Three-dimensional microstructure of human meniscus posterior horn in health and osteoarthritis

Age and anatomical region-related differences in vascularization of the porcine meniscus using microcomputed tomography imaging

Meniscal lesions in vascularized regions are known to regenerate while lack of vascular supply leads to poor healing. Here, we developed and validated a novel methodology for three-dimensional structural analysis of meniscal vascular structures with high-resolution microcomputed tomography (µCT). We collected porcine medial menisci from 10 neonatal (not-developed meniscus, n-) and 10 adults (fully developed meniscus, a-). The menisci were cut into anatomical regions (anterior horn (n-AH and a-AH), central body (n-CB and a-CB), and posterior horn (n-PH and a-PH). Specimens were cut in half, fixed, and one specimen underwent critical point drying and µCT imaging, while other specimen underwent immunohistochemistry and vascularity biomarker CD31 staining for validation of µCT. Parameters describing vascular structures were calculated from µCT. The vascular network in neonatal spread throughout meniscus, while in adult was limited to a few vessels in outer region, mostly on femoral side. n-AH, n-CB, and n-PH had 20, 17, and 11 times greater vascular volume fraction than adult, respectively. Moreover, thickness of blood vessels, in three regions, was six times higher in adults than in neonatal. a-PH appeared to have higher vascular fraction, longer and thicker blood vessels than both a-AH and a-CB. Overall, neonatal regions had a higher number of blood vessels, more branching, and higher tortuosity compared to adult regions. For the first time, critical point drying-based µCT imaging allowed detailed three-dimensional visualization and quantitative analysis of vascularized meniscal structures. We showed more vascularity in neonatal menisci, while adult menisci had fewer and thicker vascularity especially limited to the femoral surface.

Unveiling the Mechanical Role of Radial Fibers in Meniscal Tissue: Toward Structural Biomimetics

The meniscus tissue is crucial for knee joint biomechanics and is frequently susceptible to injuries resulting in early-onset osteoarthritis. Consequently, the need for meniscal substitutes spurs ongoing development. The meniscus is a composite tissue reinforced with circumferential and radial collagenous fibers; the mechanical role of the latter has yet to be fully unveiled. Here, we investigated the role of radial fibers using a synergistic methodology combining meniscal tissue structure imaging, a computational knee joint model, and the fabrication of simple biomimetic composite laminates. These laminates mimic the basic structural units of the meniscus, utilizing longitudinal and transverse fibers equivalent to the circumferential and radial fibers in meniscal tissue. In the computational model, the absence of radial fibers resulted in stress concentration within the meniscus matrix and up to 800% greater area at the same stress level. Furthermore, the contact pressure on the tibial cartilage increased drastically, affecting up to 322% larger areas. Conversely, in models with radial fibers, we observed up to 25% lower peak contact pressures and width changes of less than 0.1%. Correspondingly, biomimetic composite laminates containing transverse fibers exhibited minor transverse deformations and smaller Poisson's ratios. They demonstrated structural shielding ability, maintaining their mechanical performance with the reduced amount of fibers in the loading direction, similar to the ability of the torn meniscus to carry and transfer loads to some extent. These results indicate that radial fibers are essential to distribute contact pressure and tensile stresses and prevent excessive deformations, suggesting the importance of incorporating them in novel designs of meniscal substitutes. STATEMENT OF SIGNIFICANCE: The organization of the collagen fibers in the meniscus tissue is crucial to its biomechanical function. Radially oriented fibers are an important structural element of the meniscus and greatly affect its mechanical behavior. However, despite their importance to the meniscus mechanical function, radially oriented fibers receive minor attention in meniscal substitute designs. Here, we used a synergistic methodology that combines imaging of the meniscal tissue structure, a structural computational model of the knee joint, and the fabrication of simplistic biomimetic composite laminates that mimic the basic structural units of the meniscus. Our findings highlight the importance of the radially oriented fibers, their mechanical role in the meniscus tissue, and their importance as a crucial element in engineering novel meniscal substitutes.

Prevalence and classification of meniscal calcifications in the human knee

OBJECTIVE

To investigate the occurrence of meniscal calcifications in individuals with and without knee osteoarthritis (OA). Additionally, we aim to identify the specific types of calcifications: basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate (CPP).

