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bmsc prosthetics > Upper Limb Orthotics > Flashcards

Upper Limb Orthotics Flashcards

1
Q

What are the 2 main reasons for upper limb prosthesis

A

Congenital absence

Trauma

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2
Q

What 6 factors will affect the outcomes of a prosthetic upper limb replacement

A 
Comfort
Function
Appearance/cosmesis
Weight
Power
Control and ease of use
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3
Q

What devices allow for good function in transradial prostheses

A

Terminal devices

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4
Q

What are the 3 main categories of supplying power to artificial hands/arms

A

Body power
External power
Hybrid power
(also zero-powered/passive devices)

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5
Q

How do body powered mechanisms work

A

Cables attached to the terminal device are linked to a harness anchored around the contralateral axilla. Power is generated by either glenohumeral flexion or biscapular abduction

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6
Q

Benefits of body powered mechanism

A

Good feedback
Simple design
Lightweight
Cheaper than externally supplied methods

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7
Q

How do externally powered mechanisms work

A

Energy is derived from either battery or pneumatic/electro-hydraulic power

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8
Q

How to passive/zero power devices work

A

Static devices where the position of the parts is manually adjusted

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9
Q

What is a servomechanism

A

A device used for the automatic control of a mechanism or source of power/energy. Uses error-sensing negative feedback to correct the action of a mechanism

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10
Q

Give examples of closed loop systems and open loop systems

A

Closed loop: power steering in cars, regulatory control of a boiler for central heating
Open loop: ‘timer’ devices e.g. toasters

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11
Q

What is a ‘transducer’

A

Something that measures a variable and its changes

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12
Q

Proprioceptors are the human transducer. What are the main 2 types of proprioceptor

A

Muscle spindles

Golgi tendon organs

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13
Q

What are 2 disadvantages of body-powered prostheses

A

Rely on sequential control because of the lack of suitable control sites
Range of operation around the body is restricted due to cables

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14
Q

What is a volar plate

A

A channel-like gutter of thermoplastic strapped to the wrist. Used for holding small objects

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15
Q

What is an electromyogram

A

A noise-like signal that is the bi-product of muscle contraction. These spike of energy can be amplified and averaged to give a proportionally variable signal that allows for myoelectric control

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16
Q

Why can electromyographic control be said to have proportional control

A

The speed of the prosthetic motor can be varied according to the rate of change of the muscle signal

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17
Q

What are the main disadvantages of myoelectric control

A

Presence of artefact noise which leads to involuntary movement
Lack of muscle groups to attach the electrodes to (esp. in children with congenital absence)

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18
Q

How to 3-state control mechanisms of myoelectric control work

A

Low signal level operates one function
Increased signal level operates another antagonistic function
The third state is no action/off

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19
Q

What is extended physiological proprioception control

A

The ability to perceive the tip of a prosthetic limb. Achieved by a 5-functional arm system device with a powered hand, wrist, elbow and shoulder rotation and elevation

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20
Q

What is used to drive a prosthetic motor in a servo control mechanism

A

The difference between input and output

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21
Q

What are Force Sensitive Resistor material pressure switches

A

Thin flexible pads which can be placed in sockets and used as a method of switch control

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22
Q

When are servo-controlled prostheses considered useful

A

When reliable EMG sites are not available

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23
Q

What are the main components of a trans-radial body powered upper limb prosthesis

A 
Terminal device
Wrist unit
Socket
Harness
Motivating cord
24
Q

What are the main components of a trans-humeral upper limb prosthesis

A 
Terminal device
Wrist unit
Forearm unit
Elbow unit
Socket
Motivating cord and pulleys
Harness
25
Q

What are some key properties of a harness

A 
Tailored to the user's body
Comfortable
Easy to don and doff
Easy to clean
Lightweight 
Broad (to spread load)
26
Q

What is an advantage and a disadvantage of using leather as a harness material

A

Benefit: soft and excellent for covering sensitive areas
Disadvantage: very absorbent and difficult to clean

