Viability and volume of in situ bovine articular chondrocytes-changes following a single impact and effects of medium osmolarity

Making the Case for Hyperosmolar Saline Arthroscopic Irrigation Fluids: A Systematic Review of Basic Science, Translational, and Clinical Evidence

Commonly used isotonic arthroscopic irrigation fluids, such as normal saline or lactated Ringer's, were initially formulated for intravenous administration so they do not replicate the physiologic properties of healthy synovial fluid. Synovial fluid plays an important role in regulating joint homeostasis such that even transient disruptions in its composition and physiology can be detrimental. Previous studies suggest that hyperosmolar solutions may be a promising alternative to traditional isotonic fluids. This manuscript sought to systematically review and synthesize previously published basic science, translational, and clinical studies on the use of hyperosmolar arthroscopic irrigation fluids to delineate the optimal fluid for clinical use. A systematic literature search of MEDLINE/PubMed and Embase databases was performed in accordance with Preferred Reporting Items for Systemic Reviews and Meta-analyses (PRISMA) guidelines. The search phrases were: ("cartilage" AND "hyperosmolar"); ("arthroscopy" OR "arthroscopic" AND "hyperosmolar"). The titles, abstracts, and full texts were screened for studies on hyperosmolar solutions and articular cartilage. Study quality was assessed, and relevant data were collected. A meta-analysis was not performed due to study heterogeneity. A risk of bias assessment was performed on the included translational and clinical studies. There were 10 basic science studies, 2 studies performed in translational animal models, and 2 clinical studies included in this review. Of the basic science studies, 7 utilized a mechanical injury model. The translational studies were carried out in the canine shoulder and equine stifle (knee) joint. Clinical studies were performed in the shoulder and knee. Multiple basic science, translational, and clinical studies highlight the short-term safety, cost-effectiveness, and potential benefits associated with use of hyperosmolar solutions for arthroscopic irrigation. Further work is needed to develop and validate the ideal formulation for a hyperosmolar irrigation solution with proven long-term benefits for patients undergoing arthroscopic surgeries.

Caudal pole meniscectomy through an arthroscopic caudomedial portal in dogs: A cadaveric study

OBJECTIVE

To describe a caudomedial instrumental portal for caudal pole meniscectomy (CPM).

STUDY DESIGN

Experimental ex-vivo study.

SAMPLE POPULATION

Ten cadaveric hindlimbs of 10 large breed dogs.

METHODS

Each hindlimb was used for establishing the caudomedial portal for CPM. The surgical time was recorded. Specimens were disarticulated afterwards, and the completeness of CPM was documented. Iatrogenic injuries to the articular cartilage and the intra- and periarticular structures were assessed.

RESULTS

The extent of the CPM (mean ± SD, percentage of the resected medial meniscus) was 29.8 ± 12.9% of the area of the medial meniscus. There were no injuries to the medial collateral ligament or caudal cruciate ligament. The mean iatrogenic articular cartilage injury (IACI) was 3.71 ± 1.78% of the area of the medial meniscus.

CONCLUSION

The establishment of a caudomedial portal for CPM in canine cadavers was feasible and allowed to perform a partial caudal pole meniscectomy.

CLINICAL SIGNIFICANCE

A caudomedial portal may be considered for CPM in selected cases when caudal tears cannot be accessed through the standard portals.

Response of Articular Cartilage to Hyperosmolar Stress: Report of an Ex Vivo Injury Model

BACKGROUND

Physiological 0.9% saline is commonly used as an irrigation fluid in modern arthroscopy. There is a growing body of evidence that a hyperosmolar saline solution has chondroprotective effects, especially if iatrogenic injury occurs.

PURPOSE

To (1) corroborate the superiority of a hyperosmolar saline solution regarding chondrocyte survival after mechanical injury and (2) observe the modulatory response of articular cartilage to osmotic stress and injury.

STUDY DESIGN

Controlled laboratory study.

METHODS

Osteochondral explants were isolated from bovine stifle joints and exposed to either 0.9% saline (308 mOsm) or hyperosmolar saline (600 mOsm) and then damaged with a sharp dermatome blade to attain a confined full-thickness cartilage injury site, incubated in the same fluids for another 3 hours, and transferred to chondropermissive medium for further culture for 1 week. Chondrocyte survival was assessed by confocal imaging, while the cellular response was evaluated over 1 week by relative gene expression for apoptotic and inflammatory markers and mediator release into the medium.

RESULTS

The full-thickness cartilage cut resulted in a confined zone of cell death that mainly affected superficial zone chondrocytes. Injured samples that were exposed to hyperosmolar saline showed less expansion of cell death in both the axial (P < .007) and the coronal (P < .004) plane. There was no progression of cell death during the following week of culture. Histological assessment revealed an intact cartilage matrix and normal chondrocyte morphology. Inflammatory and proapoptotic genes were upregulated on the first days postexposure with a notable downregulation toward day 7. Mediator release into the medium was concentrated on day 3.

CONCLUSION

This in vitro cartilage injury model provides further evidence for the chondroprotective effect of a hyperosmolar saline irrigation fluid, as well as novel data on the capability of articular cartilage to quickly regain joint homeostasis after osmotic stress and injury.

CLINICAL RELEVANCE

Raising the osmolarity of an irrigating solution may be a simple and safe strategy to protect articular cartilage during arthroscopic surgery.

Review of state-of-the-art micro and macro-bioreactors for the intervertebral disc

Lower back pain continues to be a global epidemic, limiting quality of life and ability to work, due in large part to symptomatic disc degeneration. Development of more effective and less invasive biological strategies are needed to treat disc degeneration. In vitro models such as macro- or micro-bioreactors or mechanically active organ-chips hold great promise in reducing the need for animal studies that may have limited clinical translatability, due to harsher and more complex mechanical loading environments in human discs than in most animal models. This review highlights the complex loading conditions of the disc in situ, evaluates state-of-the-art designs for applying such complex loads across multiple length scales, from macro-bioreactors that load whole discs to organ-chips that aim to replicate cellular or engineered tissue loading. Emphasis was placed on the rapidly evolving more customizable organ-chips, given their greater potential for studying the progression and treatment of symptomatic disc degeneration. Lastly, this review identifies new trends and challenges for using organ-chips to assess therapeutic strategies.

Osmolarity-Induced Altered Intracellular Molecular Crowding Drives Osteoarthritis Pathology

Osteoarthritis (OA) is a multifactorial degenerative joint disease of which the underlying mechanisms are yet to be fully understood. At the molecular level, multiple factors including altered signaling pathways, epigenetics, metabolic imbalance, extracellular matrix degradation, production of matrix metalloproteinases, and inflammatory cytokines, are known to play a detrimental role in OA. However, these factors do not initiate OA, but are mediators or consequences of the disease, while many other factors causing the etiology of OA are still unknown. Here, it is revealed that microenvironmental osmolarity can induce and reverse osteoarthritis-related behavior of chondrocytes via altered intracellular molecular crowding, which represents a previously unknown mechanism underlying OA pathophysiology. Decreased intracellular crowding is associated with increased sensitivity to proinflammatory triggers and decreased responsiveness to anabolic stimuli. OA-induced lowered intracellular molecular crowding could be renormalized via exposure to higher extracellular osmolarity such as those found in healthy joints, which reverse OA chondrocyte's sensitivity to catabolic stimuli as well as its glycolytic metabolism.

To squeeze or not: Regulation of cell size by mechanical forces in development and human diseases

Physical constraints, such as compression, shear stress, stretching and tension play major roles during development and tissue homeostasis. Mechanics directly impact physiology, and their alteration is also recognized as having an active role in driving human diseases. Recently, growing evidence has accumulated on how mechanical forces are translated into a wide panel of biological responses, including metabolism and changes in cell morphology. The aim of this review is to summarize and discuss our knowledge on the impact of mechanical forces on cell size regulation. Other biological consequences of mechanical forces will not be covered by this review. Moreover, wherever possible, we also discuss mechanosensors and molecular and cellular signaling pathways upstream of cell size regulation. We finally highlight the relevance of mechanical forces acting on cell size in physiology and human diseases.

