Introduction Bone can be classified based on both anatomy and structure anatomic long bones short bones flat bones sesamoid bones irregular 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