Mechanical Properties

Question 1

If a material breaks before yield point, it’s behaviour can be described as:

Answer 1

Brittle

Question 2

Describe what is meant by time dependant viscoelastic characteristics of creep

Answer 2

The material will continue to deform as a constant load is applied

Question 3

How do stiffness, strength and toughness differ between cortical and cancellous bone?

Answer 3

Cortical: stiffer, stronger (heavier)
Cancellous: tougher (high remodelling)

Question 4

What does wolff’s law say about bone remodelling?

Answer 4

Don’t use it, you loose it. More needed- oesteoblasts, not need therefore reabsorbed- oestoclasts

Question 5

What causes the alignment of trabeculae in cancellous bone?

Answer 5

Direction of applied force

Question 6

2 roles of articular cartilage

Answer 6

Reducing contact stress

Allowing joint lubrication

Question 7

What is fluid film lubrication?

Answer 7

where a thin layer of synovial fluid forms ahead of the moving articulating surfaces (fast movements at low load)- creates a small amount of separation due to pressure of fluid. E.g. hip at swing phase of gait in walking

Question 8

What are 2 forms of lubrication in joints

Answer 8

Boundary layer lubricant: absorbed layer of synovial fluid on the articulating surface (slow movements at high load)- minimise wear on surface e.g. hip and gait while walking at stance phase

Fluid film lubricant where a thin layer of synovial fluid forms ahead of the moving articulating surfaces (fast movements at low load)- creates a small amount of separation due to pressure of fluid. E.g. hip at swing phase of gait in walking

Question 9

Define slide, glide and roll

Answer 9

Spin: pure rotation about a fixed axis
Roll: rotation & translation about a moving axis
Glide/slide: pure translation

Question 10

What are the two main forces acting on an anatomical leaver?

Answer 10

Muscle force

Resistance

Question 11

Define torque

Answer 11

A force that acts at some distance from the axis of rotation to create angular motion

Question 12

What is the most common leaver system in the body

Answer 12

3rd class lever

Question 13

In 3rd class what moment arm is smaller?

Answer 13

Effort (muscle)

Question 14

Why can’t you fully flex the hip and extend the knee?

Answer 14

2 joint muscle cannot shorten adequately to actively move both joints through their full range of motion at the same time is called active sufficiency.

Question 15

Where is the yield point on a stress strain curve

Answer 15

When the line is no longer linear

Question 16

Where is the ultimate strength on a stress strain curve

Answer 16

The failure point

Question 17

Where is the toughness reading on a stress strain curve

Answer 17

The area under the curve

Question 18

Where is the plastic region on a stress strain curve

Answer 18

After the yield point but before the break point

Question 19

Where is the elastic region on a stress strain curve

Answer 19

Linear region before the yield point

Question 20

What are the two types of bone?

Answer 20

Cortical and cancellous

Question 21

What are the properties of the two types of bone and their pros and cons

Answer 21

Cortical (compact) bone
				□ Dense
				□ Shaft of long bones
Cancellous (trabecular) bone
				□ Pourus
				□ Trabeculae- alligned in which the load is being applied
				□ End of long bones 
(**overall structures allows the best compromise between strength and toughness**) increase strength- increase mass therefore greater energy to move (inefficeint)

Question 22

What are the two different types of bone behaviour?

Answer 22

Anisotropic
□ Varies depending on the direction of the applied load (best tolerant for use)
® Tibia strongest under compression (weight bearing) and weakest under shear
® Fibular strongest under tension due to muscle attachments
Viscoelastic
□ Varies depending on the rate of loading
® At higher loading rates bone is stiffer, stronger (higher load to failure) and tougher
® E.g. running
*Faster loading rate

Question 23

What are the types of loading?

Answer 23

Tension, compression, bending, shear, torsion, combination

Question 24

Define an agonist muscle

Answer 24

A muscle that produces a desired action at a joint

Question 25

Define an isometric muscle contraction

Answer 25

A muscle contraction where active tension is being developed within the muscle but there is not change length therefore there is no movement of a segment and no change in joint position

Question 26

Define a synergistic muscle

Answer 26

A muscle that assists in producing a desired action at a joint whilst cancelling out an unwanted action caused by an agonist

Question 27

Define a concentric contraction

Answer 27

A type of muscle contraction where active tension is being developed within the muscle and the muscle is shortening

Question 28

Define a neutraliser muscle

Answer 28

A muscle that cancels out the unwanted action of an agonist

Question 29

Define an antagonist muscle

Answer 29

A muscle that produces the opposite to the desired action of a joint

Question 30

Define a stabiliser muscle

Answer 30

A muscle that controls movement at one segment to allow the desired action at an adjacent segment

Question 31

Define an eccentric contraction

Answer 31

A type of muscle contraction where active tension is being developed within the muscle and the muscle is lengthened because the magnitude of the external force is greater than the muscle force. These contractions are used to control the movement against an external force such as gravity or to slow down a moving segment

Question 32

In a stress strain curve, how can you distinguish the stiffness of a material?

Answer 32

Gradient of the curve