The synovial tissue, which is found in all joints except the spinal discs, is composed of a synovial membrane and synovial fluid.
Synovial tissue is composed up of a synovial membrane and enclosed synovial fluid that that is a component of some of our weight-bearing joints. Synovial tissue is found between the carpals of the wrist, knee joint, radiocarpal (wrist) joint, and between the ulna and the humerus. Every joint, including the synovial joint, is held together by ligaments, which form a joint capsule. Joint capsules are usually found between two articulating bones and are the reason that they don't touch or rub together. This space between the adjacent bones forms a chamber - also known as a joint capsule. The joint capsule, or chamber, has a lining known as a synovium (synovial membrane). The synovial membrane lines the various surfaces in the joint, including the articular cartilage, in order to reduce friction among any bones or joint parts that move against one another. The synovial cavity also creates a sack (pocket) which is filled with synovial fluid. The synovial cavity is enclosed by the synovial membrane, and articulate cartilage to create a fully enclosed cavity of fluid.
The synovial lining (synovial membrane) produces this viscous fluid, and fills the synovial cavity with synovial fluid. This synovial fluid provides maximum protection for the joints when the patient is healthy, and may become inflamed when its enclosing membrane becomes torn due to injury, or when inflammation of the fluid changes its composition due to infection or systemic disease (rheumatoid arthritis).
This synovial fluid creates a soft cushion between bones, helping to create separation between the bones, and providing for a lubricating factor that would prevent the surface of bones from becoming worn down. The synovial membrane also creates nutrients that it secretes into the cartilage to maintain it and keep the cartilage healthy. The overall volume of fluid is very small, yet it provides for a remarkable amount of friction reduction due to its chemical properties. The actual amount of fluid in an adult knee is actually less than ½ a teaspoon. Most joints in the human body contain synovial fluid, enclosed by a synovial membrane. The only joints that do not are the discs in the spine.
In addition to providing for shock absorption and lubricating the joints, synovial fluid is also involved in the maintenance and metabolism of the joint. Since the majority of the joint is avascular (without blood vessels), it must be able to provide nutrients, deliver new healthy cells, remove old, non-functional cells and cell components, and deliver oxygen in other ways, In joints, these functions are performed by the synovial tissue and synovial fluid.
The ligaments of the joint hold the synovial joint together. Ligaments are thick strands of connective tissue that connect the bones of a joint to each other, without the bones actually coming in contact with one another. The anatomical unit that is composed of the synovial joint, ligaments, and articulating bones is known as the joint capsule. The collagen fibers that form the dense, tough ropes of ligaments have strong properties that enable them to resist tearing, yet also elastic properties to allow for movement flexibility.
Read here for more information about ligaments.