Unit 1

Question 1

What are the 5 key values of an implant?

Answer 1

be tolerated in the human body with no short term and little long term risk of adverse effects

relieve pain and enable sufficient mobility for AoDL

Function without failure until it is no longer required (variable)

Designed for insertion such that a predictable outcome can be achieved by a competent surgeon

Be of acceptable cost to provide and insert (inc. hospital stay)

Question 2

What 5 key things are required by an implant?

Answer 2

biocompatibility 
adequate strength 
cost effective manufacture 
practicability of insertion 
safety for the surgeon and the patient

Question 3

Why is metal-metal contact not used in joint surfaces?

Answer 3

unsatisfactory bearing surface

Question 4

What material is used instead of two metal-metal components in a joint replacement?

Answer 4

polyethylene

Question 5

What metals are commonly used in implants?

Answer 5

titanium
cobalt-chrome
stainless steel

Question 6

What important material has the same stiffness as cancellous bone?

Answer 6

polyethylene

Question 7

Describe the range of orthopaedic materials used

Answer 7

limited

Question 8

What does anisotropic mean?

Answer 8

different mechanical properties in different directions

Question 9

Which important biological material is anisotropic?

Answer 9

bone

Question 10

What is a composite structure?

Answer 10

A structure made from more than one material so as to enhance its properties

Question 11

What is the main problem in orthopaedic implants?

Answer 11

infection

Question 12

Why is infection so important in orthopaedics?

Answer 12

Bacteria adhere to cement and metal surfaces and cause devastating infection - the immune system is depleted in the presence of an implant

Question 13

What are the two main structural concerns in implant design?

Answer 13

stability and strength

Question 14

What is more expensive - a hip or knee implant?

Answer 14

knee

Question 15

What are the 3 main performance categories under which an implant is looked at?

Answer 15

structural
kinematic
biocompatibility

Question 16

What structural factors are a concern?

Answer 16

strength 
stiffness
lubrication 
wear 
fatigue

Question 17

What kinematic factor is important?

Answer 17

motion

Question 18

What factors come under biocompatibility?

Answer 18

biological integration

functional integration

Question 19

Why is motion important?

Answer 19

the range of motion must be sufficient to enable daily living functions

Question 20

Why are biological and functional integration important?

Answer 20

harmful reactions of implant materials should not exceed accepted safe levels.
the implant should perform such that is does not adversely affect other parts of the body

Question 21

What kind of structure is formed when an implant is attached to bone?

Answer 21

composite

Question 22

Why are bones wider at the ends?

Answer 22

to accommodate the joints

Question 23

Why is the end of the bone made from a greater proportion of cancellous bone?

Answer 23

it is more porous and less stiff than cortical bone giving desirable shock absorbing properties

Question 24

What patterns are present in the cancellous bone?

Answer 24

trabecular align along the directions of greatest stress

Question 25

What is the region directly beneath the articular surface made from?

Answer 25

more cortical - must provide a rigid underlying surface for the joint to bear on without causing excessive deformation

Question 26

What are the shafts of bone made from?

Answer 26

mainly cortical bone - much more rigid so that it can resist deformation under bending and torsional loads

Question 27

What word describes the mechanical properties of a non-biological structural material?

Answer 27

isotropic

Question 28

what does isotropic mean?

Answer 28

mechanical properties are the same no matter what direction they are loaded

Question 29

Rank the loading types in which bone is strongest in order

Answer 29

compression
tension
shear

Question 30

Is diaphyseal cortical bones stronger than metaphyseal cortical bone?

Answer 30

yes - double

Question 31

The stiffness of bone changes according to the rate it is loaded - what is thus property called?

Answer 31

viscoelastic

Question 32

Why is cancellous bone difficult to replicate?

Answer 32

its mesh-like structure is difficult to recreate and in practice doesn’t provide a good enough bonding surface

Question 33

What is it called where an implant takes some of the load of bone?

Answer 33

stress shielding

Question 34

What can happen as a result of stress shielding in permanent implants?

Answer 34

loosening and failure

Question 35

What is Wolff’s law?

Answer 35

bone is laid down where it is needed and resorbed here it is not