Biomechanics unit 1 SAQs

Question 1

explain the difference between creep and stress relaxation?

Answer 1

creep is the phenomenon of a material changing length over a period of time, elongating when a constant load is applied to them

Question 2

what is the basic structural unit in compact bone?

Answer 2

haversian system

Question 3

the bone tissue is arranged in layers called?

Answer 3

lammellae

Question 4

and forms concentric cylinders around a central canal called a ?

Answer 4

haversian canal

Question 5

haversian canal contains?

Answer 5

nerve fibres and blood vessels

Question 6

between lamellae, there are small cavities called?

Answer 6

lacunae

Question 7

lacunae contain?

Answer 7

osteocytes

Question 8

each osteocyte is linked to other osteocytes and the central canal by minute channels called?

Answer 8

cannaliculi

Question 9

what do canalliculi do?

Answer 9

carry nutrients from the blood vessels

Question 10

what is the weakest part of the bones microstructure?

Answer 10

between haversian systems. each haversian system is surrounded by a ground like cement substance, but there are no coollagen fibres, probably accounts for less strength.

Question 11

basic structural unit in cancellous bone?

Answer 11

trabeculae (a latticework of branching sheets and columns)

Question 12

trabeculae do not contain haversian canals. Although they are similar in structure. Blood vessels travel through marrow filled spaces between the latticework of trabeculae.

Answer 12

Y

Question 13

why does cancellous bone not contain haversian systems

Answer 13

blood vessels pass through marrow filled spaces between the latticework of trabeculae and supply nutrients to the osteocytes via the canaliculi.

Question 14

units for stress?

Answer 14

Nm-2

Question 15

Is cortical bone stronger in shear or tension?

Answer 15

tension

Question 16

when is cortical bone strongest?

Answer 16

compression

Question 17

why are fractures more likely in athletes when they are fatigued?

Answer 17

muscles can’t contract to neutralise the tension and compress bones, and so more likely to fracture

Question 18

2 types of bending?

Answer 18

cantilever and three point

Question 19

What is the neutral axis?

Answer 19

point along the beam where no deformation occurs

Question 20

Along which surface will a fracture most likely occur when an excessive bending load is applied to a long bone?

Answer 20

the elongated side

Question 21

in vertical loading of the femur, which side would more likely fracture?

Answer 21

the lateral (elongated side)

Question 22

where is the neutral axis in symmetrical structures?

Answer 22

along the geometric centre

Question 23

torsional fractures have a characteristic _______appearance?

Answer 23

spiral

Question 24

in torsion, where is the greatest stress and strain on a bar?

Answer 24

outer surface of a bar

Question 25

if a torsional load is increased, where will a fracture occur

Answer 25

on the outer surface of the bar

Question 26

the hollow structure of bones increases its strength to weight ratio

Answer 26

If the same quantity of bone tissue was used to construct a completely solid bone rather than a hollow one the bone would be smaller in diameter and would be less able to resist torsional loads

Question 27

When considering torsional loads, do hollow or solid bars have the best strength-to-weight ratio?

Answer 27

hollow

Question 28

why is the distal end of the tibia more likely to fracture than the proximal?

Answer 28

the cross sectional area is reduced. There is the same amount of bone tissue, but the distal end is less able to resist torsional loads

Question 29

Name five types of loadings.

Answer 29

tension, compression, bending, shearing, torsion

Question 30

what is combined loading?

Answer 30

more than one type of loading

Question 31

What is the difference between bone hypertrophy and bone atrophy?

Answer 31

bone atrophy is bone resorption, due to lack of use. hypertrophy is bone being laid down in response to physical activity. at sites carrying greater load than usual.

Question 32

how is a fatigue fracture sustained?

Answer 32

A fracture resulting from the repeated application of a load that is smaller than the ultimate strength of the bone is called a fatigue fracture

Question 33

Why are children prone to greenstick fractures but not adults

Answer 33

children have more collagen in their bones, making them more ductile

Question 34

cartilage is a connective tissue consisting of?

Answer 34

cartilage cells, fibres, ground substance (CFG)

Question 35

In what type of joints is articular cartilage found?

Answer 35

synovial

Question 36

What are the two main roles of articular cartilage?

Answer 36

to cushion joints while at same time provides a smooth, lubricated bearing surface. also has shock absorbing properties. allows large loads to be distributed evenly over a large surface area

Question 37

which cartilage forms the tip of the nose?

Answer 37

hyaline

Question 38

epiglottis and external ear?

Answer 38

elastic cartilage

Question 39

which forms the pubic symphysis and intervertebral disks?

Answer 39

fibrocartilage

Question 40

articular cartilage is a form of ________?

Answer 40

hyaline cartilage

Question 41

hy el fi

Answer 41

hyaline, elastic, fibrocartilage

Question 42

roles of articular cartilage

Answer 42

provides a cushioning surface and also a lubricated, smooth bearing surface. also has shock absorbing properties that allows large loads to be spread evenly over a large surface area

Question 43

what is articular cartilage made of?

Answer 43

an organic matrix of non cellular material, interspersed with cells and fluid.

Question 44

what is the non cellular material mainly made of?

Answer 44

collagen

Question 45

how is collagen arranged in articular cartilage?

Answer 45

fibrils

Question 46

fibrils are enmeshed in a concentrated solution of ?

Answer 46

proteoglycans

Question 47

fibrils make up 50-80% of the dry weight and 10-20 % of the wet weight

Answer 47

y

Question 48

large protein based molecules important to the mechanical properties of articular cartilage. they make up 3-10 percent of the wet weight

Answer 48

what are proteoglycans?

Question 49

where are proteogl... most concentrated?

Answer 49

in the middle layer of the articular cartilage, less in the deeper layers associated with the bone

Question 50

what are the cells called in ac?

Answer 50

chondrocytes

Question 51

where are the cells more densely packed?

Answer 51

deeper layers more close to the bone

Question 52

what is the interstitial fluid that occupies the spaces in the matrix mainly made of?

Answer 52

water. 65-85% of weight weight in AC

Question 53

3 zones the AC can be split into?

Answer 53

superficial tangenital zone middle zone deep zone

Question 54

what is the tide mark?

Answer 54

line between the deep zone and the calcified cartilage layer

Question 55

in superficial zone, how are fibrils arranged?

Answer 55

tightly woven into sheets, parallel to articular surface

Question 56

chondrocytes in super?

Answer 56

oblong with longitudinal axis parallel to articular surface

Question 57

in middle zone, fibrils?

Answer 57

arranged more randomly but still basically parallel to AS.

Question 58

why are they less densely packed together?

Answer 58

to accommodate the high concentration of proteoglycans.

Question 59

chondrocytes in middle layer?

Answer 59

circular and randomly distributed

Question 60

deep zone?

Answer 60

the collagen fibrils are arranged in larger fibre bundles that are anchored in the underlying bone tissue. Ie they attach articular cartilage to bone

Question 61

below the deep zone there is a thin layer called the calcified cartilage layer which gradually merges with the underling subchondral bone

Answer 61

interface between the articular cartilage and the cc is called the tidemark

Question 62

how are chondrocytes arrange in the deep layer?

Answer 62

arranged in loose columns aligned perpendicular to the line dividing the articular cartilage and the underlying bone