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Cartilage & Articular Cartilage

Cartilage Types:

Articular (Hyaline)   

 Joint surfaces

Fibrocartilage   

Tendon & ligament insertion

Elastic   

Trachea, earlobe

Fibroelastic     Meniscus

Cartilage is avascular, aneural, alymphatic.

Hyaline cartilage is the most common & found in:

  1. bone apophyses 

  2. synovial joints (articular cartilage).

  3. epiphyseal plates

  4. costal cartilages

  5. majority of the fetal skeleton


Cartilage Growth

1. Appositional Growth: 

  • new cartilage is formed at cartilage surface by cells derived from chondroblasts of perichondrium (surface of hyaline cartilage)

  • with maturation, majority of cartilage growth is primarily appositional

2. Interstitial Growth: 

  • increase in internal mass of cartilage 

  • by activity of chondrocytes that multiply within their lacunae

  • in mature cartilage, cellular turnover rate is exceedingly low


Articular Cartilage Comprises:

  1. Chondrocytes (5%)

  2. Extracellular matrix (95%)

    1. Water (75%)

    2. Collagen (mainly type 2) (5%)

    3. Proteoglycans (20%)

    4. Enzymes

    5. Growth Factors (PDGF, TGF beta, FGF, IGF-1)

    6. Lipids

    7. Adhesives (fibronectin, chondronectin)


Zones 

(superficial to deep): 

  1. Surface 

  2. Superficial Tangential zone

    • collagen fibres (type 2) orientated tangential to surface

    • has greatest ability to resist shear stresses

  3. Transitional / middle zone

    • transition between the shearing forces of surface layer to compression forces in the cartilage layer

    • collagen arranged obliquely

    • composed almost entirely of proteoglycans 

  4. Radial / deep zone 

    • collagen fibers attached radially (vertical) into the tidemark

    • distributes loads and resists compression

  5. Calcified zone 

    • containing the Tidemark Layer (basophilic line which straddles the boundary between calcified and uncalcified cartilage)

    • contains Type 10 collagen

  6. Subchondral bone

 Articular Cartilage - structure   

 


Chondrocytes (5% wet weight)

Chondroblasts which are derived from mesenchymal cells become trapped in lacunae and develop into chondrocytes. Chondrocytes are important in the control of matrix turnover through production of:

  • collagen
  • proteoglycans
  • enzymes for cartilage metabolism


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© 2005-2007 Orthoteers.co.uk - last updated by Len Funk on 10 February 2005Medical Merketing and SEO by Blue Medical 
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