Articulations
An articulation is a joint, or a functional junction between bones,
Classified by movement
- Immovable joints
are called synarthroses. The bones are separated by a thin layer of fibrous connective tissue. Types of synarthroses include : sutures (originally fontanels) and gomphoses (peg-in-socket)
- Slightly movable joints
are called amphiarthroses. They are held together by disks of fibrocartilage or ligaments. Symphyses are found between vertebrae and in the pubic bone (the symphysis pubis).
- Freely movable joints
are called diarthroses and are the most complex of the joints. Due to the presence of a synovial cavity, they are also called synovial joints. Most joints are in this category.
Classified by structure
- Fibrous joints
have no joint cavity, and the amount of movement depends on the length of the fibers connecting the joints. Sutures (synostoses), gomphoses and syndesmoses are types of fibrous joints.
- Cartilaginous joints
have a cartilage union between the articulating bones. Examples of cartlaginous joints are synchrondroses and symphyses.
- Synovial joints
are always freely movable and have a synovial or joint cavity. Most of the joints of the body fall into this category.
- General synovial structure :
- Articular cartilage covering the epiphyses of the articulating bones
- Joint cavity filled with synovial fluid
- Articular capsule around the joint cavity. The outer layer of the capsule, the fibrous capsule, is continuous with the periostea of the articulating bones
- Synovial membrane lining the fibrous capsule
- Synovial fluid, composed of much hyaluronic acid, is found in the joint cavity and also within the articular cartilage. It is viscous, but thins as it warms.
- Bursa are flattened sacs of synovial fluid that are found in areas of high friction. More (false) bursa can develop if necessary.
- Types of synovial joints
- Ball and socket
- Ellipsoid (condyloid)
- Gliding (sliding, plane)
- Saddle
- Hinge
- Pivot
- Types of synovial joint movement
- Flexion/extension
- Adduction/abduction
- Circumduction
- Rotation
- Specialized movement
- Supination/pronation (forearm)
- Inversion/eversion (ankle)
- Protraction/retraction (jaw)
- Elevation/depression (jaw and shoulder)
- Opposition (thumb)