Bone L1: Biomechanics of Bone Flashcards
What graph is used for structural properties?
Load deformation graph
What graph is used for material properties?
Stress-strain graph
Why would a stress-strain graph be used?
- Can use graph to compare to other materials
- Ultimate stress can be compared to every other stress/strain graph
How does is tensile stress measured in stress-strain graph?
Can measure area = tensile stress
What is stress in a stress-strain graph?
- Length
- How much it stretches
What is the toe-region?
- where crimp is being removed, becoming less wavy.
- elastic (linear) region – slope = E (Pa), where material behaves elastically
What is modulus of elasticity?
stress/strain = E (Pa)
What is the yield point?
where permanent damage and non-linear behaviour starts
What is the plastic region?
post yield point, ductile behaviour with damage
What is the ultimate stress (strength)?
maximum stress (Pa) able to be supported
What is the ultimate strain?
maximum deformation/original length
What is the toughness?
area under curve, ‘resistance to failure’
What is the difference between a force-deformation curve and a stress-strain curve?
Basically – the units and terminology. Stress-strain curves are of more use due to the incorporation of ‘size’ of the thing under test. Normalised. This allows for comparisons with other materials in a meaningful way.
Structural VS material properties of bones
- Bone material itself = weaker material = starts to bend –> adaptive response –> produce more bone larger bone (but poor quality)
- Whole bone = good structure = relatively good strength
- It is the structure of bone that makes it strong, not the material itself
What is bone fatigue?
- Fatigue: continuous loading
- decreased modulus
- Once bone starts moving away from origin, permanent damage
- Keep bending bone –> microcrystal –> damage permanent damage –> eventually failure
Bone is _____ rate dependent
Strain
- More brittle but stronger –> increased rates of loading
- More ductile rates of loading
What is shear stress?
• More hallow (while same amount of bone) = more resistance to failure
What torsion stress?
Torsion stress = Tr/J r = moment arm T = torque
- Bone distributed further way = hollow= J = better
- Bone not distributed as far away = J = risk of fracture
What are the 2 inorganic components in bone matrix? What forces can be withstood?
- 65% of hydroapatite
- 99% of calcium
- Bone brittleness and compressive strength
What is the organic component in bone matrix? What forces can be withstood?
- 33% of collagen
- Bone tensile properties
What forces can the inorganic components withstand?
Compressive force
What force can the organic componnent withstand?
Tensile force
What are some components of dense, lamellar or cortical bone?
- Stiffness
- Increased modulus = decreased toughness
- High value of E
- Small plastic region
- High strength and density
What are some components of spongy, trabecular or cancellous bone?
- Toughness
- Decreased modulus = increased toughness
- Low value of E
- Larger plastic region
- Longer stress before failure
- Low strength and density
How is bone matrix maintained?
Bone cells account for 2% of bone, the rest is matrix Oestoblast Oestocytes Oestoclast
What are oestoblasts?
Creates bone matrix
What are oestocytes?
Maintains bone matrix
What are oestoclasts?
• Breakdown of bone matrix • Larger than blasts
What is microstructure of bone?
• Microstructure is very variable, complex but influences mechanical properties • Secondary osteons formed as replacement bone with primary bone
Bone apposition and bone resorption: Osteoclasts
Nucleated stated
Bone apposition and bone resorption: Osteocytes
Lacune
Bone apposition and bone resorption: Resorbing surface
Active at this surface
Bone apposition and bone resorption: Resting line
Bone growth stops –> restart again
Bone apposition and bone resorption: Reversal line
Bone has been formed and eaten away and starts to build again
What is parathyroid?
Chief cells = polypeptide hormone enhances Ca2+ release from bone PTH indirectly stimulates osteoclast activity
What is calcitonin?
C-cells= linear polypeptide hormone inhibits Ca2+ absorption in intestines, renal tubular cells resorption and osteoclast activity Anti-osteoporosis effect