Microscale investigation of the anisotropic swelling of cartilage tissue and cells in response to hypo-osmotic challenges

Tissue swelling represents an early sign of osteoarthritis, reflecting osmolarity changes from iso- to hypo-osmotic in the diseased joints. Increased tissue hydration may drive cell swelling. The opposing cartilages in a joint may swell differently, thereby predisposing the more swollen cartilage and cells to mechanical injuries. However, our understanding of the tissue-cell interdependence in osmotically loaded joints is limited as tissue and cell swellings have been studied separately. Here, we measured tissue and cell responses of opposing patellar (PAT) and femoral groove (FG) cartilages in lapine knees exposed to an extreme hypo-osmotic challenge. We found that the tissue matrix and most cells swelled during the hypo-osmotic challenge, but to a different extent (tissue: <3%, cells: 11%-15%). Swelling-induced tissue strains were anisotropic, showing 2%-4% stretch and 1%-2% compression along the first and third principal directions, respectively. These strains were amplified by 5-8 times in the cells. Interestingly, the first principal strains of tissue and cells occurred in different directions (60-61° for tissue vs. 8-13° for cells), suggesting different mechanisms causing volume expansion in the tissue and the cells. Instead of the continuous swelling observed in the tissue matrix, >88% of cells underwent regulatory volume decrease to return to their pre-osmotic challenge volumes. Cell shapes changed in the early phase of swelling but stayed constant thereafter. Kinematic changes to tissue and cells were larger for PAT cartilage than for FG cartilage. We conclude that the swelling-induced deformation of tissue and cells is anisotropic. Cells actively restored volume independent of the surrounding tissues and seemed to prioritize volume restoration over shape restoration. Our findings shed light on tissue-cell interdependence in changing osmotic environments that is crucial for cell mechano-transduction in swollen/diseased tissues.

Membrane stretch as the mechanism of activation of PIEZO1 ion channels in chondrocytes

Osteoarthritis is a chronic disease that can be initiated by altered joint loading or injury of the cartilage. The mechanically sensitive PIEZO ion channels have been shown to transduce injurious levels of biomechanical strain in articular chondrocytes and mediate cell death. However, the mechanisms of channel gating in response to high cellular deformation and the strain thresholds for activating PIEZO channels remain unclear. We coupled studies of single-cell compression using atomic force microscopy (AFM) with finite element modeling (FEM) to identify the biophysical mechanisms of PIEZO-mediated calcium (Ca2+) signaling in chondrocytes. We showed that PIEZO1 and PIEZO2 are needed for initiating Ca2+ signaling at moderately high levels of cellular deformation, but at the highest strains, PIEZO1 functions independently of PIEZO2. Biophysical factors that increase apparent chondrocyte membrane tension, including hypoosmotic prestrain, high compression magnitudes, and low deformation rates, also increased PIEZO1-driven Ca2+ signaling. Combined AFM/FEM studies showed that 50% of chondrocytes exhibit Ca2+ signaling at 80 to 85% nominal cell compression, corresponding to a threshold of apparent membrane finite principal strain of E = 1.31, which represents a membrane stretch ratio (λ) of 1.9. Both intracellular and extracellular Ca2+ are necessary for the PIEZO1-mediated Ca2+ signaling response to compression. Our results suggest that PIEZO1-induced signaling drives chondrocyte mechanical injury due to high membrane tension, and this threshold can be altered by factors that influence membrane prestress, such as cartilage hypoosmolarity, secondary to proteoglycan loss. These findings suggest that modulating PIEZO1 activation or downstream signaling may offer avenues for the prevention or treatment of osteoarthritis.

Healthy and Osteoarthritis-Affected Joints Facing the Cellular Crosstalk

Osteoarthritis (OA) is a chronic, progressive, severely debilitating, and multifactorial joint disease that is recognized as the most common type of arthritis. During the last decade, it shows an incremental global rise in prevalence and incidence. The interaction between etiologic factors that mediate joint degradation has been explored in numerous studies. However, the underlying processes that induce OA remain obscure, largely due to the variety and complexity of these mechanisms. During synovial joint dysfunction, the osteochondral unit undergoes cellular phenotypic and functional alterations. At the cellular level, the synovial membrane is influenced by cartilage and subchondral bone cleavage fragments and extracellular matrix (ECM) degradation products from apoptotic and necrotic cells. These "foreign bodies" serve as danger-associated molecular patterns (DAMPs) that trigger innate immunity, eliciting and sustaining low-grade inflammation in the synovium. In this review, we explore the cellular and molecular communication networks established between the major joint compartments-the synovial membrane, cartilage, and subchondral bone of normal and OA-affected joints.

Measuring chondrocyte viability of articular cartilage based on label-free two-photon microscopy and deep learning image analysis

Objective

Chondrocyte viability (CV) is an important indicator of articular cartilage health. Two-photon excitation autofluorescence (TPAF) and second harmonic generation (SHG) microscopy provide a label-free method for imaging chondrocytes. In this study, we propose an automated assessment of CV using deep learning cell segmentation and counting based on acquired TPAF/SHG images.

Design

Label-free TPAF/SHG images of cartilage samples from rats and porcine were acquired using both commercial and home-built two-photon microscopes, respectively. TPAF/SHG images were merged to form RGB color images with red, green, and blue channels assigned to TPAF (two channels) and SHG signals, respectively. To make the training datasets for the deep learning networks, individual chondrocyte areas on the RGB color images were manually circled and live or dead chondrocytes were validated by using Calcein-AM and Ethidium homodimer-1 dye labeling. We first built a chondrocyte viability network (MCV-Net) using the Mask R-CNN architecture, which could provide individual segmented cellular areas with live or dead status. Wiener deconvolution preprocessing was added before the input of MCV-Net to improve the accuracy of the CV analysis, forming the Wiener deconvolution CV network (wMCV-Net).

Results

Training (300 images) and test (120 images) datasets were built for rats and porcine cartilage respectively. Wiener deconvolution could improve the Peak Signal-to-Noise Ratio (PSNR) for 30-40%. We demonstrated that both MCV-Net and wMCV-Net significantly improved the accuracy of the CV measurement.

Conclusion

A custom desktop TPAF/SHG microscope was used in collaboration with deep learning algorithm wMCV-Net based label-free method to assess the CV and get 95% accuracy with both rats and porcine samples.

Impact of buffer composition on biochemical, morphological and mechanical parameters: A tare before dielectrophoretic cell separation and isolation

Dielectrophoresis (DEP) represents an electrokinetic approach for discriminating and separating suspended cells based on their intrinsic dielectric characteristics without the need for labeling procedure. A good practice, beyond the physical and engineering components, is the selection of a buffer that does not hinder cellular and biochemical parameters as well as cell recovery. In the present work the impact of four buffers on biochemical, morphological, and mechanical parameters was evaluated in two different cancer cell lines (Caco-2 and K562). Specifically, MTT ([3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide]) assay along with flow cytometry analysis were used to evaluate the occurring changes in terms of cell viability, morphology, and granulocyte stress formation, all factors directly influencing DEP sorting capability. Quantitative real-time PCR (qRT-PCR) was instead employed to evaluate the gene expression levels of interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS), two well-known markers of inflammation and oxidative stress, respectively. An additional marker representing an index of cellular metabolic status, i.e. the expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene, was also evaluated. Among the four buffers considered, two resulted satisfactory in terms of cell viability and growth recovery (24 h), with no significant changes in cell morphology for up to 1 h in suspension. Of note, gene expression analysis showed that in both cell lines the apparently non-cytotoxic buffers significantly modulated IL-6, iNOS, and GAPDH markers, underlining the importance to deeply investigate the molecular and biochemical changes occurring during the analysis, even at apparently non-toxic conditions. The selection of a useful buffer for the separation and analysis of cells without labeling procedures, preserving cell status, represents a key factor for DEP analysis, giving the opportunity to further use cells for additional analysis.

Endocytosis and exocytosis protect cells against severe membrane tension variations

The ability of cells to regulate their shape and volume is critical for many cell functions. How endocytosis and exocytosis, as important ways of membrane trafficking, affect cellular volume regulation is still unclear. Here, we develop a theoretical framework to study the dynamics of cell volume, endocytosis, and exocytosis in response to osmotic shocks and mechanical loadings. This model can not only explain observed dynamics of endocytosis and exocytosis during osmotic shocks but also predict the dynamics of endocytosis and exocytosis during cell compressions. We find that a hypotonic shock stimulates exocytosis, while a hypertonic shock stimulates endocytosis; and exocytosis in turn allows cells to have a dramatic change in cell volume but a small change in membrane tension during hyposmotic swelling, protecting cells from rupture under high tension. In addition, we find that cell compressions with various loading speeds induce three distinct dynamic modes of endocytosis and exocytosis. Finally, we show that increasing endocytosis and exocytosis rates reduce the changes in cell volume and membrane tension under fast cell compression, whereas they enhance the changes in cell volume and membrane tension under slow cell compression. Together, our findings reveal critical roles of endocytosis and exocytosis in regulating cell volume and membrane tension.

Migrating Progenitor Cells Derived From Injured Cartilage Surface Respond to Damage-Associated Molecular Patterns

OBJECTIVE

To delineate the response of migrating chondrogenic progenitor cells (CPCs) that arose from the surface of mechanically injured articular cartilage to proinflammatory damage-associated-molecular-patterns (DAMPs).

DESIGN

Bovine CPCs and non-CPC chondrocytes isolated from either impacted or scratched articular cartilage were studied. Those 2 types of cells were treated with mitochondrial DAMPs (MTDs; 10 nM fMLF and 10 µg/mL CpG DNA), or 10 nM HMGB1, or 10 ng/mL IL-1b for 24 hours. At the end of experiments, conditioned media and cell lysates were collected for analysis of expression levels of matrix metalloproteinases (MMPs), chemokines, and cytokines that are associated with cartilage degeneration with Western blotting and quantitative polymerase chain reaction. The difference of expression levels was compared by Welch's t-test.

