Implant Materials

Question 1

What is the most common implant material?

Answer 1

stainless steel

Question 2

Which type of stainless steel is used?

Answer 2

316L Grade

Question 3

What percentage of steel 316L is carbon?

Answer 3

0.03%

Question 4

What is advantageous about the low carbon content of steel 316L?

Answer 4

decreased sensitisation and increased corrosion resistance

Question 5

What are the elements and their proportions that make up stainless steel?

Answer 5

63% iron 
18% chromium 
13% nickel 
3% molybdenum 
2% manganese 
trace Silicon, Sulphur and Phosphorus

Question 6

What type of corrosion is stainless steel prone to?

Answer 6

crevice corrosion

Question 7

What type of implants is stainless steel mainly used for?

Answer 7

non-permanent

i.e. fracture fixation where the implant is removed after healing

Question 8

What manufacturing method of steel is strongest?

Answer 8

forged

4x as strong as cast steel

Question 9

Why is forged steel stronger?

Answer 9

work done hammering and forcing steel into place increases strength

Question 10

Which costs more - forged or cast steel?

Answer 10

cast

Question 11

Which suffers more from pitting corrosion - cobalt chrome + titanium or steel?

Answer 11

stainless steel

Question 12

Which has a lower fatigue strength - cobalt chrome or steel?

Answer 12

steel

Question 13

Which is more resistant to corrosion - cobalt chrome or steel?

Answer 13

cobalt chrome

Question 14

Which is preferred in permanent implants - cobalt chrome or steel?

Answer 14

cobalt chrome

Question 15

What does chromium add to the alloy?

Answer 15

corrosion resistance

Question 16

What is the name of the cobalt chrome alloy used in orthopaedics?

Answer 16

stellite 21

Question 17

What proportions of what metals make up Stellite 21?

Answer 17

65% cobalt
25-30% chromium
6% molybdenum
other trace elements

Question 18

How is cobalt chrome manufactured?

Answer 18

casting

Question 19

Why is cobalt chrome not suitable for fracture fixation purposes?

Answer 19

the smaller cross sections of implants have reduced strength and can fail

Question 20

Why is cobalt chromium useful in combination with polyethylene?

Answer 20

low coefficient of friction = good bearing surface

Question 21

What plastic is almost exclusively used in joint bearing surfaces?

Answer 21

polyethylene

Question 22

In what forms can titanium be utilised in orthopaedics?

Answer 22

pure metal

alloy with aluminium and vanadium

Question 23

What does anodised mean?

Answer 23

anodising is a process which increases the thickness of the passivation layer on a metal

Question 24

Which material has the best corrosion resistance?

Answer 24

titanium

Question 25

Describe the density and stiffness of titanium in relation to cobalt chrome

Answer 25

less dense

half as stiff

Question 26

In relation to fatigue strength, which material is more valuable, steel or titanium?

Answer 26

titanium

Question 27

Describe titaniums wear resistance

Answer 27

low - unsuitable for joint replacements

Question 28

What type of implant is titanium commonly used for?

Answer 28

bone fixation plates

Question 29

Describe the structure of a fibre reinforced polymer

Answer 29

very stiff high strength fibres embedded in a much more flexible resin material

Question 30

What kind of material is a fibre reinforced polymer?

Answer 30

composite

Question 31

Which fibre reinforced polymers are the most biocompatible?

Answer 31

carbon fibre

Question 32

What is the stiffness of carbon fibre reinforced polymer in relation to steel?

Answer 32

1/3

Question 33

Describe the fatigue strength properties of carbon fibre reinforced polymer in comparison to other metals

Answer 33

Much higher