Ta. Park et al., GENERATOR SOURCES FOR THE EARLY AND LATE ULNAR HYPOTHENAR PREMOTOR POTENTIALS - SHORT SEGMENT ELECTROPHYSIOLOGIC STUDIES AND CADAVERIC DISSECTION, Archives of physical medicine and rehabilitation, 77(5), 1996, pp. 467-472
Objective: Determine the generator sources for the ulnar hypothenar pr
emotor potentials (PMPs). Design: Observational. Setting: EMG laborato
ry. Subjects: Ten asymptomatic adult volunteers, three cadaver hands.
Main Outcome Measure: Far-field versus near-field characteristics of r
ecorded PMPs as determined by bipolar and referential recording electr
ode montages. A possible anatomic basis for any observed differences b
etween ulnar PMPs and previously studied median PMPs was explored thro
ugh cadaveric dissection. Results: An early PMP (E-PMP) had a latency
that varied with changes in the position of GI only. A late PMP (L-PMP
) was seen only when G(1) and G(2) were on different volumes (palm vs
fifth digit, or second digit vs fifth digit); its latency did not vary
significantly with changes in the position of G(1) and G(2). Conclusi
ons: (1) E-PMP is a near-field potential generated by the ulnar nerve
passing near the G(1) electrode. (2) L-PMP represents a far-field pote
ntial generated by the ulnar digital nerves as they traverse from the
hand volume containing G(1) to the finger volume containing G(2). (3)
Greater L-PMP-to-CMAP separation in the median than in the ulnar nerve
was explained by cadaveric dissection, which revealed that the motor
branch (responsible for the trailing CMAP) is longer in the median ner
ve than in the ulnar nerve relative to each nerve's corresponding digi
tal sensory branch (responsible for the preceding L-PMP). (4) The PMP
that is typically recorded with G(1) at the hypothenar motor point and
G(2) on the fifth digit most likely represents E-PMP, (5) Any propose
d diagnostic use of the ulnar PMPs must take into consideration these
generator sources. (C) 1996 by the American Congress of Rehabilitation
Medicine and the American Academy of Physical Medicine and rehabilita
tion