Electrophysiological Identification of the Berrettini Anastomosis in Healthy Japanese Subjects: A Detailed Nerve...

The Berrettini anastomosis (BA) is a sensory communication between the ulnar and median nerves in the palm. Although well described in anatomical studies, it has been less frequently evaluated electrophysiologically. We aimed to determine the frequency and electrophysiological characteristics of BA in healthy Japanese adults.

Bilateral sensory nerve conduction studies were performed in 32 healthy volunteers (64 hands). Sensory nerve action potentials (SNAPs) were recorded from median-innervated digits during ulnar nerve stimulation and from ulnar-innervated digits during median nerve stimulation. BA was classified as Type 1 (ulnar-to-median) or Type 2 (median-to-ulnar). To exclude unintended median nerve activation due to current spread, thumb recordings were obtained during screening for Type 1. The BA index was calculated as the ratio of the SNAP amplitude recorded from the middle finger (D3) to that recorded from the ring finger (D4) during ulnar stimulation.

BA was identified in 5 participants (15.6%) and 7 hands (10.9%), all classified as Type 1. BA-related SNAPs were recorded exclusively from D3 and not from the index finger (D2). The BA index ranged from 3.6% to 77.2% (median 5.7%). BA-related amplitudes were small relative to the corresponding ulnar SNAP amplitudes at D4.

BA can be electrophysiologically detected in a subset of healthy individuals, typically as a small ulnar-to-median crossover to D3. Although amplitudes are generally limited, awareness of this normal anatomical variant may assist in careful interpretation of sensory nerve conduction findings, particularly in borderline or asymmetric cases.