The Anatomy of Joints Related to Function
Verna Wright, Eric L. Radin in Mechanics of Human Joints, 2020
All freely movable joints are synovial (although not all synovial joints are freely mobile). The components of a typical synovial joint are illustrated in Figure 1D. As described in the anatomy texts, an individual synovial joint comprises those articular surfaces and structures enclosed within a single joint capsule (plus those extracapsular ligaments biomechanically associated with it). Such a definition has its logic in descriptive morphology and clearly has its uses—implicit in the clinical examination, pathology, and treatment of rheumatological disease, for instance. However, classification based entirely upon descriptive morphology is often not at all helpful in understanding biomechanics and locomotor function. Here it is necessary to define the functional units, which may be merely part of a single joint or may comprise a group of joints that together have an integral function.
Bone, Muscle, and Tooth
Pritam S. Sahota, James A. Popp, Jerry F. Hardisty, Chirukandath Gopinath, Page R. Bouchard in Toxicologic Pathology, 2018
A synovial joint consists of a joint cavity lined by synovial cells, the underlying fibrous joint capsule, the articular cartilage, and ligaments. Synovial cells are often one to three cell layers thick and are supported by variable amounts of fibrous connective tissue and adipose tissue. In routine toxicity studies with standard sectioning, only limited amounts of synovium may be present. If changes in joints are anticipated, standard trimming and embedding measures will need to be modified to ensure that the joints are thoroughly examined. Hyaline cartilage is present not only on the articular joints but in the physis and larynx as well. Healthy articular cartilage is a firm yet pliable tissue composed of large amounts of extracellular matrix with relatively few cells. Chondrocytes are located within well-defined lacunae and, in the articular cartilage, occur in a series of four layers. Near the surface is a zone of oval or elongate chondrocytes and collagen fibers. In the intermediate transitional zone, the cells are round to oval, and the collagen forms an open meshwork. The deeper radiate zone contains large, round chondrocytes, which may be arranged in short columns. The deepest zone is the mineralized zone, which is adjacent to the subchondral bone. A distinct basophilic tidewater mark separates the mineralized zone from the radiate zone. Water is a large component by weight of hyaline articular cartilage, and Type II and Type IX collagen, along with various proteoglycans, compromise much of the matrix.
Articular Cartilage
Manoj Ramachandran, Tom Nunn in Basic Orthopaedic Sciences, 2018
Boundary lubrication involves a monolayer of lubricant molecule (probably the glycoprotein lubricin) adsorbed on each surface (boundary) of the joint. This prevents direct articular contact and is most important at rest or under load. In fluid-film lubrication, a thin layer of fluid increases the separation of the two surfaces. The following methods are described: Hydrodynamic lubrication: the two surfaces are at an angle to each other. The viscosity in the resulting wedge of fluid separates the two surfaces.Squeeze-film lubrication: the two surfaces are parallel and move perpendicularly to each other. The viscosity of the incompressible fluid maintains the lubrication. High loads can be carried for short lengths of time. As the layer of fluid lubricant is forced out, it becomes thinner and the joint surfaces come into contact, but they are still protected by the lubricin.Elastohydrodynamic lubrication: this occurs as speed increases and is similar to squeeze film, but the yielding articular surface creates a larger surface area when compressed by the fluid. There is less dissipation of the fluid-film, and therefore the load is sustained for a longer period. This is the predominant lubrication mechanism in synovial joints during dynamic joint function.
Advances in stem cell therapy for cartilage regeneration in osteoarthritis
Published in Expert Opinion on Biological Therapy, 2018
Leire Iturriaga, Raquel Hernáez-Moya, Itsasne Erezuma, Alireza Dolatshahi-Pirouz, Gorka Orive
Synovial joint is a complex biological organ composed mainly of articular cartilage or hyaline cartilage, synovial fluid, synovium, ligaments, subchondral bone, and periarticular muscles [20]. Joints are composed of hyaline cartilage, which firstly permits proper and correct functioning of the skeleton, enabling the body to endure shocks and loads experienced during daily activities, and secondly provides the skeletal system with an almost frictionless movement to prevent bone deterioration. Furthermore, it is an avascular tissue located between the synovium and the subchondral bone, which are two highly vascularized and innervated tissues endowed with chemoreceptors and mechanoreceptors [21]. The hyaline cartilage is highly durable and resistant to shear forces and compression due to the movement created in the articular joint, thus, providing smooth frictionless surface [21]. When the integrity of this tissue is compromised by disease or trauma, the quality of life could be extremely deteriorated and limited resulting in pain and restricting mobility and autonomy.
Drug delivery targets and systems for targeted treatment of rheumatoid arthritis
Published in Journal of Drug Targeting, 2018
As shown in Figure 1, the synovial joint is composed of two articulating bones which are capped by avascular cartilages. To maintain its structural integrity, the joint is enclosed by a fibrous capsule and accessory ligaments. Within this structure lies a thin sheet of tissue called synovium (also known as synovial membrane) [6–8]. The synovium generates the synovial fluid (SF), which acts as a lubricant in the joint cavity and supplies with oxygen and nutrients to the cartilage via its rich microcirculation. In RA, a plethora of inflammatory cells infiltrate the synovium and most frequently found cell types include T cells, dendritic cells, macrophages, fibroblasts, mast cells, neutrophils and B cells. The endothelial cells express adhesion molecules that also promote the recruitment of these inflammatory cells into the joint. The activated inflammatory cells provoke the release of pro-inflammatory cytokines, including interleukins (ILs) and tumour necrosis factors (TNFs), as well as the secretion of matrix metallproteinases and prostaglands. The cytokines further stimulate the recruitment of the inflammatory cells from blood to the rheumatoid joint, resulting in the inflammation of the synovial tissues. By contrast, the matrix metalloproteinases and prostaglands secreted into the synovial fluid lead to the degradation of cartilage and bones. In addition, the activated inflammatory cells, as well as their products, can also stimulate the angiogenesis within the tissue. As a consequence, the synovial lining in RA joints becomes hypertrophic, with an increased synovial fluid volume, as well as acidosis and hypoxia [9].
Compressive stress relaxation behavior of articular cartilage and its effects on fluid pressure and solid displacement due to non-Newtonian flow
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
In the mammalian musculoskeletal system, an essential biological activity is a locomotion which is possible because the body is capable of moving with diarthrodial joints, e.g. ankle, knee, hip, etc. Simon et al. (1981) showed with experimental results that during normal gait, these joints transmit very heavy loads, one to four times body weight. Articular cartilage is a smooth layer of soft white tissue, which covers the bony ends in diarthrodial and synovial joints. Cartilage provides the joints with mechanical functions such as shock absorption, load-bearing, and wears resistance for seven or eight decades (Mankin 1982). These functional biomechanical characteristics are due to the multiphasic nature of this tissue (Linn and Sokoloff 1965; Mankin and Thrasher 1975; Maroudas 1979; Mow et al. 1980; Lai et al. 1991; Mow and Huiskes 2005).