| Introduction |
- Bone can be classified based on both anatomy and structure
- anatomic
- structure
- macroscopic level
- microscopic level
|
| 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
- Haversian canals (Volkmann's canals) connect osteons and haversian systems
- contain arterioles, venules, capillaries, and nerves
- 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
|