METHOD

We analyzed 82 meniscal posterior horn samples (medial and lateral) collected from 41 human subjects. Among them, 20 individuals underwent total knee replacement due to medial compartment OA, while 21 deceased donors had no known knee OA. The assessment of meniscal calcifications and Pauli's histopathological scoring was conducted using histological sections. Furthermore, adjacent sections underwent measurement using Raman spectroscopy to characterize BCP and CPP calcifications based on their distinct spectral fingerprints.

RESULTS

All OA individuals exhibited calcifications in at least one meniscus, compared to 9.5% (95%CI 1%, 30%) of donors. Among 35 OA menisci with calcifications, 28(80%) had BCP, 5(14%) had CPP and 2(6%) had both types. In 4 donor menisci, 3(75%) had CPP while 1(25%) had both types. We estimated the association between Pauli score and presence of BCP in OA individuals, yielding an odds ratio of 2.1 (95%CI 0.8, 5.3) per 1 Pauli score. The association between Pauli score and presence of CPP (in whole study sample) seemed weaker, with odds ratio of 1.3 (95%CI 1.1, 1.7).

CONCLUSION

The presence of BCP was predominant in menisci of OA individuals, whereas CPP exhibited similar prevalence in individuals with and without OA. The formation of BCP crystals in menisci may represent an important and specific characteristic of OA disease process that warrants further attention.

In Situ Loading and Time-Resolved Synchrotron-Based Phase Contrast Tomography for the Mechanical Investigation of Connective Knee Tissues: A Proof-of-Concept Study

Articular cartilage and meniscus transfer and distribute mechanical loads in the knee joint. Degeneration of these connective tissues occurs during the progression of knee osteoarthritis, which affects their composition, microstructure, and mechanical properties. A deeper understanding of disease progression can be obtained by studying them simultaneously. Time-resolved synchrotron-based X-ray phase-contrast tomography (SR-PhC-µCT) allows to capture the tissue dynamics. This proof-of-concept study presents a rheometer setup for simultaneous in situ unconfined compression and SR-PhC-µCT of connective knee tissues. The microstructural response of bovine cartilage (n = 16) and meniscus (n = 4) samples under axial continuously increased strain, or two steps of 15% strain (stress-relaxation) is studied. The chondrocyte distribution in cartilage and the collagen fiber orientation in the meniscus are assessed. Variations in chondrocyte density reveal an increase in the top 40% of the sample during loading, compared to the lower half. Meniscus collagen fibers reorient perpendicular to the loading direction during compression and partially redisperse during relaxation. Radiation damage, image repeatability, and image quality assessments show little to no effects on the results. In conclusion, this approach is highly promising for future studies of human knee tissues to understand their microstructure, mechanical response, and progression in degenerative diseases.

Exploratory neutron tomography of articular cartilage

OBJECTIVE

To investigate the feasibility of using neutron tomography to gain new knowledge of human articular cartilage degeneration in osteoarthritis (OA). Different sample preparation techniques were evaluated to identify maximum intra-tissue contrast.

DESIGN

Human articular cartilage samples from 14 deceased donors (18-75 years, 9 males, 5 females) and 4 patients undergoing total knee replacement due to known OA (all female, 61-75 years) were prepared using different techniques: control in saline, treated with heavy water saline, fixed and treated in heavy water saline, and fixed and dehydrated with ethanol. Neutron tomographic imaging (isotropic voxel sizes from 7.5 to 13.5 µm) was performed at two large scale facilities. The 3D images were evaluated for gradients in hydrogen attenuation as well as compared to images from absorption X-ray tomography, magnetic resonance imaging, and histology.

RESULTS

Cartilage was distinguishable from background and other tissues in neutron tomographs. Intra-tissue contrast was highest in heavy water-treated samples, which showed a clear gradient from the cartilage surface to the bone interface. Increased neutron flux or exposure time improved image quality but did not affect the ability to detect gradients. Samples from older donors showed high variation in gradient profile, especially from donors with known OA.

CONCLUSIONS

Neutron tomography is a viable technique for specialized studies of cartilage, particularly for quantifying properties relating to the hydrogen density of the tissue matrix or water movement in the tissue.