RESULTS

Our data indicated that HMGB1 and MTDs remarkably upregulated pro-MMP-13 expression in CPCs. Compared with non-CPCs, CPCs expressed significantly more baseline mRNAs of MMP-13, CXCL12, and IL-6. MTDs greatly increased the expression of MMP-13 and IL-6 in CPCs by over 100-fold (P < 0.001). MTDs also significantly increased IL-8 expression in CPCs to a similar extent (P < 0.001). However, when IL-1b was present, CPCs expressed less MMP-3 and active MMP-13 proteins as well as less CCL2 and IL-6 than did non-CPCs.

CONCLUSIONS

We concluded that CPCs were more sensitive than non-CPCs in response to DAMPs, especially MTDs. The proinflammatory nature of CPCs implied their critical role in the early phase of posttraumatic osteoarthritis development.

New Endeavors of (Micro)Tissue Engineering: Cells Tissues Organs on-Chip and Communication Thereof

The development of new therapies is tremendously hampered by the insufficient availability of human model systems suitable for preclinical research on disease target identification, drug efficacy, and toxicity. Thus, drug failures in clinical trials are too common and too costly. Animal models or standard 2D in vitro tissue cultures, regardless of whether they are human based, are regularly not representative of specific human responses. Approaching near human tissues and organs test systems is the key goal of organs-on-chips (OoC) technology. This technology is currently showing its potential to reduce both drug development costs and time-to-market, while critically lessening animal testing. OoC are based on human (stem) cells, potentially derived from healthy or disease-affected patients, thereby amenable to personalized therapy development. It is noteworthy that the OoC market potential goes beyond pharma, with the possibility to test cosmetics, food additives, or environmental contaminants. This (micro)tissue engineering-based technology is highly multidisciplinary, combining fields such as (developmental) biology, (bio)materials, microfluidics, sensors, and imaging. The enormous potential of OoC is currently facing an exciting new challenge: emulating cross-communication between tissues and organs, to simulate more complex systemic responses, such as in cancer, or restricted to confined environments, as occurs in osteoarthritis. This review describes key examples of multiorgan/tissue-on-chip approaches, or linked organs/tissues-on-chip, focusing on challenges and promising new avenues of this advanced model system. Additionally, major emphasis is given to the translation of established tissue engineering approaches, bottom up and top down, towards the development of more complex, robust, and representative (multi)organ/tissue-on-chip approaches.

Deep learning provides high accuracy in automated chondrocyte viability assessment in articular cartilage using nonlinear optical microscopy

Chondrocyte viability is a crucial factor in evaluating cartilage health. Most cell viability assays rely on dyes and are not applicable for in vivo or longitudinal studies. We previously demonstrated that two-photon excited autofluorescence and second harmonic generation microscopy provided high-resolution images of cells and collagen structure; those images allowed us to distinguish live from dead chondrocytes by visual assessment or by the normalized autofluorescence ratio. However, both methods require human involvement and have low throughputs. Methods for automated cell-based image processing can improve throughput. Conventional image processing algorithms do not perform well on autofluorescence images acquired by nonlinear microscopes due to low image contrast. In this study, we compared conventional, machine learning, and deep learning methods in chondrocyte segmentation and classification. We demonstrated that deep learning significantly improved the outcome of the chondrocyte segmentation and classification. With appropriate training, the deep learning method can achieve 90% accuracy in chondrocyte viability measurement. The significance of this work is that automated imaging analysis is possible and should not become a major hurdle for the use of nonlinear optical imaging methods in biological or clinical studies.

A Roadmap of In Vitro Models in Osteoarthritis: A Focus on Their Biological Relevance in Regenerative Medicine

Osteoarthritis (OA) is a multifaceted musculoskeletal disorder, with a high prevalence worldwide. Articular cartilage and synovial membrane are among the main biological targets in the OA microenvironment. Gaining more knowledge on the accuracy of preclinical in vitro OA models could open innovative avenues in regenerative medicine to bridge major gaps, especially in translation from animals to humans. Our methodological approach entailed searches on Scopus, the Web of Science Core Collection, and EMBASE databases to select the most relevant preclinical in vitro models for studying OA. Predicting the biological response of regenerative strategies requires developing relevant preclinical models able to mimic the OA milieu influencing tissue responses and organ complexity. In this light, standard 2D culture models lack critical properties beyond cell biology, while animal models suffer from several limitations due to species differences. In the literature, most of the in vitro models only recapitulate a tissue compartment, by providing fragmented results. Biotechnological advances may enable scientists to generate new in vitro models that combine easy manipulation and organ complexity. Here, we review the state-of-the-art of preclinical in vitro models in OA and outline how the different preclinical systems (inflammatory/biomechanical/microfluidic models) may be valid tools in regenerative medicine, describing their pros and cons. We then discuss the prospects of specific and combinatorial models to predict biological responses following regenerative approaches focusing on mesenchymal stromal cells (MSCs)-based therapies to reduce animal testing.

Mechanical properties of external confinement modulate the rounding dynamics of cells

Many studies have demonstrated that mitotic cells can round up against external impediments. However, how the stiffness of external confinement affects the dynamics of rounding force/pressure and cell volume remains largely unknown. Here, we develop a theoretical framework to study the rounding of adherent cells confined between a substrate and a cantilever. We show that the rounding force and pressure increase exclusively with the effective confinement on the cell, which is related to the cantilever stiffness and the separation between cantilever and substrate. Remarkably, an increase of cantilever stiffness from 0.001 to 1 N/m can lead to a 100-fold change in rounding force. This model also predicts an active role of confinement stiffness in regulating the dynamics of cell volume and hydrostatic pressure. We find that the dynamic changes of cellular volume and hydrostatic pressure after osmotic shocks are opposite if the cantilever is soft, whereas the dynamic changes of cellular volume and pressure are the same if the cantilever is stiff. Taken together, this work demonstrates that confinement stiffness appears as a critical regulator in regulating the dynamics of rounding force and pressure. Our findings also indicate that the difference in cantilever stiffness need to be considered when comparing the measured rounding force and pressure from various experiments.

Articular Chondrocyte Phenotype Regulation through the Cytoskeleton and the Signaling Processes That Originate from or Converge on the Cytoskeleton: Towards a Novel Understanding of the Intersection between Actin Dynamics and Chondrogenic Function

Numerous studies have assembled a complex picture, in which extracellular stimuli and intracellular signaling pathways modulate the chondrocyte phenotype. Because many diseases are mechanobiology-related, this review asked to what extent phenotype regulators control chondrocyte function through the cytoskeleton and cytoskeleton-regulating signaling processes. Such information would generate leverage for advanced articular cartilage repair. Serial passaging, pro-inflammatory cytokine signaling (TNF-α, IL-1α, IL-1β, IL-6, and IL-8), growth factors (TGF-α), and osteoarthritis not only induce dedifferentiation but also converge on RhoA/ROCK/Rac1/mDia1/mDia2/Cdc42 to promote actin polymerization/crosslinking for stress fiber (SF) formation. SF formation takes center stage in phenotype control, as both SF formation and SOX9 phosphorylation for COL2 expression are ROCK activity-dependent. Explaining how it is molecularly possible that dedifferentiation induces low COL2 expression but high SF formation, this review theorized that, in chondrocyte SOX9, phosphorylation by ROCK might effectively be sidelined in favor of other SF-promoting ROCK substrates, based on a differential ROCK affinity. In turn, actin depolymerization for redifferentiation would “free-up” ROCK to increase COL2 expression. Moreover, the actin cytoskeleton regulates COL1 expression, modulates COL2/aggrecan fragment generation, and mediates a fibrogenic/catabolic expression profile, highlighting that actin dynamics-regulating processes decisively control the chondrocyte phenotype. This suggests modulating the balance between actin polymerization/depolymerization for therapeutically controlling the chondrocyte phenotype.

Macroscopically healthy articular cartilage with fibrillar-scale early tissue degeneration subject to impact loading results in greater extent of cell-death

From previous investigations it has been shown that there exists healthy-appearing articular cartilage that contains collagen fibril network destructuring. It is hypothesised that such sub-micron scale destructuring not only presents an increased vulnerability to tissue scale damage following impact loading, but an increase in cell death as well. Cartilage-on-bone blocks from 12 patellae, six healthy (G0) and the other six with sub-micron fibrillar destructuring (G1), were obtained and subject to 2.3 J impact loading. Two sets of sub-samples were obtained for each block tested. One set was used to examine for the live/dead cell response using calcein-AM and propidium iodide staining, imaged with confocal microscopy. The tissue microstructural matrix was imaged from the other matched set, unstained and in its fully hydrated state, using differential interference contrast optical light microscopy. High speed imaging of the impact was used to calculate the velocity changes or coefficient of restitution (COR) and used as a proxy of energy that the tissue absorbed. A previously defined tissue matrix damage score was used to quantify the extent of fracturing and cracking in the matrix. The cell death (PCD) was counted and presented as a percentage against all cells live plus dead. The energy absorbed was 36.5% higher in G1 than in G0 (p = 0.034). However, the damage score and PCD of samples in the G1 group was much larger than the G0 group, ~300% and 161% respectively. Microscopy showed that cell death is associated to both matrix compaction and further fibrillar destructuring from the ECM to the territorial matrix regions of the chondron. Following impact loading, cartilage tissue that appears normal but contains sub-micron fibrillar matrix destructuring responds with significantly increased cell death.

