Biomechanics of Implant Systems

Question 1

what is strain?

Answer 1

change in length relative to initial length

Question 2

how much strain can an early/soft callous handle?

Answer 2

100% of strain

Question 3

how much strain can a cartilage/hard callous handle?

Answer 3

10-30% of strain

Question 4

does a large gap or small gap have high strain?

Answer 4

small gap typically has higher strain

Question 5

what does an intramedullary pin neutralize?

Answer 5

bending forces

Question 6

can you use cerclage wire alone in a fracture?

Answer 6

no

Question 7

what does a tension band wire do?

Answer 7

converts distractive forces to compression

Question 8

how is an interlocking nail positioned?

Answer 8

in the neutral axis of the bone

Question 9

what is a bridging application of a plate like?

Answer 9

bone not reconstructed
plate functions to secure major bone fragments
plate carries entire load

Question 10

what is the formula for strain?

Answer 10

strain= change in length/original length

Question 11

how much strain does lamellar bone (remodeling) tolerate?

Answer 11

2% strain

Question 12

what is the primary reason for fixation failure with an intramedullary pin?

Answer 12

rotational instability

Question 13

what do multiple wires neutralize?

Answer 13

shear
compression
rotation

Question 14

what do wires not neutralize?

Answer 14

bending forces

Question 15

what can you use skewer pins for?

Answer 15

to reconstruct multiple piece fractures

Question 16

where are tension-band wires usually placed?

Answer 16

greater trochanter
olecranon
tuber calcis
tibial tuberosity

Question 17

what do the screws in an interlocking nail prevent?

Answer 17

collapse and rotation

Question 18

how many pins do you need on each bone fragment with an external fixator?

Answer 18

at least 2

Question 19

what are the factors that affect the strength of an external skeletal fixator?

Answer 19

frame design
connecting bar
pin number, length, and diameter

Question 20

what should the fixation pin diameter be?

Answer 20

25-30% of bone diameter

Question 21

what is the most common hardware used?

Answer 21

intramedullary pin

Question 22

what does a single wire help with?

Answer 22

shear

Question 23

is a single wire sufficient to neutralize compression or rotation?

Answer 23

no

Question 24

does an interlocking nail neutralize all of the forces?

Answer 24

yes

Question 25

what factors affect the strength of an external skeletal fixator?

Answer 25

frame design
connecting bar
pin number, length, and diameter