This class includes majority of the joints in the body. In a diarthrodial joint the ends of the bones are free to move in relation to each other because there is no cartilaginous tissue connects the adjacent bony surfaces. However the bone ends are indirectly connected to each other by joint capsule that covers and encloses the joint.
All synovial joints have following features
1. A joint capsule formed by fibrous tissue
2. A joint cavity enclosed by a joint capsule
3. Inner surface of the capsule is lined by synovial membrane
4. Synovial fluid which forms a thin film over the joint surfaces
5. Hyaline cartilage covering the joint surface
Additionally the synovial joints may have accessory structures. The joints may be divided, completely or incompletely, by an articular disk or meniscus or labrum along with fat pads the periphery of which is continuous with the fibrous capsule while its free surfaces are covered by synovial membrane. The joints may also have tendons and ligaments within the joint capsule or immediately adjacent to the joint. Menisci or disks and synovial fluid help to prevent excessive compression of opposing joint surfaces. Ligaments and tendons assist in guiding motion and also have an important role in keeping joint surfaces together. Joint surfaces are checked by active tension in muscles and passive tension of the ligaments.
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