What are the six distinguishing features of a synovial joint?

The six distinguishing features of a synovial joint are articular cartilage, a joint (articular) cavity, an articular capsule, synovial fluid, reinforcing ligaments, and nerves and blood vessels.

Synovial joints are characterized by six structural features. Articular cartilage is a thin layer of glassy-smooth hyaline cartilage that covers the opposing bone surfaces and cushions them against compression. A joint (articular) cavity is a potential space unique to synovial joints that contains a small amount of synovial fluid. The articular capsule is a two-layered structure: a tough external fibrous layer continuous with the periostea strengthens the joint, while an inner synovial membrane lines the internal joint surfaces and secretes synovial fluid. Synovial fluid fills the joint cavity and free spaces within the capsule; it lubricates the articular cartilages, helps nourish the avascular cartilage through weeping lubrication, and contains phagocytic cells that remove debris. Reinforcing ligaments, which may be capsular, extracapsular, or intracapsular, strengthen the joint. Finally, synovial joints are richly supplied with sensory nerve fibers and blood vessels; the nerves monitor joint stretch and pain, and the vessels supply the synovial membrane with capillary beds that produce the filtrate forming synovial fluid.