Articulations

I. Classification of Joints Diagram

• Structural classification is based on material binding bones together and presence/absence of a cavity
  • Types of joints: Fibrous, Cartilaginous, Synovial.
    
• Functional classification is based on extent of movement:
  • Synarthroses - immovable joints (e.g. sternocostal, tibiofibular)
  • Amphiarthroses - slightly movable (e.g. vertebral bodies, pubic bones)
  • Diarthroses - freely movable (most appendicular)

II. Fibrous Joints (fibrous tissue, no cavity)

• Few amphiarthrotic, mostly synarthrotic
• Three types: sutures, syndesmoses, gomphoses
  
  • Sutures - e.g. skull, interdigitating articulating bone; sutures contain dense fibrous connective tissue until adulthood when they ossify (synostoses), becoming bony junctions.
  • Syndesmoses - bones connected by a filamentous sheet or cord (ligament or interosseous membrane); fibers are longer than in sutures but are only slightly more resilient, therefore still synarthrotic (e.g. tibiofibular joint, distal ends).
  • Gomphoses - articulation of tooth with bony alveolar socket (fibrous connection = periodontal ligament).

III. Cartilaginous Joints (articulating bones united by cartilage)

• Lack a joint cavity
• Two types: synchondroses and symphyses
  
  • Synchondroses - hyaline cartilage unites bones at a synchondrosis which are usually temporary joints (sites of bone growth); cartilage is replaced by bone (become synostotic); e.g. synarthrotic epiphyseal plate and manubrium/first rib & functionally amphiarthrotic ribs 2-10.
  • Symphyses - articular surfaces of bones covered by hyaline cartilage fused to an intervening pad or plate; compressible, resilient, and functionally amphiarthrotic; e.g. pubic symphysis (junction of pubic bones) and intervertebral discs.

IV. Synovial Joints (articular bones separated by a fluid-filled joint cavity) Diagram

• Joints of limbs, diarthrotic
• Five distinct features:
  1. Articular cartilage (hyaline)
  2. Joint cavity
  3. Articular capsule, containing:
     • fibrous capsule (external)
     • synovial membrane (internal)
  4. Synovial fluid
  5. Reinforcing ligaments
     • intrinsic - parallel bundles of fibers within fibrous capsule
     • extracapsular - extend bone to bone outside capsule
     • intracapsular - located inside synovial cavity
       
• Some synovial joints contain fatty pads between fibrous capsules and synovial membrane (egs knee and hip joint); others have articular discs (menisci) which are fibrocartilaginous discs extending inward from articular capsule and divide synovial cavity into two.
  
• Synovial joints have supportive structures called bursae. DIAGRAM These structures are flattened sacs lined with synovial membrane and contain a thin film of synovial fluid. Bursae are located where ligaments, muscles, and tendons overlie and rub against bone. Elongated bursae wrapping around tendons are referred to as tendon sheaths.
  
• Movements by synovial joints:
  
  • Axis of motion:
    • Nonaxial - slipping movements
    • Uniaxial - movement in one plane; phalanges, radius/ulna, femur/tibia
    • Biaxial - movement in two planes; occipital bone/atlas
    • Multiaxial - movement in three planes; scapula/humerus, and coxal bone/femur
  • Type of motion:
    • Gliding - bones displaced in relation to one another, e.g. intercarpal, intertarsal, and intervertebral joints
    • Angular - changing the angle between two bones, egs....
    • Flexion (bending, decreasing the angle)
    • Extension (stretching, increasing the angle)
    • Abduction (move away)
    • Adduction (move toward)
    • Circumduction (draw around, conical shape)
    • Rotation - turning movement of a bone around its own axis (e.g. atlas and axis of vertebrae).
      
• Types of synovial joints Diagram
  • Gliding - intercarpal and intertarsal
  • Hinge - elbow
  • Pivot - head of radius in radial norch
  • Condyloid - metacarpophalangeal
  • Saddle - carpometacarpal
  • Ball-and-socket - shoulder

V. Clinical Terms

• Sprain - stretching/tearing of a ligament
• Dislocation - (luxation), bones forced out of their normal position
• Bursitis - inflammation of bursa
• Arthritis - inflammatory or degenerative disease; synovial membrane thickens, fluid production decreases, increase in friction and pain. Types:
  • Osteo arthritis - degenerative
  • Rheumatoid arthritis - autoimmune
  • Gouty arthritis - uric acid accumulation
    
• Synovitis - inflammation of synovial membrane
• Tendinitis - inflammation of tendon sheaths