Chapter8-Joints%28Part+A%29-Belmonte

Joints: Part A

Introduction to Joints

  • Articulation: A site where two or more bones meet.
  • Classifications of Joints:
    • Functional Classification: Based on the amount of movement allowed by the joint.
    • Synarthroses: Immovable joints.
    • Amphiarthroses: Slightly movable joints.
    • Diarthroses: Freely movable joints.
    • Structural Classification: Based on the material binding the bones together and the presence/absence of a joint cavity.
    • Fibrous Joints: Bones joined by dense fibrous connective tissue, no joint cavity.
    • Cartilaginous Joints: Bones united by cartilage, no joint cavity.
    • Synovial Joints: Bones separated by a fluid-filled joint cavity.

Structural Classification of Joints

  1. Fibrous Joints:

    • Characteristics:
      • Bones joined by dense fibrous connective tissue.
      • No joint cavity.
      • Usually synarthrotic (immovable) depending on the connective tissue fiber length.
    • Types:
      • Sutures:
      • Rigid, interlocking joints.
      • Found only in the skull; designed for brain protection.
      • Contains short connective tissue fibers to allow growth in youth; ossifies in middle age.
      • Syndesmoses:
      • Bones connected by ligaments; fiber length varies.
        • Example: Inferior tibiofibular joint (little to no movement) vs. interosseous membrane connecting radius and ulna (more movement).
      • Gomphoses:
      • Peg-in-socket joints, such as teeth in alveolar sockets, connected by periodontal ligament.

  2. Cartilaginous Joints:

    • Characteristics:
      • Bones united by cartilage.
      • No joint cavity.
      • Generally not highly movable.
    • Types:
      • Synchondroses:
      • Temporary hyaline cartilage joints that become synostoses post plate closure, e.g., epiphyseal plate joints.
      • Cartilage between the 1st rib and the manubrium of the sternum.
      • Symphyses:
      • Bones united by fibrocartilage, with hyaline cartilage present as articular cartilage, allowing for strong and flexible amphiarthroses.

  3. Synovial Joints:

    • Characteristics:
      • Bones separated by a fluid-filled joint cavity.
      • All are diarthrotic (freely movable).
      • Includes most limb joints and joints in the body.
    • Examples: Various joints listed in the tables detailing structural and functional characteristics.

Synovial Joints: Structure and Features

  • Distinguishing Features of Synovial Joints:
    1. Articular Cartilage: Hyaline cartilage that prevents crushing of bone ends.
    2. Joint (Synovial) Cavity: A small fluid-filled potential space.
    3. Articular (Joint) Capsule: Two layers:
    • External Fibrous Layer: Dense irregular connective tissue.
    • Inner Synovial Membrane: Loose connective tissue that makes synovial fluid.
    1. Synovial Fluid: A viscous, slippery filtrate of plasma and hyaluronic acid that lubricates and nourishes articular cartilage, containing phagocytic cells to remove microbes and debris.
    2. Types of Reinforcing Ligaments:
    • Capsular: Thickened parts of the fibrous layer.
    • Extracapsular: Located outside the capsule.
    • Intracapsular: Located deep to the capsule and covered by synovial membrane.
    1. Nerves and Blood Vessels: Nerve fibers detect pain and monitor joint position/stretch; capillary beds supply filtrate for synovial fluid.

Additional Features of Synovial Joints

  • Fatty Pads: Provide cushioning between fibrous layer and synovial membrane or bone.
  • Articular Discs (Menisci): Fibrocartilage structures that improve the "fit" of bone ends, stabilize the joint, and reduce wear and tear.
  • Bursae: Sacs lined with synovial membrane containing synovial fluid to reduce friction between structures such as ligaments and tendons.
  • Tendon Sheaths: Specialized bursae wrapping around tendons subjected to friction.

Joint Stability

  • Factors Stabilizing Synovial Joints:
    1. Shapes of Articular Surfaces: Play a minor role in stabilization