) in advanced OA than in normal tissue across all sites except medial tibia. Our results indicated that in contrast to femoral and patellar cartilage, equilibrium, instantaneous and dynamic moduli of the tibia and trochlear cartilage decreased in early OA. These may suggest that the tibia and trochlear cartilage degrades faster than the femoral and patellar cartilage. The information is relevant for developing site-specific computational models and engineered cartilage constructs.

Mechanical and histological properties of native medial menisci compared to allograph medial menisci in the osteoarthritic knee

This study was designed to provide information on how the menisci change over the course of osteoarthritis, particularly with regard to their mechanical properties. The aim was to determine the difference between healthy menisci (fresh frozen meniscal transplants) and menisci harvested during total knee arthroplasty. The latter allows the grading of age-related and osteoarthritic changes in the menisci on macroscopic and microscopic levels. A total of 10 menisci from arthritic knee joints (medial) harvested during total knee arthroplasty were used and compared with 10 medial fresh frozen meniscal transplants. The mechanical measurements were carried out on a Mach-1 testing machine using indentation testing to determine the instantaneous modulus and the thickness of the menisci. The specimens were then embedded in paraffin, sectioned on a microtome, and stained with hematoxylin-eosin and safranin-O. All measurements were divided into the anterior horn, pars intermedia, and posterior horn. There was no significant difference in the instantaneous modulus for the posterior horn in the fresh frozen menisci with 0.27 ± 0.1 MPa compared to the arthritic menisci with 0.18 ± 0.03 MPa. No significant difference could be determined for the meniscus thicknesses. There was a significant difference in the safranin-O staining. There were also significant differences in the Pauli score: the arthrosis menisci showed a sum score that was, on average, four times higher than the sum score of the fresh frozen menisci. In the present study, it could be shown very well that there are significant differences in the mechanical properties as well as in the macroscopic and histopathological scores, such as the Pauli score, between the fresh frozen meniscus allografts considered healthy and osteoarthritic menisci resulting from total knee arthroplasty. With a degradation score of 3 (Pauli), the instantaneous modulus was reduced by more than 50% compared to healthy controls. More importantly, however, the fresh frozen menisci only show a grade 2 when converting the sum values into grades, where a grade 2 indicates slight degeneration. This is interesting because fresh frozen meniscus transplants were always considered healthy in previous publications and should, therefore, actually have a grade 1.

Biomechanics of the Human Osteochondral Unit: A Systematic Review

The damping system ensured by the osteochondral (OC) unit is essential to deploy the forces generated within load-bearing joints during locomotion, allowing furthermore low-friction sliding motion between bone segments. The OC unit is a multi-layer structure including articular cartilage, as well as subchondral and trabecular bone. The interplay between the OC tissues is essential in maintaining the joint functionality; altered loading patterns can trigger biological processes that could lead to degenerative joint diseases like osteoarthritis. Currently, no effective treatments are available to avoid degeneration beyond tissues' recovery capabilities. A thorough comprehension on the mechanical behaviour of the OC unit is essential to (i) soundly elucidate its overall response to intra-articular loads for developing diagnostic tools capable of detecting non-physiological strain levels, (ii) properly evaluate the efficacy of innovative treatments in restoring physiological strain levels, and (iii) optimize regenerative medicine approaches as potential and less-invasive alternatives to arthroplasty when irreversible damage has occurred. Therefore, the leading aim of this review was to provide an overview of the state-of-the-art-up to 2022-about the mechanical behaviour of the OC unit. A systematic search is performed, according to PRISMA standards, by focusing on studies that experimentally assess the human lower-limb joints' OC tissues. A multi-criteria decision-making method is proposed to quantitatively evaluate eligible studies, in order to highlight only the insights retrieved through sound and robust approaches. This review revealed that studies on human lower limbs are focusing on the knee and articular cartilage, while hip and trabecular bone studies are declining, and the ankle and subchondral bone are poorly investigated. Compression and indentation are the most common experimental techniques studying the mechanical behaviour of the OC tissues, with indentation also being able to provide information at the micro- and nanoscales. While a certain comparability among studies was highlighted, none of the identified testing protocols are currently recognised as standard for any of the OC tissues. The fibril-network-reinforced poro-viscoelastic constitutive model has become common for describing the response of the articular cartilage, while the models describing the mechanical behaviour of mineralised tissues are usually simpler (i.e., linear elastic, elasto-plastic). Most advanced studies have tested and modelled multiple tissues of the same OC unit but have done so individually rather than through integrated approaches. Therefore, efforts should be made in simultaneously evaluating the comprehensive response of the OC unit to intra-articular loads and the interplay between the OC tissues. In this regard, a multidisciplinary approach combining complementary techniques, e.g., full-field imaging, mechanical testing, and computational approaches, should be implemented and validated. Furthermore, the next challenge entails transferring this assessment to a non-invasive approach, allowing its application in vivo, in order to increase its diagnostic and prognostic potential.

Functional Assessment of Human Articular Cartilage Using Second Harmonic Generation (SHG) Imaging: A Feasibility Study

Many arthroscopic tools developed for knee joint assessment are contact-based, which is challenging for in vivo application in narrow joint spaces. Second harmonic generation (SHG) laser imaging is a non-invasive and non-contact method, thus presenting an attractive alternative. However, the association between SHG-based measures and cartilage quality has not been established systematically. Here, we investigated the feasibility of using image-based measures derived from SHG microscopy for objective evaluation of cartilage quality as assessed by mechanical testing. Human tibial plateaus harvested from nine patients were used. Cartilage mechanical properties were determined using indentation stiffness (Einst) and streaming potential-based quantitative parameters (QP). The correspondence of the cartilage electromechanical properties (Einst and QP) and the image-based measures derived from SHG imaging, tissue thickness and cell viability were evaluated using correlation and logistic regression analyses. The SHG-related parameters included the newly developed volumetric fraction of organised collagenous network (Φcol) and the coefficient of variation of the SHG intensity (CVSHG). We found that Φcol correlated strongly with Einst and QP (ρ = 0.97 and - 0.89, respectively). CVSHG also correlated, albeit weakly, with QP and Einst, (|ρ| = 0.52-0.58). Einst and Φcol were the most sensitive predictors of cartilage quality whereas CVSHG only showed moderate sensitivity. Cell viability and tissue thickness, often used as measures of cartilage health, predicted the cartilage quality poorly. We present a simple, objective, yet effective image-based approach for assessment of cartilage quality. Φcol correlated strongly with electromechanical properties of cartilage and could fuel the continuous development of SHG-based arthroscopy.

