VCU DPT - Biomechanics (Lecture 15)

does the type of load impact the bone's response

YES

tension vs compression vs torsion

bone is better at handling ___________ compared to ______ and ________

compression

tension, torsion

does bone like to be loaded fast or slow

FAST

injuries:

at faster load, is it ligament or bone

at slower load, is it ligament or bone

faster, ligament

slower, bone

t/f: bone behaves viscoelastically

truwe

- harder you push the more it resists

what 3 things make up bone

identify the component that makes up the biggest piece

orgnaic material

water

minerals (majority)

mineral gives bone its _____

strength and stiffness

organic material gives bone its ______

flexibility and resiliance

difference in plastic and elastic deformation

elastic will return to before, plastic is permanent change

if a system is perfectly resiliant, what is it

it returns as much work put into the system that was strained upon it

which kind of break had more energy

crack

explosion

explosion

bone is surrounded by _________

describe whatever term you put in the blank

periosteum

an outer layer that is filled with vessels and nerves

t/f: periosteum covers the ENTIRE bone

false

all of bone except joint surfaces

what is contained in the inner layers of bone?

what is the term for all inner layers

bone cells to help repair and grow (osteoblasts)

osteogenic layer

the endosteum is where?

what is it filled with

the center of the bone, medullary cavity

filled with marrow, osteoblasts and osteoclasts

osteoblasts _____, osteoclasts _____

build

destroy

cortical/compact bone is ___________

trabecular/cancellous bone is ________

outer

inner

match the pairs

a) cortical bone

b) trabecular bone

c) 5-30% porosity

d) outer bone

e) inner bone

f) 30-90% porosity

g) compact bone

h) cancellous bone

a, c, d, g

b, e, f, h

what is a structural unit of bone

osteon

what is an osteon

lamallae surrounding in concetric rings

functional unit of bone

what are volkmanns canal

path from the surfaces

wht are haversian canals

canals for blood vessels and nerves

what is a lacunae

these are at the boundaries of lamalle, and contain a SINGLE bone cell

we store energy in the __(outer/inner)___ layer of bone, and get strength from the __(outer/inner)___ layer of bone

inner

outer

stress-strain is a ______________

normalized verison of load deformation

what is a normalized version of a load-deformation plot

stress-strain plot

why is stress-strain nromalized version of load-deformation

because

stress = Force/area

strain = change Length/initial length

what does the area under the curve represent in a load-deformation curve

energy being stored in the system

stress = _____

strain = ______

force/area

change length/length

with the load-deformation curve in bone, the elastic region slope is very steep. what does this mean

you can apply a lot of load to the bone before it begins to change its shape

severity of break is related to amount of ________

energy

- aka the area under load-deformation curve

with a load deformation curve, the further right you are the ___ energy is stored in system

what happens if system fails farther to right

energy

hhigher severity of break

what does the ultiate failure point represent in a load-deformation curve

for y-axis

for x-axis

for area under curve

Y: the total amount of load a system can take before it fails, and breaks

X: the total amount of deformation the system can undergo before it breaks

AUC: amount of energy system can handle before it fails

the slope of a load-deformation curve is related to young's modulus of elasticity. the steeper it is, the more ______ it is

stiff

what are the three paramters for structure strength

1. ultimate failure point

2. deformation before failing

3. energy (area under curve)

stress-strain helps us see different mechanical properties when loaded along different axes, due to it being Force/area

what property is this referred to as

ansiotropy

what would indicate a stiff system in a stress strain curve

a steep slope

_______ curve takes into consideration the amount of change in length in relation to original position

stress strain curve

which direction is bone best loaded

- straight up and down

- at angle

- at side

straight up and down

what does it mean when i say bone is biphasic

minerals/collagen and GS

stronger in combination than its indivual parts

cortical bone is ___(stiffer/less stiff)___ than canellous bone

therefore, it has higher __(stress/strain)__ but less __(stress/strain)___

stiffer

stress, less strain

stress refers to force, strain is change in length

which has higher strain

cortical bone

cancellous bone

what does this mean

cancellous (75% strain before failure)

cortical (2% strain before failure)

cancellous bone can change length from starting length more than cortical before failing

which has higher stress

cortical bone

cancellous bone

what does this mean

cortical bone can withstand higher force per area than cancellous bone

put these into position: shear, compression, tension

bone strongest in (a) > (b) > (c)

bone strongest in (compression) > (tension) > (shear)

bone is _______ when laoded at higher speeds

brittle

which conforms to original shape, ductile or brittle

brittle does

is younger bone or older bone ductile? which is brittle?

younger bone is ductile

- can change shapes

older bone is brittle

- returns to shape

t/f: after a period of immobilization, the bone NO LONGER deforms before failing

false! it will still deform

what happens to bone after period of immobilization:

- load to failure

- energy storage

- stiffness

all decrease

load-deformation curve is shorter, less area under curve, and flatter

does all trauma result in reverisble bone loading or bone fracture

no!

rate of loading changes, also how much into plastic region we go

bone is stiffer at _____ rate of loading

bone can absorb more load at _____ rate of loading

less deformation of failure at _____ rate of loading

bone can take more energy at _____ rate of loading

all HIGHER

t/f: bone is stiffer, can absorb energy better, deforms less, and can take more energy at higher rate of loading

true

fracture can be result of single load greater than ultimate material strength OR ________

repeated lower loads, causing micro fractures

with cyclic loading, we see reversible/nonreversible behavior

nonreversible

things change over time!!

this is good, meaning if we can load the bone over time it gets stronger

what does cyclic loading produce?

micro structural damage to bone tissue

damage in bone tissue accumulates faster at ______ intensity of cyclic loading

higher

transverse patellar fracture is example of what type of load causing fx

tension

bending causes _____ on one side and _______ on the other

which side breaks

compression

tension

the tension side breaks

the butterfly fragment is always located on the (compression/tension) side of the leg

compression

as a long bone gets bent over a point, what gets created on either side

tension on the side bending

compression on side acting as fulcrum

when there is compression on bone due to bending happening on other side, what happens to compression site over time

it gets smaller as bone bends more

- leads to butterfly fx

when we get to a certain level of energy, the bone will break. the type of fracture is reliant on the ________

type of load the bone gets

there is often more soft tissue injury with __(bending/torsion)____

bending

- happens at higher load, quicker

which takes less load to cause fracture

torsion

bending

torsion

what kind of fracture is seen with torsional force

spiral fracture

axial compression and bending is reuslt of what force

torsion

torsion/spiral fractures break _______ with ___ force

heal _______, why?

easier with less force

quicker due to larger surface area and less soft tissue involvement

the butterfly fragment is on the

a) tension side

b) compression side

B

the greater the force's magntiude, the ____ its energy

implication for soft tissue?

higher

more soft tissue destruction

the more complex the fracture pattern, the ____ energy needed to produce fracture

greater

low energy is dissapated through ___ cracks than high energy load

fewer

t/f: following fractue, ductile bone does not reutrn to original form

true, brittle does

t/f: bone is stiffer when loaded at higher rates

true

a sudden change in material shape will change the way stress is distributed in the structure, giving rise to ___________

stress concetrations/risers

after material has changed shape and there are __________, these can be thought of as rocks interrupting water flow

stress concetration/risers

pathological fx through tumor

refracture near area of callus

fracture at end of internal fixation device

fracture through screw hole

these are all exmaples of fractures due to what

a stress concetraction/riser changing the distribution ability of the tissue

it takes bone roughly 8 weeks to get to normal after healing. what happens to bone strength, with 100% being normal, after you go back to get screw out

bone back at 50% strength

- like it was newly fractureed

when the stress riser defect is less than bone diameter, does bone return to normal quickly

what about when stress riser is greater than diameter

in 8 weeks yeah it gets back

no, 90% reduction and stays very low

an open section defect is when the defect is ______ than bone diameter

greater than

explain why area moment of intertia is related to bone

a larger area moment of intertia means hardest to bend

area segments further from the axis contrubte signficntly more to area moment of intertia

why does area segments further from axis contribute more to area moment of intertia than closer?

what does it mean

contribution is proportional to square of distance from neutral axis

the larger it is, harder it is to bend

describe bone's ability to resist twisting force, and relate it to polar moment of inertia

around a pole, a larger moment of inertia is more resistant to move

therefore, if a bone is thicker and as result has larger moment of inertia, it is less likely to twist than a skinnier bone (which has less resistance)

with same thickness of cortical bone, which one would break easier from a twisting force

thicker bone

skinnier bone

explain your answer

skinnier

has a smaller moment of inertia, so it would take less resistance to get it to rotate

rotating is bad for bone!

which has better mechanical advantage to resist torque

thicker bone

skinnier bone

thicker

relate how bone heals to polar moment of inertia

bone heals thicker

therefore, it will be more resistant to twisting force because higher polar moment of inertia

when does bone mineral content peak?

who get affected by resoprtion from hormonal changes mostr

30s

women

through the third decade, we have

_____ elastic modulus

______ in yeild strength

increase

increase

older bone is _______ than younger bone

stiffer, stronger

the ability of bone to elongate more until failure _________ throughout life

decreases

- deformation to failure is higher when young

old bone is ____ brittle, with _____ energy capacity

more

less

how does stress strain curve differ from load-deformation

stress strain is normalized, can compare types of bone across specturm

effect of immob on bone

decreases its strength, deformation ability, stiffness

how is ____ related to bone strength

a) polar moment of inertia

b) area moment of inertia

a) farther from axis, stronger

b) area from axis is stronger