Joints

Structural Classification of Joints

  • Fibrous Joints:
    • Joined by fibrous connective tissue, lacking a joint cavity.
    • Types:
      • Sutures: Rigid, interlocking joints (e.g., skull).
      • Syndesmoses: Bones connected by ligaments (e.g., tibia-fibula).
      • Gomphoses: Peg-in-socket joints (e.g., teeth in mandible/maxillae).
  • Cartilaginous Joints:
    • Bones joined by cartilage, lacking a joint cavity.
    • Types:
      • Synchondroses: Bones united by hyaline cartilage (e.g., epiphyseal plate joints).
      • Symphyses: Bones connected by fibrocartilage (e.g., intervertebral joints, pubic symphysis).
  • Synovial Joints:
    • Articulating bones separated by a fluid-containing joint cavity.
    • Features: articular cartilage, joint cavity, articular capsule, synovial fluid, reinforcing ligaments, nerves, and blood vessels.
    • Types: plane, hinge, pivot, condylar, saddle, and ball-and-socket.

Functional Classification of Joints

  • Synarthroses: Immovable joints held together by fibrous tissue.
  • Amphiarthroses: Slightly movable joints connected by cartilage.
  • Diarthroses: Freely movable joints (synovial joints).

Synovial Joint Features

  • Articular (Hyaline) Cartilage: Covers bone ends, absorbs compression.
  • Joint Cavity: Contains synovial fluid.
  • Articular (Joint) Capsule: Two-layered capsule enclosing joint surfaces.
    • External fibrous layer (dense irregular connective tissue).
    • Inner synovial membrane (produces synovial fluid).
  • Synovial Fluid: Lubricates and nourishes cartilage; viscous due to hyaluronic acid.
  • Reinforcing Ligaments: Strengthen and reinforce joints; capsular, extracapsular, or intracapsular.
  • Nerves and Blood Vessels: Sensory nerve fibers detect pain, joint position, etc. Blood vessels in synovial membrane.
  • Other Components:
    • Bursae: reduce friction.
    • Tendon Sheaths: protect tendons.
    • Fat Pads: cushioning.
    • Menisci (Articular Discs): improve fit and minimize wear.

Factors Influencing Synovial Joint Stability

  • Shape of articular surface
  • Ligament number and location
  • Muscle tone

Types of Synovial Joints

  • Plane Joints
  • Hinge Joints
  • Pivot Joints
  • Condyloid Joints
  • Saddle Joints
  • Ball and Socket Joints

Movements Allowed by Synovial Joints

  • Nonaxial: slipping movements only
  • Uniaxial: movement in one plane
  • Biaxial: movement in two planes
  • Multiaxial: movement in or around all three planes

Three general types of movements

  • Gliding
  • Angular Movements
  • Rotation

Special Movements

  • Supination and Pronation
  • Dorsiflexion and Plantar flexion
  • Inversion and Eversion
  • Protraction and Retraction
  • Elevation and Depression
  • Opposition

Joint Aging

  • Advancing age and overuse take a toll, especially on weight-bearing joints.
  • Excessive demands from sports increase the likelihood of injuries.
  • Extended inactivity or immobilization can be equally damaging.
  • Adhesions may form, reducing the range of motion.
  • Bone spurs may grow along joint edges.
  • Immobilization reduces synovial fluid movement, impairing cartilage nourishment.