Numerical analysis of streaming potential induced by loads in micro-pores of articular cartilage

In order to understand the distribution of streaming potentials in cartilage pores, this paper established finite element model to analyze. The results showed that the streaming potential in cartilage micro-pores increased along the axis. The electric potential in 5 μm straight micro-pore was about 50 μV, and the electric potential of curved bifurcation model was about 30 μV. The pressure and Zeta potential had a linear growth relationship with the streaming potential. The streaming potential decreased with the increase of ion concentration until ion concentration was saturated. These results could provide a theoretical basis for cartilage research.

Relations between Structure/Composition and Mechanics in Osteoarthritic Regenerated Articular Tissue: A Machine Learning Approach

In the context of a large animal model of early osteoarthritis (OA) treated by orthobiologics, the purpose of this study was to reveal relations between articular tissues structure/composition and cartilage viscoelasticity. Twenty-four sheep, with induced knee OA, were treated by mesenchymal stem cells in various preparations-adipose-derived mesenchymal stem cells (ADSCs), stromal vascular fraction (SVF), and amniotic endothelial cells (AECs)-and euthanized at 3 or 6 months to evaluate the (i) biochemistry of synovial fluid; (ii) histology, immunohistochemistry, and histomorphometry of articular cartilage; and (iii) viscoelasticity of articular cartilage. After performing an initial analysis to evaluate the correlation and multicollinearity between the investigated variables, this study used machine learning (ML) models-Variable Selection Using Random Forests (VSURF) and Extreme Gradient Boosting (XGB)-to classify variables according to their importance and employ them for interpretation and prediction. The experimental setup revealed a potential relation between cartilage elastic modulus and cartilage thickness (CT), synovial fluid interleukin 6 (IL6), and prostaglandin E2 (PGE2), and between cartilage relaxation time and CT and PGE2. SVF treatment was the only limit on the deleterious OA effect on cartilage viscoelastic properties. This work provides indications to future studies aiming to highlight these and other relationships and focusing on advanced regeneration targets.

Breast Cancer Cell Type and Biomechanical Properties of Decellularized Mouse Organs Drives Tumor Cell Colonization

Tissue engineering has emerged as an indispensable tool for the reconstruction of organ-specific environments. Organ-derived extracellular matrices (ECM) and, especially, decellularized tissues (DCL) are recognized as the most successful biomaterials in regenerative medicine, as DCL preserves the most essential organ-specific ECM properties such as composition alongside biomechanics characterized by stiffness and porosity. Expansion of the DCL technology to cancer biology research, drug development, and nanomedicine is pending refinement of the existing DCL protocols whose reproducibility remains sub-optimal varying from organ to organ. We introduce a facile decellularization protocol universally applicable to murine organs, including liver, lungs, spleen, kidneys, and ovaries, with demonstrated robustness, reproducibility, high purification from cell debris, and architecture preservation, as confirmed by the histological and SEM analysis. The biomechanical properties of as-produced DCL organs expressed in terms of the local and total stiffness were measured using our facile methodology and were found well preserved in comparison with the intact organs. To demonstrate the utility of the developed DCL model to cancer research, we engineered three-dimensional tissue constructs by recellularization representative decellularized organs and collagenous hydrogel with human breast cancer cells of pronounced mesenchymal (MDA-MB-231) or epithelial (SKBR-3) phenotypes. The biomechanical properties of the DCL organs were found pivotal to determining the cancer cell fate and progression. Our histological and scanning electron microscopy (SEM) study revealed that the larger the ECM mean pore size and the smaller the total stiffness (as in lung and ovary), the more proliferative and invasive the mesenchymal cells became. At the same time, the low local stiffness ECMs (ranged 2.8-3.6 kPa) did support the epithelial-like SKBR-3 cells' viability (as in lung and spleen), while stiff ECMs did not. The total and local stiffness of the collagenous hydrogel was measured too low to sustain the proliferative potential of both cell lines. The observed cell proliferation patterns were easily interpretable in terms of the ECM biomechanical properties, such as binding sites, embedment facilities, and migration space. As such, our three-dimensional tissue engineering model is scalable and adaptable for pharmacological testing and cancer biology research of metastatic and primary tumors, including early metastatic colonization in native organ-specific ECM.

Characterizing site-specific mechanical properties of knee cartilage with indentation-relaxation maps and machine learning

Knee cartilage experiences site-specific focal lesion and degeneration, which is likely associated with tissue inhomogeneity and nonuniform mechanical stimuli in the joint, for which a complete picture remains to be depicted. The present study aimed to develop a methodology to quantify knee cartilage inhomogeneity using porcine knee specimens. Automated indentation-relaxation and needle probing were performed on fully intact cartilage to obtain data that essentially represent continuous distributions of cartilage properties in the knee. Machine learning was then introduced to approximate the tissue inhomogeneity with several regions via clusters of indentation locations, and finite element modeling was used to obtain poromechanical properties for each region using indentation-relaxation and thickness data. Significant region dependence was established from the full time-dependent mechanical response. Seventeen regions, or clusters, were found to best approximate the site-specific poromechanical properties of articular cartilage for femoral groove, lateral and medial condyles and tibial plateaus, after up to eight clusters were tested for each of the five cartilage sections. The region partitions recommended, and tissue properties acquired would facilitate implementation of tissue inhomogeneity in future applications, e.g., contact modeling of the knee joint. The results obtained from 14 porcine knees revealed interesting region differences, for example, the two condyles have the same effective stiffness when responding to slowly applied mechanical loadings but substantially lower stiffness in the medial condyle when responding to fast loadings. This mechanical behavior may be associated with the fact that medial femoral cartilage is more prone to focal lesions than the lateral one.

