Histomorphometry of the aging human patella: histologic criteria and controls

Osteochondral Interface: Regenerative Engineering and Challenges

Osteochondral (OC) defects are debilitating for patients and represent a significant clinical problem for orthopedic surgeons as well as regenerative engineers due to their potential complications, which are likely to lead to osteoarthritis and related diseases. If they remain untreated or are treated suboptimally, OC lesions are known to impact the articular cartilage and the transition from cartilage to bone, that is, the cartilage-bone interface. An important component of the OC interface, that is, a selectively permeable membrane, the tidemark, still remains unaddressed in more than 90% of the published research in the past decade. This review focuses on the structure, composition, and function of the OC interface, regenerative engineering attempts with different scaffolding strategies and challenges ahead of us in recapitulating the native OC interface. There are different schools of thought regarding the structure of the native OC interface: stratified and graded. The former assumes the cartilage-to-bone interface to be hierarchically divided into distinct yet continuous zones of uncalcified cartilage-calcified cartilage-subchondral bone. The latter assumes the interface is continuously graded, that is, formed by an infinite number of layers. The cellular composition of the interface, either in respective layers or continuously changing in a graded manner, is chondrocytes, hypertrophic chondrocytes, and osteoblasts as moved from cartilage to bone. Functionally, the interface is assumed to play a role in enabling a smooth transition of loads exerted on the cartilage surface to the bone underneath. Regenerative engineering involves, first, a characterization of the native OC interface in terms of the composition, structure, and function, and, then, proposes the appropriate biomaterials, cells, and biomolecules either alone or in combination to eventually form a structure that mimics and functionally behaves similar to the native interface. The major challenge regarding regeneration of the OC interface appears to lie, in addition to others, in the formation of tidemark, which is a thin membrane separating the OC interface into two distinct zones: the avascular OC interface and the vascular OC interface. There is a significant amount of literature on regenerative approaches to the OC interface; however, only a small portion of them consider the importance of tidemark. Therefore, this review aims at highlighting the significance of the structural organization of the components of the OC interface and increasing the awareness of the orthopedics community regarding the importance of tidemark formation after clinical interventions or regenerative engineering attempts.

Roles of the calcified cartilage layer and its tissue engineering reconstruction in osteoarthritis treatment

Sandwiched between articular cartilage and subchondral bone, the calcified cartilage layer (CCL) takes on both biomechanical and biochemical functions in joint development and ordinary activities. The formation of CCL is not only unique in articular cartilage but can also be found in the chondro-osseous junction adjacent to the growth plate during adolescence. The formation of CCL is an active process under both cellular regulation and intercellular communication. Abnormal alterations of CCL can be indications of degenerative diseases including osteoarthritis. Owing to the limited self-repair capability of articular cartilage and core status of CCL in microenvironment maintenance, tissue engineering reconstruction of CCL in damaged cartilage can be of great significance. This review focuses on possible tissue engineering reconstruction methods targeting CCL for further OA treatment.

Lipid metabolism in cartilage and its diseases: a concise review of the research progress

The homeostasis of the vertebrate body depends on anabolic and catabolic activities that are closely linked the inside and outside of the cell. Lipid metabolism plays an essential role in these metabolic activities. Although a large amount of evidence shows that normal lipid metabolism guarantees the conventional physiological activities of organs in the vertebrate body and that abnormal lipid metabolism plays an important role in the occurrence and deterioration of cardiovascular-related diseases, such as obesity, atherosclerosis, and type II diabetes, little is known about the role of lipid metabolism in cartilage and its diseases. This review aims to summarize the latest advances about the function of lipid metabolism in cartilage and its diseases including osteoarthritis, rheumatoid arthritis, and cartilage tumors. With the gradual in-depth understanding of lipid metabolism in cartilage, treatment methods could be explored to focus on this metabolic process in various cartilage diseases.

