Aims. Osteoarthritis (OA) is a common degenerative joint disease worldwide, which is characterized by articular cartilage lesions. With more understanding of the disease, OA is considered to be a disorder of the whole joint. However, molecular communication within and between tissues during the disease process is still unclear. In this study, we used transcriptome data to reveal crosstalk between different tissues in OA. Methods. We used four groups of transcription profiles acquired from the Gene Expression Omnibus database, including articular cartilage, meniscus, synovium, and subchondral bone, to screen differentially expressed genes during OA. Potential crosstalk between tissues was depicted by ligand-receptor pairs. Results. During OA, there were 626, 97, 1,060, and 2,330 differentially expressed genes in articular cartilage, meniscus, synovium, and subchondral bone, respectively. Gene Ontology enrichment revealed that these genes were enriched in extracellular matrix and structure organization, ossification, neutrophil degranulation, and activation at different degrees. Through ligand-receptor pairing and proteome of OA synovial fluid, we predicted ligand-receptor interactions and constructed a crosstalk atlas of the whole joint. Several interactions were reproduced by transwell experiment in chondrocytes and synovial cells, including TNC-NT5E, TNC-SDC4, FN1-ITGA5, and FN1-NT5E. After lipopolysaccharide (LPS) or interleukin (IL)-1β stimulation, the ligand expression of chondrocytes and synovial cells was upregulated, and corresponding receptors of co-culture cells were also upregulated. Conclusion. Each tissue displayed a different expression pattern in transcriptome, demonstrating their specific roles in OA. We highlighted tissue molecular crosstalk through ligand-receptor pairs in OA pathophysiology, and generated a crosstalk atlas. Strategies to interfere with these candidate ligands and receptors may help to discover molecular targets for future OA therapy. Cite this article: Bone Joint Res 2022;11(12):862–872

Aims. Cartilage injuries rarely heal spontaneously and often require surgical intervention, leading to the formation of biomechanically inferior fibrous tissue. This study aimed to evaluate the possible effect of amelogenin on the healing process of a large osteochondral injury (OCI) in a rat model. Methods. A reproducible large OCI was created in the right leg femoral trochlea of 93 rats. The OCIs were treated with 0.1, 0.5, 1.0, 2.5, or 5.0 μg/μl recombinant human amelogenin protein (rHAM. +. ) dissolved in propylene glycol alginate (PGA) carrier, or with PGA carrier alone. The degree of healing was evaluated 12 weeks after treatment by morphometric analysis and histological evaluation. Cell recruitment to the site of injury as well as the origin of the migrating cells were assessed four days after treatment with 0.5 μg/μl rHAM. +. using immunohistochemistry and immunofluorescence. Results. A total of 12 weeks after treatment, 0.5 μg/μl rHAM. +. brought about significant repair of the subchondral bone and cartilage. Increased expression of proteoglycan and type II collagen and decreased expression of type I collagen were revealed at the surface of the defect, and an elevated level of type X collagen at the newly developed tide mark region. Conversely, the control group showed osteoarthritic alterations. Recruitment of cells expressing the mesenchymal stem cell (MSC) markers CD105 and STRO-1, from adjacent bone marrow toward the OCI, was noted four days after treatment. Conclusion. We found that 0.5 μg/μl rHAM. +. induced in vivo healing of injured articular cartilage and subchondral bone in a rat model, preventing the destructive post-traumatic osteoarthritic changes seen in control OCIs, through paracrine recruitment of cells a few days after treatment. Cite this article: Bone Joint Res 2023;12(10):615–623

Aims. Rotational acetabular osteotomy (RAO) has been reported to be effective in improving symptoms and preventing osteoarthritis (OA) progression in patients with mild to severe develomental dysplasia of the hip (DDH). However, some patients develop secondary OA even when the preoperative joint space is normal; determining who will progress to OA is difficult. We evaluated whether the preoperative cartilage condition may predict OA progression following surgery using T2 mapping MRI. Methods. We reviewed 61 hips with early-stage OA in 61 patients who underwent RAO for DDH. They underwent preoperative and five-year postoperative radiological analysis of the hip. Those with a joint space narrowing of more than 1 mm were considered to have 'OA progression'. Preoperative assessment of articular cartilage was also performed using 3T MRI with the T2 mapping technique. The region of interest was defined as the weightbearing portion of the acetabulum and femoral head. Results. There were 16 patients with postoperative OA progression. The T2 values of the centre to the anterolateral region of the acetabulum and femoral head in the OA progression cases were significantly higher than those in patients without OA progression. The preoperative T2 values in those regions were positively correlated with the narrowed joint space width. The receiver operating characteristic analysis revealed that the T2 value of the central portion in the acetabulum provided excellent discrimination, with OA progression patients having an area under the curve of 0.858. Furthermore, logistic regression analysis showed T2 values of the centre to the acetabulum’s anterolateral portion as independent predictors of subsequent OA progression (p < 0.001). Conclusion. This was the first study to evaluate the relationship between intra-articular degeneration using T2 mapping MRI and postoperative OA progression. Our findings suggest that preoperative T2 values of the hip can be better prognostic factors for OA progression than radiological measures following RAO. Cite this article: Bone Joint J 2021;103-B(9):1472–1478

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by progressive cartilage degradation, synovial membrane inflammation, osteophyte formation, and subchondral bone sclerosis. Pathological changes in cartilage and subchondral bone are the main processes in OA. In recent decades, many studies have demonstrated that activin-like kinase 3 (ALK3), a bone morphogenetic protein receptor, is essential for cartilage formation, osteogenesis, and postnatal skeletal development. Although the role of bone morphogenetic protein (BMP) signalling in articular cartilage and bone has been extensively studied, many new discoveries have been made in recent years around ALK3 targets in articular cartilage, subchondral bone, and the interaction between the two, broadening the original knowledge of the relationship between ALK3 and OA. In this review, we focus on the roles of ALK3 in OA, including cartilage and subchondral bone and related cells. It may be helpful to seek more efficient drugs or treatments for OA based on ALK3 signalling in future

Aims. Osteoarthritis (OA) is a prevalent joint disorder with inflammatory response and cartilage deterioration as its main features. Dihydrocaffeic acid (DHCA), a bioactive component extracted from natural plant (gynura bicolor), has demonstrated anti-inflammatory properties in various diseases. We aimed to explore the chondroprotective effect of DHCA on OA and its potential mechanism. Methods. In vitro, interleukin-1 beta (IL-1β) was used to establish the mice OA chondrocytes. Cell counting kit-8 evaluated chondrocyte viability. Western blotting analyzed the expression levels of collagen II, aggrecan, SOX9, inducible nitric oxide synthase (iNOS), IL-6, matrix metalloproteinases (MMPs: MMP1, MMP3, and MMP13), and signalling molecules associated with nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways. Immunofluorescence analysis assessed the expression of aggrecan, collagen II, MMP13, and p-P65. In vivo, a destabilized medial meniscus (DMM) surgery was used to induce mice OA knee joints. After injection of DHCA or a vehicle into the injured joints, histological staining gauged the severity of cartilage damage. Results. DHCA prevented iNOS and IL-6 from being upregulated by IL-1β. Moreover, the IL-1β-induced upregulation of MMPs could be inhibited by DHCA. Additionally, the administration of DHCA counteracted IL-1β-induced downregulation of aggrecan, collagen II, and SOX9. DHCA protected articular cartilage by blocking the NF-κB and MAPK pathways. Furthermore, DHCA mitigated the destruction of articular cartilage in vivo. Conclusion. We present evidence that DHCA alleviates inflammation and cartilage degradation in OA chondrocytes via suppressing the NF-κB and MAPK pathways, indicating that DHCA may be a potential agent for OA treatment. Cite this article: Bone Joint Res 2023;12(4):259–273

3D printing and Bioprinting technologies are becoming increasingly popular in surgery to provide a solution for the regeneration of healthy tissues. The aim of our project is the regeneration of articular cartilage via bioprinting means, to manage isolated chondral defects. Chrondrogenic hydrogel (chondrogel: GelMa + TGF-b3 and BMP6) was prepared and sterilised in our lab following our standard protocols. Human adipose-derived mesenchymal stem cells were harvested from the infrapatellar fat pad of patients undergoing total knee joint replacements and incorporated in the hydrogel according to our published protocols. The chondrogenic properties of the chondrogel have been tested (histology, immunohistochemistry, PCR, immunofluorescence, gene analysis and 2. nd. harmonic generation microscopy) in vitro and in an ex-vivo model of human articular defect and compared with standard culture systems where the growth factors are added to the media at repeated intervals. The in-vitro analysis showed that the formation of hyaline cartilage pellet was comparable between the two strategies, with a similar metabolic activity of the cells. These results have been confirmed in the ex-vivo model: hyaline-like cartilage was observed within the chondral defect in both the chondrogel group and the control group after 28 days in culture. The use of bioprinting techniques in vivo requires the ability of stem cells to access growth factors directly in the environment they are in, as opposed to in vitro techniques where these factors are provided externally at recurrent intervals. This study showed the successful strategy of incorporating chondrogenic growth factors for the formation of hyaline-like cartilage in vitro and in an ex-vivo model of chondral loss. The incorporation of chondrogenic growth factors in a hydrogel is a possible strategy for articular cartilage regeneration

