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55 Cards in this Set
- Front
- Back
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What are the two main structural categories of bone?
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1) Trabecular (a.k.a cancellous, a.k.a spongy)
2) Cortical (a.k.a compact) > All Fracture applies to cortical only |
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Where is the cancellous and cortical bone located in long bones?
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>Cancellous bone is found largely in the interior of the bone ends (epiphysial region)
> COrtical bone is found largely in the middle of the bone (diaphysial region) Note: Outer shell of all bones is cortical bone!!! |
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What is bone called that isn't part of an osteon?
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Interstitial Lamellae
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What is a lacuna?
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>Lacuna: Void between concentric lamellae in where osteocytes live
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What are the different types of bone cells and their function?
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1) Osteoprogenitor cells
>Stem cells for bone > Differentiate into osteoblasts 2) Osteoblast (OB) > regulate mineralization > secrete osteoid (unmineralized bone matrix) 3) Bone Lining Cells (BLC) > inactive osteoblasts found on bone surface 4) Osteocyte (OC) > Inhabit lacunae between layers of lamellae 5) Osteoclast (OCL) > Break down/ demineralize bone |
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What engineering material has compressive stress strain curves similar to trabecular bone?
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Aluminum honeycomb compressed along its side
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What is the difference between density and apparent density?
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> Apparent density: Macroscopic density (aka measurements and weight of overall sample used)
> Density: true density (aka density of only solid bone portion and not voids) Note as apparent density approaches density the bone becomes less cancellous. |
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How does the ratio of apparent to true density affect trabelcular bone's compressive stress strain curve?
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as rho*/rho_s --> 1, the bone displays increasing linear elasticity.
> Plastic Buckling / Collapse region becomes increasingly shorter |
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How is apparent modulus (E*) determined and why is it designated "apparent"?
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E* is calculated by converting the load-displacement to stress and strain using sample dimensions.
> Cannot be considered true modulus because the voids within the bone (which would detract from the area) are neglected. Note!: Non-apparent modulus is referred to as modulus of the solid |
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What is the modulus and ultimate strength of cortical bone?
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Modulus: 10-15 GPa
Ultimate Strength: 100-150 MPa |
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What is the Ultimate Strength of Trabecular Bone?
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8-50 MPa
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For Trabecular bone, list the loading directions in order of decreasing modulus, and decreasing strength.
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For Modulus:
-Longitudinal>transverse>shear For Strength -Longitudinal>transverse>shear |
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For Trabecular bone, list the types of applied in order of decreasing strength.
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Compression>tension>shear
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List the following materials in order of decreasing strength
> tendon > Metals > ceramics >polymer > ligament > trabecular bone > cortical bone |
For Strength:
metals> ceramics>cortical bone>trabecular bone~tendon~ligament~polymer |
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List the following materials in order of decreasing modulus
> tendon > Metals > ceramics >polymer > ligament > cortical bone |
For Modulus:
cereamics>metals>cortical bone>polymer~tendon~ligament |
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What does it mean when bone is damaged?
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It means that small elliptical (in plane) cracks have formed. If unloaded, when damaged in this way the bone will return to its original length.
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What are the three main forms that damage takes in bone?
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1) linear cracks
2) cross-hatched cracks 3) diffuse damage (microcracks each ~1um in length) |
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What indicates the presence of bone damage on a stress strain curve?
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The exceeding of the linear elastic region (0.2% offset method)
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What are the three sources of inelasticity in bone?
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1) Damage
> loss of material continuity due to cracks 2) Plasticity > irrecoverable strain without change in stiffness and signs of strain hardening 3) Viscoelasticity > increases stiffness with loading rate, strains are recoverable Note: Loading and reloading required to determine presence of each of these. |
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How bone damage affects material properties
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> Modulus of elasticity and strength reduced when reloaded
> doesn't depend on apparent density (volume fraction) > does depend on amount of applied strain |
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How do you know that viscoelastic effects are present from a stress strain curve?
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The sample must actually be forced to zero strain (stress goes negative)
Also, while being held at zero strain the stress should relax. |
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How do you know that plastic deformation is present from a stress strain curve?