Iatrogenic Articular Cartilage Injury in Arthroscopic Hip and Knee Videos and the Potential for Cartilage Cell Death When Simulated in a Bovine Model

PURPOSE

To determine the incidence and characterize the severity of iatrogenic cartilage injuries.

METHODS

Technique videos of arthroscopic femoral acetabular impingement procedures and meniscus repairs on VuMedi (n = 85) and Arthroscopy Techniques (n = 45) were reviewed and iatrogenic cartilage injuries were identified and graded (minor, intermediate, and major injury) by 2 independent reviewers. To demonstrate that even minor injuries on a cellular scale result in damage, a bovine osteochondral explant was used to create comparable minor iatrogenic injuries at varied forces that do not disrupt the articular surface (1.5 N, 2.5 N, and 9.8 N). Dead chondrocytes at the site of injury were stained with ethidium homodimer-2 and imaged with an Olympus FV1000 confocal microscope. χ² tests were used for analysis; all results with P < .05 were considered significant.

RESULTS

In total, 130 videos of arthroscopic meniscus and femoral acetabular impingement procedures were analyzed and the incidence of iatrogenic cartilage injury was 73.8%. There were 110 (70.0%) minor, 35 (22.3%) intermediate, and 11 (7.0%) major iatrogenic injuries. All forces tested in the minor injury bovine model resulted in chondrocyte death at the site of contact.

CONCLUSIONS

Iatrogenic articular cartilage injuries are common in arthroscopy, occurring in more than 70% of the surgeon-published instructional videos analyzed. At least some chondrocyte death occurs with minor simulated iatrogenic injuries (1.5 N).

CLINICAL RELEVANCE

The high rate of cartilage damage during arthroscopic technique videos likely under-represents the true incidence in clinical practice. Cell death occurs in the bovine minor injury model with minimal contact forces. This suggests iatrogenic cartilage damage during arthroscopy could contribute to clinical outcomes.

Damage control articular surgery: Maintaining chondrocyte health and minimising iatrogenic injury

Articular cartilage has limited intrinsic regenerative potential. The maintenance of healthy articular cartilage is essential to prevent joint degeneration and the morbidity associated with arthritis. In this review, we outline the structure and function of healthy articular cartilage. We summarise some of the recent literature outlining the influence of surgical factors on chondrocyte health. These factors include mechanical injury from instrumentation and drilling, drying, and the influence of irrigation fluids, antimicrobial solutions and local anaesthetics. We demonstrate that there is scope for improving cartilage viability at the time of surgery if simple chondroprotective measures are routinely adopted.

Evidence that reduction in volume protects in situ articular chondrocytes from mechanical impact

Chondrocytes, the resident cells in articular cartilage, carry the burden of producing and maintaining the extracellular matrix (ECM). However, as these cells have a low proliferative capacity and are not readily replaced, chondrocyte death due to extreme forces may contribute to the pathogenesis of osteoarthritis (OA) after injury or may inhibit healing after osteochondral transplantation, a restorative procedure for damaged cartilage that requires a series of mechanical impacts to insert the graft. Consequently, there is a need to understand what factors influence the vulnerability of in situ chondrocytes to mechanical trauma. To this end, the objective of this study was to investigate how altering cell volume by different means (hydrostatic pressure, uniaxial load, and osmotic challenge with and without inhibition of regulatory volume decrease) affects the vulnerability of in situ chondrocytes to extreme mechanical forces. Using a custom experimental platform enabling testing of viable and intact murine cartilage-on-bone explants, we established a strong correlation between chondrocyte volume and vulnerability to impact injury wherein reduced volume was protective. Moreover, we found that the volume-perturbing interventions did not affect cartilage ECM mechanical properties, suggesting that their effects on chondrocyte vulnerability occurred at the cellular level. The findings of this study offer new avenues for novel strategies aimed at preventing chondrocyte loss during osteochondral grafting or to halting the progression of cell death after a joint destabilizing injury.

Nonlabeling and quantitative assessment of chondrocyte viability in articular cartilage with intrinsic nonlinear optical signatures

Chondrocyte viability is a crucial factor for evaluating cartilage health. Most prevalent cell viability assays rely on dyes and are not applicable for in vivo or longitudinal studies. Here we demonstrated that the two-photon excited autofluorescence and second harmonic generation microscopy provided high-resolution imaging of cartilage tissue and distinguished live/dead chondrocytes by visual assessment. Furthermore, the normalized autofluorescence ratio was proposed as a quantitative indicator to determine chondrocyte viability. Based on the indicator, a curve fitting and simulated receiver operating characteristic method was proposed to identify the live/dead cell populations as well as the indicator threshold without dye labeling. Thus, it established the label-free imaging method for chondrocyte viability assay in cartilage tissue.

Impact statement

Chondrocytes are the only cellular component found in the cartilage, playing a critical role in maintaining the homeostasis of articular cartilage. The viability of chondrocytes is a crucial factor for evaluating cartilage health. However, the current prevalent cell viability assays rely on dye staining and thereby are not applicable in vivo or in longitudinal assessments. In this study, we demonstrate that the intrinsic signals such as two-photon excited autofluorescence and second harmonic generation can be used to classify live and dead chondrocytes in cartilage tissue. A quantitative measure is also proposed allowing development of automated assessment algorithms. The nonlabeling nature of this method suggests the potential applicability to nondestructive and in vivo assessment of cartilage health.

An in vitro study of the effect of the optimal irrigation solution conditions during canine articular surgery

OBJECTIVES

To establish whether chondrocyte viability, matrix degradation and the induction of proteolytic gene expression in canine cartilage is independent of irrigation fluid osmolality and time following exposure to the irrigation fluid.

METHODS

Canine cartilage explants were exposed to one of three different solution types i) Culture medium (270-280 mOsmol/kg) ii) NaCl 0.9% (302 mOsmol/kg) iii) NaCl 0.9% with sucrose (600 mOsmol/kg). Chondrocyte viability and selected proteolytic gene expression were measured at two time points; immediately following exposure and 24 h following exposure. The media samples at 24 h following exposure were assessed for sulphated glycosaminoglycan (sGAG) release.

RESULTS

In all samples, no cell death was observed across the superficial or deeper layers of the cartilage. When adjusting for time, gene expression was not shown to be dependent on solution type. However for all solution types, Matrix Metalloproteinase 13 (MMP13) and A Disintegrin and Metalloproteinase with Thrombospondin Motifs 5 (ADAMTS5) expression was significantly decreased in cartilage samples at 24 h post exposure comparatively to samples tested immediately post exposure. No significant differences were identified in the relative sGAG release between the solution types.

CLINICAL SIGNIFCANCE

Arthroscopic solution irrigation of cartilage explants had no effect on cell viability or proteinase production. At present there is no indication to optimise irrigation fluid osmolarity, as conventional arthroscopic solution was not deleterious to healthy cartilage in this model.

Degrading products of chondroitin sulfate can induce hypertrophy-like changes and MMP-13/ADAMTS5 production in chondrocytes

Chondroitin sulfate (CS) is the most abundant glycosaminoglycan (GAG) in articular cartilage and the loss of CS-GAG occurs early in OA. As a major component of perichondral matrix interacting directly with chondrocytes, the active turnover of CS can affect to break the homeostasis of chondrocytes. Here we employ CS-based 3-dimensional (3D) hydrogel scaffold system to investigate how the degradation products of CS affect the catabolic phenotype of chondrocytes. The breakdown of CS-based ECM by the chondroitinase ABC (ChABC) resulted in a hypertrophy-like morphologic change in chondrocytes, which was accompanied by catabolic phenotypes, including increased MMP-13 and ADAMTS5 expression, nitric oxide (NO) production and oxidative stress. The inhibition of Toll-like receptor 2 (TLR2) or TLR4 with OxPAPC (TLR2 and TLR4 dual inhibitor) and LPS-RS (TLR4-MD2 inhibitor) ameliorated these catabolic phenotypes of chondrocytes by CS-ECM degradation, suggesting a role of CS breakdown products as damage-associated molecular patterns (DAMPs). As downstream signals of TLRs, MAP kinases, NF-kB, NO and STAT3-related signals were responsible for the catabolic phenotypes of chondrocytes associated with ECM degradation. NO in turn reinforced the activation of MAP kinases as well as NFkB signaling pathway. Thus, these results propose that the breakdown product of CS-GAG can recapitulate the catabolic phenotypes of OA.