This study aims to assess the changes in mechanical behaviour over time in ‘haemarthritic’ articular cartilage compared to ‘healthy’ articular cartilage. Pin-on-plate and indentation tests were used to determine the coefficient of friction (COF) and deformation of ‘healthy’ and ‘haemarthritic articular cartilage. Osteochondral pins (8 mm) were extracted from porcine tali and immersed in exposure fluid for two hours prior to test. Pins were articulated against a larger bovine femoral plate for 3600 seconds under a load of 50 N. Osteochondral pins (8 mm) were loaded during indentation testing for 3600 seconds under a load of 0.25 N. To mimic the effect of a joint bleed in vitro; serum, whole blood and 50% v/v were used as exposure and lubricant fluids. COF and deformation were expressed as mean (n=3) and statistically analysed using a one-way ANOVA and post-hoc Tukey test (p>0.05). The serum condition yielded a COF of 0.0428 ± 0.02 with 0.08mm ± 0.04 deformation. The 50% v/v condition produced a higher COF of 0.0485 ± 0.02 and 0.21mm ± 0.04 deformation. The lowest COF and deformation were produced by the whole blood condition (0.0292 ± 0.02 and 0.06mm ± 0.006 respectively). Statistical analysis indicated no significant difference across the friction test conditions but a significant difference across all indentation test conditions (ANOVA, p>0.05). Combination of creep deformation and wear was observed on the articular surface up to 24 hours post-test in 50% v/v and whole blood conditions. The average haemophilia patient can experience multiple joint bleeds per year of which this study demonstrates the effect of just one joint bleed. This study has provided evidence of potential reversible and irreversible mechanical changes to articular cartilage surface during a joint bleed

Osteoarthritis (OA) is mainly caused by ageing, strain, trauma, and congenital joint abnormalities, resulting in articular cartilage degeneration. During the pathogenesis of OA, the changes in subchondral bone (SB) are not only secondary manifestations of OA, but also an active part of the disease, and are closely associated with the severity of OA. In different stages of OA, there were microstructural changes in SB. Osteocytes, osteoblasts, and osteoclasts in SB are important in the pathogenesis of OA. The signal transduction mechanism in SB is necessary to maintain the balance of a stable phenotype, extracellular matrix (ECM) synthesis, and bone remodelling between articular cartilage and SB. An imbalance in signal transduction can lead to reduced cartilage quality and SB thickening, which leads to the progression of OA. By understanding changes in SB in OA, researchers are exploring drugs that can regulate these changes, which will help to provide new ideas for the treatment of OA. Cite this article: Bone Joint Res 2023;12(9):536–545

Aims. After a few passages of in vitro culture, primary human articular chondrocytes undergo senescence and loss of their phenotype. Most of the available chondrocyte cell lines have been obtained from cartilage tissues different from diarthrodial joints, and their utility for osteoarthritis (OA) research is reduced. Thus, the goal of this research was the development of immortalized chondrocyte cell lines proceeded from the articular cartilage of patients with and without OA. Methods. Using telomerase reverse transcriptase (hTERT) and SV40 large T antigen (SV40LT), we transduced primary OA articular chondrocytes. Proliferative capacity, degree of senescence, and chondrocyte surface antigen expression in transduced chondrocytes were evaluated. In addition, the capacity of transduced chondrocytes to synthesize a tissue similar to cartilage and to respond to interleukin (IL)-1β was assessed. Results. Coexpression of both transgenes (SV40 and hTERT) were observed in the nuclei of transduced chondrocytes. Generated chondrocyte cell lines showed a high proliferation capacity and less than 2% of senescent cells. These cell lines were able to form 3D aggregates analogous to those generated by primary articular chondrocytes, but were unsuccessful in synthesizing cartilage-like tissue when seeded on type I collagen sponges. However, generated chondrocyte cell lines maintained the potential to respond to IL-1β stimulation. Conclusion. Through SV40LT and hTERT transduction, we successfully immortalized chondrocytes. These immortalized chondrocytes were able to overcome senescence in vitro, but were incapable of synthesizing cartilage-like tissue under the experimental conditions. Nonetheless, these chondrocyte cell lines could be advantageous for OA investigation since, similarly to primary articular chondrocytes, they showed capacity to upregulate inflammatory mediators in response to the IL-1β cytokine. Cite this article: Bone Joint Res 2023;12(1):46–57

Abstract. OBJECTIVES. An unresolved challenge in osteoarthritis research is characterising the localised intra-tissue mechanical response of articular cartilage. The aim of this study was to explore whether laboratory micro-computed tomography (micro-CT) and digital volume correlation (DVC) permit non-destructive visualisation of three-dimensional (3D) strain fields in human articular cartilage. METHODS. Human articular cartilage specimens were harvested from the knee (n=4 specimens from 2 doners), mounted into a loading device and imaged in the loaded and unloaded state using a micro-CT scanner. Strain was calculated throughout the volume of the cartilage using the CT image data. RESULTS. Strain was calculated in the 3D volume with a spatial resolution of 75 µm, and the volumetric DVC calculated strain was within 5% of the known applied stain. Variation in strain distribution between the superficial, middle and deep zones was observed, consistent with the different architecture of the material in these locations. CONCLUSIONS. The DVC method is suitable for calculating strain in human articular cartilage. This method will be useful to generate chondral repair scaffolds that that seek to replicate the strain gradient in cartilage. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Electrospinning is an advantageous technique for cartilage tissue engineering (CTE) applications due to its ability to produce nanofibers recapitulating the size and alignment of the collagen fibers present within the articular cartilage superficial zone. Moreover, coaxial electrospinning allows the fabrication of core-shell fibers able to encapsulate and release bioactive molecules in a sustained manner. Kartogenin (KTG) is a small heterocyclic molecule, which was demonstrated to promote the chondrogenic differentiation of human bone marrow-derived mesenchymal stem/stromal cells(hBMSCs)[1]. In this work, we developed and evaluated the biological performance of core-shell poly(glycerol sebacate)(PGS)/poly(caprolactone)(PCL) aligned nanofibers (core:PGS/shell:PCL) mimicking the native articular cartilage extracellular matrix(ECM) and able to promote the sustained release of the chondroinductive drug KTG[2]. The produced coaxial aligned PGS/PCL scaffolds were characterized in terms of their structure and fiber diameter, chemical composition, thermal properties, mechanical performance under tensile testing and in vitro degradation kinetics, in comparison to monoaxial PCL aligned fibers and respective non-aligned controls. KTG was incorporated into the core PGS solution to generate core-shell PGS-KTG/PCL nanofibers and its release kinetics was studied by HPLC analysis. KTG-loaded electrospun aligned scaffolds capacity to promote hBMSCs chondrogenic differentiation was evaluated by assessing cell proliferation, typical cartilage-ECM production (sulfated glycosaminiglycans(sGAG)) and chondrogenic marker genes expression in comparison to non-loaded controls. All the scaffolds fabricated showed average fiber diameters within the nanometer-scale and the core-shell structure of the fibers was clearly confirmed by TEM. The coaxial PGS-KTG/PCL nanofibers evidenced a more sustained drug release over 21 days. Remarkably, in the absence of the chondrogenic cytokine TGF-β3, KTG-loaded nanofibers promoted significantly the proliferation and chondrogenic differentiation of hBMSCs, as suggested by the increased cell numbers, higher sGAG amounts and up-regulation of the chondrogenic genes COL2A1, Sox9, ACAN and PRG4 expression. Overall, our results highlight the potential of core-shell PGS-KTG/PCL aligned nanofibers for the development of novel MSC-based CTE strategies. Acknowledgements: The authors thank FCT for funding through the project InSilico4OCReg (PTDC/EME-SIS/0838/2021) and to institutions iBB (UID/BIO/04565/2020) and Associate Laboratory I4HB (LA/P/0140/2020)

The superficial zone (SFZ) of articular cartilage has unique structural and biomechanical features, and is important for joint long-term function. Previous studies have shown that TGF-β/Alk5 signaling upregulating PRG4 expression maintains articular cartilage homeostasis. However, the exact role and molecular mechanism of TGF-β signaling in SFZ of articular cartilage homeostasis are still lacking. In this study, a combination of in vitro and in vivo approaches were used to elucidate the role of Alk5 signaling in maintaining the SFZ of articular cartilage and preventing osteoarthritis initiation. Mice with inducible cartilage SFZ-specific deletion of Alk5 were generated to assess the role of Alk5 in OA development. Alterations in cartilage structure were evaluated histologically. The chondrocyte apoptosis and cell cycle were detected by TUNEL and Edu staining, respectively. Isolation, culture and treatment of SFZ cells, the expressions of genes associated with articular cartilage homeostasis and TGF-β signaling were analyzed by qRT-PCR. The effects of TGF-β/Alk5 signaling on proliferation and differentiation of SFZ cells were explored by cells count and alcian blue staining. In addition, SFZ cells isolated from C57 mice were cultured in presence of TGF-β1 or SB505124 for 7 days and transplanted subcutaneously in athymic mice. Postnatal cartilage SFZ-specific deletion of Alk5 induced an OA-like phenotype with degradation of articular cartilage, synovial hyperplasia as well as enhanced chondrocyte apoptosis, overproduction of catabolic factors, and decreased expressions of anabolic factors in chondrocytes. qRT-PCR and IHC results confirmed that Alk5 gene was effectively deleted in articular cartilage SFZ cells. Next, the PRG4-positive cells in articular cartilage SFZ were significantly decreased in Alk5 cKO mice compared with those in Cre-negative control mice. The mRNA expression of Aggrecan and Col2 were decreased, meanwhile, expression of Mmp13 and Adamts5 were significantly increased in articular cartilage SFZ cells of Alk5 cKO mice. In addition, Edu and TUNEL staining results revealed that slow-cell cycle cell number and increase the apoptosis positive cell in articular cartilage SFZ of Alk5 cKO mice compared with Cre-negative mice, respectively. Furthermore, all groups of SFZ cells formed ectopic solid tissue masses 1 week after transplantation. Histological examination revealed that the TGF-β1-pretreated tissues was composed of small and round cells and was positive for alcian blue staining, while the SB505124-pretreated tissue contained more hypertrophic cells though it did stain with alcian blue. TGF-β/alk5 signaling is an essential regulator of the superficial layer of articular cartilage by maintaining chondrocyte number, its differentiation properties, and lubrication function. Furthermore, it plays a critical role in protecting cartilage from OA initiation

