Lecture Notes: Classification of Joints

Definition of a Joint

• Joint: A connection between two or more bones, bone and cartilage, or teeth and bone.

Classification of Joints

• Joints can be classified in two main ways:
  • Structurally: Based on the presence of a cavity and the type of connective tissue.
  • Functionally: Based on the degree of movement allowed.

Structural Classification

• Fibrous Joints:

  • Held together by fibrous connective tissue.
  • Examples:
    • Synarthrosis: Little or no movement (e.g., sutures in the skull, syndesmosis such as interosseous membranes between the radius/ulna and tibia/fibula, gomphosis for teeth).
    • Amphiarthrosis: Slight movement (e.g., intervertebral discs, pubic symphysis).

• Cartilaginous Joints:

  • Held together by cartilage; can transition to bone and lose mobility with age.
  • Types:
    • Synchondrosis/Synarthrosis: Joined by hyaline cartilage, immovable (e.g., epiphyseal plate, first sternocostal joint).
    • Symphysis: Secondary cartilaginous joint, fibrocartilage, allows slight movement (e.g., pubic symphysis).

• Synovial Joints:

  • Allow free movement between bones.
  • Features:
    • Covered with articular cartilage for protection.
    • Contains a synovial cavity.
    • Surrounded by accessory ligaments.
  • Examples: Hip, knee, shoulder, elbow.

Functional Classification

• Synarthroses: No movement.
  • Examples: Sutures, syndesmosis, gomphosis.
• Amphiarthrosis: Little movement.
  • Examples: Pubic symphysis, intervertebral discs.
• Diarthroses: Freely movable (synovial joints).
  • Examples: Hip, knee, shoulder, elbow.

Key Points

• The stability of a joint is inversely related to its mobility; more movable joints are less stable.
• Synovial joints are the most freely movable and least stable due to reliance on ligaments and tendons.