11 Electric Control
Tips for myotesting
- Start with wrist flexors then add fingers, if necessary
- Co-contraction needs to be a sharp spike
- snap fingers
- flick water
- fist pump
- Be conscientious of the pts endurance level – (mental and physical) training
- Set the gain at the patient’s level of perceived effort. E.g., on at 2/10 and off at 8/10 perceived effort
- Begin by flexing/extending the wrist, not the fingers
- Assess signals at different locations (at waist, above head, in work space)
- Hardware: Ottobock myoelectrodes
- When placing the wire in the electrode: Grey goes up (the skies are grey in Seattle)
- Red = open
- Blue = close
Features to assess when myotesting for Single or Dual sites
|
Potential locations of myoelectric signals
| Amputation Level | Muscles for Myotesting |
| Partial hand | PADs Abductor digiti minimi |
| Transradial | Flexor Carpi Radialis, Flexor Carpi Ulnaris, Extensor Carpi Radialis Longus and Brevis, Extensor Digitorum |
| Transhumeral | Biceps Brachii, Triceps Brachii, Deltoid |
| Shoulder disarticulation | Pectoralis Major & Minor, Trapezius, Teres Minor, Latisimus Dorsi, Supraspinatus, Infraspinatus |
| Reference: OttoBock[/footnote] |
Switching/Selection Mechanisms
Terms: Ottobock “Switch” and Ossur/Touch Bionics “Trigger”
Method of mode selection |
Description |
Manufacturer |
| Single site | Ottobock Double channel control: 2 functions controlled with 1 signal. Quick, strong signal results in function 1; mild, slow signal results in function 2. | |
| Co-contraction | Mode is triggered by a co-contraction | All mfg. |
| Quick-slow scheme: Rapid contraction of either muscle selects one device (rate dependent) | Quick-slow with co-contraction scheme:E.g., Set up: biceps flexing elbow and closing hand, triceps extending elbow and opening hand.
Requires a reliable zero-state, e.g.After zero-state, biceps contract, then elbow control is initiated; After zero-state, triceps contract first, then TD control is initiated. |
OttoBock Four-channel control (aka fast access): 4 functions with 2 signals. Speed or intensity determines whether it controls the hand of the wrist: slow, gentle signals operate the hand; whereas a quick, strong signals operate the wrist.
Motion Control – fast access
|
| Impulse (single, double, triple) | Reliable impulse sends command to controller to operate component | Ottobock uses single and double impulse
Ossur-Touch bionics uses all three |
| Hold open | ||
| Switches/buttons
E.g. Rocker, bump, pull |
May be incorporated as a rocker, pull or push device to shift control between devices | |
| Movement of device | To operate, the arm must be held horizontal to activate this and hold open (the arm will “twitch” when the mode is selected) | Quantum iLimb |
| Blue tooth beacons (aka grip chips) | Ossur-Touch bionics | |
| RFID Tags | IBT Morph | |
| IMU (Inertial moment unit) | Mobius Luke arm | |
| Automatic switchback | Timer starts after small signal over threshold after working the elbow |
- Wrist and TD gain settings:
- If the wrist and TD are from different manufacturers, the gain settings in the wrist may interfere with the gain settings in the TD because the signal goes through the wrist first before getting to the TD.
- Switching methods
- If co-contraction is used to switch from one component to another, then co-contraction cannot be used as one of the selection modes for grasp patterns.
- Control system: Be aware of the control system (developed to avoid problems with co-contraction), e.g., Ottobock 1st over or largest wins or Motion Control 1st over or differential control