Lesions in the joint surface are commonly treated with osteoarticular autograft transfer system (OATS), autologous cell implantation (ACI/MACI), or microfracture. Tissue formed buy the latter commonly results in mechanically inferior fibrocartilage that fails to integrate with the surrounding native cartilage, rather than durable hyaline cartilage. Fractional laser treatment to make sub-millimeter (<500 µm) channels has been employed for tissue regeneration in the skin to facilitate rejuvenation without typical scarring. Additionally, we have pioneered a means to generate articular cartilage matrix from chondrocytes—dynamic Self-Regenerating Cartilage (dSRC). Combining these two approaches by performing fractional laser treatment of the joint cartilage and treating with dSRC is a new paradigm for joint surface restoration. This approach was refined in a series of in vitro experiments and tested in swine knee defects during a 6-month study in 12 swine. dSRC are generated by placing 10. 7. swine knee chondrocytes into sealed 15-mL polypropylene tubes and cultured on a rocker at 40 cycles per minute for 14 days at 37°C. The chondrocytes aggregate and generate new extracellular matrix to form a pellet of dSRC. Channels of approximately 300-500 µm diameter were created by infrared laser ablation in swine cartilage (in vitro) and swine knees (in vivo). The diameter and depth of the ablated channel in the cartilage was controlled by the light delivery parameters (power, spot size, pulse duration) from a fractional 2.94 µm Erbium laser. The specimens were evaluated with histology (H&E, safranin O, toluidine blue) and polarized-sensitive optical coherence tomography for collagen orientation. We can consistently create laser-ablated channels in the swine knee and successfully implant new cartilage from dSRC to generate typical hyaline cartilage in terms of morphology and biochemical properties. The neocartilage integrates with host cartilage in vivo. These findings demonstrate our novel combinatorial approach for articular cartilage rejuvenation

The avascular nature of articular cartilage relies on diffusion pathways to obtain essential nutrients and molecules for cellular activity. Understanding these transport pathways is essential to maintaining and improving the health of articular cartilage and ultimately synovial joints. Several studies have shown that joint articulation is associated with fluid and solute uptake although it remains unclear what role sliding motion independently plays. This study investigates the role of sliding with a non-stationary contact area on the uptake of small molecular weight tracers into articular cartilage. Ten-millimeter diameter cartilage-bone plugs were obtained from porcine knee joints and sealed into purpose made diffusion chambers. The chambers were designed to eliminate diffusion from the radial edge and only allow diffusion through the articular surface. The bone side of the chamber was filled with PBS to maintain tissue hydration while the cartilage side was filled with 0.01mg/ml fluorescein sodium salt (FNa) prepared using PBS. Sliding loads with a non-stationary contact area were applied across the articular surface by a custom apparatus using a 4.5 mm diameter spherical indenter. A moving contact area was chosen to represent physiological joint motions. Reciprocal sliding was maintained at a rate of 5 mm/s for 2 and 4 hours. Control samples were subject to passive diffusion for 0, 4, and 88 hours. After diffusion tests, samples were snap frozen and 20 µm cross-sectional cuts were taken perpendicular to the sliding direction. Samples were imaged using a Zeiss AxioImager M2 epifluorescent microscope under 5× magnification with a filter for FNa. Intensity profiles were mapped from the articular surface to the subchondral bone. Unloaded control samples demonstrated minimal solute uptake at 4 hours penetrating less than 5% of the total cartilage depth. By 88 hours solute penetration had reached the subchondral bone although there was minimal accumulation within the cartilage matrix indicated by the relatively low intensity profile values. Samples that had been subjected to reciprocal sliding demonstrated accelerated penetration and solute accumulation compared to unloaded samples. After 1 hour of reciprocal sliding, the solute had reached 40% of the cartilage depth, this increased to approximately 80% at 4 hours, with much higher intensities compared to unloaded controls. Sliding motion plays an important role in the uptake of solutes into the cartilage matrix. Maintaining joint motion both post injury and in the arthritic process is a critical component of cartilage nutrition. Samples that had been subject to reciprocal sliding demonstrated accelerated solute penetration and accumulation in the cartilage matrix, exceeding steady state concentrations achieved by passive diffusion

Mincing cartilage with commercially available shavers is increasingly used for treating focal cartilage defects. This study aimed to compare the impact of mincing bovine articular cartilage using different shaver blades on chondrocyte viability. Bovine articular cartilage was harvested using a scalpel or three different shaver blades (2.5 mm, 3.5 mm, or 4.2 mm) from a commercially available shaver. The cartilage obtained with a scalpel was minced into fragments smaller than 1 mm. 3. All four conditions were cultivated in a culture medium for seven days. After Day 1 and Day 7, metabolic activity, RNA isolation, and gene expression of anabolic (COL2A1, ACAN) and catabolic genes (MMP1, MMP13), Live/Dead staining and visualization using confocal microscopy, and flow cytometric characterization of minced cartilage chondrocytes were measured. The study found that mincing cartilage with shavers significantly reduced metabolic activity after one and seven days compared to scalpel mincing (p<0.001). Gene expression of anabolic genes was reduced, while catabolic genes were increased after day 7 in all shaver conditions. The MMP13/COL2A1 ratio was also increased in all shaver conditions. Confocal microscopy revealed a thin line of dead cells at the lesion site with viable cells below for the scalpel mincing and a higher number of dead cells diffusely distributed in the shaver conditions. After seven days, there was a significant decrease in viable cells in the shaver conditions compared to scalpel mincing (p<0.05). Flow cytometric characterization revealed fewer intact cells and proportionally more dead cells in all shaver conditions compared to the scalpel mincing. Mincing bovine articular cartilage with commercially available shavers reduces the viability of chondrocytes compared to scalpel mincing. This indicates that mincing cartilage with a shaver should be considered a matrix rather than a cell therapy. Further experimental and clinical studies are required to standardize the mincing process with a shaver. Acknowledgements: This study received unrestricted funding from KARL STORZ SE & Co. KG

Aims. To determine the relationship between articular cartilage status and clinical outcomes after medial opening-wedge high tibial osteotomy (MOHTO) for medial compartmental knee osteoarthritis at intermediate follow-up. Methods. We reviewed 155 patients (155 knees) who underwent MOHTO from January 2008 to December 2016 followed by second-look arthroscopy with a mean 5.3-year follow-up (2.0 to 11.7). Arthroscopic findings were assessed according to the International Cartilage Repair Society (ICRS) Cartilage Repair Assessment (CRA) grading system. Patients were divided into two groups based on the presence of normal or nearly normal quality cartilage in the medial femoral condyle: good (second-look arthroscopic) status (ICRS grade I or II; n = 70), and poor (second-look arthroscopic) status (ICRS grade III or IV; n = 85) groups at the time of second-look arthroscopy. Clinical outcomes were assessed using the International Knee Documentation Committee (IKDC) score, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and 36-Item Short Form survey. Results. Significant improvements in all clinical outcome categories were found between the preoperative and second-look arthroscopic assessments in both groups (p < 0.001). At the latest follow-up, the mean IKDC and WOMAC scores in the good status group further improved compared with those at the time of second-look arthroscopic surgery (p < 0.001), which was not shown in the poor status group. The mean IKDC (good status, 72.8 (SD 12.5); poor status, 64.7 (SD 12.1); p = 0.002) and mean WOMAC scores (good status, 15.7 (SD 10.8); poor status, 21.8 (SD 13.6); p = 0.004) significantly differed between both groups at the latest follow-up. Moreover, significant correlations were observed between ICRS CRA grades and IKDC scores (negative correlation; p < 0.001) and WOMAC scores (positive correlation; p < 0.001) at the latest follow-up. Good cartilage status was found more frequently in knees with the desired range of 2° to 6° valgus correction than in those with corrections outside this range (p = 0.019). Conclusion. Second-look arthroscopic cartilage status correlated with clinical outcomes after MOHTO at intermediate-term follow-up, despite the relatively small clinical differences between groups. Cite this article: Bone Joint J 2021;103-B(11):1686–1694

Articular cartilage has poor repair potential and the tissue formed is mechanically incompetent. Mesenchymal stromal cells (MSCs) show chondrogenic properties and the ability to re-grow cartilage, however a viable human model for testing cartilage regeneration and repair is lacking. Here, we describe an ex vivo pre-clinical femoral head model for studying human cartilage repair using MSCs. Human femoral heads (FHs) were obtained following femoral neck fracture with ethical permission/patient consent and full-depth cartilage wells made using a 3mm biopsy punch. Pancreas-derived mesenchymal stromal cells (P-MSC) were prepared in culture media at ~5000 cells/20µl and added to each well and leakage prevented with fibrin sealant. After 24hrs, the sealant was removed and medium replaced with StemPro. TM. chondrogenesis differentiation medium. The FHs were incubated (37. o. C;5% CO. 2. ) for 3wks, followed by a further 3wks in standard medium with 10% human serum with regular medium changes throughout. Compared to wells with medium only, A-MSCs produced a thin film across the wells which was excised en-block, fixed with 4% paraformaldehyde and frozen for cryo-sectioning. The cell/tissue films varied in thickness ranging over 20-440µm (82±21µm; mean±SEM; N=3 FHs). The thickness of MSC films abutting the cartilage wells was variable but generally greater (15-1880µm) than across the wells, suggesting an attachment to native articular cartilage. Staining of the films using safranin O (for glycosaminoglycans; quantified using ImageJ) was variable (3±8%; mean±SEM; N=3) but in one experiment reached 20% of the adjacent cartilage. A preliminary assessment of the repair tissue gave an O'Driscoll score of 10/24 (24 is best). These preliminary results suggest the ex vivo femoral head model has promise for studying the capacity of MSCs to repair cartilage directly in human tissue, although optimising MSCs to produce hyaline-like tissue is essential. Supported by the CSO (TCS/17/32)

