Ulnar sensory palmar crossover to digit three (D3), the Berrettini anastomosis, is measurable in routine electrodiagnostic nerve conduction studies. The crossover is reported as occurring in 60% of anatomic dissections, but the frequency of measurable ulnar crossover to D3 and its potential as a nerve conduction pitfall is not established. The purpose of this article was to present descriptive statistics regarding the frequency of measurable Berrettini anastomosis in nerve conduction studies.
A retrospective chart review and data analysis was completed on 248 patients representing 411 extremities with a main outcome measure of ulnar sensory stimulated nerve conduction simultaneous waveform recording on D3 and digit four (D4). Consistent electrodiagnostic technique with waveform recording data analysis in a private practice and independent university waveform verification was completed on sequential patients referred for upper extremity electrodiagnostic testing.
Measurable ulnar stimulated D3 sensory nerve action potentials were demonstrated in 34% of patients with amplitudes of 27%, the simultaneously recorded corresponding ulnar D4 amplitudes representing electrophysiological evidence of ulnar sensory crossover.
The Berrettini anastomosis can frequently be seen as a small amplitude sensory nerve action potential response, but at times can be observed with an amplitude greater than 10 μV. It is possible that patients with an absent or significantly delayed median nerve response may have simultaneous inadvertent spread of stimulus to ulnar axons measurable on D3 that may be interpreted as a falsely normal response. All electromyographers need to be aware of this potential pitfall.