Osteochondral Injury, Management and Tissue Engineering Approaches

Osteochondral lesions (OL) are a common clinical problem for orthopedic surgeons worldwide and are associated with multiple clinical scenarios ranging from trauma to osteonecrosis. OL vary from chondral lesions in that they involve the subchondral bone and chondral surface, making their management more complex than an isolated chondral injury. Subchondral bone involvement allows for a natural healing response from the body as marrow elements are able to come into contact with the defect site. However, this repair is inadequate resulting in fibrous scar tissue. The second differentiating feature of OL is that damage to the subchondral bone has deleterious effects on the mechanical strength and nutritive capabilities to the chondral joint surface. The clinical solution must, therefore, address both the articular cartilage as well as the subchondral bone beneath it to restore and preserve joint health. Both cartilage and subchondral bone have distinctive functional requirements and therefore their physical and biological characteristics are very much dissimilar, yet they must work together as one unit for ideal joint functioning. In the past, the obvious solution was autologous graft transfer, where an osteochondral bone plug was harvested from a non-weight bearing portion of the joint and implanted into the defect site. Allografts have been utilized similarly to eliminate the donor site morbidity associated with autologous techniques and overall results have been good but both techniques have their drawbacks and limitations. Tissue engineering has thus been an attractive option to create multiphasic scaffolds and implants. Biphasic and triphasic implants have been under explored and have both a chondral and subchondral component with an interface between the two to deliver an implant which is biocompatible and emulates the osteochondral unit as a whole. It has been a challenge to develop such implants and many manufacturing techniques have been utilized to bring together two unalike materials and combine them with cellular therapies. We summarize the functions of the osteochondral unit and describe the currently available management techniques under study.

Insights on Molecular Mechanisms of Chondrocytes Death in Osteoarthritis

Osteoarthritis (OA) is a joint pathology characterized by progressive cartilage degradation. Medical care is mainly based on alleviating pain symptoms. Compelling studies report the presence of empty lacunae and hypocellularity in cartilage with aging and OA progression, suggesting that chondrocyte cell death occurs and participates to OA development. However, the relative contribution of apoptosis per se in OA pathogenesis appears complex to evaluate. Indeed, depending on technical approaches, OA stages, cartilage layers, animal models, as well as in vivo or in vitro experiments, the percentage of apoptosis and cell death types can vary. Apoptosis, chondroptosis, necrosis, and autophagic cell death are described in this review. The question of cell death causality in OA progression is also addressed, as well as the molecular pathways leading to cell death in response to the following inducers: Fas, Interleukin-1β (IL-1β), Tumor Necrosis factor-α (TNF-α), leptin, nitric oxide (NO) donors, and mechanical stresses. Furthermore, the protective role of autophagy in chondrocytes is highlighted, as well as its decline during OA progression, enhancing chondrocyte cell death; the transition being mainly controlled by HIF-1α/HIF-2α imbalance. Finally, we have considered whether interfering in chondrocyte apoptosis or promoting autophagy could constitute therapeutic strategies to impede OA progression.

Tougu Xiaotong capsule inhibits the tidemark replication and cartilage degradation of papain-induced osteoarthritis by the regulation of chondrocyte autophagy

The tidemark is located between calcified and non-calcified cartilage matrices. Tidemark replication plays an important role in the pathogenesis of osteoarthrosis (OA). Autophagy, or cellular self-digestion, is an essential cellular homeostasis mechanism that was found to be deficient in osteoarthritic cartilage. This study evaluated the effects of Tougu Xiaotong capsule (TXC) on the tidemark replication and cartilage degradation, and also investigated LC3 I/II, which executes autophagy, the potential role of ULK1, an inducer of autophagy, and Beclin1, a regulator of autophagy, in the development of a papain-induced OA in rat knee joints. Using a papain-injected knee rat model, standard histological methods were used to validate our model as well as treatment with TXC or glucosamine (GlcN). After 12 weeks of treatment, the changes of cartilage structure were observed by digital radiography (DR), optical microscopy, scanning electron microscopy and transmission electron microscopy, and the LC3 I/II, ULK1 and Beclin1 levels were measured by western blotting. Cartilage degradation was evaluated by the Mankin score on paraffin-embedded sections stained with Safranin O-fast green. TXC was found to improve the arrangement of subchondral bone collagen fibers and calcium phosphate crystals, inhibit the tidemark replication and delay the cartilage degradation in the papain-induced OA. Our results also showed that LC3 I/II, ULK1 and Beclin1 levels in both the TXC+OA and GlcN+OA groups were significantly increased compared to those in the OA group. The results indicate that TXC could inhibit the tidemark replication and cartilage degradation by the regulation of chondrocyte autophagy.