Even minor lesions in articular cartilage (AC) can cause underlying bone damage creating an osteochondral (OC) defect. OC defects can cause pain, impaired mobility and can develop to osteoarthritis (OA). OA is a disease that affects nearly 10% of the population worldwide. [1]. , and represents a significant economic burden to patients and society. [2]. While significant progress has been made in this field, realising an efficacious therapeutic option for unresolved OA remains elusive and is considered one of the greatest challenges in the field of orthopaedic regenerative medicine. [3]. Therefore, there is a societal need to develop new strategies for AC regeneration. In recent years there has been increased interest in the use of tissue-specific aligned porous freeze-dried extracellular matrix (ECM) scaffolds as an off-the-shelf approach for AC repair, as they allow for cell infiltration, provide biological cues to direct target-tissue repair and permit aligned tissue deposition, desired in AC repair. [4]. However, most ECM-scaffolds lack the appropriate mechanical properties to withstand the loads passing through the joint. [5]. One solution to this problem is to reinforce the ECM with a stiffer framework made of synthetic materials, such as polylactic acid (PLA). [6]. Such framework can be 3D printed to produce anatomically accurate implants. [7]. , attractive in personalized medicine. However, typical 3D prints are static, their design is not optimized for soft-hard interfaces (OC interface), and they may not adapt to the cyclic loading passing through our joints, thus risking implant failure. To tackle this limitation, more compliant or dynamic designs can be printed, such as coil-shaped structures. [8]. Thus, in this study we use finite element modelling to create different designs that mimic the mechanical properties of AC and prototype them in PLA, using polyvinyl alcohol as support. The optimal design will be combined with an ECM scaffold containing a tailored microarchitecture mimicking aspects of native AC. Acknowledgments: This project has received funding from the European Union's Horizon Europe research and innovation MSCA PF programme under grant agreement No. 101110000

Aims. The intra-articular administration of tranexamic acid (TXA) has been shown to be effective in reducing blood loss in unicompartmental knee arthroplasty and anterior cruciate reconstruction. The effects on human articular cartilage, however, remains unknown. Our aim, in this study, was to investigate any detrimental effect of TXA on chondrocytes, and to establish if there was a safe dose for its use in clinical practice. The hypothesis was that TXA would cause a dose-dependent damage to human articular cartilage. . Materials and Methods. The cellular morphology, adhesion, metabolic activity, and viability of human chondrocytes when increasing the concentration (0 mg/ml to 40 mg/ml) and length of exposure to TXA (0 to 12 hours) were analyzed in a 2D model. This was then repeated, excluding cellular adhesion, in a 3D model and confirmed in viable samples of articular cartilage. Results. Increasing concentrations above 20 mg/ml resulted in atypical morphology, reduced cellular adhesion and metabolic activity associated with increased chondrocyte death. However, the cell matrix was not affected by the concentration of TXA or the length of exposure, and offered cellular protection for concentrations below 20 mg/ml. Conclusion. These results show that when in vitro chondrocytes are exposed to higher concentrations of TXA, such as that expected following recommended intra-articular administration, cytotoxicity is observed. This effect is dose-dependent, such that a tissue concentration of 10 mg/ml to 20 mg/ml could be expected to be safe. Cite this article: Bone Joint J 2018;100-B:404–12

Abstract. Introduction. This study aimed to assess the effect of PRP on knee articular cartilage content (thickness and/or volume) and establish if there is a correlation between changes in cartilage and clinical outcomes in patients with knee osteoarthritis. Methodology. A systematic review was performed following the Cochrane methodology. Studies were included if they reported on cartilage content with MRI or Ultrasound before and after the injection. A random-effects model meta-analysis was performed. Results. 11 studies (n=786) from 1,453 records met the inclusion criteria, with five (n=444) being RCTs. The PRP treatment protocol varied widely. Follow-up ranged from 6–12 months. Eight studies reported increase in cartilage content in the PRP group as compared to control (four showing significant difference). In meta-analysis: PRP treatment was not associated with a significant increase in cartilage thickness in medial and lateral femoral condyle, or in the overall cartilage content (4 studies, n=187, Hedges’ g: 0.079; 95%CI: 0.358-0.516; p=0.723). Meta-analysis of 3 RCTs (n=112) showed no significant difference in increasing cartilage content overall with PRP injections compared with no PRP (Hedges’ g: 0.217; 95%CI: -0.177 – 0.611; P=0.281). There was no correlation between changes in cartilage and clinical outcomes following PRP treatment. Conclusion. Treatment of knee osteoarthritis with PRP is not associated with a significant increase in articular cartilage content and any effect on cartilage is not associated with better clinical outcomes. A multi-centre, adequately powered RCT, with a standardized preparation / administration protocol assessing long-term effect of PRP in knee osteoarthritis is needed to guide clinical care

This systematic review examines the current literature regarding surgical techniques for restoring articular cartilage in the hip, from the older microfracture techniques involving perforation to the subchondral bone, to adaptations of this technique using nanofractures and scaffolds. This review discusses the autologous and allograft transfer systems and the autologous matrix-induced chondrogenesis (AMIC) technique, as well as a summary of the previously discussed techniques, which could become common practice for restoring articular cartilage, thus reducing the need for total hip arthroplasty. Using the British Medical Journal Grading of Recommendations, Assessment, Development and Evaluation (BMJ GRADE) system and Grade system. Comparison of the studies discussed shows that microfracture has the greatest quantity and quality of research, whereas the newer AMIC technique requires more research, but shows promise. Cite this article: W. E. Hotham, A. Malviya. A systematic review of surgical methods to restore articular cartilage in the hip. Bone Joint Res 2018;7:336–342. DOI: 10.1302/2046-3758.75.BJR-2017-0331

The aim of this study was to determine whether subchondral bone influences in situ chondrocyte survival. Bovine explants were cultured in serum-free media over seven days with subchondral bone excised from articular cartilage (group A), subchondral bone left attached to articular cartilage (group B), and subchondral bone excised but co-cultured with articular cartilage (group C). Using confocal laser scanning microscopy, fluorescent probes and biochemical assays, in situ chondrocyte viability and relevant biophysical parameters (cartilage thickness, cell density, culture medium composition) were quantified over time (2.5 hours vs seven days). There was a significant increase in chondrocyte death over seven days, primarily within the superficial zone, for group A, but not for groups B or C (p < 0.05). There was no significant difference in cartilage thickness or cell density between groups A, B and C (p > 0.05). Increases in the protein content of the culture media for groups B and C, but not for group A, suggested that the release of soluble factors from subchondral bone may have influenced chondrocyte survival. In conclusion, subchondral bone significantly influenced chondrocyte survival in articular cartilage during explant culture. The extrapolation of bone-cartilage interactions in vitro to the clinical situation must be made with caution, but the findings from these experiments suggest that future investigation into in vivo mechanisms of articular cartilage survival and degradation must consider the interactions of cartilage with subchondral bone

Cells with stem/progenitor characteristics can be isolated from articular cartilage and may have utility in cartilage repair and regeneration therapies. Unlike other adult cell types with differentiation capabilities, clonal chondroprogenitors differentiate into cartilage that resembles stable cartilage rather than endochondral cartilage. We have isolated a large series of chondroprogenitor clones from normal human articular cartilage from individuals of one to forty-five years of age and characterized them with known and novel markers. The clones were isolated separately from different zones of the articular cartilage. As first reported by others, the cloneable cells were mainly found in the upper zones. However, there are clones with chondroprogenitor status in the deeper zones, albeit at far lower frequency. These deep zone clones have different characteristics to those from the upper zones. We have used selected clones to re-engineer stable cartilage with use of the right environmental conditions (growth factors, oxygen level etc)

Matrix metalloproteinase enzymes (MMPs) play a crucial role in the remodeling of articular cartilage, contributing also to osteoarthritis (OA) progression. The pericellular matrix (PCM) is a specialized space surrounding each chondrocyte, containing collagen type VI and perlecan. It acts as a transducer of biomechanical and biochemical signals for the chondrocyte. This study investigates the impact of MMP-2, -3, and -7 on the integrity and biomechanical characteristics of the PCM. Human articular cartilage explants (n=10 patients, ethical-nr.:674/2016BO2) were incubated with activated MMP-2, -3, or -7 as well as combinations of these enzymes. The structural degradative effect on the PCM was assessed by immunolabelling of the PCM's main components: collagen type VI and perlecan. Biomechanical properties of the PCM in form of the elastic moduli (EM) were determined by means of atomic force microscopy (AFM), using a spherical cantilever tip (2.5µm). MMPs disrupted the PCM-integrity, resulting in altered collagen type VI and perlecan structure and dispersed pericellular arrangement. A total of 3600 AFM-measurements revealed that incubation with single MMPs resulted in decreased PCM stiffness (p<0.001) when compared to the untreated group. The overall EM were reduced by ∼36% for all the 3 individual enzymes. The enzyme combinations altered the biomechanical properties at a comparable level (∼36%, p<0.001), except for MMP-2/-7 (p=0.202). MMP-induced changes in the PCM composition have a significant impact on the biomechanical properties of the PCM, similar to those observed in early OA. Each individual MMP was shown to be highly capable of selectively degrading the PCM microenvironment. The combination of MMP-2 and -7 showed a lower potency in reducing the PCM stiffness, suggesting a possible interplay between the two enzymes. Our study showed that MMP-2, -3, and -7 play a direct role in the functional and structural remodeling of the PCM. Acknowledgements: This work was supported by the Faculty of Medicine of the University of Tübingen (grant number.: 2650-0-0)

