Myoelectric Prostheses Flashcards
Myoelectric Prostheses
EXTERNALLY POWERED artificial limbs
Using BATTERIES AND ELECTRONIC SYSTEM to control movement of a TERMINAL DEVICE
Sensors used with prosthesis to detect minute MUSCLE, NERVE, and EMG (Electromyography) SIGNALS, primarily from FLEXORS and EXTENSORS
Translates MUSCLE ACTIVITIES into information that controls ARTIFICIAL LIMB MOVEMENTS
Myo Advantages
DOES NOT REQUIRE STRAPS OR HARNESSES to function, usually fit as supracondylar or suction suspension
USER CONTROLLED STRENGTH AND SPEED of limb’s movements and grip by varying muscle intensity
GOOD DEXTERITY allow manipulations of small items through function of the fingers
MINIMAL COSMETIC APPEARANCE SACRIFICE
Offer GREATER ROM during functional movement. Ex. performs both opening and closing of terminal device voluntarily (not exclusively one or the other)
Myo Disadvantages
WEIGHT, batteries, electronic components, terminal device, do not use harnesses to counter balance weight across the body
COST, since more electronic components are added to provide more functionality ex.. wrist rotator offers pronation/supination
LACK OF SENSORY FEEDBACK
SUSCEPTIBILITY TO WATER DAMAGE
Patient Considerations for Myoelectric Prostheses
AMPUTATION LEVEL
CONTOUR of residual limb
COGNITIVE FUNCTION of the patient
ACTIVITIES of patient
COSMETIC IMPORTANCE of the prosthesis
FINANCIAL RESOURCES of the patient
Patient Indications for Myoelectric Prosthesis
Muscles in the residual limb must be CAPABLE OF EMITTING SUFFICIENT EMG signals to operate myoelectric prosthesis
COMMITMENT TO THERAPY, to “learn” how to use prosthesis
COMPLIANT WITH LIMITATIONS of myoelectric use, battery charging, service required
FUNDING AVAILABLE $$
Patient Contraindications for Myoelectric Prosthesis
Muscles of residual limb UNABLE TO PRODUCE SUFFICIENT EMG signal
EXCESSIVE SCAR TISSUE on residual limb
COGNITIVE IMPAIRMENT
LIFESTYLE/JOB would damage myoelectric components (Ex. Extreme Sports, Manual Labour, Exposure to Water)
Components of Transradial Myoelectric Prosthesis
Internal socket
Forearm Outer shell
Electrodes
Controller
Batteries
Wrist
Terminal Device
Internal Socket
SELF SUSPENDING SOCKETS
Need to have CLOSE FIT TO MAINTAIN CONTACT with ELECTRODES
Get HAND POSITION in casting
- Northwestern (Supracondylar)
- 3/4’’
- Muenster (Narrow A-P)
- Basic socket type
Silicone and thermoplastics (Seaflex 200) commonly used in myoprostheses
Forearm Outer Shell
Can be exoskeletal laminated forearm or endoskeletal forearm
Section is where all electronic components are housed
Electrodes
ELECTRONIC SENSORS
SMALL METALLIC CONTACTS that rest against skin on the electrode sites
Find ideal locations in order to detect the best myoelectric circuit
Signal sent to myoelectric circuit, designed to LOCATE< AMPLIFY, FILTER and RECTIFY the EMG signal from a normal muscle
DIALS ON THE SENSORS can be adjusted for the AMPLIFICATION of the EMG signals to further control SENSITIVITY
Controllers
LOGIC SENSORS
Once EMG is RECEIVED, CONTROLLER OPERATES THE TERMINAL DEVICE
Numerous control options such as
- DMC (Dynamic Mode Control), which CONTROLS the HAND PROPORTIONATELY based on MUSCLE SIGNAL SPEED and STRENGTH
- DIGITAL, that can be used with 1 or 2 electrodes or switches
CHANGES can be made using COMPUTER SOFTWARE such as MyoSelect, MotionContol, Liberating Control or changing coloured “coding plugs” directly within the device
Myoelectric Batteries
Patient ACTIVITY LEVEL, along with COMPONENTRY to be used should be considered
Factors when choosing battery
- CAPACITY (milliamp/hour) (mAh)
- VOLTAGE (V), CORRECT FOR TERMINAL DEVICE selected (pediatric or adult)
- CHARGING TIME (in hours)
- SIZE AND WEIGHT
ENERGY DENSITY is of interest - more energy dense, more mAH per volume (mAH/volume)
Types of Batteries
Nickel Cad (NiCd)
- old tech
- cheap
- memory effects
Nickel Metal Hydride (NiMH)
- newer
- less memory effect
- mid range in expense
Lithium Ion
- newest
- more energy dense
- small battery
Wrist units