Efeitos dos glicosaminoglicanos e sulfato de condroitina A sobre a cartilagem articular normal e com doença articular degenerativa em cães

Avaliaram-se os efeitos dos precursores dos glicosaminoglicanos (GAG) e do sulfato de condroitina A (SC) sobre a histomorfometria da cartilagem articular normal ou de cartilagem de cães com doença articular degenerativa (DAD) experimental. Os grupos experimentais constituíram-se de animais com articulação direita normal, que não foi submetida a procedimento cirúrgico, e com articulação esquerda osteoartrótica e que foi submetida à intervenção cirúrgica. Os grupos foram subdivididos em animais com articulação não tratada e tratada, portanto: normais (N) (n=5), NGAG (n=5) e NSC (n=4); e osteoartróticos (O) (n=5), OGAG (n=5) e OSC (n=4). Secções de cartilagens do fêmur, da tíbia e da patela foram utilizadas neste estudo. Nos normais (N, NGAG e NSC), não se encontraram lesões que caracterizassem a DAD, embora tenha havido diminuição na celularidade nos de NGAG e NSC, em relação a N. Foram observadas alterações em graus variáveis entre os grupos osteoartróticos. Houve redução acentuada dos condrócitos no grupo O em comparação aos normais enquanto os grupos osteoartróticos tratados apresentaram celularidade semelhante aos normais tratados. Estes resultados foram confirmados pela análise do índice de proporção (IP), que se mostrou elevado em O, indicando menor síntese de proteoglicanos. Não houve diferença significativa entre os IPs dos grupos osteoartróticos tratados (OGAG, OSC) apesar do comportamento distinto do OSC ao assemelhar-se aos grupos N e NSC. Estes resultados sugeriram que o SC agiu na cartilagem osteoartrótica de maneira mais eficaz, reduzindo a perda de proteoglicanos e estimulando a viabilidade celular e a atividade metabólica.

Heberden's nodes and what Heberden could not see: the pivotal role of ligaments in the pathogenesis of early nodal osteoarthritis and beyond

Despite its relatively high prevalence, polyarticular nature, limited treatment options and recognized genetic contribution, the study of generalized OA (GOA) has lagged behind that of isolated knee OA. Whilst the pathogenesis of OA has been viewed in relation to either articular cartilage or bone disease, this article offers a viewpoint on why GOA may, in fact, be primarily a disorder of ligaments, and to a lesser extent tendon and joint capsule dysfunction. A relatively fast presentation of GOA, typically in the perimenopausal period, and its recognition on clinical grounds alone makes this type of OA potentially useful for pathogenic studies in OA, in general. The recent high-resolution MRI studies, microanatomical studies and animal models, in addition to established clinical and radiographic data that support this ligament-centric perspective of disease, are reviewed. The earliest structural abnormalities in GOA may be evident in ligaments and the ligament-associated 'enthesis organ', where degenerative changes are evident. Ligaments also influence the expression of joint damage including Heberden's node and joint erosion formation. Joint inflammation in a 'periarthritis' pattern is well recognized in GOA, and histological studies have shown that the ligament and capsule could represent the epicentre of such inflammatory changes. A perspective is also offered on how ligaments could play a pivotal role in OA in general; for example, the loss of joint space in knee OA due to meniscal extrusion could ultimately be related to derangement of the medial collateral ligament to which the meniscus is anchored.

The normal human chondro-osseous junctional region: evidence for contact of uncalcified cartilage with subchondral bone and marrow spaces

BACKGROUND

The chondro-osseous junctional region of diarthrodial joints is peculiarly complex and may be considered to consist of the deepest layer of non-calcified cartilage, the tidemark, the layer of calcified cartilage, a thin cement line (between the calcified cartilage and the subchondral bone) and the subchondral bone. A detailed knowledge of the structure, function and pathophysiology of the normal chondro-osseous junction is essential for an understanding of the pathogenesis of osteoarthrosis.

METHODS

Full thickness samples from human knee joints were processed and embedded in paraffin wax. One hundred serial sections (10 mum thick) were taken from the chondro-osseous junctional region of a block from the medial tibial plateau of a normal joint. They were stained with haematoxylin and eosin and photographed. For a simple physical reconstruction images of each 10th sequential tissue section were printed and the areas of the photomicrographs containing the chondro-osseous junctional region were cut out and then overlaid so as to create a three-dimensional (3D) model of this region. A 3D reconstruction was also made using computer modelling.