The zonal organization of articular cartilage is crucial in providing the tissue with mechanical properties to withstand compression and shearing force. Current treatments available for articular cartilage injury are not able to restore the hierarchically organized architecture of the tissue. Implantation of zonal chondrocyte as a multilayer tissue construct could overcome the limitation of current treatments. However, it is impeded by the lack of efficient zonal chondrocyte isolation protocol and dedifferentiation of chondrocytes during expansion on tissue culture plate (TCP). This study aims to develop a protocol to produce an adequate number of high-quality zonal chondrocytes for clinical application via size-based zonal chondrocyte separation using inertial spiral microchannel device and expansion under dynamic microcarrier culture. Full thickness (FT) chondrocytes isolated from porcine femoral condyle cartilage were subjected to two serial of size-based sorting into three subpopulations of different cell sizes, namely small (S1), medium (S2), and large (S3) chondrocytes. Zonal phenotype of the three subpopulations was characterised. To verify the benefit of stratified zonal chondrocyte implantation in the articular cartilage regeneration, a bilayer hydrogel construct composed of S1 chondrocytes overlaying a mixture of S2 and S3 (S2S3) chondrocytes was delivered to the rat osteochondral defect model. For chondrocyte expansion, two dynamic microcarrier cultures, sort-before-expansion and sort-after-expansion, which involved expansion after or before zonal cells sorting, were studied to identify the best sort-expansion strategy. Size-sorted zonal chondrocytes showed zone-specific characteristics in qRT-PCR with a high level of PRG4 expression in S1 and high level of aggrecan, Type II and IX collagen expression in S2 and S3. Cartilage reformation capability of sorted zonal chondrocytes in three-dimensional fibrin hydrogel showed a similar trend in qRT-PCR, histology, extracellular matrix protein quantification and mechanical compression test, indicating the zonal characteristics of S1, S2 and S3 as superficial (SZ), middle (MZ) and deep (DZ) zone chondrocytes, respectively. Implantation of bilayered zonal chondrocytes resulted in better cartilage tissue regeneration in a rat osteochondral defect model than FT control group, with predominantly Type II hyaline cartilage tissue and significantly lower Type I collagen. Dynamic microcarrier expansion of sorted zonal chondrocytes was able to retain the zonal cell size difference that correlate to zonal phenotype, while maintaining the rounded chondrocyte morphology and F-actin distribution similar to that in mature articular cartilage. With the better retention of zonal cell size and zonal phenotype relation on microcarrier, zonal cells separation was achievable in the sort-after-expansion strategy with cells expanded on microcarrier, in comparison to cells expanded on TCP. Inertial spiral microchannel device provides a label-free and high throughput method to separate zonal chondrocytes based on cell size. Stratified implantation of zonal chondrocytes has the potential to improve articular cartilage regeneration. Dynamic microcarrier culture allows for size-based zonal chondrocyte separation to be performed on expanded chondrocytes, thus overcoming the challenge of limited tissue availability from the patients. Our novel zonal chondrocyte isolation and expansion protocol provide a translatable strategy for stratified zonal chondrocyte implantation that could improve articular cartilage regeneration of critical size defects

This review briefly summarises some of the definitive studies of articular cartilage by microscopic MRI (µMRI) that were conducted with the highest spatial resolutions. The article has four major sections. The first section introduces the cartilage tissue, MRI and µMRI, and the concept of image contrast in MRI. The second section describes the characteristic profiles of three relaxation times (T. 1. , T. 2. and T. 1ρ. ) and self-diffusion in healthy articular cartilage. The third section discusses several factors that can influence the visualisation of articular cartilage and the detection of cartilage lesion by MRI and µMRI. These factors include image resolution, image analysis strategies, visualisation of the total tissue, topographical variations of the tissue properties, surface fibril ambiguity, deformation of the articular cartilage, and cartilage lesion. The final section justifies the values of multidisciplinary imaging that correlates MRI with other technical modalities, such as optical imaging. Rather than an exhaustive review to capture all activities in the literature, the studies cited in this review are merely illustrative

Objectives. Patient-specific (PS) implantation surgical technology has been introduced in recent years and a gradual increase in the associated number of surgical cases has been observed. PS technology uses a patient’s own geometry in designing a medical device to provide minimal bone resection with improvement in the prosthetic bone coverage. However, whether PS unicompartmental knee arthroplasty (UKA) provides a better biomechanical effect than standard off-the-shelf prostheses for UKA has not yet been determined, and still remains controversial in both biomechanical and clinical fields. Therefore, the aim of this study was to compare the biomechanical effect between PS and standard off-the-shelf prostheses for UKA. Methods. The contact stresses on the polyethylene (PE) insert, articular cartilage and lateral meniscus were evaluated in PS and standard off-the-shelf prostheses for UKA using a validated finite element model. Gait cycle loading was applied to evaluate the biomechanical effect in the PS and standard UKAs. Results. The contact stresses on the PE insert were similar for both the PS and standard UKAs. Compared with the standard UKA, the PS UKA did not show any biomechanical effect on the medial PE insert. However, the contact stresses on the articular cartilage and the meniscus in the lateral compartment following the PS UKA exhibited closer values to the healthy knee joint compared with the standard UKA. Conclusion. The PS UKA provided mechanics closer to those of the normal knee joint. The decreased contact stress on the opposite compartment may reduce the overall risk of progressive osteoarthritis. Cite this article: K-T. Kang, J. Son, D-S. Suh, S. K. Kwon, O-R. Kwon, Y-G. Koh. Patient-specific medial unicompartmental knee arthroplasty has a greater protective effect on articular cartilage in the lateral compartment: A Finite Element Analysis. Bone Joint Res 2018;7:20–27. DOI: 10.1302/2046-3758.71.BJR-2017-0115.R2

Objectives. Recent studies have shown that systemic injection of rapamycin can prevent the development of osteoarthritis (OA)-like changes in human chondrocytes and reduce the severity of experimental OA. However, the systemic injection of rapamycin leads to many side effects. The purpose of this study was to determine the effects of intra-articular injection of Torin 1, which as a specific inhibitor of mTOR which can cause induction of autophagy, is similar to rapamycin, on articular cartilage degeneration in a rabbit osteoarthritis model and to investigate the mechanism of Torin 1’s effects on experimental OA. Methods. Collagenase (type II) was injected twice into both knees of three-month-old rabbits to induce OA, combined with two intra–articular injections of Torin 1 (400 nM). Degeneration of articular cartilage was evaluated by histology using the Mankin scoring system at eight weeks after injection. Chondrocyte degeneration and autophagosomes were observed by transmission electron microscopy. Matrix metallopeptidase-13 (MMP-13) and vascular endothelial growth factor (VEGF) expression were analysed by quantitative RT-PCR (qPCR).Beclin-1 and light chain 3 (LC3) expression were examined by Western blotting. Results. Intra-articular injection of Torin 1 significantly reduced degeneration of the articular cartilage after induction of OA. Autophagosomes andBeclin-1 and LC3 expression were increased in the chondrocytes from Torin 1-treated rabbits. Torin 1 treatment also reduced MMP-13 and VEGF expression at eight weeks after collagenase injection. Conclusion. Our results demonstrate that intra-articular injection of Torin 1 reduces degeneration of articular cartilage in collagenase-induced OA, at least partially by autophagy activation, suggesting a novel therapeutic approach for preventing cartilage degeneration and treating OA. Cite this article: N-T. Cheng, A. Guo, Y-P. Cui. Intra-articular injection of Torin 1 reduces degeneration of articular cartilage in a rabbit osteoarthritis model. Bone Joint Res 2016;5:218–224. DOI: 10.1302/2046-3758.56.BJR-2015-0001

Aims. Extracellular matrix (ECM) and its architecture have a vital role in articular cartilage (AC) structure and function. We hypothesized that a multi-layered chitosan-gelatin (CG) scaffold that resembles ECM, as well as native collagen architecture of AC, will achieve superior chondrogenesis and AC regeneration. We also compared its in vitro and in vivo outcomes with randomly aligned CG scaffold. Methods. Rabbit bone marrow mesenchymal stem cells (MSCs) were differentiated into the chondrogenic lineage on scaffolds. Quality of in vitro regenerated cartilage was assessed by cell viability, growth, matrix synthesis, and differentiation. Bilateral osteochondral defects were created in 15 four-month-old male New Zealand white rabbits and segregated into three treatment groups with five in each. The groups were: 1) untreated and allogeneic chondrocytes; 2) multi-layered scaffold with and without cells; and 3) randomly aligned scaffold with and without cells. After four months of follow-up, the outcome was assessed using histology and immunostaining. Results. In vitro testing showed that the secreted ECM oriented itself along the fibre in multi-layered scaffolds. Both types of CG scaffolds supported cell viability, growth, and matrix synthesis. In vitro chondrogenesis on scaffold showed an around 400-fold increase in collagen type 2 (COL2A1) expression in both CG scaffolds, but the total glycosaminoglycan (GAG)/DNA deposition was 1.39-fold higher in the multi-layered scaffold than the randomly aligned scaffold. In vivo cartilage formation occurred in both multi-layered and randomly aligned scaffolds treated with and without cells, and was shown to be of hyaline phenotype on immunostaining. The defects treated with multi-layered + cells, however, showed significantly thicker cartilage formation than the randomly aligned scaffold. Conclusion. We demonstrated that MSCs loaded CG scaffold with multi-layered zonal architecture promoted superior hyaline AC regeneration. Cite this article: Bone Joint Res 2020;9(9):601–612

Abstract. Objectives. In the human knee, the cells of the articular cartilage (AC) and subchondral bone (SB) communicate via the secretion of biochemical factors. Chondrocyte-based AC repair strategies, such as articular chondrocyte implantation, are widely used but there has been little investigation into the communication between the native SB cells and the transplanted chondrocytes. We hypothesise that this communication depends on the health state of the SB and could influence the composition and quality of the repair cartilage. Methods. An indirect co-culture model was developed using transwell inserts, representing a chondrocyte/scaffold-construct for repair of AC defects adjoining SB with varying degrees of degeneration. Donor-matched populations of human bone-marrow derived mesenchymal stromal cells (BM-MSCs) were isolated from the macroscopically and histologically best and worst osteochondral tissue, representing “healthy” and “unhealthy” SB. The BM-MSCs were co-cultured with normal chondrocytes suspended in agarose, with the two cell types separated by a porous membrane. After 0, 7, 14 and 21 days, chondrocyte-agarose scaffolds were assessed by gene expression and biochemical analyses. Results. Matched healthy and unhealthy BM-MSCs from five patients undergoing knee arthroplasty (2 male, 3 female; 72.8±2.2. SD. years-old) were used, together with normal chondrocytes from a healthy patient (male; 24 years-old). At day 21, there was significantly more glycosaminoglycan per chondrocyte in the scaffolds co-cultured with healthy BM-MSCs (4.37×10. −4. μg/cell±2.69×10. −5. SEM. ) than in those cultured with unhealthy BM-MSCs (3.52×10. −4. μg/cell±2.19×10. −5. SEM. ; p<0.001). Co-culture with unhealthy BM-MSCs caused a difference in expression of COL2A1 (day 0–21 fold change; unhealthy:-32.8±12.9. SEM. ; healthy:-7.82±4.46. SEM. ; p<0.001) and ACAN (unhealthy:+1.51±0.51. SEM. ; healthy:+4.05±0.49. SEM. ; p=0.002). Conclusions. Co-culture with unhealthy BM-MSCs caused a reduction in GAG deposition and expression of genes encoding matrix-specific proteins, compared to culturing with healthy BM-MSCs. There are clinical implications for cell-based cartilage repair, where the health of the SB may influence the outcome of chondrocyte-based therapies

