In joint: Articular cartilage. This chapter outlines the architectural and compositional features of … In ball and socket joints, one bone surface is almost spherical in form and the other distinctly and deeply concave, providing a connection which provides maximum range of movement with a lower risk of dislocation. Cartilage function is more than structural, and has different functions in the life cycle. M.I. The COL network resists the swelling tendency of PG molecules and provides cartilage functional integrity, tensile and shear stiffness and strength. It acts as a transition between cartilage and the underlying subchondral bone, allowing strong adhesion of the two different tissue types. provide lubrication of articular surfaces. Articular cartilage (AC) is a connective tissue covering the ends of bones that functions as a load-bearing, low-friction, and wear-resistant surface to facilitate joint movement. To protect the smooth hyaline surface, all diarthroidal joints are covered by a synovial membrane filled with synovial fluid. The successful management of articular cartilage lesions is challenging for both the surgeon and patient. Restoring articular cartilage can relieve pain and allow better function. The cartilage provides a smooth surface that facilitates easy movement. By using sensitive immunoassays such fragments can be quantified in synovial fluid or serum. Examples of planar joints are the carpals of the hand and the tarsals of the foot, and in the temporomandibular joint as shown below. As discussed earlier, some of the fragments released will activate immune responses with the potential to further enhance disease activity. specialized tissue precisely suited for withstanding large compressive joint loads and transferring that load in a nondestructive manner to the bone below What are the (4) functions of articular cartilage? Articular cartilage consists of specialized cells called chondrocytes that are essential for its maintenance and overall integrity, the degeneration of which is a hallmark of degenerative joint diseases such as osteoarthritis (OA). The function of articular cartilage is dependent on the molecular composition of the extracellular matrix (ECM), which consists mainly of proteoglycans and collagen. While the intricate ultrastructure of articular cartilage is critical for proper function, these same properties create challenges for cartilage restoration. It also allows gliding motions. The articular cartilage function is dependent on the molecular composition of the extracellular matrix (ECM). Animal studies using mTOR inhibitors or genetic deletion show protection from cartilage-degenerative mechanisms in mouse models of OA, suggesting the therapeutic potential of inhibiting the mTOR signaling pathway to achieve articular cartilage homeostasis [1,3]. Thus, the knee joint is supplied by branches from the femoral, sciatic, and obturator nerves, which among them supply the various muscles moving the joint. The articulating surface of the femoral condyles, tibial plateaus and the back of the patella are covered with this cartilage. Hypertrophic chondrocytes, which secrete mineralized matrix, are present in the deepest region of the deep zone, where it meets the subchondral bone. Articular cartilage, which makes possible the painless, low-friction movement of synovial joints, consists of a sparsely distributed population of highly specialized cells called chondrocytes that are embedded within a matrix and provide articular cartilage with remarkable mechanical properties. coefficient (Figure 1). Articular cartilage is the hyaline cartilage. It helps in the formation of bones in growing children. Cartilage is a flexible connective tissue that differs from bone in several ways; it is avascular and its microarchitecture is less organized than bone. The term hyaline comes from the Greek word “hyalos,” which means glassy. Unlike bone, it is easily cut by a sharp knife. The x-ray featured below shows the healthy, undamaged sternoclavicular joint of a young male on the left-hand side, and the same joint after trauma and subsequent osteoarthritis to the right. Above that layer, large, negatively charged macromolecules attract and bind water. Additionally, each patient is unique and must be evaluated individually to determine the best course of treatment. While there are other cartilage repair methods being researched, this chapter will focus on cell therapies that could be conjoined with tissue engineering strategies. Articular cartilage is composed of hyaline cartilage which functions to minimize friction between the articulations of synovial joints and act as a shock absorber of the daily loads applied to the joints: both of