Integrating MR imaging with full-surface indentation mapping of femoral cartilage in an ex vivo porcine stifle

The potential of MRI to predict cartilage mechanical properties across an entire cartilage surface in an ex vivo model would enable novel perspectives in modeling cartilage tolerance and predicting disease progression. The purpose of this study was to integrate MR imaging with full-surface indentation mapping to determine the relationship between femoral cartilage thickness and T2 relaxation change following loading, and cartilage mechanical properties in an ex vivo porcine stifle model. Matched-pairs of stifle joints from the same pig were randomized into either 1) an imaging protocol where stifles were imaged at baseline and after 35 min of static axial loading; and 2) full surface mapping of the instantaneous modulus (IM) and an electromechanical property named quantitative parameter (QP). The femur and femoral cartilage were segmented from baseline and post-intervention scans, then meshes were generated. Coordinate locations of the indentation mapping points were rigidly registered to the femur. Multiple linear regressions were performed at each voxel testing the relationship between cartilage outcomes (thickness change, T2 change) and mechanical properties (IM, QP) after accounting for covariates. Statistical Parametric Mapping was used to determine significance of clusters. No significant clusters were identified; however, this integrative method shows promise for future work in ex vivo modeling by identifying spatial relationships among variables.

High spatial resolution analysis using automated indentation mapping differentiates biomechanical properties of normal vs. degenerated articular cartilage in mice

Characterizing the biomechanical properties of articular cartilage is crucial to understanding processes of tissue homeostasis vs. degeneration. In mouse models, however, limitations are imposed by their small joint size and thin cartilage surfaces. Here we present a three-dimensional (3D) automated surface mapping system and methodology that allows for mechanical characterization of mouse cartilage with high spatial resolution. We performed repeated indentation mappings, followed by cartilage thickness measurement via needle probing, at 31 predefined positions distributed over the medial and lateral femoral condyles of healthy mice. High-resolution 3D x-ray microscopy (XRM) imaging was used to validate tissue thickness measurements. The automated indentation mapping was reproducible, and needle probing yielded cartilage thicknesses comparable to XRM imaging. When comparing healthy vs. degenerated cartilage, topographical variations in biomechanics were identified, with altered thickness and stiffness (instantaneous modulus) across condyles and within anteroposterior sub-regions. This quantitative technique comprehensively characterized cartilage function in mice femoral condyle cartilage. Hence, it has the potential to improve our understanding of tissue structure-function interplay in mouse models of repair and disease.

Optimization of In Situ Indentation Protocol to Map the Mechanical Properties of Articular Cartilage

Tissue engineering aims at developing complex composite scaffolds for articular cartilage repair. These scaffolds must exhibit a mechanical behavior similar to the whole osteochondral unit. In situ spherical indentation allows us to map the mechanical behavior of articular cartilage, avoiding removal of the underlying bone tissue. Little is known about the impact of grid spacing, indenter diameter, and induced deformation on the cartilage response to indentation. We investigated the impact of grid spacing (range: a to 3a, where a is the radius of the contact area between cartilage and indenter), indenter diameter (range: 1 to 8 mm), and deformation induced by indentation (constant indentation depth versus constant nominal deformation) on cartilage response. The bias induced by indentations performed in adjacent grid points was minimized with a 3a grid spacing. The cartilage response was indenter-dependent for diameters ranging between 1 and 6 mm with a nominal deformation of 15%. No significant differences were found using 6 mm and 8 mm indenters. Six mm and 8 mm indenters were used to map human articular cartilage with a grid spacing equal to 3a. Instantaneous elastic modulus E₀ was calculated for constant indentation depth and constant nominal deformation. E₀ value distribution did not change significantly by switching the two indenters, while dispersion decreased by 5-6% when a constant nominal deformation was applied. Such an approach was able to discriminate changes in tissue response due to doubling the indentation rate. The proposed procedure seems to reduce data dispersion and properly determine cartilage mechanical properties to be compared with those of complex composite scaffolds.

Automated Indentation Demonstrates Structural Stiffness of Femoral Articular Cartilage and Temporomandibular Joint Mandibular Condylar Cartilage Is Altered in FgF2KO Mice

OBJECTIVE

Employ an automated indentation technique, using a commercially available machine, to assess the effect of fibroblast growth factor 2 (FGF2) expression on structural stiffness over the surface of both murine femoral articular cartilage (AC) and temporomandibular joint (TMJ) mandibular condylar cartilage (MCC).

DESIGN

Experiments were performed using 3-month-old female homozygote Fgf2KO mice with wild type (WT) littermates. After euthanization, isolated mandibles and hindlimbs were either processed for histology or subjected to automated indentation on a Biomomentum Mach-1 v500csst with a 3-axis motion controller in a phosphate buffered saline bath using a 0.3 mm spherical tip indenter. The effect of indentation depth on normal force was characterized, then structural stiffness was calculated and mapped at multiple positions on the AC and MCC.

RESULTS

Automated indentation of the AC and TMJ MCC was successfully completed and was able to demonstrate both regional variation in structural stiffness and differences between WT and Fgf2KO mice. Structural stiffness values for Fgf2KO AC were significantly smaller than WT at both the medial/anterior (P < 0.05) and medial/posterior (P < 0.05) positions. Global Fgf2KO also lead to a decrease in MCC thickness of the TMJ compared with WT (P < 0.05) and increased structural stiffness values for Fgf2KO at both the posterior and anterior location (P < 0.05).

CONCLUSIONS

Automated indentation spatially resolved differences in structural stiffness between WT and Fgf2KO tissue, demonstrating FGF2 expression affects femoral AC and TMJ MCC. This quantitative method will provide a valuable approach for functional characterization of cartilage tissues in murine models relevant to knee joint and TMJ health and disease.