The weight-bearing status of articular cartilage has been shown to affect its biochemical composition. We have investigated the topographical variation of sulphated glycosaminoglycan (GAG) relative to the DNA content of the chondrocyte in human distal femoral articular cartilage. Paired specimens of distal femoral articular cartilage, from weight-bearing and non-weight-bearing regions, were obtained from 13 patients undergoing above-knee amputation. After papain enzyme digestion, spectrophotometric GAG and fluorometric DNA assays assessed the biochemical composition of the samples. The results were analysed using a paired t-test. Although there were no significant differences in cell density between the regions, the weight-bearing areas showed a significantly higher concentration of GAG relative to DNA when compared with non-weight-bearing areas (p = 0.02). We conclude that chondrocytes are sensitive to their mechanical environment, and that local loading conditions influence the metabolism of the cells and hence the biochemical structure of the tissue

Objectives. Mesenchymal stem cells have the ability to differentiate into various cell types, and thus have emerged as promising alternatives to chondrocytes in cell-based cartilage repair methods. The aim of this experimental study was to investigate the effect of bone marrow derived mesenchymal stem cells combined with platelet rich fibrin on osteochondral defect repair and articular cartilage regeneration in a canine model. Methods. Osteochondral defects were created on the medial femoral condyles of 12 adult male mixed breed dogs. They were either treated with stem cells seeded on platelet rich fibrin or left empty. Macroscopic and histological evaluation of the repair tissue was conducted after four, 16 and 24 weeks using the International Cartilage Repair Society macroscopic and the O’Driscoll histological grading systems. Results were reported as mean and standard deviation (. sd. ) and compared at different time points between the two groups using the Mann-Whitney U test, with a value < 0.05 considered statistically significant. Results. Higher cumulative macroscopic and histological scores were observed in stem cell treated defects throughout the study period with significant differences noted at four and 24 weeks (9.25, . sd. 0.5 vs 7.25, . sd. 0.95, and 10, . sd. 0.81 vs 7.5, . sd. 0.57; p < 0.05) and 16 weeks (16.5, . sd. 4.04 vs 11, . sd. 1.15; p < 0.05), respectively. Superior gross and histological characteristics were also observed in stem cell treated defects. Conclusion. The use of autologous culture expanded bone marrow derived mesenchymal stem cells on platelet rich fibrin is a novel method for articular cartilage regeneration. It is postulated that platelet rich fibrin creates a suitable environment for proliferation and differentiation of stem cells by releasing endogenous growth factors resulting in creation of a hyaline-like reparative tissue. Cite this article: D. Kazemi, K. Shams Asenjan, N. Dehdilani, H. Parsa. Canine articular cartilage regeneration using mesenchymal stem cells seeded on platelet rich fibrin: Macroscopic and histological assessments. Bone Joint Res 2017;6:98–107. DOI: 10.1302/2046-3758.62.BJR-2016-0188.R1

Objectives. Adult mice lacking the transcription factor NFAT1 exhibit osteoarthritis (OA). The precise molecular mechanism for NFAT1 deficiency-induced osteoarthritic cartilage degradation remains to be clarified. This study aimed to investigate if NFAT1 protects articular cartilage (AC) against OA by directly regulating the transcription of specific catabolic and anabolic genes in articular chondrocytes. Methods. Through a combined approach of gene expression analysis and web-based searching of NFAT1 binding sequences, 25 candidate target genes that displayed aberrant expression in Nfat1. -/-. AC at the initiation stage of OA, and possessed at least four NFAT1 binding sites in the promoter of each gene, were selected and tested for NFAT1 transcriptional activities by chromatin immunoprecipitation (ChIP) and promoter luciferase reporter assays using chondrocytes isolated from the AC of three- to four-month-old wild-type mice or Nfat1. -/-. mice with early OA phenotype. Results. Chromatin immunoprecipitation assays revealed that NFAT1 bound directly to the promoter of 21 of the 25 tested genes encoding cartilage-matrix proteins, growth factors, inflammatory cytokines, matrix-degrading proteinases, and specific transcription factors. Promoter luciferase reporter assays of representative anabolic and catabolic genes demonstrated that NFAT1-DNA binding functionally regulated the luciferase activity of specific target genes in wild-type chondrocytes, but not in Nfat1. -/-. chondrocytes or in wild-type chondrocytes transfected with plasmids containing mutated NFAT1 binding sequences. Conclusion. NFAT1 protects AC against degradation by directly regulating the transcription of target genes in articular chondrocytes. NFAT1 deficiency causes defective transcription of specific anabolic and catabolic genes in articular chondrocytes, leading to increased matrix catabolism and osteoarthritic cartilage degradation. Cite this article: M. Zhang, Q. Lu, T. Budden, J. Wang. NFAT1 protects articular cartilage against osteoarthritic degradation by directly regulating transcription of specific anabolic and catabolic genes. Bone Joint Res 2019;8:90–100. DOI: 10.1302/2046-3758.82.BJR-2018-0114.R1

Adult articular cartilage mechanical functionality is dependent on the unique zonal organization of its tissue. Current mesenchymal stem cell (MSC)-based treatment has resulted in sub-optimal cartilage repair, with inferior quality of cartilage generated from MSCs in terms of the biochemical content, zonal architecture and mechanical strength when compared to normal cartilage. The phenotype of cartilage derived from MSCs has been reported to be influenced by the microenvironmental biophysical cues, such as the surface topography and substrate stiffness. In this study, the effect of nano-topographic surfaces to direct MSC chondrogenic differentiation to chondrocytes of different phenotypes was investigated, and the application of these pre-differentiated cells for cartilage repair was explored. Specific nano-topographic patterns on the polymeric substrate were generated by nano-thermal imprinting on the PCL, PGA and PLA surfaces respectively. Human bone marrow MSCs seeded on these surfaces were subjected to chondrogenic differentiation and the phenotypic outcome of the differentiated cells was analyzed by real time PCR, matrix quantification and immunohistological staining. The influence of substrate stiffness of the nano-topographic patterns on MSC chondrogenesis was further evaluated. The ability of these pre-differentiated MSCs on different nano-topographic surfaces to form zonal cartilage was verified in in vitro 3D hydrogel culture. These pre-differentiated cells were then implanted as bilayered hydrogel constructs composed of superficial zone-like chondro-progenitors overlaying the middle/deep zone-like chondro-progenitors, was compared to undifferentiated MSCs and non-specifically pre-differentiated MSCs in a osteochondral defect rabbit model. Nano-topographical patterns triggered MSC morphology and cytoskeletal structure changes, and cellular aggregation resulting in specific chondrogenic differentiation outcomes. MSC chondrogenesis on nano-pillar topography facilitated robust hyaline-like cartilage formation, while MSCs on nano-grill topography were induced to form fibro/superficial zone cartilage-like tissue. These phenotypic outcomes were further diversified and controlled by manipulation of the material stiffness. Hyaline cartilage with middle/deep zone cartilage characteristics was derived on softer nano-pillar surfaces, and superficial zone-like cartilage resulted on softer nano-grill surfaces. MSCs on stiffer nano-pillar and stiffer nano-grill resulted in mixed fibro/hyaline/hypertrophic cartilage and non-cartilage tissue, respectively. Further, the nano-topography pre-differentiated cells possessed phenotypic memory, forming phenotypically distinct cartilage in subsequent 3D hydrogel culture. Lastly, implantation of the bilayered hydrogel construct of superficial zone-like chondro-progenitors and middle/deep zone-like chondro-progenitors resulted in regeneration of phenotypically better cartilage tissue with higher mechanical function. Our results demonstrate the potential of nano-topographic cues, coupled with substrate stiffness, in guiding the differentiation of MSCs to chondrocytes of a specific phenotype. Implantation of these chondrocytes in a bilayered hydrogel construct yielded cartilage with more normal architecture and mechanical function. Our approach provides a potential translatable strategy for improved articular cartilage regeneration using MSCs