Cell mechanical microenvironment for cell volume regulation

Cell volume regulation, as one of the fundamental homeostasis of the cell, is associated with many cellular behaviors and functions. With the increased studies on the effect of environmental mechanical cues on cell volume regulation, the relationship between cell volume regulation and mechanotransduction becomes more and more clear. In this paper, we review the mechanisms and hypotheses by which cell maintains its volume homeostasis both in vivo and in constructed cell mechanical microenvironment (CMM) in vitro. We discuss how the growth-division regulation maintains the volume homeostasis of cells in the cell cycle and how the cell cortex/membrane tension mediates the effect of CMM (i.e., osmotic pressure, matrix stiffness, and mechanical force) on cell volume regulation. We also highlight the roles of cell volume as a perfect integrator of the downstream signals of mechanotransduction from different aspects of CMM and an effective indicator for the mechanical condition that cell confronts. This interdisciplinary perspective can provide new insight into biomechanics and may shed light on bioengineering and pathological research work. We hope this review can facilitate future studies on the investigation of the role of cell volume in mechanotransduction.

The Role of Chondrocyte Morphology and Volume in Controlling Phenotype-Implications for Osteoarthritis, Cartilage Repair, and Cartilage Engineering

PURPOSE OF REVIEW

Articular chondrocytes are exclusively responsible for the turnover of the extracellular matrix (ECM) of hyaline cartilage. However, chondrocytes are phenotypically unstable and, if they de-differentiate into hypertrophic or fibroblastic forms, will produce a defective and weak matrix. Chondrocyte volume and morphology exert a strong influence over phenotype and a full appreciation of the factors controlling chondrocyte phenotype stability is central to understanding (a) the mechanisms underlying the cartilage failure in osteoarthritis (OA), (b) the rationale for hyaline cartilage repair, and (c) the strategies for improving the engineering of resilient cartilage. The focus of this review is on the factors involved in, and the importance of regulating, chondrocyte morphology and volume as key controllers of chondrocyte phenotype.

RECENT FINDINGS

The visualisation of fluorescently-labelled in situ chondrocytes within non-degenerate and mildly degenerate cartilage, by confocal scanning laser microscopy (CLSM) and imaging software, has identified the marked heterogeneity of chondrocyte volume and morphology. The presence of chondrocytes with cytoplasmic processes, increased volume, and clustering suggests important early changes to their phenotype. Results from experiments more closely aligned to the normal physico-chemical environment of in situ chondrocytes are emphasising the importance of understanding the factors controlling chondrocyte morphology and volume that ultimately affect phenotype. An appreciation of the importance of chondrocyte volume and morphology for controlling the chondrocyte phenotype is advancing at a rapid pace and holds particular promise for developing strategies for protecting the chondrocytes against deleterious changes and thereby maintaining healthy and resilient cartilage.

The influence of the irrigating solution on articular cartilage in arthroscopic surgery: A systematic review

Purpose

Arthroscopic surgery has become an important and popular orthopedic procedure for numerous joint disorders. Continuous irrigation is performed to replace synovial fluid for optimal joint distension and clear visualization of the synovial cavity. Irrigation solutions may, however, negatively impact articular cartilage and chondrocyte viability. This systematic review aims to compare different irrigating solutions and their properties to determine whether one is superior in its effects on articular cartilage and chondrocytes.

Methods

A systematic literature review was conducted. The online databases: Embase, Medline, HealthStar, Emcare and PubMed were searched from 1946 to August 2018. Methodological index for non-randomized studies (MINORS) was used to assess methodological quality of the included studies.

Results

Sixteen studies met the inclusion/exclusion criteria and were included in this review. Although the studies used different criteria to define superiority, solution superiority was based on results that focused on articular cartilage and chondrocyte viability. Seven of the sixteen included studies compared Ringer's/lactate solution or Ringer's lactate to normal saline. Three found Ringer's solution or Ringer's lactate to be superior to saline, whereas, three studies found no significant differences and one study found Ringer's lactate to be inferior to saline only when their osmolarities differed. Four studies compared ionic to non-ionic solutions. Two of the four studies demonstrated non-ionic solutions to be superior, one had demonstrated no significant differences between solutions, while one had mixed results. Six of the sixteen included studies compared differing osmolarities. One found no statistically significant differences between solutions of differing osmolarities, whereas, the remaining five studies found superiority with hyperosmolarity. Two of the sixteen included studies examined the effects of different temperatures. Both studies concluded that the use of a warmer (more physiological) temperature is more ideal. Two of the sixteen studies included in this review compared solutions with differing pH levels. Both studies concluded on the importance of utilizing the more physiological solutions for arthroscopic procedures.

Conclusion

Ringer's Lactate and Ringer's Solution as well as non-ionic solutions may have merit over the use of the normal saline for irrigation. Hyperosmolarity, warmer solutions and ones with more physiological pH values may be beneficial when considering potential effects on articular cartilage and chondrocytes. The current review demonstrated trends found in the current literature, which require human studies - preferably high quality RCTs -to make recommendations that aid surgeons in making the best decision regarding the ideal irrigation solution to use on their patients.

Level of evidence

Level IV, Systematic review of Level IV studies.

Controlling Cellular Volume via Mechanical and Physical Properties of Substrate

The mechanical and physical properties of substrate play a crucial role in regulating many cell functions and behaviors. However, how these properties affect cell volume is still unclear. Here, we show that an increase in substrate stiffness, available spread area, or effective adhesion energy density results in a remarkable cell volume decrease (up to 50%), and the dynamic cell spreading process is also accompanied by dramatic cell volume decrease. Further, studies of ion channel inhibition and osmotic shock suggest that these volume decreases are due to the efflux of water and ions. We also show that disrupting cortex contractility leads to bigger cell volume. Collectively, these results reveal the "mechanism of adhesion-induced compression of cells," i.e., stronger interaction between cell and substrate leads to higher actomyosin contractility, expels water and ions, and thus decreases cell volume.

Cellular Volume and Matrix Stiffness Direct Stem Cell Behavior in a 3D Microniche

The central question addressed in this study is whether cells with different sizes have different responses to matrix stiffness. We used methacrylated hyaluronic acid (MeHA) hydrogels as the matrix to prepare an in vitro 3D microniche in which the single stem cell volume and matrix stiffness can be altered independently from each other. This simple approach enabled us to decouple the effects of matrix stiffness and cell volume in 3D microenvironments. Human mesenchymal stem cells (hMSCs) were cultured in individual 3D microniches with different volumes (2800, 3600, and 6000 μm³) and stiffnesses (5, 12, and 23 kPa). We demonstrated that cell volume affected the cellular response to matrix stiffness. When cells had an optimal volume, cells could form clear stress fibers and focal adhesions on soft, intermediate, or stiff matrix. In small cells, stress fiber formation and YAP/TAZ localization were not affected by stiffness. This study highlights the importance of considering cellular volume and substrate stiffness as important cues governing cell-matrix interactions.

Chondroprotection in Models of Cartilage Injury by Raising the Temperature and Osmolarity of Irrigation Solutions

Objectives During arthroscopic or open joint surgery, articular cartilage may be subjected to mechanical insults by accident or design. These may lead to chondrocyte death, cartilage breakdown and posttraumatic osteoarthritis. We have shown that increasing osmolarity of routinely used normal saline protected chondrocytes against injuries that may occur during orthopedic surgery. Often several liters of irrigation fluid are used during an orthopedic procedure, which is usually kept at room temperature, but is sometimes chilled. Here, we compared the effect of normal and hyperosmolar saline solution at different temperatures on chondrocyte viability following cartilage injury using in vitro and in vivo models of scalpel-induced injury. Design Cartilage injury was induced in bovine osteochondral explants and the patellar groove of rats in vivo by a single pass of a scalpel blade in the presence of normal saline (300 mOsm) or hyperosmolar saline solution (600 mOsm, sucrose addition) at 4°C, 21°C, or 37°C. Chondrocytes were fluorescently labeled and visualized by confocal microscopy to assess cell death. Results Hyperosmolar saline reduced scalpel-induced chondrocyte death in both bovine and rat cartilage by ~50% at all temperatures studied (4°C, 21°C, 37°C; P < 0.05). Raising temperature of both irrigation solutions to 37°C reduced scalpel-induced cell death ( P < 0.05). Conclusions Increasing the osmolarity of normal saline and raising the temperature of the irrigation solutions to 37°C reduced chondrocyte death associated with scalpel-induced injury in both in vitro and in vivo cartilage injury models. A hyperosmolar saline irrigation solution at 37°C may protect cartilage by decreasing the risk of chondrocyte death during mechanical injury.

