1. Bones Adaptation n Overuse: Exercise

2. Bone Adaptation n Disuse: bone mass is reduced

3. Aging and Bone n Is it possible that we can compensate to age related changes in decreased bone density by changing geometry? n Hip fractures

4. Bone Biology n Cells in fibrous organic matrix

5. Collagen

6. Cells n Osteoblasts- n Osteoclasts- n Osteocytes-

7. Bone classification n Cortical Bone n Trabecular Bone

8. X-section of Bone

9. Bone architecture

10. Trabecular Bone (aging)

11. Review???? n Deformation of an axially loaded long rod? F F

12. Review

13. Bone Shape n Since bone isn’t straight, the compressive loads also cause bending

14. Bone stresses n Bending an I beam, n But... Long bones are subjected to???

15. Bone Loading n Axial compressive load n Bending (multiple directions) n Torsion n So, why is the bone hollow?

16. Bone Loading

17. Bone Loading-Aging n Elderly increase both surfaces n Appear that elderly bones see because of geometry, but their is higher, so material properties.

18. Bone-Aging n Change in geometry is not enough to make up for decreased material properties n And--- they have a decline in their “senses” as well with age-so less stable and fall more often.

19. Bone-Torsion n Angle of Twist in a circular bar subjected to a known torque, T?

20. Aging σ ult age men Women-due to estrogen Estrogen inhibits bone resorption

21. Material Prop. of Cortical Bone n Rate of loading (strain rate, ε) –Normal activities (walking)

24. Material Prop. of Cortical Bone n Rate of loading n Orientation of microstructure w/r/t loading direction

27. Material Prop. Of Trabecular Bone Modulus trabecular bone~50MPa, tensile strength ~3MPa

28. Material Prop. Of Trabecular Bone n Yielding occurs as trabeculae fracture *** Example 6 in book ***

29. Age-geometry changes n Men compensate more than women by changing their cortical bone diaphyseal geometry to counter the decrease in strength *** Examples 8 in book*****

30. Fracture Risk/Prediction n * when we finish this section, hopefully we will understand why women fracture hip more often n Yes, increased hip span-which relates to increased moment arm out to muscles, so slight increases in contact forces in hip--- but….. You don’t fracture your hip due to contact forces while walking.

31. Fracture Risk/Prediction n By definition, Fracture:.

32. Fracture Risk/Prediction n Load-Bearing capacity: n Determining bone fracture:

33. Fracture Risk/Prediction n hip fractures occur during a fall n Fracture in bone of hip n Fewer than 2% of falls in elderly result in hip fracture

34. Fracture Risk/Prevention n Factors related to the tendency to fall – not study in this class n Fall severity (i.e. mag. and dir. of loads) n Strength of femur

35. Fall severity n Fall to the side rather than other direction n Increase in potential energy n Arm strength to break fall n Muscle activity n Soft tissue thickness over hip

36. Influences strength of proximal femur n Material properties n Size (total amount) n Shape (spatial distribution, I,J)