Non-invasive Electroarthrography Measures Load-Induced Cartilage Streaming Potentials via Electrodes Placed on Skin Surrounding an Articular Joint

OBJECTIVE

We aimed to demonstrate that electroarthrography (EAG) measures streaming potentials originating in the cartilage extracellular matrix during load bearing through electrodes adhered to skin surrounding an articular joint.

DESIGN

Equine metacarpophalangeal joints were subjected to simulated physiological loads while (1) replacing synovial fluid with immersion buffers of different electrolyte concentrations and (2) directly degrading cartilage with trypsin.

RESULTS

An inverse relationship between ionic strength and EAG coefficient was detected. Compared to native synovial fluid, EAG coefficients increased (P < 0.05) for 5 of 6 electrodes immersed in 0.1X phosphate-buffered saline (PBS) (0.014 M NaCl), decreased (P < 0.05) for 4 of 6 electrodes in 1X PBS (0.14 M NaCl), and decreased (P < 0.05) for all 6 electrodes in 10X PBS (1.4 M NaCl). This relationship corresponds to similar studies where streaming potentials were directly measured on cartilage. EAG coefficients, obtained after trypsin degradation, were reduced (P < 0.05) in 6 of 8, and 7 of 8 electrodes, during simulated standing and walking, respectively. Trypsin degradation was confirmed by direct cartilage assessments. Streaming potentials, measured by directly contacting cartilage, indicated lower cartilage stiffness (P < 10-5). Unconfined compression data revealed reduced Em, representing proteoglycan matrix stiffness (P = 0.005), no change in Ef, representing collagen network stiffness (P = 0.15), and no change in permeability (P = 0.24). Trypsin depleted proteoglycan as observed by both dimethylmethylene blue assay (P = 0.0005) and safranin-O stained histological sections.

CONCLUSION

These data show that non-invasive EAG detects streaming potentials produced by cartilage during joint compression and has potential to become a diagnostic tool capable of detecting early cartilage degeneration.

Anisotropy and inhomogeneity of permeability and fibrous network response in the pars intermedia of the human lateral meniscus

Within the human tibiofemoral joint, meniscus plays a key role due to its peculiar time-dependent mechanical characteristics, inhomogeneous structure and compositional features. To better understand the pathophysiological mechanisms underlying this essential component, it is mandatory to analyze in depth the relationship between its structure and the function it performs in the joint. Accordingly, the aim of this study was to evaluate the behavior of both solid and fluid phases of human meniscus in response to compressive loads, by integrating mechanical assessment and histological analysis. Cubic specimens were harvested from seven knee lateral menisci, specifically from anterior horn, pars intermedia and posterior horn; unconfined compressive tests were then performed according to three main loading directions (i.e., radial, circumferential and vertical). Fibril modulus, matrix modulus and hydraulic permeability of the tissue were thence estimated through a fibril-network-reinforced biphasic model. Tissue porosity and collagen fibers arrangement were assessed through histology for each region and related to the loading directions adopted during mechanical tests. Regional and strain-dependent constitutive parameters were finally proposed for the human lateral meniscus, suggesting an isotropic behavior of both the horns, and a transversely isotropic response of the pars intermedia. Furthermore, the histological findings supported the evidences highlighted by the compressive tests. Indeed, this study provided novel insights concerning the functional behavior of human menisci by integrating mechanical and histological characterizations and thus highlighting the key role of this component in knee contact mechanics and presenting fundamental information that can be used in the development of tissue-engineered substitutes. STATEMENT OF SIGNIFICANCE: This work presents an integration to the approaches currently used to model the mechanical behavior of the meniscal tissue. This study assessed in detail the regional and directional contributions of both the meniscal solid and fluid phases during compressive response, providing also complementary histological evidence. Within this updated perspective, both knee computational modeling and meniscal tissue engineering can be improved to have an effective impact on the clinical practice.

Comparison of properties determined using electromechanical assessment (Arthro-BST™) with macroscopic and histological properties in symptomatic human articular cartilage of the hip

BACKGROUND

Cartilage degeneration is assessed using various methods. Although macroscopic evaluation can directly measure cartilage degeneration, it cannot accurately assess cartilage properties. Histological examination is one of the most accurate methods for evaluating cartilage degeneration. However, it is invasive and requires collection of cartilage tissue. In contrast, the Arthro-BST™ probe can assess cartilage properties noninvasively. This study aimed to evaluate the effectiveness of the Arthro-BST in assessing cartilage degeneration by comparing macroscopic (International Cartilage Repair Society [ICRS] classification) and histological evaluations (modified Mankin score and Osteoarthritis Research Society International [OARSI] histological grade).

METHODS

Fourteen femoral heads were excised from 13 patients during surgery to treat hip osteoarthritis or femoral fracture. The ICRS score was used for macroscopic evaluation of cartilage degeneration. The Arthro-BST was applied at sites matching the areas of cartilage damage. The sites assessed using the ICRS classification and Arthro-BST were evaluated histologically (modified Mankin score and OARSI histological grade), and these were compared with the Arthro-BST results.

RESULTS

The ICRS classification identified significant differences between grades 1 and 3 (p < 0.01), between grades 1 and 4 (p < 0.01), between grades 2 and 3 (p < 0.01), and between grades 2 and 4 (p < 0.01). Significant correlations were observed between the Arthro-BST results and the ICRS score, modified Mankin score (structure, cellularity, matrix staining, total score), and OARSI histological grade.

CONCLUSIONS

In the assessment of hip osteoarthritis, the Arthro-BST results correlated with those of macroscopic and histological evaluations. The Arthro-BST is useful for assessing hip osteoarthritis and may be helpful for noninvasive assessment of cartilage degeneration.

Can UVA-light-activated riboflavin-induced collagen crosslinking be transferred from ophthalmology to spine surgery? A feasibility study on bovine intervertebral disc

Background

Collagen cross-links contribute to the mechanical resilience of the intervertebral disc (IVD). UVA-light-activated riboflavin-induced collagen crosslinking (UVA-CXL) is a well-established and effective ophthalmological intervention that increases the mechanical rigidity of the collagen-rich corneal matrix in Keratoconus. This study explores the feasibility, safety and efficacy of translating this intervention in reinforcing the IVD.

