JOINT

• Fibrous joint (synarthosis)


  Sutures in skull
• Articular cartilage

  • Does not contain nerves (pain receptors), blood or lymphatic vessels
  • Firmly attached to subchondral bone
  • Little capacity for repair
  • Nutrients provided by synovial fluid
• Synovial fossae

  Bilateral depression with no cartilage, not clearly visible at birth
• Fibrillation

  Early degenerative change of articular cartilage, characterized by loss of proteoglycans, degradation of collagen fibers, increase in water content, dull yellowish appearance
• Fibrillation

  1. Vertical fissures in cartilage

  2. Fissures filled with synovial fluid and granulation tissue

  3. Fissures expand to reach subchondral bone

  4. Surrounding cartilage becomes loose and detaches
• Eburnation


  Degenerative condition characterized by loss of entire articular cartilage and exposure of subchondral bone, subchondral bone becomes polished and thickened (osteosclerosis)
• Eburnation

  • Femoral head showing thickened, polished and smooth subchondral bone

  
• Joint mice

  • Viable pieces of detached articular cartilage free floating in synovial cavity
• Osteophytes


  Bone outgrowths derived from chondrification of fibrous tissue, found at junctions of cartilage with periosteum or along insertions of synovial capsules to bone

  
• Osteophyte formation (osteophytosis)


  Starts earlyas three days after injury but only detected grossly around 2 weeks and radiographically in 5 weeks
• Osteophytes

  • Acetabulum of cow with chronic joint disease showing massive numbers of osteophytes
• Osteophytes


  • Cause joint deformity, sometimes seen as incidental findings in old animals
• Pannus

  Focal aggregate of granulation tissue starting at synovial membrane and extending into articular cartilage, associated with chronic synovial injury and synovitis
• Synovial villous hyperplasia

  Non-specific change resulting from persistent low-grade irritation of synovial membrane, often accompanied by excessive synovial fluid production
• Synovial villous hyperplasia


  • Synovial membrane covered by countless villous projections, giving a velvety appearance
• Synovial villous hyperplasia

  • Synoviocytes type A are phagocytic, synoviocytes type B are responsible for synovial fluid production, both proliferate in response to injury
• Joint response to injury

  • Fibrillation
  • Eburnation
  • Osteophytes
  • Villous hyperplasia
  • Joint mice
  • Capsular fibrosis
  • Pannus formation
• End-stage joint

  • Large number of osteophytes, hyperemic and thickened synovial membrane, small pannus formations, adhesions between cartilage and synovial membrane, fibrotic and thickened articular capsule
• Cartilaginous (amphiarthrosis)


  e.g. ribs
• Synovial (diathrosis)


  e.g. limbs
• Nutrients for cartilage are provided by synovial fluid
• Eburnation


  A degenerative condition characterized by the loss of the entire articular cartilage and exposure of the subchondral bone in one or more areas of the joint
• Eburnation


  • Subchondral bone becomes polished and takes an ivory-like appearance
  • Subchondral bone thickens, creating a condition known as osteosclerosis
• Confirming eburnation

  1. Clapping the affected joint with a knife or any other metal object

  2. Reveals an abnormal sound (bone to metal) rather than the dull sound (metal on cartilage)

  3. Routinely used during a postmortem examination