Bone Structure and Elastic Properties

Question 1

6 functions of bones

Answer 1

support
locomotions - joints allow motion
protection of organs
storage of chemicals e.g. calcium
nourishment - teeth break food
sound transmission - ossicles in middle ear

Question 2

osteocytes

Answer 2

cells which keep the bone in a healthy condition

Question 3

aseptic necrosis

Answer 3

If these cells die (perhaps due to a poor blood supply), the bone will die and lose strength

Question 4

bone remodelling

Answer 4

a continuous process of destroying old bone and building new bone

Question 5

cells involved in bone remodelling

Answer 5

osteoclasts

osteoblasts

Question 6

osteoclast function

Answer 6

destroy bone containing about 0.5 grams of calcium per day.

Question 7

osteoblast function

Answer 7

build new bone using about the same amount of calcium.

Question 8

below 35-40 yrs old osteoblast and osteoclast ratio

Answer 8

Below the age of 35-40 years old, osteoblast activity dominates over osteoclast activity
Skeleton grows

Question 9

osteoclast and osteoblast ratio after 40

Answer 9

more osteoclast than osteoblast activity

bone mass decreases gradually until death

Question 10

collagen

Answer 10

Organic material. Constitutes 40% of the weight of bone and 60% of the volume.

Question 11

bone material

Answer 11

Inorganic material. Constitutes 60% of the weight of the bone and 40% of the volume.

Question 12

bone mineral crystals have what kind of shape

Answer 12

rod shaped

Question 13

5 categories of bones by size

Answer 13

flat
long
cylindrical
irregular 
others

Question 14

trabecular bone location

Answer 14

at the end of long bones in the centre

Question 15

compact bone location

Answer 15

around the edge/ around the centre of long bones

Question 16

elastic properties of biological materials

Answer 16

all materials undergo deformation (change in shape) when stress is added

Question 17

what does deformation depend on

Answer 17

the FORCE PER UNIT AREA, not on the total force

Question 18

stress

Answer 18

in a material with cross-sectional area A subjected to a force F is given by
force /area (N/m^2)

Question 19

how is the stress in an object resisted

Answer 19

The stress in any object is resisted by intermolecular forces within the object

Question 20

3 types of stresses applied

Answer 20

compression
tension
shear stress

Question 21

strain/ fractional change in length

Answer 21

when a material of length (L) is subjected to a compressional or tensional stress - a change of length (omegaL) occurs
=omegaL/L

Question 22

how are stress and strain related

Answer 22

when low volumes of stress is added the strain is directly proportional - has a linear limit
after limit elastic limit - it is no longer linear stretch elastic permanently
after maximum stress before it breaks or deforms

Question 23

elastic deformation

Answer 23

from 0 to point B

Question 24

plastic deformation

Answer 24

point B to D

Question 25

youngs modulus

Answer 25

(E) is defined as the ratio of Stress to Strain, i.e. stress/strain E = s/e (N m^-2)

Question 26

youngs modulus is a measure of ...

Answer 26

stiffness or rigidity | slope of stress/strain

Question 27

What does Young’s Modulus tell us?

Answer 27

lower slope is more elastic deforms easily | the smaller the value of young's modulus the more elastic a material is

Question 28

Is Young’s Modulus the same for different types of Stress??

Answer 28

no

Question 29

anisotropy

Answer 29

if a stress applied in a particular direction will the bone act the same if that same stress is applied in a different direction

Question 30

materials can be

Answer 30

ductile - more elastic | brittle

Question 31

Bones and joints which are heavily used for prolonged periods may suffer from ...

Answer 31

fatigue

Question 32

ultimate tensile strength

Answer 32

12 x 10^7 Nm^-2

Question 33

ultimate compressive strength

Answer 33

17x107 Nm-2

Question 34

bone tension

Answer 34

1.6 x 10^10 N m-2

Question 35

bone compression

Answer 35

0.9 x 1010 N m-2

Question 36

greenstick fracture results from

Answer 36

direct trauma

Question 37

why do greenstick fracture arises

Answer 37

fact that bone is more elastic and ‘stronger’ under compression than under tension (smaller Young’s modulus value, greater compressive strength).

Question 38

how do intermolecular forces try to restore its original shape under tension

Answer 38

is under tension and the intermolecular forces are trying to ‘pull’ the surface back into its original shape

Question 39

how do intermolecular forces try to restore its original shape under compression

Answer 39

under compression and the intermolecular forces are trying to ‘push’ the surface back into its original shape.

Question 40

neutral surface

Answer 40

a surface in between which undergoes NO change in length

Question 41

where does the greatest intermolecular resisting forces occur

Answer 41

occur at the surfaces which undergo greatest tension or compression

Question 42

further you from neutral surface

Answer 42

the bigger contribution you will get from restoring torque

Question 43

how do the resisting forces change the further they are from the neutral surface

Answer 43

Since the resisting forces increase the further they are from the neutral surface,

Question 44

neutral surface of long cylindrical bone

Answer 44

centre

Question 45

what kind of bone will have more resistance to bending a solid bone or hollow

Answer 45

hollow will have more resistance

Question 46

goal of bones in terms of physical properties

Answer 46

maximum resistance and minimum weight

Question 47

why do other connective tissue e.g. tendon, skin no display a linear behaviour at stress below their elastic limit

Answer 47

presence of collagen in these tissues

Question 48

what does the spine support

Answer 48

offering maximum load-bearing support.

Question 49

what does the spine support

Answer 49

the head, upper limbs and thoracic cage during movement and weight bearing activities

Question 50

what type of stress can the vertebrae resist

Answer 50

compressional, tensional and torsional stresses associated with various movements.

Question 51

how come the vertebrae is able to resist certain stresses

Answer 51

is due to the orientation of the trabeculae within the vertebrae.

Question 52

when does crushing of vertebral disc occur

Answer 52

common when the disc receives excessive loading that the ‘intervertebral disc’ can bulge, causing a ‘squeeze’ on the spinal cord, or in severe cases rupture.

Question 53

what type of stress is vertical trabeculae resistant to

Answer 53

compressional load

Question 54

what type of stress is horizontal trabeculae resistant to

Answer 54

tensional tress