Methods

Annulus fibrosus (AF) cells were isolated from bovine IVDs and treated with different combinations of riboflavin (RF) concentrations (0.05–8 mM) and UVA light intensities (0.3–4 mW/cm²). Metabolic activity (resazurin assay), cell viability (TUNEL assay), and gene expression of apoptosis regulators C-FOS and PT5 were assessed immediately and 24 hours after treatment. Biomechanical effects of UVA-CXL on IVDs were measured by indentation analysis of changes in the instantaneous modulus and by peel-force delamination strength analysis of the AF prior and after treatment.

Results

Different intensities of UVA did not impair the metabolic activity of AF cells. However, RF affected metabolic activity (p < 0.001). PT53 expression was similar in all RF conditions tested while C-FOS expression decreased 24 hours after treatment. Twenty-four hours after treatment, no apoptotic cells were observed in any condition tested. Biomechanical characterizations showed a significant increase in the annular peel strength of the UVA-CXL group, when compared to controls of UVA and RF alone (p < 0.05). UVA-CXL treated IVDs showed up to 152% higher (p < 0.001) instantaneous modulus values compared to the untreated control.

Conclusion

This is the first study on UVA-CXL treatment of IVD. It induced significantly increased delamination strength and instantaneous modulus indentation values in intact IVD samples in a structure–function relationship. RF concentrations and UVA intensities utilized in ophthalmological clinical protocols were well tolerated by the AF cells. Our findings suggest that UVA-CXL may be a promising tool to reinforce the IVD matrix.

Osteoarthritis-Related Degeneration Alters the Biomechanical Properties of Human Menisci Before the Articular Cartilage

An exact understanding of the interplay between the articulating tissues of the knee joint in relation to the osteoarthritis (OA)-related degeneration process is of considerable interest. Therefore, the aim of the present study was to characterize the biomechanical properties of mildly and severely degenerated human knee joints, including their menisci and tibial and femoral articular cartilage (AC) surfaces. A spatial biomechanical mapping of the articulating knee joint surfaces of 12 mildly and 12 severely degenerated human cadaveric knee joints was assessed using a multiaxial mechanical testing machine. To do so, indentation stress relaxation tests were combined with thickness and water content measurements at the lateral and medial menisci and the AC of the tibial plateau and femoral condyles to calculate the instantaneous modulus (IM), relaxation modulus, relaxation percentage, maximum applied force during the indentation, and the water content. With progressing joint degeneration, we found an increase in the lateral and the medial meniscal instantaneous moduli (p < 0.02), relaxation moduli (p < 0.01), and maximum applied forces (p < 0.01), while for the underlying tibial AC, the IM (p = 0.01) and maximum applied force (p < 0.01) decreased only at the medial compartment. Degeneration had no influence on the relaxation percentage of the soft tissues. While the water content of the menisci did not change with progressing degeneration, the severely degenerated tibial AC contained more water (p < 0.04) compared to the mildly degenerated tibial cartilage. The results of this study indicate that degeneration-related (bio-)mechanical changes seem likely to be first detectable in the menisci before the articular knee joint cartilage is affected. Should these findings be further reinforced by structural and imaging analyses, the treatment and diagnostic paradigms of OA might be modified, focusing on the early detection of meniscal degeneration and its respective treatment, with the final aim to delay osteoarthritis onset.

In vivo biochemical assessment of cartilage with gagCEST MRI: Correlation with cartilage properties

To assess articular cartilage in vivo, a noninvasive measurement is proposed to evaluate damage of the cartilage. It is hypothesized that glycosaminoglycan chemical exchange saturation transfer (gagCEST) can be applied as a noninvasive imaging technique as it would relate to electromechanical indentation and GAG content as measured with biochemical assays. This pilot study applies gagCEST MRI in total knee arthroplasty (TKA) patients to assess substantially damaged articular cartilage. The outcome was verified against electromechanical indentation and biochemical assays to assess the potential of gagCEST MRI. Five TKA patients were scanned on a 7.0 T MRI with a gagCEST sequence. Articular resurfacing cuts after TKA were obtained for electromechanical and biochemical analyses. The gagCEST MRI measurements on the medial condyle showed a moderate correlation with the GAG content, although sensitivity on the lateral condyle was lacking. Additionally, a strong negative correlation of gagCEST MRI with the electromechanical measurements was observed in the regression analysis. Correlation of gagCEST MRI with electromechanical measurements was shown, but the correlation of gagCEST MRI with GAG content was not convincing. In conclusion, gagCEST could be a useful tool to assess the GAG content in articular cartilage noninvasively, although the mismatch in heterogeneity requires further investigation.

Evaluation of cartilage biomechanics and knee joint microenvironment after different cell-based treatments in a sheep model of early osteoarthritis

PURPOSE

Aiming to prevent cartilage damage during early osteoarthritis (OA), the therapeutic challenge is to restore and maintain the physiological and functional properties of such a tissue with minimally invasive therapeutic strategies.

METHODS

Accordingly, an in vivo model of early OA in sheep was here treated through three different cell therapies (culture expanded ADSCs, SVF, and culture expanded AECs) thus to preserve the joint surface from the progression of the pathology. Three months after the treatment injections, their performance was assessed through mechanical automated mapping (Young's modulus and cartilage thickness), gross evaluation of articular surfaces, and biochemical analysis of the synovial fluid.

RESULTS

No severe degeneration was observed after three months from OA induction. Cartilage mechanical properties were crucial to identify early degeneration. All the treatments improved the macroscopic cartilage surface aspect and reduced pro-inflammatory cytokines in the synovial fluid. Among the three treatments, SVF highlighted the best performance while ADSCs the worst.

