A comparison of close proximity concentric and modified single fiber electromyographic recordings from extensor digitorum communis.

Using a combined concentric (CN) and modified single fiber (MSF) electromyography (EMG) needle electrode with both recording surfaces at the tip approximately 25 microns apart, 30 motor unit action potentials (MUAP) were recorded from one extensor digitorum communis (EDC) muscle, triggering from the CN and averaging both the CN and MSF recordings. Correlations of MUAP amplitude (r = 0.767), number of turns (r = 0.839), and number of negative-going-positive-going turn (NT) (r = 0.737) between the CN and MSF recordings were statistically significant (p < 0.001). For NTs common to both recordings, correlations of rise time (r = 0.866), amplitude (r = 0.816), and interpeak interval (IPI) (r = 0.999) were statistically significant (p < 0.001). Mean +/- SD single fiber potentials (SFP), approximate SFP with rise times less than 500 microseconds, and NTs for the MSF recordings and NTs for the CN recordings were 0.73 +/- 0.69, 1.20 +/- 0.48, 1.83 +/- 0.87, and 1.93 +/- 0.78, respectively. This study supports evidence that one or a few SFP contribute to the spike component of the MUAP.