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8.1A: Structural Classification of Joints

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  • Page ID
    7508
  • There are three structural classifications of joints: fibrous, cartilaginous, and synovial.

     

    LEARNING OBJECTIVES

     

    Describe the three structural categories of joints

     

    KEY TAKEAWAYS

    Key Points

     

    • The type
      and characteristics of a given joint determine the degree and type of movement.
    • Structural classification categorizes joints based on the type of
      tissue involved in their formations.
    • There are three structural
      classifications of joints: fibrous, cartilaginous, and synovial.
    • Of the three types of fibrous joints, syndesmoses are the most movable.
    • Cartilaginous
      joints allow more movement than fibrous joints
      but less than synovial joints.
    • Synovial joints ( diarthroses ) are the most movable joints of the body and contain synovial fluid.

     

    Key Terms

     

    • periosteum: A membrane that covers the outer surface of all bones.
    • manubrium: The broad upper part of the sternum.
    • synovial fluid: A viscous fluid found in the cavities of synovial
      joints that reduces friction between the articular cartilage during movement.

    A joint, also known as an articulation or articular surface, is a connection that occurs between bones in the skeletal system. Joints provide the means for movement. The type and characteristics of a given joint determines its degree and type of movement. Joints can be classified based on structure and function.

    Structural classification of joints categorizes them based on the type of tissue involved in formation. There are three structural classifications of joints: fibrous, cartilaginous, and synovial.

    Fibrous Joints

    Fibrous joints are connected by dense, tough connective tissue that is rich in collagen fibers. These fixed or immovable joints are typically interlocked with irregular edges. There are three types of fibrous joints.

    Sutures are the types of joint found in the cranium (skull). The bones are connected by Sharpey’s fibres. The nature of cranial sutures allows for some movement in the fetus. However, they become mostly immovable as the individual ages, although very slight movement allows some necessary cranial elasticity. These rigid joints are referred to as synarthrodial.

    Syndesmoses are found between long bones of the body, such as the radio-ulnar and tibio-fibular joints. These moveable fibrous joints are also termed amphiarthrodial. They have a lesser range of movement than synovial joints.

    Gomphosis is a type of joint found at the articulation between teeth and the sockets of the maxilla or mandible (dental-alveolar joint). The fibrous tissue that connects the tooth and socket is called the periodontal ligament.

    Image demonstrating the three types of fibrous joints and delineating structures including suture line, suture, dense fibrous connective tissue, ulna, radius, syndesmosis, antebrachial interosseous membrane, socket, gomphosis, root of tooth, and periodontal ligament.

    Fibrous joints: Image demonstrating the three types of fibrous joints. (a) Sutures (b) Syndesmosis  (c) Gomphosis.

    Cartilaginous Joints

    Cartilaginous joints are connected by fibrocartilage or hyaline cartilage. They allow more movement than fibrous joints but less than that of synovial joints. These types of joints are further subdivided into primary (synchondroses) and secondary (symphyses) cartilaginous joints. The epiphyseal (growth) plates are examples of synchondroses. Symphyses are found between the manubrium and sternum (manubriosternal joint), intervertebral discs, and the pubic symphysis.

    Image demonstration a synchondrosis joint (a) and a symphysis joint.

    Cartilaginous Joints: Image demonstrates a synchondrosis joint with epiphyseal plate (temporary hyaline cartilage joint) indicated (a) and a symphysis joint (b).

    This figure shows a synovial joint. The cavity between two bones contains the synovial fluid which lubricates the two joints.

     

    Synovial Joint: This diagram of a synovial joint delineates the articular cartilage, articular capsule, bone, synovial membrane, and joint cavity containing synovial fluid.

     

    Synovial Joints

     

    This is the most common and movable joint type in the body. These joints (also called diarthroses) have a synovial cavity. Their bones are connected by dense irregular connective tissue that forms an articular capsule surrounding the bones’ articulating surfaces.

    A synovial joint connects bones with a fibrous joint capsule that is continuous with the bones’ periosteum. This joint capsule constitutes the outer boundary of a synovial cavity and surrounds the bones’ articulating surfaces.

    Synovial cavities are filled with synovial fluid. The knees and elbows are examples of synovial joints.