Upper Limb Orthotics Flashcards
What are the 2 main reasons for upper limb prosthesis
Congenital absence
Trauma
What 6 factors will affect the outcomes of a prosthetic upper limb replacement
Comfort Function Appearance/cosmesis Weight Power Control and ease of use
What devices allow for good function in transradial prostheses
Terminal devices
What are the 3 main categories of supplying power to artificial hands/arms
Body power
External power
Hybrid power
(also zero-powered/passive devices)
How do body powered mechanisms work
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
Benefits of body powered mechanism
Good feedback
Simple design
Lightweight
Cheaper than externally supplied methods
How do externally powered mechanisms work
Energy is derived from either battery or pneumatic/electro-hydraulic power
How to passive/zero power devices work
Static devices where the position of the parts is manually adjusted
What is a servomechanism
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
Give examples of closed loop systems and open loop systems
Closed loop: power steering in cars, regulatory control of a boiler for central heating
Open loop: ‘timer’ devices e.g. toasters
What is a ‘transducer’
Something that measures a variable and its changes
Proprioceptors are the human transducer. What are the main 2 types of proprioceptor
Muscle spindles
Golgi tendon organs
What are 2 disadvantages of body-powered prostheses
Rely on sequential control because of the lack of suitable control sites
Range of operation around the body is restricted due to cables
What is a volar plate
A channel-like gutter of thermoplastic strapped to the wrist. Used for holding small objects
What is an electromyogram
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
Why can electromyographic control be said to have proportional control
The speed of the prosthetic motor can be varied according to the rate of change of the muscle signal
What are the main disadvantages of myoelectric control
Presence of artefact noise which leads to involuntary movement
Lack of muscle groups to attach the electrodes to (esp. in children with congenital absence)
How to 3-state control mechanisms of myoelectric control work
Low signal level operates one function
Increased signal level operates another antagonistic function
The third state is no action/off
What is extended physiological proprioception control
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
What is used to drive a prosthetic motor in a servo control mechanism
The difference between input and output
What are Force Sensitive Resistor material pressure switches
Thin flexible pads which can be placed in sockets and used as a method of switch control
When are servo-controlled prostheses considered useful
When reliable EMG sites are not available
What are the main components of a trans-radial body powered upper limb prosthesis
Terminal device Wrist unit Socket Harness Motivating cord
What are the main components of a trans-humeral upper limb prosthesis
Terminal device Wrist unit Forearm unit Elbow unit Socket Motivating cord and pulleys Harness