Comparison between in vitro and in vivo cartilage overloading studies based on a systematic literature review

Methodological differences between in vitro and in vivo studies on cartilage overloading complicate the comparison of outcomes. The rationale of the current review was to (i) identify consistencies and inconsistencies between in vitro and in vivo studies on mechanically-induced structural damage in articular cartilage, such that variables worth interesting to further explore using either one of these approaches can be identified; and (ii) suggest how the methodologies of both approaches may be adjusted to facilitate easier comparison and therewith stimulate translation of results between in vivo and in vitro studies. This study is anticipated to enhance our understanding of the development of osteoarthritis, and to reduce the number of in vivo studies. Generally, results of in vitro and in vivo studies are not contradicting. Both show subchondral bone damage and intact cartilage above a threshold value of impact energy. At lower loading rates, excessive loads may cause cartilage fissuring, decreased cell viability, collagen network de-structuring, decreased GAG content, an overall damage increase over time, and low ability to recover. This encourages further improvement of in vitro systems, to replace, reduce, and/or refine in vivo studies. However, differences in experimental set up and analyses complicate comparison of results. Ways to bridge the gap include (i) bringing in vitro set-ups closer to in vivo, for example, by aligning loading protocols and overlapping experimental timeframes; (ii) synchronizing analytical methods; and (iii) using computational models to translate conclusions from in vitro results to the in vivo environment and vice versa. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. J Orthop Res 9999:1-11, 2018.

Osteochondral Graft Size Is Significantly Associated With Increased Force and Decreased Chondrocyte Viability

BACKGROUND

Insertion force has been shown to significantly reduce chondrocyte viability during osteochondral allograft transplantation. How graft size influences the required insertion force and chondrocyte viability has yet to be determined. Hypothesis/Purpose: The purpose was to characterize how graft size influences insertion force requirements and chondrocyte viability during osteochondral transplantation. The hypothesis was that larger grafts would require greater force and reduce chondrocyte viability.

STUDY DESIGN

Controlled laboratory study.

METHODS

Four graft sizes-15 × 5 mm, 15 × 10 mm, 25 × 5 mm, and 25 × 10 mm (diameter × depth)-were harvested from 13 thawed fresh-frozen human cadaveric distal femurs. Average, maximum, and cumulative force and number of impacts were recorded for 44 grafts by a surgical mallet embedded with a calibrated force sensor. In a separate experiment, fresh osteochondral tissues were subjected to mechanical loading. To capture a range of clinically important forces, categories were selected to correspond to impaction force data. Chondrocyte viability was assessed with confocal laser microscopy and live/dead staining.

RESULTS

Total force for all grafts averaged 4576 N. Median number of impacts for all grafts was 20 (range, 7-116). The mean number of impacts for 5-mm-deep grafts was 14.2 (95% CI, 10.8-18.6), as compared with 26.3 (95% CI, 19.9-34.4) for 10-mm-deep grafts ( P < .001). The mean cumulative force for 5-mm-deep grafts was 2128 N (95% CI, 1467-3087), as opposed to 4689 N (95% CI, 3232-6803) for 10-mm-deep grafts ( P = .001). For every 1 mm in graft depth, an average of 13.1% (95% CI, 6.2%-20.3%) more impacts are required when controlling for diameter and density ( P < .001). For every 1 mm in graft depth, the force required increases on average by 17.1% (95% CI, 7.7%-27.4%) when controlling for diameter and density ( P = .001). There was a significant reduction in chondrocyte viability for the forces required for graft thickness values >10 mm. Only forces associated with graft thickness <10 mm had chondrocyte viabilities consistently >70%.

CONCLUSION

Insertion force increases significantly with increasing graft depth. Controlling for diameter and bone density, a 1-mm increase in graft depth is associated with 13.1% more impacts and 17.1% more force. Chondrocyte viability was significantly reduced to <70% at average forces associated with grafts thicker than 10 mm.

CLINICAL RELEVANCE

Based on the current data, graft depth is an important consideration for surgeons when sizing osteochondral allograft transplant for chondral lesions of the knee.

DAMPs Synergize with Cytokines or Fibronectin Fragment on Inducing Chondrolysis but Lose Effect When Acting Alone

OBJECTIVE AND DESIGN

To investigate whether endogenous damage-associated molecular patterns (DAMPs) or alarmins originated from mitochondria or nucleus stimulates inflammatory response in articular chondrocytes to cause chondrolysis which leads to cartilage degradation featured in posttraumatic osteoarthritis (PTOA).

MATERIALS

Primary cultures of bovine or human chondrocytes isolated from cartilage of weight-bearing joints.

TREATMENT

Chondrocytes were subjected to mitochondrial DAMPs (MTDs) or HMGB1, a nuclear DAMP (NuD), with or without the presence of an N-terminal 29 kDa fibronectin fragment (Fn-f) or proinflammatory cytokines (IL-1β and TNF-α). Injured cartilage-conditioned culturing medium containing a mixture of DAMPs was employed as a control. After 24 hrs, the protein expression of cartilage degrading metalloproteinases and iNOS in culture medium or cell lysates was examined with Western blotting, respectively.

RESULTS

HMGB1 was synergized with IL-1β in upregulating expression of MMP-3, MMP-13, ADAMTS-5, ADAM-8, and iNOS. Moreover, a moderate synergistic effect was detected between HMGB1 and Fn-f or between MTDs and TNF-α on MMP-3 expression. However, when acting alone, MTDs or HMGB1 did not upregulate cartilage degrading enzymes or iNOS.

CONCLUSION

MTDs or HMGB1 could only stimulate inflammatory response in chondrocytes with the presence of cytokines or Fn-f.

Safety and efficacy of hyperosmolar irrigation solution in shoulder arthroscopy

BACKGROUND

A hyperosmolar irrigation solution has been reported to be safe and have potential benefits for use during shoulder arthroscopy in an animal model study. In this study, the clinical effects of a hyperosmolar solution were compared with a standard isotonic solution when used for shoulder arthroscopy.

METHODS

A prospective, double-blind, randomized controlled trial was performed to compare isotonic (273 mOsm/L) and hyperosmolar (593 mOsm/L) irrigation solutions used for arthroscopic rotator cuff repair. Primary outcomes focused on the amount of periarticular fluid retention based on net weight gain, change in shoulder girth, and pain. All patients were tracked through standard postsurgical follow-up to ensure no additional complications arose. Patients were contacted at 1 year to assess American Shoulder and Elbow Surgeon score, visual analog scale pain score, and the Single Assessment Numeric Evaluation shoulder scores RESULTS: Fifty patients (n = 25/group) were enrolled and completed the study. No statistically significant differences were noted between cohorts in demographics or surgical variables. The hyperosmolar group experienced significantly less mean weight gain (1.6 ± 0.82 kg vs. 2.25 ± 0.77 kg; P = .005), significantly less change in shoulder girth (P < .05), and a significantly lower immediate postoperative visual analog scale pain score (P = .036). At 1 year postoperatively, the differences between groups for American Shoulder and Elbow Surgeons, visual analog scale pain, and Single Assessment Numeric Evaluation were not significant (P > .2).

CONCLUSION

A hyperosmolar irrigation solution provides a safe and effective way to decrease periarticular fluid retention associated with arthroscopic rotator cuff surgery without any adverse long-term effects. Use of a hyperosmolar irrigation solution for shoulder arthroscopy has potential clinical benefits to surgeons and patients.

Low-energy impact of human cartilage: predictors for microcracking the network of collagen

OBJECTIVE

We aimed to determine the minimum mechanical impact to cause microstructural damage in the network of collagen (microcracking) within human cartilage and hypothesized that energies below 0.1 J or 1 mJ/mm³ would suffice.

DESIGN

We completed 108 low-energy impact tests (0.05, 0.07, or 0.09 J; 0.75 or 1.0 m/s²) using healthy cartilage specimens from six male donors (30.2 ± 8.8 yrs old). Before and after impact we acquired, imaging the second harmonic generation (SHG), ten images from each specimen (50 μm depth, 5 μm step size), resulting in 2160 images. We quantified both the presence and morphology of microcracks. We then correlated test parameters (predictors) impact energy/energy dissipation density, nominal stress/stress rate, and strain/strain rate to microcracking and tested for significance. Where predictors significantly correlated with microstructural outcomes we fitted binary logistic regression plots with 95% confidence intervals (CIs).

RESULTS

No specimens presented visible damage following impact. We found that impact energy/energy dissipation density and nominal stress/stress rate were significant (P < 0.05) predictors of microcracking while both strain and strain rate were not. In our test configuration, an impact energy density of 2.93 mJ/mm³, an energy dissipation density of 1.68 mJ/mm³, a nominal stress of 4.18 MPa, and a nominal stress rate of 689 MPa/s all corresponded to a 50% probability of microcracking in the network of collagen.

CONCLUSIONS

An impact energy density of 1.0 mJ/mm³ corresponded to a ∼20% probability of microcracking. Such changes may initiate a degenerative cascade leading to post-traumatic osteoarthritis.

