Bones Adaptation n Overuse: Exercise

Bone Adaptation n Disuse: bone mass is reduced

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

Bone Biology n Cells in fibrous organic matrix

Collagen

Cells n Osteoblasts- n Osteoclasts- n Osteocytes-

Bone classification n Cortical Bone n Trabecular Bone

X-section of Bone

Bone architecture

Trabecular Bone (aging)

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

Review

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

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

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

Bone Loading

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

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.

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

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

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

Material Prop. of Cortical Bone n Rate of loading n 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 n Yielding occurs as trabeculae fracture *** Example 6 in book ***

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*****

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.

Fracture Risk/Prediction n By definition, Fracture:.

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

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

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

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

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