Joints and Their Classifications

Joints

• Joints are where two or more bones meet.
• Classified as fibrous, cartilaginous, or synovial based on structure and mobility.

Fibrous Joints (Synarthroses)

• Connected by fibrous tissue, permitting little or no movement.
• Examples:
  • Sutures of the skull (tight connections, often ossify with age)
  • Syndesmoses (e.g., distal tibiofibular joint, connected by ligaments)
  • Gomphoses (e.g., teeth in sockets)

Cartilaginous Joints (Amphiarthroses)

• Connected by cartilage, allowing some movement.
• Types:
  • Primary cartilaginous (synchondroses):
    • Connected by hyaline cartilage; usually temporary and ossify with age.
    • Examples: epiphyseal cartilages, first sternocostal joint
  • Secondary cartilaginous (symphyses):
    • Connected by fibrocartilage; permit limited movement.
    • Examples: intervertebral discs, pubic symphysis

Synovial Joints (Diarthroses)

• Freely movable joints.
• Structure:
  • Articular cartilage covers bone surfaces.
  • Joint cavity is enclosed by a fibrous capsule.
  • Synovial membrane lines the capsule, secreting synovial fluid.
  • Often have ligaments, menisci, or bursae.
• Types of Synovial Joints Based on Axes of Movement:

  • Uniaxial: Movements occur in one axis;

    • Hinge joints: flexion/extension (elbow)
    • Pivot joints: rotation (atlanto-axial joint)

  • Biaxial: Movements occur in two axes;

    • Ellipsoid/Condyloid joints: flexion/extension, abduction/adduction (wrist)
    • Saddle joints: flexion/extension, abduction/adduction, opposition (thumb)
    • Condylar joints: flexion/extension, abduction/adduction (modified ellipsoidal, knee)

  • Multiaxial: Movements occur in multiple axes;

    • Ball-and-socket joints: flexion/extension, abduction/adduction, rotation (hip, shoulder)

  • Plane/Gliding joints: Limited gliding movements (acromioclavicular joint)

• Ligaments provide additional support and stability.
• Extracapsular and intracapsular ligaments are also important structural factors.