There Are Three Electrodes Used For An EMG Guidance Procedure:
- a surface reference electrode
- a surface ground electrode
- a hypodermic needle electrode
This is the basis of what is required to measure a usable biosignal using a differential amplifier to improve the quality of the signal by subtracting out the common mode noise.
Think about it like this: The hypodermic needle electrode signal is subtracted from the reference electrode signal to yield the signal that is outside of the noise that is common to both. Both those signals are based upon the ground electrode. This presents a reasonably clean EMG signal.
This is the reason why better results occur when the reference electrode is located close to the needle electrode.
The ground electrode is needed as the base from which the overall signals arise. In the case of recording signals, it’s nice to have the ground in the vicinity, but more or less central to both the needle and reference electrodes.
Reference electrodes can also be central to multiple areas being injected if it’s position is reasonably equidistant to those sites. This can save time and improve signal quality by not having to reposition the surface electrodes.
Where the position of the ground electrode becomes very important is when the electrodes are used to stimulate. While not the focus of this topic, keep in mind that the ground is part of the stimulation pathway, and the shorter this path is, the less work the stimulator has to do, to deliver the selected current based stimulation pulse through the needle electrode. So, in summary, try to keep electrodes in the general immediate area of concern. There is no benefit locating the ground electrode too far away from the action.
The hypodermic needle electrode is designed to function for both EMG recording or electrical stimulation, right at the selected site for Botulinum Toxin (or other medication) injection.
The beauty of the process is that once an optimal site is located, the medication can be injected immediately through the hypodermic needle electrode itself.
- Trigger points are located with the help of EMG audio (sound)
- Signal display (sight, which is important for silent procedures),
- processed EMG indicators (quantitative measures),
- possibly stimulation location (used to distinguish specific digits)
Dry needling would simply replace the hypodermic needle with a thin needle electrode for monitoring the site. All the benefits of the procedure would be in place to support optimal electrode placement.