CONCLUSION

Despite that the evaluated experimental time is an early follow-up and, thus, longer trial is mandatory to properly assess treatments effectiveness, the proposed multidisciplinary approach allowed to obtain preliminary, but also crucial, results concerning the reduction in OA signs on cartilage properties, in osteophyte development and in all the inflammatory markers.

Modulation of Hedgehog Signaling by Kappa Opioids to Attenuate Osteoarthritis

OBJECTIVE

Inhibition of hedgehog (HH) signaling prevents cartilage degeneration and promotes repair in animal models of osteoarthritis (OA). This study, undertaken in OA models and in human OA articular cartilage, was designed to explore whether kappa opioid receptor (KOR) modulation via the inhibition of HH signaling may have therapeutic potential for achieving disease-modifying activity in OA.

METHODS

Primary human articular cartilage and synovial tissue samples from patients with knee OA undergoing total joint replacement and from healthy human subjects were obtained from the National Disease Research Interchange. For in vivo animal studies, a partial medial meniscectomy (PMM) model of knee OA in rats was used. A novel automated 3-dimensional indentation tester (Mach-1) was used to quantify the thickness and stiffness properties of the articular cartilage.

RESULTS

Inhibition of HH signaling through KOR activation was achieved with a selective peptide agonist, JT09, which reduced HH signaling via the cAMP/CREB pathway in OA human articular chondrocytes (P = 0.002 for treated versus untreated OA chondrocytes). Moreover, JT09 markedly decreased matrix degeneration induced by an HH agonist, SAG, in pig articular chondrocytes and cartilage explants (P = 0.026 versus untreated controls). In vivo application of JT09 via intraarticular injection into the rat knee joint after PMM surgery significantly attenuated articular cartilage degeneration (60% improvement in the tibial plateau; P = 0.021 versus vehicle-treated controls). In JT09-treated rats, cartilage content, structure, and functional properties were largely maintained, and osteophyte formation was reduced by 70% (P = 0.005 versus vehicle-treated controls).

CONCLUSION

The results of this study define a novel mechanism for the role of KOR in articular cartilage homeostasis and disease, providing a potential unifying mechanistic basis for the overlap in disease processes and features involving opioid and HH signaling. Moreover, this study identifies a potential novel therapeutic strategy in which KOR modulation can improve outcomes in patients with OA.

Viscoelasticity and histology of the human cartilage in healthy and degenerated conditions of the knee

BACKGROUND

There are many studies on osteoarthritis, but only a few studies deal with human arthrosis, comparing the mechanical properties of healthy and diseased samples. In most of these studies, only isolated areas of the tibia are examined. There is currently only one study investigating the complete mapping of cartilage tissue but not the difference between instantaneous modulus (IM) in healthy and diseased samples. The aim of this study is to investigate the relationship between the biomechanical and histological changes of articular cartilage in the pathogenesis of osteoarthritis.

METHODS

The study compared 25 tibiae with medial gonarthrosis and 13 healthy controls. The IM was determined by automated indentation mapping using a Mach-1 V500css testing machine. A grid was projected over the sample and stored so that all measurements could be taken at the same positions (100 ± 29 positions across the tibiae). This grid was then used to perform the thickness measurement using the needle method. Samples were then taken for histological examinations using a hollow milling machine. Then Giemsa and Safranin O staining were performed. In order to determine the degree of arthrosis according to histological criteria, the assessment was made with regard to Osteoarthritis Research Society International (OARSI) and AHO scores.

RESULTS

A significant difference (p < 0.05) could be observed in the measured IM between the controls with 3.43 ± 0.36 MPa and the samples with 2.09 ± 0.18 MPa. In addition, there was a significant difference in IM in terms of meniscus-covered and meniscus-uncovered areas. The difference in cartilage thickness between 2.25 ± 0.11 mm controls and 2.0 ± 0.07 mm samples was highly significant with p < 0.001. With regard to the OARSI and AHO scores, the samples differed significantly from the controls. The OARSI and AHO scores showed a significant difference between meniscus-covered and meniscus-uncovered areas.

CONCLUSIONS

The controls showed significantly better viscoelastic behavior than the arthrotic samples in the measured IM. The measured biomechanical values showed a direct correlation between histological changes and altered biomechanics in gonarthrosis.

Cartilage mechanical tests: Evolution of current standards for cartilage repair and tissue engineering. A literature review

BACKGROUND

Repair procedures and tissue engineering are solutions available in the clinical practice for the treatment of damaged articular cartilage. Regulatory bodies defined the requirements that any products, intended to regenerate cartilage, should have to be applied. In order to verify these requirements, the Food and Drug Administration (FDA, USA) and the International Standard Organization (ISO) indicated some Standard tests, which allow evaluating, in a reproducible way, the performances of scaffolds/treatments for cartilage tissue regeneration.

METHODS

A review of the literature about cartilage mechanical characterization found 394 studies, from 1970 to date. They were classified by material (simulated/animal/human cartilage) and method (theoretical/applied; static/dynamic; standard/non-standard study), and analyzed by nation and year of publication.

FINDINGS

While Standard methods for cartilage mechanical characterization still refer to studies developed in the eighties, expertise and interest on cartilage mechanics research are evolving continuously and internationally, with studies both in vitro - on human and animal tissues - and in silico, dealing with tissue function and modelling, using static and dynamic loading conditions.

INTERPRETATION

there is a consensus on the importance of mechanical characterization that should be considered to evaluate cartilage treatments. Still, relative Standards need to be updated to describe advanced constructs and procedures for cartilage regeneration in a more exhaustive way. The use of the more complex, fibre-reinforced biphasic model, instead of the standard simple biphasic model, to describe cartilage response to loading, and the standardisation of dynamic tests can represent a first step in this direction.

Full biomechanical mapping of the ovine knee joint to determine creep-recovery, stiffness and thickness variation

BACKGROUND

Clinical cartilage repair strategies can be tested using the sheep model as suggest by the European Medicines Agency. To characterize variation within the joint a full biomechanical mapping is necessary. The aim of this study is to establish a loading model, to map regional differences within the knee and determine reference areas for area specific replacement techniques.

