The selection of electromyographic needle electrodes

Monopolar and concentric reusable and disposable EMG needle electrodes from several manufacturers were studied at various stages of usage. Needle tips were examined and measured microscopically, and needles were tested for spontaneous noise and resistive and capacitative characteristics at four different test signal frequencies. Resistive and capacitative characteristics were found to be frequency dependent. Needle tip areas differed by as much as 10 times among the various electrodes. The amount of noise correlated most highly with resistive characteristics. Monopolar and concentric needles differed in respect to tip area, noise, and all resistive and capacitative measures. Coaxial disposable and reusable electrodes did not differ significantly and minor differences were noted in electrical characteristics between reusable and disposable monopolar needles, even from the same manufacturer. There was considerable variability among manufacturers for both needle types. In choosing an electrode, consistent tip area is probably the most important consideration to ensure repeatable quantifiable results, but minimizing needle impedance is useful to reduce noise.