Revealing the complexity of meniscus microvasculature through 3D visualization and analysis

Three-dimensional information is essential for a proper understanding of the healing potential of the menisci and their overall role in the knee joint. However, to date, the study of meniscal vascularity has relied primarily on two-dimensional imaging techniques. Here we present a method to elucidate the intricate 3D meniscal vascular network, revealing its spatial arrangement, connectivity and density. A polymerizing contrast agent was injected into the femoral artery of human cadaver legs, and the meniscal microvasculature was examined using micro-computed tomography at different levels of detail and resolution. The 3D vascular network was quantitatively assessed in a zone-base analysis using parameters such as diameter, length, tortuosity, and branching patterns. The results of this study revealed distinct vascular patterns within the meniscus, with the highest vascular volume found in the outer perimeniscal zone. Variations in vascular parameters were found between the different circumferential and radial meniscal zones. Moreover, through state-of-the-art 3D visualization using micro-CT, this study highlighted the importance of spatial resolution in accurately characterizing the vascular network. These findings, both from this study and from future research using this technique, improve our understanding of microvascular distribution, which may lead to improved therapeutic strategies.

On the fractional transversely isotropic functionally graded nature of soft biological tissues: Application to the meniscal tissue

This paper focuses on the origin of the poroelastic anisotropic behaviour of the meniscal tissue and its spatially varying properties. We present confined compression creep test results on samples extracted from three parts of the tissue (Central body, Anterior horn and Posterior horn) in three orientations (Circumferential, Radial and Vertical). We show that a poroelastic model in which the fluid flow evolution is ruled by non-integer order operators (fractional Darcy's law) provides accurate agreement with the experimental creep data. The model is validated against two additional sets of experimental data: stress relaxation and fluid loss during the consolidation process measured as weight reduction. Results show that the meniscus can be considered as a transversely isotropic poroelastic material. This behaviour is due to the fluid flow rate being about three times higher in the circumferential direction than in the radial and vertical directions in the body region of the meniscus. The 3D fractional poroelastic model is implemented in the finite element software to estimate the weight loss during the confined compression tests.

Micro-computed Tomography-Based Collagen Orientation and Anisotropy Analysis of Rabbit Articular Cartilage

The collagen network is the highly organized backbone of articular cartilage providing tissue tensile stiffness and restricting proteoglycan bleaching out of the tissue. Osteoarthritis (OA) diminishes proper collagen network adaptation. Our aim was to provide quantitative three-dimensional (3D) information of the cartilage collagen network adaptation in early osteoarthritis using high resolution micro-computed tomography (µCT)-imaging. Osteochondral samples from the femoral condyles were collected from healthy (N = 8, both legs) and experimental OA rabbit model with anterior cruciate ligament transection (N = 14, single leg). Samples were processed for cartilage µCT-imaging and histological evaluation with polarized light microscopy (PLM). Structure tensor analysis was used to analyse the collagen fibre orientation and anisotropy of the µCT-images, and PLM was used as a validation for structural changes. Depth-wise comparison of collagen fibre orientation acquired with µCT-imaging and PLM correlated well, but the values obtained with PLM were systematically greater than those measured with µCT-imaging. Structure tensor analysis allowed for 3D quantification of collagen network anisotropy. Finally, µCT-imaging revealed only minor differences between the control and experimental groups.

3D analysis and grading of calcifications from ex vivo human meniscus

OBJECTIVE

Meniscal calcifications are associated with the pathogenesis of knee osteoarthritis (OA). We propose a micro-computed tomography (μCT) based 3D analysis of meniscal calcifications ex vivo, including a new grading system.

METHOD

Human medial and lateral menisci were obtained from 10 patients having total knee replacement for medial compartment OA and 10 deceased donors without knee OA (healthy references). The samples were fixed; one subsection was imaged with μCT, and the adjacent tissue was processed for histological evaluation. Calcifications were examined from the reconstructed 3D μCT images, and a new grading system was developed. To validate the grading system, meniscal calcification volumes (CV_M) were quantitatively analyzed and compared between the calcification grades. Furthermore, we estimated the relationship between histopathological degeneration and the calcification severity.

RESULTS

3D μCT images depict calcifications in every sample, including diminutive calcifications that are not visible in histology. In the new grading system, starting from grade 2, each grade results in a CV_M that is 20.3 times higher (95% CI 13.3-30.5) than in the previous grade. However, there was no apparent difference in CV_M between grades 1 and 2. The calcification grades appear to increase with the increasing histopathological degeneration, although histopathological degeneration is also observed with small calcification grades.