Use of Saline as a Placebo in Intra-articular Injections in Osteoarthritis: Potential Contributions to Nociceptive Pain Relief

Background:

Osteoarthritis of the knee (OAK) is a severe debilitating condition characterized by joint pain, stiffness, and resultant limited mobility. In recent years, intra-articular (IA) injections have been used to relieve symptoms and have succeeded to varying degrees either with sodium hyaluronate preparations or with a biologic.

Objective:

The objective of this review is to evaluate multiple studies that demonstrate some relief from the symptoms of OAK in the saline arm of various clinical trials.

Method:

A thorough literature search (PubMed) was performed assessing the pain efficacy of various compounds compared to saline injections in clinical trials. A total of 73 studies were identified in the literature search including a total of 5,816 patients. These clinical trials all involved the IA injection of a viscosupplement (hyaluronate, platelet rich plasma (PRP), etc.) or a biologic (the low molecular weight fraction (< 5kDa) of human serum albumin (LMWF-5A)). For all of these studies, the control arm was injection of sterile physiological saline that approximates the salt concentration and total solute concentration of blood and most tissues.

Results:

Based on our review of the current literature, the tested compounds performed with mixed results when compared to saline injections. Moreover, OAK is a variable disease, with severity measured on the Kellgren and Lawrence (KL) scale where various hyaluronate preparations have a therapeutic effect mostly on KL 2-3 patients while a biologic works best on KL 3-4 patients.

Conclusion:

Since the effect of saline injection is always greater than no treatment, the evaluations of these treatments can be confounded in clinical trials. Therefore, the question of whether there are known therapeutic effects of saline injections might explain these results.

Changes in Membrane Receptors and Ion Channels as Potential Biomarkers for Osteoarthritis

Osteoarthritis (OA), a degenerative joint condition, is currently difficult to detect early enough for any of the current treatment options to be completely successful. Early diagnosis of this disease could increase the numbers of patients who are able to slow its progression. There are now several diseases where membrane protein biomarkers are used for early diagnosis. The numbers of proteins in the membrane is vast and so it is a rich source of potential biomarkers for OA but we need more knowledge of these before they can be considered practical biomarkers. How are they best measured and are they selective to OA or even certain types of OA? The first step in this process is to identify membrane proteins that change in OA. Here, we summarize several ion channels and receptors that change in OA models and/or OA patients, and may thus be considered candidates as novel membrane biomarkers of OA.

Hyperosmolar irrigation compared with a standard solution in a canine shoulder arthroscopy model

BACKGROUND

A hyperosmolar irrigation solution may decrease fluid extravasation during arthroscopic procedures. Demonstrating the safety of a hyperosmolar irrigation solution with respect to chondrocyte viability and cartilage water content was deemed necessary before designing a clinical efficacy study.

METHODS

We designed a translational animal model study in which hyperosmolar arthroscopy irrigation fluid (1.8%, 600 mOsm/L) was compared with normal saline (0.9%, 300 mOsm/L). Purpose-bred research dogs (n = 5) underwent bilateral shoulder arthroscopy. Irrigation fluid was delivered to each shoulder joint (n = 10) at 40 mm Hg for 120 minutes using standard ingress and egress portals. The percentage change in shoulder girth was documented at the completion of 120 minutes. Articular cartilage sections from the glenoid and humeral head were harvested from both shoulders. Chondrocyte viability and tissue water content were evaluated. Differences between groups and compared with time 0 controls were determined, with significance set at P <.05.

RESULTS

The mean percentage change in shoulder girth was higher in the isotonic control group (13.3%) than in the hyperosmolar group (10.4%). Chondrocyte viability and tissue water content for glenoid and humeral head cartilage were well maintained in both treatment groups, and differences were not statistically significant.

CONCLUSIONS

The data from this study suggest that doubling the osmolarity of the standard irrigation solution used for arthroscopy was not associated with any detrimental effects on chondrocyte viability or tissue water content after 2 hours of arthroscopic irrigation. On the basis of potential benefits in conjunction with the safety demonstrated in these data, clinical evaluation of a hyperosmolar solution for irrigation during shoulder arthroscopy appears warranted.

An Equilibrium Constitutive Model of Anisotropic Cartilage Damage to Elucidate Mechanisms of Damage Initiation and Progression

Traumatic injuries and gradual wear-and-tear of articular cartilage (AC) that can lead to osteoarthritis (OA) have been hypothesized to result from tissue damage to AC. In this study, a previous equilibrium constitutive model of AC was extended to a constitutive damage articular cartilage (CDAC) model. In particular, anisotropic collagen (COL) fibril damage and isotropic glycosaminoglycan (GAG) damage were considered in a 3D formulation. In the CDAC model, time-dependent effects, such as viscoelasticity and poroelasticity, were neglected, and thus all results represent the equilibrium response after all time-dependent effects have dissipated. The resulting CDAC model was implemented in two different finite-element models. The first simulated uniaxial tensile loading to failure, while the second simulated spherical indentation with a rigid indenter displaced into a bilayer AC sample. Uniaxial tension to failure simulations were performed for three COL fibril Lagrangian failure strain (i.e., the maximum elastic COL fibril strain) values of 15%, 30%, and 45%, while spherical indentation simulations were performed with a COL fibril Lagrangian failure strain of 15%. GAG damage parameters were held constant for all simulations. Our results indicated that the equilibrium postyield tensile response of AC and the macroscopic tissue failure strain are highly dependent on COL fibril Lagrangian failure strain. The uniaxial tensile response consisted of an initial nonlinear ramp region due to the recruitment of intact fibrils followed by a rapid decrease in tissue stress at initial COL fibril failure, as a result of COL fibril damage which continued until ultimate tissue failure. In the spherical indentation simulation, damage to both the COL fibril and GAG constituents was located only in the superficial zone (SZ) and near the articular surface with tissue thickening following unloading. Spherical indentation simulation results are in agreement with published experimental observations. Our results indicate that the proposed CDAC model is capable of simulating both initial small magnitude damage as well as complete failure of AC tissue. The results of this study may help to elucidate the mechanisms of AC tissue damage, which initiate and propagate OA.

In vitro models for the study of osteoarthritis

Osteoarthritis (OA) is a prevalent disease of most mammalian species and is a significant cause of welfare and economic morbidity in affected individuals and populations. In vitro models of osteoarthritis are vital to advance research into the causes of the disease, and the subsequent design and testing of potential therapeutics. However, a plethora of in vitro models have been used by researchers but with no consensus on the most appropriate model. Models attempt to mimic factors and conditions which initiate OA, or dissect the pathways active in the disease. Underlying uncertainty as to the cause of OA and the different attributes of isolated cells and tissues used mean that similar models may produce differing results and can differ from the naturally occurring disease. This review article assesses a selection of the in vitro models currently used in OA research, and considers the merits of each. Particular focus is placed on the more prevalent cytokine stimulation and load-based models. A brief review of the mechanism of these models is given, with their relevance to the naturally occurring disease. Most in vitro models have used supraphysiological loads or cytokine concentrations (compared with the natural disease) in order to impart a timely response from the cells or tissue assessed. Whilst models inducing OA-like pathology with a single stimulus can answer important biological questions about the behaviour of cells and tissues, the development of combinatorial models encompassing different physiological and molecular aspects of the disease should more accurately reflect the pathogenesis of the naturally occurring disease.

Cartilage and chondrocyte response to extreme muscular loading and impact loading: Can in vivo pre-load decrease impact-induced cell death?

BACKGROUND

Impact loading causes cartilage damage and cell death. Pre-loading prior to impact loading may protect cartilage and chondrocytes. However, there is no systematic evidence and understanding of the effects of pre-load strategies on cartilage damage and chondrocyte death. This study aimed at determining the effects of the pre-load history on impact-induced chondrocyte death in an intact joint.

METHODS

Patellofemoral joints from 42 rabbits were loaded by controlled quadriceps muscle contractions and an external impacter. Two extreme muscular loading conditions were used: (i) a short-duration, high intensity, static muscle contraction, and (ii) a long-duration, low-intensity, cyclic muscle loading protocol. A 5-Joule centrally-oriented, gravity-accelerated impact load was applied to the joints. Chondrocyte viability was quantified following the muscular loading protocols, following application of the isolated impact loads, and following application of the impact loads that were preceded by the muscular pre-loads. Joint contact pressures were measured for all loading conditions by a pressure-sensitive film.

FINDINGS

Comparing to cartilage injured by impact loading alone, cartilage pre-loaded by static, maximal intensity, short-term muscle loads had lower cell death, while cartilage pre-loaded by repetitive, low-intensity, long-term muscular loads has higher cell death. The locations of peak joint contact pressures were not strongly correlated with the locations of greatest cell death occurrence.

