Joint Types

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.
    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)

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.
    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.

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.

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