CONCLUSIONS

3D μCT grading of meniscal calcifications is feasible. Interestingly, it seems that there are two patterns of degeneration in the menisci of our sample set: 1) with diminutive calcifications (calcification grades 1-2), and 2) with large to widespread calcifications (calcification grades 3-5).

Advanced glycation end-product accumulation differs by location and sex in aged osteoarthritic human menisci

OBJECTIVE

There is a clear link between increasing age and meniscus degeneration, leading to increased injury, osteoarthritis (OA) progression, and often total knee replacement. Advanced glycation end-products (AGEs) are non-enzymatic crosslinks and adducts that accumulate in collagen with age, altering tissue mechanics and cell function, ultimately leading to increased injury and inflammation. AGEs, both fluorescent and non-fluorescent, play a central role in age-related degradation of tissues throughout the body; however, little is known about their role in meniscus degeneration. The objective of this study was to characterize changes in aged OA menisci, specifically evaluating zonal AGE accumulation, to gain a better understanding of changes that may lead to age-related meniscal degeneration.

METHOD

Deidentified human menisci (N = 48, 52-84 years old) were obtained from subjects undergoing total knee replacement. Changes in extracellular matrix (ECM) were assessed by gross morphology, confocal analysis, and biochemical assays. Deoxyribonucleic acid (DNA), glycosaminoglycan (GAG), collagen, and AGE accumulation were compared with patient age, zonal region, and patient sex.

RESULTS

There were minimal changes in DNA, GAG, and collagen concentration with age or zone. However, collagen fraying and AGEs increased with age, with more AGEs accumulating in the meniscal horns compared to the central body and in male menisci compared to females.

CONCLUSIONS

Overall, this work provides greater insights into regional changes that occur in human menisci with age and OA. These results suggest AGEs may play a role in the degeneration of the meniscus, with AGEs being a possible target to reduce age-related tears, degeneration, and OA progression.

The Mineralization of Various 3D-Printed PCL Composites

In this project, different calcification methods for collagen and collagen coatings were compared in terms of their applicability for 3D printing and production of collagen-coated scaffolds. For this purpose, scaffolds were printed from polycaprolactone PCL using the EnvisionTec 3D Bioplotter and then coated with collagen. Four different coating methods were then applied: hydroxyapatite (HA) powder directly in the collagen coating, incubation in 10× SBF, coating with alkaline phosphatase (ALP), and coating with poly-L-aspartic acid. The results were compared by ESEM, µCT, TEM, and EDX. HA directly in the collagen solution resulted in a pH change and thus an increase in viscosity, leading to clumping on the scaffolds. As a function of incubation time in 10× SBF as well as in ALP, HA layer thickness increased, while no coating on the collagen layer was apparently observed with poly-L-aspartic acid. Only ultrathin sections and TEM with SuperEDX detected nano crystalline HA in the collagen layer. Exclusively the incubation in poly-L-aspartic acid led to HA crystals within the collagen coating compared to all other methods where the HA layers formed in different forms only at the collagen layer.

Phase-contrast enhanced synchrotron micro-tomography of human meniscus tissue

OBJECTIVE

To investigate the feasibility of synchrotron radiation-based phase contrast enhanced micro-computed tomography (SR-PhC-μCT) for imaging of human meniscus. Quantitative parameters related to fiber orientation and crimping were evaluated as potential markers of tissue degeneration.

DESIGN

Human meniscus specimens from 10 deceased donors were prepared using different preparation schemes: fresh frozen and thawed before imaging or fixed and paraffin-embedded. The samples were imaged using SR-PhC-μCT with an isotropic voxel size of 1.625 μm. Image quality was evaluated by visual inspection and spatial resolution. Fiber voxels were defined using a grey level threshold and a structure tensor analysis was applied to estimate collagen fiber orientation. The area at half maximum (FAHM) was calculated from angle histograms to quantify orientation distribution. Crimping period was calculated from the power spectrum of image profiles of crimped fibers. Parameters were compared to degenerative stage as evaluated by Pauli histopathological scoring.