these serve to protect the underlying bone. This chapter outlines the architectural and compositional features of articular cartilage. The thickness of the subchondral bone end plate varies also as the vascular supply with age, body weight, location, function, and genetics. As a person ages, this cartilage can wear away, leading to joint pain and swelling that is sometimes only alleviated by surgery. Articular cartilage is devoid of blood vessels, nerves, and lymphatics cells. Articular cartilage (cartilage that covers the articulating part of a bone) is of the type called hyaline (glasslike) because thin sections of it are translucent, even transparent. The ECM consists mainly of proteoglycan and collagens.The main proteoglycan in cartilage is aggrecan, which, as its name suggests, forms large aggregates with hyaluronan.These aggregates are negatively charged and hold water in the tissue. This may allow the withstanding of pressure and weight-bearing brought a… All of these structures of the articular capsule of the joint (outer layer, inner layer, synovial fluid, bursae, fat pad) all have specific functions in the knee. The subchondral bone plate possesses an irregular surface to which the articular cartilage is keyed in. The extracellular matrix of these four layers are further split into three regions called the pericellular region (immediately surrounding the chondrocyte), the territorial region (protective, collagen-rich area), and the interterritorial region (largest region with high amounts of collagen and proteoglycans, and structurally important). Mechanisms that trigger chondrocytes to lose their ability to maintain articular cartilage homeostasis as well as their own survival are not well understood. A lesser-known example is the sternoclavicular joint. The basic science of articular cartilage: structure, composition, and … The air-tent system requires a pump that must be constantly operating to maintain inflation of the tent because of leaks in the fabric. Some of the fragments formed will no longer be retained in the tissue but are released to surrounding body fluids. This was recognized as early as in 1743 by Hunter who stated that cartilage “once destroyed is not repaired.” This is because none of the normal inflammatory and reparative processes of the body are available to repair the tissue. It is very smooth (its coefficient of friction is less than one-third of ice on ice) highly compressible and resilient. In OA cartilage, enhanced mTOR signaling is associated with the suppression of key autophagy mediators and increased chondrocyte cell death [1–3]. The articular cartilage covers the articulating bony surfaces and is composed of hyaline cartilage. Nutrients are provided directly from the synovial fluid and not from the perichondrium, which is absent in articular cartilage. The structure of articular cartilage into three zones with different characteristics allows for an efficient, load-bearing surface which distributes compressive forces generated during diarthroidal joint loading and diarthroidal joint motion. This causes it to heal very slowly. Under the subchondral plate, the bony surfaces are composed of trabecular bone. Articular cartilage is a white, smooth tissue which covers the ends of bones in joints. Articular cartilage is the highly specialized connective tissue of diarthrodial joints. The term ‘articular cartilage’ does not refer to the type of cartilage structure, but to its location. The junction where cartilage and bone meet is called the chondro-osseous junction or osteochondral interface. The best-known example of the saddle joint is the first metacarpal joint between thumb and wrist. At this level there are fewer proteoglycans and higher numbers of organized collagen fibrils. The joint range of movement depends on the specific type of diarthroidal joint. While the PCM was first observed nearly a century ago, its role is still under investigation. This itself is a result of its isolation from the systemic regulation, and lack of blood vessels and nerve supply (Mankin, 1982). Joint - Joint - Articular nerves: The sources of nerve fibres to a joint conform well to Hilton’s law—the nerves to the muscles acting on a joint give branches to that joint as well as to the skin over the area of action of these muscles. Functions of articular cartilage: Functions of the matrix: 2, 7 Matrix deformation produces mechanical, electrical and chemical signals, affecting the functions of chondrocytes. The first three layers of articular cartilage are shown in the simple diagram below. The remaining 30% of the articular cartilage is the deep zone. allow movement of bony surfaces with minimal friction (minimal wear) improve fit of