biomechanics of skeletal tissue

Question 1

what gives bone its hardness and rigidity

Answer 1

calcium and phosphate

Question 2

another name for compact bone

Answer 2

cortical bone

Question 3

basic structural unit of cortical bone

Answer 3

haversian system

Question 4

what layer of bone does cortical bone form

Answer 4

outer

Question 5

what do haversian canals contain

Answer 5

blood vessels and nerve fibres

Question 6

what are the layers called that form cylinders round the haversian canals

Answer 6

lamellae

Question 7

what are the cavities called that contain osteocytes

Answer 7

lacunae

Question 8

what connects osteocytes to haversian canals and other lacunae

Answer 8

minute channels called canaliculi

Question 9

what is each haversian system surrounded by

Answer 9

cement like ground substance

Question 10

what is the inner part of bone called

Answer 10

cancellous or spongy bone

Question 11

what do the spaces between the mesh of cancellous bone contain

Answer 11

red bone marrow

Question 12

basic structural unit of cancellous bone

Answer 12

trabecula

Question 13

equation for stress

Answer 13

force / area

Question 14

units for stress

Answer 14

Nm-2 (N/m2)

Question 15

equation for strain

Answer 15

change in length / original length

Question 16

what does youngs modulus describe

Answer 16

how flexible or stiff a material is

Question 17

equation for youngs modulus

Answer 17

stress / strain

Question 18

units for youngs modulus

Answer 18

same as stress since strain has no units

> N m-2

Question 19

what does small youngs modulus mean

Answer 19

the material is flexible

Question 20

what are the 2 types of bending loading

Answer 20

cantilever (one end fixed and load applied at the other end)

3 point

Question 21

what is the neutral axis

Answer 21

between the side of an object being compressed and the side being elongates. if symmetrical this is along the geometric centre.
along this line there is NO DEFORMATION

Question 22

is bone stronger under compression or tension

Answer 22

compression

Question 23

appearance of fracture resulting from torsional loading

Answer 23

spiral

Question 24

how are long bones designed to resist torsion loads

Answer 24

they are hollow with strong cortical bone outer layer

|&raquo_space; strength to weight ratio maximised

Question 25

why are torsional fractures of the tibia more common distally

Answer 25

because the cross sectional area is smaller at the distal end so less able to resist torsional loads

Question 26

what is wolffs law

Answer 26

bone is laid down where needed and resorbed where not needed

Question 27

why may fracture fixation cause bone atrophy

Answer 27

'stress shielding' - the plate will carry most of the load >> Bone weakens

Question 28

do children have a greater or smaller proportion of collagen

Answer 28

greater

Question 29

what is a greenstick fracture

Answer 29

incomplete fracture one end buckled one and bent more common in kids because their bones are more flexible due to higher proportion of collagen

Question 30

at what age does bone tissue begin to be lost

Answer 30

35 - 40

Question 31

what type of cartilage covers surfaces of bones in synovial joints

Answer 31

hyaline

Question 32

what type of cartilage forms the IV discs

Answer 32

fibro cartilage

Question 33

articular cartilage composition and structure

Answer 33

mainly made up of collagen structured into fibrils | the fibrils are meshed in a concentrated solution of proteoglycans

Question 34

in articular cartilage where are proteoglycans most concentrated

Answer 34

middle portion

Question 35

what cells in artic cartilage manufacture, secrete and maintain the organic matrix

Answer 35

chondrocytes

Question 36

what is below the deep zone of articular cartilage than then merges with subchondral bone, and what is this interface called?

Answer 36

calcified cartilage | interface between artic cartilage and calcified cartilage = "tidemark"

Question 37

is artic cartilage - elastic - viscous - viscoelastic

Answer 37

viscoelastic

Question 38

articular cartilage - when load removed will it return to normal?

Answer 38

yes but the response is not immediate

Question 39

what two properties does articular cartilage display

Answer 39

creep | stress relaxation

Question 40

what is creep

Answer 40

increase in strain under a constant stress

Question 41

what is stress relaxation

Answer 41

reduction in stress under a constant strain | load required to maintain the deformation decreases with time

Question 42

name the 3 main types of lubrication in synovial joints

Answer 42

elastohydrodynamic boosted boundary

Question 43

what characteristic of articular cartilage does boosted lubrication rely on?

Answer 43

its permeability

Question 44

describe the permeability of articular cartilage and how this enhances lubrication

Answer 44

it is permeable only to small molecules such as water. as the gap between the 2 surfaces becomes smaller, resistance to sideways flow of lubricant becomes greater than resistance of small molecules into the articular cartilage >> water moves into the cartilage, leaving a thick viscose gel behind >> enriched lubricant

Question 45

describe boundary lubrication

Answer 45

if loads are sustained for long enough to deplete fluid completely, lubricant molecules attach themselves chemically to the surfaces creating a boundary layer. this layer has a low shear strength, offering a lower friction than the bare surfaces

Question 46

what is the protein in synovial joints that acts as boundary lubrication

Answer 46

lubricin

Question 47

what do tendons and ligaments both contain

Answer 47

fibroblasts

Question 48

in which are the collagen fibres parallel: | tendons or ligaments? why?

Answer 48

tendons | because the need to withstand large loads in one direction only

Question 49

which is bone - bone and which is bone - muscle

Answer 49

``` tendon = muscle - bone ligament = bone - bone ```

Question 50

are tendons and ligaments - elastic - viscous - viscoelastic

Answer 50

viscoelastic

Question 51

do tendons and ligaments display creep and stress relaxation?

Answer 51

yes

Question 52

beyond joint displacement of how much will pain and damage occur in the ACL beyond what will it rupture

Answer 52

> 4mm - pain and damage | > 7 mm - rupture