Two articulation classification systems
Functional and Structural
- Determined by the degree of movement permitted by the joint. An inverse relationship exists between joint mobility and stability.
The functional classification types are:
- Synarthrosis joints, which are immovable and stable.
- Amphiarthrosis joints, which are slightly moveable and slightly stable.
- Diarthrosis, which are freely moveable and very unstable.
- Determined by the joint’s connective tissue type and whether there is a cavity within the joint.
The structural classification types are:
- Fibrous joints, which are connected by fibrous connective tissue.
Three subtypes of fibrous joints:
Syndemosis (as between the bones of the forearm)
Suture (as between the bones of the skull)
Gomphosis (as between the teeth and the bones of the jaws)
- Cartilaginous, which are connected via cartilage.
Two subtypes of cartilaginous joints:
Symphysis joints (joined via a fibrocartilage pad, as the two pubic bones)
Synchondrosis joints (joined by hyaline cartilage, as between the ribs and the sternum)
- Comprises an articular cavity enclosed in a deep synovial membrane and a superficial fibrous membrane. The synovial and fibrous membranes comprise the articular capsule.
There are several subtypes of synovial joints:
- Gliding joints occur where flat surfaces meet to allow sliding and twisting. The wrist bones, or carpals, are joined by gliding joints.
- Pivot joints form where a round projection fits inside a ring to allow rotation. The first and second cervical vertebrae articulate via a pivot joint.
- Condylar joints occur where one bone fits into an oval-shaped depression in another bone, such as where the radius cradles the carpals.
- Saddle joints occur when the saddle-shaped region of one bone articulates with a depression on another bone, such as where the carpal and first metacarpal (the thumb) meet.
- Ball-and-socket joints form where a ball-like process fits inside a cup-like depression, which allows maximum freedom of motion, such as between the head of the humerus and the glenoid cavity of the scapula.
- Synovitis is a painful inflammatory condition of the synovial membrane that commonly occurs in rheumatologic conditions such as rheumatoid arthritis, lupus, gout, or simply by overuse injury.