articular surfaces. The typical response to cartilage injury in which the subchondral plate is fractured is the formation of fibrocartilage, a scarlike tissue unsuited to… Many arterial terminal branches, probably end arteries, are present in the subchondral bone plate and end in sinusoids of uneven caliber and an irregular distribution. Ball and socket joints are found in the hips and shoulders. With the ability to move along two axes (up and down, side to side), ellipse-shaped bone surfaces – one concave and one convex – are found primarily in the hand and wrist, and the foot. This structure is at right angles to the underlying bone – an arrangement that provides the most resistance to compressive forces. During growth and maturation of AC, there are significant changes in cellular distribution, cartilage composition, structure, and mechanical function. Low levels of oxygen mean chondrocytes primarily depend upon anaerobic metabolism. articular cartilage is 2 to 4 mm thick in length. Wrong movement in load bearing cartilage, for example at a joint between the long bones, is the reason why the knee (between the femur and tibia) is the location of frequent articular cartilage injury. Mechanical injury to the articular cartilage is a key risk factor in joint damage and predisposition to osteoarthritis. decreases friction and distributes loads. Articular cartilage matrix is rich in collagen (especially collagen type II), proteoglycans (especially aggrecan), and glycosaminoglycans, especially hyaluronan, a water-retentive molecule which is responsible for the high water content of articular cartilage (Leyett et al., 2014). The uppermost layer of the articular cartilage is known as the superficial zone, which comprises about 10%–20% of the total articular cartilage thickness, and contains linearly-arranged collagen fibers interspersed with occasional flattened chondrocytes. Articular cartilage derives its powers from its very organized and efficiently constructed microanatomy. Rotation is not possible in condyloid joints. Is healthy articular cartilage vascularized? The two major problems that need to be addressed in repair of articular cartilage are the filling of the defect void with a tissue that has the same mechanical properties as articular cartilage and the promotion of successful integration between the repair tissue and the native articular cartilage and calcified cartilage. The lower portion of the middle zone contains linear collagen fibrils arranged perpendicular to the surface, with rounded chondrocytes arranged in short stacks in alignment with the fibers (Fox et al., 2009). In the lower limbs, the weight-bearing properties of articular cartilage are unable to properly distribute weight and the shock-absorbant characteristics of cartilage are lost. Dick HeinegÃ¥rd, ... Tore Saxne, in Rheumatology (Sixth Edition), 2015. A second type of cartilage in the knee joint is the smooth shiny white articular cartilage. These sinusoids terminate in venous radicles forming a transverse sinus, perpendicular to the tiny venous branches. Thus, matrix also plays a role in recording a loading history of the articular cartilage. One example is the demonstration that COMP can be used to identify patients who will have the most extensive joint destruction in both osteoarthritis and rheumatoid arthritis.33,79 Also, a number of collagen fragments created by cleavage with collagenases, as well as by subsequent gelatinase activity, have been used to monitor disease.80,81 With further development of the technology we hope to be able to identify indicators specific to a particular pathologic process in a given tissue. The articular cartilage _____ surface area and _____ stress, is nearly frictionless aiding lubrication and minimizing wear of opposing bone surfaces Increasing the surface area and decreasing stress allows the articular cartilage to function in Any pain is not caused by damage to the cartilage itself, as cartilaginous connective tissues are aneural (without a nerve network). Since articular cartilage is a postmitotic tissue, it depends on processes such as autophagy to remove damaged organelles, misfolded or aggregated proteins, as well as eliminating pathogens in response to stress. The latter is pictured below, showing the projection of the dens from the second cervical vertebra (C2), or axis, into the arch of the first cervical vertebra (C1), or atlas. Here, proteoglycans are more prevalent than in any of the other layers, while collagen fibrils are relatively disorganized in comparison to the layer above. Kyle R. Flik, ... Brian J. Cole, in Clinical Sports Medicine, 2006. It is also in direct contact with the synovial fluid of the joint capsule. There are