METHODS

A porous indenter was selected to evaluate 22 defined test locations (femoral condyles, tibia plateau, patella, femoral groove) on ovine knees (n = 7). A high-dynamic force-controlled micro creep and creep-recovery indentation test system applied five loading (0.11 MPa) and unloading (5.6 kPa) cycles for 60 s each and recorded creep-recovery. Needle indentation was used to measure cartilage thickness and calculate total strain.

FINDINGS

Steady state behaviour was observed from the third cycle and further evaluated. Little variation of stiffness in N/mm was found within the patella (4.3SD0.5) and femoral groove (8.1SD0.7) compared to larger variations in the femur (7.9SD2.0) and tibia (7.5SD3.2). Creep indentation showed values of 14.5%(SD2.7%) for the patella and 17.4%(SD3%) for the femoral grove opposed to 13.4%(SD4.3%) for the femoral condyles and 21.8%(SD6.6%) for the tibia plateau. Similar trends were observed analysing creep-recovery. Values were normalized to cartilage thickness which ranged between 0.36 mm and 1.14 mm.

INTERPRETATION

Our setup allows a reliable evaluation of zonal differences. Homogenous biomechanical behaviour is found within the patella and femoral groove whereas significant biomechanical variation within the femoral condyles and tibia plateau indicates the need for site-specific cartilage repair products.

Automated Indentation Mapping of Vocal Fold Structure and Cover Properties Across Species

OBJECTIVES/HYPOTHESIS

Various animal models have been employed to investigate vocal fold (VF) and phonatory function. However, biomechanical testing techniques to characterize vocal fold structural properties vary and have not compared critical properties across species. We adapted a nondestructive, automated indentation mapping technique to simultaneously quantify VF structural properties (VF cover layer and intact VF) in commonly used species based on the hypothesis that VF biomechanical properties are largely preserved across species.

STUDY DESIGN

Ex vivo animal model.

METHODS

Canine, leporine, and swine larynges (n = 4 each) were sagittally bisected, measured, and subjected to normal indentation mapping (indentation at 0.3 mm; 1.2 mm/s) with a 2-mm spherical indenter to quantify normal force along the VF cover layer, structural stiffness, and displacement at 0.8 mN; two-dimensional maps of the free VF edge through the conus elasticus were created for these characterizations.

RESULTS

Structural stiffness was 7.79 gf/mm (0.15-74.55) for leporine, 2.48 gf/mm (0.20-41.75) for canine, and 1.45 gf (0.56-4.56) for swine. For each species, the lowest values were along the free VF edge (mean ± standard deviation; leporine: 0.40 ± 0.21 gf/mm, canine: 1.14 ± 0.49 gf/mm, swine: 0.89 ± 0.28 gf/mm). Similar results were obtained for the cover layer normal force at 0.3 mm. On the free VF edge, mean (standard deviation) displacement at 0.08 gf was 0.14 mm (0.05) in leporine, 0.11 mm (0.03) in canine, and 0.10 mm (0.02) in swine.

CONCLUSIONS

Automated indentation mapping yielded reproducible biomechanical property measurement of the VF cover and intact VF. Divergent VF structural properties across canine, swine, and leporine species were observed.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:E26-E31, 2019.

Glycation marker glucosepane increases with the progression of osteoarthritis and correlates with morphological and functional changes of cartilage in vivo

Background

Changes of serum concentrations of glycated, oxidized, and nitrated amino acids and hydroxyproline and anticyclic citrullinated peptide antibody status combined by machine learning techniques in algorithms have recently been found to provide improved diagnosis and typing of early-stage arthritis of the knee, including osteoarthritis (OA), in patients. The association of glycated, oxidized, and nitrated amino acids released from the joint with development and progression of knee OA is unknown. We studied this in an OA animal model as well as interleukin-1β-activated human chondrocytes in vitro and translated key findings to patients with OA.

Methods

Sixty male 3-week-old Dunkin-Hartley guinea pigs were studied. Separate groups of 12 animals were killed at age 4, 12, 20, 28 and 36 weeks, and histological severity of knee OA was evaluated, and cartilage rheological properties were assessed. Human chondrocytes cultured in multilayers were treated for 10 days with interleukin-1β. Human patients with early and advanced OA and healthy controls were recruited, blood samples were collected, and serum or plasma was prepared. Serum, plasma, and culture medium were analyzed for glycated, oxidized, and nitrated amino acids.

Results

Severity of OA increased progressively in guinea pigs with age. Glycated, oxidized, and nitrated amino acids were increased markedly at week 36, with glucosepane and dityrosine increasing progressively from weeks 20 and 28, respectively. Glucosepane correlated positively with OA histological severity (r = 0.58, p < 0.0001) and instantaneous modulus (r = 0.52–0.56; p < 0.0001), oxidation free adducts correlated positively with OA severity (p < 0.0009–0.0062), and hydroxyproline correlated positively with cartilage thickness (p < 0.0003–0.003). Interleukin-1β increased the release of glycated and nitrated amino acids from chondrocytes in vitro. In clinical translation, plasma glucosepane was increased 38% in early-stage OA (p < 0.05) and sixfold in patients with advanced OA (p < 0.001) compared with healthy controls.

Conclusions

These studies further advance the prospective role of glycated, oxidized, and nitrated amino acids as serum biomarkers in diagnostic algorithms for early-stage detection of OA and other arthritic disease. Plasma glucosepane, reported here for the first time to our knowledge, may improve early-stage diagnosis and progression of clinical OA.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1636-6) contains supplementary material, which is available to authorized users.

Quantitative Arthroscopic Assessment of Articular Cartilage Quality by Means of Cartilage Electromechanical Properties

Arthroscopic surgery has grown rapidly in recent decades. Despite accurately diagnosed clinical cases, the previous pain is retained in some patients after the operation, even though no visible chondral lesions are found during the procedure. A minimally invasive arthroscopic method of measuring articular cartilage electromechanical properties enables rapid and reliable intraoperative articular cartilage quality evaluation.

