bones in biomechanics

Question 1

draw a deformation curve

Answer 1

load/ stress on y axis

deformation on x axis

elastic region- deformation can be tempoary

yield point- when deformation becomes permenant

ultimate failure

plastic region

Question 2

direction of load

Answer 2

compression - both direction

tension- opposite direction

bending- same direction in U shape

shear- different directions from side on

torsion- circular motion

Question 3

compressions cause what type of injuries

Answer 3

fractures

Question 4

tension result in

Answer 4

bone wil respond to the demands it is placed in

great tension results in periosteum stress/ inflamtion

evulsion fractures- portion of bone is torne away with ligament and tendon

Question 5

shear force results in

Answer 5

valgus and varum force

children may fracture epiphyseal plate

spondylotheisas

Question 6

bending force results in

Answer 6

multipl force acting in different directions
stress fractures

e.g when running tensile force on superior and compresion on inferior head of femur

Question 7

torsion force results in

Answer 7

fails first in shear direction and

second aong plane f maxial tensile stress

Question 8

anisotrophy

Answer 8

describes tissue that responds differently depending on direction of force

Question 9

viscoelasticity

Answer 9

tissue responds differently depending on rate and duration of loading

fast/ high load - wont budge

but slow and increased load- will cause it to stretch

Question 10

fracture production type

Answer 10

single load- exccedes maximal and ultimate stregnth

repeated action of low magnitude of load

Question 11

how to fractures occur in repeated action

Answer 11

1. muscle fatigue
2. decrease muscle ability to contract
3. decrease ability of muscle to neutralise stress on bone

leads to common stress fractures- femoral head, proximal tibia, humerus, ribs, lumbrical verterbrae

Question 12

moment of inertia

Answer 12

anility to resist change

Question 13

in a fracture what forms in healing

Answer 13

callus increases inertia
this increase stiffness and hardness

callus cuff will form once break and will then become spongy and then be reabsorbed into compact

Question 14

articular cartlige

Answer 14

hayline cartledge
chondrocytes, avascular, extracellular matrix= stiffness. strength
proteoglycans- watarproof

-increase surface area of articular surface for force to be distributed
- shock absorb resist compresion force
- decrease friction

Question 15

3 layers of hayline carteledge

Answer 15

superficial zone- 10-20 percent collagen volume// resist tensile force and shear force

middle zone- 40-60 percent more PG thick first line against compresion

deep zone- 30 percent volume- high PG low water

Question 16

how does cartlidge resist compression

Answer 16

swelling pressure- develop fluid

frictional drag from fluid- resist fluid leaving

stress developed in collagen protion

Question 17

how does collagen resist tensile strength

Answer 17

collagen will straighten out and align on axis of tension

toe region

Question 18

articular cartlidge repair

Answer 18

limited capacity

1. magnitude if imposed stress- rapid high load= insurficent time for fluid redistribution= meniscus tears
2. total number of sustrained stress- fatigue and wear// low load over time= washes out fluid- stiffness decrease
3. change in intrinsic structure-

Question 19

breakdown of cartlidge

Answer 19

permability- ease which fluid flows through
low in carltidge because of fluid drag

osteoarthritis- increase permability decrease space between articular surfaces in joints

Question 20

3 lines of defence in cartlidge

Answer 20

1- fluid
2- movement of fluid
3- solid matrix