six types of synovial joint. The function of articular cartilage is to absorb shock and provide an extremely smooth surface to make movement easier. Medical definition of articular cartilage: cartilage that covers the articular surfaces of bones. It contains fatty bone marrow and trabecular bone. As mentioned previously, the main proteoglycan in cartilage is aggrecan , which forms large aggregates with hyaluronan and are negatively charged to hold water in the tissue. It is deformable but elastic, and…. Akihiro Nakamura, Mohit Kapoor, in Molecules to Medicine with mTOR, 2016. One articular cartilage function is to provide smooth and low-friction interaction between the bones of a joint. This so-called molecular marker technology (biomarkers) is intended to provide new means of assaying ongoing active processes in, Biology of Normal Joint and Evaluation of the Joint Including Clinical, Imaging, and Pathologic Evaluation, Melanie Fisher, ... Caroline N. Dealy, in, The Role of Subchondral Bone in Osteoarthritis, Johanne Martel-Pelletier, ... Jean-Pierre Pelletier, in, Postoperative Cartilage Repair Rehabilitation, Tissue Engineering and Regenerative Medicine: Applications, Arthroscopy: The Journal of Arthroscopic & Related Surgery. Articular cartilage serves a vital role in maintaining joint function by minimising friction and distributing load. Articular cartilage is devoid of blood vessels, nerves, and lymphatics cells. The mineralized matrix of the deep zone provides a gradual transition in mechanical stiffness of the cartilage tissue as it merges with the supporting underlying subchondral bone. Johanne Martel-Pelletier, ... Jean-Pierre Pelletier, in Osteoarthritis, 2007. The articular cartilage allows low-friction joint movement, absorbs the biomechanical forces, and stabilizes the joint. The main cell types in cartilage are chondrocytes, the ground substance is chondroitin sulfate, and the fibrous sheath is called perichondriu… Articular cartilage locations are found throughout the body. One of the mechanisms through which autophagy is suppressed in the articular chondrocytes is through increased mTOR signaling. Articular cartilage is a white elastic tissue that allows bones to glide smoothly against each other. Articular cartilage is the hyaline cartilage. Integrative multi-omics approaches provide a valuable tool to understand tissue behavior in response to mechanical injury insult and help to identify key pathways linking injury to tissue damage. Even a small defect caused by mechanical damage will fail to heal and degenerate over time, progressing to osteoarthritis (OA). The extracellular matrix of the middle zone is rich in proteoglycans, especially aggrecan. If a portion of ‘wet’ articular cartilage with all of its layers was separated into the most important individual elements, water would provide 65–80% of its weight, type II collagen fibrils would account for 10–20% (along with very small percentages of other collagen types), and 10–15% would be made up primarily of Aggrecan, but also other proteoglycans. The basic science of articular cartilage: structure, composition, and function. mTOR signaling is implicated in cell growth, proliferation, as well as its ability to negatively regulate autophagy—a cell survival and adaptation process. What is articular cartilage? Because cartilage does not heal itself well, doctors have developed surgical techniques to stimulate the growth of new cartilage. Cartilage is not innervated and therefore relies on diffusion to obtain nutrients. Cartilaginous joints (growth plates, the symphysis, the spine, and the ribs) have very little movement and no synovial membrane. We will also discuss the potential of mTOR as a therapeutic target in delaying or stopping the cartilage-degenerative process. From: Comprehensive Biomaterials II, 2017, Lily Jeng, ... Myron Spector, in Principles of Regenerative Medicine (Second Edition), 2011. In humans, vascular perfusion slowly declines until about the age of 70.37 However, this perfusion declines not only due to age but individually within joints and in load-bearing areas. The knee, with a wider range of motion, is considered to be a modified hinge joint. Functions of Cartilage Cartilage holds some bones together, for instance, rib cartilage. To reduce this friction, all articulating surfaces involved in movement are covered with a white, shiny, slippery layer called articular cartilage. 1 ). Recent studies suggest that the mammalian (or mechanistic) target of rapamycin (mTOR) is crucial for maintenance of articular cartilage homeostasis and could be a potential therapeutic target in delaying the degenerative process. 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