RESULTS

Image quality was similar between frozen and embedded samples and spatial resolutions ranged from 5.1 to 5.8 μm. Fiber structure, including crimping, was clearly visible in the images. Fibers appeared to be less organized closer to the tip of the meniscus. Fiber density might decrease slightly with degeneration. FAHM and crimping period did not show any clear association with histopathological scoring.

CONCLUSION

SR-PhC-μCT is a feasible technique for high-resolution 3D imaging of fresh frozen meniscus tissue. Further work is needed to establish quantitative parameters that relate to tissue degeneration, but this imaging technique is promising for future studies of meniscus structure and biomechanical response.

IKKβ-NF-κB signaling in adult chondrocytes promotes the onset of age-related osteoarthritis in mice

[Figure: see text].

Extra-Corporeal Membrane Oxygenation Cadaver Donors: What about Tissues Used as Allografts?

Several studies demonstrated the efficacy of post-mortem extracorporeal membrane oxygenation (ECMO) on donors in preserving organ function addressing organ transplantation. Nevertheless, no common and shared evidence was reached about the possibility of using ECMO donors in tissue harvesting. Therefore, this work aimed first to review the current scientific literature about ECMO donors, and then to focus on the use of ECMO tissues as allografts, mainly addressing musculoskeletal tissues, which are of the most interest for reconstruction. A search was conducted on the current scientific literature, focusing on the keywords "ECMO" and "Donor". Several online databases were used, including PubMed, Scopus, and Web of Science. From the preliminary search, 478 articles were obtained, out of which 173 specifically reported the use of ECMO for donation and transplantation purposes. Literature reported extensive analyses of ECMO organs-overall from the abdomen-both in pre- and post-transplantation studies. On the other hand, ECMO tissues were explanted only in a very limited number of cases; moreover, no information was referred about their status and use. A revision of the current scientific literature highlighted the lack of information concerning ECMO tissues and the necessity to perform preclinical, ex vivo studies to compare allografts from ECMO donors, with respect to standard donors, and, thus, to verify whether they can be harvested and implanted safely and with efficacy.

Quantitative three-dimensional collagen orientation analysis of human meniscus posterior horn in health and osteoarthritis using micro-computed tomography

OBJECTIVE

Knee osteoarthritis (OA) is associated with meniscal degeneration that may involve disorganization of the meniscal collagen fiber network. Our aims were to quantitatively analyze the microstructural organization of human meniscus samples in 3D using micro-computed tomography (μCT), and to compare the local microstructural organization between OA and donor samples.

METHOD

We collected posterior horns of both medial and lateral human menisci from 10 end-stage medial compartment knee OA patients undergoing total knee replacement (medial & lateral OA) and 10 deceased donors without knee OA (medial & lateral donor). Posterior horns were dissected and fixed in formalin, dehydrated in ascending ethanol concentrations, treated with hexamethyldisilazane (HMDS), and imaged with μCT. We performed local orientation analysis of collagenous microstructure in 3D by calculating structure tensors from greyscale gradients within selected integration window to determine the polar angle for each voxel.

RESULTS

In donor samples, meniscus bundles were aligned circumferentially around the inner border of meniscus. In medial OA menisci, the organized structure of collagen network was lost, and main orientation was shifted away from the circumferential alignment. Quantitatively, medial OA menisci had the lowest mean orientation angle compared to all groups, -24° (95%CI -31 to -18) vs medial donor and -25° (95%CI -34 to -15) vs lateral OA.

CONCLUSIONS

HMDS-based μCT imaging enabled quantitative analysis of meniscal collagen fiber bundles and their orientations in 3D. In human medial OA menisci, the collagen disorganization was profound with overall lower orientation angles, suggesting collagenous microstructure disorganization as an important part of meniscus degradation.

Proteomic comparison of osteoarthritic and reference human menisci using data-independent acquisition mass spectrometry

OBJECTIVE

Recent research in knee osteoarthritis (OA) highlights the role of the meniscus in OA pathology. Our aim was to compare the proteomes of medial and lateral menisci from end-stage medial compartment knee OA patients, with reference menisci from knee-healthy deceased donors, using mass spectrometry.

