Bones adaptation
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Bones Adaptation. Overuse: Exercise. Bone Adaptation. Disuse: bone mass is reduced. Aging and Bone. Is it possible that we can compensate to age related changes in decreased bone density by changing geometry? Hip fractures. Bone Biology. Cells in fibrous organic matrix. Collagen. Cells.

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Bones Adaptation

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Bones Adaptation

  • Overuse: Exercise

Bone Adaptation

  • Disuse: bone mass is reduced

Aging and Bone

  • Is it possible that we can compensate to age related changes in decreased bone density by changing geometry?

  • Hip fractures

Bone Biology

  • Cells in fibrous organic matrix



  • Osteoblasts-

  • Osteoclasts-

  • Osteocytes-

Bone classification

  • Cortical Bone

  • Trabecular Bone

X-section of Bone

Bone architecture

Trabecular Bone (aging)


  • Deformation of an axially loaded long rod?




Bone Shape

  • Since bone isn’t straight, the compressive loads also cause bending

Bone stresses

  • Bending an I beam,

  • But... Long bones are subjected to???

Bone Loading

  • Axial compressive load

  • Bending (multiple directions)

  • Torsion

  • So, why is the bone hollow?

Bone Loading

Bone Loading-Aging

  • Elderly increase both surfaces

  • Appear that elderly bones see because of geometry, but their is higher, so material properties.


  • Change in geometry is not enough to make up for decreased material properties

  • And--- they have a decline in their “senses” as well with age-so less stable and fall more often.


  • Angle of Twist in a circular bar subjected to a known torque, T?




Women-due to estrogen


Estrogen inhibits bone resorption

Material Prop. of Cortical Bone

  • Rate of loading (strain rate, ε)

    • Normal activities (walking)

Material Prop. of Cortical Bone

  • Rate of loading

  • Orientation of microstructure w/r/t loading direction

Material Prop. Of Trabecular Bone

Modulus trabecular bone~50MPa, tensile strength ~3MPa

Material Prop. Of Trabecular Bone

  • Yielding occurs as trabeculae fracture

*** Example 6 in book ***

Age-geometry changes

  • Men compensate more than women by changing their cortical bone diaphyseal geometry to counter the decrease in strength

*** Examples 8 in book*****

Fracture Risk/Prediction

  • * when we finish this section, hopefully we will understand why women fracture hip more often

  • 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.

Fracture Risk/Prediction

  • By definition, Fracture:.

Fracture Risk/Prediction

  • Load-Bearing capacity:

  • Determining bone fracture:

Fracture Risk/Prediction

  • hip fractures occur during a fall

  • Fracture in bone of hip

  • Fewer than 2% of falls in elderly result in hip fracture

Fracture Risk/Prevention

  • Factors related to the tendency to fall

    • not study in this class

  • Fall severity (i.e. mag. and dir. of loads)

  • Strength of femur

Fall severity

  • Fall to the side rather than other direction

  • Increase in potential energy

  • Arm strength to break fall

  • Muscle activity

  • Soft tissue thickness over hip

Influences strength of proximal femur

  • Material properties

  • Size (total amount)

  • Shape (spatial distribution, I,J)

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