Basic Mechanical Concepts

Question 1

What are the 2 factors that influence mechanical competence of bones and implants for fracture fixation?

Answer 1

1. Material properties

2. Structural properties

Question 2

What thus material properties characterize?

Answer 2

Characterize the DEFORMATION and FAILURE of material under loading, without considering the geometry of its structure.

Question 3

How to determine material stiffness?

Answer 3

The material is compressed, and the change in height is measured.

Question 4

What is strain (or resulting compression)?

Answer 4

Amount of compression divided by the original height

Question 5

Loading is expressed in terms of stress or strain?

Answer 5

Stress

Question 6

How to calculate stress?

Answer 6

Divide the load by the area the load is acting upon.

Question 7

What is Elastic (E-modulus) or Young’s modulus?

Answer 7

It is the expression of stress.

Question 8

How to calculate E-modulus?

Answer 8

E = stress / strain

Question 9

E- modulus describes?

Answer 9

Deformation in response to loading within the linear or elastic “working region” of a material.

Question 10

How to determine strength of a material?

Answer 10

The material must be loaded beyond its elastic region to induce failure.

Question 11

What is yield strength?

Answer 11

Load at which permanent plastic deformation begins to occur.

Question 12

What is ultimate strength?

Answer 12

The load at which the material is fractured.

Question 13

Example of a yield strength?

Answer 13

Contouring a metal plate.

Question 14

What is ductile?

Answer 14

Represents a large deformation of a material before failure.

Question 15

Example of a ductile material?

Answer 15

Stainless steel

Question 16

What is brittle?

Answer 16

It represents very little deformation property before failure.

Question 17

Example of a brittle material?

Answer 17

Methyl-meth-acrylate

Question 18

What is fatigue failure?

Answer 18

Repetitive loading below the ultimate strength limit.

Question 19

What thus repetitive loading below ultimate strength results to?

Answer 19

Micro cracks

Question 20

What is fatigue limit?

Answer 20

Describes maximal load that will not induce micro-cracks and not lead to fatigue failure, regardless of the loading cycles.

Question 21

What is a mechanical property where stiffness depends on the loading direction?

Answer 21

Anisotropy

Question 22

What is a mechanical property where stiffness depends on the loading rate?

Answer 22

Viscoelasticity

Question 23

What is a mechanical property where stiffness have the same properties regardless of the direction of loading?

Answer 23

Isotropic

Question 24

What 2 materials are considered isotropic?

Answer 24

Titanium and Stainless steel

Question 25

A sample of a viscoelastic tissue?

Answer 25

Articular cartilage

Question 26

What do you call a gradual increase in deformation under constant loading of viscoelastic tissue?

Answer 26

Creep

Question 27

In fracture surgery, what are the 2 objects with corresponding structural properties being considered?

Answer 27

1. Fixation device

2. Bone

Question 28

True or false, cortical bone is weaker than trabecular bone?

Answer 28

False: trabecular bone is far weaker than cortical bone

Question 29

Structural stiffness and strength of trabecular bone are defined by this property or characteristic, what is it?

Answer 29

Porosity

Question 30

What is the range in percentage of porosity of a trabecular bone?

Answer 30

30% - 90% depending on the individual and anatomic location

Question 31

Method of measuring density of a trabecular bone?

Answer 31

Radiographic densitometry