In: Anatomy and Physiology
Articular Cartilage: Articular cartilage is the smooth, white tissue that covers the ends of bones where they come together to form joints. Healthy cartilage in our joints makes it easier to move. It allows the bones to glide over each other with very little friction.Articular cartilage is hyaline cartilage and is 2 to 4 mm thick. Unlike most tissues, articular cartilage does not have blood vessels, nerves, or lymphatics. It is composed of a dense extracellular matrix (ECM) with a sparse distribution of highly specialized cells called chondrocytes.
1) Arrangement of chondrocytes and collagen fibers in the middle zone of Articular Cartilage: The middle zone represents 40% to 60% of the total cartilage volume, and it contains proteoglycans and thicker collagen fibrils. In this layer, the collagen is organized obliquely, and the chondrocytes are spherical and at low density. ... Of note, the collagen fibrils are arranged perpendicular to the articular cartilage.Cartilage and Bone are specialised forms of connective tissue. They are both made up of cells embedded in an extracellular matrix. It is the nature of the matrix that defines the properties of these connective tissues. Cartilage is thin, avascular, flexible and resistant to compressive forces.
Collagen of articular cartilage. Eyre D(1). The extracellular framework and two-thirds of the dry mass of adult articular cartilage are polymeric collagen. Type II collagen is the principal molecular component in mammals, but collagens III, VI, IX, X, XI, XII and XIV all contribute to the mature matrix.Osteoarthritis—the most common type of arthritis—is a result of degenerated articular cartilage, causing pain, swelling, and reduced motion. While it can occur in any joint, one in two adults will develop symptoms of knee osteoarthritis during their lives, according to The Arthritis Foundation.
The chondrocytes are typically arranged in columnar orientation, parallel to the collagen fibers and perpendicular to the joint line. ... The calcified layer plays an integral role in securing the cartilage to bone, by anchoring the collagen fibrils of the deep zone to subchondral bone.Chondrocytes, or chondrocytes in lacunae, are cells found in cartilage connective tissue. They are the only cells located in cartilage. They produce and maintain the cartilage matrix, which is a type of lake in which the chondrocytes swim.
collagen fibrils are arranged perpendicular to the articular cartilage. The calcified layer plays an integral role in securing the cartilage to bone, by anchoring the collagen fibrils of the deep zone to subchondral bone. In this zone, the cell population is scarce and chondrocytes are hypertrophic.
2) Collagen fibers stronger in tension than compression: Generally, macroscale tensile strength of collagen is provided by tight packing of collagen molecules into bundles via hydrophobic interactions between molecules that can be cross-linked together by enzymes like lysyl oxidase to further enhance tensile strength.Collagen fiber is made from fibrous protein subunits linked together to form a long and straight fiber. Collagen fibers, while flexible, have great tensile strength, resist stretching, and give ligaments and tendons their characteristic resilience and strength.Collagen is a type of protein fiber found abundantly throughout our body. It provides strength and cushioning to many different areas of the body, including the skin. More specifically, collagen is found in our various types of connective tissues such as cartilage, tendons, bones, and ligaments.The smallest building blocks of collagen, called tropocollagen molecules, are five to ten times stronger than steel, while sustaining enormous tensile strains of up to fifty percent before fracture occurs. In comparison, steel typically sustains only small strains of a few percent before it breaks.
Collagen fibres are the main tension resistant elements in connective tissues. Their presence in articular cartilage suggests that tensile stresses are present, even though the tissue is loaded predominantly in compression perpendicular to the articular surface.
3) The termination of creep in the biphasic creep response of articular cartilage : Biphasic creep and stress relaxation of articular cartilage in compression. Articular cartilage is a biphasic material composed of a solid matrix phase ( ~ 20 percent of the total tissue mass by weight) and an interstitial fluid phase ( ~ 80 percent).
Articular cartilage also exhibits a creep and stress-relaxation response. When a constant compressive stress is applied to the tissue, its deformation increases with time, and it will deform or creep until an equilibrium value is reached.
4) The nonlinear permeability of articular cartilage: The fluid flow is in turn governed by the permeability of the tissue and the loading imposed upon its surface. But for articular cartilage, the permeability depends nonlinearly on the strain; k = ko exp (Me). Here, M is the nonlinear flow-limiting parameter and e is the dilatation.
The compressive viscoelastic behavior of articular cartilage, a fiber-reinforced, porous, permeable solid matrix filled with water, is predominately governed by the flow of the interstitial water within the tissue and its exudation across the articular surface. The fluid flow is in turn governed by the permeability of the tissue and the loading imposed upon its surface. But for articular cartilage, the permeability depends nonlinearly on the strain; k = ko exp (Me). Here, M is the nonlinear flow-limiting parameter and e is the dilatation.
5. The ability of articular cartilage to withstand an enormous range of loading conditions throughout our lifetime with minimal wear:
Articular cartilage is a thin layer of specialized connective tissue with unique viscoelastic properties. Its principal function is to provide a smooth, lubricated surface for low friction articulation and to facilitate the transmission of loads to the underlying subchondral bone.
Broadly taken, there are five major types of articular cartilage repair:
Articular cartilage does not usually regenerate (the process of repair by formation of the same type of tissue) after injury or disease leading to loss of tissue and formation of a defect. ... Several surgical techniques have been developed in the effort to repair articular cartilage defects.