Objectives. The purpose of this study was to create a novel ex vivo organ culture model for evaluating the effects of static and dynamic load on cartilage. Methods. The metatarsophalangeal joints of 12 fresh cadaveric bovine feet were skinned and dissected aseptically, and cultured for up to four weeks. Dynamic movement was applied using a custom-made machine on six joints, with the others cultured under static conditions. Chondrocyte viability and matrix glycosaminoglycan (GAG) content were evaluated by the cell viability probes, 5-chloromethylfluorescein diacetate (CMFDA) and propidium iodide (PI), and dimethylmethylene blue (DMMB) assay, respectively. Results. Chondrocyte viability in the static model decreased significantly from 89.9% (. sd. 2.5%) (Day 0) to 66.5% (. sd. 13.1%) (Day 28), 94.7% (. sd. 1.1%) to 80. 9% (. sd. 5.8%) and 80.1% (. sd. 3.0%) to 46.9% (. sd. 8.5%) in the superficial quarter, central half and deep quarter of cartilage, respectively (p < 0.001 in each zone; one-way analysis of variance). The GAG content decreased significantly from 6.01 μg/mg (. sd. 0.06) (Day 0) to 4.71 μg/mg (. sd. 0.06) (Day 28) (p < 0.001; one-way analysis of variance). However, with dynamic movement, chondrocyte viability and GAG content were maintained at the Day 0 level over the four-week period without a significant change (chondrocyte viability: 92.0% (. sd. 4.0%) (Day 0) to 89.9% (. sd. 0.2%) (Day 28), 93.1% (. sd. 1.5%) to 93.8% (. sd. 0.9%) and 85.6% (. sd. 0.8%) to 84.0% (. sd. 2.9%) in the three corresponding zones; GAG content: 6.18 μg/mg (. sd. 0.15) (Day 0) to 6.06 μg/mg (. sd. 0.09) (Day 28)). Conclusion. Dynamic joint movement maintained chondrocyte viability and cartilage GAG content. This long-term whole joint culture model could be of value in providing a more natural and controlled platform for investigating the influence of joint movement on articular cartilage, and for evaluating novel therapies for cartilage repair. Cite this article: Y-C. Lin, A. C. Hall, A. H. R. W. Simpson. A novel organ culture model of a joint for the evaluation of static and dynamic load on articular cartilage. Bone Joint Res 2018;7:205–212. DOI: 10.1302/2046-3758.73.BJR-2017-0320

Articular cartilage is attached to subchondral bone but it is not clear whether the tissues interact and influence in situ (within the matrix) chondrocyte survival. The aim of this study was to determine whether subchondral bone influences in situ chondrocyte survival. Articular cartilage explants harvested from the meta-carpophalangeal joints (N=6) of three-year old cows were placed into three groups:. subchondral bone excised from articular cartilage (Group A). subchondral bone left attached to articular cartilage (Group B). subchondral bone excised, but co-cultured with articular cartilage (Group C). Explants were cultured in serum-free media over 7 days. Using confocal laser scanning microscopy, fluorescent probes and biochemical assays, in situ chondrocyte viability and biophysical parameters (cartilage thickness, cell density, culture medium composition) were quantified over time (2.5 hours vs. 7 days) for Groups A, B and C. With excision of subchondral bone from articular cartilage (Group A), there was a marked increase in chondrocyte death over 7 days primarily within the superficial zone (p< 0.05). There was no significant increase in chondrocyte death within the superficial zone over the same time period for Groups B and C (p> 0.05). There was no significant difference in cartilage thickness or cell density between Groups A, B and C (p> 0.05). Corresponding increases in the protein content of the culture media for Groups B and C but not for Group A, suggested that the release of soluble factors from subchondral bone may have influenced chondrocyte survival. Subchondral bone significantly influences chondrocyte survival in articular cartilage in vitro. These data support the concept of a functional bone-cartilage system in vivo

One reason why NICE (National Institute for Clinical Excellence) does not support operations by the NHS to heal hyaline cartilage lesions using a patients own cells is because there is no clear evidence to show that these operations are beneficial and cost-effective in the long term. Specifically, NICE identified a deficiency of high quality cartilage being produced in repaired joints. The presence of high quality cartilage is linked to long-lasting and functional repair of cartilage. The benchmark for quality, NICE stipulate, is repair cartilage that is stiff and strong and looks similar to the normal tissue surrounding it, i.e. mature hyaline articular cartilage. Biopsy material from autologous cartilage implantation surgical procedures has the appearance of immature articular cartilage and is frequently a mixture of hyaline and fibrocartilage. Osteoarthritic cartilage, in its early stages, also exhibits characteristics of immature articular cartilage in that it expresses proteins found in embryonic and foetal developmental stages, and is highly cellular as evidenced through the presence of chondrocyte clusters. Therefore, an ability to modulate the phenotype and the structure of the extracellular matrix of articular cartilage could positively affect the course of repair and regeneration of articular cartilage lesions. In order to do this, the biochemical stimuli that induce the transition of an essentially unstructured amorphous cartilage mass (immature articular cartilage) to one that is highly structured and ordered, and biomechanically adapted to its particular function (mature articular cartilage) has to be identified. We show for the first time, that fibroblast growth factor-2 and transforming growth factor beta-1 induce precocious maturation of immature articular cartilage. Our data demonstrates that it is possible to significantly enhance maturation of cartilage tissue using growth factor stimulation; consequently this may have applications in transplantation therapy, or through phenotypic modulation of osteoarthritic chondrocytes in diseased cartilage in order to stimulate growth and maturation of repair tissue

Abstract. Objective. Clinical treatments to repair articular cartilage (AC) defects such as autologous cartilage implantation (mosaicplasty) often suffer from poor integration with host tissue, limiting their long-term efficacy. Thus to ensure the longevity of AC repair, understanding natural repair mechanisms that allow for successful integration between cartilaginous surfaces, as has been reported in juvenile tissue, may be key. Here, we evaluated cartilage integration over time in a pig explant model of natural tissue repair by assessing expression and localisation of major ECM proteins, enzymatic cross-linkers including the five isoforms of lysyl oxidase (LOX), small leucine-rich repeat proteoglycans (SLRP's), and proteases (e.g. ADAMTS4). Methods. AC was retrieved from the femoral condyles of 8-week-old pigs. Full thickness 6mmØ AC discs were prepared, defects were induced, and explants cultured for up to 28 days. After fixation, sections were stained using Safranin-O and antibodies against Collagen types I & II, LOX, and ADAMTS4. Gene expression analyses were performed using qPCR. We also cultured devitalized samples, either with or without enzymatic treatment to deplete proteoglycans, for 28 days and similarly assessed repair. Results. Safranin-O staining demonstrated successful integration of cartilage defects over a 28-day period. No significant regulation in the expression of Col1a1, Col2a1, LOX or SLPR genes was observed at any time point. Immunofluorescence staining revealed that only ADAMTS4 localized at the injury surface in integrated samples. Interestingly, we also observed successful spontaneous integration of proteoglycan-depleted devitalized tissue. Conclusion. Cartilage integration in our pig cartilage explant model did not appear to be mediated by upregulation of major cartilage ECM components, enzymatic cross-linkers, or SLRPs. However, spontaneous integration of devitalized, proteoglycan-depleted AC, and localised upregulation of ADAMTS4 at the injured surface in successfully integrated samples, suggest that ADAMTS4 may enhances normal repair in injured AC through local aggrecan depletion, therefore enabling spontaneous cross-linking of collagen fibrils. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Introduction: Articular cartilage has compressive stiffness determined primarily by the matrix and it is quite characteristic and distinct from that of degenerative articular cartilage or regenerative fibrocartilage.Alterations that are evident when articular cartilage begins to degenerate include a decrease in proteoglycan content and water content and resultant reduction in stiffness. Regenerative fibrocartilage has greatly reduced stiffness with functional implications. Identification of cartilaginous stiffness for various sites of normal articular cartilage in the knee is important to enable comparison measures of suspected degenerative cartilage and regenerative articular cartilage either hyaline, fibrocartilage or mixed. Aim: To map the biomechanical properties of normal human articular cartilage in vivo using the Artscan 1000 arthroscopic cartilage stiffness tester (Artscan Oy, Finland). Method: Over a period of 12 months, 94 patients (aged 15 to 69 years) undergoing a knee arthroscopy consented to having their normal articular surfaces evaluated biomechanically for stiffness. Cartilage stiffness (N) was defined by the mean indenter force at each site where the applied force on the measurement rod equalled 10 ±1.5N. `Results: Medial femoral condyle stiffness (mean ± SD; 3.71 ± 1.28N) was greater than all other sites and was significantly greater than mean values obtained for proximal, distal and lateral trochlea (1.87 ± 0.91, 2.44 ±1.02 and 2.69 ±1.52N, respectively); medial (1.71 ± 0.70N) and lateral patella (2.18 ± 1.03N); and medial and lateral tibial plateaux for all subjects (2.33 ± 1.26 and 2.27 ± 1.19N, respectively; p < 0.05). There were no significant differences between sexes for each site. There was no trend for cartilage stiffness to be lower in patients over forty compared with younger patients for both sexes, for all sites. There was however, statistically significant less stiffness of the distal trochlea for females under 40 when compared with that of females older than 40 years. The clinical significance of this is under review. Conclusion: Further research involving the characterisation of cartilage stiffness in pathological situations and evaluation of stiffness following articular cartilage repair is now possible

Articular cartilage repair remains a challenge to surgeons and basic scientists. The field of tissue engineering allows the simultaneous use of material scaffolds, cells and signalling molecules to attempt to modulate the regenerative tissue. This review summarises the research that has been undertaken to date using this approach, with a particular emphasis on those techniques that have been introduced into clinical practice, via in vitro and preclinical studies

Healthy cartilage is essential for optimal joint function. Although, articular cartilage defects are highly prevalent in the active population and might hamper joint function, the effect of articular cartilage defects on knee contact forces and pressures is not yet documented. Therefore, the present study compared knee contact forces and pressures between patients with a tibiofemoral cartilage defect and healthy controls. This might provide additional insights in movement adaptations and the role of altered loading in the progression from defect to OA. Experimental gait data was collected in 15 patients with isolated articular cartilage defects (8 medial-affected, 7 lateral-affected) and 19 healthy asymptomatic controls and was processed using a musculoskeletal model to calculate contact forces and pressures. Differences between medial-affected, lateral-affected and controls were evaluated using Kruskal-Wallis tests and individually compared using Mann-Whitney-U tests (alpha <0.05). The lateral-affected group walked significantly slower compared to the healthy controls. No adaptations in the movement pattern that resulted in decreased loading on the injured condyle were observed. Additionally, the location of loading was not significantly affected. The current results suggest that isolated cartilage defects do not induce changes in the knee joint loading pattern. Consequently, the involved condyle will be equally loaded, indicating that a similar amount of force should be distributed over the remaining cartilage surrounding the articular cartilage defect and may cause local degenerative changes in the cartilage. This in combination with inflammatory responses might play a key role in the progression from articular cartilage defect to a more severe OA phenotype