INTERPRETATION

Static, high intensity, short muscular pre-load protected cells from impact injury, whereas repetitive, low intensity, prolonged muscular pre-loading to the point of muscular fatigue left the chondrocytes vulnerable to injury. However, cell death seems to be unrelated to the peak joint pressures.

Inflammatory Pathways in Knee Osteoarthritis: Potential Targets for Treatment

Osteoarthritis (OA) of the knee is a wide-spread, debilitating disease that is prominent in Western countries. It is associated with old age, obesity, and mechanical stress on the knee joint. By examining the recent literature on the effect of the anti-inflammatory prostaglandins 15d-PGJ2 and Δ12-PGJ2, we propose that new therapeutic agents for this disease could facilitate the transition from the COX-2-dependent pro-inflammatory synthesis of the prostaglandin PGE2 (catalyzed by mPGES-1), to the equally COX-2-dependent synthesis of the aforementioned anti-inflammatory prostaglandins. This transition could be instrumental in halting the breakdown of cartilage via matrix metalloproteinases (MMPs) and aggrecanases, as well as promoting the matrix regeneration and synthesis of cartilage by chondrocytes. Another desirable property of new OA therapeutics could involve the recruitment of mesenchymal stem cells to the damaged cartilage and bone, possibly resulting in the generation of chondrocytes, synoviocytes, and, in the case of bone, osteoblasts. Moreover, we propose that research promoting this transition from pro-inflammatory to anti-inflammatory prostaglandins could aid in the identification of new OA therapeutics.

The use of hyperosmotic saline for chondroprotection: implications for orthopaedic surgery and cartilage repair

OBJECTIVE

Articular cartilage may experience iatrogenic injury during routine orthopaedic/arthroscopic procedures. This could cause chondrocyte death, leading to cartilage degeneration and posttraumatic osteoarthritis. In an in vitro cartilage injury model, chondrocyte death was reduced by increasing the osmolarity of normal saline (NS), the most commonly-used irrigation solution. Here, we studied the effect of hyperosmolar saline (HS) on chondrocyte viability and cartilage repair in an in vivo injury model.

DESIGN

Cartilage injury was induced by a single scalpel cut along the patellar groove of 8 week old rats in the absence of irrigation or with either NS (300 mOsm) or HS (600 mOsm). The percentage of cell death (PCD) within the injured area was assessed using confocal microscopy. Repair from injury was evaluated by histology/immunostaining, and inflammatory response by histology, cytokine array analysis and ELISA (enzyme-linked immunosorbent assay).

RESULTS

The PCD in saline-irrigated joints was increased compared to non-irrigated (NI) joints [PCD = 20.8% (95%CI; 14.5, 27.1); PCD = 9.14% (95%CI; 6.3, 11.9); P = 0.0017]. However, hyperosmotic saline reduced chondrocyte death compared to NS (PCD = 10.4% (95%CI; 8.5, 12.3) P = 0.0024). Repair score, type II collagen and aggrecan levels, and injury width, were significantly improved with hyperosmotic compared to NS. Mild synovitis and similar changes in serum cytokine profile occurred in all operated joints irrespective of experimental group.

CONCLUSIONS

Hyperosmotic saline significantly reduced the chondrocyte death associated with scalpel-induced injury and enhanced cartilage repair. This irrigation solution might be useful as a simple chondroprotective strategy and may also reduce unintentional cartilage injury during articular reconstructive surgery and promote integrative cartilage repair, thereby reducing the risk of posttraumatic osteoarthritis.

Airflow accelerates bovine and human articular cartilage drying and chondrocyte death

OBJECTIVE

Exposure of articular cartilage to static air results in changes to the extracellular matrix (ECM) and stimulates chondrocyte death, which may cause joint degeneration. However during open orthopaedic surgery, cartilage is often exposed to laminar airflow, which may exacerbate these damaging effects. We compared drying in static and moving air in terms of cartilage appearance, hydration and chondrocyte viability, and tested the ability of saline-saturated gauze to limit the detrimental effects of air exposure.

DESIGN

Articular cartilage from bovine metatarsophalangeal joints (N = 50) and human femoral heads (N = 6) was exposed for 90 min to (1) static air (2) airflow (up to 0.34 m/s), or (3) airflow (0.18 m/s), covered with gauze. Following air exposure, cartilage was also rehydrated (0.9% saline; 120 min) to determine the reversibility of drying effects. The influence of airflow was assessed by studying macroscopic appearance, and quantifying superficial zone (SZ) chondrocyte viability and cartilage hydration.

RESULTS

Airflow caused advanced changes to cartilage appearance, accelerated chondrocyte death, and increased dehydration compared to static air. These effects were prevented if cartilage was covered by saline-saturated gauze. Cartilage rehydration reversed macroscopic changes associated with drying but the chondrocyte death was not altered. Chondrocytes at the cut edge of cartilage were more sensitive to drying compared to cells distant from the edge.

CONCLUSIONS

Airflow significantly increased articular cartilage dehydration and chondrocyte death compared to static air. As laminar airflow is routinely utilised in operating theatres, it is essential that articular cartilage is kept wet via irrigation or by covering with saline-saturated gauze to prevent chondrocyte death.

The rate of hypo-osmotic challenge influences regulatory volume decrease (RVD) and mechanical properties of articular chondrocytes

OBJECTIVES

Osteoarthritis (OA) is associated with a gradual reduction in the interstitial osmotic pressure within articular cartilage. The aim of this study was to compare the effects of sudden and gradual hypo-osmotic challenge on chondrocyte morphology and biomechanics.

METHODS

Bovine articular chondrocytes were exposed to a reduction in extracellular osmolality from 327 to 153 mOsmol/kg applied either suddenly (<5 s) or gradually (over 180 min). Temporal changes in cell diameter and the existence of regulatory volume decrease (RVD) were quantified along with changes in cortical actin and chromatin condensation. The cellular viscoelastic mechanical properties were determined by micropipette aspiration.

RESULTS

In response to a sudden hypo-osmotic stress, 66% of chondrocytes exhibited an increase in diameter followed by RVD, whilst 25% showed no RVD. By contrast, cells exposed to gradual hypo-osmotic stress exhibited reduced cell swelling without subsequent RVD. There was an increase in the equilibrium modulus for cells exposed to sudden hypo-osmotic stress. However, gradual hypo-osmotic challenge had no effect on cell mechanical properties. This cell stiffening response to sudden hypo-osmotic challenge was abolished when actin organization was disrupted with cytochalasin D or RVD inhibited with REV5901. Both sudden and gradual hypo-osmotic challenge reduced cortical F-actin distribution and caused chromatin decondensation.

CONCLUSIONS

Sudden hypo-osmotic challenge increases chondrocyte mechanics by activation of RVD and interaction with the actin cytoskeleton. Moreover, the rate of hypo-osmotic challenge is shown to have a profound effect on chondrocyte morphology and biomechanics. This important phenomenon needs to be considered when studying the response of chondrocytes to pathological hypo-osmotic stress.

Osmolarity influences chondrocyte repair after injury in human articular cartilage

Background

The purpose was to determine the influence of irrigation solution osmolarity on articular chondrocytes survival and metabolic state following mechanical injury.

Methods

Osteochondral explants were harvested from patients undergoing total knee arthroplasty for osteoarthritis and then cut through their full thickness to establish mechanical injury models. Cartilage explants were incubated in irrigation solutions (saline and balanced salt) with different osmolarities (180, 280, 380, 580 mOsm/L) for 2 h. The percentage of cell death (100 × number of dead cells/number of dead and live cells) was quantified with the laser confocal microscopy. The terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay was performed to detect apoptosis index of injured cartilage. The contents of proteoglycan elution were determined by spectrophotometer at 530 nm, and HIF-1α and type II collagen mRNA yields were quantified with real-time PCR.

Results

In situ dead chondrocytes were mainly localized to the superficial tangential region of injured cartilage edge after mechanical injury. The percentage of cell death was decreased, and proteoglycan elution was gradually reduced with the increasing of osmolarity. The apoptosis indices of TUNEL assay in different osmolarities had no significant difference (P = 0.158). HIF-1α and type II collagen mRNA yields were the least for chondrocytes exposed to 180 mOsm/L medium and were the greatest for chondrocytes exposed to 380 mOsm/L medium. Compared with the saline group, the cell death of superficial zone was significantly decreased (P = 0.001) and contents of proteoglycan elution were also significantly decreased (P = 0.045) in the balanced salt. HIF-1α (P = 0.017) and type II collagen (P = 0.034) mRNA yields in the chondrocytes exposed to the balanced salt were significantly more than the saline group.

Conclusion

The osmolarity of irrigation solutions plays an important role in the survival and metabolic state of chondrocytes following mechanical injury, and the chondrocyte death is not caused by apoptosis. Increasing osmolarity of irrigation solutions may be chondroprotective with decreasing the chondrocyte death, reducing inhibition of metabolism and proteoglycan elution, ultimately preventing cartilage degeneration and promoting integrative repair.