QUICK DISCONNECT - allows patient to use MORE THAN ONE TERMINAL DEVICE such as hand or greifer, mounted inside forearm using a lamination ring, 4 metal bands on the coaxial plug send power and control info to the hand via the coaxial bushing
FLEXION/EXTENSION
Units are available in different sizes
Terminal Devices
Depending on NEEDS and LEVEL OF FUNCTION of the patient, many options available
MODIFIED VERSIONS available for WRIST DISARTIC and TRANSCARPAL
Commonly used “ELECTRIC HANDS”
- SENSORHAND SPEED, fast, sensors on thumb automatically adjust to grip
- DIGITAL TWIN, combines both classical digital control (open and close) and double channel control in a single hand, constant speed and grip force to open close the hand
- DMC
Myoelectric Site Selection and Signal Training Criteria
Selecting muscles used for control, must be
- SUPERFICIAL AND ACCESSIBLE with prosthetic design/space considerations
- NOT INTERFERE with or inhibit normal activity
- APPROXIMATE normal movement
- GENERATE SIGNALS of sufficient STRENGTH
- be completely UNDER VOLUNTARY CONTROL
One site (Single site)
PEDIATRIC site selection usually starts with ONE SITE
SINGLE SITE
VOLUNTARY OPEN system using EXTENSOR muscles
USUALLY FITTED BETWEEEN 10-12 months to 3 yrs of age
VOLUNTARY OPEN / AUTOMATIC CLOSE
“COOKIE CRUSHER”
3 STATE (rate or level sensitive)
USUALLY HAS PARENTAL/THERAPIST TRAINING SWITCH, allows therapist or parent to place objects in hand for grasp and release training or playing
ELECTRODE SENSITIVITY is usually set to high for EASY ACTIVATION to catch attention of the child
LEVEL REDUCED GRADUALLY, until OPTIMAL LOWEST LEVEL is achieved and the child can open hand fully at will
Two Site
Occurs when PRESCHOOL AGE is reached between 3-4 yrs of age
Child has improved COMMUNICATION/COGNITIVE skills, TRANSFERRED from 1 site –> 2 site
FLEXOR MUSCLE SITE MUST BE ACCESSIBLE with prosthetic design and space available
Site must not interfere with normal daily activities
MUSCLE MUST GENERATE SUFFICIENT STRENGTH and be completely UNDER VOLUNTARY CONTROL
Ottobock components
Electrodes
Electrode cables
Coaxial plug
Battery cable
Battery Box
Lamination Collar
How to Activate Terminal Device
SWITCHES
-Rocker, pull push, multi positional, harness mount
FORCE SENSITIVE RESISTOR
CAPACITIVE TOUCH CONTROL
LINEAR TRANSDUCER- device that USES BODY MOVEMENT TO TRANSLATE TO ELECTRONIC SIGNAL
MYOELECTRIC SIGNAL
Electrodes Detect
EMG
Wave of depolarization
Put It All Together
Connection cables
Battery to everything
Amplifiers to control board
Control board to motor if necessary
Trouble Shooting - Hand does not function at all
Both electrodes not working (not likely)
Battery
Coaxial plug
Hand
Trouble Shooting - Hand operates in one direction
Electrodes or cables
Coaxial plug
Hand malfunction
Thresholds
- used to ELIMINATE UNWANTED INPUT from the electrode, caused by either external or internal signals
- SET AS LOW AS POSSIBLE to allow client GREATEST ACCESS to signal generation
Rate vs. Level Sensitive
Rate - SPEED of contraction
Level- STRENGTH of contraction
Internal Power Source
Pros
- cosmetic
- lighter
- can’t lose battery
Cons
- can’t swap out when power is drained
- need to install a switch for “off”
External Power source
Pros
- INTERCHANGEABLE for charged, when on the go
Cons
- Cosmesis
- Charger can be bulkier
Pattern Recognition
- uses algorithms to identify the muscle pattern generated when user performs a certain movement
- classifier then links the pattern to the specific movement of the component
- uses array of electrodes instead of 1 or 2 as in direct control to gather more data from the muscles
- aims to provide intuitive and simultaneous control of myoelectric components
TMR
Targeted Muscle Reinnervation
- surgical procedure that aims to provide easier and more intuitive prosthetic control for UE amputees
- typically performed for higher amputation levels, fore quarter, shoulder disartic, transhumeral
- residual nerves in amputated limb transferred to target muscles (pectoral muscles)
- additional signal sites allow users to operate 2 components independently without having to switch modes
