Is healthy articular cartilage vascularized? Articular cartilage is the hyaline cartilage. Articular cartilage is the highly specialized connective tissue of diarthrodial joints. 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 image below shows the characteristic ball and socket shape of the prosthetic hip joint to the left, and an arthritic natural hip joint to the right. 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. Movement of the bones causes friction between the articulating surfaces. By using sensitive immunoassays such fragments can be quantified in synovial fluid or serum. 3. The articular cartilage allows low-friction joint movement, absorbs the biomechanical forces, and stabilizes the joint. The extracellular matrix of the middle zone is rich in proteoglycans, especially aggrecan. Cartilage is not innervated and therefore relies on diffusion to obtain nutrients. Very few chondrocytes are found in this layer. The unique structure of articular cartilage provides the intrinsic functional properties that enable the knee joint to withstand and resist excessive compressive and biomechanical loads, facilitating almost frictionless knee movement. Because cartilage does not heal itself well, doctors have developed surgical techniques to stimulate the growth of new 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. At the base, horizontal fibers are firmly adherent to the subchondral bone. Most importantly, it can delay or prevent the onset of arthritis. Kyle R. Flik, ... Brian J. Cole, in Clinical Sports Medicine, 2006. Articular Cartilage: A Brief Review of its Structure, Function, and Repair Wayne H. Akeson MD William Bugbee MD Key Points Few mechanical devices even remotely approach the durability and efficiency of cartilage. The term hyaline comes from the Greek word “hyalos,” which means glassy. Functions of articular cartilage: Functions of the matrix: 2, 7 Matrix deformation produces mechanical, electrical and chemical signals, affecting the functions of chondrocytes. cartilage exhibits stress-shielding of the solid matrix components due to its high water content, the incompressibility of water, and the structural organization of the proteoglycan and collagen molecules. 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]. However, it is generally much thicker in the central weight-bearing area. The upper portion of the middle zone contains randomly (isometrically) arranged collagen fibrils, and rounded chondrocytes that are sparsely but fairly evenly distributed. These sinusoids terminate in venous radicles forming a transverse sinus, perpendicular to the tiny venous branches. In the embryo, it provides support and is a precursor to bone. Chondrocytes in articular cartilage are surrounded by a narrow pericellular matrix (PCM) that is both biochemically and biomechanically distinct from the extracellular matrix (ECM) of the tissue. One of the most common orthopedic surgeries in elderly populations, a total hip replacement replaces hip joints where arthritis has worn away the articular cartilage, leading to loss of motion and pain. By continuing you agree to the use of cookies. The main function of the articular cartilage is to provide a smooth surface where the bones connect and touch. Articular cartilage damage most commonly occurs in the knee, but the elbow, wrist, ankle, shoulder, and hip joint can also be affected. Tiny vessels penetrate the cortical end plate and can invade the calcified cartilage zone up to the tidemark. This structure is at right angles to the underlying bone – an arrangement that provides the most resistance to compressive forces. It is deformable but elastic, and…. Examples are the proximal radioulnar joint, and the joint between the first and second cervical vertebrae. 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. In this chapter, we will discuss the most uptodate knowledge of mTOR in chondrocyte biology and articular cartilage homeostasis. Full-thickness defects induce mesenchymal chondroprogenitor cells to differentiate into repair tissue, but this is predominantly fibrous in nature and degenerates with time. We use cookies to help provide and enhance our service and tailor content and ads. 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. Unlike bone, it is easily cut by a sharp knife. The main cell types in cartilage are chondrocytes, the ground substance is chondroitin sulfate, and the fibrous sheath is called perichondriu… Medical definition of articular cartilage: cartilage that covers the articular surfaces of bones. One articular cartilage function is to provide smooth and low-friction interaction between the bones of a joint. Here, proteoglycans are more prevalent than in any of the other layers, while collagen fibrils are relatively disorganized in comparison to the layer above. They allow for movement in at least one axis. This causes it to heal very slowly. All diarthroidal joints, in which articular cartilage is found, have certain characteristics. Air-tent analogy with articular cartilage. 