Comparison of Regenerative Tissue Quality following Matrix-Associated Cell Implantation Using Amplified Chondrocytes Compared to Synovium-Derived Stem Cells in a Rabbit Model for Cartilage Lesions

Known problems of the autologous chondrocyte implantation motivate the search for cellular alternatives. The aim of the study was to test the potential of synovium-derived stem cells (SMSC) to regenerate cartilage using a matrix-associated implantation. In an osteochondral defect model of the medial femoral condyle in a rabbit, a collagen membrane was seeded with either culture-expanded allogenic chondrocytes or SMSC and then transplanted into the lesion. A tailored piece synovium served as a control. Rabbit SMSC formed typical cartilage in vitro. Macroscopic evaluation of defect healing and the thickness of the regenerated tissue did not reveal a significant difference between the intervention groups. However, instantaneous and shear modulus, reflecting the biomechanical strength of the repair tissue, was superior in the implantation group using allogenic chondrocytes (p < 0.05). This correlated with a more chondrogenic structure and higher proteoglycan expression, resulting in a lower OARSI score (p < 0.05). The repair tissue of all groups expressed comparable amounts of the collagen types I, II, and X. Cartilage regeneration following matrix-associated implantation using allogenic undifferentiated synovium-derived stem cells in a defect model in rabbits showed similar macroscopic results and collagen composition compared to amplified chondrocytes; however, biomechanical characteristics and histological scoring were inferior.

Quantifying the Effects of Different Treadmill Training Speeds and Durations on the Health of Rat Knee Joints

Background

Walking and running provide cyclical loading to the knee which is thought essential for joint health within a physiological window. However, exercising outside the physiological window, e.g. excessive cyclical loading, may produce loading conditions that could be detrimental to joint health and lead to injury and, ultimately, osteoarthritis. The purpose of this study was to assess the effects of a stepwise increase in speed and duration of treadmill training on knee joint integrity and to identify the potential threshold for joint damage.

Methods

Twenty-four Sprague-Dawley rats were randomized into four groups: no exercise, moderate duration, high duration, and extra high duration treadmill exercise. The treadmill training consisted of a 12-week progressive program. Following the intervention period, histologic serial sections of the left knee were graded using a modified Mankin Histology Scoring System. Mechanical testing of the tibial plateau cartilage and RT-qPCR analysis of mRNA from the fat pad, patellar tendon, and synovium were performed for the right knee. Kruskal-Wallis testing was used to assess differences between groups for all variables.

Results

There were no differences in cartilage integrity or mechanical properties between groups and no differences in mRNA from the fat pad and patellar tendon. However, COX-2 mRNA levels in the synovium were lower for all animals in the exercise intervention groups compared to those in the no exercise group.

Conclusions

Therefore, these exercise protocols did not exceed the joint physiological window and can likely be used safely in aerobic exercise intervention studies without affecting knee joint health.

Electromechanical properties of human osteoarthritic and asymptomatic articular cartilage are sensitive and early detectors of degeneration

OBJECTIVE

To evaluate cross-correlations of ex vivo electromechanical properties with cartilage and subchondral bone plate thickness, as well as their sensitivity and specificity regarding early cartilage degeneration in human tibial plateau.

METHOD

Six pairs of tibial plateaus were assessed ex vivo using an electromechanical probe (Arthro-BST) which measures a quantitative parameter (QP) reflecting articular cartilage compression-induced streaming potentials. Cartilage thickness was then measured with an automated thickness mapping technique using Mach-1 multiaxial mechanical tester. Subsequently, a visual assessment was performed by an experienced orthopedic surgeon using the International Cartilage Repair Society (ICRS) grading system. Each tibial plateau was finally evaluated with μCT scanner to determine the subchondral-bone plate thickness over the entire surface.

RESULTS

Cross-correlations between assessments decreased with increasing degeneration level. Moreover, electromechanical QP and subchondral-bone plate thickness increased strongly with ICRS grade (ρ = 0.86 and ρ = 0.54 respectively), while cartilage thickness slightly increased (ρ = 0.27). Sensitivity and specificity analysis revealed that the electromechanical QP is the most performant to distinguish between different early degeneration stages, followed by subchondral-bone plate thickness and then cartilage thickness. Lastly, effect sizes of cartilage and subchondral-bone properties were established to evaluate whether cartilage or bone showed the most noticeable changes between normal (ICRS 0) and each early degenerative stage. Thus, the effect sizes of cartilage electromechanical QP were almost twice those of the subchondral-bone plate thickness, indicating greater sensitivity of electromechanical measurements to detect early osteoarthritis.

CONCLUSION

The potential of electromechanical properties for the diagnosis of early human cartilage degeneration was highlighted and supported by cartilage thickness and μCT assessments.

Development of an Electromechanical Grade to Assess Human Knee Articular Cartilage Quality

Quantitative assessments of articular cartilage function are needed to aid clinical decision making. Our objectives were to develop a new electromechanical grade to assess quantitatively cartilage quality and test its reliability. Electromechanical properties were measured using a hand-held electromechanical probe on 200 human articular surfaces from cadaveric donors and osteoarthritic patients. These data were used to create a reference electromechanical property database and to compare with visual arthroscopic International Cartilage Repair Society (ICRS) grading of cartilage degradation. The effect of patient-specific and location-specific characteristics on electromechanical properties was investigated to construct a continuous and quantitative electromechanical grade analogous to ICRS grade. The reliability of this novel grade was assessed by comparing it with ICRS grades on 37 human articular surfaces. Electromechanical properties were not affected by patient-specific characteristics for each ICRS grade, but were significantly different across the articular surface. Electromechanical properties varied linearly with ICRS grade, leading to a simple linear transformation from one scale to the other. The electromechanical grade correlated strongly with ICRS grade (r = 0.92, p < 0.0001). Additionally, the electromechanical grade detected lesions that were not found visually. This novel grade can assist the surgeon in assessing human knee cartilage by providing a quantitative and reliable grading system.