Comparison of recording characteristics of monopolar and concentric needle electrodes

Although both monopolar and concentric needle electrodes (MNE and CNE) are widely used in clinical EMG examinations, relatively little attention has been paid to the different recording characteristics of these electrodes. We compared motor unit potentials (MUPs) recorded with MNE and CNE and confirmed that larger MUP pick-up fields and amplitudes are recorded with MNE than with CNE but found no differences in duration or the number of phases. To determine the cause of these differences, we analyzed fibrillation potentials (FPs) recorded with MNE and CNE in patients with peripheral nerve injury. The FPs recorded had similar wave forms and amplitudes. The pick-up field for the FPs, however, was about 2 times larger for MNE than for CNE. We conclude that the differences of the recording characteristics of MNE and CNE for MUPs mainly are produced by their different pick-up fields.