DESIGN

Tissue plugs of Ø3 mm were obtained from the posterior horns of the lateral and medial menisci from one knee of 10 knee-healthy deceased donors and 10 patients undergoing knee replacement. Proteins were extracted and prepared for mass spectrometric analysis. Statistical analysis was conducted on abundance data that was log₂-transformed, using a linear mixed effects model and evaluated using pathway analysis.

RESULTS

We identified a total of 835 proteins in all samples, of which 331 were included in the statistical analysis. The largest differences could be seen between the medial menisci from OA patients and references, with most proteins showing higher intensities in the medial menisci from OA patients. Several matrix proteins, e.g., matrix metalloproteinase 3 (MMP3) (4.3 times higher values [95%CI 1.8, 10.6]), TIMP1 (3.5 [1.4, 8.5]), asporin (4.1 [1.7, 10.0]) and versican (4.4 [1.8, 10.9]), all showed higher abundance in medial menisci from OA patients compared to medial reference menisci. OA medial menisci also showed increased activation of several pathways involved in inflammation.

CONCLUSION

An increase in protein abundance for proteins such as MMP and TIMP1 in the medial menisci from OA patients suggests simultaneous activation of both catabolic and anabolic processes that warrants further attention.

Proteomic characterization of the normal human medial meniscus body using data-independent acquisition mass spectrometry

Recent research suggests an important role of the meniscus in the development of knee osteoarthritis. We, therefore, aimed to analyze the proteome of the normal human meniscus body, and specifically to gain new knowledge on global protein expression in the different radial zones. Medial menisci were retrieved from the right knees of 10 human cadaveric donors, from which we cut a 2 mm radial slice from the mid-portion of the meniscal body. This slice was further divided into three zones: inner, middle, and peripheral. Proteins were extracted and prepared for mass spectrometric analysis using data-independent acquisition. We performed subsequent data searches using Spectronaut Pulsar and used fixed-effect linear regression models for statistical analysis. We identified 638 proteins and after statistical analysis, we observed the greatest number of differentially expressed proteins between the inner and peripheral zones (163 proteins) and the peripheral and middle zones (136 proteins), with myocilin being the protein with the largest fold-change in both comparisons. Chondroadherin was one of eight proteins that differed between the inner and middle zones. Functional enrichment analyses showed that the peripheral one-third of the medial meniscus body differed substantially from the two more centrally located zones, which were more similar to each other. This is probably related to the higher content of cells and vascularization in the peripheral zone, whereas the middle and inner zones of the meniscal body appear to be more similar to hyaline cartilage, with high levels of extracellular matrix proteins such as aggrecan and collagen type II.

Relating MR relaxation times of ex vivo meniscus to tissue degeneration through comparison with histopathology

Background

Quantitative magnetic resonance imaging (MRI), e.g. relaxation parameter mapping, may be sensitive to structural and compositional tissue changes, and could potentially be used to non-invasively detect and monitor early meniscus degeneration related to knee osteoarthritis.

Objective

To investigate MR relaxation times as potential biomarkers for meniscus degeneration through comparisons with histopathology.

Methods

We measured MR relaxation parameters in the posterior horn of 40 menisci (medial and lateral) at a wide range of degenerative stages. T1, T2 and T2* were mapped using standard and ultrashort echo time sequences at 9.4 T and compared to gold standard histology using Pauli's histopathological scoring system, including assessment of surface integrity, collagen organization, cellularity and Safranin-O staining.

Results

All three relaxation times increased with total Pauli score (mean difference per score (95% CI) for T2*: 0.62 (0.37, 0.86), T2: 0.83 (0.53, 1.1) and T1: 24.7 (16.5, 32.8) ms/score). Clear associations were seen with scores of surface integrity (mean difference per score for T2*: 3.0 (1.8, 4.2), T2: 4.0 (2.5, 5.5) and T1: 116 (75.6, 156) ms/score) and collagen organization (mean difference between highest and lowest score for T2*: 5.3 (1.6, 8.9), T2: 6.1 (1.7, 11) and T1: 204 (75.9, 332) ms). The results were less clear for the remaining histopathological measures.

Conclusions

MR relaxation times T1, T2 and T2* of ex vivo human menisci are associated with histologically verified degenerative processes, in particular related to surface integrity and collagen organization. If confirmed in vivo, MR relaxation times may thus be potential biomarkers for meniscus degeneration.