27
Q

What method of suspension is usually used in trans-radial prostheses

A

Elastic or Velcro cuff

28
Q

What are the 4 main types of body powered terminal device

A

The volar plate
The split hook
The mechanical hand
The mechanical elbow

29
Q

What are the benefits of using a volar plate

A

Lightweight, portable and good sensory feedback from the residual limb

30
Q

Describe a split hook

A

2 curved tines (1 fixed, 1 movable)
Extension projecting medially from the movable tine which ends in a rounded hole for cable attachment#
A pretensioned rubbed band that holds the tines together

31
Q

How does a split hook work

A

The user provides the motive power to open the hook

The elastic bands provide the restoring force

32
Q

What materials are tines made from

A

Aluminium for light work

Steel for heavy duty use

33
Q

What are 2 major advantages of split hooks

A

Good quality feedback from the cable

Visually minimal: good visual feedback

34
Q

What are the main disadvantages of split hooks

A

Functional appearance

Rigid and limited sized gripping areas

35
Q

What are the benefits of mechanical hands

A

Good cosmesis

Better for gripping large or rounded objects

36
Q

Disadvantages of mechanical hands

A

Heavier
Require more energy to operate
Design may restrict visual cues

37
Q

What movement do mechanical hands typically allow

A

Uniplanar movement between the first and second fingers, and the opposing thumb

38
Q

What are the components of an electric hand device

A

Outer cosmetic glove made from PVC
Shaping mechanism of plastic/foam/laminate material
Uniplanar grip between the 1st and 2nd fingers and the thumb
Battery power which drives the motors for finger movement

39
Q

In mechanical terms, Power = Torque x ?

A

Angular speed

40
Q

What is a problem associated with the stall point of a direct current motor (if a locking feature is not incorporated)

A

The electric motor continues to generate its stall torque = consumes its stall current = rapidly drains electrical energy

41
Q

What are 3 examples of externally powered elbows

A

Boston
Hosmer
Utah elbows

42
Q

What is the only commercially available elbow devices for children

A

The Variety Ability elbow

43
Q

What are the 3 main battery types

A

Nickel Cadmium (NiCad)
Nickel Metal Hydride (NiMH)
Lithium

44
Q

How is the capacity of a battery quoted

A

In milli-amp hours

45
Q

What are the benefits of NiMH over NiCad

A

Better energy-to-weight ratio

Considered more environmentally friendly

46
Q

What are the benefits of lithium batteries over NiCad

A

Much better energy-to-weight ratio

Reduces the need to change the batteries during the day

47
Q

What are problems associated with lithium batteries

A

Safety: cell rupture
Geometry: cylindrical shape which limits where it can be placed in the prosthesis

48
Q

What is a problem with NiCad batteries in terms of charging

A

Tends to develop a memory of the most frequently used charge histories. If energy is only partially used and frequently charged then in time the battery will retain a reduced amount of charge

49
Q

How do smart chargers differ from conventional batteries

A

Discharge the battery first before starting the charging process. Prevents the battery from developing a ‘memory’ of its charge history

50
Q

What are the 3 main control components for externally-powered prosthesis devices

A

Switches
Proportional transducers
Myoelectric processors

51
Q

Explain the differences between traction, touch, and pressure switches

A

Traction: different functions are activated by different relative body movements
Touch: activated by residual body movement
Pressure: made from Force Sensitive Resistor material, mounted within sockets to give switch control or proportional control

52
Q

What concept do portable transducers apply to drive prosthetic function

A

The magnitude of the error signal between the displacement of the activation cables and the displacement of the prosthetic finger/thumb unit

53
Q

Boston elbow devices use linear potentiometers. What does this mean

A

Resistance varies with cable displacement

54
Q

What are myoelectric transducers

A

Electrodes and amplifiers that are mounted within the socket over the controlling muscle site. Detect muscle electrical signals which are used to drive the electronics of the prosthesis

55
Q

What material has traditionally been used to cover a prosthetic hand

A

PVC

56
Q

What is a disadvantage of a PVC cosmetic glove

A

Easily stains and colour/strength is influenced by UV light

57
Q

What are the benefits and disadvantages of silicone cosmetic gloves

A

Benefits: readily moulded, takes good skin details, realistic pigmentation, resistant to staining
Disadvantages: poor tensile strength, prone to tearing

bmsc prosthetics (4 decks)

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