Is there any difference in the recording quality between concentric and monopolar needles?
Yes, there is a difference in the recording characteristics between a concentric and a monopolar needle. In the concentric design the electrode wire is located inside the lumen of the cannula and thereby shielded, giving a more stable baseline. The cannula shields the wire from picking up potentials from fibres located behind the tip. The sensitivity of the concentric EMG needle is therefore largest in the hemisphere facing the oblique elliptical surface. Due to the asymmetric sensitivity function, the wave shape of the recorded potentials will vary if the electrode is rotated about its axis. This problem is not observed with the asymmetric monopolar EMG needle. However, this electrode has a more unstable baseline (noise) due to the unshielded lead wire and the remote location of the reference electrode. It is thus more likely to pick up potentials from remote motor units.