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 deep zone is divided by the tidemark into an upper hyaline cartilage portion that is continuous with the lower middle zone, and extends its linear arrangement of collagen fibrils and chondrocyte stacks; and a lower region which is calcified (mineralized). Thus, it should be possible to identify the activity of a process in the meniscus on the one hand and activity in cartilage on the other. The two bone surfaces are of different shapes. Download as PDF. A further function of articular cartilage is the ability for that part of the anatomy to move on one or more planes. In processes resulting in destruction of cartilage tissue, proteolytic enzymes degrade ECM proteins. The function of articular cartilage is dependent on the molecular composition of the extracellular matrix (ECM), which consists mainly of proteoglycans and collagen. introduced a cell-based therapy in which culture-expanded chondrocytes were transplanted into defects, raising the expectations of a breakthrough in repairing damaged articular cartilage (Brittberg et al., 1994). As with all types of cartilage, the absence of blood vessels and lymph vessels creates a very slow metabolic environment. Copyright © 2020 Elsevier B.V. or its licensors or contributors. It makes the area shock-proof. 2. The basic science of articular cartilage: structure, composition, and … One is rounded, the other hollowed. The knee, with a wider range of motion, is considered to be a modified hinge joint. 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. Cartilage function is more than structural, and has different functions in the life cycle. 1. The successful management of articular cartilage lesions is challenging for both the surgeon and patient. The composition, structure and functions of chondrocytes vary depending on the depth from the surface of the cartilage. Cartilage is a flexible connective tissue that differs from bone in several ways; it is avascular and its microarchitecture is less organized than bone. articular cartilage is 2 to 4 mm thick in length. Any pain is not caused by damage to the cartilage itself, as cartilaginous connective tissues are aneural (without a nerve network). Restoring articular cartilage can relieve pain and allow better function. Most important, articular cartilage has a limited capacity for intrinsic healing and repair. In support … Some of the fragments formed will no longer be retained in the tissue but are released to surrounding body fluids. Note the shiny hyaline layer in the humeroulnar joint of the elbow below. Articular (hyaline) Cartilage Components. 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. Dendrite: Definition, Function, and Malfunction, Cholinergic: Definition, Effects, and Function, Temporal Bone: Definition, Anatomy, and Fracture, Spongy Bone(Cancellous Bone): Definition & Function. Akihiro Nakamura, Mohit Kapoor, in Molecules to Medicine with mTOR, 2016. Articular cartilage can be damaged by injury or normal wear and tear. Even a small defect caused by mechanical damage will fail to heal and degenerate over time, progressing to osteoarthritis (OA). Articular cartilage derives its powers from its very organized and efficiently constructed microanatomy. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. URL: https://www.sciencedirect.com/science/article/pii/B9780123814227100422, URL: https://www.sciencedirect.com/science/article/pii/B978032302588150052X, URL: https://www.sciencedirect.com/science/article/pii/B978032309138100005X, URL: https://www.sciencedirect.com/science/article/pii/B978012386456704301X, URL: https://www.sciencedirect.com/science/article/pii/B9780128027332000190, URL: https://www.sciencedirect.com/science/article/pii/B9780128012383641193, URL: https://www.sciencedirect.com/science/article/pii/B9780323039291500070, URL: https://www.sciencedirect.com/science/article/pii/B9781437708783100245, URL: https://www.sciencedirect.com/science/article/pii/B9780128035818093048, Principles of Regenerative Medicine (Second Edition), In processes resulting in destruction of cartilage tissue, proteolytic enzymes degrade ECM proteins. M.I. Articular cartilage locations are found throughout the body. Joints between the bones, knee, elbow, and rib cage are some typical locations. The articular cartilage function is dependent on the molecular composition of the extracellular matrix (ECM). 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. Mechanical injury to the articular cartilage is a key risk factor in joint damage and predisposition to osteoarthritis. 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). So, you can find hyaline cartilage in the larynx and trachea in the throat portion of the body, and then also in all of the joints where the surfaces of bones are articulating each other. 