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BMSC > Biomechanics unit 1 SAQs > Flashcards

Biomechanics unit 1 SAQs Flashcards

1
Q

explain the difference between creep and stress relaxation?

A

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

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2
Q

what is the basic structural unit in compact bone?

A

haversian system

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3
Q

the bone tissue is arranged in layers called?

A

lammellae

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4
Q

and forms concentric cylinders around a central canal called a ?

A

haversian canal

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5
Q

haversian canal contains?

A

nerve fibres and blood vessels

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6
Q

between lamellae, there are small cavities called?

A

lacunae

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7
Q

lacunae contain?

A

osteocytes

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8
Q

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

A

cannaliculi

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9
Q

what do canalliculi do?

A

carry nutrients from the blood vessels

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10
Q

what is the weakest part of the bones microstructure?

A

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.

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11
Q

basic structural unit in cancellous bone?

A

trabeculae (a latticework of branching sheets and columns)

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12
Q

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

A

Y

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13
Q

why does cancellous bone not contain haversian systems

A

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

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14
Q

units for stress?

A

Nm-2

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15
Q

Is cortical bone stronger in shear or tension?

A

tension

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16
Q

when is cortical bone strongest?

A

compression

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17
Q

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

A

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

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18
Q

2 types of bending?

A

cantilever and three point

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19
Q

What is the neutral axis?

A

point along the beam where no deformation occurs

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20
Q

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

A

the elongated side

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21
Q

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

A

the lateral (elongated side)

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22
Q

where is the neutral axis in symmetrical structures?

A

along the geometric centre

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23
Q

torsional fractures have a characteristic _______appearance?

A

spiral

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24
Q

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

A

outer surface of a bar

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25
Q

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

A

on the outer surface of the bar

26
Q

the hollow structure of bones increases its strength to weight ratio

A

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

27
Q

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

A

hollow

28
Q

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

A

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

29
Q

Name five types of loadings.

A

tension, compression, bending, shearing, torsion

30
Q

what is combined loading?

A

more than one type of loading

31
Q

What is the difference between bone hypertrophy and bone atrophy?

A

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.

32
Q

how is a fatigue fracture sustained?

A

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

33
Q

Why are children prone to greenstick fractures but not adults

A

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

34
Q

cartilage is a connective tissue consisting of?

A

cartilage cells, fibres, ground substance (CFG)

35
Q

In what type of joints is articular cartilage found?

A

synovial

36
Q

What are the two main roles of articular cartilage?

A

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

37
Q

which cartilage forms the tip of the nose?

A

hyaline

38
Q

epiglottis and external ear?

A

elastic cartilage

39
Q

which forms the pubic symphysis and intervertebral disks?

A

fibrocartilage

40
Q

articular cartilage is a form of ________?

A

hyaline cartilage

41
Q

hy el fi

A

hyaline, elastic, fibrocartilage

42
Q

roles of articular cartilage

A

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

43
Q

what is articular cartilage made of?

A

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

44
Q

what is the non cellular material mainly made of?

A

collagen

45
Q

how is collagen arranged in articular cartilage?

A

fibrils

46
Q

fibrils are enmeshed in a concentrated solution of ?

A

proteoglycans

47
Q

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

A

y

48
Q

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

A

what are proteoglycans?

49
Q

where are proteogl… most concentrated?

A

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

50
Q

what are the cells called in ac?

A

chondrocytes

51
Q

where are the cells more densely packed?

A

deeper layers more close to the bone

52
Q

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

A

water. 65-85% of weight weight in AC

53
Q

3 zones the AC can be split into?

A

superficial tangenital zone
middle zone
deep zone

54
Q

what is the tide mark?

A

line between the deep zone and the calcified cartilage layer

55
Q

in superficial zone, how are fibrils arranged?

A

tightly woven into sheets, parallel to articular surface

56
Q

chondrocytes in super?

A

oblong with longitudinal axis parallel to articular surface

57
Q

in middle zone, fibrils?

A

arranged more randomly but still basically parallel to AS.

58
Q

why are they less densely packed together?

A

to accommodate the high concentration of proteoglycans.

59
Q

chondrocytes in middle layer?

A

circular and randomly distributed

60
Q

deep zone?

A

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

61
Q

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

A

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

62
Q

how are chondrocytes arrange in the deep layer?

A

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

BMSC (16 decks)

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