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After testing is complete zero-stress corresponds to positive strain.
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What is the standard clinical measure for risk of bone fracture?
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Bone mineral density (BMD)
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Is it normal for bone to have microcracks?
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Yes, microcracks are completely normal. However,
If microcrack accumulation rate > remodeling rate --> trouble |
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What are the three modes of failure in cellular solids theory?
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1) Plastic collapse by elastic buckling
2) Plastic hinges 3) Brittle crushing |
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Which material property is more affected by bone damage, modulus of elasticity, or strength?
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%E changes >> %S changes
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At what level does bone damage occur (material, architectural, whole bone)
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It occurs at the material level. This partially explains why type of bone and species do not matter
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What are the four different ways to describe toughness?
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1) Work to failure
2) Linear elastic Fracture mechanics 3) Crack resistance curves 4) Non-linear Fracture mechanics |
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How does the nomenclature work for fracture toughness samples?
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> 1st letter is crack plane normal
> 2nd letter is crack propagation direction |
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For what fracture toughness samples does the crack propagate parallel to osteons?
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Anything ending in an L aka
> C-L > R-L |
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What is used to measure fracture toughnesses that aren't constant valued?
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R-curve aka Resistance Curve
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What does the y intercept of an R curve represent?
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Ko, the crack initiation toughness
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If a material has extrinsic toughening mechanisms, what will its R-curve look like?
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It will have a positive slope
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What is the difference between extrinsic and intrinsic toughening mechanisms
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> Intrinsic toughening mechanisms operate in front of the crack
> extrinsic mechanisms operate behind the crack tip (aka in already cracked material) |
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How does age affect bone's R-curve?
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Increasing Age...
> Decreases Ko, crack initiation toughness > Decreases crack growth toughness (slope of R-curve) |
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Rank the following sample directions in order of increasing fracture toughness: C-L, C-R, L-C.
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C-R<C-L<L-C
2.2 < 3.5 < 5.3 |
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What is crack growth toughness?
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The slope of the R-curve. If it is positive there are extrinsic toughening mechanisms present
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What does an R-curve plot
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R-curve = toughness vs crack extension da
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Explain how toughening through microcracks works
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microcracks form in the bone surrounding the primary crack. The material in this increasingly microcracked zone tries to expand but is constrained by surrounding material. This causes a compressive force to be applied to the crack which helps keep it closed.
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Explain how toughening through bridging by collagen fibers works
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Collagen fibers bridge the already cracked material reducing the stress on the crack tip
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Why doesn't bridging by collagen fibers contribute significantly to extrinsic crack toughening?
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Because the collagen fibers are so small and will operate over such a small area behind the crack tip, they don't have a large effect.
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Explain how toughening through crack deflection works
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As cracks approach osteons, they are forced to change directions to propagate further. They deflect 90 degrees.
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What are four local factors that contribute to mineral deposition?
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1) ion concentration
2) Removal of inhibitors 3) Collagen template 4) Non-collagenous proteins (NCP's) |
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What is the importance of microcracks to bone remodeling?
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Microcracks signal osteoclasts to resorb the bone so that osteoblasts can build new bone.
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What are the two different types of sub-critical crack growth?
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1) sustained: aka quasi-static loading
2) cyclic loading |
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What is at the center of an osteon?
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Haversian canal
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What connects osteons laterally?
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Volkman's Canal
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What are trabeculae? What shapes can they be?
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The structural units of trabecular bone
They can be in rods or plates |
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Is trabecular bone vascular or avascular? Cortical Bone?
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Trabecular: avascular
Cortical: vascular (blood vessels in Haversian canal) |
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What is a canaliculi
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A small passageway between lacunae in bone
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What are the structural units of cortical bone and trabecular bone?
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Cortical bone: osteon
trabecular bone: trabeculae |
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In what type of bone are osteoblasts, Osteocytes, Osteoclasts, and bone lining cells found?
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THey are all found in both
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In what orientations is crack bridging by coll fibers observed?
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C-R, C-L
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In what direction is crack deflection observed?
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L-C, L-R
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In what directions do uncracked ligament fibers contribute to toughening?
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C-R, C-L
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