Articulations (Joints)
Two articulation classification systems
Functional and Structural
Functional classification
- 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.
Structural classification
- 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.
- Cartilaginous, which are connected via cartilage.
Synovial
- Comprises an articular cavity enclosed in a deep synovial membrane and a superficial fibrous membrane. The synovial and fibrous membranes comprise the articular capsule.
- 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.
Clinical Correlation:
- 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.