Synovial joints are the most common joints in the human body. They are movable and composed of bone, kept in place by ligaments, their entirety protected within a joint capsule covered by cartilage. A substance called synovial fluid is produced in the synovial joints. It prevents the friction caused by movement from wearing away the bones and cartilage, as well as nourishes the cartilage. The synovial joints are also called diarthroses.