10 Electric Control
Features to assess when myotesting for Single or Dual sites
- Location of the signal: to identify the location, start by palpating the residual limb.
- Where do you feel the greatest contracture?
- This is the best location to start looking for a signal; the most electrical signal will be found at the location of the most myofibers.
- Number of signals
- Isolation of signals (including isolation from natural arm movements)
- Strength of the signal
- On 20 (0.54v)
- Low 45
- High 65>1.5v
- 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)
- Assessment of various myosignal-switching/selection capability
- Ability/potential to co-contract , produce rapid signal, produce sustained signal
| 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 |
| *** Electrode wires: Grey goes up[1] |
- Ottobock myoelectrodes
- When placing the wire in the electrode: Grey is up (the skies are grey in Seattle)
- Red = open
- Blue = close
- Wrist and TD gain settings:
- o 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
- o 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
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 |
- Reference: Otto Bock ↵