RESULTS

Histochemical staining revealed some instances where prolongations of uncalcified cartilage, delineated by the tidemark, dipped into the calcified cartilage and, in places, abutted onto subchondral bone and marrow spaces. Small areas of uncalcified cartilage containing chondrocytes (virtual islands) were seen, in two-dimensional (2D) sections, to be apparently entombed in calcified matrix. The simple physical 3D reconstruction confirmed that these prolongations of uncalcified cartilage were continuous with the cartilage of zone IV and demonstrated that the virtual islands of uncalcified cartilage were cross-sections of these prolongations. The computer-generated 3D reconstructions clearly demonstrated that the uncalcified prolongations ran through the calcified cartilage to touch bone and marrow spaces and confirmed that the apparent entombment of chondrocytes was a 2D artefact.

CONCLUSION

This study demonstrates that the chondro-osseous junctional region is more complex than previously described. The tidemark is a clearly defined boundary delineating uncalcified from calcified cartilage. It is not a straight line across a joint, but a complex three-dimensional structure that follows uncalcified cartilage prolongations dipping down through the calcified cartilage to abut onto subjacent bone or marrow spaces.

The tidemark of the chondro-osseous junction of the normal human knee joint

The chondro-osseous junction includes the junction between calcified and non-calcified cartilage matrices often referred to as the tidemark. A detailed knowledge of the structure, function and pathophysiology of the chondro-osseous junction is essential for an understanding both of the normal elongation of bones and of the pathogenesis of osteoarthrosis. In this study the molecular anatomy of the tidemark was studied using histochemical techniques, including lectin histochemistry, on blocks of normal cartilage from human knee joints. The tidemark stained with H and E, picro-sirius red, toluidine blue, safranin O and methyl green, but not with alcian blue in the presence of magnesium chloride at 0.05 M or above. It stained with only four lectins, those from Datura stramonium, Maclura pomifera, Erythrina crystagalli and Helix pomatia, out of the 19 used. Therefore, it is rich in collagen and contains hyaluronan, but appears to lack the glycosaminoglycans of 'conventional' proteoglycans and it expresses a very limited and distinctive lectin staining glycoprofile, which is probably attributable to specific glycoproteins. In addition, the tidemark had a distinct microanatomical trilaminate appearance. From all of these results it is clear that this part of the chondro-osseous junctional region is chemically more complex and distinctive than has previously been described.

Macroscopic and radiological grading of osteoarthritis correlates inadequately with cartilage height and histologically demonstrable damage to cartilage structure

INTRODUCTION

The aim of the present study was to investigate different methods for determining osteoarthritis-related (OA) cartilaginous changes.

MATERIALS AND METHODS

Human tibial heads were investigated radiologically, macroscopically and microscopically. The height of the hyaline cartilage was measured with the aid of a computerised digital image analysis system.

RESULTS

The comparison of the different evaluation systems revealed, in part, appreciable variations in severity and produced correlations of r=-0.312-0.673. In none of the methods was a linear correlation between the histomorphometrically measured decrease in cartilage height and the increasing grade of OA evident.

DISCUSSION

The microscopic scores are superior, since they provide the most precise description of cartilaginous structure. The variation in cartilage height with increasing OA is not a linear process; measurement of the cartilage height alone is not a valid parameter for determining the grade of OA.

Articular cartilage and changes in arthritis. An introduction: cell biology of osteoarthritis

The reaction patterns of chondrocytes in osteoarthritis can be summarized in five categories: (1) proliferation and cell death (apoptosis); changes in (2) synthetic activity and (3) degradation; (4) phenotypic modulation of the articular chondrocytes; and (5) formation of osteophytes. In osteoarthritis, the primary responses are reinitiation of synthesis of cartilage macromolecules, the initiation of synthesis of types IIA and III procollagens as markers of a more primitive phenotype, and synthesis of active proteolytic enzymes. Reversion to a fibroblast-like phenotype, known as "dedifferentiation", does not appear to be an important component. Proliferation plays a role in forming characteristic chondrocyte clusters near the surface, while apoptosis probably occurs primarily in the calcified cartilage.