Bone Growth & Repair

1. Bone Growth & Repair

2. Bone Development Osteogenesis (Ossification) • The process of bone tissue formation • Embryos: The formation of a bony skeleton • Children: Bone growth • Adults: Bone remodeling & repair

3. Intramembranous Ossification • Prior to ossification, structures exist as fibrous membranes made of embryonic connective tissue known as mesenchyme. • Skull (frontal, parietal, temporal, and occipital bones) • Facial bones • Clavicles • Pelvis • Scapulae

4. Intramembranous Ossification

5. Endochondral Ossification • Begins with the formation of a hyaline cartilage model which will later be replaced by bone. • Most bones in the body develop via this model. • More complicated than intramembranous because the hyaline cartilage must be broken down as ossification proceeds. • Epiphyseal plate remains during adolescence to facilitate continued bone growth.

7. Review • In a brief sentence, compare and contrast Intramembranous and Endochondral ossification. • Turn to your neighbor so that your knees are facing each other • Share your analysis with each other

8. Infantile Skull • At birth an infants skull is not completely formed • Allows skull to compress and change shape • Intramembranous regions are known as fontanels

9. Structure of Bone • Consists of multiple cylindrical structural units known as osteons (haversian systems). • Imagine these osteons as weight-bearing pillars.

10. Osteons Each osteon consists of: • A single central canal (haversian canal) • Concentric layers of calcified bone matrix (lamellae). • Haversian canals allow the passage of blood vessels, lymphatic vessels, and nerve fibers.

11. Interstitial Lamellae Interstitial lamellae • Incomplete lamellae lying in between intact osteons. • These fill the gaps between osteons or are remnants of bone remodeling.

13. Review • In a brief sentence, write down the three most important concepts about osteons. • Turn to your neighbor so that your knees are facing each other • Share your analysis with each other

14. Growth in Bone Length • Epiphyseal cartilage (close to the epiphysis) of the epiphyseal plate divides to create more cartilage • The diaphyseal cartilage (close to the diaphysis) of the epiphyseal plate is replaced with bony tissue.

15. A remnant (epiphyseal line) is visible on X-rays (do you see them in the adjacent femur, tibia, and fibula?)

16. Bone Remodeling • Bone is a dynamic tissue. • What does that mean? • Wolff’s law holds that bone will grow or remodel in response to the forces or demands placed on it. Examine this with the bone on the left. • http://www.youtube.com/watch?v=78RBpWSOl08

17. Bone Cells • Osteoblasts • Create bone – secrete components of bone matrix • Osteoclasts • Dissolve bone • Concentrated in the endosteum • Osteocytes • Osteoblasts trapped in bone matrix • Maintain bone tissue

18. Why might you suspect someone whose been a power lifter for 15 years to have heavy, massive bones, especially at the point of muscle insertion? • Astronauts tend to experience bone atrophy after they’re in space for an extended period of time. Why?

19. Fractures • Bone can crack or even break • Extreme loads • Sudden impacts • Stresses from unusual directions • Healing of a fracture depends on whether or not, the blood supply and cellular components of the periosteum and endosteum survive.

20. Fracture Repair • Blood vessels burst and form a hematoma. • Cells die due to lack of nutrition • Macrophages remove dead and damaged tissue. • A fibrocartilaginous callus forms to splint the broken bone. • Fibroblasts create collagen, chondroblasts create cartillage, and osteoblasts create spongy tissue to fill the break

21. Fracture Repair • Bony callus forms from the fibrocartilaginous callus • 6-8 weeks • Over several months the bony callus is remodeled. • Osteoclasts work to remove the temporary supportive structures while osteoblasts rebuild the compact bone and reconstruct the bone so it returns to its original shape/structure.

22. Simple Fracture • A break that does not break the skin. Simple fracture of the radius and ulna

23. Compound Fracture • Breaks the skin and is open to infection Compound fracture of the humerous

24. Spiral Fracture • A twisting motion breaks the bone at an angle Spiral fracture of the femur

25. Greenstick Fracture • Incomplete break of the bone (like a young tree branch) • Common in young children

26. What Type of Fracture? Simple Fracture

27. What Type of Fracture? Spiral Fracture

28. Spiral fracture after surgery. You can see the pins that were placed through the bone.

29. What Type of Fracture? • Compound fracture of the tibia and fibula • http://trumbore.com/leg/