Progressive teflon denudation of the monopolar needle: effects on motor unit potential parameters

This paper reports on the effects of an increase in size of the recording surface of monopolar needles on motor unit potentials (MUPs). The teflon coating of the TECA monopolar needles MG37 and MF37, commonly used in clinical electromyography, was progressively denuded to increase the length of the recording tip to 2, 3, 5, and 10 times the normal exposure, with resultant increase in the area of the recording portion. Low threshold MUPs obtained on minimal contraction from the tibialis anterior were analyzed for amplitude, duration, area, phases, turns, peak duration, and index. The amplitude and area of the MUP showed the most change, both decreasing with progressive denudation. The number of turns and phases were also reduced, more for the MF than for the MG needle. Duration, peak duration, and index showed insignificant changes. These findings give further support to the use of duration for representation of the MUP, since this is the most stable parameter even under poor recording conditions.