Structural Classification of Joints

• The structural classification of joints is based on the material that binds the bones together and whether or not a joint cavity is present.

There are three primary structural classification of joints:

1) Fibrous Joints

• These joints are connected by dense connective tissue, primarily composed of collagen.
• They do not have a joint cavity.
• Types:
  • Sutures: Found between the bones of the skull. These joints are immovable (synarthrosis).
  • Syndesmoses: Bones are connected by a ligament or an interosseous membrane, allowing for very limited movement. Example: the distal connection between the tibia and fibula.
  • Gomphoses: A type of joint where a peg fits into a socket, such as the connection between a tooth and its socket in the jawbone (alveolar socket).

2) Cartilaginous Joints

• In these joints, bones are connected entirely by cartilage (either hyaline or fibrocartilage).
• They also lack a joint cavity.
• Types:
  • Synchondroses: Bones are united by hyaline cartilage. Most are temporary joints that eventually ossify. Example: the epiphyseal plates in long bones during growth.
  • Symphyses: Bones are united by fibrocartilage. These joints allow for slight movement (amphiarthrosis). Example: the pubic symphysis and intervertebral discs.

3) Synovial Joints

• These joints have a fluid-filled joint cavity, surrounded by a joint capsule, and allow for a wide range of movements.
• Components:
  • Articular Cartilage: Covers the ends of bones, reducing friction and absorbing shock.
  • Joint (Synovial) Cavity: The space between the bones, filled with synovial fluid.
  • Articular Capsule: A two-layered structure that encloses the joint. The outer layer is fibrous, while the inner layer (synovial membrane) secretes synovial fluid.
  • Synovial Fluid: Lubricates the joint, nourishes the articular cartilage, and acts as a shock absorber.
  • Reinforcing Ligaments: Strengthen and support the joint.
  • Nerves and Blood Vessels: Provide the joint with sensory input and nutrients.

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