Lecture Notes: Synovial Joints

Overview of Synovial Joints

• Synovial joints are characterized by:
  • Bones separated by a fluid-filled joint cavity.
  • Freely movable (diarthrotic).
  • Commonly found between limbs.
• Types of synovial joints based on range of motion include:
  • Plane
  • Hinge
  • Pivot
  • Condylar
  • Saddle
  • Ball and Socket

Anatomy of a Synovial Joint

Components

• Articular Cartilage
  • Hyaline cartilage at ends of bones.
  • Thin layer (~1 mm thick) to prevent bone-on-bone contact.
• Joint (Synovial) Cavity
  • Small space filled with synovial fluid.
  • Surrounded by a joint capsule with two layers:
    • Outer Layer: Dense irregular connective tissue (fibrous layer).
    • Inner Layer: Synovial membrane made of loose connective tissue.
• Synovial Fluid
  • Derived from plasma, includes hyaluronic acid.
  • Acts as a lubricant, facilitating "weeping lubrication."
  • Contains phagocytic cells to remove debris/pathogens.

Reinforcing Structures

• Ligaments
  • Capsular (thickened part of fibrous layer), extracapsular, and intracapsular ligaments reinforce structure.
• Blood Vessels and Nerve Fibers
  • Vessels supply nutrients, nerve fibers monitor joint position, stretch, and pain.
• Fatty Pads
  • Provide extra cushioning in certain joints.
• Articular Discs/Menisci
  • Fibrocartilage that stabilizes joints and reduces wear, found in joints like the knee.

Associated Structures

• Bursa
  • Sacs filled with synovial fluid, lined by synovial membrane, reduce friction in high-friction areas.
  • Example: Subacromial bursa in the shoulder.
• Tendon Sheaths
  • Modified bursae wrapped around tendons to minimize friction.
  • Example: Tendon sheath around biceps brachii.

Stabilizing Factors of Synovial Joints

• Articulating Surfaces
  • Provide minor stability, especially in ball and socket joints.
• Ligaments
  • Number increases stability, but overstretching can reduce effectiveness.
• Muscle Tendons
  • Most important stabilizers due to muscle tone.
  • Keep tendons taut, reinforcing joints such as shoulders, knees, and foot arches.