Chapter 9 (1)

• Joint (or articulation) is any point where two bones meet, whether or not the bones are movable at that interface, meaning that it does not matter if the bones are movable or not.
• Arthrology is the science of joint structure, function, and dysfunction. Kinesiology is the study of musculoskeletal movement. It is a branch of biomechanics, that deals with a broad variety of movements and mechanical processes.
• Joint names are typically derived from the names of the bones involved (for example: radioulnar joint). Bone joints are classified according to how the bones are bound to each other.
• There are four major joint categories:– Bony joints. Fibrous joints. Cartilaginous joints. AND Synovial joints.
• A bony joint, or synostosis, is an immobile joint formed when the gap between two bones ossifies, and the bones become, in effect, a single bone. Examples: Left and right mandibular bones in infants, cranial sutures in the elderly, or the attachment of the first rib and sternum with old age. This can occur in either fibrous or cartilaginous joints.
• The fibrous joint, synarthrosis, or synarthrodial joint are adjacent bones that are bound by collagen fibers that emerge from one bone and penetrate into the other. There are three kinds of fibrous joints; Sutures. Gomphoses. AND Syndesmoses.
• Sutures are immobile or slightly mobile fibrous joints in which short collagen fibers bind the bones of the skull to each other. Sutures can be classified as; (1)Serrate: interlocking wavy lines, e.g. coronal, sagittal, and lambdoid sutures. (2)Lap (squamous): overlapping beveled edges, e.g. temporal and parietal bones. (3)Plane (butt): straight, non-overlapping edges, e.g. palatine processes of the maxillae.
• Gomphosis (fibrous joint) helps in the attachment of a tooth to its socket. It is held in place by fibrous periodontal ligaments which are collagen fibers that attach the tooth to the jawbone and allows the tooth to move a little under the stress of chewing. It allows the tooth to move as we chew because if the teeth don't move the pressure of our chewing will break them.
• A syndesmosis is a type of joint where two bones are held together by interosseous ligaments made of collagen fibers. An example of a very mobile syndesmosis is the interosseus membrane joining the radius to the ulna and allowing supination and pronation. An example of a less mobile syndesmosis is the joint between the tibia to the fibula.
• Cartilaginous joint, amphiarthrosis, or amphiarthrodial joint are two bones that are linked by cartilage. The two types of cartilaginous joints are synchondroses and symphyses.
• Synchrondrosis are bones joined by hyaline cartilage, e.g. Temporary joints in the epiphyseal plates in children that bind the epiphysis to the diaphysis. AND the first rib attachment to the sternum and other costal cartilages joined to the sternum by synovial joints.
• Symphysis are two bones joined by fibrocartilage, e.g. Pubic symphysis joins the right and left pubic bones with interpubic disc. AND Bodies of vertebrae are joined by intervertebral discs where there are only slight movements between adjacent vertebrae. The collective effect of all 23 discs gives the spine considerable flexibility.
• Synovial joint, diarthrosis, or diarthrodial joint are joints in which two bones are separated by a joint cavity. They are the most familiar type of joint, most are freely mobile, and they are the most structurally complex type of joint. They are also the most likely to develop painful dysfunctions. They are the most important joints for physical and occupational therapists, athletic coaches, nurses, and fitness trainers. Their mobility makes them very important to the quality of life.
• General Anatomy of Synovial Joints; (1)Articular cartilage which is a layer of hyaline cartilage that covers the facing surfaces of two bones, usually 2 or 3 mm thick. (2)The joint (articular) cavity separates articular surfaces. (3)The synovial fluid is the slippery lubricant in the joint cavity, it is rich in albumin and hyaluronic acid, gives it a viscous, slippery texture like raw egg whites, nourishes articular cartilage and removes waste, and makes the movement of synovial joints almost friction-free.
• General Anatomy of Synovial Joints; The joint (articular) capsule is the connective tissue that encloses the cavity and retains the fluid. The outer fibrous capsule is continuous with the periosteum of adjoining bones. The inner, cellular, synovial membrane is composed mainly of fibroblast-like cells that secrete synovial fluid and macrophages that remove debris from the joint cavity.
• General Anatomy of Synovial Joints; In a few synovial joints, the fibrocartilage grows inward from the joint capsule, i.e. the articular disc that forms a pad between articulating bones that cross the entire joint capsule. An example is found in the temporomandibular joint. The meniscus is a moon-shaped cartilage in the knee; in each knee, menisci extend inward from the left and right. These cartilages absorb shock and pressure, guide bones across each other, improve their fit together, and stabilize the joints, reducing the chance of dislocation.
• Accessory structures of the Synovial Joints; (1)A tendon is the strip of collagenous tissue attaching muscle to bone. (2) A ligament is a strip of collagenous tissue attaching one bone to another. (3) The bursa is a fibrous sac filled with synovial fluid, located between muscles, where tendons pass over bone, or between bone and skin. The bursa cushions muscles, helps tendons slide more easily over joints and modifies the direction of tendon pull. (4) A tendon sheath is an elongated cylindrical bursa wrapped around a tendon. It is found in the hand and the foot.
• Exercise warms synovial fluid and helps it become less viscous, and more easily absorbed by cartilage. The cartilage then swells and provides a more effective cushion. The warm-up period before vigorous exercise helps protect cartilage from undue wear and tear.
• Repetitive compression of nonvascular cartilage during exercise squeezes fluid and metabolic waste out of the cartilage. When weight is removed, cartilage absorbs synovial fluid like a sponge, taking in oxygen and nutrients to the chondrocytes. Without exercise, the cartilage deteriorates more rapidly from inadequate nutrition and waste removal.