Introduction: The load bearing status of articular cartilage has been shown to affect its biochemical composition. This study investigates the topographical variation of glycosaminoglycan (GAG) relative to DNA content in human distal femoral articular cartilage. Methods: 26-paired specimens of distal femoral articular cartilage, from weight bearing and non-weight regions, were obtained from thirteen patients undergoing amputation. Following papain enzyme digestion, spectropho-tometric (GAG) and fluorometric (DNA) assays assessed the biochemical composition of the explants. Data was analysed using a paired T test. Results: Despite no significant differences in absolute DNA concentrations, weight-bearing regions of articular cartilage showed a significantly higher concentration of GAG relative to DNA compared with non-weight bearing areas (p=0.021). Discussion: This study suggests that chondrocytes in weight bearing regions of human articular cartilage produce a greater quantity of GAG than those located in non-weight bearing areas. We conclude that mechanical loading is essential in maintaining the biochemical composition of human articular cartilage

Articular cartilage is attached to subchondral bone but little is known regarding bone-cartilage interactions important for chondrocyte survival. In this study, bovine articular cartilage has been evaluated in vitro to determine if the presence of subchondral bone influences chondrocyte survival. We hypothesised that. Excision of subchondral bone from articular cartilage would increase in situ chondrocyte death in explant culture and,. Chondrocyte death could be abrogated by co-culturing articular cartilage with the excised subchondral bone. Articular cartilage explants (n=132) harvested from the metacarpophalangeal joints of three-year old cows (N=12) were placed into three groups:. subchondral bone excised from articular cartilage (Group A). sub-chondral bone left attached to articular cartilage (Group B). subchondral bone excised, but co-cultured with articular cartilage (Group C). Explants were cultured in serum-free media over 7 days with or without media changes to assess the effect of potential soluble mediators. Using confocal laser scanning microscopy to image in situ chondrocytes, fluorescent probes to determine cell viability and biochemical assays to detect alterations in the culture media, differences in the chondrocyte responses (cell density, spatial distribution, percentage cell death) and culture medium composition between Groups A, B and C were quantified over time (2.5 hours versus 7 days). There was no significant change in cell density for Groups A, B and C over 7 days (t-test, p> 0.05). With excision of subchondral bone from articular cartilage (Group A), there was a marked increase in chondrocyte death over 7 days primarily within the superficial zone involving an extensive area of the articular surface (p< 0.05). There was no significant increase in chondrocyte death over the same time period for Groups B and C (p> 0.05). Corresponding increases in the protein content of the culture media for Groups B and C but not for Group A, suggested that the release of soluble factors from subchondral bone may have influenced chondrocyte survival in the superficial zone. Subchondral bone interacts with articular cartilage in vitro and promotes chondrocyte survival in the superficial zone. These data support the concept of a functional bone-cartilage system in vivo

Articular cartilage injury has a high prevalence in elite and recreational athletes. Articular cartilage repair remains a challenge due to cost effectiveness and clinical effectiveness issues. There are now several effective technologies and it is possible to return to competitive sports following many of the procedures available. The durability of repair tissue is variable and there remains extensive growth in the Scientific world. Evolving cartilage restoration technologies focus on increasing cartilage quality and quantity, while optimising surgery and rehabilitation. In UK ACI has undergone extensive cost effectiveness analysis and the in-depth review has shown that ACI is cost effective compared to microfracture. ACI is indicated for lesions >2cm sq but NICE has considered that it is not indicated for problems after microfracture. This presentation details the various options available to surgeons and examines the cost effectiveness

1. Isografts of articular cartilage of young rats, with mucoproteins labelled with . 35. S, extracellular fibrous proteins labelled with . 3. H-glycine, and nuclei labelled with . 3. H-thymidine, were transplanted into the anterior chamber of the eye. 2. Thin split-thickness transplants of the cells of the gliding surface of immature articular cartilage induced the formation of fibrous tissue. 3. Thick transplants and subsurface slices of immature articular cartilage, containing germinal cells of the epiphysial cartilage, induced the formation of new bone consistently within 4 weeks. 4. Full-thickness transplants in articular cartilage from senile rats induced only the formation of fibrous tissue. 5. Slices of growing cartilage, devitalised by cryolysis, or extraction of acid-soluble proteins, produced scanty deposits of bone or cartilage, or both, but only infrequently and generally after a lag phase extending from six to twelve weeks. 6. Reduction in the amount of mucoprotein in the cartilage matrix by papain, and suppression of the resynthesis of tissue proteins by cortisone, retarded but did not prevent bone induction. 7. Bone induction is the product of a series of interactions between inducing cells and responding cells by intracellular and intercellular reactions too complex to characterise in physico-chemical terms at this time

Articular cartilage has compressive stiffness determined primarily by the matrix which is quite characteristic and distinct from that of degenerative articular cartilage or regenerative fibrocartilage. Alterations evident when articular cartilage begins to degenerate include a decrease in proteoglycan content and water content and resultant reduction in stiffness. Regenerative fibro-cartilage has greatly reduced stiffness with functional implications. Identification of cartilaginous stiffness for various sites of normal articular cartilage in the knee is important to enable comparison measures of suspected degenerative cartilage and regenerative articular cartilage either hyaline, fibrocartilage or mixed. The aim of this study was to map the in vivo biomechanical properties of normal human articular knee cartilage using the Artscan 1000 arthroscopic cartilage stiffness tester (Artscan Oy, Finland). It has been shown that the Artscan 1000 is reliable when measuring the stiffness of thin articular cartilage (Lyra et al., 1999). Over a period of 12 months, 94 patients (age 15–69 yr) undergoing a knee arthroscopy consented to having their normal articular surfaces biomechanically evaluated for stiffness. Cartilage stiffness (N) was defined by the mean indenter force at each site where the applied force on the measurement rod equalled 10 ±1.5 N. Medial femoral condyle stiffness (M ±SD; 3.71 ±1.28 N) was greater than all other sites and was significantly greater than mean values obtained for proximal, distal and lateral trochlea (1.87 ±0.91, 2.44 ±1.02 and 2.69 ±1.52 N, respectively); medial (1.71 ±0.70 N) and lateral patella (2.18 ±1.03 N); and medial and lateral tibial plateau for all subjects (2.33 ±.1.26 and 2.27 ±1.19 N, respectively; p < 0.05). There were no significant differences between sexes for each site. There was no trend for cartilage stiffness to be lower in patients over forty compared to younger patients for both sexes for all sites. There was, however, statistically significant less stiffness of the distal trochlea for females under 40 years when compared to that of females older than 40 years. The clinical significance of this is under review. Further research involving the characterisation of cartilage stiffness in pathological situations and evaluation of stiffness following articular cartilage repair is now possible

Aims

To identify unanswered questions about the prevention, diagnosis, treatment, and rehabilitation and delivery of care of first-time soft-tissue knee injuries (ligament injuries, patella dislocations, meniscal injuries, and articular cartilage) in children (aged 12 years and older) and adults.

The aim of this study was to determine whether exposure of human articular cartilage to hyperosmotic saline (0.9%, 600 mOsm) reduces in situ chondrocyte death following a standardised mechanical injury produced by a scalpel cut compared with the same assault and exposure to normal saline (0.9%, 285 mOsm). Human cartilage explants were exposed to normal (control) and hyperosmotic 0.9% saline solutions for five minutes before the mechanical injury to allow in situ chondrocytes to respond to the altered osmotic environment, and incubated for a further 2.5 hours in the same solutions following the mechanical injury. Using confocal laser scanning microscopy, we identified a sixfold (p = 0.04) decrease in chondrocyte death following mechanical injury in the superficial zone of human articular cartilage exposed to hyperosmotic saline compared with normal saline. These data suggest that increasing the osmolarity of joint irrigation solutions used during open and arthroscopic articular surgery may reduce chondrocyte death from surgical injury and could promote integrative cartilage repair

It is well known that articular cartilage in adults has a limited capacity for self-repair. Numerous methods have been devised to augument its natural healing response, but these methods generally lead to filling of the defect with fibrous tissue or fibrocartilage, which lacks the mechanical characteristics of articular cartilage and fails with time. Tissue engineering combines aspects of cell biology, engineering, material science and surgery to generate new functional tissue and provides an important approach to the repair of articular cartilage lesions and, ultimately, functional success. The purpose of our study was to perform experimental resurfacing of articular cartilage in 18 sheep using different techniques: before implantation in all sheep a full-thickness chondral lesion of medial femoral condyle was created; subsequently, autologous chondrocytes seeded into the matrix were implantd into five sheep; a periosteum flap was implanted in five sheep; and, as source of growth factors, adipocytes by vascular peduncle of Hoffa tissue were implanted in five sheep. The reparative tissue of the chondral lesion was compared with uninjured contralateral knee. The results present the bonding between implantation tissue and host tissue, preservation of phenotypic stability of chondrocytes culture, standard dosage of growth factor secreted by adipocytes and characterisation of the histological properties of reparative tissue, comparing different surgical techniques

The medial meniscus was resected from the right knees of twelve young grivet monkeys that were killed at intervals of twenty-one to 252 days after operation. The knees operated upon and the control knees were investigated radiologically and histologically. Degenerative changes occurred in the medial femoral and tibial condyles. At first there was loss of cells from the superficial layer of the articular cartilage, with a marked decrease in the acid mucopolysaccharide content of the matrix. The chondrocytes in the deeper layer of the non-calcified zone proliferated to form clones before finally degenerating. The acellular cartilage showed splitting, and with progress of the degenerative process there was thinning and erosion of the cartilage. Eventually there was complete loss of articular cartilage with thickening and exposure of the subchondral bone. These degenerative changes were confined to a small area of the articular cartilage and had occurred despite regeneration of the meniscus. The rest of the cartilage looked normal. It is concluded that articular cartilage deprived of the protection of a meniscus may undergo arthritic changes