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8.1B: Functional Classification of Joints

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  • Functional classification of joints is based on the type and degree of movement permitted.

    Learning Objectives

    • Describe the three functional categories of joints

    Key Points

    • Synarthrosis joints are immobile or have limited mobility and include fibrous joints.
    • Amphiarthrosis joints allow a small amount of mobility and include cartilaginous joints.
    • Diarthrosis joints are the freely movable synovial joints.
    • Synovial joints can also be classified as nonaxial, monoaxial, biaxial, and multiaxial.
    • The various movements permitted by synovial joints are abduction, adduction, extension, flexion, and rotation.

    Key Terms

    • fibrous joints: Fixed or immobile joints that are connected by dense, tough connective tissue that
      is rich in collagen fibers.
    • cartilaginous joints: Joints connected by fibrocartilage or hyaline cartilage. They allow more movement than fibrous joints but less than synovial joints.
    • gomphosis joints: Joints of very limited mobility. These are found at the articulation
      between teeth and the sockets of maxilla or mandible (dental-alveolar joint).

    Joints or articulations (connections between bones) can be classified in a number of ways. The primary classifications are structural and functional. Functional classification is based on the type and degree of movement permitted.

    Image of a skeleton and schematics of the different classes of synovial joints.Terms include pivot joint (between C1 and C2 vertebrae), ball and socket joint (hip joint), hinge joint (elbow), condyloid joint (between radius and carpal bones of wrist), plane joint (between tarsal bones), saddle joint (between trapezium carpal bone and first metacarpal bone).

    Types of Synovial Joints.jpg: Image of a skeleton and skematics of the different classes of synovial joints.

    Three Categories of Functional Joints

    • Synarthrosis: These types of joints are immobile or allow limited mobility. This category includes fibrous joints such as suture joints (found in the cranium) and gomphosis joints (found between teeth and sockets of the maxilla and mandible).
    • Amphiarthrosis: These joints allow a small amount of mobility. Most joints in this category
      include cartilaginous joints such as those found between vertebrae and the pubic symphysis.
    • Diarthrosis: These are the freely-movable synovial joints. Synovial joints are further classified based on the different types of movement they provide, including:
      • Plane joint
      • Ball and socket joint
      • Hinge joint
      • Pivot joint
      • Condyloid joint
      • Saddle joint

    Movement of Synovial Joints

    Joints can also be classified by the number of axes of movement they permit:

    • Nonaxial (gliding): Found between the proximal ends of the ulna and radius.
    • Monoaxial (uniaxial): Movement occurs in one plane. An example is the elbow joint.
    • Biaxial: Movement can occur in two planes. An example is the wrist.
    • Multiaxial: Includes the ball and socket joints. An example is the hip joint.

    The movements possible with synovial joints are:

    • Abduction: movement away from the body’s midline
    • Adduction: movement toward the body’s midline
    • Extension: straightening limbs at a joint
    • Flexion: bending the limbs at a joint
    • Rotation: a circular movement around a fixed point