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. From: Comprehensive Biomaterials II, 2017, Lily Jeng, ... Myron Spector, in Principles of Regenerative Medicine (Second Edition), 2011. The joint range of movement depends on the specific type of diarthroidal joint. It acts as a transition between cartilage and the underlying subchondral bone, allowing strong adhesion of the two different tissue types. As further advances are made in this exciting area of orthopedics, promising new methods will evolve to improve the treatment of articular cartilage lesions and narrow the use of total joint arthroplasty. While the intricate ultrastructure of articular cartilage is critical for proper function, these same properties create challenges for cartilage restoration. AC is composed of chondrocytes embedded in a hydrated and specialized extracellular matrix (ECM) that consists mostly of collagen type II (COL) and proteoglycan (PG) (Maroudas, 1979). When articulation is smooth, less stress is exercised on the cartilage surface and the tissue is more resistant to wear, in the same way oil added to a squeaky door hinge prevents the erosion of the touching surfaces. Cartilage has several functions in the human body: Reduces friction and acts as a cushion between joints and helps support our weight when we run, bend, and stretch. Nutrients are provided directly from the synovial fluid and not from the perichondrium, which is absent in articular cartilage. Johanne Martel-Pelletier, ... Jean-Pierre Pelletier, in Osteoarthritis, 2007. 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. The articular cartilage allows low-friction joint movement, absorbs the biomechanical forces, and stabilizes the joint. Patients are charged with the responsibility of committing to a strict postoperative regimen on which the success of the operation depends. 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. The remaining 30% of the articular cartilage is the deep zone. Articular cartilage serves a vital role in maintaining joint function by minimising friction and distributing load. To protect the smooth hyaline surface, all diarthroidal joints are covered by a synovial membrane filled with synovial fluid. 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). To reduce this friction, all articulating surfaces involved in movement are covered with a white, shiny, slippery layer called articular cartilage. 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. From: Comprehensive Biomaterials II, 2017. Also called rotary or trochoid joints, pivot joints have a circular range of motion on a single axis due to one bone surface having a ring-like shape. Additionally, each patient is unique and must be evaluated individually to determine the best course of treatment. Hypertrophic chondrocytes, which secrete mineralized matrix, are present in the deepest region of the deep zone, where it meets the subchondral bone. 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. Saddle joints have a slightly higher range of non-rotary movement than condyloid joints. Articular cartilage is devoid of blood vessels, nerves, and lymphatics cells. Unlike bone, it is easily cut by a sharp knife. What are the (4) functions of articular cartilage? It is deformable but elastic, and… There was no promising solution to this problem until Brittberg et al. Cell and matrix contents, as well as mechanical properties of cartilage, vary with depth from the superficial surface. The elbow is the best example of a simple hinge joint. Chondrocytes are rounder in this second layer. The middle-zone comprises 40%–60% of the articular cartilage. 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. Under the subchondral plate, the bony surfaces are composed of trabecular bone. This chapter outlines the architectural and compositional features of … Articular cartilage is devoid of blood vessels, lymphatics, and nerves and is subject to a harsh biomechanical environment. Articular cartilage is the hyaline cartilage. Inflammation and friction where the surfaces of two bones rub against each other cause pain and limited mobility. Articular cartilage is usually found in layers of between 2 and 4 mm thick. Articular Cartilage Function. Normal human articular cartilage is 2–4 mm thick (Shepherd and Seedhom, 1999); 10% of the tissue is cells (chondrocytes), 10%–25% is the extracellular matrix the chondrocytes synthesize (Eyre, 2002; Archer and Francis-West, 2003; Quinn et al., 2013; Martel-Pelletier et al., 2016), and 65%–80% of the tissue is water (Fox et al., 2009). Raleigh, ... R.L. Although bone is a harder tissue than articular cartilage it is actually a better shock absorber and hence the normal subchondral bone tissue protects articular cartilage against damage caused by excessive loads. The cartilage provides a smooth surface that facilitates easy movement. 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 The air-tent system requires a pump that must be constantly operating to maintain inflation of the tent because of leaks in the fabric. The subchondral bone plate possesses an irregular surface to which the articular cartilage is keyed in. 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). This itself is a result of its isolation from the systemic regulation, and lack of blood vessels and nerve supply (Mankin, 1982). Articular cartilage has a limited capacity for self-regeneration after injury. 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