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http://upload.orthobullets.com/topic/9001/images/lamellar bone.jpg
http://upload.orthobullets.com/topic/9001/images/cancellous.jpg
http://upload.orthobullets.com/topic/9001/images/woven bone.jpg
http://upload.orthobullets.com/topic/9001/images/lamellar bone histo.jpg
Introduction
  • Bone can be classified based on both anatomy and structure
    • anatomic
      • long bones
      • flat bones
    • structure
      • macroscopic level
        • cortical
        • cancellous
      • microscopic level
        • lamellar
        • woven bone
Anatomic classification
  • Long bones
    • e.g. femur, humerus, tibia, forearm bones
    • three anatomic regions in long bones
      • diaphysis
        • thick cortical bone surrounding a central canal of cancellous bone
        • outer region covered by periosteum 
      • metaphysis
        • thin cortical bone surrounding loose trabecular bone
      • epiphysis
        • end of bone that forms the articular surface
        • contains the physis and the subchondral region under the articular cartilage
  • Flat bones
    • e.g. skull, pelvis, scapula
    • varied structure of either purely cortical bone or cortical bone with a thin central trabecular region
Macroscopic structural classification
  • Cortical
    • 80% of skeleton
    • metabolism
      • characterized by slow turnover rate and high Young's modulus
    • structure
      • made of packed osteons or Haversian systems
        • osteons
          • outer border defined by cement lines
        • vascular canals 
          • contain arterioles, venules, capillaries, and nerves
          • if oriented along long axis of bone: Haversian canals 
          • if oriented transversely to long axis of bone: Volkmann canals
        • interstitial lamellae
          • the region between osteons
  •  Cancellous bone (spongy or trabecular bone)
    • metabolism
      • lower Young's modulus and more elastic
      • high turnover to remodel according to stress across the bone
    • structure
      • boney struts organized into a loose network
      • each strut is approximately 200 micrometers in diameter
      • 30-90% of bone is porous and contains bone marrow
      • increased porosity in osteoporosis
Microscopic structural classification
  •  Woven bone
    • immature or pathologic bone that is woven and random and is not stress oriented
    • compared to lamellar bone, woven bone has:
      • more osteocytes per unit of volume
      • higher rate of turnover
    • weaker and more flexible than lamellar bone
  • Lamellar bone
    • secondary bone created by remodeling woven bone
    • organized and stress oriented
    • stronger and less flexible than woven bone
 

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