Upper Limb Orthotics

Question 1

What are the 2 main reasons for upper limb prosthesis

Answer 1

Congenital absence

Trauma

Question 2

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

Answer 2

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

Question 3

What devices allow for good function in transradial prostheses

Answer 3

Terminal devices

Question 4

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

Answer 4

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

Question 5

How do body powered mechanisms work

Answer 5

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

Question 6

Benefits of body powered mechanism

Answer 6

Good feedback
Simple design
Lightweight
Cheaper than externally supplied methods

Question 7

How do externally powered mechanisms work

Answer 7

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

Question 8

How to passive/zero power devices work

Answer 8

Static devices where the position of the parts is manually adjusted

Question 9

What is a servomechanism

Answer 9

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

Question 10

Give examples of closed loop systems and open loop systems

Answer 10

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

Question 11

What is a ‘transducer’

Answer 11

Something that measures a variable and its changes

Question 12

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

Answer 12

Muscle spindles

Golgi tendon organs

Question 13

What are 2 disadvantages of body-powered prostheses

Answer 13

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

Question 14

What is a volar plate

Answer 14

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

Question 15

What is an electromyogram

Answer 15

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

Question 16

Why can electromyographic control be said to have proportional control

Answer 16

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

Question 17

What are the main disadvantages of myoelectric control

Answer 17

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

Question 18

How to 3-state control mechanisms of myoelectric control work

Answer 18

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

Question 19

What is extended physiological proprioception control

Answer 19

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

Question 20

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

Answer 20

The difference between input and output

Question 21

What are Force Sensitive Resistor material pressure switches

Answer 21

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

Question 22

When are servo-controlled prostheses considered useful

Answer 22

When reliable EMG sites are not available

Question 23

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

Answer 23

Terminal device
Wrist unit
Socket
Harness
Motivating cord

Question 24

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

Answer 24

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

Question 25

What are some key properties of a harness

Answer 25

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

Question 26

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

Answer 26

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

Question 27

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

Answer 27

Elastic or Velcro cuff

Question 28

What are the 4 main types of body powered terminal device

Answer 28

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

Question 29

What are the benefits of using a volar plate

Answer 29

Lightweight, portable and good sensory feedback from the residual limb

Question 30

Describe a split hook

Answer 30

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

Question 31

How does a split hook work

Answer 31

The user provides the motive power to open the hook | The elastic bands provide the restoring force

Question 32

What materials are tines made from

Answer 32

Aluminium for light work | Steel for heavy duty use

Question 33

What are 2 major advantages of split hooks

Answer 33

Good quality feedback from the cable | Visually minimal: good visual feedback

Question 34

What are the main disadvantages of split hooks

Answer 34

Functional appearance | Rigid and limited sized gripping areas

Question 35

What are the benefits of mechanical hands

Answer 35

Good cosmesis | Better for gripping large or rounded objects

Question 36

Disadvantages of mechanical hands

Answer 36

Heavier Require more energy to operate Design may restrict visual cues

Question 37

What movement do mechanical hands typically allow

Answer 37

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

Question 38

What are the components of an electric hand device

Answer 38

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

Question 39

In mechanical terms, Power = Torque x ?

Answer 39

Angular speed

Question 40

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

Answer 40

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

Question 41

What are 3 examples of externally powered elbows

Answer 41

Boston Hosmer Utah elbows

Question 42

What is the only commercially available elbow devices for children

Answer 42

The Variety Ability elbow

Question 43

What are the 3 main battery types

Answer 43

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

Question 44

How is the capacity of a battery quoted

Answer 44

In milli-amp hours

Question 45

What are the benefits of NiMH over NiCad

Answer 45

Better energy-to-weight ratio | Considered more environmentally friendly

Question 46

What are the benefits of lithium batteries over NiCad

Answer 46

Much better energy-to-weight ratio | Reduces the need to change the batteries during the day

Question 47

What are problems associated with lithium batteries

Answer 47

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

Question 48

What is a problem with NiCad batteries in terms of charging

Answer 48

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

Question 49

How do smart chargers differ from conventional batteries

Answer 49

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

Question 50

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

Answer 50

Switches Proportional transducers Myoelectric processors

Question 51

Explain the differences between traction, touch, and pressure switches

Answer 51

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

Question 52

What concept do portable transducers apply to drive prosthetic function

Answer 52

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

Question 53

Boston elbow devices use linear potentiometers. What does this mean

Answer 53

Resistance varies with cable displacement

Question 54

What are myoelectric transducers

Answer 54

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

Question 55

What material has traditionally been used to cover a prosthetic hand

Answer 55

PVC

Question 56

What is a disadvantage of a PVC cosmetic glove

Answer 56

Easily stains and colour/strength is influenced by UV light

Question 57

What are the benefits and disadvantages of silicone cosmetic gloves

Answer 57

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